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Sheet Molding Vs. Casting Epoxy Resins

Plastic is used to produce everything from computer keyboards and toothbrush handles, to televisions and auto bumpers, but not all plastics are the same. Some plastics originate as a liquid and go through a chemical process to produce a finished product, while others start as a thick film that can mimic the form of the mold to which it is introduced. Sheet molding and cast epoxy resin are types of plastics that eventually form a myriad of products, but begin in very different forms.

Material
- Cast epoxy resin is a synthetic thermosetting polymer. It consists of the resin and a hardener that must be mixed in exact proportions in order for the resin to set properly. It is a versatile material that takes on a glass-like finish, which makes it ideal for hobbies such as jewelry making, but has industrial value as well.
  
  Sheet molding is a blend of polyester material and finely shredded glass that is formed into a film. It comes on a roll and is ready to use, and is used primarily in compression molding.
Technique
- For solid projects such as bead making or production of figurines, the liquid cast epoxy resin and hardener are injected into the desired mold. The resin begins to set and harden, and once solid, it is easily removed from the mold. For coating or insulating purposes, the liquid is poured onto the surface or the item is dipped into the liquid epoxy blend then removed and allowed to dry and harden.
  
  Sheet molding is used for everything from car bodies to rain boots, and is usually formed through the process of compression molding. The sheet molding material is unrolled and stretched across a mold. The sheet molding is heated to a pliable state, and then a hydraulic press mashes the sheet molding into the mold. The press is released and the finished product is removed from the mold.
Cost
- Cast epoxy resin is expensive. For an average project, cast epoxy resin will cost almost double what it would cost to produce in sheet molding.
Use
- Epoxy can be used in large scale production, but due to its more expensive cost, it is often used on smaller items. Small, detailed projects often call for cast epoxy resin. Because cast epoxy resin is dispensed in a liquid form, it conforms well to molds, and is able to pick up fine details. The glassy quality of the finished product works well as an insulator, and is frequently used in electrical applications.
  
  Because of its low cost and the speed of the compression molding process associated with sheet molding, it is often used in mass production of plastic items such as toys and parts. Sheet molding can come on very large bolts so it is an ideal material for molding large pieces, such as sections of automobile bodies.

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