Hemming and seaming are two similar metalworking

Metalworking

Metalworking is the process of working with metals to create individual parts, assemblies, or large scale structures. The term covers a wide range of work from large ships and bridges to precise engine parts and delicate jewelry. It therefore includes a correspondingly wide range of skills,...

 processes in which a sheet metal

Sheet metal

Sheet metal is simply metal formed into thin and flat pieces. It is one of the fundamental forms used in metalworking, and can be cut and bent into a variety of different shapes. Countless everyday objects are constructed of the material...

 edge is rolled over onto itself. A hem is when the edge is rolled flush to itself, while a seam joins the edges of two materials.

Hems are commonly used to reinforce an edge, hide burrs and rough edges, and improve appearance.

Seams are commonly used in the food industry on canned goods, on amusement park

Amusement park

thumb|Cinderella Castle in [[Magic Kingdom]], [[Disney World]]Amusement and theme parks are terms for a group of entertainment attractions and rides and other events in a location for the enjoyment of large numbers of people...

cars, and in the automotive industry.

Process

The process for both hemming and seaming are the same, except that the tonnage requirement is greater for seaming. The process starts by bending the edge to an acute angle. A flattening die is then used to flatten the hem.

Types

There are two types of hemmed edges: closed hems and open hems. Closed hems are completely flush while open hems have an air pocket in the bend. The major difference is that the tonnage required for a closed hem is much greater than that for an open hem.

Tons per meter requirement for hemming cold-rolled steel and stainless steel

Material thickness [mm]	Open hem	Closed hem
0.6	9	23
0.8	12	32
1.0	15	40
1.2	17	50
1.6	24	63
2.0	30	80
2.6	55	90
3.2	70	100
4.5	105	200