Coining 0.010" half-hard brass with 8-ton press br

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ttok1152

Coining 0.010" half-hard brass with 8-ton press br

Post by ttok1152 » Tue Aug 17, 2004 7:12 pm

I would like to coin some .010" half-hard shim stock brass to obtain the SHARPEST 90* OUTER CORNER possible. I have a Di-Acro 8-ton manual (really manual - with a lever!) 24" press brake, and I would like to have some 90* dies made for this purpose. The brass is shimstock in 24" lengths off a 6' roll and will be bent along the direction of stress in the metal - ie. lengthwise down the roll. Some pieces will have thin paper or plastic glued to the brass with an even application of spray glue.

Before I spend some BIG BUCKS on new press brake dies, I would like to hear your input as to whether I am on the right track!

Question No. 1: Can I coin 24" of .010" half-hard brass with only an 8-ton press brake? I would like to be in the coining range because the most important feature of the finished brass angle is the very sharp outside corner.

Question No. 2: What effect, if any, will the paper/plastic glued to the brass have on the "bend radius" in the coining range? The paper/plastic will be on the inside of the final bent piece. I am assuming a 90* die set will suffice for the plain brass (if the press brake will handle it), but will I need another angle with the paper/plastic? The entire blank will be between the dies - it is only .080" or so wide.

Thank you in advance for your replies! This is a great forum and I have enjoyed it for several years. Great advice! A.T.

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Doug_C
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Re: Coining 0.010" half-hard brass with 8-ton press br

Post by Doug_C » Wed Aug 18, 2004 1:32 am

The sharpest radius you can expect will be on the high order of .02 on the outer bend. More realistic at .035+ . If this material has a compression strength of near 15kpsi to coin. How many square inches of material in compression will the capacity of the hand press run out? Keeping the top die at 88-89 degrees will focus the coining to the corner. The penetration will be critical prior to snipping all the way through it.

I won't go as far as to say this CAN'T be done, but the chances of success for coining the full 24" consistently is nearly impossible with a hand press. The deflection of the press would be very difficult to keep the dies parallel to the degree necessary for that thickness of stock. If they could, I would guess the result may be an arched piece after bending. Coining the material means the material expands at the bend and must go somewhere. Also, the dies would need to be highly polished if finish transfer is an issue.

The best bet will be trial and error to find a process that will work for your needs. Coining may not be it. The material and what is available to work it, will dictate the physics of the results. Even with added material of differing properties on one surface as you already suspect, will change the approach or make it impossible due to the most important criteria is the sharp outside corner. I'd expect the bonded facing material to delaminate under compression without a radius to eat up the excess material in the sharp inside corner.

All one can do is give it a go and see what can be lived with. Then change to accommodate the positives and reduce the negatives.

It may be beneficial to bend a wider section than .08 ,add the facing material after it is bent and trim off the excess of each leg to achieve the desired results?

Bending over a neoprene block with a sharp top die? You can line a bottom die with a soft material to protect the material to be bent, but the minimum bend radius desired may not be obtainable.

Consider some of the extruded stock at hobby supply stores trimmed to size?

Misc. Ramblings........


DC

ttok1152

Re: Coining 0.010" half-hard brass with 8-ton press br

Post by ttok1152 » Thu Aug 19, 2004 1:20 pm

Thank you very much Doug C!! I have enjoyed your excellent posts on this subject on other threads and learned a lot! Incidentally, this is my 5th time trying to respond and thank you!

ttok1152

Re: Coining 0.010" half-hard brass with 8-ton press br

Post by ttok1152 » Thu Aug 19, 2004 2:03 pm

Fifth attempt at a post was successful - sixth was not!! I am trying again - this time in short posts! Maybe that is what I am doing wrong.

You guessed correctly - I am trying to avoid using those extruded brass shapes from the hobby shop. I am making 1/48 size brass model railroad bridges. The first one is a plate girder type with vertical angle stiffeners on the prototype - on the model they do not have to contribute to the girder's strength. The sharp bend radius is for appearance sake only. I was hoping to get .003" to .005" outer radius on the angles with .010" brass. Will have to live with .020" if physics so dictates!

It appears from your information that my Di-Acro press brake will coin up to 12" or so of .010" brass. .080" X 24" = 1.92 sq.in. My 8-ton brake will only achieve 8,300 psi on a 24" piece. I'll have to use shorter pieces!

ttok1152

Re: Coining 0.010" half-hard brass with 8-ton press br

Post by ttok1152 » Thu Aug 19, 2004 2:15 pm

THAT IS IT - I am too long-winded!!! Another short post coming up!

My press brake is almost new. It has dies in it that were previously used to make electrical boxes out of 16 gge stee. I need new dies. The whole press brake with dies, all 600# worth, cost only $175 on Ebay - surplus from Texas Instruments (tool gloat - my only opportunity - usually I pay too much). It will bend 24" of brass straight, without a perceptable bow.

My process is as follows: First, laminate a paper pattern to the brass. The glue is pliable for a while. Second, shear the blanks to be angles using the pattern lines as guides. Third, pre-bend the angles in a modified bar folder. This is done because I cannot figure out how to gauge the location of the bend in the press brake. Fourth, mash the angle to final bend radius in the press brake. Fifth, make "dimples" representing rivets on the prototype girder along the brass angle, according to locations on the pattern. Distortion int he .080" dimension caused by the press brake is ok - the location of the dimples along the angle is important. The dimples are done against a guide.

More to follow if this posts successfully! A.T.

ttok1152

Re: Coining 0.010" half-hard brass with 8-ton press br

Post by ttok1152 » Thu Aug 19, 2004 2:28 pm

Fantastic!! I just tried too long posts!!!

Correction or clarification on last post - step three. The bar folder is used to bend the angle-to-be along a bend line drawn on the pattern. With angles of various dimensions on a single girder, it is too hard to gauge the location of the bends unless I do it this inelegant way.

The above is the reason for the paper laminated on the brass. I am going to order a new set of vee dies from Power Brake Dies - one of the model train guys used to work ther , so they may not laugh too hard at my request. I will send a piece of paper laminated brass to them for testing. I think a 90* female vee 1/4" across (their smallest stock size) and a male 89* vee die is what I will order. The finish, other than bend radius, on the angles is not that important - the current dies work ok for that. Will have to experiment with how much force to use to keep from shearing the angle into two pieces.

This whole press thing is really an art! I tried to read up on these things, but there is no substitute for help from someone with experience! Thanks again! A.T.

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Doug_C
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Re: Coining 0.010" half-hard brass with 8-ton press br

Post by Doug_C » Thu Aug 19, 2004 5:39 pm

Hello AT,

The amount of material under compression using the 89* die will not be the full .080 cross section. The capacity of your machine is 16,000 lbs total. If the pressure can be focused on the bend area, it may coin it. Whether it will form the material into a tighter outside corner without severe distortion is subjective to trial. My concerns in a positive outcome was speculative without direct experience with the combination of press and materials. It just does not seem realistic to get the material to act in that manner(sharp outer radius) knowing that the inside bend is under compression and the outside is under tension as it is formed. Even though the material you have chosen has an elongation of around 20%.

I took a guess at the 15kpsi compression strength as a point of reference for 260 half hard brass. I could not find the actual figure. 15kpsi is what A36 mild steel plate can handle before sinking into its surface.

Locating the stock on the bend would be a bit tuff, eh? The lower die width you should be using would be somewhat less than .08. I have made special dies for short bends that incorporate a stop or gap step-up in the top of the die ledges to register the material against or cradle capture it. Any ingenious way of getting it done is acceptable if it works out in the end. If it were not a succesful attempt, it is always part of the learning curve an your way to finding that ingenious method.

So far I have never procrastinated anything into getting itself done! [img]/ubb/images/graemlins/grin.gif"%20alt="[/img]

DC

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Steve_in_Mich
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Re: Coining 0.010" half-hard brass with 8-ton press br

Post by Steve_in_Mich » Fri Aug 20, 2004 12:44 pm

Some questions; Why are you using brass rather than steel or extruded plastic etc.? Will the brass have a finish on it to look like the material you are trying to copy?

To get the sharp outside corner (short of very expensive precision matched dies to force the detail) I wonder if after the barfold bend you might then place one side of the 24" angle strip in a step clamp and bias roll the brass material to form the sharp corner against a fence (step) in the clamp. The 8 ton press could be used to hold the clamp tight while rolling the corner sharp. ($175. what a gloat!) [img]/ubb/images/graemlins/wink.gif"%20alt="[/img]
Just because you don’t believe it - doesn’t mean it’s not so.

ttok1152

Re: Coining 0.010" half-hard brass with 8-ton press br

Post by ttok1152 » Wed Aug 25, 2004 1:42 pm

Thanks again, guys!!

Doug C - I finally figured it out, thanks to you, that the coining tonnage drops with the 89* angle because the square footage in compression is somewhat less! I will have fun experimenting with the new die set. I really pondered the location of the bend line. It can be seen easily on the barfolder, and with many sizes of pangles, I don't have to worry about resetting back gages.

Steve - Model train guys use brass - it is almost a cult thing. Probably because TOY trains were made of tin plated steel. Had to gloat about the press brake. When I bought it through "buy it now" they had a phone number on the listing. I called them immediately and arranged to pick it up with cash in hand the next morning! Showed up there with a trailer - did not want them to figure some way to weasel out of the deal!

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