Last week my students began the next steps of creating an aluminum die for hydraulic die forming. In this blog post installment we'll look at the process of removing the section of material where the sheetmetal will be formed. The main idea here is to utilize the holes that are drilled around the perimeter as a way in which to remove the bulk of the material easily and quickly.
By drilling holes that are close together, we can use a jewelers saw to cut the thin webbing between holes. A coping saw could be used here and the coping saw wood blade would actually work quite well for the soft aluminum. In this particular instance I utilized a #6 jewelers blade.
With a little cutting fluid, it is easy to saw through the aluminum and the holes make quick work of stock removal.
The resulting interior has ridges left from the contour of the drilled holes. In this case, the jewelers saw could be used to come back and saw closely to the edge of the layout line making sure to preserve the layout line for final finishing via file and sandpaper OR you could go to work smoothing the ridges with an aggressive file. I chose to do the later.
Bracing the die (or any piece of metal) for filing is a must. I used some scrap copper to keep the jaws of the vise from marking the die face. This isn't absolutely necessary, but it makes for a smooth finish on the face of the die where sheetmvetal will be placed for forming. You wouldn't want to transfer these marks to the pressed sheetmetal so there is an attempt to keep the die faces looking good.
A few properly placed file strokes makes quick work of the aluminum. Rubbing some chalk on the file before filing helps to cut down on clogging of the file and make cleaning with a file card easier. I personally love the repetition of filing. I find that the beginning student sees no value in a file and is quite lazy in form when yielding a file. Proper form of following the interior shape of the cutout, as one files, will reveal a smooth interior die edge in very little time. That said, I've seen students labor at this for hours due to weak file strokes, working in one concentrated area at a time, and not pushing the file away from themselves. I think I had about 30 minutes of file time since I didn't first cut closer to the layout line.
For those that get tired easily or who don't have the physical strength, then a Foredom flexshaft with a sanding band can ease some of the pain. That said, I find that the flex shaft does not have the precision of the file and should be reserved for final smoothing once the ridges are gone via the file. Regardless, I still have a few students who insist on starting with the Foredom. I can usually spot their dies as they have lumpy surfaces. Trust me a file is the right tool for the job and quick; if executed properly.
I ended with the file to reveal a smooth and clean interior. The surface quality is not as important as the accuracy and edge of the contour. Making sure to file perpendicular to the face of the metal die is also important, especially if you are pressing a left and right side handle as they will need to match. If the die interior is beveled then your handles won't match up. I then relieved the edge of die slightly (although not shown here) as this will help the metal "flow" over the edge as it is pushed into the void.
We'll look at sheetmetal prep and stainless steel blade prep next.