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Thread: 20 Ton press for injection molding machine

  1. #21
    Gold Member LeeWay's Avatar
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    Default Re: 20 Ton press for injection molding machine

    Thanks for that. Very nice upgrade.
    The proper drafts and what would work best for this type of part will be some of the learning curve.
    Of that I have no doubt. That will be part of the fun in it.

    I have seen quite a few different small hobby and benchtop setups.
    I haven't seen any of those that were rated for 20 tons, so one of the issues I may have is too much pressure.
    I would probably need to cap the air pressure while still maintaining the ram speed. I have seen those type valves, but have no clue how they work. I bought a big 1/2" pressure regulator for this, but I have already hijacked it to use in my whole shop air system.
    The one for this will just have to come a little later. I do have some smaller ones and will use one inline temporarily with quick disconnects.
    I was working on machining the plasticizer this evening, but while my collect seemed like it was holding the rod well, it slid some and so I have broken my first threading insert. The first of many I think.
    So, tomorrow evening I will install my lathe chuck for the first time and go from there.

    Lee


  2. #22
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    Default Re: 20 Ton press for injection molding machine

    Before buying my larger machine, I was thinking about modifying the medium machinery machine I had. I'm still wondering if it would have worked. I think there are two possible opions: Making it manually operated like the one seen
    at the end of this video: . This would give you a much higher injection speed but you would loose a lot of injection pressure. It might also possible to somehow make a semi manual machine, where
    you start the injection process manually and just use the ram to pack the mold once it is full.

    Another option that I was thinking about was to pre-load a huge spring (think car suspension) that will store a lot of energy that could then be used to power the injection ram. I'm just not sure how you would control injection speed etc. and having
    a lot of energy stored in a big spring can be dangerous. Still like the idea though....

    BTW, it is a whole lot easier to inject HDPE or PP than ABS / PC-ABS. HDPE has usually a higher mold flow index but I'm not sure if it would be suited for your part.



  3. #23
    Gold Member LeeWay's Avatar
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    Default Re: 20 Ton press for injection molding machine

    Now that is what I call a manual machine.
    I do have a decent model started on what my intentions are so far with this hot press.

    20 Ton press for injection molding machine-press1-jpg

    The vise shown is a 6" and I will be using a 4".

    Most of the knobs I use are polypropylene, so I will probably just end up using that material. They are strong enough to do the job. ABS is just something I am familiar with.

    I have been considering using a rather large short ball screw. They come up on EBAY often enough.
    Then drive it with a double chain sprocket from a gear head motor. That might give me all the strength and speed I would need for the ram. That is if the air hydraulic jack doesn't do the job. Mold heating or cooling should not be an issue at the hobby level.
    If I wanted to produce a number of these, I would make more molds.
    I have also considered a large air cylinder, but until I have some numbers or an idea how much pressure the ram may need, I would not know what size to buy. Plenty of large US made ones on Ebay. If I had to go that route though, I would just make a full fledged horizontal bench to sized machine.
    Now that would be a project. I would look around for a smaller used machine before tackling something like that.

    Lee


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    Default Re: 20 Ton press for injection molding machine

    To be honest, financially speaking it would probably be better to just buy a small molder or mill the knobs/out source them. If you are doing it as a hobby it is of course an entirely different story. ABS is usually injected with 4500-15000 psi. If you know the projected area of your part (including runners etc.), you can now calculate how much force you need to keep your mold clamped shut. But as I said earlier... your main issue will be speed. Smaller parts like your knob are usually injected within 1-2 seconds, a hydraulic car jack is just not nearly fast enough. Check youtube, there's a bunch of small molders that use air cylinders which are much faster but usually aren't too strong.



  5. #25
    Gold Member LeeWay's Avatar
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    Default Re: 20 Ton press for injection molding machine

    I have only scratched the surface on the higher Fusion 360 stuff.
    It will tell you the volume of the mold cavity if you do it right.
    I was attempting to get the volume of the sprue and runners, gates to add to the modeled knob volumes, but I did something wrong.
    I will keep trying till I get it.

    As to the hobby part, I have been interested in IM since before I bought a 3D printer. That is actually why I bought that kit or at least one reason. Making formed stuff out of plastic cheaply.
    Using the knobs as a mold here to start with is because it is a current pet peeve with knob producers.
    I can buy knobs that will work.
    The cost is nearly the same if I buy 50 or 1200. I guess those are still small quantities where injection molding is concerned. The 1200 count takes about 6 weeks on the lead time.
    They are not really the knobs I want for my product, though they do work.
    I am paying a premium price for them. I should be able to get what I want.
    That is the driving point for me. An interest and a need collide.

    I also understand that some guys that have this press might also use it more often than me. I do have another use for it coming up.
    So a dual purpose machine. Probably not great for either purpose. All of the IM parts on this press would come off with a couple set screws and maybe a couple bolts. Then it is an actual 20 ton press again.
    That's gotta be cool.


    Lee


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    Default Re: 20 Ton press for injection molding machine

    The volume is not really important. The projected area is what matters. Post some pictures if you get it working, I'm curious how it will turn out :-)



  7. #27
    Gold Member LeeWay's Avatar
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    Default Re: 20 Ton press for injection molding machine

    Projected area is different than volume?
    I do have a learning curve.

    Lee


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    Default Re: 20 Ton press for injection molding machine

    You mean surface area.
    I think that is the difference from the total volume to the outside shell.?

    Lee


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    Default Re: 20 Ton press for injection molding machine

    yes it is different from volume and also different from surface area. The projected area is the area of the shadow that part (including runners) would cause when lit with a lamp. Multiply it with your injection pressure and you have an estimate of the required clamping force you need to keep the mold shut.



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    Default Re: 20 Ton press for injection molding machine

    The normal for clamp pressure/Tonnage needed is 3 to 5 Ton per square Inch this is the normal requirement,and yes surface area of the molded part, any surface area that will be affected by the injected Plastic, is to be calculated, to know what clamp pressure is needed, for a Hobby molding like you are doing, if you, inject the plastic into the mold, and you get flash, between the 2 mold faces, then you either need more clamp or less injection pressure, hard to control on a Hobby machine

    Mactec54


  11. #31
    Gold Member LeeWay's Avatar
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    Default Re: 20 Ton press for injection molding machine

    Thanks, Guys.
    I may get a chance to move a little farther along with this over the weekend.
    I will try machining the first mold design and see what needs to be seen on it.
    I am going to mount the chuck in the lathe and turn a few parts of this on it as well.

    I think I have determined that I will most likely just be using TPE. At least initially.
    That stuff seems pretty painless, assuming I am close to the city where the ball park is located.

    Lee


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