Basic die clearance/fit question

I would think the easiest way would be to make another male component from 14mm stock (aluminium would suffice) and use that as the reference for making the female part. Engineer's blue on the male part would transfer to the female hi-spots to indicate where to remove some material.

Another thought, since the female part is plastic, you could heat the metal to the melting point of the plastic, and push it in to shape its own recess.

The groove in the female section would be the radius of a (an approximately) .580" rod. You could make a gauge to see how well your sizing operation is progressing. I wouldn't expect the .040" metal stock to form well with this type of die set, especially not if it's steel that you want to form.

As for a technique to cut the groove, I dunno, since I don't think a trammel/circle cutter in the drill press would work well for this job. Maybe melt a hot .580" ring into the material, as suggested by another reply, but that may present other problems (such as bending the rod).

WB ..............

Richard Fergus> I think that this is a simple question, but I don't know the answer. I

In most diemaking, rads on the sheetmetal part are created only with male rads on the punch and male rads on the die. While there are instances where one requires the female rad in the die section to form the part correctly (coining or corner setting), in the the vast majority of cases it is merely clearnace. Indeed, in an instance where the female rad is required, a plastic die section would probably fail virtually instantly due to the massive force required to coin the rad.

I would recommend building the punch as previously perscribed, but instead of the suggested female die cavity, use only a slot (14mm+ wide) with rads between the top surfaces and the side walls. The rads on the die section should be as large as possibe, but I would recommend nothing less than 1mm.

Perhaps I'm misunderstaning the OP's description but this die sounds much more like a stretch/draw die than a bending die.

While a plastic die section (ideally nested into a steel yoke) would probably make a number of good parts, the OP may want to consider making it out of steel instead. 1mm material is not all that thin (we use 0.8mm material to make outer body panels for cars) and he may well see rapid wear/failure.

Regards,

Robin

Thanks to all for their thoughts.

A couple of comments: The material worked would be copper, aluminum, and perhaps other metals, and is not likely to include steel.

I will think some more about the suggestion that I do not need a perfect fit with the female die, that a slot is enough. On at least part of the die, I need a good fit, since I am trying to form the sheet metal in two directions, so I need to shrink/stretch the material rather than simply form/bend it. But perhaps I don't need a good fit the whole length of the die.

I am not sure about plastic dies either. I was going to prototype with a wood upper die. Perhaps aluminum or steel would be a better choice, although that could require getting the fit more precise.

I like the idea of putting bluing on the male die and having it transfer to the female die. But how do I allow for the thickness of the material? Do I need to put a part in there and blue the part?

Richard

Richard Fergus> I think that this is a simple question, but I don't know the answer. I

Since your targets are softer metals, you might look into using a non-conforming die. With this approach, the female "die" is simply a flat urethane pad (in the 80 to 90 durometer range) at least twice as thick as the desired deformation, backed by a flat steel plate. When pressure is applied, the urethane flows around the male die, shaping the work material as it goes. For all its simplicity, this approach can produce amazing results in the right application. You can get urethane pads at MSC or McMaster-Carr; they can be reused many times. (Other types of rubber will work but not as well.)

Bert

I like the urethane suggestion a lot, not least of which because I could use one upper die with different lower dies. The amount of skilled labor needed on my part would also be relatively low, as well. I notice, however, that polyurethane is relatively expensive, with a 6 inch by 1.5 inch by 1.5 inch piece costing around $25. But maybe I only need one piece. I have a couple of questions, however.

When you say 80 durometer, do you mean Shore A, Shore D, or Shore 00?

How can I attach the urethane to a flat piece of steel, probably 1/2 inch flat bar? Can I just drill it and through bolt it? Can I use sheet metal screws?Or is there a better solution?

I should say that I am planning to use a small power hammer in a blacksmith style spring die to do this. Spring dies are not known for keeping perfect alignment of top and bottom dies, but urethane solves that problem.

Richard

Bert wrote:

Unless you're making hundreds of thousands of parts, you'll only need one piece.

There is an excellent chance the urethane will cause issues with wrinkling. You will have no control over material flow because you do not have a binder/pressure pad. Depending on the depth of your draw/strech, you may even get folding. Hard dies with binders/pressure pads solve this problem, but are not easily implimented.

You have not given us enough information about the part you're making. For instance, what is the depth of the draw/stretch? What is the material condition of your blank(soft/semi hard/hard), and alloy ? How many parts do you want to make? Do you have a blank size yet, or will you cut them to suit, as the die requires? Is the part cosmetic, or purely functional? Can your part tolerate wrinkles?

You mentioned that you think you require a fitted die cavity to make your part. Whether you believe me or not, I can tell you that you will _not_ require such a cavity. Where I work, we do some of the most complicated deep drawing operations with very difficult materials, to make very large parts. While your part *may* benifit from a perfectly spotted draw cavity, it is unlikely that you will be willing to take the time given the benifits versus having an empty cavity. It is also a learned skill to be able to accurately spot a part into a die cavity.

If you insist on spotting the part into the die cavity, the sequence is this: Spot the punch into the die first (assuming starting from scratch). Once that's good, you'll have to open up the draw rads (between the top face of the die section and the cavity walls) to allow for the part to flow over the die section, and then hit a part. Apply blue to the ouside of the part (which touches the die cavity) and hit it again. Wherever the blue has not only transfered to the die cavity but also been hit so hard as to go white in the middle, take that area down. At the beginning you can be very agressive. I'd recommend a die grinder with a carbide burr, and then a pink mounted stone. Repeat as necessary. Once you're getting many "hard spots" all over the cavity, you have to slow down to do the final spotting. Stop when you're only moving the hard spots around as opposed to smoothing them out. Use a polishing stone and then fine sand paper to finish if you're inclined.

You can drill/c-bore it and use socket head cap screws. Remember that there is virtually zero force pulling the urethane off the steel bar. Our urethane bumpers are glued to their steel plates (not sure what kind of glue).

If you are unable to make a good part with the urethane, you should consider hard tooling with a die set for alignment. Depending on the requirements of the part, draw dies can be *very* intolerant of misalignment.

Regards,

Robin

Maybe your backing plate could have channels along a couple of edges? Or there may be some kind of adhesive that would work. I've never tried to permanently attach urethane to anything. Before drilling or sawing, be sure to read the MSDS. If I recall correctly, toxic fumes can be released in some machining operations.

If the size of the part allows it, you might be better off building a shallow box into which you could stack the male die, work piece, urethane pad, and backing plate.

I've only used the urethane pads in a hydraulic press, so I can't say if they'll work with a power hammer. I've never heard of them being used like this, and I suspect the results will not be great, but I don't know. Depending on the size of the part, the size of the hammer, and the amount of deformation, you may not be able to generate enough force, and even if you do, you may not have enough control over the amount of force applied. Depending on the shape and how much deformation is involved, you may need to do the forming in multiple steps, annealing the part between steps, to avoid tearing.