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Complexity/cost of making small press die?

Repoman

Plastic
Joined
Feb 14, 2021
Hello

I trying to figure out how to make a simple press die, I am having a very hard time finding any information at all on how press dies are made and was hoping someone with experience could help me out with some questions or suggestions on where to head with this.

I am attempting to build guitar pickup covers of my own design, the method I have been trying to use with limited success is having two blocks of aluminum that have guide rods to align them and the actual male and female dies made of aluminum epoxy (EpoxAcast 655). I made a dummy of the pickup cover, put it in a cavity in one block and pour the epoxy around it, then remove it, fill the formed cavity with a sheet of 0.02" machinist wax and cast the male die with the epoxy. I then put a 0.02" sheet of annealed brass or nickel silver, have a top plate that screws down onto the sheet then press it in a little Harbor Freight 12 ton press.

This method works surprisingly well...for the first 1 or 2 covers, but then the dies become damaged by stress risers, particularly at the corners, the dies become more and more damaged.

So the epoxy is not strong enough for this application. I am not a skilled enough machinist to manufacture something like the male and female dies that I can get with the epoxy (I have a small Precision Mathews PM25 with a DRO but doing this manually is most likely far outside my capabilities).

Does anyone know how dies like what I'm attempting to build are made? Are they made of steel or aluminum? Are dies like this extremely expensive to have manufactured? Is there some form in the die I am lacking that would alleviate the stress risers? Is there a stronger epoxy that anyone knows of that might work? Diamant Moglice maybe? Would I be able to cut costs if I learned a CAD program in which I could send a file to a CNC machine shop? Is something like this achievable for under a grand?

Thanks

IMG_0260.jpg

IMG_0261.jpg
 
Old school...
Make an oversize model of the male die, such as plastic resin
trace it on a 3D pantograph into steel block.
Detail with files and polish.
Use rubberform press to form the annealed sheet metal over the male form.

Rubberform press gives very smooth work, and obviates the need for a precision fit female die.
It might not give quite as sharp details in corners. Some experimenting with rubber durometer might be in order, but your forms are gentle as it is. ("good")

New school - write a CAD program and have someone run it in a steel male die.
Find a contractor to do the rubberform pressing, find out how to mount your die with locating features for the sheets, and let them stamp them out

smt
 
why not search the internet.
you will find what you need either in detailed text. Or on youtube.

you can do your homework there, as it has already been detailed.
 
I've seen some interesting videos of people using 3d printed dies to do sheet metal forming, both press dies and bending dies. Not sure how they hold up long term, but it works fairly well in the videos. For a longer term solution, and not speaking from experience, but I would imagine aluminum dies would be sufficient for low volume runs, especially if you minimize sharp corners to round over. The cost would greatly depend on the size, complexity and tolerances of the dies. And you should definitely learn CAD if you want to do any kind of serious designing/prototyping. Especially if you're doing it on a budget. It will need to be drawn in CAD one way or another, so you can either do it yourself or pay someone else to do it.
 
Hi Repoman:
When I look at the finished parts I see wrinkles where the original flat plate has been drawn up to form the sidewalls of the box shape that the final part has.
The epoxy die is crumbling because of the high localized forces the corners of the die experience when the metal wrinkles.
Do you care about the presence of those wrinkles?

If you do, you need to invest in something more capable of controlling the metal flow as it is drawn into a cup shape from a flat sheet.
This is often done with pressure pads which hold the sheet over the die opening, and through which the punch penetrates, squeezing the sheet enough that the wrinkles can't form in the first place...the metal must flow between the pressure plate and the top of the die opening so it is coaxed into the new shape.

All this is an art that takes years to learn, so you will have a very hard time with the details of how to make this shape unless you change it to be easier to make.
If you can get rid of the vertical side walls and just have the embossing on a flat sheet with maybe part of the radii of the outside edges, you can probably get away with just pushing a steel punch into a urethane pad, especially if you make a simple sprung pressure pad that goes around the punch to help keep the sheet flat as you push with the press.

From the sounds of it, making the punch and the pressure pad mechanism is beyond your ability and equipment.
So I'd find a retired diemaker with his own garage shop, ask him to design and build a simple tool for you and expect to spend at least a thousand bucks to do it.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
 
I think if you can get this into a CAD file - .step .sldprt. xt, some form of a solid model I think under $1000 is doable. If you are forming brass and aluminum shim, I think aluminum (maybe hard anodize) would hold up fine. If you want more long term 4140ht would probably do it, for added cost. Expect a tool steel/alloy to run you around $150-200 for material, unless someone has drops that would work. I am *guessing* this die is about 4"x6", maybe 1/2"-1" thick...
 
Learn CAD...yes.
Investigate rubber pad forming....yes
Ditch HF 12 ton press.....yes
Look at Kpotter's website....yes
Potter USA - Fine Tools

Hi, thanks for the response, I have never heard of this rubber pad forming, I will give this a shot. I'll have to find a bigger press, I've spotted a 30 ton on CL.


why not search the internet.
you will find what you need either in detailed text. Or on youtube.

you can do your homework there, as it has already been detailed.

Why did you even bother replying? I don't get people like you.

I've seen some interesting videos of people using 3d printed dies to do sheet metal forming, both press dies and bending dies. Not sure how they hold up long term, but it works fairly well in the videos. For a longer term solution, and not speaking from experience, but I would imagine aluminum dies would be sufficient for low volume runs, especially if you minimize sharp corners to round over. The cost would greatly depend on the size, complexity and tolerances of the dies. And you should definitely learn CAD if you want to do any kind of serious designing/prototyping. Especially if you're doing it on a budget. It will need to be drawn in CAD one way or another, so you can either do it yourself or pay someone else to do it.

Thanks for the advice, I have started learning some Fusion360 but the demo ran out, contemplating if I should fork over the 500 a year or maybe just go into FreeCAD. Any thoughts?

Hi Repoman:
When I look at the finished parts I see wrinkles where the original flat plate has been drawn up to form the sidewalls of the box shape that the final part has.
The epoxy die is crumbling because of the high localized forces the corners of the die experience when the metal wrinkles.
Do you care about the presence of those wrinkles?

If you do, you need to invest in something more capable of controlling the metal flow as it is drawn into a cup shape from a flat sheet.
This is often done with pressure pads which hold the sheet over the die opening, and through which the punch penetrates, squeezing the sheet enough that the wrinkles can't form in the first place...the metal must flow between the pressure plate and the top of the die opening so it is coaxed into the new shape.

All this is an art that takes years to learn, so you will have a very hard time with the details of how to make this shape unless you change it to be easier to make.
If you can get rid of the vertical side walls and just have the embossing on a flat sheet with maybe part of the radii of the outside edges, you can probably get away with just pushing a steel punch into a urethane pad, especially if you make a simple sprung pressure pad that goes around the punch to help keep the sheet flat as you push with the press.

From the sounds of it, making the punch and the pressure pad mechanism is beyond your ability and equipment.
So I'd find a retired diemaker with his own garage shop, ask him to design and build a simple tool for you and expect to spend at least a thousand bucks to do it.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Hi Marcus,
Yes the wrinkles are the areas that are from the die becoming damaged from high points of stress. I do use a pressure plate but it must not provide enough pressure, especially with non-annealed nickel silver (It actually popped all the screws out of their sockets on the last pressing)! I suspect that maybe the pressure plate should more closely conform to the opening with beefier fasteners, I will remake the plate to do so to see what happens. I'm wondering if the pressure plate should go right up to the edge of the cavity, or if it should be the difference in the height of the sidewalls. I'm guessing the sheet will tear if the pressure plate goes right up to the edge of the cavity. Unfortunately the sidewalls are necessary.
 
I think if you can get this into a CAD file - .step .sldprt. xt, some form of a solid model I think under $1000 is doable. If you are forming brass and aluminum shim, I think aluminum (maybe hard anodize) would hold up fine. If you want more long term 4140ht would probably do it, for added cost. Expect a tool steel/alloy to run you around $150-200 for material, unless someone has drops that would work. I am *guessing* this die is about 4"x6", maybe 1/2"-1" thick...


Probably only doing 0.020" brass with it (maybe nickel silver but that stuff has become really expensive in the past year)
Yes the male/female die is 4x6" and they are 1" thick, the actual part being formed is about 1.5"x3" and 0.650" deep.
 
Hi again Repoman:
How many of these do you have to make in a year?
How cheap do you want each individual part to be?
How badly do you need those vertical sidewalls, 0.650" deep?

Is this a show part, whose quality will describe your guitar pickup's overall quality to anyone who looks and wants to buy?
If so, you need it to be as perfect as you can make it.
So NO sidewall wrinkles!

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
 
Thanks for the advice, I have started learning some Fusion360 but the demo ran out, contemplating if I should fork over the 500 a year or maybe just go into FreeCAD. Any thoughts?

I would avoid Fusion360, but many think it's fine. FreeCAD is decent for being completely free, but for more complex work or any surfacing, it falls apart quickly. I'd recommend Rhino 3D. If you can qualify for a student license it's only $140 from Novedge. Otherwise is still only $900 for a commercial license, which is a steal IMO considering how versatile it is. They also don't charge maintenance, so patches are free and updates to the next version every 3-5 years are only $400. Be aware it is a direct modeler and is not parametric.
 
Hi yet again Repoman:
I didn't see your post #8 because I was typing my reply at the time.
Anyway, you need to understand some basic things about sheet metal forming that I think you're missing.

What you are trying to do is called "drawing" in the industry and it is fundamentally different from bending, which is the other common sheet metal forming process.

Drawing requires the metal to flow in a way that bending does not.
Part of that process requires you to constrain the metal as much as possible so it cannot fold...you can either stretch the metal into its new shape (like blowing up a balloon), or you can compress the metal until it flows into a new position.
If you don't keep the metal surrounded by something incompressible, it'll fold before it flows, and that's where the wrinkles come from.

So the pressure pad I'm talking about are not the blocks you put under and on top of your forming die; the pressure pad sits around the male part (the draw post), and also sits on top of the female part, sandwiching the metal sheet between the top of the female part and the underside of the pressure pad.
The draw post is longer than the female cavity is deep by the thickness of the pressure pad, and before the draw post even touches the sheet metal, the pressure pad is holding but not really clamping the sheet onto the top of the die opening.
There is a hole cut in the pressure pad the same shape as the draw post so the draw post can go through it.

Now when the draw post goes through the pressure pad and into the cavity, the sheet is forced to stay flat as the metal is pulled through the gap between pressure pad and die opening and into the gap between draw post and die.
The sheet metal blank needs to be pre-cut to the proper size so when the draw post is all the way home, the edges of the sheet metal are clear of the gap between pressure plate and die unless you want a flat flange on your part.
The top of the die opening needs to have a polished radius on the corner and it needs to be very smooth and just the right size.
The pressure pad or binder needs to hold the sheet metal with just the right amount of resistance and draw beads are often added to the design to control that element of the design.

This all gets pretty complicated and almost all of it comes from the fact that your part has vertical sidewalls.
The tendency of unconstrained sheet metal to wrinkle when it's drawn CAUSED the epoxy die to crumble, the defects in the die didn't make the wrinkles appear.

Making the metal flow takes a lot of force as you can imagine...so you cannot draw a part like you've shown without a metal die; the epoxy dies you've made are fine for a 2 dimensional bend but not for drawing.

So I still think you need to find a retired diemaker to help you.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
 
I used to run a rubberform press at a small bike mfg that did aluminum sheet metal frames, (each half, welded together) and we would press the soft (T-0) aluminum, pull the die with the part out and using a plastic hammer hammer down the wrinkles. Did this 3 or 4 times per part and they were wrinkle free when done.
The rubber or elastomer you want will be really high durometer and make the box that contains it not uch bigger that your actual part. As a guess I would be 1/2" bigger all around the part, so if your part is 2"x3" make box 3"x4" and not a lot deeper than the part.
 
Hi again Repoman:
How many of these do you have to make in a year?
How cheap do you want each individual part to be?
How badly do you need those vertical sidewalls, 0.650" deep?

Is this a show part, whose quality will describe your guitar pickup's overall quality to anyone who looks and wants to buy?
If so, you need it to be as perfect as you can make it.
So NO sidewall wrinkles!

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Hi Marcus,

Yes, unfortunately the sidewalls need to be quite deep, I may be able to get away with something more like 0.400", I need to be able to fit a guitar pickup coil assembly within it:

1Dgugwt.jpg

I'm building these weird guitars that have aluminum necks, I'm sort of taking this as an opportunity to be introduced to machining and TIG welding. Here is sort of a prototype I'm working on with one of the pickup covers.

GCH9Qkq.jpg

Here is the back of one I finished that sort of shows the welding/machining stuff

kdHFcdj.jpg


I wouldn't be selling them individually, but I would like to get them at least SORT OF in the ball park of a professional product...some of the hand made nature of what I'm doing isn't necessarily a bad thing but it's not a great thing either. I would need to produce around 50 of these covers a year.

Here is an old cover I am doing a sort of "inspired by" with my cover:

Screen Shot 2021-06-14 at 5.32.06 PM.jpg
 
Hi yet again Repoman:
I didn't see your post #8 because I was typing my reply at the time.
Anyway, you need to understand some basic things about sheet metal forming that I think you're missing.

What you are trying to do is called "drawing" in the industry and it is fundamentally different from bending, which is the other common sheet metal forming process.

Drawing requires the metal to flow in a way that bending does not.
Part of that process requires you to constrain the metal as much as possible so it cannot fold...you can either stretch the metal into its new shape (like blowing up a balloon), or you can compress the metal until it flows into a new position.
If you don't keep the metal surrounded by something incompressible, it'll fold before it flows, and that's where the wrinkles come from.

So the pressure pad I'm talking about are not the blocks you put under and on top of your forming die; the pressure pad sits around the male part (the draw post), and also sits on top of the female part, sandwiching the metal sheet between the top of the female part and the underside of the pressure pad.
The draw post is longer than the female cavity is deep by the thickness of the pressure pad, and before the draw post even touches the sheet metal, the pressure pad is holding but not really clamping the sheet onto the top of the die opening.
There is a hole cut in the pressure pad the same shape as the draw post so the draw post can go through it.

Now when the draw post goes through the pressure pad and into the cavity, the sheet is forced to stay flat as the metal is pulled through the gap between pressure pad and die opening and into the gap between draw post and die.
The sheet metal blank needs to be pre-cut to the proper size so when the draw post is all the way home, the edges of the sheet metal are clear of the gap between pressure plate and die unless you want a flat flange on your part.
The top of the die opening needs to have a polished radius on the corner and it needs to be very smooth and just the right size.
The pressure pad or binder needs to hold the sheet metal with just the right amount of resistance and draw beads are often added to the design to control that element of the design.

This all gets pretty complicated and almost all of it comes from the fact that your part has vertical sidewalls.
The tendency of unconstrained sheet metal to wrinkle when it's drawn CAUSED the epoxy die to crumble, the defects in the die didn't make the wrinkles appear.

Making the metal flow takes a lot of force as you can imagine...so you cannot draw a part like you've shown without a metal die; the epoxy dies you've made are fine for a 2 dimensional bend but not for drawing.

So I still think you need to find a retired diemaker to help you.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Marcus, does the pressure plate have two halves that are separate from the male and female dies? This is the part I made to hold onto the sheet as its pressed, the male die is cast with this part in place with 0.020" shim under it so it has enough length to compress the sheet fully. The first one I made like this was actually pretty much wrinkle free, but then of course the epoxy takes too much of a beating. I will try to find someone in my area, I don't know anyone involved in machining though!

Do you think I should even try the rubber pad forming method or will the sidewalls require too much force for the sidewalls (or introduce wrinkling)?

IMG_0263.jpg
 
The bike frame halves we made were were about 2" deep. They were made of .050 thick sheets.
Rubber forming is nice if you dont want to invest in hard tooling. All you need is the inner form to shape the metal around.
Aluminum neck, sweet! Do you know about Gary Kramer and/or Travis Bean?
If you could find out how altoids tins are made you might go that route, they are similar size to what you are doing.
 
Hi again Repoman:
Here is a schematic I pulled from the Internet:

The pressure plate is a simple ring that the punch fits into and it lays on top of the die and the sheet metal blank.
Sometimes they are just pushed onto the blank with heavy springs, sometimes they are held in position with standoffs so they can't squeeze the blank too hard.
It's called the "blank holder" in this schematic.

With regard to rubber forming this part...you can certainly try, and you'll lose nothing in the attempt except the cost of the rubber and the time it takes to make a box for it.
If it doesn't work, you'll already have the punch...you'll just need to make the die and the pressure pad.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
 

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The pressure plate is good, like has been said.
I used to maintain 2500 ton Toggle presses that had the outer ring clamp the sheet with just the right amount of pressure to keep a steady hold on the sheet while the inner punch would form and stretch the sheet to prevent wrinkles, but with light enough pressure to allow the sheet to slip enough to not tear the sheet.
Quite an art to place shims on top of the stop blocks to vary the pressure at certain points to get the correct hold in giant ancient worn presses.

In small prototype work, I like making the model out of Cerro-Bend and use a thick rubber block, like has been suggested already, to press the sheet.
The rubber has a firm enough grip to stretch and form, but elastic enough to allow slippage.

Cerro Bend, Wood's Metal, melts at about 145 degrees so it is easy to work with, but strong enough to withstand blows as a hammer form.

You could make a silicone mold to pour the molten Cerrobend into to easily make a new one if it wears in a longer production run.

Mike
 
If you want to make a quality part with no wrinkles you need to forget about using these blocks of magic goo. You need a proper die made out of heat treated steel. I would think that in Vermont there should be no shortage of Tool & Die shops that can make a proper die that will make a part you will be pleased to use on your guitar. You need to decide what your willing to pay for this part. That will determine what you can spend on tooling.
 
R:
One of the problems you're having with those vertical walls is that frequently for deep draws like what you're trying, there are several stages of draw, with anneals in between.

So a suggestion would be to use your female die with urethane pads to 'blow' the blank into the void in the female die without trying to get anywhere near the full form. Then pull it out, anneal it, and *then* try doing it with both halves of the die. It'll start out half way into the die already, so you'll have less stress trying to get those walls to go vertical without wrinkling.

Two suggestions: look at 'Bonny-Doon" press tooling, or Kevin Potter's stuff. or google 'hydraulic press forming for metalsmithing". Jewelers use one-sided dies for press forming all the time, and have gotten quite good at it. Many useful tricks to be learned.

Second suggestion: forget nickle silver. Evil stuff. If you're going to do this, use sterling. The cost of the metal won't be enough more to be a big deal, once you count what you're going to have to charge for labor. Yes, you're going to have to charge for these things.

Hope this helps.
Regards,
Brian
 








 
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