What is SMC/BMC molding process?
Molding process including SMC and BMC is one of the oldest and infinitely dynamic molding methods in the production of composite products. It is a method of curing a certain amount of premixture or prepreg in the mold by heating and pressing.
There are many kinds of moulded materials, which can be prepreg material, premixed material, or billet. The main types of molding materials currently are prepreg, fiber premixture, BMC, DMC, HMC, SMC, XMC, TMC and ZMC.
Molding process can be divided into several kinds below as per the state of the reinforced material and the variety of mould press material:
To form FRP composite products by putting the premixed or pretreated fiber casting material into the metal mold at certain temperature and pressure.
Crushed fabric molding method
Suitable for the product with simple shape and simple performance.
Put pre-weaved two dimensional or three-dimensional fabric with desired shape into the resin adhesive to form composite within the metal mold after heating and pressing.
Laminated molding press
Tailor the glass fiber cloth or other fabric pretreated with resin glue into the desired shape, then form the composite products in the metal mold by heating or pressing.
Impregnated continuous fiber or cloth within resin is wrapped on the core mold by special winding machine, which provides a certain tension and temperature. Then put them together into the mold to warm and pressurize the composite products.
Sheet molding (SMC) compound method
To tailor SMC sheet to product size, shape, thickness and so on. Then put multi-layered sheets into metal mold to heat and pressurize molding products.
Preformed blank molding
Put preformed billet with similar shape and size made of short cut fiber into the metal mold, then inject the prepared binder (resin mixture) into the mold to form at a certain temperature and pressure.
Directional auxiliary mold pressing
To lay the main stress direction of unidirectional prepreg products and mold them. The fiber content can reach up to 70%, which is suitable for products required high unidirectional strength.
Molding powder molding method
Molding powder mainly consists of resin, filler, curing agent, colorant and demoulding agent. The resins are mainly thermosetting resins, such as phenolic resin, epoxy resin, amino resin, etc.Thermoplastic resin, which is with high molecular weight, poor fluidity and high melting temperature not easy to inject and extrude can also be made into moulding powder
Adsorption preformed molding method
This method with low material cost, long chopped fibers possible used, suitable for complex shape, no problem to achieve automation, but high the equipment cost.
Bulk molding compound method(BMC)
Bulk molding compound (BMC) is a fiber reinforced thermosetting plastic usually made of unsaturated polyester resin, short fiber, filler and various additives, and is fully mixed into a group of prepreg. A low shrinkage additive is added to the BMC, which greatly improves the appearance of the BMC products.
Mat molding method
This method uses resin (mostly phenolic resin) to impregnate fiberglass mat then dries it as prepreg mat, tailor it into the desired shape, heat and press it inside the mold to form product. This method is suitable for forming large thin wall products with relatively simple shape and little change in single thickness.