Sheet moulding compounds are transformed into finished parts by a processing technique known as compression moulding.These  techniques of compression  ensure part consistency within precise tolerance.A pre-weighted charge  of material is placed into a matched a  large press.The tool is heated up tp 140-165℃ depending on the formulation and other factors.Hydraulic rams then compress the material under a pressure of around 100 bar of projected area.It’s the combination of heat and pressure that softens the SMC/BMC and forces the material to flow throughout the mould cavity.

The curing agent within the compound is stable at room temperature but is activated by the heat of the mould.Cure time depends on the type of resin in the matrix,the level of curing agent and the thickness of the component.Thick sections take longer to heat through and can generate excessive exothermic temperatures,whcih is why tool temperature is generally lower and the moulding cycle longer for thicker part.Mould cycle time consequently depends on the size,thickness and complexity of the part,but a typical compression moulding cycle would be  below two minutes.When the cycle is complete the tool is opened and the part removed ready for finishing operations such as de-flaching,machining and painting.

                                    
 

ALICE CHEN

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