Let’s explore the unique characteristics of welding stainless steel to maximise its overall result.

The Challenges in Welding Stainless Steel

Stainless steel welding, in particular, presents a unique set of challenges in welding from its mechanical properties. Its various grades and types (such as austenitic, ferritic, martensitic, precipitation-hardened, Duplex, etc) add an extra layer of complexity to the subject.

Let’s explore a few of the challenges in welding stainless steel and learn how to overcome them.

Warping & Cracking

Stainless steel has low thermal conductivity and high thermal expansion, making it susceptible to warping and cracking. Excessive heat input during welding or a rapid change in the temperature puts the metal under stress, resulting in distortion as it cools down.

There are a few ways to prevent warping and cracking, one of which is through working with lower heat input. While it may seem logical, it also may result in poor weld quality due to incomplete fusion between the workpieces. So it is always important to strike a balance between the two extremes. Another solution is to create a heat sink by clamping copper or brass behind the seam, absorbing unnecessary heat into the copper alloys.

Rust

Stainless steel is known to have high corrosion resistance, yet excess heat may still generate rust in the weld. It may also form as the carbon from the filler material contaminates the heat-affected zone.

Choosing an optimal welding temperature and a stainless steel filler alloy depending on the job greatly reduces the risk of forming rust in the material.

Welding Dissimilar Steels

Welding dissimilar metals or various stainless steel grades together can be challenging, especially if their melting points are far apart. It might cause great trouble in fusing the metals effectively.

Selecting the optimal filler rod is necessary when welding stainless steel and another alloy. Preheating the metals can also alleviate this problem.

Switching Between Jobs

The lower melting temperature of stainless steel (1375 – 1530°C) compared to mild steel (1425-1540°C) might become problematic when switching between the two.

Toxic Fumes

Stainless steel welds produce toxic fumes in the form of hexavalent chromium gas. It develops as the chromium oxide layer is destroyed and may occur either during the heating or cooling process.

An effective breathing mask combined with proper ventilation in the area is key to ensuring the welder’s safety.

Stainless Steel Welding Methods

Depending on the project’s requirements, several welding processes can be performed to join stainless steel parts. We’ll highlight a few of those processes but this is not an exhaustive list, processes such as plasma welding, electron beam welding, submerged arc welding, etc are all perfectly capable of welding stainless steels as well.

TIG Welding (GTAW)

TIG welding is widely used in the fabrication sector for stainless steel since it has a stable arc and the process is automated. In the TIG process, the heat applied to the weld can precisely be controlled through a foot pedal or finger control, minimising the possibility of warping. TIG welding machines can also switch between AC and DC polarities, offering flexibility and convenience simultaneously.

Gas tungsten arc welding stainless steel is rather costly since the process needs consumables such as shielding gas (usually pure argon) and optional filler rods. Selecting the right geometry and size of the electrode depending on the welding variables should definitely be considered beforehand.

MIG Welding (GMAW)

MIG welding is another popular choice for welding stainless steel. It offers faster speeds than TIG welding mainly thanks to its continuously fed electrode. One downside of this technique is that it doesn’t look as pleasing to the eye as properly executed TIG welds.

A Teflon wire liner in the MIG gun allows for a consistent wire feed to the weld pool and added protection from contamination. Backstepping, staggering or allowing the joint to undergo a bit of the cooling process helps avoid warpage since stainless steel retains heat well.

Shielded Metal Arc Welding (SMAW)

Stick-welding stainless steel is often the practical choice regarding cost, portability and simplicity. SMAW can be performed in almost any environment and thus is great for various repair jobs and welding stainless steel outdoors.

Thicker pieces of stainless steel (above 2mm) are most suitable for SMAW since it is harder to control the heat input than with other methods. Selecting the electrode (typical grades: 316, 308, or 312) is an important part of the project. Beware of slag removal after the welding as it might be a bit of a struggle.

Flux Cored Arc Welding (FCAW)

Flux-cored arc welding stainless steel is sometimes preferred over SMAW since it generally creates a more uniform weld bead. FCAW can be performed with a shielding gas when working with varying material thicknesses or in demanding welding conditions.

A 10° drag angle allows the flux to rise at the weld pool and gives enough bead coverage.

Resistance Welding

Resistance welding (spot welding, seam welding) stainless steel creates clean welds compared to arc welding processes since it doesn’t use filler material and has no risk of weld spatter. The high electrical resistance of stainless steel is also favorable since it can complete a weld in a short amount of time.

A good quality welder with sufficient power output is necessary for resistance welding stainless steel to prevent the areas close to the HAZ from deformities. It is recommended to have higher current and voltage values when welding stainless steels compared to, for example, copper and aluminium alloys due to the difference in electrical conductivity.

Friction Welding

Friction Welding Stainless Steel to Carbon Steel

Friction welding stainless steel, similar to resistance welding, doesn’t use consumables, making it an economical choice when the part geometries allow for it. It is most suitable for welding austenitic stainless steel due to its composition of chromium (16-26%) and nickel (8-22%).

Some factors that need to be considered are friction pressure, burn-off length and rotational speed. Some sub-types of friction welding may be suitable for specific applications: friction hydro pillar processing (FHPP), friction stir welding (FSW) and friction plunge welding.

Stainless Steel Welding Best Practices

Safety and Preparation

Preparation of equipment, materials and the work area is essential before engaging in any kind of welding process suitable for stainless steels. A dedicated stainless steel wire brush to prepare the metals will decrease the chances of contamination. Gloves, goggles and other protective gear will minimise the risk of accidents such as exposure to fumes and injury due to spatter.

Filler Metal Selection

Choosing the appropriate filler material depending on the scope of work is really important. Most of the time it should match the grade of the stainless steel, achieving almost the same properties. Other considerations in choosing filler material include weld joint design, aesthetics and overall weld performance.

Parameters

An experienced welding provider understands the finer details of each stainless steel grade, weldable metals and welding method. It leads to a better choice when fine-tuning the parameters such as the power supply, torch angle, travel speed and deposition rate. Effective use of these welding parameters will help to achieve the highest quality welds.

Shielding Gas

The choice of shielding gas in processes such as MIG and TIG welding is crucial in protecting the weld pool from contamination. The correct shielding gas composition will reduce the risk of weld defects and improve the weld’s overall outcome.

Heat Input

Consider the variables of the welding project in determining the ideal heat input to weld stainless steel. Generally, the welding current should be about 20% less than for carbon steel to prevent corrosion.

The post Stainless Steel Welding – Challenges, Methods & Best Practices appeared first on Fractory.

Aluminium welding faces a set of unique challenges though, to achieve a successful and defect-free result.

The Challenges in Welding Aluminium

Welding aluminium is a complex process that requires knowledge, skill, and experience. Understanding the different welding processes suitable for aluminium and the challenges and workarounds regarding those methods is paramount for achieving successful welding joints.

Oxidation

Aluminium rapidly oxidises when exposed to the atmosphere, forming a thin oxide layer with a higher melting temperature (2072 C°) than aluminium (660 C°). Welding through this barrier might burn holes through the workpiece.

The oxide layer can be dissolved using solvents or acids before welding the workpiece. It can be physically removed through mechanical abrasive techniques through an exclusive stainless steel wire brush or sandblasting.

Porousness

Aluminium in its molten state, absorbs high amounts of hydrogen, resulting in tiny voids or bubbles forming in the weld metal. This weakens the structural integrity of the metal, making it vulnerable to failure from pressure and stress.

Porosity is minimised by using clean materials and equipment, removing oil and grease from the metal’s surface, and using a shielding gas to limit contamination.

Impurities

Oil, dirt, air and debris can negatively impact the weld zone, affecting the strength and appearance of the workpiece. These impurities can come from multiple sources, such as the environment, equipment, preparation and storage. Discolouration, graining, corrosion and oxidation present signs of impurities in a weld joint.

Proper storage, equipment maintenance and metal preparation are the steps to take to avoid impurities.

Thickness

Working with aluminium typically involves welding materials with varying thicknesses. Welding through a combination of thin and thick material simultaneously can be tricky. Heat applied to the workpiece might melt through the thin material or not penetrate the thick material enough to create a strong weld joint.

A thorough understanding of the aluminium grades, welding methods, and techniques is the key to success in effectively welding different aluminium sheet thicknesses. Welders can effectively weld these metals by setting the parameters such as amperage and heat input to optimal levels.

Hot Cracking

High levels of thermal stress can lead to hot cracking or solidification cracking in aluminium welds. It is one of the reasons why aluminium was once deemed unsuitable for arc welding.

Combining various alloying elements and treating aluminium alloys can drastically improve its mechanical properties. (Al-Cu) 2xxx and (Al-Zn) 7xxx grade series are aluminium alloys that can heat-treated.

Thermal Conductivity

The high thermal conductivity of aluminium makes it challenging to penetrate the weld joint successfully, as it absorbs and dissipates heat quickly.

Adjusting the settings on the welding equipment to higher heat input improves penetration.

Aluminium Welding Methods

Several welding processes are used for aluminium, each having its own strengths and weaknesses. Welders usually choose TIG and MIG welding, yet other methods can fill in for a unique, desirable result.

Factors to consider when choosing the type of welding method are the supply, cost (equipment, filler material, other consumables), weld performance, joint design, repeatability, distortion tolerance, production speed, and safety.

TIG Welding

Gas tungsten arc welding (GTAW) or TIG welding is one of the most common welding techniques for joining aluminium because of its precision and quality. It can operate on AC (alternating current) polarity, offering stability to the arc and wiping off the oxide layer. A TIG welder can consistently generate enough heat to fuse aluminium alloys, with the ability to weld both thin and thick sections.

Inert shielding gas, most commonly argon, is fed to the TIG torch to keep the weld puddle free from contamination. Thus, protecting the sensitive aluminium. When the project requires the use of aluminium filler rods, then series 4xxx aluminium filler metal is the most common choice.

MIG Welding

Gas metal arc welding (GMAW) or MIG welding is a great welding technique for thicker aluminium sheets as the heat input is higher than in TIG welding. This welding method is quite similar to the TIG process but instead of a non-consumable tungsten electrode, MIG welding utilises an automatically fed electrode wire. The mechanical wire feeding system offers faster travel speeds from its spool gun. Shielding gases are used to protect the welds from contamination.

Laser Welding

Laser welding is a fast welding process that concentrates a high power density beam at the aluminium surface. It offers precision to weld both narrow widths and large weld depths, resulting in clean weld zones with the supplement of shielding gas. 6xxx aluminium alloys are generally safe for laser welding and are most commonly paired with a 4032 or 4047 aluminium-grade filler rod.

Electron Beam Welding

Electron beam welding aluminium is an option for thick sections as it produces a small and precise weld pool. This welding method is performed inside a vacuum chamber, protecting the weld from impurities without the need for additional shielding gases.

Resistance Welding

Resistance welding aluminium involves the application of pressure and current to undergo fusion. Spot and seam welding is often used to join aluminium sheets. One downside of this technique is the possible challenges when experiencing high thermal and electrical conductivity.

Friction Welding

Friction welding is a solid-state fusion welding process wherein mechanical friction between aluminium metals generates heat. The nature of this process removes the necessity to add a shielding agent to protect the weld pool. Friction welding is used across all aluminium alloy grades, including the hard-to-weld 2xxx and 7xxx series.

What Processes to Avoid When Welding Aluminium?

Processes that use flux (filler material containing flux, granular flux, or other forms) aren’t ideally suitable to weld aluminium as it faces a greater risk to porosity.

• Flux-cored arc welding

• Shielded metal arc welding

• Submerged arc welding

Aluminium Welding Best Practices

1. Safety and preparation – Wearing protective gear (goggles, helmet, gloves, etc.) is necessary as with any other welding method. Knowing and understanding how the project will be executed beforehand is a great way to prepare for the welding process. Some preparation may include removing the metal’s oxide layer through chemicals or a steel brush and ensuring that the equipment is clean.

2. Understanding the finer details – Experienced welders bring much value in understanding how things should pan out in executing a project. Finer details such as the welding processes, equipment parameters and approach will ensure a successful project. Getting your assemblies welded by experienced welding service providers helps to prevent problems down the line.

3. Patience – It takes time to execute a stellar welding job perfectly, so it is important to be patient and continually test the parameters. Reproducible results with high weld quality are keys when welding multiple pieces in succession.

4. Storage – Aluminium is stored indoors at room temperature and must be kept dry. It is best not to stack these metals if possible (ex. aluminium sheets), but rather vertically since the metal is soft.

5. Bead profile – A stringer bead profile is preferred in welding aluminium most of the time, unlike in welding steel, which uses a weaving technique.

The post Aluminium Welding – Challenges, Methods & Best Practices appeared first on Fractory.

Take a dive into the different types of welding joints, each with its own unique characteristics, suitable for various applications.

Welding Joint Types

Force, load, thickness, resistance and aesthetics are some of the contributing factors when it comes to determining suitable welding joints for a project. These joints may also be influenced by the type of welding process as some processes are better suited for welding in certain positions.

There are five main welding joint types used across the welding industry:

Butt Joint

Butt joints are one of the most common types of welding joints and are often used in the piping, construction, and fabrication sector. Flat pieces of metal are laid parallel with their edges touching or at a 135° to 180° angle from each other. Correctly formed butt joints where the weld metal fully penetrates the joint with complete root fusion achieve good mechanical strength, while poor welding techniques can lead to failure from incomplete penetration, burn-through, cracking or distortion.

Butt joint welding requires little to no edge preparation. Applications that require edge preparation of the edge joints would typically require specific bevel angles depending on the project’s scope. The design of a butt welding joint will greatly depend on the material thickness, backing material, edge preparation, and overall fit.

For thicker materials, a square butt joint might not be able to do the trick anymore and it becomes unavoidable to utilise some kind of groove to ensure a sound weld with proper penetration.

Butt joints can be subdivided into the following groove welds:

• Square groove

• Single or double bevel groove weld

• Single or double J-groove weld

• Single or double U-groove weld

Tee Joint

Tee joints are done by welding two perpendicular pieces of metal, forming a T-shape intersecting at approximately 90°. Tee joint is considered to be a type of fillet weld and they are also formed when welding a pipe onto a baseplate.

It is mostly used on structural steel, equipment manufacturing, and tubing since it requires little to no preparation while effectively achieving optimal mechanical strength. Fillet welds account for roughly around 70% of all joints created by various arc welding methods, such as MIG, TIG and stick welding.

Tee joints may be welded on one side where the load will be applied or at both ends to achieve maximum strength. The design of tee joints makes them susceptible to lamellar tearing since it is restricted between the two workpieces.

Tee joint design would vary depending on the material thickness, edge preparation, and work angle. Tricky work angles also exclude some types of welding methods.

Tee joints can be subdivided into these weld types:

• Bevel groove weld

• Fillet weld

• Flare-bevel-groove weld

• J-groove weld

• Melt-through weld

• Plug weld

• Slot weld

Lap Joint

A lap joint is a modified butt joint more suited for materials with varying thicknesses. This is formed by overlapping the metals, forming an angle of 0-5°. Lap joints are common in the repair and sheet metal industry, wherein thin metals are used.

Welding joints using this method adds more reinforcement to the weld, given that it is properly done with no gap between the overlapping metals. Corrosion and lamellar tearing are the leading causes of failure when using this joint.

Here are the welding styles for lap joints:

• Bevel-groove weld

• Flare-bevel-groove weld

• J-groove weld

• Slot weld

• Spot weld

Corner Joint

Corner joints are similar to tee joints, with two metal bars forming a 90° fit with each other at the corner, forming an L-shape. It is popular for sheet metal welding and constructing various frames and tables.

There are two approaches when corner welding a joint, either an open or closed corner is formed. Open corner joints form a V-shape between the two metals, with the two metal edges touching each other. Closed corner joints are formed with one edge of the metal touching the face of the other metal. While a closed corner joint is more complicated than an open corner joint, it generally provides a higher overall mechanical strength.

Type of welds used for corner joints:

• Bevel-groove weld

• Corner-flange weld

• Edge weld

• Fillet weld

• Flare-V-groove weld

• J-groove weld

• Spot weld

• Square-groove weld or Butt weld

• U-groove weld

• V-groove weld

Edge Joint

Edge joints are similar to corner joints wherein two metals intersect at a common mating edge but have the two metals side by side. Either of the two workpieces may be bent at an angle depending on the application.

The type of edge joint will depend on how the edge of the metals is prepared. Some of these preparations include cutting, grinding, or machining into various groove types that lead to different amounts of penetration. Depending on the project requirements, edge joints may also be welded only on the edge or all around.

An edge joint may be constructed using these types of welds:

• Bevel-groove weld

• Corner-flange weld

• Edge-flange weld

• J-groove weld

• Square-groove weld or butt weld

• U-groove weld

• V-groove weld

The Importance of Using the Right Type of Joint

Understanding weld joint design makes it an essential tool for determining the success of any welding project. Selecting the appropriate weld joint along with the equipment and the choice of welding method and technique is key to achieving the most robust and durable joints.

It is crucial to recognise and anticipate the forces applied to the workpiece, as it will certainly be one of the deciding factors whether the design is effective. Integrating this into the joint design will prevent structural failure down the line and helps to achieve weld integrity and quality.

Fractory offers welding services as a part of our full service – from quoting to delivery. Our network of pre-vetted manufacturing partners offers access to a wide range of processes and capabilities.

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The term welding is generally associated with joining metal parts, so using the term with plastics might sound a bit foreign. But by definition, welding is the process of fusing two or more parts by heat, whether the parts are from metal or plastic, does not play a role here.

What Is Plastic Welding

Plastic welding is used to join thermoplastics by heating plastic pieces until they are malleable and then joined into a unified structure. It is used in a wide range of sectors from infrastructure building, automotive repairs, plumbing, and manufacturing of water tanks and heat exchangers.

Plastic welding can be used on the following materials:

• Acrylonitrile-butadiene-styrene (ABS)

• Polycarbonate (PC)

• Polyethylene (PE)

• Polyethylene terephthalate (PETE or PET)

• Acrylic or polymethyl methacrylate (PMMA)

• Polypropylene (PP)

• Polyvinyl chloride (PVC)

• Other materials

As with other welding methods, surfaces must be clean to achieve the highest weld quality. Plastics are joined at their melting point. Once cooled, they are fused completely.

Plastic Welding Advantages

Plastic welding is becoming increasingly popular among manufacturers in various industries since it is highly efficient and covers a wide array of materials. Unlike some other joining methods, such as fasteners and adhesive bonding, in most cases, it eliminates the need to purchase additional components and materials. Plastic welds are also lightweight and cost-effective while still achieving quality results.

Additionally, plastic welding offers versatility and compatibility with different joint shapes. The welds are permanent and the process is safer when compared to some other traditional welding methods since it produces minimal fumes.

Plastic Welding Methods

There are many methods for plastic welding, each with its advantages and disadvantages. The methods are classified as internal and external

The chosen method should depend on the type of welded materials and their shape as well as the required weld strength. We’ll highlight some of the most common ones below:

Hot Gas Welding

Hot Gas Welding HDPE

Hot gas welding uses a specially designed heat gun with additional plastic welding rods or sheets in order to create malleable and easy-to-join pieces of plastic. The equipment doesn’t require electricity. It is portable and easy to use. The downside of hot gas welding is the slow heating rate compared to other methods. Hot gas welding isn’t suitable for thicker plastics such as PVCs and acrylics.

• Free-hand welding (fan welding)

  A stream of hot air is applied to the weld joint and the plastic weld rod. The melted welding rod is fused into the joint as it reaches working temperature.

• Speed welding (speed tip welding)

  Speed tip welding uses a plastic welder with a working principle similar to a soldering iron. It softens up the plastic and the molten weld rod continuously exits a feed tube, fusing with the workpiece.

Laser Beam Welding (LBW)

Laser Beam Welding of Plastics

Laser welding is a fast and accurate plastic welding process that uses a concentrated heat source while subjecting the workpiece to pressure. Laser welding can be automated through robots, creating clean welds that require little to no post-weld processing. LBW equipment is initially expensive and the process isn’t suitable for plastics with thicknesses above 0.5 inches (12.7 mm). Laser beam welding can sometimes lead to porosity and brittle results.

Ultrasonic Welding

Ultrasonic Plastic Welding

Ultrasonic welding uses high-frequency, low-amplitude mechanical vibrations (15kHz – 40kHz) to generate heat. The vibrations create friction, which allows the plastic polymers to melt, creating a bond between two plastic surfaces. Ultrasonic welding is fast and doesn’t use direct heat application. This makes it an excellent choice for joining plastics such as polyvinyl chloride that are prone to generating fumes when used with other techniques. However, it can only be used to create overlapping joints on thin strips of low-moisture plastics. So the field of application is rather limited for this process.

Spin Welding

Spin Welding Plastic in Slow Motion

Spin welding is a rotational friction welding process that uses pressure and friction between a stationary and moving plastic (lathe, milling machine, drill press). Heat and pressure melt and bond the two pieces of plastic as it cools down. This process is quick and straightforward, which makes it compatible with most plastics. Surface preparation is required to achieve symmetrical surfaces before joining the plastic parts.

Vibration Welding

Vibration Welding of Plastics - Linear Welding

Vibration welding joins plastic materials by heat generated through pressure and friction between rubbing parts. It has two classifications:

• Linear

  One plastic part is stationary while the other material moves back and forth, rubbing the inert plastic at a set frequency and amplitude.

• Orbital

  The upper plastic material moves through a circular motion, creating a welded joint to the stationary plastic material. The process is similar to spin welding but uses a more complex machine, in which the moving part rotates in a small circle. Significantly smaller than the size of the whole joint.

Vibration welding doesn’t need any consumables or surface preparation, making it suitable for creating welded joints between irregularly shaped plastics. The downside is that it requires expensive vibration welding equipment and can only weld specific plastics.

Hot Plate Welding

Hot Plate Welding Plastic

Hot plate welding is a plastic welding technique that uses a hot plate to melt the surfaces of the plastics. The pieces combine to create strong, welded plastic as it cools down. This method is preferred when welding large parts of plastic. It is also faster than other welding techniques. As a drawback, it cannot weld plastics below 0.1 inches (2.5 mm). Hot plate plastic welder also requires frequent maintenance.

High-Frequency Welding

Radio-Frequency aka High-Frequency Welding Explained

High-frequency or radio-frequency welding uses an electromagnetic field (13MHz-100MHz) to melt and join plastic polymers. As the high-frequency generator creates heat and melts plastic by causing the molecules to oscillate at high speeds, pressure is simultaneously applied to create a strong weld joint. This method is incredibly efficient as it can reach weld speeds at around 100 to 120 m/min. Welding operators must wear protective gear and take precautions, as the generator can radiate a large amount of heat.

Solvent Welding

Solvent Welding Acrylics

A solvent or a solvent blend (commonly methyl ethyl ketone) is applied between plastic parts to create a strong weld joint. Unlike other methods that use a plastic filler rod or softened plastic to join plastics, solvent welding uses the chemical bond of the solvent. This technique is simple and inexpensive, perfect for plastic pipes, scale models, and general fabrication. Improper surface preparation or solvent application may cause stress cracking and weak joint integrity.

Plastic Welding Safety

Although plastic welding is generally deemed safer and simpler than known welding methods such as flux-cored welding, for example, it is still best to understand the safety precautions. Protection from fumes and burns can be practiced by having proper ventilation and wearing protective clothing.

Wrapping It Up

Plastic welding covers a wide range of applications such that many industries take advantage of creating strong material bonds. Destructive and non-destructive testing methods are essential in making sure that the plastic welding process is kept at a high quality. While these testing methods minimise risk and improve welding safety, a software-operated welding process further improves the precision of welding plastic.

The post Welding Processes for Plastics Explained appeared first on Fractory.

While this welding technology has been around for almost a century, it is still an essential choice for many industries.

What Is Submerged Arc Welding?

Submerged arc welding (SAW) is a welding method where similarly to other arc welding processes, the base metals are joined by forming an electric arc between the workpiece and an electrode.

SAW process’s defining element is how it protects the weld metal from atmospheric contamination. Submerged arc welding uses a powdered flux layer, generating shielding and slag while creating a smooth and clean weld. Other methods use shielding gas (MIG/TIG welding), flux-cored wire (FCAW), flux-coated electrode (SMAW), or controlled environment (plasma welding) for protecting the weld.

How Does the Submerged Arc Welding Process Work?

Submerged arc welding creates consistent welds by using a blanket of granulated flux. For this reason, the process can be operated only on positions that are flat and horizontal, with the weld advancing by either moving the welding system or the workpiece.

Flux is fed into the joint manually or by using a flux hopper. A single electrode or multiple wire electrode system is placed into the working area, surrounded by the flux blanket. Parameters such as the welding current, arc voltage, and wire feed speed are set depending on the type of metal, its thickness, and desired mechanical properties. Electric current is supplied to the electrodes, producing intense heat that melts and fuses the base material and the filler wire to the bead.

The molten metal cools down, creating strong uniform welds and reusable granular flux at the surface and slag underneath. A hopper collects the reusable flux, while slag is usually peeled off manually.

SAW produces high-quality welds with fewer weld defects than other processes. However, this does not mean that defects won’t ever occur. When they do, it’s generally related to wrongly set welding parameters.

Flux

Granular Flux

Granular flux inside a hopper is usually composed of oxides from aluminium, calcium, magnesium, manganese, silicon, titanium, and zirconium. This composition suits the type of electrode to achieve the metal’s desired properties as it chemically reacts as it melts.

Bonded Flux

Bonded flux is produced by drying the composition and slowly baking it, usually with a compound such as sodium silicate. As an advantage, bonded flux can contain alloying elements, offering flexibility for some applications and protection against rust.

Fused Flux

Fused flux is produced by melting the composition inside an electric furnace. The molten flux is formed into homogenous particles as it solidifies. It is excellent for creating consistent welds along the bead.

Wire Electrode

SAW uses a wire spool to feed the wire electrode into the weld. The wire’s thickness is usually between 1.6mm and 6mm. Electrodes may come in the form of solid, twisted, or cored wire and may be operated using different power sources.

Specific circumstances may need the use of modified wire electrodes and electrode systems to achieve the desired weld profile:

• Twin-wire

• Multiple wires

• Single wire with hot/cold addition

• Metal powder additive

• Tubular wire

Multiple wire systems typically use a lead wire to improve penetration, while a trailing wire is used to add extra fill and improve the bead profile. Additional wires are used in the electrode system to add more deposition to the weld pool.

Materials

Submerged arc welding process is used with the following materials:

• Copper alloys

• Low to medium-carbon steels

• Low-alloy steels

• Mild steels

• Nickel-based alloys

• Quenched and tempered steel

• Stainless steels

• Uranium alloys

Power Source

Submerged arc welding can operate on multiple power outputs, allowing it to manipulate the weld results. Multiple electrode systems enable SAW to run wires at different power sources, to better control the bead profile and penetration.

DCEP offers the most stability and penetration, while DCEN is optimal in increasing deposition rates. Running this welding process in AC is the middle ground where a balance between the two is achieved.

Applications and Industries

Submerged Arc Welding

Fabrication

SAW is one of the preferred welding processes in fabricating pressure vessels, pipes, and boilers due to its strength in longitudinal and circumferential welding. This welding operation achieves a smooth weld pool from the continuously fed electrode.

Shipbuilding

The flexibility of SAW process allows it to be performed both indoors and outdoors which makes it suitable for shipbuilding. It’s perfect for creating long, straight welds for heavy metals which make up ship parts.

Automotive

Metals used in the automotive and military industry are fit for SAW, along with the speed and efficiency it brings. This welding method is also perfect for automation, with the option to have multiple or single-pass welds based on the metal’s thickness.

Railways

The submerged arc process allows deep weld penetration, which is attractive to the railway industry.

Advantages of SAW

1. The blanket of granular flux creates minimal welding fume and spatter.

2. Allows performing semiautomatic or fully automatic welding.

3. Flexible for both indoor and outdoor applications.

4. Creates smooth, uniform and deep welds.

5. Around 50-90% of the flux is reusable and recyclable.

Limitations of SAW

1. Limited to flat and horizontal welding positions

2. A rather narrow range of weldable metals.

3. Requires post-welding slag removal.

4. Practically restricted to circumferential and long straight beads.

5. Precise parameters are required to achieve desired weld deposit since welds aren’t visible while welding.

The post Submerged Arc Welding (SAW) Explained appeared first on Fractory.

Despite all that, the gas welding process still has its place among hobbyists and smaller metal workshops due to its simplicity and wide scope of applications. However, its usage is now mostly limited to thinner stock and repair operations.

What Is Gas Welding?

Gas welding or oxy-fuel welding is a process that uses heat generated from burning a combination of different gases to melt and fuse metals. Although it is possible to join the metal workpieces without any additional filler material, the use of filler rods is encouraged to guarantee strong and lasting welds.

Unlike most processes that use electricity to create heat (arc welding techniques like MIG, TIG, and SMAW), the flame from gas welding is created by just burning a mixture of gases. Oxygen and acetylene are regarded as the primary gas combination since it is the most effective in generating heat to weld steel, thus making the process known as oxy-fuel or oxy-acetylene welding.

Other fuel gases used in the process are propane, hydrogen and coal gas. These combinations can be used for welding non-ferrous metals and specific applications such as brazing and silver soldering.

The same oxy-welding equipment can be used for oxy-acetylene cutting by adjusting the flame profile and adding a rather inexpensive cutting attachment. The cutting torch features an oxygen-blast trigger helping to burn and blast the molten metal out of the cut.

Oxy-Fuel Welding Process

Oxyacetylene welding uses the concept of generating heat from the combustion of oxygen and fuel gas. Gas supply stored in high-pressure cylinders flows through the flexible hoses (an oxygen hose and a fuel gas hose) by adjusting the gas regulators. The gases are combined in the mixing chamber of the hand-held oxy-fuel torch and exit through the orifice in the tip. Welding tip orifice size is an important factor and thus, it should be chosen in accordance with the application.

As heat is applied to the base metal, it reaches a melting point (around 3200°C), wherein fusion welding occurs. Other welding techniques that use electricity can reach higher temperatures (above 5000°C), making oxyacetylene welding most suitable for thin metals. Using filler rods is optional and depends on the scope of the project.

Since gas welding operates with combustible materials, it is vital to practice proper safety measures.

Types of Flames

The type of welding flame plays an important role in determining the resulting weld joint and its properties. The flame profile is manipulated by adjusting the fuel gas and oxygen flow rate.

Higher amounts of oxygen lead to a hotter flame, which might cause the metal to warp. A colder flame occurs when the amount of fuel gas is higher than oxygen, which might cause poor weld quality.

Neutral Flame

Equal amounts of welding gases by volume result in a neutral flame. The complete combustion of the fuel gas and compressed oxygen means that the properties of the weld metals aren’t affected while producing minimal smoke at the same time.

This welding flame has two zones, a white inner zone of about 3100°C and a blue outer zone with a temperature of about 1275°C. Neutral flame is preferred when welding metals such as cast iron, mild steel and stainless steel.

Carburising Flame

Carburising aka reducing flame is achieved by supplying higher amounts of fuel gas compared to pure oxygen. The flame produced is smoky and has a quiet flame that chemically forms metal carbide.

Three zones are produced in this flame: a white inner zone (2900°C), a red intermediate zone (2500°C), and a blue outer zone (1275°C). Carburising flame is preferred for welding nickel, steel alloys and non-ferrous metals.

Oxidising Flame

Oxidising flames are produced when the supplied gas from the oxygen cylinder is higher than the fuel gas – the excess oxygen results in higher flame temperatures exiting the welding torch than neutral flame.

This type of flame produces two zones, a white inner zone at around 3500°C and a blue outer zone at 1275°C. Oxidising flame is used for welding metals such as brass, copper, bronze and zinc.

Welding Techniques

Leftward

The torch travels from the right to the joint’s left side with a tip forming a 60-70 degree work angle to the workpiece. The filler material is angled at 30 to 40 degrees to the plate. Three movements create uniform fusion through its flame: circular, rotational, or side-to-side.

Leftward welding is mainly used to weld unbevelled plates up to 5mm, cast iron, and non-ferrous metals.

Rightward

Opposite to leftward welding, the rightward technique starts at the left side of the joint and travels towards the right end. An angle of 40-50 degrees is established between the torch tip and the workpiece, while the filler rod makes a 30-40 degree angle to the work material.

Rightward welding is generally faster than leftward welding, with less distortion, and filler metal consumed. It creates denser and stronger welds, which are perfect for protection against contamination.

All-Positional Rightward

This technique is a modification to rightward welding used mainly for steel plate welding, also some pipework and butt welds (5-8mm thick) wherein complete view and movement are required.

Vertical

The joint is created with an oscillating rod and torch travelling from the bottom toward the top. The rod makes a 30-degree angle, while the torch makes a 25 to 90-degree angle with the workpiece, depending on its thickness.

A single operator may use this technique for steel plates up to 5 mm thick, while two operators working in harmony are required for thicker metals.

Materials

• Aluminium

• Brass

• Bronze

• Carbon steels

• Cast iron

• Copper

• Magnesium

• Mild steel

• Nickel

• Stainless steel

• Steel alloys

• Zinc

Advantages of Gas Welding

1. The process is suitable for a variety of ferrous and non-ferrous metals.

2. Gas welding doesn’t require electricity.

3. It is a simple and straightforward welding technique.

4. Gas welding equipment is cheap and portable compared to other welding processes.

Disadvantages of Gas Welding

1. Gas welding offers less penetration and heat than arc welding techniques, such as TIG and MIG welding.

2. The process requires post-weld finishing to improve its aesthetic look.

3. Oxyacetylene welding is prone to weld defects since it doesn’t have weld pool shielding.

4. Gas welding has a slower rate of heating and cooling compared to modern methods.

5. It isn’t suitable for welding high-strength steel since it can alter its mechanical properties.

Wrapping It Up

Oxy-fuel welding is one of the pioneers of the industrial revolution, offering versatility in its wide range of applications. Today, it is not much used in industries as it has been before, as newer and more innovative welding techniques have replaced it. Still, gas welding remains a reliable choice for some applications and is preferred by some hobbyists and professionals.

The post Oxy-Acetylene Welding Explained appeared first on Fractory.

Let’s cover some key points that make electron beam welding stand out from other welding methods.

What Is Electron Beam Welding?

Electron Beam Welding

Electron beam welding (EBW) uses a high-velocity beam of electrons to melt and fuse metals together. The electron beam can be focused to create a small weld area, which makes it ideal for welding delicate parts or complex designs.  On top of that, EBW works at a rapid rate, making it one of the fastest processes in assembly welding.

Electron beam welding machines are quite complicated, requiring skilled operators to achieve optimal results. On the other hand, it offers a wide range of penetration depth, generally from 0.127 mm to 50 mm/0.005 to 2 inches (although much higher depth can be achieved for certain materials) when using a filler material with the latter, making it stand out compared to common welding techniques like MIG, TIG, and stick welding. EBW fusion welding process run on a single pass creates joints with minimal distortion and possesses the ability to join different metals.

Electron Beam Welding Process

The working principle behind electron beam welding is emitting a focused beam of high-velocity electrons into a joint. This process is usually performed inside a vacuum chamber to improve efficiency and prevent the electron beam from dispersing.

High voltages are supplied into an electron gun, which then expels a high-velocity stream of electrons with the help of cathodes, anodes, focusing coils, and magnetic fields. The intensity of electron beams is 100-1000 times higher than arc welding, allowing deep penetration and narrow heat-affected zones.

Similarly to plasma welding, the EBW process can be run in low power, medium power and high power aka keyhole mode. The low power mode is used to produce extremely fine welds, which can be as small as 20µm. Medium power is generally used for weld thicknesses from 1mm to 20mm, anything over that is in the domain of high power electron beam welding. Running the machine in keyhole mode can penetrate up to 300mm of steel and is known to create stable, good-quality welds for material thicknesses over 200mm.

Recent breakthroughs in EBW allow local welding with a workpiece larger than the vacuum chamber adding a bit more versatility to the welding process. This welding technology is achieved by having only the electron beam gun inside a vacuum box while the workpiece itself remains outside of the vacuum chamber.

Materials

The technology behind electron beam welding allows various metals to be welded together, including dissimilar metals, since it is mostly performed in a vacuum environment. EBW is mainly used with these materials:

• Aluminium

• Bronze

• Cobalt alloys

• Copper

• Hastalloy

• Inconel

• Carbon steel

• Magnesium

• Nickel

• Stainless steel

• Titanium

• Zinc

Equipment

The main components of electron beam welding equipment are the following:

Electron Gun

The main components of an electric gun are the cathode, anode, grid cup and focusing unit. There are two types of electron guns. Self-accelerated electrons are accelerated using the potential difference between the cathode and the anode. Work-accelerated electrons are accelerated using the potential difference between the cathode and the workpiece.

Power Supply

DC power is used in the electron beam welding method with 5-30 volts for small equipment and 70-150 volts for large equipment.

Vacuum Chamber

The pressure for partial vacuum is at 10^-2 to 10^-3 mbar, while hard vacuum uses a range of 10^-4 to 10^-5 mbar.

Applications

The diversity of EB welding allows the ability to weld metals with varying thicknesses, making it a flexible option for welding complex parts such as transmission assemblies or small electronic components. It’s also a great option for welding metals with different melting points and thermal conductivities.

As electron beam welding technology is highly automated and delivers a clean result with repeatable accuracy and minimal distortion, there is no need for post-weld machining. Some of the industries benefitting from this include aerospace, automotive, medical, nuclear, oil and gas.

Electron Beam Welding vs Laser Welding

While the basic principle of electron beam welding and laser welding is similar on the surface, there are some distinct differences that make each of them unique:

Heat source

EBW uses a focused beam of electrons, while the laser welding process uses photons to generate heat.

Vacuum environment

Both processes can be performed in a vacuum environment, protecting the weld pool from contamination against air molecules and improving the weld quality. Conventional laser welding is done under atmospheric conditions with the help of inert gas shielding or a combination of gases.

Welding speed

Laser beams require high welding speeds since it vaporises the base materials, creating fumes. The electron beam welding process can accommodate different welding speeds while still achieving deep welds.

Power consumption

Electron beam welding converts around 85% of the electrical input into usable power. In comparison, laser welding only converts up to 40% of electricity to usable power, even with the use of modern tools.

Advantages of Electron Beam Welding

1. Can reproduce precise welds at rapid weld speeds.

2. A narrow heat-affected zone allows for welding delicate assemblies.

3. Clean welds since EBW is done in a vacuum environment.

4. Ability to join dissimilar metals.

5. High weld penetration range.

6. Most penetration depths don’t require filler material.

Disadvantages of Electron Beam Welding

1. High initial costs.

2. EBW machinery requires frequent maintenance to function correctly.

3. The process requires highly skilled machine operators.

4. The size of the vacuum chamber limits weld size for traditional EBW.

5. Extreme precaution is required from radiation.

The post Electron Beam Welding (EBW) Explained appeared first on Fractory.

Let’s dig deeper and explore what plasma welding is all about.

What Is Plasma Welding?

Plasma arc welding (PAW) is a fusion welding process that uses a non-consumable electrode and an electric plasma arc to weld metals. Similarly to TIG, the electrode is generally made out of thoriated tungsten. Its unique torch design produces a more focused beam than TIG welding, making it a great choice for welding both thin metals and creating deep narrow welds.

Plasma welding is often used to weld stainless steel, aluminum, and other difficult metals compared to traditional methods. Similarly to oxy-fuel welding, this process can also cut metal (plasma cutting), making it a versatile tool for fabricators and manufacturers.

Plasma Arc Welding Process

Plasma Arc Welding

The plasma arc welding process revolves around the principle of striking an arc between a non-consumable tungsten electrode and the workpiece. The plasma nozzle has a unique design feature, where the electrode is located within the body of the torch. This allows the arc plasma to exit the torch separated from the shielding gas envelope.

Additionally, the narrow opening of the nozzle increases the plasma gas flow rate, allowing for deeper penetration. While filler metal is typically supplied at the weld pool’s leading edge, it is not the case when creating root pass welds.

The complexity of the plasma welding torch sets it apart from gas tungsten arc welding. Plasma welding torches operate at very high temperatures, which can melt away their nozzle, making it a requirement to always be water-cooled. While these torches can be manually operated, nowadays, most modern plasma welding guns are designed for automatic welding.

The most common defects associated with plasma welding are tungsten inclusions and undercutting. Tungsten inclusions occur when the welding current exceeds the capabilities of the tungsten electrode and small droplets of tungsten get entrapped in the weld metal. Undercuts are generally associated with keyhole mode PAW welding and can be avoided by using activated fluxes.

Plasma Arc Welding Operating Modes

Three operating modes are used in plasma welding, wherein it can be operated at varying currents:

Microplasma (0.1 – 15A)

This operating mode can run arcs at low currents and remain stable up to 20mm arc length.

Microplasma welding is used to join thin sheets up to 0.1 mm in thickness, which is optimal for creating wire meshes with minimal distortion.

Medium current (15 – 200A)

The characteristics of the plasma arc are quite similar to TIG welding, but the arc is stiffer since the narrow opening of the torch restricts the plasma. We can increase weld pool penetration by speeding up the plasma flow rate, but this increases the risk of shielding gas contamination.

Medium current or melt-in mode offers better penetration than TIG and improved protection. The only drawback is that the torch requires maintenance and is bulkier compared to a TIG torch.

Keyhole mode (over 100A)

A powerful plasma beam is used to engage in high-current aka keyhole mode by increasing the gas flow and welding current. This mode allows deep penetration, using a single pass (up to 10mm thick for some materials) to create a consistent weld pool from molten metal.

Similarly to electron beam welding, the keyhole mode is great for welding thicker materials at high welding speeds. To guarantee satisfactory welds, filler material is generally added. Its welding applications include mechanised welding, positional welding, and pipe welding.

Comparison of Plasma and TIG Welding

Normally, a tungsten electrode is used in TIG welding to strike an arc between the torch and the workpiece. The plasma process works similarly but uses a different setup in its welding torch. The constricted nozzle design allows electrons to move at high velocities. This ionises the gas, creating a plasma jet with a high heat concentration, offering deeper penetration.

As plasma welding offers greater precision than TIG welding, it has a smaller heat-affected zone which is perfect for creating narrower welds. Ideally, plasma welding is a better choice than TIG welding, as it is an evolution of the latter. The technology behind its equipment allows it to run with lower current demand, and better arc stability which leads to better stand-off distance, and better tolerances if the arc length is changed.

TIG welding however is a simpler method due to the complex parameters available for plasma gas welding. An operator would need extra training in order to transition from the already advanced TIG welding to PAW. And last, TIG welding equipment is cheaper and requires less maintenance than plasma arc welding’s sensitive and complex torch.

Materials

Similarly to TIG welding, plasma welding is suitable for the majority of well-known metals, although it might not be the most cost-effective solution for some of them:

• Alloy Steel

• Aluminium

• Bronze

• Carbon Steel

• Copper

• Iron

• Inconel

• Lead

• Magnesium

• Monel

• Nickel

• Stainless Steel

• Titanium

• Tool Steel

• Tungsten

Equipment

The key components of plasma welding equipment are:

Plasma torch

The unique design of the water-cooled plasma torch is the main distinguishing factor from other welding processes. Its operating principles have already been explained in previous sections.

Depending on the weld material and desired weld characteristics, different types of nozzle tips can be selected.

Control console

While conventional welding techniques directly connect a torch to a power source, plasma arc welding uses a control console between the two.

Some of the console features are the torch protection circuit, high-frequency arc starting unit, power supply for the pilot arc, water, and gas valves, individual meters for plasma, and shielding gas flows.

Power supply

Plasma arc welding uses DC power (rectifiers or generators) of at least 70 volts for open circuit voltage with drooping characteristics to have greater control in generating weld beads.

Gases used

• Plasma gas – exits the constricting nozzle separately from the shielding gas envelope and becomes ionised

• Shielding gases (argon, helium, hydrogen) – inert gas protects the weld from the atmosphere

• Back-purge and trailing gas – certain materials require special conditions

Wire feeder

Plasma welding may use wire feeders with a constant velocity that can be modified to run from 254 mm per minute to 3180 mm per minute.

Applications

Steel tubes

PAW is a great welding method in manufacturing steel tubes as it can be performed at high-speed welding with great metal penetration. Some industries prefer the plasma welding process to conventional TIG since its system is faster and uses less filler material.

Electronics

One of the welding parameters of the plasma welding process is it can run at low current modes. This mode allows small metal component welding, which deals with delicate materials sensitive to environmental factors.

Medical industry

Medical devices require precise components in order to run effectively. PAW is perfect for welding these components as it can reliably create a consistent weld bead.

Advantages of Plasma Welding

1. Can be operated in every welding position.

2. Fast travel speeds from concentrated heat input.

3. Keyhole welding allows for complete penetration.

4. Low current mode is suitable for thin and sensitive components.

Disadvantages of Plasma Welding

1. Expensive equipment and components.

2. Requires training and skill to create good welds.

3. Produces 100dB noise.

4. Creates ultraviolet and infrared radiation.

5. Water cooling is necessary because of high working temperatures.

6. Delicate equipment needs a higher amount of maintenance.

The post Plasma Arc Welding (PAW) Explained appeared first on Fractory.

Let’s dive deeper into the concept behind laser welding.

What Is Laser Welding?

Laser welding or laser beam welding (LBW) is a process that uses a concentrated heat source in the form of a laser to melt the materials, which fuse together as they cool down. It is a versatile process since it can weld thin materials at rapid welding speeds while running narrow and deep welds for thicker materials.

While laser welding equipment costs more than traditional welding processes, its operating costs are lower since it doesn’t necessarily require additional filler material and post-processing. Also, the high welding speeds allow the production of more parts per hour. The technology behind this process distinguishes significantly from conventional arc welding processes such as MIG, TIG and SMAW. Modern laser welding applications use programmable robots incorporated with advanced optics to precisely target an area in the workpiece.

Types of Laser Beam Welding

There are two different types of laser beam welding, both with unique operating principles to suit specific applications. The way that the material interacts depends on the laser beam’s power density.

Heat Conduction Welding

In this method, a focused laser beam is used to melt the surface of the base materials. When the joint solidifies, a precise and smooth weld seam is produced. Welds created using the head conduction method do not generally need any additional finishing, the quality is great “out of the box”.

The energy enters the weld zone only by heat conduction. This limits the welding depth and thus the process is great for joining thin materials. Heat conduction welding is often used for visible weld seams which need to be aesthetically pleasing.

There are two subcategories of heat conduction welding:

• Direct heating – the laser beam directly applies its power on the surface of the metals.

• Energy transmission – absorbing ink is applied to the joint, soaking up the energy that the laser beam applies.

Deep Penetration/Keyhole Welding

Running the process in keyhole welding (deep penetration) mode creates deep, narrow welds with uniform structure. For metals, power densities of about 1 megawatt per square centimetre are applied. This does not only melt the metal but vapourises it, creating a narrow vapour-filled cavity.

This is called a keyhole cavity or vapour capillary and is filled with molten metal as the laser beam advances through the workpiece. Keyhole welding is a high-speed process and thus, the distortion and the formation of a heat-affected zone are kept to a minimum.

Laser Beam Welding Process

Automated Laser Welding

Laser beam welding works on the principle of using a laser with high power density to apply heat to a joint between the surface of two metals. The material melts at the joint, and it permits fusion between the metals as it solidifies.

Laser welding is typically carried out by welding robots that can precisely apply a large amount of energy at high speeds, guided by flexible optical fibres. This results in melting a sufficient amount of metal in the joint, creating narrow welds with minimal distortion. Handheld laser welding systems seemingly offer a great alternative to bulky industrial machines, but those welders’ safety is being questioned.

The welding process can be performed under atmospheric conditions but for more reactive materials inert gas shielding is recommended to eliminate the risk of contamination. Similarly to electron beam welding, laser welding could be carried out in a vacuum but it is not deemed economically feasible. Thus, laser welders come equipped with gas nozzles that supply inert gas to the weld area.

Many laser welding applications are carried out without the need for additional filler material. However, some challenging materials and applications require filler material to produce satisfactory welds. Adding filler material improves the weld profile, reduces solidification cracking, gives the weld better mechanical properties and allows for more precise joint fit-up. The filler material can come in powder form or as filler wire but since powders are generally more expensive for most materials, using wire feedstock is more common.

The four most common joint types utlised by laser welding are butt welds, edge flange welds, filler lap welds and overlap welds.

Laser welding can be performed on a variety of metallic materials including low-carbon steel, stainless steel, aluminium, titanium, etc. It can also fuse materials that aren’t as widespread as the aforementioned, such as Kovar and material combinations deemed not easy to weld such as copper-copper, copper-aluminium, etc. Welding high-carbon steels is generally not recommended due to the high cooling rate which tends to cause cracks. 

Types of Lasers

There are three primary types of laser welders used for the welding process:

Gas laser (CO2)

A CO2 laser source is a mixture of gases with CO2 being the main component alongside nitrogen and helium. These lasers can operate in a continuous or pulsed mode at a low current and high voltage to excite the gas molecules. Carbon dioxide lasers are also used in special circumstances, such as in dual-beam laser welding, wherein two beams are produced and arranged either in tandem or side-by-side.

Solid-state laser

Solid-state lasers use Diode Pumped Solid State (DPSS) technology to pump ore such as ruby, glass or yttrium, aluminium, and garnet (YAG), or yttrium vanadate crystal (YVO4) with a laser diode to produce laser rays. These lasers are operated in either continuous wave or pulsed beam mode. The pulsed mode produces joints similar to spot welds but with complete penetration. These lasers have their fair share of disadvantages when compared to modern fibre lasers but we can’t deny that solid-state lasers still have excellent beam stability and quality along with high efficiency.

Semiconductor-based lasers are also in the solid state but are generally considered a separate class from solid-state lasers. These lasers are only used for cheaper and small projects. But they’re sometimes used when welding in hard-to-access areas since the equipment is more compact. The quality of the beam is far worse when compared to other types of lasers and thus, it is not as common in industrial settings.

Fibre laser

Fibre lasers are the newer type of solid-state lasers that offer more power, better quality and safer operation. In fibre lasers, the laser beam is created when the fibre absorbs raw light from the pump laser diodes. To achieve this transformation, the optical fibre is doped with a rare-earth element. By using different doping elements, laser beams with a wide range of wavelengths can be created and this makes fibre lasers perfect for a variety of applications, including laser welding and laser cutting. However, it’s worth noting that a standard laser cutting head cannot be used for welding and a laser welding head cannot meet the cutting speeds and quality demanded in most industrial applications.

Advantages of Laser Welding

• Great quality thanks to low heat input and precise laser power control.

• The process is fast which allows for low unit costs.

• Great welding depth resulting in high-strength welds.

• Allows welding material combinations that other methods can’t join.

• The simple welding equipment allows welding under special conditions.

Disadvantages of Laser Welding

• High initial investment

• Strict tolerances require perfect workpiece assembly and laser calibration.

• Materials with high reflectivity and conductivity (aluminium and copper) can create a fussy weld result (in the case of Co2 lasers).

• Porosity and brittleness might result from rapid solidification.

• Laser optics are quite delicate and can easily be damaged.

Laser-Hybrid Welding

Laser-hybrid welding combines the concepts of electric arc and laser beam. The two simultaneously act in the same welding zone, complimenting each other and creating a unique welding process. Although laser welding can be used in conjunction with virtually any arc welding process, there are some that stand out and are used more commonly.

There are three main types of laser-hybrid welding:

• MIG augmented welding (often synonymous with laser-hybrid welding)

• TIG augmented welding

• Plasma-arc augmented welding

The hybrid welding process offers deep penetration brought by laser welding and a weld cap profile achieved comparable to arc welding processes. Using protective shielding gases and other arc welding consumables offers greater control over the weld characteristics than laser welding would allow just by itself. Laser-hybrid welding is definitely a process that is on the rise and will be utilised more and more in the shipbuilding, railroad, automotive industries and large-scale pipe welding projects in the future.

The post Laser Welding Explained appeared first on Fractory.

Modern welding was pioneered in 1800 when Sir Humphry Davy struck an electric arc using a battery and two carbon electrodes. Since then, welding has developed into highly versatile forms, paving the way for its use in a variety of applications, from small DIY projects to large-scale manufacturing assemblies.

Different welding processes are a staple in most industry sectors and thus, let’s understand how these work and the principles behind them.

How Does Welding Work?

Welding is a high-heat process that melts the base materials. This is also the main differentiating factor from soldering and brazing where only the filler material is melted and no fusion between the parent materials occurs.

Welding works by joining two or more workpieces together at high temperatures. The heat causes a weld pool of molten material which after undergoing cooling, solidifies as one piece, forming a weld. The weld can even be stronger than the parent metals.

There are many different types of welding but all of them involve heat or pressure to melt the metals to create welded joints. The source of heat or pressure may vary depending on the application and the material used.

Metals are known as the most commonly welded materials, given their easy and straightforward welding principles. Plastic welding is also quite widespread but welding wood is just in its nascent phase.

The welding process is influenced by many factors, such as the need for specific additional tools, shielding gases, welding electrodes and filler material. Let’s have a closer look at some of the most common welding methods used today and find out what makes each of them unique.

Different Welding Types

Although the fundamental concept of welding is rather simple, we categorise them by the energy source used. As we break these subcategories down even further, we can dive deeper into the operating principles behind each separate method.

Arc Welding

Arc welding includes some of the most well-known welding processes and these are most likely what come to mind when visualising the welding process in general. In these processes, an electric arc generates heat between the electrode and the metal to be welded. The electrode may be consumable or non-consumable, and its power source can vary from alternating (AC) to direct current (DC).

MIG/MAG Welding

Gas metal arc welding (GMAW), also known as MIG/MAG welding (metal inert gas/metal active gas), uses a continuous wire electrode fed through a welding gun. As the electric arc melts the electrode wire it is then fused along with the base metals in the weld pool.

Shielding gas is simultaneously supplied to the weld area to create a protective layer from atmospheric contamination.

The simplicity of this welding technique allows it to be one of the preferred choices for industrial welding, manufacturing, construction and for the automotive sector. GMAW has pretty much replaced atomic hydrogen welding (AHW), mainly because of the availability of inexpensive inert gases.

TIG Welding

Tungsten inert gas welding uses a non-consumable tungsten electrode and an inert shielding gas. In contrast to MIG/MAG welding, using separate filler metal in TIG welds is optional and depends on the project.

The gas tungsten arc welding (GTAW) process creates accurate and high-quality welds with great penetration making it suitable for several applications, such as aerospace and automotive industries. While TIG welding has a steeper learning curve than MIG welding, the many adjustable features and functions of a TIG welder make it a very versatile process.

Shielded Metal Arc Welding

Shielded metal arc welding (SMAW) also known as manual metal arc welding (MMAW/MMA) or just stick welding, uses a consumable flux-coated metal electrode to join metals.

As we strike the electrode with the base metal, it creates an arc that melts down the materials in the weld pool. The flux releases a shielding gas to protect the weld metal from contamination. Slag deposits are removed after the cooling process using common shop tools such as a wire brush.

SMAW is a reliable welding process that offers versatility in welding different metals and various conditions. It’s also portable and lightweight, with no need for a gas tank as with some of the other welding methods mentioned previously. The welding electrode comes as a welding rod, making it perfect for tight spaces and awkward welding positions.

Flux-Cored Arc Welding

Flux-cored arc welding (FCAW) is an automatic or semiautomatic process that uses a welding electrode that contains a flux core that acts as a shielding agent. Additional protection from contaminants is called dual-shielded FCAW, wherein a shielding gas is used along with the flux-cored electrode.

FCAW is well-suited for ferrous metals and operations requiring little pre-cleaning. It is best used for repairs, pipes, shipbuilding, outdoor and underwater welding because of its incredible protection from external conditions.

Although FCAW and GMAW are two separate welding types, the only major difference lies in shielding the weld zone using electrodes and shielding gases.

Gas Welding

Gas welding, or oxy-fuel welding, is one of the oldest forms of heat-based welding that uses oxygen and fuel gases to join metal surfaces. This welding method typically uses acetylene or gasoline as its fuel gas, which makes it known as oxyacetylene, oxy-gasoline welding. Other gases, such as hydrogen and propane, can be used to braze and solder non-ferrous metals but they do not generate enough heat to melt steel.

A unique property of gas welding is that it doesn’t run on electricity, making it a viable choice if it isn’t available. This welding method allows fusion between ferrous and non-ferrous metals and allows the welding of both thin metal sections and steel plates. The process is relatively easy to learn and low-cost in nature.

The same equipment can be used for oxy-fuel cutting when adjusting the gas flow to manipulate the flame profile.

Plasma Welding

Plasma Arc Welding

Plasma arc welding works in a similar concept to TIG welding, but the torch is designed in a manner that the inert gas exits the nozzle at a higher velocity in a narrow and constricted path. Plasma is created as the arc is struck with the inert gas, ionising as it flows into the region. This leads to welding temperatures up to 28000 °C, which can melt any metal. The high operating temperatures of plasma torches (along with gas torches), enable the processes to be used for welding and cutting.

Plasma welding is one of the cleanest welding techniques since the highly concentrated heat creates a narrow bead, which results in minimal spatter. It’s perfect for applications such as aerospace manufacturing that require pinpoint precision. Plasma welding is one of the most sought automated welding processes since it operates at low running costs while providing accurate and neat welds.

Submerged Arc Welding

Submerged Arc Welding

Submerged arc welding (SAW) works similarly to SMAW, which protects the weld metal by using flux. The welding technology behind this automatic or semiautomatic welding process uses a separate flux hopper that deposits granular filler metal to the weld.

This welding technique creates stable and clean welds, which makes it better than most conventional manual welding processes. It’s an excellent choice for metals such as nickel, steel, and stainless steel and is often used for manufacturing pipes, pressure vessels and boilers.

Resistance Welding

Resistance or pressure welding uses the application of pressure and current between two metal surfaces to create fusion. Workpieces are placed in contact together at high pressure with a current passing through the contact point. The resistance in the metals generates heat which fuses together the metal surfaces of the workpiece.

Spot Welding

Resistance spot welding (RSW) uses two electrodes to press together overlapping metals while a welding current is applied through the resistive metals. Heat is generated and the metal surfaces fuse together to create a weld joint in the shape of a button or nugget.

Metals are fused using large amounts of energy in a short time span (approx. 10-100 milliseconds) joining the workpieces almost instantaneously. The area around the weld nugget stays unharmed by the excessive heat, thus the heat-affected zone is minimal with spot welding.

Spot welding is most often automated by using welding robots. This makes it one of the most efficient welding methods used in assembly lines and thus an attractive choice for the automotive, electronics and manufacturing industries.

Seam Welding

Seam Welding

Seam welding is a subcategory of spot welding that uses two electrode wheels to apply pressure while current is applied through the workpiece. The welding machine can create individual weld nuggets to the workpiece by applying current at intervals, or it can be continuous, depending on the project.

The joints created by resistance seam welding are tight and the process is incredibly fast and clean, making it an ideal choice for automated welding. The sheet metal industry uses seam welding to manufacture tin cans, radiators and steel drums.

Laser Welding

Laser Beam Welding

Laser beam welding (LBW) uses, as the name suggests, a laser beam as a concentrated heat source to melt metals and create welds. LBW’s high power density results in small heat-affected zones. The spot size of the laser ranges from 0.2 to 13 mm which makes it suitable for welding materials with varying thicknesses, generating a better result than conventional welding process.

Laser welding rapidly creates high-quality welds under fine tolerances. The process is generally automated and is used by the automotive, medical and jewellery industries.

Although one might think that since oxy-fuel and plasma torches can be used for both welding and cutting, this applies to laser torches as well but this is generally not the case. A standard laser cutting head cannot be used for welding and a laser welding head cannot meet the cutting speeds and quality demanded in most industrial applications.

Electron Beam Welding

Electron Beam Welding

Electron beam welding (EBW) is a fusion welding process where electrons generated by an electron gun are accelerated to high speeds. The electron beam creates kinetic heat as it contacts the base metals, causing them to melt and form a weld pool. A weld is created as the joint cools down. This welding procedure is performed in a controlled vacuum to prevent the beams from scattering.

Electron beam welding offers precision, making it a valuable process for applications requiring minimal distortion. Some of its applications include electronic components, aircraft parts, storage tanks and bridge components. EBW allows to weld materials that are prone to contamination.

Friction Welding

Friction Welding

Friction welding is a solid-state process that uses, as the name suggests, friction to fuse metals together. Unlike most welding processes, it doesn’t use a welding torch, welding rods or a shielding gas to create welds. The process only uses the heat generated from high rotational, vibrational or lateral contact speeds between two clean metals to create a bond. The metal residue formed during this procedure is removed after the cooling process.

The welding equipment used in friction welding is more eco-friendly than other methods as it doesn’t emit harmful welding fumes or release toxins into the atmosphere. Its simplicity makes it a great option for welding drill bits, connection rods, axle tubes and valves.

Welding Safety

All manufacturing processes come with some risks and welding is not an exception here. It is important to have the proper knowledge and welding equipment to protect yourself from any hazards. Along with practicing safety precautions, using up-to-date protective gear, such as the appropriate welding helmet, gloves, etc, is just as necessary.

Today, modern technologies are helping to improve welding safety significantly, taking workers out of harm’s way and introducing increased automation to boot. For instance, the use of industry-leading six-axis robots allows even the most complex welds to be executed without the need for a human worker to interact with tools during the operation.

Flesh and blood specialists are still an essential part of the welding process, of course. It’s just that they no longer need to get up close and personal with material or equipment to get the job done.

Wrapping Up

Welding has come a long way since its discovery in the Bronze Age when primitive forge welding methods were developed. Today, it has become an irreplaceable tool used by hobbyists and large-scale industries alike. It became one of the driving forces of industrialisation and continues to transform how things are manufactured to this day.

As welding continues to evolve, its standards and norms also improve with time. New possibilities constantly arise, allowing us to weld new material combinations while guaranteeing and improving weld strength and process safety. With the recent developments in hybrid welding, we can only expect welding technology to continue shaping the future of engineering.

Fractory offers welding services as a part of our full service – from quoting to delivery. Our network of pre-vetted manufacturing partners offers access to a wide range of processes and capabilities.

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Welding services are mainly used in the manufacturing industry for joining metals in constructing buildings, bridges, automobiles, aircraft, pipes, and many other objects. However, welding is not a perfect process as numerous types of welding defects can occur internally or externally in the welded metal.

Let’s explore some of the more common weld defects, their causes, and remedies.

What Is a Weld Defect?

A weld defect results from a poor weld, weakening the joint. It is defined as the point beyond the acceptable tolerance in the welding process.

Imperfections may arise dimensionally, wherein the result is not up to standard. They may also take place in the form of discontinuity or in material properties. Common causes of welding defects come from incorrect welding patterns, material selection, skill, or machine settings, including welding speed, current, and voltage.

When a welded metal has a welding defect present, there are multiple options for resolving the issue. In some cases, the metal can be repaired, but at other times the metal itself has melted and the welding procedure needs to be restarted.

Weld irregularities occur for a variety of reasons and it results in different welding defects. They can be classified into two major categories: internal welding defects and external welding defects.

External Welding Defects

External welding defects refer to discontinuities in the weld metal that are noticeable to the naked eye.

Cracks

Cracks are the worst welding defect since they can rapidly progress to larger ones, which inevitably leads to failure. Weld cracks are mainly classified depending on how they form in the weld bead.

Longitudinal cracks form parallel to the weld bead while transverse cracks form across the width. Crater cracks form at the end of the bead, where the arc concludes.

Welding cracks can also appear at varying temperatures:

• Hot cracks form when weld joints crystallise as the parent and base metals are heated above 10000°C. The primary reasons for hot cracks is when an incorrect filler metal is used and when the workpieces undergo high heating and cooling rates in processes such as laser welding.

• Cold cracks form after the cooling process of the weld metal. The weld crack may form hours or days after the metal’s cooling process.

Causes

1. Using hydrogen shielding gas in welding ferrous metals.

2. Ductile base metal and the application of residual stress.

3. Rigid joints that constrain the expansion and contraction of the metal.

4. Use of high levels of sulphur and carbon.

Prevention

1. Preheating the metals and gradually cooling the weld joints.

2. Maintaining acceptable weld joint gaps.

3. Selection of the correct welding materials.

Porosity

Porosity is the formation of holes in the weld pool resulting from gas bubbles that cannot escape. It is usually one of the common welding defects when using shielding gas, which is present in welding techniques such as TIG and stick welding. Absence, lack, or too much shielding gas may lead to metal contamination, which reduces the strength of the weld.

On the other hand, severe versions of porosity come in the form of blow holes or pits when large gas bubbles get trapped in the weld pool. Additionally, smaller gas molecules can blend with the weld metal, forming an impure compound.

Causes

1. Unclean welding surface.

2. Wrong electrode selection.

3. Lack or absence of shielding gas.

4. Mishandled or damaged shielding gas cylinder.

5. Either too low or too high welding current.

6. Fast travel speed.

Prevention

1. Cleaning the weld surface.

2. Using the correct welding electrode.

3. Preheating the metals before welding.

4. Proper gas flow rate setting to achieve the right amount of shielding.

5. Regularly checking for moisture contamination in the shielding gas cylinder.

6. Adjustment of welding current and travel speed settings.

Undercut

An undercut can be formed in various ways but mainly it is tied to two reasons. The first is using excessive current – the edges of the joint melt and drain into the weld. The second reason is not that enough filler metal is deposited into the weld. This results in a reduced cross-section meaning that there are notches or grooves along the weld, which increase stress when the material is subjected to fatigue loading. This defect occurs at the toe of the weld or in the case of multi-run welds, in the fusion face. An undercut may come from continuous, intermediate, and inter-run.

Additionally, water and dirt are prone to get stuck into the groove and this can accelerate corrosion in the already weakened area.

Causes

1. High arc voltage.

2. Incorrect electrode selection or wrong electrode angle.

3. High travel speed.

Prevention

1. Smaller arc length, voltage, and travel speed.

2. 30 to 45-degree electrode angle.

3. Reducing the electrode diameter.

Overlap

Overlap is the excess metal that spreads out around the bead. The spread-out filler metal is not properly mixed with the base metals. Typically, it comes in a round shape over the weld joint.

Causes

1. Incorrect welding procedure.

2. Wrong selection of welding materials.

3. Improper preparation of base metals.

Prevention

1. Smaller welding current.

2. Use of proper welding techniques.

3. Shorter welding electrode.

Burn-Through

An open hole is exposed when the welding process accidentally penetrates the whole thickness of the base metal, creating a burn-through or melt-through. This is one of the common weld defects when welding thin metals.

Causes

1. High welding current.

2. Extreme gap to the root.

3. Not enough root face metal.

Prevention

1. Maintaining a proper root gap.

2. Control in the application of welding current.

3. It can be repaired in some cases wherein the hole is removed and re-welded.

Spatter

Spatter is a welding defect that occurs when metal droplets are discharged on the metal surface. It solidifies and becomes stuck on the metal surface once it cools down. In most cases, spatter does not alter the structural integrity of the weld but generally, it has to be removed, adding to the total costs.

Causes

1. High arc length.

2. High welding current.

3. Improper shielding of the heat-affected zone.

4. Using the wrong polarity may create excessive spatter.

Prevention

1. Choosing the correct weld polarity.

2. Selecting a better shielding gas and better shielding technique.

3. Reducing the welding current and arc length to optimal condition.

Under Filled

Underfill occurs when too little weld metal is deposited into the joint. As a result, some of the parent material remains unfused and the joint is under filled. These unfused sections, even when small, act as potential stress raisers. 

Causes

1. Low welding current.

2. Too high travel speeds.

3. Incorrect weld bead placement.

4. Laying weld beads too thinly in multi-pass welds.

Prevention

1. Proper electrode size selection.

2. Selecting the right current setting.

3. Avoid moving too fast.

Excess Reinforcement

Excess reinforcement (overfilled) describes a weld that has too much build-up. It is the opposite of underfilled welds as excessive amounts of filler metal is deposited into the joint. With this defect, high levels of stress concentration build up in the toes of the welds.

Causes

1. Low travel speeds.

2. Incorrect procedures.

3. Excess flux on the feed wire.

Prevention

1. Maintaining an optimal pace with the torch.

2. Avoiding excess heat by making sure to use the correct voltage and amperage.

3. Aligning the workpieces properly to ensure that the gap between the parts is not too large.

Mechanical Damage

Mechanical damage is indentations present in the weld due to damage from preparation, handling, welding, equipment usage, and other factors.

Causes

1. Unnecessary application of external force before, during, or after an operation.

2. Incorrect handling of welding equipment

3. Not engaging the arc before the welding procedure

Prevention

1. Safe and correct handling of welding equipment.

2. Consistently engaging the arc in the metal parts before starting welding.

Distortion

Distortion or warping is an accidental change in the shape of the surrounding metal of the weld. Excessive heating around the weld joint is the main reason for distortion around its area.

Warpage or distortion mostly occurs in thin metals and is classified into four types: angular, longitudinal, fillet, and neutral axis.

Causes

1. Thin weld metal.

2. Incompatible base metal and weld metal.

3. High amount of weld passes.

Prevention

1. Using suitable weld metals.

2. Optimising the number of weld passes.

3. Selection of better welding methods for the metal type.

Misalignment

Improper positioning of metals before or during a welding operation may result in misalignment. Poor metal alignment is susceptible to fatigue conditions especially if it is used in pipe welding.

Causes

1. Rapid welding process.

2. Incorrect metal alignment or metals aren’t secured properly.

3. Lack of welder skills.

Prevention

1. Employing a slower and more stable welding procedure.

2. Securing the metals firmly before and during operation.

3. Using the correct welding techniques and conducting checks regularly.

Internal Welding Defects

Welding processes that create weld defects invisible to the naked eye are categorised as internal welding defects.

Slag Inclusion

A weld bead that contains slag in its composition compromises the toughness and structure of the metal. Slag inclusion may occur either on just the surface of the weld metal or in between welding cycles. This weld defect is common to processes that use flux, such as stick, flux-cored, submerged arc welding, and brazing.

Causes

1. Incorrect welding angle and travel speed of the welding torch.

2. Poor pre-cleaning of the edge of the weld surface.

3. Low welding current density resulting in inadequate heating of the metals.

Prevention

1. Higher welding current density.

2. Optimal welding angle and travel speed to avoid slag inclusion in the weld pool.

3. Consistent weld edge cleaning and slag removal of each layer.

Incomplete Fusion

Incomplete fusion results from poor welding wherein the metals pre-solidify, forming gaps in the weld zone. When the welder cannot properly melt the parent metal with the base metal, it results in a lack of fusion.

Causes

1. Low heat input resulting in metals not melting.

2. Wrong joint angle, torch angle, and bead position.

3. Extremely large weld pool.

Prevention

1. Higher welding current and slower travel rate to ensure the melting process of the metals.

2. Improving welding positions such as joint angle, torch angle, and bead position.

3. Lower deposition rate.

Incomplete Penetration

Incomplete penetration generally occurs during butt welding, wherein the gap between the metals isn’t filled completely through the joint thickness. This means that one side of the joint is not fused in the root.

1. Incorrect use of the welding technique.

2. Wrong electrode size.

3. Low deposition rate.

Prevention

1. Using the correct welding technique and procedure.

2. Higher deposition rate.

3. Proper electrode size selection.

Other Welding Defects

Whiskers

Whiskers are a specific weld defect in the MIG welding process. This occurs when the root side of a weld joint has remnants of the wire electrode.

Causes

1. The electrode is positioned ahead of the leading edge of the weld puddles.

2. Fast wire feed speed of the electrode wire to the MIG torch.

3. High travel speed while welding

Prevention

1. Snipping off the small blob of the electrode before welding

2. Reducing the wire feed speed in the machine settings.

3. Slowing down the travel speed or using welding techniques as countermeasures, such as whipping the electrode.

Necklace Cracking

Necklace cracking is a welding defect associated with electron beam welding. This defect occurs when the molten metal can’t sufficiently flow into the cavity, resulting in incomplete penetration.

Causes

1. Using metals such as stainless steel, carbon steel, tin, and nickel-based alloys.

2. Improper welding technique application.

3. High operation speed in electron beam welding.

Prevention

1. Better material selection for electron beam welding.

2. Using constant speed to achieve uniformity.

3. Applying proper welding technique and procedure.

How to Detect Welding Defects

Testing methods are a great way to check if the welding patterns meet specific criteria. It allows us to find the causes and remedies for why welding defects occur. While it takes some time, it ensures that the welds are safe and risk-free.

There are two standard procedures for finding defects in a weld metal:

Non-Destructive Testing

Non-destructive testing allows us to observe discontinuities in the weld incurring no damage. This testing method is essential in high-speed production wherein a sample is tested from a batch.

Non-destructive testing and evaluation is usually done by utilising visual inspection, liquid penetrants, magnetic particles, eddy currents, ultrasonics, acoustics, emissions or radiography.

Destructive Testing

Destructive testing acquires information by subjecting the finished projects to strenuous methods until it reaches their limits. Some cases require destructive testing in addition to non-destructive tests in order to reduce weld defects in production significantly.

Some destructive methods used to identify the limits of the weld metal are acid etch, guided bend, free bend, back bend, nick break, and tensile strength.

Final Thoughts

Welding defects pose serious risks that can lead to dangerous issues if not addressed. They can be expensive and time-consuming to correct but are always worth it in exchange for quality. This is why welders need to understand the fundamentals of welding.

Modern technology allows us to perform welding techniques more efficiently. Along with numerous testing methods facilitating the discovery of different types of welding defects, the execution and correction of these imperfections is constantly getting better. Focusing on improving both the machinery and technical skill make up a difference when it comes to limiting weld defects. This leads many industries to manufacture products of higher quality than ever before.

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Although brazing is one of the oldest joining methods, it is still used today for a good reason.

What Is Brazing?

Brazing joins metal surfaces together with a filler metal which has a low melting point. The process uses capillary action wherein the homogenous liquid flow of the filler material bonds with the base metals.

A unique quality in the brazing process is that it keeps the mechanical properties of the metals which are useful in applications such as silver brazing or other similar metals.

Brazing Process

One of the most crucial steps in the metal joining process is the cleaning of the base metal surfaces. Emery cloth or wire brush are both great tools to remove contaminants.

Having calculated joint gaps for the liquid filler metal to achieve surface tension with the workpiece, the brazing operation begins with properly positioning the assembly. A torch is normally used to slowly heat the workpiece’s metal surface and filler metal into its brazing temperature.

As the filler metal liquefies, capillary action lets it pass through the tight spaces, thus forming a bond between the surface of the base metals.

The brazed joints are formed as it cools down with the assembly.

Materials

These are the metals that are often joined by brazing:

1. Aluminium

2. Cast iron

3. Magnesium

4. Copper and copper alloys

5. Silver

Filler metal requirements

1. Once the molten flux and filler metal solidify, the brazed joint should possess the expected mechanical properties.

2. Brazing temperatures must efficiently achieve a proper liquid flow from the molten braze alloy into the joints.

3. Filler metals must achieve proper wetting conditions in order to create strong bonds.

Difference Between Brazing, Soldering & Welding

Brazing uses capillary action to join different metal surfaces. It makes use of a process called wetting, wherein the base metals are bonded with a melted filler material. The brazing filler metal has a melting point above 450 °C.

Soldering uses filler metals that have a melting point below 450 °C. Although soldering uses the same concept as brazing, the main difference lies in their working temperatures and thus in the strength of the created joint.

Welding also melts the workpieces in addition to the filler metal. This allows the creation of stronger bonds than with brazing. Processes such as TIG, MIG, and stick welding operate at much higher temperatures.

Braze welding is a type of MIG/MAG welding. The difference lies in the melting point of the filler wires which is significantly lower than the parent metal. The filler metal is deposited in order to fill in the gaps via capillary action. There is no significant fusion of the parent metals but it may occur in a limited amount.

Different Methods of Brazing

Brazing uses different heating methods to suit a variety of purposes and applications. Heat can either be applied directly to a joint (localised) or to the whole workpiece (diffuse heating).

Localised Heating Techniques

Torch brazing – Combusted fuel gas is formed by burning acetylene, propane, or hydrogen with oxygen to heat and melt the filler metal. Flux is required while using this technique in order to protect the joint, which requires post-cleanup later on. Torch brazing is mainly used for small production assemblies where metal weight is unequal. The process is often performed with gas welding equipment.

Induction Brazing

Induction brazing – High-frequency alternating current is supplied into a coil to achieve brazing temperature, which heats the workpiece and melts the filler material.

Resistance brazing – Heat is generated from the electrical resistance of the brazing alloy, which is perfect for highly conductive metals. This heating technique is best suited for creating simple joints between metals.

Diffuse Heating Techniques

Furnace brazing – Gas firing or heating elements are used to bring the furnace to the desired temperature. The brazing filler metal is applied to the surfaces to be joined and then the entire assembly is placed into the furnace and brought to brazing temperature. Furnace brazing allows accuracy in controlling the heating and cooling cycles of the metals. The process is often performed in a vacuum to protect the braze alloy from atmospheric conditions. This also negates the need for flux protection.

Dip brazing – The workpiece or assembly is immersed in a bath of molten filler metal (molten metal bath brazing) or molten salt (chemical bath dip brazing). Brazing flux is applied to the parts to prevent oxidation. The assembly can be removed once the molten brazing filler metal has solidified.

Advantages

1. Can join dissimilar metals, unlike most welding methods.

2. High production rates.

3. Consumes less power than welding.

4. Produces cleaner joints compared to most welding processes.

5. Base metals don’t melt, keeping their shape and mechanical properties.

Disadvantages

1. Weaker results compared to welded joints.

2. Cannot join components operated at high temperatures.

3. Requires tight, uniform joint gaps to achieve capillary action.

4. Unclean or contaminated metals may cause leaky joints.

Brazing is used in a wide range of industries due to its flexibility and ability to join dissimilar metals. Fractory’s carefully selected manufacturing partners have experience and expertise in this field as brazing is part of the welding services we offer.

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