Injection molding (of toys and action figures)

[sonambulo]

Can anyone explain to me how molds were made in the past?

I understand that modern molds are made with CNC machines but how were the molds of, say, GI JOE figures and other extremely detailed toys made in the 70's and 80's? Were CNC machines already that precise or were the molds engraved by hand?

 

[Jimmah]

I went to school for CNC machining, which a huge part was mold design. Depending on the mold, iirc, they were machined then hand sanded to shape/design. Part of the course involved us making simple mold, then hand sanding it smooth (about a week worth of casual sanding). I do not know the history that well so I cannot comment on much else.

With CNC though you still have to sand and polish, depending on how much time the mold is being cut you can end up with tiny steps or effing massive ones that make polishers cry.

 

[CycloWizard]

I think most molds were probably hand-carved. The methods for doing so have been around for centuries - the same methods used to cast bronze sculpture and such by artists. This can be accomplished by carving a positive mold for plastics, while I believe a negative mold is generally used for bronze. The two halves of the mold are then just stuck together and filled with the material of choice.

For something simple like GI Joe, they may have used a more general method, such as drilling a tapered hole of a specific size for the upper leg, then carving out the details for an individual figure. This would just cut down the modeling time and allow all of the models to end up the same size without too much effort. You can also look at the modeling techniques used by Games Workshop, as they give a good amount of detail in how they work up their models. They "carve" them out of a piece of a putty-like material, then create a negative mold around the carving.