Introduction and application of compression moulding

Compression moulding is a moulding method for composite materials. Usually the preheated moulding material is first placed in an open heated mould cavity. The mould uses a hydraulic press to force the material into contact with all mould areas while maintaining temperature and pressure until the moulding material is cured. The compression moulding method uses a thermosetting resin in a partial curing stage in the form of a pellet, a putty or a prepreg.

Compression moulding is a high-capacity, high-pressure method suitable for moulding complex high-strength glass fiber reinforced materials. Advanced composite thermoplastics can also be moulded using unidirectional tapes, woven fabrics, randomly oriented fiber mats, or chopped strands. The compression moulding advantage is that it can mould large, fairly complex parts. In addition, it is one of the lowest cost moulding methods compared to other methods such as transfer moulding and injection moulding. In addition, it wastes relatively little material, which has advantages when using expensive compounds. Compression moulding is also suitable for the production of very large parts. Materials for compression moulding include: polyester glass fiber resin (SMC / BMC), carbon fiber, etc.

Compression moulding is often used to make larger flat or moderately curved parts. This moulding method is widely used to make automotive parts such as covers, fenders, spoons, spoilers and smaller and more complex parts. The material to be moulded is positioned in the mould cavity, and the heated platen is closed by a hydraulic press. The bulk moulding compound (BMC) or sheet moulding compound (SMC) undergoes a curing reaction by applying pressure and heat. SMC moulding is usually cut to conform to the shape of the mould.

Thermoplastics are common in the mass production industry. For example, leading technologies in automotive applications are long fiber reinforced thermoplastics (LFT) and glass fiber mat reinforced thermoplastics (GMT).

In moulding, engineers should keep in mind six important factors:

• 1. moulding needs to determine the right amount of material.
• 2. Determine the minimum energy required to heat the material.
• 3. Determine the minimum time required to heat the material.
• 4. Determine the appropriate heating technique.
• 5. Predict the required pressure to ensure that the correct shape is reached during the compression moulding process.
• 6. After the material is compressed into the mould, design the mould for rapid cooling.

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