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Author Topic: Plastic Injection Molding  (Read 17081 times)

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Plastic Injection Molding
« on: January 07, 2014, 06:56:40 PM »
I am aware, that this is not a mach 3 project (although mach 3 was used in carving the pattern for the actual mold). But I thought that I would post this here, to see if others have tried such a project. I started construction on this machine 2 months ago, and am finally down to the final stages of being ready to test it out for the very first time. (However, a cold wave has invaded Georgia, and it is simply too cold to be out in my unheated shop for the next few days).
The inspiration for this machine, was (of course) a You tube video. As a way of recycling plastic soda bottles, etc. Although the first one I saw, was actually marketing a kit for installation onto a drill press (and selling plastic beads to feed into it). In my case, I have sliced up several empty 2 liter soda bottles into little squares about 1/2" each. And designed a funnel opening on the machine into which I can pour them for melting.
Anyway, I am just curious to see what others have done along these lines.
As I said, it is COLD here now, so I will post pictures in a couple of days when the weather warms up enough to take the camera to the shop, (without fogging the lens!).

Online Tweakie.CNC

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Re: Plastic Injection Molding
« Reply #1 on: January 08, 2014, 01:35:26 AM »
Sounds like a very interesting project, I look forward to seeing the pictures of the build.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Plastic Injection Molding
« Reply #2 on: January 08, 2014, 04:33:20 AM »
Sounds great I'm very interested to as soon as you get working on it Start posting it
Re: Plastic Injection Molding
« Reply #3 on: January 08, 2014, 07:24:38 AM »
Me too, but I would like to see the temperature go up soon, Damn it's cold this year. (-15F -26C)
« Last Edit: January 08, 2014, 07:26:32 AM by Ya-Nvr-No »
Re: Plastic Injection Molding
« Reply #4 on: January 10, 2014, 11:32:42 PM »
Well, the weather finally warmed up here (after 2 days of dealing with busted water pipes!). So I got back in my shop today, and took a few photos of the machine. The original design I saw on Youtube was a gizmo the fellow had mounted in the chuck of a drill press. Not willing to tie up my drill press for such purposes, I set about re-inventing the wheel (so to speak). I built a rack and pinion out of oak, which was carved by Mach3 on my CNC Router table. I mounted an aluminum block, which I had bored to function as the combination heater, and injector assembly. This block has four 350 cartridge heaters installed (one in each corner of the block, with the center bored 1" diameter to accommodate the 1" diameter plunger shaft). A cheap chinese purchase on ebay for the heat controller yielded a box which is at least useful for measuring the temperature. There is no output voltage to the relay, but is still useful for controlling the heat manually. (When the output light is on, I turn the heaters on, when the output light goes off, I turn the heaters off). This was my first purchase from a Chinese dealer on ebay, so.... Anyway, the first test of the machine revealed the importance of acurate heat control. Also, the reason the fellow I saw on Youtube is selling plastic beads for the injection molding machine he was selling. My thoughts of slicing up soda bottles, and feeding them into the funnel mounted on top of the aluminum block failed. The reason being, by the time one is able to drop enough of the little 1/2" square flakes of plastic into the cylinder to fill it, the plastic in the bottom is charred! Further experimentation with lower temperatures is on the agenda. But I can see a definite advantage in buying plastic beads which can be quickly poured into the cylinder, and immediately plunged into the mold. This project has been a real learning experience. The actual mold was a challenge in itself. I carved a wooden pattern using MechCAM Art of a 3D Heart with a Holy Cross in the center. Two concave images were carved into oak, to form the pattern for the mold. This pattern was then used to form a sand mold, and the actual mold was poured with molten aluminum from my foundery oven. After cooling, I mounted the mold onto my lathe, and faced off the mating surfaces of the mold to machine them flat. I then drilled guide holes in one half of the mold, and ended up carving a wooden positive image of the mold to act as a "Key" for aligning the first half of the mold to the second half (in order to determine exactly where the guide holes for the second half of the mold needed to be drilled for perfect alignment with the first half). I.E. I inserted the wooden Key into the first half of the mold, and placed the second half of the mold also onto the Key, and used the guide holes of the first half of the mold to locate the guide holes for the second half of the mold. I determined that the prime location for filling the mold was the base of the Heart, therefore the Heart would be injected upside down. I scribed a line from the center of the base of the Heart, to the edge of the mold to determine exactly where it needed to be drilled, then placed the assembled mold into the drill press vise, and drilled the mold halves at centerline where the two faces meet. I then filed two small scrathes into the face of one half of the mold, to create overflow ports to alert me when the mold is full. The machine I built features a vise assembly for holding the mold in alignment with the injector assembly. Linear rails were used to guide the injector to the center of the mold. However, further work is needed in my design. A locking mechanism needs to be added to keep the injector nozzle firmly inserted into the mold, while plunging the plastic into the mold (because the back pressure pushes it back out of the mold- I learned this the hard way). Anyway, here are a few pictures of the machine so far. Notice the "guillotine" shut-off valve. It's just a piece of angle steel mounted on a ball bearing slide assembly which is spring loaded. A wooden handle was needed to prevent burned hands, when opening the valve for a charge into the mold. The spring load was needed to immediately slam the valve shut, once the injector assembly has been raised 1/8" off the surface of the mold. It will probably take me a few days of experimenting with different temperatures, before I will get a successful cast. I have already learned, that if the plastic is heated too hot, or too long, it becomes a useless mass of brittle, black plastic. Instead of the clear plastic it started out as.

Offline jeep534

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Re: Plastic Injection Molding
« Reply #5 on: January 12, 2014, 08:34:26 PM »
keep Up the good work and keep posting 

Happy hunting
Re: Plastic Injection Molding
« Reply #6 on: January 28, 2014, 06:05:37 AM »
Interesting project. I used to have a bunch of hand operated molding machines in my workshop 20 years ago. A couple of them are still stashed away in the attic. Those machines were used to produce low volume production parts and gave out good, precise results from ABS, PP and Acetal. We used virgin and dyed plastic pallets and mostly CNC machined mild steel molds.

Zafar

« Last Edit: January 28, 2014, 06:14:40 AM by zafarsalam »
Re: Plastic Injection Molding
« Reply #7 on: January 28, 2014, 08:28:15 AM »
Interesting project. I used to have a bunch of hand operated molding machines in my workshop 20 years ago. A couple of them are still stashed away in the attic. Those machines were used to produce low volume production parts and gave out good, precise results from ABS, PP and Acetal. We used virgin and dyed plastic pallets and mostly CNC machined mild steel molds.

Zafar
The single mold I have made for this machine, is made from an aluminum cast. I machined a wooden pattern out of oak, and used it to form the sand mold from which I cast the mold with molten aluminum. This project has been a many-faceted challenge, that is still in progress. The first attempt, (using plastic soda bottles, which I cut up into .500" square flakes) taught me the importance of starting with plastic beads, or at least something small enough to simply be poured into the cylinder, and immediately injected into the mold.
 If one takes the time, to drop them into the cylinder just a few at a time, then what happens is the first few get so hot, that they actually burn before enough flakes can be dropped into the cylinder to fill it. Another item, also learned thru experimentation, is that the mold itself must be heated along with the cylinder.
  Otherwise, when injecting the plastic into the mold, what happens is that the fill port of the mold is all that ever gets filled, before the plastic solidifies (and therefore closes the fill port). The current status, is to build another machine to chop, or grind the plastic soda bottles into much smaller pieces, so that the cylinder can be filled immediately (and the plastic immediately injected).
   The mold heating problem can be overcome, by simply allowing the injector assembly to rest in contact with the mold. I do not have the resources to order plastic beads to test the machine with, so at this point it will have to wait until I can devise a method of producing much smaller pieces to fill the injector cylinder with.

Re: Plastic Injection Molding
« Reply #8 on: January 28, 2014, 08:45:59 AM »
Oh, I forgot to mention the problem I was having with the cheap chinese ebay purchase for the heat controller. I finally figured out, that it needed an external DC power supply (which I happened to have a 24VDC unit in my shop- left over after upgrading my CNC Router table from 24VDC to a 48VDC unit). I THINK that the heat controller unit is supposed to be supplying it's own DC power, but simply isn't. However, it's internal relay does function to control the series circuit of an external DC power supply. (For controlling the external relay for switching the cartridges heaters on and off). Anyway, the system does function to maintain the temperature automatically to whatever level one chooses to set the target temperature at. It has an upper limit of 400 degrees C. This made things a little less frustrating, without the need to manually flip the switch ON to the heaters every time the output light of the heat controller came on. (And OFF every time it turned off).
Re: Plastic Injection Molding
« Reply #9 on: January 28, 2014, 08:52:41 AM »
Maybe you should try milk bottles instead of soda bottles. Soda bottles are normally made from PET while milk bottles are mostly HDPE. HDPE's flow is better suited for hand molding. Put heaters on the lower half of the molten metal barrel. So that only the lower half gets melted and the top half is in solid state which you can push with a plunger. The reason your molten plastic gets solid in the runner might be because of less material flow for the mold size. Try a smaller cavity and runner size.

Zafar

P.S.  a few photos of your mold would be interesting
« Last Edit: January 28, 2014, 08:55:41 AM by zafarsalam »