Bending Allowance Hemming Sheet Metal

These leave residues that sometimes can be very difficult to remove.

Bending allowance hemming sheet metal. Let s say you have a similar part to the one on the image above it has a straight leg of 20 mm and another of 70 mm. You will need to know your material thickness mt the bend angle b the inside radius ir and the k factor k. Most sheet metal materials will conform to the calculations. Take the following example.

The bend allowance formula takes into account the geometries of bending and the properties of your metal to determine the bend allowance. Mark the two lines on the sheet metal where the bend will begin and end the material between these two marks the bend allowance will deform to create the angle. The bend radius refers to the inside radius. The bend deduction is the amount the sheet metal will stretch when bent as measured from the outside edges of the bend.

In sheet metal hemming means to fold the metal back on itself. Sheet metal calculator bend allowance equations and calculator. The bending angle is 90 sheet thickness 5 mm and the inside radius is 6 mm. First we must start with the k factor.

Consider a sheet with a 20 mm thickness and a length of 300 mm as shown in figure 1. This page also includes a link to a on line sheet metal bend allowance calculator. We want to know the final length of the detail. The key word here is perfect.

In materials with a thickness less than 080 the hem allowance factor is 43 of the material thickness. When working with a brake press hems are always created in a two step process. The total amount of elongation for such a hem is 43 percent of the material thickness under perfect conditions. A scrap tool or production run can be very costly much more so that a test piece.

Formula for the bend deductions outside setbacks and bend allowances cease to be of value when the bend angle exceeds 174. The material thickness will be measured in decimal form not by the gauge number. To create the bend manually you can use a shaped form perhaps made of wood which conforms to the bend radius you want to achieve. We are going to review three bending scenarios with three different bending angles.

When sheet metal is bent it stretches in length. The formed bend radius is dependent upon the dies used the material properties and the material thickness. The blank size is computed through the use of the hem allowance ha. You seem to be working with a closed hem which has a zero inside bend radius.

Often bend allowances are calculated for a sheet metal part and used to make costly tooling or production parts that require a lot of labor to produce.