Today I want to talk about how to make a flange which is to be fitted around a radius. Making a straight flange is easy, simply put a piece of sheet in folder and fold, though it is a little more complicated creating a curved one.
The application here is for the rear quarter panel of the morris minor we are restoring. The wheel arch joins to the quarter panel via a spot welded flange, this has corroded away and needs a new section making.
The first step is to clean back the area to identify where the corrosion ends, followed by cutting out the rotten section. Using a piece of string, measure around the curved section and mark the string where the new panel will end. Ensure a cm or two extra is allowed for shrinkage due to the radius. Measure the width of the flange and the width of the required wheel arch section, add the thickness of the steel sheet and mark the combined total as the width on a metal sheet. Use the length from the string measurement earlier. For example:
Flange width = 15 mm
Wheel arch section = 20mm
Sheet thickness = 1.5 mm
String length 450 mm
Total mark area = 36.5mm x 450mm
Using a bench folder, fold a 90° bend (adding half of the material thickness to the required flange width to allow for the bend radius = 15.75mm) to create a straight flange.
Now comes the curving part, a curve is formed by either stretching of shrinking the flange. This can be done manually, which requires a lot of skill patience and time or with the use of a shrink / stretch tool.
First step is to work out if you need to stretch or shrink you material. Stretching will push the edges of the flange away from the tool whilst shrinking will pull them in.
Best practice is to start at one end of the flange, pushing with a gentle tap on the lever and moving the flange a jaws width along. This will give you a controlled and continuous curve.
Not the nice even curve achieved using the stretching tool. It is important to trial fit the flange to prevent over shaping the material.
Now the correct radius is achieved, final trimming of the flange and the vehicle panel allows the flange to be tacked and welded into place.
Here is the fabricated flange welded in place with the weld bead cleaned. Note its nice close fit to the adjacent wheel arch panel. This is to be spot welded together at a later date.