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smythe
06-23-2004, 07:14 PM
Hello-

Hopefully someone will be able to give me some advice on this. I am building a press that will consist of a bottom mold (female) and a top mold (male). I would like to make the molds out of aluminum plate, but I need them to have a specific shape/conture in them. Imagine a shape like this: ~ that would have its male counterpart. Is it possible to shape a plate/sheet of aluminum like this? Also would it be able to hold its shape while under pressure (not much..maybe 70 psi), while being heated to about 175 degrees? I am not to familiar with the aluminum grades and quages so any help would be appreciated.

I apologize if I posted this in the wrong place.

Thank you in advance.

j

HuFlungDung
06-23-2004, 07:57 PM
I think aluminum would be okay at that temperature. It all depends on how well you back up the dies, and how thick they are, as well as how heavy and strong the stock is going to be.

The shape is not really a problem if you have the right software to accomodate your model.

Don't forget to allow for springback of the stock, if it is undergoing elastic deformation. Don't forget to allow for stock thickness in the offset between your dies at shut height.

smythe
06-23-2004, 09:23 PM
Thanks for the reply-

Any suggestions on how I would be able to bend the sheet/plate so it would retain the the needed shape? I would like to use 1/2 inch or 3/4 inch sheets.


Thanks again-

j

ger21
06-23-2004, 09:51 PM
I think he's saying you can mill it to the shape you need, not bend it.

smythe
06-23-2004, 09:59 PM
I know, but funds are limited to get it milled. I figured I could get the results I needed by bending it as well.

Ken_Shea
06-23-2004, 10:07 PM
You will probably want to use 7075-T6 aluminum alloy which has about a 80,000 psi tensile strength, you can forget any precise shaping on a small press, you probably could bend 1/2" a bit but that would be about it.

Ken

smythe
06-23-2004, 10:16 PM
Ken- my intention is not to bend the aluminum in the press that I am making, the aluminum will be the molds for some material that I will be laminating.

j

HuFlungDung
06-23-2004, 10:54 PM
Smythe

Give us the low down. How large are the dies? How thick is the sheet you intend to bend? What kind of material is used in the sheet stock?

smythe
06-25-2004, 04:11 PM
HFD- I am only going to be pressing composite material..I would like to make the top and bottom molds
out of either 3/8" or 1/2" sheet aluminum, length is around 70" width is about 18". I want to bend these sheet
to a specific shape and then press my composites together, while heating the aluminum to cure the material.
I am going to try to attach an image, hopefully it will go through.

IJ.
06-25-2004, 05:53 PM
I do quite a bit of work with 1/2" plate (esp the length and width) and short of a big hydraulic press I can't see an easy way of getting the shape you need.

My suggestion would be ask if there are any of the CNCZone guys in your area that have access to a large roller.

HuFlungDung
06-26-2004, 12:13 PM
You know, Smythe, that shape reminds me of the shape of galvanized guard rail for highways, etc. Maybe you can buy a couple of pieces....

smythe
06-26-2004, 05:31 PM
IJ. - What kind of facillities would have a large roller? Also, what are the possiblilities of heating the plate up and then bending it to the shape that I need?

HFD- lol- I wish it were that simple, keep in mind that each one of the lines in the image is roughly about 70 inches long...



j

IJ.
06-26-2004, 06:10 PM
Smythe: I'd grab the phone book and ring a few of the medium to large engineering firms in your area, most will have power rollers.
How precise does the form need to be?

The amount of heat needed to bend an 18x70 sheet of 1/2 inch would be amazing as aluminium disipates heat quite well, then you would need a master form to bend it to........could be done but the logistics of handling a huge heavy sheet of HOT aluminium would take some working out.

smythe
06-26-2004, 06:22 PM
IJ. - Thanks for the info, it the bends need to be pretty acurate in order for the laminated material to come out correctly.


j

metlmunchr
06-26-2004, 08:19 PM
A 6' long piece of aluminum plate will sag noticably under its own weight when supported at the ends. The stiffness won't be there for laminating press use unless it's attached to some supporting structure which would provide the necessary section depth and attendant stiffness. One psi applied across an 18 X 70 surface produces a distributed load in excess of a half ton.

If the budget is tight, you might look at wood (logs, not lumber) for something cheap to get the necessary section depth. The deflection under load will vary inversely with the elastic modulus, but it will vary inversely with the cube of the section depth. This is why things which cannot stand deflection HAVE to be thick. For starters, you'll need to know the required laminating pressure for your materials. That will allow you to calculate the loading and deflection of various materials and sections. Trying to decide what will work without knowing those basics would be akin to designing a bridge without being told whether it had to support a Honda or a battleship.

smythe
06-26-2004, 10:26 PM
metlmunchr- point noted and appreciated. As it stands right now I am currently working with wood for the mold. The reason I was looking for an alternative with the aluminum, was its heating characteristics. There would of course be a supporting structure behind each half of the mold to support it while under pressure.


j

ger21
06-27-2004, 01:24 PM
Why not use a thin aluminum sheet attached to the wood substrate?

smythe
06-27-2004, 01:55 PM
ger21- thats the current plan, I am just worried that the heating element that I will use will make the surface uneven.

Ries
08-05-2004, 08:08 PM
Did you ever try to build this mold?
You probably couldnt get the profile you want with rolls- rolls leave a flat spot at each end of the curve, and are really for making parts of circles- the way to make this from sheet would probably be with a large press brake- but to bend 6' of aluminum that is 1/2" thick, you are probably talking something like a 100 ton press brake.
Big fabricating shops and some larger sheet metal places might have a brake this big.
But what about starting with a solid block of aluminum, and routing out the depressions you want- aluminum will rout pretty easily with carbide bits, and then you could touch up with a belt sander. Use a circular saw or table saw to mill slots in the back, and put in strip heaters- how hot does your composite need to be to go off? plexiglas bending strip heaters are basically just resistance heat tape, 110 volts, get to around 2 or 300 degrees, so you could put a bunch of them in the back of your aluminum form, and wait for it to get hot.
This kind of 3 d form is exactly how they make carbon fiber and composite parts for B-1 bombers- except the molds cost hundreds of thousands, if not millions, and the composite fiber is laid up by cnc robots, and then the whole thing goes into room sized ovens to set off the presoaked composite. Boeing only pays 10's of millions of dollars for setups like this, so there is no reason you shouldnt be able to duplicate their effort for nothing with no tools, right?
I have a neighbor who could make you this form, no problem- he makes em for Boeing- he has a room sized cnc router to do just this- but I think he is a little above your budget- Janicki Industries in Sedro Wooley Wa.

High Seas
08-05-2004, 08:32 PM
HFD- I am only going to be pressing composite material..I would like to make the top and bottom molds
out of either 3/8" or 1/2" sheet aluminum, length is around 70" width is about 18". I
I confuse easily sometimes - but maybe its just 'cruise-heimers!

I know you asked about "SHAPING ALUMINUM" but:

What type of composite materials are you considering? Foam and 'glass with epoxy/poly resins? Or honeycomb - boron fibers or something simple, paper and glass ala TPG?
There may be a number of ways to get the project done with a variety of different materials and a range of dimensional tollerances.
You don't have to let on to what your building - but a few details might help focus the forum help - maybe you "don't need" alluminum to press it!
Maybe a simple vacuum set up over a single male mold with pre-preg might get you where you want to be? Maybe I missed the details in the previous posts?
My 2 pennies - odd isn't that? money is metric yet inches are not?
:cheers: Jim

smythe
08-06-2004, 12:35 PM
Ries- Yes, I have started. I am moving forward with my original plan making the mold out of wood and then covering the surface with thin aluminum that will be heated. Regarding having have the molds milled from block aluminum, this of course is what I would like to do eventually once I get the final shapes of the molds dialed in. The reason I wanted to know about "shaping aluminum", my thinking was is that it might have been cheaper to use a sheet/plate of aluminum and then bracing the shaped sheet so it would not distort under pressure. Thanks for the info on the rollers and for the contact.

High Seas- Materials would be thin wood to plastic with glass and epoxy. Yes a vacuum table works, but press times are increased with the table. Even with a heat source for the table, cure/press times are longer than with press both surfaces. Pre-preg could be an option but then I would need an oven. '

Thanks to both of you for the suggestions and info.. I appreciate it.


J