at the place i work at, we have to bend custom aluminum extrusions to make doors and windows for trains and transit. Our company has decided to start using a new CNC router they bought to do the drilling of the frames. The benders we are using are pipe benders. We make all of the dies for them in-house. The frames we are making now are not consistent enough, in my opinion, to be drilled without a human eye watching every hole placement. On top of that, the frames must be stacked and drilled at the same time as the retaining rings.
the tolerances we have now are +/- .06 or more. the longer sides of the frames are usually bowed. I myself am not a bender operator, but I was wondering if it is even possible to make perfect 90 deg. angles, eliminate bows, and stay within +/- .01.
As usual, buying a new machine is virtually out of the question. I will post some pics Monday or Tuesday, but until then, what can be done in general to help the situation?
If the current crop of parts are good enough to be used as they are ( meaning they fit the train even with the warping), I would make a fixture for the CNC machine to flex the parts to the correct position.
My guess would be an outside frame the part sits into and then enough horizontal pneumatic clamps to force the aluminum out to the frame. You don't have to flex the part all the way to perfection, just enough to take out most of the variation between parts.
A high tech alternative would be a probe in the CNC that measures where the part is and then the machine could automatically correct the hole placement. This is probably too slow.
As a suggestion:
High tech ( CNC) is not always the best or fastest way to go. Depending on the quantity, a holding fixture with permanently mounted pneumatic drill units would probably be much quicker. Operator loads both pieces that need to be drilled together, clamps and hits the switch to active the drills. Presto one set finished. Of course you have to weigh the cost of a dedicated drill fixture against the number of pieces and the amount of repeat orders.
Last edited by PlasticWorker; 08-15-2008 at 02:14 PM. Reason: additional thought