Home sheet metal stamping help needed!!!

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The ingenuity and dynamism of participants of these groups continues to impress me.

I think I understand your product/problem (and then again maybe not.)

The sides and ends form well because these are flat curves. The corners however are compound curves that bend two directions at the same time with the result there is an excess of material and it wrinkles. This is the same problem that you encounter when you wrap a package, and have to fold the corners over to make everything fit. Indeed, many cookie sheets have "envelope" or folded ends, or the corners are "fluted" for just this reason. Therefore, it is doubtful that binders will help the problem, because the [extra] material is not moving in from the sides/ends during forming, but is preexisting in the flat sheet.

In some deep draw products (such as sinks) the extra corner material problem is "solved" by placing anchors completely around the part. This forces the edges and ends to stretch and get thinner, thus there is no "extra" material in the corners, but just enough. The trade-off is the tooling is complex, the presses big [i.e. expensive] (or they use stretcher-hydro forming and expensive tooling) and the material gets thinner, and is deformed extensively, which may cause problems with work hardening, i.e. stainless.

As anyone who has attempted automotive bodywork knows, shrinking metal, i.e. pounding out dents where the material was actually stretched is very difficult. Indeed, it is so difficult that normal practice is to "get it pretty close" and fill in the rest of the way with lead or Bondo, which is then planed/sanded to fit.

See

And about 890 more when googling on < forming "urethane pad">

Good luck on your product, what ever it may be.

One final thought - have you contacted Elko or other cookie sheet manufacturers? They may have something off the shelf.

Unka George (George McDuffee) ............................... So long as a man rides his Hobby-Horse peaceably and quietly along the King's highway, and neither compels you or me to get up behind him-pray, Sir, what have either you or I to do with it? Laurence Sterne (1713-68), English author. Tristram Shandy, bk. 1, ch. 7 (1759-67).

I build automotive body panel dies. The most important part of this affair is to understand what kind of part you expect out of the die. If you're expecting a cosmetically perfect piece of sheet metal that, if painted, looks like a mirror, you're expecting way too much. It sounds like you have never built a die at all, so you're missing some basic knowledge and a whole lot of experience. But since you asked...

Typically the entire blank is held in a binder. This may not be absolutely necessary, however. Indeed, it takes quite a bit of work to make a binder actually do its job. It should be understood that it is not the job of the binder to squeeze the snot out of the panel. The binder is only there to prevent wrinkling. It does this by being

*exactly* one sheet metal thickness away from the draw cavity which it faces. This is achieved by the long and tedious process of spotting. Additionally, binders have balance blocks which actually prevent the binder from squeezing the material.

Beads, on the other hand, are a bit different. Draw beads increase the resistance to the metal flow into the die cavity. A bottom line rule is that when you get wrinkling, you're getting excessive flow and you need to reduce it. When you get thinning/tearing, you're getting insufficient flow and you need to increase it. Beads are used by the toolmaker to adjust this flow. Beads which are rads will cause resistance where as lock beads which have a square profile (with small rads) will actually prevent virtually any metal from flowing (causing stretching instead of drawing). Typically you start out with a rather excessive bead which is sure to tear your panel. Then, you grind away the bead until the tearing disappears, and you ideally get what you want (much easier said than done).

Note: the binder force must ensure that the panel's tendancy to wrinkle does not push the binder away from the panel itself. Remember that the force available from the press will have to oppose the binder force while forming the panel as well. Nitro springs are good if you don't have a draw cushion (you don't) but in your case, die springs may work. It's difficult to tell.

Since your corners are wrinkling, you need to add beads around them. The beads should taper into nothing (or at least be reduced) as they enter the straights. Running a bead around your entire profile will allow you more control over the flow into your die, but adds complexity.

You just need to understand that if this doesn't work out the way you wanted, it is unlikely you will ever find out why. This type of skill cannot be learned from printed words. Only experience under someone more capable can give you the ability to create excellent results. Indeed, making a toolmaker who can build and tryout a class A draw die (outer sheet metal, cosmetically "perfect") usually takes 5+ years after apprenticeship. To give you an idea, complex body panel draw dies can cost in excess of $500k each.

Other important points:

Any rad which the metal is flowing over *needs* to be polished to a mirror. This typically requires polishing stones (up to 100 grit) and then emery cloth up to 600 grit (120, 240, 400, 600).

Any rad which the metal is flowing over *needs* to be a true rad. If you can feel edges around any part of the rad, you are increasing the resistance to flow and you're likely to get a tear or at least thinning in that area.

Spotting blue is nearly a requirement unless you have virtually no specifications beyond the part not splitting in half (and maybe even so). Again, the requirements of the panel need to be specified.

Smaller femal rads shall not spot into the panel. Metal flows over male rads only. Female rads are to be cleared out.

If this die has to make more than about 1000 parts, flame hardening the rads is virtually a necessity. The rads will get scored with any debris on the panels and will eventually wear away if left soft.

Draw beads will solve the problem, assuming the OP is capable of adjusting them correctly (very unlikely, but that depends on the requirements of the panel). A binder by itself is indeed very unlikely to solve the problem.

By *far* the best advice available.

Regards,

Robin

Have you considered explosive forming? ONly need one die, plus a swimming pool or such. Cheap but noisy & wet ;)

Hey Robin,

Cudos on your reply to the OP. Very well done.

Take care.

Brian Lawson, Bothwell, Ontario.

ps...I d>

Unfortunately I'm gone to Europe on Friday so I likely won't see the conclusion of this project. I hope the OP posts pictures if he is successful.

Ah, the good ol' days (when I was cutting metal for my own entertianment). I recently got my German papers. One more year until my Ontario papers.

Regards,

Robin

Robin, Thank you so much for you explanation!!! That is exactly the kind of input I need. I am an Auto Tech and self taught bodyman. The part I'm needing to make is actually an inner door panel from a late

1920's car. I suspect the original part was crush formed, but since I don't have the proper equipment, that's not happening. That was how I performed my first attempts, and the panel is perfect, except for the corners. The part is slightly concave, wich I've managed to achieve. I will try using the draw bead approach (When I said binder, that's actually what I meant) Surface finish is not terribly important. I'm by no means a die maker, but I have set myself on a mission. It's not a very complex piece, which is why when I look at it I say," I can make this". If I fail, I fail. But if I succeed...oh the pride. I would like to get 50 parts out, but I only need one. I looked into having the part made, and your estimate was about right, even for the short run. BTW, the Die is poured of alloy. (yes I built a smelter capable of 50 lbs Al). If I succeed, and even if I don't, I'd be happy to share the results. Any more suggestions would be great. I'm open to any ideas.

Tim

Rob> > Hey Robin,

Any more suggestions would be great. I'm open to any ideas.

If I were trying this, I would put notches in the corners to eliminate the wrinkles. And then weld up the seams in the corners and grind and flap sand to blend the welds in. I expect you have thought of that. You are way ahead of me.

Dan

Thanks Dan. I did do this with the first few, but didn't like the hardening caused by the weld. It can (has) be done that way. But it's only 1" deep, there must be a hillbilly way of doing this.

Tim

snipped-for-privacy@krl.org wrote:

Indeed, cars go *out* of production with cosmetic and dimensional issues still in the dies. Just too expensive/difficult to fix.

At that point, you should only really be worried about thinning in the rads. When you shine a light from the top of the rads down, if you see any slight shadow which looks like a line running along the rad, that's probably thinning. Mind you, this isn't easy to see, but you should be at least aware of it. You should ease off the bead until it disappears. If your panel splits at the beginning, remember these areas as they will continue to be in danger of thinning/splitting even after you think you've gotten rid of it.

Well, unfortunately the actual technique required to tryout your die is not something I can write about.

Remember that the draw punch (male) is master to the cavity. Further, cavity is then master to the binder. I'm not sure how much spotting you'll end up doing, but *never* adjust the draw punch! It must stay flat and straight in all respects. Do not grind it. Only stone and polish it as required. I wouldn't even recommend using a draw cavity really (the female part) given your requirements. Basically the binder must hold the sheet metal before the draw punch makes contact. Once the panel is held, the punch is pushed into the sheet and the sheet is drawn over it (all motion is relative).

So, one half (we'll say the "lower" as it would be in toolmaking terms) will have your draw puch, and your binder, which sits above the top of the draw punch when the die is open, and below the bottom of the rads on the draw punch when the die is in the closed position. So that's two main parts.

The third (on the "upper" side) will be a ring which faces the binder. The ring will have pockets to accomodate the draw beads on the binder. Given your requirements, it should be sufficient to have the ring and the binder be as flat as can be made, ideally surface ground, but machined would likely work (indeed, perhaps having just cold-rolled finish would work for you). Balance blocks probably won't be necessary to get your one or 50 parts. The binder and the ring should be of adequate thickness to not flex when the punch goes through. You didn't specify the outside dimensions of your panel, but probably steel plate roughly 3/4-1" thich would be alright. You may get away with less (you won't know any of this until you try). Since your production run is so small, you can probably just use c-clamps or whatever to hold the panel between the binder and ring. Nuts to the springs.

A note on beads. You may find it much simpler to just weld the beads on and spot them into the pockets on the ring (use a die grinder with carbide burr to make the pockets). The beads cannot have a "welded" finish. They must be welded too large and then ground down until they are straight (with rads over which the metal flows) and have only bare metal. Again, hard to describe, easy to show. Mig or stick is your best bet. Whatever will stick to the binder.

Understand that if the panel, during drawing, flows over the beads and then off the beads completely, you will get excessive flow at the end of the stroke. What I'm saying is that you need to make your blank panels big enough such that they do not get sucked past the beads once the panel is hit. Mind you, you *can* use this to your advantage when performing tryout. If you're not getting enough flow, cut your blank back in the torn/thinning areas and you'll notice greater flow (similar effect of actually grinding the beads).

BTW, grinding straight beads is done with a disc grinder using the flat face of the disc. Do NOT use the bloody edge of the grinder wheel! You will take the straightness out of the bead and it's a pain to get it back. Remember to always recreate your rads once you've reduced the height of the bead. Not having rads will give you splits and thinning (and overall wacky results).

Grinding beads which follow a rad is done with a die grinder. Use a carbide burr to remove material quickly, and always finish with a pink stone to give a nice finish and to cut the rads again.

Stoning your beads after grinding them is *highly* recommended unless you're getting huge splits down the panel, in which case stoning them is only a drop in the bucket.

The above are general guidelines. Your milage *will* vary. Keep your expectations low and you'll be surprised by your results. How many hours did you plan on investing in this little diddy? Can you sell the panels?

Regards,

Robin

Snip a whole lot of very on-topic technical stuff explaining why this isn't nearly as simple as it appears on the surface.

And where I was going to go too, till I saw it. There are many companies that make "stock" deep drawn shapes for many different industries like restaurant steam tray pans and cover lids, those cookie sheets you mentioned, etc.

And they make stock electronics enclosures like that too, Bud Industries springs to mind.

Be inventive - if you can use a stock piece that is close to what you envisioned and drill a few holes in it, you'll be a whole lot further ahead actually making what you want and moving forward than trying to build a draw die system at home.

If the only difference is the material - like you don't want it in Stainless, or you only want the deep draw and not the rim beading or edge finishing detail done - call the company that makes them. They may be able to blank a few out for you in mild steel the next time they have that particular die set up on the presses, or pull you one between the drawing and finishing process stops...

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Robin, WOW!! I have to say that I really appreciate your encouragement. I had thought about just using the draw punch, but there is a slight impression in the center of the panel I'd like to get from the stamping. My whole dilemma was where to place the draw beads, and if I understand correctly, around the corners is where I'd want them. I will follow your direction to the best of my ability (or lack of) and see what happens. I'm still planning my next attempt, so it may be a few weeks before the first try. I currently have about 10 hours work in the first 10 or so I made using a welded up bar stock skeleton of a male and female die. The panel is about 21" x 30". I can sell then and afford to buy a real press with the profits if I can make then successfully. Hence the need for one but the desire for 50. If it helps, a cutaway of the panel would look something like below. __ | | ___ |_I

Tim

Rob> > Robin, Thank you so much for you explanation!!! That is exactly the

Unless that you *need* that impression in order for the panel to be usable, I would strongly suggest against trying to create it. Not only do you then have to have a female cavity, you also have to contend with what we call "inside metal". This means that you do not have the luxury of a draw bead beside that feature. If you have problems creating that feature (and you *will* of course), you cannot just adjust the draw bead to suit. This is because the draw bead with affect the large rads as well as your impression.

Notice the area above gas caps on car bodysides/quarter panels. This area frequently has cosmetic issues because of this exact problem. Indeed even Mercedes and BMWs have this problem because of the difficulty of removing it (and they're a lot more picky than the big three or any of the Japanese makers).

Now, I'm assuming this impression is a formed impression, not just stamped. If it's stamped, it won't be a big issue and you should not try to stamp using the draw die (certainly possible, but not simple).

Yes, exactly.

It's a good thing that's an inner panel. It has features similar to door inner panels today. Very deep draws which we must do it one or two hits (you get 5 or less operations to make a complete panel).

If I'm seeing your drawing correctly (it's just a section of half the panel, right?) you're going to have problems because of the reversed nature of the draw on the inside. This will necessitate a female half of the die which will bring the inside back in. Remember that all male rads are master. In this case, the draw cavity will have male rads (nearly a draw punch in itself) which will be master.

I'd recommend instead of a solid draw punch, only create the ring (with a hollow center). Flats on draw dies serve much less of a purpose than rads. The female die cavity will need to be solid so that you can get your impression in the center.

Good luck with this. While you're *only* having trouble with the corners wrinkling, this is a much more significant problem than perhaps you may think. It would be helpful if I had time to make some sketches, but that's unfortunately unlikely to occure given my time constraints. Keep the questions coming.

Regards,

Robin

================== I was unable to locate a site, but I have seen articles on forming wing ribs for home built aircraft using a hard wood form.

The sheet metal is heavely clamped and gradually moulded to the hard wood [as I recall maple] form using a soft faced hammer and many, many light blows.

From what I recall of the photographs the draw was about 1 inch deep and the forming around even external and internal compound curves appeared even with no buckles.

The material was most likely soft aluminium, so this may not work with steel, but should be cheap/easy enough to try.

An OBTW -- What temper of sheet are you using and how are you annealing the steel to maintain ductility?

If this looks like it might work, it should be easy enough to rig up an urathane tip for an air palm nailer or impact gun.

How are you getting the big curve in the panels? English Wheel?

I don't have these books, but they will have some of the old techniques that could apply to your needs.

part about ... "You'll see a man removing wrinkles from a curved sheet using a planishing hammer and bumping stake." may be of help. You may find some ideas for something you can rig up on the following sites. ?itemID=1495&itemType=CATEGORY&iMainCat=688&iSubCat=1495 Unka George (George McDuffee) ............................... So long as a man rides his Hobby-Horse peaceably and quietly along the King's highway, and neither compels you or me to get up behind him-pray, Sir, what have either you or I to do with it? Laurence Sterne (1713-68), English author. Tristram Shandy, bk. 1, ch. 7 (1759-67).

=20 It sounds as if you need to control the sheet at the corners only. You don't need a pre-loaded binder as such, but some means to keep the corners from wrinkling. A piece of flat steel bolted diagonally across each corner might just do the trick. =20

How's that for a hillbilly approach

The shape of the blank sheet is important; If you cut corners (pun intended) the corners will draw/form more easily. Remember, you'll need

*less* material in the corners than on the sides.

If you do the draw in steps, you could try annealing the critical parts (the corners) between the draws. The sheet will work harden when cold forming. Heating to cherry red will normalize the material. =20 =20

--=20

-JN-

Ok, I like the ideas you guys are giving me. A lot of is re-asserting what I kinda thought. Before I posted this question, my idea was to make the female dies to "exact" size. Use draw beads where appropriate (hence the questions) and press the sheet into the female with a hollow punch, just the ID of the part, to get the recess pressed into the panel. I have tried hammerforming as one person mentions, It works well for a lot of things, but I know this can be done with a lot less work. Everyone seems like they need a good laugh. I've posted pictures on Photobucket. Please be kind. I should at least get an "A" for effort. I just took these today. It's been several months since I visited this project, so things have gotten a little rusty.

Keep in mind this was just a quick throw together to see how close I could get before I invested any real time or money on materials. Let me know your thoughts.

J. Nielsen wrote:

Good Post Robin, nice to see helpful information posted.

Regards Daveb

Hi Tim, Have a look at this page, a fellow making a door for a divco milk truck.

regards,