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Mold for sheet aluminum

Posted By:
David Walter
7
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#1 Posted: 5/8/2011 10:13:24

I own an out of production Lake Amphib. I need a frame for the engine compartment. I have friend that has a table cutting machine. I want to build a mold out of steel press a new frame, but I know very little about this. Some of the questions I have:

1. I going to use .032 aluminum. What type of aluminum (Soft material from Spruce?)

2. How much space do I allow between the inside and outside parts of the mold.

3. Is there a book or information available to guide me though this?

 



reefmaker
Grant Smith
Homebuilder or Craftsman
135
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#2 Posted: 5/9/2011 12:20:06

You will need to determine the alloy of the part you are replacing. This is a certified aircraft and your work will need to be signed off by an A&P. Start searching for one who is willing to work with you. Depending on the part you may only need one mold. A good metal worker may make the part without a mold. More information is required on the part that is needed in order to determine the tool requirements.  



Grant Smith CFI
Craig Cantwell
43
Posts
8
#3 Posted: 5/9/2011 12:42:43

David: You are probably better off just making one out of MDF rather than steel. You can then use either traditional sheet metal processes or something like Kent White's flow forming techniques. Hard tooling is fine if you are going to build hundreds of a part, but little sense for a single part.

Material should be of the same thickness as the original part. If it's structural, It's most likely 2024T3.

 

As to tips and techniques, there a number of books and videos out there. You could also take the Sheet Metal Basic's workshop. The part is going to need to be as closely identical as you can make it. You are replacing an engineered structural part. When you start deviating from making an exact copy of a part, you are now altering the known engineering configuration and need to understand that altering it could have a profound effect on the structure. In otherwords, if you are not up to speed on that part of what you would be doing, then concentrate on making the absolute best copy of the original as you can. I'm not trying to scare you away from making the part, but I would rather see you bash several in practice and then produce a perfect copy of the original part. A poorly made part can have the potential for letting you down and failing at a most inopportune moment and that could ruin your day. I'd also hook up with guys in your local chapter. There are undoubtedly a couple of tin bashers within it that would be most willing to help you along the correct path to getting your Lake back airworthy.

 

As you are going to be producing a repair part for a TC'd aircraft, you should also familiarize yourself with the regs and requirements for owner produced parts.



David Walter
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#4 Posted: 5/10/2011 08:41:26

My plan was to build a steel mold, make my part and rent the mold to other A&P's to recover my cost. This part is no longer available and most Lake's are experiencing cracks in this part. I thought I would need soft aluminum sheet and have have it hardened before installation. I just don't have any experience in forming aluminum in a press brake. It has rounded corners, so it would be difficult to form it by hand. If you know of a source of information that would be helpful, I would appreciate it.  



reefmaker
Craig Cantwell
43
Posts
8
#5 Posted: 5/10/2011 09:43:14

You would be suprised at what can be done with handforming. The kind of die you are talking about, generally would not be made of steel plate, but of kirksite, and would be polished to a mirror like finish. Any imperfections in the die surface would be imprinted on the part during the forming process. Frames and bulkheads would not be formed in pressbrake dies, unless they were straightline pieces. Most are formed either in drop hammers, rubber forming or by hydroforming, so contours and curves are not big deals.

 

There are various books and guides out there, but for some quick, but general knowledge, try looking through youtube. Here's a nice one that forms a fairly straight line rib, but has a contour change in one face: http://www.youtube.com/watch?v=5loIfMfOV5Y .

About the only way you would be able to really make your money back on building some hard tooling, is to go through the process and get a PMA for the particular part and produce them in bulk.  Designing a die doesn't have to be very difficult, but there are quite a few parameters that you have to have onhand before you start.  These include forming method, press size, tonnage required to for the part in the material condition that you choose, heat treat requirements and so on. There are numerous volumes out there on die design that can be referenced. Additionally, you are going to have the problem that if your die is for a drop hammer, anyone that wants to use it will also have to have a drop hammer....likewise if it's a hydroform die. I can guarantee that there are very few repair shops out there that have of the heavy forming capabilities. Offhand, I can think of less than a dozen restoration shops that have any of the processes in-house.

 

The last thing to consider also is just flat out the cost of the die. Although I haven't been around any die fabrication in a lot of years, I can tell you that it gets pricey real quick. If the part can't be contained within an area of about the size of a #10 envelope, you are going to be above a couple of thousand bucks.

 

If this is a problem part for all of the Lakes out there, it might just be better for the owners to all get together and bite the cost and have a die made and get the PMA for the part and split the costs between everyone.



Niel Petersen
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#6 Posted: 5/12/2011 20:33:45

Most important - what is the configuration & size of the part?  If a lot of them are cracking maybe some re-engineering or other beefing up is called for.  Don't just repeat the problem

Forming 2024-0 aluminum & then heat treating to a T42 is straight forward although the 920 degF temp must be held within about 10 deg before you quench it in cold water.  there will be distortion but you can still cold form the part for about 1/2 hr before it begins to precipitation harden.  Something thin like .032 can be probably done on Benelex (sp?) dies - a tooling Masonite, or even on oak dies.   L Pazmany did a lot of the PL-2 and PL-1 [parts from 2024T-0 and then heat treated.  The physical properties after the heat treat and age hardening is practically the same as 2024T-3.  Maybe that's how the original part was made?



David Walter
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#7 Posted: 5/12/2011 21:27:57

The orginal part was .028, so I thought .032 would be better. The part is about 2 ft X 3 ft. with the center open for the back of the engine to fit though. The problem with cracking is due a poorly designed baffling system that transfers engine vibration to this part. I'm solving that problem with a mod from Ron Vanslooten. I have a friend that will do a steel mold for free with a plasma table cutting machine, but neither he nor I know anything about molds. I was going to send it somewhere and have it hardened. I ordered 3003-H14 ALUM from Spruce. Will that work?



reefmaker
Craig Cantwell
43
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8
#8 Posted: 5/13/2011 10:14:53

David: If this part carries any structural load then 3003 is most like the wrong alloy to be using. Also, at that size of a part, you are getting into some serious machinery to stamp it out.  I just ran a quick, rough order calculation of the press size required, and it's going to be about 230 tons to form 2024, 3003 would required over 40 tons. I got these numbers from running the equations for forging pressure requirements so they will be a bit high, but close enough for quick estimation work.   Either way, with a physical part size approximating 2' x 3', you are going to have to go to a big fabricator to find presses that have the tonnage and the platen size to handle that die. I think that you are also going to find that unless the die has been engineered and correctly built, they won't touch running it. Most places that have that capability are not going to chance damaging a very high dollar press with a homebrew die from someone with no die design experience.

Something else to think about, is that any forming die is going to have to have the edge radius and springback allowances ground into the die. A plasma cut isn't going to do it, even waterjetting isn't good enough. This type work is typically done with wire EDM and surface grinders coupled with lots of polishing.

Before you go too much further, you really need to hit the books and do some serious reading on forming and die design.  I don't want to discourage you, but you are trying to build a precision, repeatable part with axe and chainsaw techniques and it isn't going to give you the results that you need.



David Walter
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#9 Posted: 5/13/2011 11:00:14

WOW! I had no idea. I was thinking a 20 ton jack. This part holds the shape of the engine compartment, but doesn't carry a load. All I really need is a 1/2" 90 degree lip around the outside of the part. The rest is flat. I need to get you a picture. Is they anyone that I could send this part to duplicate it for a reasonable price. I'd say if you got it with an 1/8" it would work fine.  



reefmaker
Craig Cantwell
43
Posts
8
#10 Posted: 5/14/2011 13:28:52

Total force divided by the area applied to gives you the force per unit area. Using a 2' x3' part, with a 1/2" flange, gives you a total flat plate area of 925 inches. Divide that by 20 tons and you get an applied force of only 43 pounds per square inch. That's not much force available to form the part. You might get away with that if you were forming dead soft material at elevated temps, but even so, it would take building a fairly large bridge to evenly apply the force to the die and not have any flexing.

I think that you would be much better off and have an easier time if you looked at Kent White's video on Fluid Forming..ie home shop hydroforming with water and a wet form. For annealed Al, the water pressure is not too high and can be provided by a cheapo pressure washer. That's the method that Kent used to form parts for the Hughes H1 replica a number of years ago. Following Kent's method, it results in an easier to build form and should provide you good and repeatable results.

The other  thing you need to do is correctly identify what material the part is made from. I have a feeling that it's not 3003, but more likely 2024T3, and that will take more effort to form. It sounds like it's part of a high vibration environment and any failure is going to possibly result in bits and pieces going through the prop arc if they are shed.

Be aware and do your homework before flying the part. You don't want a failure in flight. It could ruin your day.



David Walter
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#11 Posted: 5/15/2011 07:22:55

Thanks! I rented the video.



reefmaker
James Thompson
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#12 Posted: 5/27/2011 15:09:38

I have over 30 years experience with metal forming dies and agree with others not to make this in steel.  The cost of a die will exceed $12,000.  The die would be a wiping die which requires a mirror finish on the surfaces.  Any dirt or rough areas will create scratches, stress areas, where corrosion or cracks will occur.  A better solution might be a welded fabrication or hand forming.  You must be very careful to eliminate any scratches.  The radius is needed to spread stress so do not make sharp bends.



David Walter
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#13 Posted: 5/27/2011 16:32:00

You have convinced me. I was able to purchase the part new. The out of business factory had a few in stock. However my friend and are going to experiment with the mold just for fun. I'll let you know how we make out.



reefmaker
Bob Hartunian
Homebuilder or Craftsman
3
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#14 Posted: 5/27/2011 21:13:58

Dave;

Would it be acceptable to make part out of fiberglass? If so, mold making could be relatively simple, like sweeping a form from plaster, releasing surface and laying up a part with room temp cure resin stsyem.

Also, glass has better fatigue properties than aluminum and may withstand vibration better. You can tailor the stiffness of the part by making it a sandwich construction if dims allow.

Should you choose to do this, I can give detailed instructions.

Bob Hartunian



David Walter
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#15 Posted: 5/28/2011 07:51:38

It's possible. I have an A&P friend that works at a plant. They do a lot of carbon fiber and he offered to make one from that. The problem comes from it being a certified plane and meeting FAA regs. I really appreciate the offer to help, but I've solved my problem with the new part I purchased. In addition, I found an acceptable mod to decrease the engines contact with the engine housing. That should prevent any future cracking of this part.  



reefmaker
Niel Petersen
3
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#16 Posted: 5/30/2011 13:18:41 Modified: 5/30/2011 13:27:31

If you have a factory original replacement new part you should be good to go.  If you want to come up with a heavier cross section than .032, assuming the part is a ring that only has the 1/2 inch flanges around the perimeter (and inside?), it can readily be formed with a simple but hardwood dies, C clamps etc using 2024-T0 aluminum and heat treated to 2024-T42 condition.  The heat treat quench will require the part to be straightened afterwards before it age hardens.

I formed fuselage ribs for a PL-2 that are from .032  or .040 2024-T0 and have about 5/8 inch flanges with no problem just jacking against the ceiling beam of my basement.  Some of the parts required a clamp down die so that the flanges requiring compression forming could be formed without buckling.  Again all "die" parts were wood (mostly plywood but sometimes oak).

Any inside flange can be easily done in a second operation.  This involves only stretching the blank material and that can be done with a heavy steel rod, some grease, clamps and again some simple wood dies.  

Several parts could probably be made from a set of wood dies without significant die problems.  It isn''t rocket science and does not require a large press or metal dies.  PM me if you are interested but I definitely want to see a PIX of  the part first.

Whatever, you don't want to make the part out of carbon fiber, nor 3003 aluminum, and you don't need metal dies.