I'm embarking on a molding project that will duplicate a small scale production mold. We've all seen the molded boards, such a Inland Surfer or Placebo. For boards that are going to be mass produed this methodology offers many advantages.
1) Identical production
2) Parts (boards) come out of the mold nearly finished
3) Lower direct materials inventory needed
4) There is no shaping involved so less skilled labor is required. The "press" can be run by less skilled labor.
Molding a board requires a multi-part mold. I plan on just using two parts a TOP and a BOTTOM. The two will mate during production to create the board that is INSIDE.
The process of creating a mold with fiberglass as opposed to metal of some kind, uses a plug. I will be duplicating an existing board so my plug, in effect becomes the board.
In typical mold production the plug, in situations like this, is disposable. I will in fact be "screwing" the board down to a table to prevent movement and create flanges in the mold top. Also, I will be using tooling gelcoat to form the inner most layer of the mold's surface, subsequent layers will be chopped strand mat and polyester resin. The heat generated by the curing polyester resin can reach temperatures in excess of 300 degrees which is hot enough to create dimples in EPS foam. If the plug is a simple EPS structure, it can be ruined from the mold making process.
I have chosen an old board that has no tucked under rails. Negative relief angles are exceptionally hard to mold and require complex mold building. When building yoru mold you need to always rememer de-molding. A negative relief angle will prevent the board from popping out of the mold unless there are multiple pieces of the mold that can be removed.
This is a picture of the rail of my donor board. You'll note that the bottom is flat with no tuck in the rails to create a negative relief issues.