Introduction

I needed a quick and relatively cheap way of bending 1/2” x 2” 6061-T6 aluminum bar stock to manufacture a custom strut tower brace for a BMW Z3. Outsourcing the bending to another shop would have eaten away at all my profits, so that wasn’t an option. My immediate resources where a SWAG Off Road 20 Ton Finger Brake Kit and a hydraulic press capable of providing enough pressure to bend the bar stock for the brace. The only missing piece to the equation was the proper bending die, and the only bending dies available were those that came with the press. Unfortunately, their bend radii where all much too small to properly bend the 1/2” material without causing serious deformation. Alternative solutions would be a custom made die from a tool manufacture or an off the shelf tool. Both options where way out of budget at the time so what remained was designing and making my own.

It was time to put my design skills to the work. Researching bending science, I learned of a general rule for bending. This rule states that, at minimum, the radius of the bend die must be equal to the thickness of the material being bent. With that in mind, I went ahead and designed an upper and lower die to be made out of 1/2” steel plate that I could have SendCutSend cut for me. Initially I wanted to use 4140 chromoly steel for the upper and lower portions of my die due to its high yield strength but, that material was unavailable to me. So a quick calculation with some worst case surface area contact assumptions allowed me to estimate the pressures my bending die components would be experiencing which to my benefit was well below the yield strength of A36 (low carbon cheaper steel) and available to me. So I had the plates cut from A36 steel and prepared for the build.

Design

The Lower die was designed to have a 2” bend radius on the bending surface areas where the aluminum bar stock rolls over during the bending process. The trough of the die was designed with extra relief so the bar stock could be bent further than designed just in case I needed to account for any spring back effects. Bevels where cut into the plates to maximize weld penetration between plates and make for a sturdy bound. The idea behind this design was to slap 4+ of these plates back to back and weld them together to make a surface large enough for the bar stock to sit on during bending.

In the Image to the right, one can see the stack of upper and lower plates with bevels aligned. The upper bend die also has the hardened steel shaft attached to the stack of plate steel on the curved surface. All plates are MIG welded together and the steel shaft is centered about the upper plates and TIG welded to them for aesthetics but it could have been MIG welded as well.

Build

Watch the video below to see the steps taken to build up the custom finger brake bending die.