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| clamping problem |
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| DMIOM:
When I was a kid, I can remember that some households had a special sleeve ironing board (although they were made of wood). With those ironing boards. it was gravity that kept the material flat against the board or platen. In your case, how about letting atmospheric pressure help ..... My idea would be to make a fixture with a vacuum platen along the same lines as the sleeve ironing board - i.e. cantilevered so the pipe can be slid over. Not sure exactly what scale would fit, but have, say a 4 inch wide platen, with a 1 inch blank strip down the middle as the 'anvil' and then a 1 inch wide strip either side drilled with lots of small holes (*) down into a channel which is running through the platen, from which you draw a vacuum. This way you have no impedimentia on the top surface leaving access completely clear for the welder (**). I'm not sure what your welding process requires, but having a flat top to the platen would mean the edges would be butted square to each other, alternatively having a slight crown to the platen would present the work with a slight V between the edges. If the welding process works best with a backing plate then leave the central strip of the platen flat; if it produces any sort of bead on the back then you could machine a relief groove down the centre of the platen. To help with loading, you could make the platen so that the two sides each had their own vacuum line and you could then open one side and place one edge, then fold the other one over and then open its line. Would suggest you provide some proportional valving so you could clamp enough to align then hit it with full vacuum prior to starting bending/welding. Depending on how many pair(s) of hands are available to load the fixture, you may find it useful to provide foot-pedal control of solenoid valving. To get the first edge aligned with the centre of the platen, you could have a few drop-in or pop-up stops or dowels or similar arranged off-centre so that when the first sheet was butted up against them then its edge would be on-centre; then pop the stops out of the way to clear the way for the second edge. If the stops were pop-up with just had a weak spring then you might be able to leave them in place and let the second sheet just press them out of the way (or if you wanted to be really clever make the stops as tiny pistons that were sucked down when you applied vacuum to the second side....) You could make the fixture as long as your max length and then just throw a rubber blanket over the un-used portion. (*) vacuum holes - I'd machine them as, say, 4mm pockets 4mm deep with a 1mm drilling down into the vacuum. The vacuum chamber beneath, rather than a tube could be a slot milled into the base of the platen which was then sealed with a plate. I might also be inclined to look at segregating the length into several zones and providing each with a decent diameter line back to the vacuum set. You could also provide a suitably two-way-valved arrangement to allow you to blow-down with compressed air if you needed to clear the holes occaisionally. (**) because of the open access this will provide, it could also be possible to have rail(s) above with a trolley on for the welder to run the gun/torch on to keep height/line. Dave |
| Lew_Merrick_PE:
Shipto -- Is the ID of the tube the critical dimension or is it the OD of the tube? That will really be the driving criterion to any tooling. I assume that you already have the base-wrap mandrels to hand and you really do not want to replace them if at all possible. I am unclear as to whether or not the plastic sheet has already been trimmed to size before the forming/welding operation or if it is cut-to-fit when clamped to the mandrel. That makes a difference in the approach. However, assuming that the ID is the critical dimension and that the sheet has been cut-to-width in a previous sizing operation, how about a fairly stiff piece of bar that will orient radially to the mandrel that has an elastomer face to clamp along the length. It could even be pre-formed in an appropriate cubic curve such that restraining force straightens it out. That gets one edge clamped. Another clamp bar would be used to close the joint. The two would be connected with a fabric collar that is also elastomer faced. A bit of trial and error and you should have a clamp that wraps the material about the mandrel and holds everything tight and close, yet installs and removes quickly. ??? |
| shipto:
lew sorry but you are giving the company i work for WAY too much credit. The "mandrils" before i made the tool consisted of two bits of 50mm angle welded to form a flat surface which was held between two workmate benches. now it is pretty much the same except I have made it so the two bits of angle can pivot together after the guys have clamped the work up. The guys cut out the flat sheet to size then fold it and weld it, the ideal way would be for the tight wad who owns the company to invest in a oven but that is not gonna happen so the guys are left to manhandle cold plastic into tubes. |
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