Time to build a machine to automate a process, Anyone want to help my first journey? - Page 2
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  1. #21
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    Half degree per side is customary but something like acetal you could get by with a quarter. I haven't seen quotes for molds lately, but I would guess that $5000 wouldn't be enough for material. With a part as thick as it is, unless it can be cored that is a lot of material. I think sinks and distortion would be a problem. Without careful thinking and redesign, I can't see a mold. From the standpoint of a press, there several considerations. The size of the mold with the side draws, the clamp tonnage and the barrel size. Tonnage wise, a 75 ton should work. Barrel would probably need to be 16-20 oz. Platen size could only be determined once the mold is layed out. The barrel sizing would have to be carefully sized as too long in the barrel can decompose acetal which releases formaldehyde. Good way to clear out a mold shop in a hurry.

    You have 1.5 minutes per part in a two up nest? How much is the machining short of the side drills?

    Tom

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    A the parts symmetrical top to bottom? How do they come out of the mill, can they be dropped onto a conveyor? I assume the parts have to oriented. I see the parts on the conveyor, moved to a station that determines orientation either by probes or vision and then a means of turning the part orientation. The next issue is the orientation of the holes to be drilled to what feature of the part? It looks like there are three holes on the top face. Can these be used for location? Assuming so, I see a shuttle moving the part into position, a plate with dowels pickup the holes and move the part vertically as Robert R has suggested against a fixed to plate. The holes are drilled. The elevator drops down, the dowels disengage and the finished part is discharged by the part being loaded. The discharged part could then be loaded into a magazine.

    Tom

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    Quote Originally Posted by TDegenhart View Post
    Half degree per side is customary but something like acetal you could get by with a quarter. I haven't seen quotes for molds lately, but I would guess that $5000 wouldn't be enough for material. With a part as thick as it is, unless it can be cored that is a lot of material. I think sinks and distortion would be a problem. Without careful thinking and redesign, I can't see a mold. From the standpoint of a press, there several considerations. The size of the mold with the side draws, the clamp tonnage and the barrel size. Tonnage wise, a 75 ton should work. Barrel would probably need to be 16-20 oz. Platen size could only be determined once the mold is layed out. The barrel sizing would have to be carefully sized as too long in the barrel can decompose acetal which releases formaldehyde. Good way to clear out a mold shop in a hurry.

    You have 1.5 minutes per part in a two up nest? How much is the machining short of the side drills?

    Tom
    Roughly 4 minutes per part not including the holes, call it 5 min with the holes.

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    Quote Originally Posted by TDegenhart View Post
    A the parts symmetrical top to bottom? How do they come out of the mill, can they be dropped onto a conveyor? I assume the parts have to oriented. I see the parts on the conveyor, moved to a station that determines orientation either by probes or vision and then a means of turning the part orientation. The next issue is the orientation of the holes to be drilled to what feature of the part? It looks like there are three holes on the top face. Can these be used for location? Assuming so, I see a shuttle moving the part into position, a plate with dowels pickup the holes and move the part vertically as Robert R has suggested against a fixed to plate. The holes are drilled. The elevator drops down, the dowels disengage and the finished part is discharged by the part being loaded. The discharged part could then be loaded into a magazine.

    Tom
    The orientation of the part on the conveyor isnt so much of an issue. An operator can load them with the "dot" pointed in the direction towards the drill machine, with a long enough line of them it should be easy to spot a bad one if needed.

    If vision stuff isnt that difficult or expensive to add, there is a "dimple" on each part that could be used for orientation visually.

    The holes on the top could be used for positioning as long as they retract but I think that might be too much trouble compared to a table with two perpendicular sides to locate off of.

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    To save some money and time you could near-net-shape mold it (cheaper tool) and then just drill the precision holes? May need a redesign as that section width could give porosity issues in acetal. We had a hydraulic quad drill table at the old day job where an operator set the part into the fixture, hit the footswitch, and then swapped the part a few seconds later. You could do the same with linear actuators instead of hydraulic cylinders, and you could feed it all day and night with a robot. Just a table with four drill heads and some dowel pins and a toggle clamp (which could also be controlled with a linear actuator and a bell crank).

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    I use this arrangement on my 4 axis mills. You would get one part complete per cycle.

    164664d1456923067-b-precision-tooling-block.jpg

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    Still would be 2 operations because of the 4 side holes.

    Doing it this way would take forever for 4000 pieces a month.

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    You get the side holes by rocking the tombstone +/- 90.

    Yeah, you're looking at sub 2 min cycle for 5k a month running one shift.

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    I've never seen a big slab of a part injection molded. I'd think there would be prohibitive issues: sink, warp, etc.

    .001" concentric hole to the one on the other side? That seems borderline unreasonable for any process considering it's plastic.

    I think you can do something for 4k, but it won't be robotic load unload off a conveyor. Catch part from conveyor and orient: 4k by itself if that. Good luck. Looks like a fun project

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    Quote Originally Posted by CosmosK View Post
    I've never seen a big slab of a part injection molded. I'd think there would be prohibitive issues: sink, warp, etc.

    .001" concentric hole to the one on the other side? That seems borderline unreasonable for any process considering it's plastic.

    I think you can do something for 4k, but it won't be robotic load unload off a conveyor. Catch part from conveyor and orient: 4k by itself if that. Good luck. Looks like a fun project
    If you can't core it out then chemical foaming agent will be needed. The foaming agent is REALY interesting if you have never used it. You get a solid wall along the cavity with a foamed center. You can control the wall thickness and foamed core density with mold temp and other parameters.

    A mold for that part looks pretty simple to me. You have 4 slides that are all the same with round pin cores shutting off on a vertical surface so minimal heel blocks will be needed. Draft is optional and not really needed, just add a little more ejector area and your good. Another bonus of molding them is it will open up what plastics are available to make it from. Unless you are going to spring for custom extrusions your options are very limited. Oh, and I would make the mold out of aluminum, all of it.

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    DavidScott I'm with you. looks very simple to make the mold for it and even steel wouldnt be an issue.

    I calculate id need 48 tons with the 10% safety. Would a 50 ton machine work? Ive found a few for $5000 but im sure it will need more....I could technically make up the difference on the cost for plastics.

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    Quote Originally Posted by Booze Daily View Post
    You get the side holes by rocking the tombstone +/- 90.

    Yeah, you're looking at sub 2 min cycle for 5k a month running one shift.

    There are 4 side holes total. One on each side. We probably have close to 2 min a cycle in just opening the doors blowing chips off, clearing the vises, etc.

    If you meant sub 2 min cycle for just the drilling, id agree with that however that is 170+ hours on an already booked up cnc machine that is expensive to operate. Pulling it off a $100,000 machine and sticking it on a $5000 machine for that op makes a ton more sense.

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    Quote Originally Posted by CosmosK View Post
    I've never seen a big slab of a part injection molded. I'd think there would be prohibitive issues: sink, warp, etc.

    .001" concentric hole to the one on the other side? That seems borderline unreasonable for any process considering it's plastic.

    I think you can do something for 4k, but it won't be robotic load unload off a conveyor. Catch part from conveyor and orient: 4k by itself if that. Good luck. Looks like a fun project
    I dont think robotic load/unload is feasible (we have fanuc robots)

    Im thinking an operator can pull from the cnc machine, lay the 2 parts on a short conveyor, and the machine will drill the holes and push the parts into a plastic tote. After a counter has been reached, pause the machine so the operator can swap out the tote for an empty one.

    I'm thinking doing this first, then working towards injection molding them so that an operator can injection mold then drill in the same machine. That to me...sounds like a real solid plan.

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    DaveScott do you have photos of the mold you are talking about?

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    Quote Originally Posted by as9100d View Post
    I dont think robotic load/unload is feasible (we have fanuc robots)

    Im thinking an operator can pull from the cnc machine, lay the 2 parts on a short conveyor, and the machine will drill the holes and push the parts into a plastic tote. After a counter has been reached, pause the machine so the operator can swap out the tote for an empty one.

    I'm thinking doing this first, then working towards injection molding them so that an operator can injection mold then drill in the same machine. That to me...sounds like a real solid plan.
    Forewarned! I know I am a negative nelly personality, so take that into account...

    You said (paraphrasing) "move parts from a 100k+ machine into something around 5k". Isn't that what all the hobby people try to do and we shit all over them? I am just thinking the reason you currently (wag) do them the way you do them is because "that's how it's done" ie a cnc machine... Now to build something that will hold cnc tolerances (I did not look and see if you posted tolerances) for 5k seems unreasonable to me. Not saying it *can't* be done, but I imagine the labor, and the investment in getting a reliable process will shortly make your 4 axis cnc look mighty fine.


    opinions and all that jazz applies as always

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    Oh im not looking to move it to a hobby machine. I'm looking to spend $5000 in parts only to build a custom machine, I figure with labor and design it would be close to a $20,000 machine when im done with it. What im running in to is operator fatigue and a traditional pick and place type robot isnt fast enough compared to a human.

    Agree though, another mill looks mighty nice but they just require so much money to run compared to a small machine that only drills holes.

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    First thing to figure out is shot size. The biggest question here is can you core the part out so it has consistent wall thicknesses. If not the shot size will go way up, and the cost of the finished part because it will use a lot of plastic.

    Aluminum is MUCH better than steel for plastic injection molds!!!!!!! You can run them around 40% faster than steel molds and they are easier to make. Don't go cheap on the aluminum, get Alcoa QC-7 or 9 for the A and B plates, inserts, cores, slides, and heel blocks. It doesn't gaul like other aluminums so don't worry about it, the stuff is incredible.

    The machine is just a small part of a molding setup. You will also a mold temp control, can be real cheap, and a good dryer, don't go cheap on the dryer because if it doesn't work well nothing else will no matter what. You will want a little grinder too, eventually.

    No pictures of the mold, it's just in my head. But just sink enough of the part into the ejector side so the core pins have enough metal above them to be safe, say 1/8" or so. If you can bore holes accurately then build your own base, they are very simple.

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    by core you mean remove material? The part has to be the way it is. No additional pockets. Is what it is. Currently we pay $6 per block of material, precut to size and delivered. Material cost will be a moot point really compared to that.

    Where would I go to buy plastic pellets?

  20. #39
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    Coring is removing material so as to get as close to uniform wall thickness as practical. If material can't be removed by coring, this part is not practical for molding. The reason is that in order to fill the extremes the melt temperature must be higher than needed for the heavy sections. This will mean more cooling time and because of the differential cooling, warpage, distortion and sinks.

    Mold building, not just cutting the cavities, is a whole different world from machining. Same goes for the molding press. Clearly its not like turning lead into gold, there are people that design, build and run molds all over the world. The issue is knowing what all the elements are. Similar to a machinist that's only run manual machines and having them self learn to setup and run a 5 axis cnc without automatic tool path generating programs.

    Best way for you to get an idea of what is involved is to take a part to a mold shop and talking with them.

    Tom

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    Id love to but those dont exist here and I already have a business to run.


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