Press Feeder

JimDawson

JimDawson

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Lately my project posts have been few and far between, not because I haven't been doing anything, but rather what I have been doing is protected by NDAs and I'm not allowed to show my work to the general public. I've actually been doing some pretty cool stuff, some of which has very interesting setups, work holding and machining challenges that tax my abilities.

I finally have a project that I can show.

Some of you may remember the servo driven punch press I built for a customer about 18 months ago. https://www.hobby-machinist.com/threads/servo-punch-press.72601/

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It works OK, but there has been one nagging problem since day one. When the material spool is full, they can't run it at high feed rates because mass of the spool is more than the feed rolls can accurately accelerate. This means that someone has to stand there and spool off the material to keep some slack in the material so the feeder is free to accurately feed the material. I should note that we are trying to hold +/- 0.001 inch or better on feed position and thus the punched hole spacing. That sounds like a crazy tight tolerance, but concider that's 0.1 inch over 100 inches which is bordering on unacceptable. The good news is that the hole to hole actual position is + or - a bit so the average is pretty good.

Since this press is designed to allow variation of the feed length at a push of a button to make different product styles, the longer the distance between the punches means the more mass that needs to be accelerated between the punches, and the press is not able to position accurately at longer feed lengths without operator intervention. So to overcome this problem the customer has commissioned a pre-feeder, similar to a common punch press material spooler.

The goal is to try to keep a constant amount of loop in the material to minimize any feed error at any possible feed rate. And do it all automatically, while being able to feed material from spools staged on a seperate rack system.

Here is the overall concept. This is shown in the rest position, material flow is left to right. The feed arm senses the loop height, and as the the loop height changes, the feed motor speeds up or slows down as needed to try to maintain a constant loop length. The sensor arm is connected to a pot that controls the VFD.
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I'll post pictures of the pallet of raw materials and parts in the morning. All of the bits & pieces arrived yesterday, and I went shopping today to buy the steel, aluminum, and plastic needed to hang all of the parts on. Then you'll get to see it all take shape over the next couple of weeks.

Not a terribly complex project, but should be fun.

Stay tuned............
 
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I cut all of the material to roughly part sized chunks a couple days ago, and spent yesterday doing all of the CAM work to develop the tool paths.

The first step in the machining process is to make a fixture plate to hold the parts while machining. So a 6x8x5/8 chunk of aluminum will nicely fit in the vice and all of the parts except the main mount plate will fit in that envelope. All of the parts were designed to have hold down holes in them that have no function in the final assembly, only to facilitate machining.

Nothing worse than trying to figure out how to hang onto a part when you start making chips. I ''machine'' all of the parts in my head during the design phase, taking into account work holding and tools required. All of the raw pieces are cut at least 1/4'' oversize to insure plenty of material to cut all the way around.

So first I turn the fixture plate into Swiss cheese, drill and tap all of the needed holes for all of the parts. The the hole dimensions are just to remind me what a particular hole is supposed to be, it would suck to tap a hole 1/4-20 when it was supposed to be 10-24. The hole dimensions are shown as the bolt size rather than the tap drill size.
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All of the parts have 0,0 located at the top right corner and are offset 1/8 inch from that point.

Here are the gussets overlayed on the fixture plate. It was a little bit of a challenge to place all of the parts and locate the holes so they didn't interfere with each other. These parts are held down with the four 0.250 bolts on the red lines. The fixture plate holds 7 different parts.
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I may go through and pre-drill all of the pieces, then do the fixture plate last. I think that will be more efficient and I won't have to mess around clamping the pieces down to the fixture plate for drilling. That way, all I have to do is screw down the part and start cutting. The starting location of the workpiece is not critical, anywhere +/- 0.01 or so is fine and I'm pretty sure I can get there. When finished, the final dimensions will be relative to the fixture plate 0,0 point, if the hold down holes are off slightly from the design it won't make any difference because for the most part they have no function other than to hold the work while machining.

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This is a good approach. It reminds me of the way a tape tension arm maintains the right pull while a digital tape recorder is going from forward to fast forward to rewind, etc. You drive one reel as master and use tape tension as motor control input for the slave reel.

Oh man, I am speaking of antiquities here.
 
Here is all of the material roughly cut to size.
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I got all of the part blanks drilled for mounting and the fixture plate drilled & tapped. That's enough for one day.
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Machine 0,0 is set at the top right of the fixture plate, this will not change until all of these parts are complete. The bolt holes in the blanks will set the blank to the top right.

I'll take a facing cut on the fixture plate in the morning just to make sure it's flat. Then it's time to make chips.
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Looks cool . I used to love making this kind of stuff . I take it the middle roller is the " dance roller " ? Most of our lines are equipped with either dance roller sets or accummulator rollers that keep the tension at a desired set point . Occasionally , the operators would thread the material wrong and we had a mess on our hands ! :big grin:
 
mmcmdl said:
Looks cool . I used to love making this kind of stuff . I take it the middle roller is the " dance roller " ? Most of our lines are equipped with either dance roller sets or accummulator rollers that keep the tension at a desired set point . Occasionally , the operators would thread the material wrong and we had a mess on our hands ! :big grin:
Click to expand...

I have never heard the term ''dance roller'' before, but yes, that is what it does. That arm is connected to the pot that controls the VFD.
 
I think we all call them dance rollers because they seem to " dance " while running . We made sets for shrink sleeve machines that would accumulate 5 minutes worth of run time when the rolls ran out . The operators had 5 minutes to splice the new rolls to the expiring rolls , thus the line never stopped . :encourage:
 
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