Sheet Metal Hemming: A Comprehensive Guide to Hem Types and Methods

Sheet metal bending is a key technique in metal fabrication, and it is often complemented by methods like punching, welding, and laser cutting for creating precise prototypes and parts. However, these processes sometimes require additional steps to reinforce edges, improve aesthetics, or hide imperfections like burrs. This is where sheet metal hemming comes in. This guide explores hemming methods and types, helping you determine their fit for your project.

Exploring sheet metal hemming

Sheet metal hemming is a specialized form of bending that focuses on the part's edges. It involves folding the sheet metal edge back onto itself, enhancing strength and durability while also improving the part's appearance. The process can be likened to edge stitching in textiles, where one part can be folded over another to create a joint. Hemming typically involves two stages: (1) Creating an acute bend using acute tooling, such as a V-die, and (2) Flattening the return flange with a flattening die.

The benefits of sheet metal hemming

As a critical sheet metal bending process, hemming offers several advantages:

Strengthens the edge of the sheet metalEnhances surface quality and visual appealConceals burrs, rough edges, and other defectsJoins parts togetherImproves the safety of the edges for handling

Understanding different hem types

Flat or closed hem - This type involves bending a part of the edge entirely over the rest of the sheet metal, creating a 180-degree angle with a zero inner radius.Open hem - The returning flange folds over the sheet metal with an air pocket in between, also featuring a 180-degree bend angle.Teardrop hem - Here, the returning flange's bend angle exceeds 180 degrees, resembling a teardrop. This sheet metal bending technique is ideal for materials that lack the ductility required for closed hems, like aluminum.Rope -The returning flange (already formed into an open hem shape) is further pinched or crimped onto the sheet metal surface for added strength.Rolled hem -The edge is rolled over and slightly overlapped onto the sheet metal surface, creating a smooth, rounded edge.

Methods of hemming

Different methods are employed for sheet metal hemming, including:

Die hemming - This traditional method uses a die and press and is best suited for simple, flat panels.Roller hemming –This is an automated process managed by robots, which use rollers to precisely bend edges. This method is cost-effective and speeds up both low- and high-volume production.

To learn more about sheet metal bending and hemming, contact HLH Proto for a quote. As a reputable manufacturer, they can assist in reducing time to market and costs for both prototyping and production of end-use parts.

About the Company:

HLH Proto Ltd is a leading provider of premium rapid prototyping services, encompassing 3D printing, injection molding [ sheet metal prototyping, metal machining, vacuum casting, die casting, and more, all offered at competitive rates. Our team of skilled and dedicated engineers ensures top-notch performance and guaranteed results. Explore our website for more information.