In compression molding, two matching mold halves are installed in a press (usually hydraulic), and their movement is limited to an axis perpendicular to the plane of the mold. The mixture of resin, filler, reinforcing material, curing agent, etc. is pressed and cured in the state that it fills the entire cavity of the molding die. This process is often associated with multiple materials, including:
Epoxy resin prepreg continuous fiber
Sheet molding compound (SMC)
Dumpling model material (DMC)
Bulk Molding Compound (BMC)
Glass mat thermoplastic (GMT)
Compression molding steps
1. Preparation of molding materials
Generally, powdered or granular molding materials are put into the cavity, but if the production volume is large, pretreatment is usually advantageous.
2. Preheating of molding materials
By heating the molding material in advance, the molded product can be uniformly cured, and the molding cycle can be shortened. In addition, since the molding pressure can be reduced, it also has the effect of preventing damage to the insert and the mold. Hot air circulation dryers are also used for preheating, but high frequency preheaters are widely used.
3. Molding operation
After the molding material is put into the mold, the material is first softened and fully flowed under low pressure. After exhausting, the mold is closed and pressurized again to cure for a predetermined time.
<Note>
Unsaturated polyester and epoxy resins that do not generate gas do not require exhaust.
When degassing is required, the scheduling time should be controlled. If the time is earlier, the amount of released gas is small, and a large amount of gas will be sealed in the product, which may generate bubbles on the molding surface. If the time is late, the gas has been trapped in the partially cured product, it is difficult to escape, and may cause cracks in the molded product.
For thick-walled products, the curing time will be very long, but if the curing is not complete, bubbles may be generated on the molding surface, and defective products may be produced due to deformation or post-shrinkage.
Post time: Apr-15-2021