i have a customer who needs a square copper tube with square insides. he thought that edm would be the way to go but i'm skeptical that this would be a cost effective as compared to some other method. i have about 72 tubes to make and they are just over 12" long. my other process would be get some round tubing and shape it with a die and a pin.

What are the outside and inside dimensions and tolerances?

sorry i guess that would help. the outside of the tubing is .675x.675 and the wall thickness is .065, the od tolerance is +.010/-.005 the id tolerance is .610 min

Wouldn't the wall thickness be .0325 ?

I am thinking it would need to be drawn or extruded.

Investment casting possibly? Simple mold, and should hold numbers well. You could EDM it, mill to shape and plunge a though hole and wire out the center.

the reason for the question was to figure out if edm is a more cost effective process than something else. seeing other suggestions on the board of ways of making this i'm guessing that it can be done with edm but would be cost prohibitive. personally i'm a fan of drawing and forming, thats what i suggested.

EDM is a fantastic process, but the first thing I tell anyone that walks in my door is: "if there's another way to make your part that meets all your requirements, you should do so".

EDM'ing 72 tubes like that would be EX-PENSIVE!.

If I could reach your hands I would smack them...

What about the ease of unattended running???
I have had plenty of parts in my machines that could have been ground....
The fact that I could cut 50 in a stack and ten stacks in a fixture made EDM the obvious choice...
Hourly rate is of course adjusted to reflect the fact that I'm at home playing the latest PS3 game while parts are being produced.
Not always should it be done else-where just cause it can be...

The only hard part of that copper job is getting the start holes through 12".
Otherwise that would be a great one to throw a big block in the machine and walk away for two days...

SDConcepts,

EDM is not a bad alternative, but one would be foolish not to examine the costs of alternatives. Simply viewing EDM and an EXPENSIVE solution or method might not be an accurate statement. As suggested, extruding, drawing, or casting this part is possible (which would produce these parts much more quickly than EDM), but would require a longer lead time to design and produce the required tooling. A Cost-Benefit-Analysis needs to be performed here to evaluate the "Per Part" costs between direct machining (EDM & Milling) and pressworking. Since this order is for only 72 pieces, it will make pressworking more expensive because this is too small a batch size to amortize the tooling costs over. Pressworking becomes more attractive and lowers the per piece costs as the production numbers increase.

EDM does offer some advantages on this small production run. You can most definitely achieve good unattended machining time on these parts, so your direct labor costs will be low. The tolerances on the part are wide open for EDM, but in an effort to produce these parts in the fastest time possible, Mill what you can first. I would mill the outside of the part complete first, and then drill a start hole in the center for Wire EDMing.

EDMing is a slower process than compared to Milling, but EDM can be automated and run unattended more easily. For this part, to machine the inner cavity, you are looking in the neighborhood of 4 to 5 hours for each part. This totals roughly 360 EDM machining hours for the 72 parts, with the bulk of this time being 100% unattended machining. You could Wire EDM both the inside and outside shape (gains you more unattended machining time), but your part tolerances really don’t support this approach, as you can more quickly and cost effectively produce these parts to the required tolerance by Milling.

-Brian

so at 360 edm hours whats the shop rate on something like that? i'm figuring about 70/hr and your looking at $25000 for the batch? is that about right? if so then that is clearly not cost effective for 72 pcs. for one part maybe.

SDConcepts,

Your rate of 25k for 72 parts is correct if you charge your full hourly shop labor rate, and it is high! Depending on how you want to attack and bid this, many EDM shops do not charge FULL hourly rates for jobs they know they will achieve unattended machining time. I have seen people use $40 per hour when estimating for extended unattended WEDM machining time. In this case, maybe estimate 1/2 an hour setup labor time for each part @ $70, and then 4.5 hours @ $40 an hour...this gives you a ballpark figure around $15,500.

-Brian

for 15,500 i can buy more than 200 lbs of copper material drawn and formed into the exact shape i need. then i can remake this job about 45 times before i run out of material. again if it was one part or one set of parts then i would consider edm but again its just not the process for this as a cost effective alternative.

Exactly.

I don't think I would want to run one of my machines for $40/hr. Or at least not plan on running it at that price I can easily screw things up and work for that price. Specially since it would require a larger machine that can cut 12" thick and than tie up the machine for 3 or more weeks all for $15K.

But I guess if you have nothing else to do it might be better than a bunch of hand holding jobs for $40/hr.

Wire EDM is obviously not the most cost effective process to use to produce these parts. It's common sense to use the cheapest manufacturing process possible while being able to achieve the needed part tolerances. In this case, the stated tolerances of +0.010" / -0.005" is SUPER wide open for WEDM. If these tolerances were more in the neighborhood of +/-0.001", then maybe WEDM would be a more attractive solution. Just trying to help!

-Brian

Make a form and have a sheet metal shop bend these up, then have a welder weld the corner seam. Finish them by whatever method you want.