'You've learned by now that if you break the Bow Tie off your grille, you should be able to find one on eBay or at a swap meet. But what about that 383 Magnum hood script or Buick GS fender insignia? We're always on the lookout for new and interesting techniques, and we are also always breaking stuff; it's how we have developed some of our repair and restoration skills, which brings us to the subject of casting plastics.
Typically, plastic parts are injection-molded by the manufacturer or an aftermarket company using tooling and machines to which the average person has no access. That, however, is not the case here. Using a few products readily available from Freeman Supply, anyone can mold and cast his own creations or reproduce OE parts that are no longer available. It may sound complicated, but it is really quite simple.
The process is called mass casting, and if you follow a few simple rules, you can cast pretty much whatever you want in the comfort of your own garage. Simple mass casting is used for three-dimensional castings with flat open backs. Think of an emblem without mounting studs. The back side of the cast would remain open, where the liquid plastic can be poured in.
Complex mass casting is the next step in casting, where a single parting line runs through the part connecting two halves of the whole. This requires two molds that fit together, such as a flat, front-side emblem attached to a back side that has the studs attached to it.
Thin-wall casting is used for parts such as armrest bases to replicate the thin walls with a cavity on the back side of the part.
Complex irregular casting is the most difficult of the casting techniques, as this process involves multiple steps and features an irregular-shaped parting line and possibly a hollow or thin-wall section combined into one piece.
We re-created an SS396 fender badge to demonstrate the mass-casting technique using silicone rubber tooling material and clear liquid polyurethane. Using silicone rubber to create the mold eliminates the need for special mold releases, since it acts as its own release agent.
The results of the plastic-casting process yield many different products. With some practice and patience, some very cool trick parts are waiting to be created. |
The SS396 emblem we re-created in cast plastic was cleaned and the painted inner portions sanded with 500-grit paper. |
Since the emblem was broken, the front side was taped with thick, three-day tape from 3M. The cheap stuff leaves residue that gets transferred into the mold, which is not good. |
With the emblem pieced back together, some super glue was added to the back side to make the badge whole again. Care was taken to ensure the glue didn't run through and get on the front side of the badge. |