Here’s where I’m at:
Still many missing components and systems, most notably: mold cooling system, pneumatics controls, part ejection cylinder, microcontroller, sensors, power supply, mounting locations for most components, and many many more.
The pump that transfer the molten plastic is a simple piston pump using two check valves:
In my first design I created my own check valves by integrating a ball bearing and spring into the actual pump body. While this made the pump more compact, it also added several machining steps which would have increase the price. So instead I’m using off the shelf check valves that screw into the pump body. Much cheaper, much simpler, and likely to work better.
In another bit of “don’t-redesign-the-wheel” thinking I’m using an electric deep fryer as the melting pot. Candles makers already are using this as a melting vessel. This already has a heating element and thermostat built-in, and it only costs ~$30. Compare that to several hundred dollars had I made my own vessel from stainless, used silicone band heaters, and made my own temperature regulation. The latter would have definitely been cooler looking, but for this project I’m trying to keep costs low.
Not as cool as stainless steel and band heaters.
I am at a bit of a crossroads design wise. I’m deciding between using pneumatics or electric actuators for motion control. Pneumatics are more impressive visually and give me a chance to learn about pneumatic systems (plus they make a neat pssst pssst sound), however they require an air compressor (loud) and are more expensive. Using electric motors would make the system smaller, as I don’t need to house a compressor and air tank in the enclosure.
I’m leaning towards pneumatics provided I can find a quiet air compressor. I’ve read of people re-purposing a refrigerator compressor, but I’m concerned about their CFM rating and live span.
I’m also looking very seriously at buying a small mini mill. I should recover the cost of the machine and then some verses paying to have it done. Ideally I could find a small Chinese mini-mill on Craigslist, but I haven’t seen much out there. Maybe I’ll just break down and get this guy:
Things I'm Doing 
I think you should let your hot girlfriend machine those parts for you at MIT. Rumor has it she needs more hobbies.
Howdy! I ran across you blog when looking in to DIY injection molding. I tend to get wild ideas and try them. Long story short, I am a machinist that specializes in prototypes. I’m trying to find a way to do prototypes of injection molded parts that I simply can’t machine. That said, I think we might be able to benefit from some mutual assistance. Feel free to send me an e-mail so we can chat.
How is this project going. I want my product to be injected molded. It is going to be sort of a toy and thought wouldn’t it be awesome if I could use this to make the experience interactive?
Hi,
I just started back up on this project. I’ll post an update in the next few days. Goal is to have it completed by Feb 2013 at the latest.