Bending Allowance Hemming Sheet Metal

Formula for the bend deductions outside setbacks and bend allowances cease to be of value when the bend angle exceeds 174.

Bending allowance hemming sheet metal.

The formed bend radius is dependent upon the dies used the material properties and the material thickness. This page also includes a link to a on line sheet metal bend allowance calculator. The following illustration shows the equation calculation for determining the bend allowance when forming sheet metal. The material thickness will be measured in decimal form not by the gauge number.

You seem to be working with a closed hem which has a zero inside bend radius. The bend allowance formula takes into account the geometries of bending and the properties of your metal to determine the bend allowance. In sheet metal hemming means to fold the metal back on itself. 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.

Sheet metal calculator bend allowance equations and calculator. 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. Create a bend with acute angle tooling in the metal 30 is preferable but 45 will work for some circumstances. The bending angle is 90 sheet thickness 5 mm and the inside radius is 6 mm.

These leave residues that sometimes can be very difficult to remove. Consider a sheet with a 20 mm thickness and a length of 300 mm as shown in figure 1. When working with a brake press hems are always created in a two step process. The bend radius refers to the inside radius.

We want to know the final length of the detail. Most sheet metal materials will conform to the calculations. A scrap tool or production run can be very costly much more so that a test piece. 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.

In materials with a thickness less than 080 the hem allowance factor is 43 of the material thickness. 60 90 and 120 and we will calculate k factor bend allowance and bend deduction for them. The total amount of elongation for such a hem is 43 percent of the material thickness under perfect conditions. The bend deduction is the amount the sheet metal will stretch when bent as measured from the outside edges of the bend.

When sheet metal is bent it stretches in length. The blank size is computed through the use of the hem allowance ha. 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. The key word here is perfect.

First we must start with the k factor.