Machining a cast iron bush in bulk. Any advice ?
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    Default Machining a cast iron bush in bulk. Any advice ?

    Im a foundry man, we make cast iron parts usually small items weighing not more than 5kg

    Although we cast around more than 100k pieces each month but recently we have acquired an order to machine them as well.

    img_6256.jpg

    Currently we machine around ~600 pieces on a single manual lathe in a 8hr shift. Operations include boring and facing one side. The other face is done by a different person. In past we used a Nakamura CNC Turning machine as well, but were not satisfied with a ~450 piece output in 8hrs. Subsequently sold the machine (which we shouldn't have).

    I would like some advice on how to improve my machining throughput.

    Thanks

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    Your speeds and feeds will be the same if your running manual or C.N.C.

    Show us your tooling, and sequence of operations.

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    At something on the order of 45 seconds a piece I am going to say your machining is not so bad but I will bet part changing is a big part of that

    You might need to figure out what you need to get done in a day and figure a way backward to that

    There is little way to massively improve part changing on a lathe, but if tolerances allow you could fixture multiple parts on a CNC mill

    You would have similar or maybe longer machining time, but your part change time could drop dramatically, since you would load parts offline while the machine is running then change quickly push the botton and go

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    If the OP would provide a size, it might just run on an old National-Acme
    8 spindle chucker.

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    How round are these things after the first turning op? Looks like a flimsy part and with the irregular surface on the OD, I can't see how you'd avoid distortion.

    I'm wondering if you wouldn't be better off to Blanchard grind both sides parallel first. Then you'd need some sort of pull-down chuck to clamp the part axially, with only a gentle 3 point support for centering. After boring them one at a time, you could gang turn several at once on a mandrel.

    Greenleaf ceramics could also be used for turning at some ungodly speed that would produce a rain of fire.

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    First question that occurs to me - are you casting and then machining each small piece individually? Could you cast a tube of some length, bore it all at once, then part off the pieces? I don't know enough about the casting end of things to know if this would add up to less time overall, or more ... but I'd think it would definitely reduce the machining time, just because of not having to load and unload all the little parts.

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    Quote Originally Posted by rshafique View Post

    img_6256.jpg

    Currently we machine around ~600 pieces on a single manual lathe in a 8hr shift. Operations include boring and facing one side. The other face is done by a different person.
    The other face can be machined in the first set up as well with a back boring bar IMHO


    Peter

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    I don't have pictures right now but here are the steps that we do;
    - Take a rough cut manually
    - Then put it on auto line (Im not sure what its called)
    - Then take the face off on the way back

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    Quote Originally Posted by awake View Post
    First question that occurs to me - are you casting and then machining each small piece individually? Could you cast a tube of some length, bore it all at once, then part off the pieces? I don't know enough about the casting end of things to know if this would add up to less time overall, or more ... but I'd think it would definitely reduce the machining time, just because of not having to load and unload all the little parts.
    This is something I've been thinking myself, but haven't tried. According to my brother who's been in this for longer says they tried it but the long bars take more time to bore to size then lets say if 5 pieces individually considering if the pipe was also similar in length to five pieces.

    Id love to try this again though this bush comes in two sizes one with 108mm ID and the other being 120mm ID the wall thickness is around 4.2mm. What sort of lathe would you recommend if we do it the pipe style around 300mm long tube?
    Last edited by rshafique; 04-25-2019 at 04:42 AM.

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    Quote Originally Posted by Peter from Holland View Post
    The other face can be machined in the first set up as well with a back boring bar IMHO


    Peter
    Looks like a really good idea! But I think we risk to introduce some ovality?
    We have modified 3 jaw chuck with a welded larger sized bush to fit in smaller bush, the piece sits on a seat. Which chuck would you think will work for this?

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    The same chuck but instead pushing it against a seat at the back of the jaws you align it with the front of the jaws
    Hold a big washer agains the face of the workpiece and then chuck it holding the washer against the face of the jaws
    Or some small magnets in the washer to hold it easier

    On edit
    Another idea is to drill 3 holes on the soft jaws that can hold pins
    You seat your work against those pins
    Then a big ring with 3 cams on the inside that push the pins inwards when you rotate that ring
    If you turn on the lathe the ring turns backwards and the pin(with springs if need be ) will follow
    Now you have space to use a back boring bar
    Peter
    Last edited by Peter from Holland; 04-25-2019 at 07:24 AM.

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    Would a large adjustable David Brown floating reamer let you bore a few at a time before parting off?.

    S15 FLOATING REAMER ADJUSTABLE MT 5 REAMER CNC ENGINEERING MADE IN UK 4" - 5" | eBay

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    Quote Originally Posted by rshafique View Post
    Im a foundry man, we make cast iron parts usually small items weighing not more than 5kg

    Although we cast around more than 100k pieces each month but recently we have acquired an order to machine them as well.

    img_6256.jpg

    Currently we machine around ~600 pieces on a single manual lathe in a 8hr shift. Operations include boring and facing one side. The other face is done by a different person. In past we used a Nakamura CNC Turning machine as well, but were not satisfied with a ~450 piece output in 8hrs. Subsequently sold the machine (which we shouldn't have).

    I would like some advice on how to improve my machining throughput.

    Thanks
    I never would have suspected you were from Pakistan based on your well written posts. Very impressive.

    Equally impressed that you guys are slamming that much production through a manual lathe in only 8 hours.

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    Do you combine tooling? The idea is to combine the boring with the facing for the first operation. If possible given the tolerances, then tool changing might be eliminated.

    This is taking some ideas from turret lathe operation. Combine the roughing and finishing of the bore in one tool with two cutting sections. Possibly multiple cutters for each section so that the feed rate can be increased by the number of cutters.

    The facing might then be done at the end of the feed, when the facing portion of the tool contacts the part.

    Tool would have a smaller diameter holding the cutters for the boring, in one or two sections (two for roughing and finishing), then a larger diameter that holds the cutter for facing. The facing cutter would not be fed radially, it would be set to face true. Inserts would be best for easy changing without needing to reset he cutters.

    Feed the tool into the bushing, and limit the stroke to do the facing while leaving enough material to face the opposite side to length. Both operations would be finished in one movement of the tool.

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    Quote Originally Posted by rshafique View Post
    This is something I've been thinking myself, but haven't tried. According to my brother who's been in this for longer says they tried it but the long bars take more time to bore to size then lets say if 5 pieces individually considering if the pipe was also similar in length to five pieces.

    Id love to try this again though this bush comes in two sizes one with 108mm ID and the other being 120mm ID the wall thickness is around 4.2mm. What sort of lathe would you recommend if we do it the pipe style around 300mm long tube?
    I would think any decent lathe with a swing of 12" / 300mm or larger would handle this without trouble. That said, I should quickly confess that my machining knowledge is all self taught and mostly TLAR ("that looks about right").

    The 12" / 300 mm depth could be a problem for boring ... except that with a 108mm ID, you've got room for a really big boring bar. I don't know what sort of tooling availability (or budget) you have, but I wonder if this is an appropriate place for a DIY solution. An Armstrong-style boring bar holder is awfully easy to make* and can be really rigid. Maybe a 2" / 50mm diameter boring bar - ? As noted above, I operate on the TLAR method, but maybe some of the experts here can chime in with actual experience as to what size boring bar would give the rigidity for good results at 300mm depth.

    *awfully easy to make, as witnessed by the attached pictures - this is the one I made as one of my first projects when I was learning to machine. Despite that, it continues to work quite well. It only goes up to a 1" / 25mm diameter boring bar, which is more than enough for anything I've ever done, but as long as you have the raw material on hand to make the parts, and sufficient swing, you could make it as big as you like.
    onlathe2.jpg
    finished-assembled.jpg
    finished-components.jpg

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    Thanks everyone for joining this thread and offering to help. Id like to keep this alive (wondering why I forgot about it in initial place) as we are still in this and looking for solutions. Its easy to buy more lathes and hire more people but who wants to do that!

    Id like to make a correction that its not 600 pieces/person/shift its more like 350-550 and rarely going to 600.

    One thing we have learned is that for greater throughput we need to think outside the lathe more like a special purpose machine. We are thinking of a double headed lathe/like machine with work piece in the middle and two tool posts on the sides
    with an auto feeder or just a manually fed pneumatic holder. Do let me know what you guys think!

    Thank you for your time!

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    Quote Originally Posted by HuFlungDung View Post
    How round are these things after the first turning op? Looks like a flimsy part and with the irregular surface on the OD, I can't see how you'd avoid distortion.

    I'm wondering if you wouldn't be better off to Blanchard grind both sides parallel first. Then you'd need some sort of pull-down chuck to clamp the part axially, with only a gentle 3 point support for centering. After boring them one at a time, you could gang turn several at once on a mandrel.

    Greenleaf ceramics could also be used for turning at some ungodly speed that would produce a rain of fire.

    Yes this is a rough casting, with sand on all surfaces, it needs to be sufficiently round because our clients will further machine these further 1.5mm-2mm. Grinding seems to be an overkill and the price doesn't justify it!


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