Bending Allowance Hemming Sheet Metal

Most sheet metal materials will conform to the calculations.

Bending allowance hemming sheet metal.

These leave residues that sometimes can be very difficult to remove. When working with a brake press hems are always created in a two step process. A scrap tool or production run can be very costly much more so that a test piece. Take the following example.

First we must start with the k factor. 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. The bend radius refers to the inside radius. When sheet metal is bent it stretches in length.

You will need to know your material thickness mt the bend angle b the inside radius ir and the k factor k. Formula for the bend deductions outside setbacks and bend allowances cease to be of value when the bend angle exceeds 174. Sheet metal calculator bend allowance equations and calculator. You seem to be working with a closed hem which has a zero inside bend radius.

The key word here is perfect. This page also includes a link to a on line sheet metal bend allowance calculator. We are going to review three bending scenarios with three different bending angles. 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.

Create a bend with acute angle tooling in the metal 30 is preferable but 45 will work for some circumstances. The blank size is computed through the use of the hem allowance ha. The bending angle is 90 sheet thickness 5 mm and the inside radius is 6 mm. Consider a sheet with a 20 mm thickness and a length of 300 mm as shown in figure 1.

In sheet metal hemming means to fold the metal back on itself. The following illustration shows the equation calculation for determining the bend allowance when forming sheet metal. We want to know the final length of the detail. 60 90 and 120 and we will calculate k factor bend allowance and bend deduction for them.

The material thickness will be measured in decimal form not by the gauge number. The formed bend radius is dependent upon the dies used the material properties and the material thickness. 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 deduction is the amount the sheet metal will stretch when bent as measured from the outside edges of the bend.