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Seeking Advice On Sheet Metal Stamping

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Seeking Advice On Sheet Metal Stamping

Seeking Advice On Sheet Metal Stamping

JanusCole

(Automotive)

(OP)

4 Jul 08 19:29

Hello,

I produce rear end deck lids for Porsche 911's in my basement workshop using traditional hammer forming techniques. I do them in aluminum since OEM parts in aluminum are NLA and so owners are willing to pay a premium. That said, each part takes a lot of time and may ability to add new parts to my product line is extremely limited (it can take months to build a proper hammer form). So I'd like to have the parts stamped in aluminum instead. Now to be perfectly honest, deck lids aren't incredibly complicated parts (see attached picture). There is a top exterior piece and a bottom structural piece and that is pretty much it. No complicated features or curves. And yet, I have approached a couple of shops that claim to do metal stamping and they all say that the tooling would be prohibitively expensive and difficult. Of course, they won't give me any ball park figures or explain why it would be so difficult. So I am baffled.

Now, I am accustomed to doing this stuff by hand in my workshop. So I know little about having manufacturing done for me. Can anyone give me some advice or point me to a place where I can learn how this is all done? I assumed I'd  just have someone scan the top and bottom sides with a laser scanner into a CAD file and then I'd pay someone to cut a die. Then, presumably, I'd just have someone else do the stamping in aluminum. What am I missing here? Can anyone give me a ball park figure of what it might cost? I am encountering roadblocks at every turn and it is very frustrating.

Thanks,

-Janus Cole

RE: Seeking Advice On Sheet Metal Stamping

patprimmer

(Publican)

4 Jul 08 21:48

Maybe the guys blow you off because you present like you have no idea of the costs, or because they presume you can't afford or justify it. If so, their fault, but you might do better if you play there game and dress the part when you visit.

A wild thought, is the OEM stamping die available, maybe as scrap.

I know nothing of stamping dies, but I do know something of plastics injection moulding moulds. The plastics moulds will be more complex, but would cost several  tens of thousands of dollars. Just the steel would be thousands of dollars.

Your link is password protected, so I cannot see the part, but I am reasonably familiar with 911s. Some early ones are fairly simple, but later ones are very complex with whale tails that hold A/C condensers etc.Maybe the guys blow you off because you present like you have no idea of the costs, or because they presume you can't afford or justify it. If so, their fault, but you might do better if you play there game and dress the part when you visit.A wild thought, is the OEM stamping die available, maybe as scrap.I know nothing of stamping dies, but I do know something of plastics injection moulding moulds. The plastics moulds will be more complex, but would cost several tens of thousands of dollars. Just the steel would be thousands of dollars.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
 

RE: Seeking Advice On Sheet Metal Stamping

JanusCole

(Automotive)

(OP)

4 Jul 08 22:20

If startup costs were in the tens of thousands, then frankly, that would be okay. A halfway decent 30 yr old OEM 911 deck lid in AL goes for about $1,000 - $1,500 each - and AL hoods or duck tails would go for much more - if anybody made them. So I'm just amazed they aren't even willing to talk to me. I can recoup tooling costs pretty quickly...even substantial tooling costs.

Oddly enough, a friend in the garment industry tells me he had a similar problem until he moved his manufacturing overseas. He said American companies were routinely dismissive and rude. But when he went to India, he got a completely different attitude. I'd rather stay domestic. But I'll go overseas if I have no other choice. I just today emailed about 20 companies in India. We'll see what they say.

As for acquiring the original dies, I believe they were bought by a US company that specializes in steel reproductions. So I am out of luck there.

• http://files.engineering.com/getfile.aspx?folder=2f79c518-b9bb-4c3c-aaa1-3b

Thanks for the advice. It is genuinely appreciated. I didn't know that the picture would be password protected so I have uploaded a jpg. The ones I make are replicas of the original AL deck lid with no spoilers of any kind. Very simple stuff.If startup costs were in the tens of thousands, then frankly, that would be okay. A halfway decent 30 yr old OEM 911 deck lid in AL goes for about $1,000 - $1,500 each - and AL hoods or duck tails would go for much more - if anybody made them. So I'm just amazed they aren't even willing to talk to me. I can recoup tooling costs pretty quickly...even substantial tooling costs.Oddly enough, a friend in the garment industry tells me he had a similar problem until he moved his manufacturing overseas. He said American companies were routinely dismissive and rude. But when he went to India, he got a completely different attitude. I'd rather stay domestic. But I'll go overseas if I have no other choice. I just today emailed about 20 companies in India. We'll see what they say.As for acquiring the original dies, I believe they were bought by a US company that specializes in steel reproductions. So I am out of luck there.

RE: Seeking Advice On Sheet Metal Stamping

patprimmer

(Publican)

4 Jul 08 22:29

The same guys who were arrogant to you will be the first to complain when challenged by imports.

You will also have an export market for your product. I can fix you up with people here who know that market.

 

My advice is to seek alternate supply, in USA, China and possibly Australia. China, like USA normally only like long run production. Australia specialises in short run production and has a high ratio of skilled people in the workforce like other developed countries. Our $ is strong, so costs will he high.The same guys who were arrogant to you will be the first to complain when challenged by imports.You will also have an export market for your product. I can fix you up with people here who know that market.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
 

RE: Seeking Advice On Sheet Metal Stamping

MikeHalloran

(Mechanical)

5 Jul 08 13:59

An injection molded plastic part is, allowing for shrinkage, a geometric complement of the cavity that made it, so you can make an acceptable mold for a plastic reproduction from a cast of the finished part.

Not so for metal, which has to be overbent, working it along the stress/strain curve, which just for fun is different for steel and aluminum, and for different heats of each.  Stamping dies bear only a passing resemblance to the finished part geometry, and there may be more than one pair of dies involved in progressively refining the shape from flat to whatever.

Metal also presents as sheet, not meltable pellets.  The dies have to draw the metal from the blank into their cavity.  In the process, the metal rubs, hard, on the die surface, possibly scarring the metal and eventually wearing the die.

Wait; it gets worse.  The metal often wrinkles as it's drawn, so the dies may contain odd features to control the wrinkling, or to induce it to occur in a portion of the workpiece that will later be removed.

For exammple, I think the "SME Die Design Handbook" carries a photo of an old Ford rear roof section, mid- process, with a big ugly wrinkle right in the middle of it... where a hole would later be punched for the rear window.

That book would be a good investment for you.

 

Stamping dies are different from injection molding dies because metal is not always plastic. Okay, duh, but bear with me.An injection molded plastic part is, allowing for shrinkage, a geometric complement of the cavity that made it, so you can make an acceptable mold for a plastic reproduction from a cast of the finished part.Not so for metal, which has to be overbent, working it along the stress/strain curve, which just for fun is different for steel and aluminum, and for different heats of each. Stamping dies bear only a passing resemblance to the finished part geometry, and there may be more than one pair of dies involved in progressively refining the shape from flat to whatever.Metal also presents as sheet, not meltable pellets. The dies have to draw the metal from the blank into their cavity. In the process, the metal rubs, hard, on the die surface, possibly scarring the metal and eventually wearing the die.Wait; it gets worse. The metal often wrinkles as it's drawn, so the dies may contain odd features to control the wrinkling, or to induce it to occur in a portion of the workpiece that will later be removed.For exammple, I think the "SME Die Design Handbook" carries a photo of an old Ford rear roof section, mid- process, with a big ugly wrinkle right in the middle of it... where a hole would later be punched for the rear window.That book would be a good investment for you.

Mike Halloran
Pembroke Pines, FL, USA

RE: Seeking Advice On Sheet Metal Stamping

EdDanzer

(Mechanical)

6 Jul 08 12:27

As with any new expensive project many shops will be wary of spending a lot of time quoting a project like this. If you find a few places with actual capabilities and ask for a ball park range after supplying a digitized model and what they need as a down payment to get started you will be better received.

One place to start is www.mfgquote.com . You will have better luck if you have one company digitize the part so other shops can import the data for modeling. You will need NDA's for anyone who works on the project. As MikeHalloran mentioned spring back needs to be allowed for in the die shape and there is software to help get it right the first time. It may be advantageous to know if the shop has advanced modeling software to determine actual die shape.As with any new expensive project many shops will be wary of spending a lot of time quoting a project like this. If you find a few places with actual capabilities and ask for a ball park range after supplying a digitized model and what they need as a down payment to get started you will be better received.

Ed Danzer
www.danzcoinc.com
www.dehyds.com

RE: Seeking Advice On Sheet Metal Stamping

GregLocock

(Automotive)

7 Jul 08 04:45

Aston Martin or Lotus would be the obvious people with expertise with low volume tooling. I think for aluminium you could use a soft form tool, in which the male part is a rubber block. I don't know what the quality would be like.

To be honest I think you are barking up the wrong tree, steel dies are designed for parts (or more) per annum, and need enormous presses.

Howver, if you /do/ find a method that works there are a lot of car companies that would be interested, prototyping is a lucrative if challenging business.

Concur on the sticker shock.Aston Martin or Lotus would be the obvious people with expertise with low volume tooling. I think for aluminium you could use a soft form tool, in which the male part is a rubber block. I don't know what the quality would be like.To be honest I think you are barking up the wrong tree, steel dies are designed for parts (or more) per annum, and need enormous presses.Howver, if you /do/ find a method that works there are a lot of car companies that would be interested, prototyping is a lucrative if challenging business.

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: Seeking Advice On Sheet Metal Stamping

JanusCole

(Automotive)

(OP)

7 Jul 08 22:29

Thanks very much! This info is incredibly helpful. I clearly came to the right place. I can't thank you enough. I am quite familiar with the traditional metal forming with hammer form and hand held hammers. But taking the leap to automation has proved a daunting task.

PATPRIMMER WROTE: The same guys who were arrogant to you will be the first to complain when challenged by imports.

Funny you should mention this because I got the following today...I don't think I have ever called a client a "crybaby" at any point in my entire career...I replied to him saying he had done me the favor of removing his company from my list of prospects...

And to establish the context, he is correct that I didn't include size measurements - however I did include a PHOTOGRAPH of the part in question clearly showing the size...

Amazing...will I need to beg US metal working companies to even talk to me?

-Janus Cole

--- On Sat, 7/5/08, John Baker wrote:

 From: John Baker
 Subject: RE: Contact Us Form for General A&E
 To: JanusCole
 Date: Saturday, July 5, , 4:44 PM

 Don't be a cry baby.  

 Consider other alternatives.  You haven't even said how big the lids are.  If they're bigger than a foot in either direction then of course tooling would be prohibitive.  You should look at other ways of manufacturing it that specialize in larger items.  Why not consider hyroforming or vacuum forming.  Cheaper tooling, slightly higher unit price.  The Internet should  make your work easy.
  

RE: Seeking Advice On Sheet Metal Stamping

GregLocock

(Automotive)

7 Jul 08 22:40

Hydroforming is an interesting suggestion - I haven't seen it suggested for a body panel.

What sort of quantites were you thinking of?

John must be my twin brother, that's one reason I don't work in sales!Hydroforming is an interesting suggestion - I haven't seen it suggested for a body panel.What sort of quantites were you thinking of?

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: Seeking Advice On Sheet Metal Stamping

MikeHalloran

(Mechanical)

7 Jul 08 23:12

If a low production rate can be tolerated, the tooling can be relatively inexpensive, e.g. stacked plates bolted together instead of an actual press.  It might be possible to do both the shell and the reinforcement in one inflation cycle.

 

Hydroforming is an excellent suggestion for the parts in question. It can do the large radius forming and the small radius drawing, in one step.If a low production rate can be tolerated, the tooling can be relatively inexpensive, e.g. stacked plates bolted together instead of an actual press. It might be possible to do both the shell and the reinforcement in one inflation cycle.

Mike Halloran
Pembroke Pines, FL, USA

RE: Seeking Advice On Sheet Metal Stamping

GregLocock

(Automotive)

7 Jul 08 23:22

Mike do you think you'd get a Class 1 finish?

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: Seeking Advice On Sheet Metal Stamping

JanusCole

(Automotive)

(OP)

7 Jul 08 23:29



Thanks,

-Janus Cole

Yes, excellent point. I will begin obsessively googling "hydroforming" to learn as much as I can. I did actually take the content of Mr Baker's seriously. It was just his introduction that I didn't like so much.Thanks,-Janus Cole

RE: Seeking Advice On Sheet Metal Stamping

BrianPetersen

(Mechanical)

8 Jul 08 08:23

Hydroforming as I know it is incredibly expensive. The process as I know it consists of taking a pre-formed (generally steel) tube, placing it in what amounts to a mold, then essentially "inflating" the inside of it with high pressure liquid, forcing the tube to shape itself to the inside of the mold. It's used for frame members and similar tubular parts. The equipment to do this costs millions and it's only practical / cost effective for parts produced in the hundreds of thousands (e.g. GMT900 frame members).

Vacuum forming, or possibly something like it (with a little more pressure from the open side of the mold, perhaps) might be what some people really mean. Vacuum forming as I know it is used for thermoplastic parts. You take a thermoplastic flat sheet, heat it up uniformly so that it is soft but not melted, place it over a mold that has many openings to allow vacuum to be applied underneath it, and suck the sheet into the shape of the mold. It's limited to parts for which a flat sheet can seal against the outside of the mold - otherwise, the vacuum just leaks in from around the edges. Of course, if this is not convenient for the finished part, it's possible to make the part bigger than necessary so that it *does* satisfy this limitation, then trim it to suit. I've never seen this done with metal, but that doesn't mean it's impossible. Controlling wrinkles could be an interesting challenge. With softened thermoplastic, this is not a problem.

RE: Seeking Advice On Sheet Metal Stamping

GregLocock

(Automotive)

8 Jul 08 08:36

However those are all for tubular constructions more than external panels, hence my question to Mike.

We use hydroforming for prototyping and production, maybe there are similar but different techniques with the same name. Lotus were certainly interested in it for low volume production, as I remember Matra use it as well.However those are all for tubular constructions more than external panels, hence my question to Mike.

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: Seeking Advice On Sheet Metal Stamping

MikeHalloran

(Mechanical)

8 Jul 08 11:56

Free-form hydroforming is also possible, as in welding up the edges of two suitably pre-shaped blanks, and inflating two boat hulls, just by pumping oil into the space between the blanks.  Essentially no tooling cost, but limited control over the finished article shape.

I was thinking in terms of a traditional blanket type hydroforming press, except without the press, and doubled up with two blankets and two workpieces sandwiched  between two platens with simple tools affixed.

 

Long before anybody thought to hydroform a tube into a usefully distorted shape, people were selling and using hydroform presses, principally for making aircraft parts of aluminum. In those, a rubber blanket is forced, by means of pressurized hydraulic fluid behind it, against a flat blank which is partially supported by the male tool behind it. The tool takes the form of, say, profiles for a whole set of wing ribs. Given a urethane blanket and some sharp edges in the tool, it was possible to also cut out relief holes and edges.Free-form hydroforming is also possible, as in welding up the edges of two suitably pre-shaped blanks, and inflating two boat hulls, just by pumping oil into the space between the blanks. Essentially no tooling cost, but limited control over the finished article shape.I was thinking in terms of a traditional blanket type hydroforming press, except without the press, and doubled up with two blankets and two workpieces sandwiched between two platens with simple tools affixed.

Mike Halloran
Pembroke Pines, FL, USA

Goto Aomate to know more.

RE: Seeking Advice On Sheet Metal Stamping

carnage1

(Electrical)

9 Jul 08 14:11

If you are going to hydroform I suggest explosive forming. from a practical standpoint there would be less cost for the explosives than for pump equipment for small runs, and more importantly explosions are cool :)

the biggest benefit I see is the need for only one Die.

RE: Seeking Advice On Sheet Metal Stamping

NickE

(Materials)

10 Jul 08 08:46

Have you tried talking to prototype sheet houses out of detroit? Business is kinda slow here, most places seem to need some work.

http://www.thomasnet.com/products/stampings-short-run--1.html

I can honestly say that I've been to these three: Matrix, Oakley, and Quasar, seemed like good shops.


Nick
 

For the kind of quatities it seems you are talking about, a kirksite tool in a simple press would work.Have you tried talking to prototype sheet houses out of detroit? Business is kinda slow here, most places seem to need some work.I can honestly say that I've been to these three: Matrix, Oakley, and Quasar, seemed like good shops.Nick

RE: Seeking Advice On Sheet Metal Stamping

GregLocock

(Automotive)

10 Jul 08 20:07

 

Do any of these single step processes get a class 1 finish?

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: Seeking Advice On Sheet Metal Stamping

patprimmer

(Publican)

10 Jul 08 22:21

They probably produce an A1 finish with less finishing work than free form hand beating.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
 

RE: Seeking Advice On Sheet Metal Stamping

EdDanzer

(Mechanical)

10 Jul 08 22:31

I think explosive hydro-forming will provide a finish equal to the die. The explosion will have to provide enough energy to exceed the yield strength of the material as it work-hardens during the deforming process and enough volume to fill the deformed shape. The die and backer need to be structurally strong enough to take the pressure which should be over 16,000 psi (the yield strength of 0 grade aluminum.

Ed Danzer
www.danzcoinc.com
www.dehyds.com

RE: Seeking Advice On Sheet Metal Stamping

NickE

(Materials)

11 Jul 08 08:32

So I dont know Greg, seems to me that you still would need to do a FLD and "massage" the die (any process is going to need that anyway), but yes a simple stamping operation would do it.  

I've seen (Techrepped) DDQIF steel hit with kiksite dies to create A1 prototype panels, but I've only walked by real PPAP'ed (or whatever the OEM internal quality requirements are) stamping operations.So I dont know Greg, seems to me that you still would need to do a FLD and "massage" the die (any process is going to need that anyway), but yes a simple stamping operation would do it.

Nick
I love materials science!

RE: Seeking Advice On Sheet Metal Stamping

GregLocock

(Automotive)

13 Jul 08 02:48

Thanks. Is the OP still reading? Are we on the right track?

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: Seeking Advice On Sheet Metal Stamping

patprimmer

(Publican)

13 Jul 08 08:47

He has only ever posted in this thread, and he logged on today, so I guess he is still checking in.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
 

RE: Seeking Advice On Sheet Metal Stamping

JanusCole

(Automotive)

(OP)

23 Jul 08 16:28

Yes, I am still checking in. I was just keeping quiet because I am being a fly on the wall and you guys know tons more than I do. I've also been waiting for the various companies I've contacted to reply to me. And responses have trickled in slowly. So I didn't really have anything useful to offer except to keep saying, "That's interesting."



Most of the responses I've gotten have told me that they don't have the tonnage/tooling required to stamp parts in the size I am making - about 120 cm x 90 cm. And that's okay. It's a bummer but I understand.

That said, I've recently been emailing companies that do hydroforming. I used ThomasNet to find them. Again, most specialize in small parts. So I've no luck yet. But I haven't given up hope.

There was a thread by a guy on MetalMeet who posted pictures of some molds he was making of original Willys doors. Claims he used the molds to pour kirksite dies and then had the parts formed by a local hydroforming company. If he can do it, I am certain I can. I actually create my hammer forms by pouring a mold off of an OEM part in ultracal cement and then coating it in Devcon Plastic Steel. So I am already half way there. I can make cement tooling molds until the cows come home. However, I am unfamiliar with kirksite and with the task of finding a company to do the hydroforming. But hey, that's why I'm here.

Mike Halloran wrote: If a low production rate can be tolerated, the tooling can be relatively inexpensive, e.g. stacked plates bolted together instead of an actual press.  It might be possible to do both the shell and the reinforcement in one inflation cycle.

I actually ordered this video on that very topic...

http://www.tinmantech.com/html/vid_fluid_forming_alum.php

Seems like complete madness to me! Only thing crazier (and yet way cooler) would be to use "explosions"! I was planning to leave the manufacturing to the pros. But I suppose it can't hurt to try some hydroforming experiments with small parts. If I don't post anytyhing in the next six months, you'll know I blew up the shop during a horrible "home hydroforming" experiment.



Thanks,

-Janus Cole

Greg Locock wrote:Thanks. Is the OP still reading? Are we on the right track?Yes, I am still checking in. I was just keeping quiet because I am being a fly on the wall and you guys know tons more than I do. I've also been waiting for the various companies I've contacted to reply to me. And responses have trickled in slowly. So I didn't really have anything useful to offer except to keep saying, "That's interesting."Most of the responses I've gotten have told me that they don't have the tonnage/tooling required to stamp parts in the size I am making - about 120 cm x 90 cm. And that's okay. It's a bummer but I understand.That said, I've recently been emailing companies that do hydroforming. I used ThomasNet to find them. Again, most specialize in small parts. So I've no luck yet. But I haven't given up hope.There was a thread by a guy on MetalMeet who posted pictures of some molds he was making of original Willys doors. Claims he used the molds to pour kirksite dies and then had the parts formed by a local hydroforming company. If he can do it, I am certain I can. I actually create my hammer forms by pouring a mold off of an OEM part in ultracal cement and then coating it in Devcon Plastic Steel. So I am already half way there. I can make cement tooling molds until the cows come home. However, I am unfamiliar with kirksite and with the task of finding a company to do the hydroforming. But hey, that's why I'm here.Mike Halloran wrote: If a low production rate can be tolerated, the tooling can be relatively inexpensive, e.g. stacked plates bolted together instead of an actual press. It might be possible to do both the shell and the reinforcement in one inflation cycle.I actually ordered this video on that very topic...Seems like complete madness to me! Only thing crazier (and yet way cooler) would be to use "explosions"! I was planning to leave the manufacturing to the pros. But I suppose it can't hurt to try some hydroforming experiments with small parts. If I don't post anytyhing in the next six months, you'll know I blew up the shop during a horrible "home hydroforming" experiment.Thanks,-Janus Cole

RE: Seeking Advice On Sheet Metal Stamping

MikeHalloran

(Mechanical)

23 Jul 08 17:38

 

The beauty of using liquid for hydroforming is that _relatively_ little energy is stored in the liquid. You can still make a pretty good 'bang' when something ruptures, but you probably won't lose the roof...

Mike Halloran
Pembroke Pines, FL, USA

RE: Seeking Advice On Sheet Metal Stamping

richardbuss

(Materials)

5 Aug 08 03:10

Bit late - I think the OEM tool was a mono block casting in a grade similar to P20.

RE: Seeking Advice On Sheet Metal Stamping

pressedmetalguy

(Structural)

19 Aug 08 08:27

Dont know if this is a bit late,, i manufacture heritage pressed tin ciellings out of aluminum and the parts can get quite big, a non shrinking resin die will do what you need it to and be relativly inexpensive, you make a master in tooling plastic or magneesium and for a resin die from that, rubber stamps dont work because your putting uneven tension on your part causing thinning and possibly ripping, if you need to know how to get a resin die made me and ill talk to you about my manufacturing tequniques and maybe they can be applied to you, oh by the way you will need a hydraulic press $  magneesium master $200 sq ft resin $ per 20 gallon

RE: Seeking Advice On Sheet Metal Stamping

thruthefence

(Aerospace)

19 Aug 08 19:34

Years ago there was a homebuilt kit aircraft called a "Questair Venture", retractable gear, many compound curves,sorta looks like a flying egg. As I recall the airframe panels were hydroformed. You can't much lower production numbers then a homebuilt kit. Somebody had found a way to produce them in small numbers at a profit.

RE: Seeking Advice On Sheet Metal Stamping

ajack1

(Automotive)

25 Aug 08 04:28

We have dealt with these people on a few occasions and I would highly recommend them, well worth speaking to.

http://www.superform-aluminium.com/technical/technical-summar.html

If you want to form aluminium then super forming is the way to go, I have no idea how complicated your part is but you can achieve amazing results with this process.We have dealt with these people on a few occasions and I would highly recommend them, well worth speaking to.

RE: Seeking Advice On Sheet Metal Stamping

griffengm

(Industrial)

25 Aug 08 06:59

FWIW, During the WWII era, there were Al forming dies for aircraft skin parts made of concrete.  I have no experience with these other than having read about them.  IIRC, high wear areas were built in with steel inserts.
good luck, Janus.

Griffy

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News

Selecting the stamping die's pressure system can be a critical decision. Many questions must be answered to determine what type of pressure system best suits your application.

Controlling Factors

1. Pressure requirements
Simple conventional metal cutting dies, such as those used in blanking and piercing operations, often do not require a high-force pressure system. In most cases, coil spring pressures are sufficient. However, specialty-cutting operations such as fine blanking and Grip flow®, may require forces unobtainable with a conventional coil spring. Also, metal forming operations, such as drawing, flanging, and bending often require higher forces. The type of metal being formed and cut also affects the pressure requirements. Higher strength material, such as that used in the automotive industry, usually requires higher holding, forming, and stripping forces.

2. Die height and shut height requirements
The finished height of the die, otherwise known as its shut height, must be manufactured to a set of given parameters that are controlled primarily by the amount that the press can be adjusted. In other words, the die must be manufactured to meet a certain thickness tolerance when fully closed in order to fit and operate in a given press.

Items, such as coil spring, have limited deflection rates. The deflection rate of each type of spring varies with respect to the strength of the spring. Most medium-strength coil springs have a deflection rate of approximately 30 percent of their free length. For example, if you needed 3 inches of travel on a spring, the spring would have to be at least 10 inches long. (10 in. time 30 percent = 3 in.) This additional thickness adds to the thickness of the die and can add additional die cost. Figure 1 shows this example.

3. Volume requirements and tooling cost
Justifying the cost of a long-life pressure system for a die used to produce a very high volume of parts for a long period of time is very easy. However, low-cost, low-production tools rarely justify the high cost of such a system. For this reason, a less expensive system often will be used with low-production or prototype tools.

4. Press capacity
Keep in mind that a high-pressure hydraulic or gas system can exert a force on the press ram that exceeds its rated tonnage at that particular point during its stroke. With the exception of specialty servo and hydraulic presses, most mechanical crank presses don't achieve their rated tonnage capacity until the ram is near the bottom of the stroke. Be careful to not overload your press at any point during the stroke.

5. Pressure distribution and pressure rise
During sheet metal drawing, pressure on the blank holder must be distributed as evenly as possible throughout the entire pressure pad surface. Coil springs have a tendency to fatigue and lose pressure. This can result in poor pressure distribution. In addition, stand-alone gas cylinders have a great pressure rise on the down stroke. This dramatic increase in pressure can cause excessive pressure on the blank causing the drawn part to fracture if pad equalizers are not being used. This problem can be overcome easily by using a manifold or by adding a surge tank to the pressure system.

Pressure Systems Available

1. Urethane (rubber) springs
Urethane springs are very popular in the manufacture of both low- and high-production tooling. Available in various sizes and shapes as well as different hardness grades, urethane springs provide sufficient force necessary for stripping pierce punches, as well as other pressure pad requirements. Urethane punch strippers also are easy to replace.

Urethane springs also provide suitable pressure for special stamping operations that require a non-marking pressure system, such as using pre-painted material. The springs are very reasonably priced, and tremendous improvements have been made regarding their strength and life. Urethane springs also can be custom molded for specialty operations. Best applications: Punch stripping, pressure pads, prototype work, low production tools. Figure 2 shows urethane strippers and various available shapes.

2. Coil springs
Coil springs have been used longer than any other pressure system. They come in numerous diameters, lengths, and strengths. They cost much less than gas springs. They are suitable for both stripping and holding pressure. Readily available and in stock from a number of distributors, they are best-suited for stripping and holding during bending and flanging, but are poor candidates for drawing dies. Figure 3 shows coil springs used in the manufacture of stamping dies.

One of the disadvantages of coil springs is that they fatigue and break differently from spring to spring. Also, if a coil spring breaks and the breakage is not confined within a spring can or cage, flying debris can cause die damage or personal injury. A coil spring's pressure cannot be monitored or regulated. Coil springs have a poor stroke to length ratio and poor pressure distribution.

An advantage of coil springs is that they are relatively inexpensive. They can provide adequate force requirements and are easy to maintain, install, and replace.

3. Stand-alone nitrogen and gas springs
Gas springs are becoming more and more popular in stamping die manufacturing. Stand-alone springs are springs that work individually. They have many advantages over conventional coil springs. They are available in many diameters, stroke lengths, and pressures. Because there are many providers of gas cylinders, availability is high.

Gas springs can provide the force necessary to function as the pressure system for almost any stamping die application, with the exception of specialty applications in which extremely high holding forces are necessary. Unlike coil springs, gas spring force can be regulated and controlled by changing nitrogen gas pressures. Figure 4 shows a stand-alone nitrogen spring.

Nitrogen gas spring advantages include a high contact force; a good stroke to free length ratio (as much as 40 percent of the free length), which allows the dies to be manufactured with a smaller shut height; and they are less likely to break than coil springs. These long-life springs can achieve pressure unobtainable with coil springs. Fewer springs can be used in the tool and they can be plumbed together to create a system with even pressure distribution. Also, with gas springs, pressure can be monitored during production.

Disadvantages of the gas springs include the fact that they are more expensive than coil springs. They cannot and should not be preloaded and excessive pressure will occur if they are not used with a surge tank. Gas springs must be mounted square to the die plate surface and take longer to install than coil springs. And gas springs can leak.

Part II of this series will discuss the use of gas manifolds, plumbed gas systems, both hydraulic and air press cushions, and gas stock lifter springs.

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