To continue from a tangential topic from another thread, I felt a new topic here may help (a little).
- Plastic models can be formed to a sprue, or single-piece ejected mold.
- Molds themselves are replaceable components that fit into the mold-machine, and can be swapped out with (general) ease.
- Molds are often machined into a type of stainless steel, but other materials can be used (aluminum, copper). The harder (mechanical property of hardness) the material is, it will typically last longer, but can cost more due to labor & time.
- Fabrication is often done by conventional computer-numerical-control machining (CNC), and then final shaping / finished by electro-static discharge machining (EDM), electro-polishing, or chemical-etching.
- Because molds are rigid, in order to allow for a smooth mold separation and (completed) part-ejection, slides and multi-part sections can be engineered to create complex features and under-cuts.
- Mold Plates: Large piece molds which may contain two or more pieces, and can contain slides; Mold Plates for the typical plastic model air-plane kit of the 80's may be 18" x 24" x 12", to form ONE template for an 8"x12" model sprue. A mold this size could effectively weigh 1300lb or more... and a single model airplane may have required multiple. Cost: $10k-30k, on up.
- Mold "Muds": Being far more typical compared to prior decades because of improvements to manufacturing equipment and materials, Mold Muds are small, replaceable inserts that can be (usually) easily swapped in and out of a Mold Mud frame; These may contain a single model / miniature per mud, depending on the size, and may also contain multi-part engineering and/or slides. Mud's can be as small as 4" x 4" x 4", but for Battletech miniatures-scale (if single mini per mold) may be ~6" x 6" x 4", and approximately 2" greater in size than the MadCat & BLR sprue from the latest box-sets (or roughly 8" x 10" x 4"). Weight ranges from 30lb to 100lb; Cost of the Frame: $~5k, cost of Mud's (each: $3k - 7k (and on up).
(See http://www.g-mold.com/Mold-tech/What-is-Mud-mold.htm for a basic example)
The actual resin/plastic used is typically determined on a cost & performance analysis, and occasionally will include "regrinds" (failed / re-used / recycled plastics) which may or may not affect the finished product.
** Disclaimer - any of these details are statements of my own (except for G-mold, as its' a random site I found that has decent info on the subject) and is typical of the mold-making industry - nothing here reflects CGL's actual manufacturing processes or procedures...
