Shop Air Injection Molder

I got around to heating up the extruder and putting some plastic in it. Results were poor. The extruder did not have even heating due to the uneven winding of the wire. The whole mess had to be pushed out with a metal rod and it came out like clay despite being well over 230 F.

According to the source below, ABS has a molten viscosity at the lowest of 155 Pa*s. Corn syrup is between 1-2. Vegetable shortening is 250 so molten ABS is about half as viscous as vegetable shortening. No wonder common injection pressure is 15000 PSI. Other sources say peanut butter has a viscosity of about 150-250 Pa*s. So I'll probably use that for testing.

http://plastics.ulprospector.com/generics/1/c/t/acrylonitrile-butadiene-styrene-abs-properties-processing

I also found this cool write up on ABS plastic.

http://www.cheme.utm.my/mpj/images/090402_3asif.pdf

Lots of research to be done on translating shear rates and viscosity into molding pressure.

Printed Parts:

I finished printing all the parts I needed to make a PVC hydraulic cylinder. Only to discover the parts don't fit any PVC pipe available at Home Depot. Luckily the parts are simple enough to design myself in Autocad with the correct dimensions. It's a real bummer though, 6 hours of printing wasted.

The government has found a way to delay my project. Gathering info for taxes will eat up a few days.

Thanks Obama! </sarcasm>

I discovered I had some Nichrome wire, 24 gauge, lying around from a hair dryer. I wrapped Kapton tape around black pipe and wrapped the nichrome around it. I bought a $6 dimmer from home depot, wired it up and plugged it all in.

Success! The makeshift wire reach 200 F before the tape I used to hold it together melted.

I then proceeded to slice my finger open while building an enclosure. Never used dull drill bits and always clamp down the workpiece folks! The drill quickly snagged the workpiece and split me open pretty good. No stitches will be needed.

Also, I printed most of the parts for the PVC pneumatic cylinder.

I am also working on a laser cut tumbler to finish the 3d printed parts.

Next steps:

I need a reliable way of winding Nichrome around the pipe evenly. I plan to make a jig out of threaded rod and power drill to wind the Nichrome. I will probably use a gloved hand to apply tension as it winds.

I need to figure out how to secure the heater while pressure is applied by the ram. I think the answer is a coupler for black pipe...

At 90 PSI the 3d printed plastic parts are undergoing 1300 lbs of force. They'd pop right off the pipe at probably around 300 lbs. Yet, PVC pipes are used for dangerous (but working) rocket engines and the nozzles don't shear away from the pipe (every time).

A 12 ton pneumatic jack will only cost me $80 at home depot though, so I may do the testing with the jack while I figure out the 3d printed cylinder. I may forego the 3d printed cylinder in favor of a $180 metal cylinder, but that would set future build costs at a $360 minimum before fittings, framing, etc.

Priority #1 is making a working heater. I will order 38 gauge NiChrome and a lamp dimmer tonight. The shipping time will give me time to research insulation materials.

There's a few things I need help on.

1. I've never used a hobby injection molder. If you have one, there's many assumptions I'd like clarified!
2. Feel free to check my assumptions and math on how the heater will work.
3. Please suggest sourcing!
4. I'd like to use a metal version of the 3d printed parts. Accepting donations.

Here is a similar idea

Here is another similar machine but closer to my aim of full automation.

http://aceautomation.in/injection-moulding-machine.htm