{"id":19476,"date":"2022-11-22T14:55:58","date_gmt":"2022-11-22T12:55:58","guid":{"rendered":"https:\/\/fractory.com\/?p=19476"},"modified":"2024-01-26T13:25:19","modified_gmt":"2024-01-26T11:25:19","slug":"sheet-metal-hemming","status":"publish","type":"post","link":"https:\/\/fractory.com\/sheet-metal-hemming\/","title":{"rendered":"Sheet Metal Hemming"},"content":{"rendered":"
Hemming is a common metalworking process<\/a> mainly carried out to reinforce an edge, hide burrs or just improve the overall appearance of sheet metal<\/a> parts. When hemming is carried out in a way that a joint between two sheet metal parts is created, it is called seaming but more on that later.<\/p>\n So, without further ado, let’s dive into the subject.<\/p>\n Hemming in sheet metal operations refers to the bending of a sheet metal<\/a> edge onto itself. It is very similar to edge stitching in clothes. Similar to how an edge stitch strengthens the edge and makes it more durable, a hem imparts strength to the metal edge and improves its appearance. The edge of one part may also be folded onto another part to create a joint.<\/p>\n Hemming is usually done in two stages. The first stage creates an acute bend using acute tooling (V die) followed by a flattening of the return flange using a flattening die.<\/p>\n A complete list of hemming benefits<\/strong> on a sheet metal product is as follows:<\/p>\n Hems strengthen the sheet metal edge<\/p>\n<\/li>\n They improve the surface appearance and surface quality<\/p>\n<\/li>\n They hide defects such as rough edges and burrs<\/a><\/p>\n<\/li>\n They can connect parts<\/p>\n<\/li>\n They make the edges safer to handle<\/p>\n<\/li>\n<\/ul>\n The different sheet metal hems based on the hem shape are as follows:<\/p>\n Flat or closed hem<\/p>\n<\/li>\n Open hem<\/p>\n<\/li>\n Teardrop hem<\/p>\n<\/li>\n Rope hem<\/p>\n<\/li>\n Rolled hem<\/p>\n<\/li>\n<\/ul>\n In a flat or closed hem, the part of the edge that bends sits completely flush over the rest of the metal sheet. The angle between the returning flange and the sheet metal is 180 degrees. The inside radius is zero and thus, there is no gap between the returning flange and the metal sheet.<\/p>\n Closed hems require a lot more power and tonnage from the presses than open or teardrop hems and it is also not advised for metal sheets that are over 2-3mm in thickness since the sheets are likely to fracture.\u00a0<\/p>\n In an open hem, the returning flange is folded over the sheet metal but there remains an air pocket between the two. The bend angle in this hem type is also 180 degrees.<\/p>\n In a teardrop hem, the returning flange is bent beyond 180 degrees. The resulting shape resembles a teardrop.<\/p>\n It is perfect for materials that do not have the required ductility to provide closed hems. Teardrop hems are used for fragile materials such as aluminium<\/a>.<\/p>\n A rope hem has a returning flange at a bent of more than 180 degrees. Once the hem achieves the shape of an open hem, the returning flange is pressed onto the part surface through a flattening die.<\/p>\n The edge is bent in shape similar to an open hem and then the second piece to be connected is inserted into the gap between the metal sheet and the returning flange. Further pressing takes place making the second parts sit flush between the metal sheet and the returning flange and create a joint.<\/p>\n In a rolled hem, the bent portion of the sheet metal is tucked back into itself.\u00a0 This creates smooth round edges all around for holding the part from the hemmed edges. This process is also commonly referred to as curling<\/strong>.<\/p>\n What Is Sheet Metal Hemming?<\/h2>\n
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Hem Types<\/h3>\n
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Flat or closed hem<\/h4>\n
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Open hem<\/h4>\n
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Teardrop hem<\/h4>\n
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Rope hem<\/h4>\n
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Rolled hem<\/h4>\n
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