This Instructable explains how to make real injection molded plastic parts using a simple hand-operated machine. I realize most of you reading this don't have one of these machines, but I decided to post here anyway just to let all the garage inventors out there know that such a cool tool even exists.
More details about the machine can also be found at www.injectionmolder.net
Step 1: Machine set up
a) Plug in the machine. b) Turn on the power switch. c) Adjust the thermostat to the desired temperature.
Step 2: Insert the mold
a) Place a mold in the machine. b) Make sure the sprue hole on top of the mold lines up exactly with the injection nozzle. c) Clamp the mold in place by turning the vise handle clockwise.
Inexpensive homemade molds can be made using an epoxy or urethane resin. Or, by machining a desired cavity into an aluminum block using a benchtop CNC machine.
Step 3: Pour in some plastic pellets
Pour some plastic pellets into the injection tube. Wait until they melt (1-2 minutes).
Step 4: Pull down handle to inject plastic
Pull down on the handle with a quick, but steady motion. You will feel a solid resistance when the mold cavity is full. Hold the handle there for a few seconds, and then lift it back up until it locks place.
The downward force on the handle causes the injection nozzle to press down tightly against the top of the mold, allowing the molten plastic to flow directly into the sprue hole.
The time it takes to pull down the handle will vary, depending on how much plastic you are injecting. A small part (1-2 grams) may only take about 2-3 seconds to inject (plus a few seconds holding time). A larger part (5-10 grams) may take 10-15 seconds or longer to inject (plus a few seconds holding time).
Step 5: Unclamp and remove the mold
Wait for the molten plastic to cool in the mold for a short while (usually 5-30 seconds depending on size and shape of part). Then, unclamp the mold and remove it from the machine. Then, separate the two mold halves from each other.