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Author Topic: So..... injection molding.  (Read 522 times)

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Howard_Casto

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So..... injection molding.
« on: February 13, 2018, 03:00:52 pm »
My 3d printing experiments are going well, but I think it might be time to move towards something a little quicker.  I had originally thought that injection molding would be too expensive due to the machined molds, but I ran across this article:

http://www.instructables.com/id/Home-Plastic-Injection-Molding-with-an-Epoxy-Mold/

An epoxy based mold would probably cost around 50-100 bucks to make, which is costly, but considering you could churn out 50 copies of a piece in a few minutes it isn't terrible. 

So the injection machine would be the other costly item, but yesterday I stumbled across this:

http://www.instructables.com/id/Plastic-injection-molding-and-extruding/

It's very crude, but it's also very cheap and easy to build.    Also since it's using sturdy black pipe as the chamber, a car jack or something similar could be attached to the jack for higher pressure injection. 


So is anyone else interested in this area of parts production and/or has anyone attempted plastic injection before?  I get the feeling I might have to be the guinnea pig on this one, but once summer starts I might try it anyway. 

jennifer

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Re: So..... injection molding.
« Reply #1 on: February 13, 2018, 03:50:35 pm »
    Oddly enough Jenn tried that in her younger days. I found a old Hobart commercial oven (and controller) in salvage and retroed on a pellet hopper, on a potato gun kind of setup with a hydraulic cylinder, and that worked quite well. The problem was the molds, Apparently that pressure has to go somewhere, and they must have vent holes for the goo to squeeze out (its harder than it sounds from a design standpoint) And that's when I gave up.... A odd fella like yourself most likely could make it work however, I would love to see any results. (good or bad) ;D 

pbj

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Re: So..... injection molding.
« Reply #2 on: February 13, 2018, 04:40:14 pm »
Made pewter molds 20 years ago... pretty sure this is the same company... and their ads used to show how you could make a perfect copy of a quarter.

http://www.miniaturemolds.com/MAKE-YOUR-OWN-MOLD_c80.htm

RandyT

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Re: So..... injection molding.
« Reply #3 on: February 13, 2018, 09:35:29 pm »
Depending on what you are making, you'll probably find pbj's method much easier to deal with (i.e casting.)  Injection molding is tricky business, and it's easy to get hurt, especially with make-shift machinery. 

The big issue with injection molding is that complicated parts require complicated and expensive molds.  Things like a solid fish, or items with holes in the direction perpendicular to the seam, can use a simple two-piece mold.  Anything more than that and you need more pieces and more complicated frames to hold them.   It's also tricky to properly design vents.  The vents not only allow for air to escape, but it also helps to regulate and direct the flow of molten plastic.  Demolding can also be a pain.  Most commercial molds have ejector pins built in to force the parts out, once they have solidified.  Chilled water is run through the mold to expedite this, and to control mold temps.

I actually picked up a tabletop injector, but quickly found that the items I wanted to make were too large or too complex for it to be of practical use.  Mold design and cost is also a barrier.  3D printers blow DIY injection molding out of the water for everything other than speed.  And if speed is what you need, you can often do better by simply buying multiple 3D printers (up to a point, of course.)

Howard_Casto

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Re: So..... injection molding.
« Reply #4 on: February 13, 2018, 11:13:29 pm »
Well there are really only three types of things I'm interested in.  I would like to do my own take on amiibo and make figures of characters that are too unpopular for Nintendo to ever produce and/or characters from other companies.  I can do one-offs of course, but it kind of seems like a shame to only do one copy.  I also want to be able to make low-yield reproduction parts as it pertains to our hobby....like those drop targets that got all crusty on pbj.  I've also always wanted to make my own line of action figures.... nothing fancy.... I'm talking 80's era points of articulation and levels of detail. 

I'm not too concerned about safety hazards..... the diy injector I linked to is a bit too wibbly-wobbly for me.  It's really good for understanding the components needed, but I would have to modify it before I even attempted a build.... the heated sections need a safety cage at the least and 240v = no thank you.  I've got welders gloves lying around somewhere as well. 

Aside from speed, the main issue I'm having with 3d prints is the finish work.  It takes a lot of time and/or effort to get a smooth object, especially if it's small.  That's fine if you are doing one thing, but not so much if you want 10 copies. 

I looked into regular mold making, but the thing that was killing it for me was the material cost for the pours.  The closest thing I found to plastic was a polyurethane resin and it was something ridiculous like 60 bucks for a few ounces.  Anything that melts will work for injection molding. 

Anyway, thanks for the suggestions guys, I'll look into it a bit more.

RandyT

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Re: So..... injection molding.
« Reply #5 on: February 14, 2018, 12:42:17 pm »
I looked into regular mold making, but the thing that was killing it for me was the material cost for the pours.  The closest thing I found to plastic was a polyurethane resin and it was something ridiculous like 60 bucks for a few ounces. 

https://www.homedepot.com/p/3M-Bondo-118-oz-Fiberglass-Resin-00404/205798046

$40 a gallon, and works fine with silicone molds.  Just make sure you get enough hardener, otherwise, soft and sticky is the result.

Should be good for painted figurines.  Not sure about mechanical parts.

JDFan

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Re: So..... injection molding.
« Reply #6 on: February 14, 2018, 01:27:47 pm »
Too bad they don't still make toys like they used to - I remember having one of the Hot Wheels Factories that was a mini plastic injection molding device to make hot wheels cars out of plastic sticks that is very similar to what you are talking about and could probably be repurposed for your usage. Had aluminum molds of the car bodies that you placed the wheels into and then melted the plastic in the machine and pressed it into the molds to make the cars.


Howard_Casto

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Re: So..... injection molding.
« Reply #7 on: February 14, 2018, 02:15:53 pm »
Eh some slow kid probably melted their eyebrows off so they took it off the market.  I don't remember those, but I remember one with plastic molds and a kind of wax used to make the cars.  I also remember erector sets made out of real metal, and chemistry sets that could burn down the house.  I also remember wood burning kits... or as we called them "teach your kids once and for all not to touch hot things kits". 

Mike A

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Re: So..... injection molding.
« Reply #8 on: February 14, 2018, 03:46:16 pm »

nitrogen_widget

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Re: So..... injection molding.
« Reply #9 on: February 14, 2018, 08:34:34 pm »
Eh some slow kid probably melted their eyebrows off so they took it off the market.  I don't remember those, but I remember one with plastic molds and a kind of wax used to make the cars.  I also remember erector sets made out of real metal, and chemistry sets that could burn down the house.  I also remember wood burning kits... or as we called them "teach your kids once and for all not to touch hot things kits".

metal erector set here.
Wood burners in boyscout camp.
Also had a science kit with:
shrimp
model rocket
weather balloon +helium and a bunch of other stuff I could've used to cause mass destruction if I was Lex Luther.


  
 

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