I use BobCAD 17 & 18 to design the molds for an older Arburg plastic injection (air operated). The max width is 4" but the length can be up to 6-8" if needed but cooling too fast becomes a problem. Most of the molds I make are 4X4 or 4X5. I use 7075 aluminum with steel mounting/backing plates. I make simple spring ejection systems with nitrided pins on the parts and runners.
The small molds are cut on a Sherline CNC mill (with Flashcut) or a Bridgeport Series I CNC machine. We cut the larger molds on a new Hurco vertical machining center (faster and a nice big toy with 15 HP motor).
Almost all of the parts I make are for my father-in-law's antique car restoration business. I learning more as I go along but most of my learning has been from books and trial and error.
Alignment pins and draft lines are critical to mold success. You really need to think it out properly before you cut. Also you must cut proper air evacuation routes or you will trap air in the platic mold.
I perform all the final fitting and alignment by hand. I do not care if it is cnc cut or not it will still need some fitting play.
I also make rubber compression mold for rubber parts such as seals, rubber bumpers, motor mounts, etc. That is a really neat process. 375 to 450 temperature with 10-15 minute cure time at 40,000 PSI. The operation is a one time deal. If you trap air in the mold you ruin the part (there is no melting real rubber) it becomes garbage! Those molds can be several plates/parts (up to 7 individual mold parts so far max). Dimensions range from 4X4 to 10x16 with an average around 8X10. The molds all need to be pried apart when coming out of the press. Trying to pry 450 degree plates apart with heavy heat resistant gloves is not easy. The molds must be at temperature to start with so you can not let them cool much.
Just thought you might like to know.
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