Compression Moulding – Q and A

1. What is compression moulding?

Compression moulding is a manufacturing process that uses composite raw materials to produce a finished component through a moulding press. There are a wide variety of processing techniques to manufacture composite components and compression moulding uses heat and the application of pressure to produce robust, repeatable parts with relatively low cycle times.

2. What raw materials are used in the compression moulding process?

Sheet moulding compound is predominantly used as the raw material for compression moulding. Sheet moulding compound (SMC) consists of chopped glass fibre reinforcing strands, fillers, pigments, additives and resin in the form of a matt.

3. What type of products can be created?

The moulding process is ideally suited to products that require certain characteristics including:

• Unique design features – including bosses, stiffeners, brackets, alignments, locations etc.

• One piece mould production

• Low unit cost

• A tailored material specification

• Strong fatigue performance

• Corrosion resistant

• Lightweight

• Robust and durable

• Excellent strength to weight ratio

• Excellent acoustic and thermal performance

Current production includes automotive parts, engine covers, forklift truck panels, vending machine doors, and products for the construction industry, enclosures and more.

4. Briefly describe the process

The process involves a large closed moulding press. The press holds a removable male and female tool -milled from P-20 grade solid steel.

The sheet moulding compound charge is inserted into the open press after being weighed and located. The press is then closed and applies the pre-arranged optimum tonnage as well as heating the mould tool with steam to a pre-arrange temperature. This combination of pressure and heat allows the SMC material to flow into the cavity of the tool forming the part shape.

The moulding cycle then continues (usually between 2 and 7 minutes), the press opens, and the finished part can be removed by hand or by robot.

Depending on the composite design, the part may just need to be ‘de-flashed’ where excess material is cut from the outside edges of the part or it may require specialised trimming.

Parts can be robotically transferred to CNC trimming centres where a programme is activated to precisely trim features out of the part.

Parts can also be painted and sub component assembly may take place – for example, bonding of rubber seals, attaching brackets, clips, latches, hinges, glass etc.

5. What are the advantages over other manufacturing techniques?

Compression moulding can provide a range of benefits when moulding composite components such as good part to part repeatability, low unit cost, reduced cycle time of parts, ability to add more design features than other processes, good A and B surface finish, excellent dimensional stability and the ability to mould large and complex parts with very little material wastage.

6. Are specialised compression moulding machines required?

Each machine is built to order and very much depends on the experience of the company and the intended use of the machine. Features including the tonnage and platen size are also flexible. The platen size determines how large the mould tools can be and therefore dictates the maximum part size that can be manufactured by a press.

For example, ‘Active parallel control’ is a feature in a compression moulding press that measures the tonnage applied to all four corners of the press during the moulding cycle. When the raw material begins to flow within the mould cavity the press can detect the corners which require more or less pressure to maintain an even flow of material which ultimately gives higher quality parts with a superior surface finish.


Post time: 12-17-2016