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Your complete guide to compression moulding
Compression moulding is an excellent option for your new or upgraded product line. It’s widely used for strong, heat-resistant components. But whether it’s right for you depends on what you need your component to do.
This page contains a complete guide to what compression moulding is, how it works, when to use it, and how to decide if it’s the right manufacturing method for your parts.
What is compression moulding?
Compression moulding is a manufacturing process in which a measured amount of material is placed into a heated mould cavity. The mould then presses the material under pressure, causing it to flow and then chemically harden through cross-linking (when heat causes a plastic’s molecules to bond into a fixed network), permanently setting its shape.
The compression moulding process is especially effective for producing strong, intricate, heat-resistant plastic and composite parts. Manufacturers usually use thermoset plastics and composites for compression moulding, as these permanently harden (through cross-linking) during curing to provide excellent rigidity and stability.
How the compression moulding process works
Although specific manufacturers may use slightly different equipment and materials, the basic steps of compression moulding are as follows:
- A precise amount of moulding material (called a charge) is placed into a heated mould.
- The mould closes and pressure forces the material to flow and fill the cavity.
- The heat triggers curing and cross-linking, which permanently hardens the material.
- The mould opens and the finished part is removed.
The industrial presses used in compression moulding can apply extremely high force. For example, our highest-pressure units have a 450‑tonne clamp capacity. You don’t always need that much pressure (our lowest-pressure presses start at 20 tonnes).
Regardless, high pressure is important to ensure the material fully fills the mould and forms with consistent density. The result is a series of uniform parts with fewer internal stress points or defects.
What materials can you use in compression moulding?
Compression moulding most commonly uses thermoset plastics or fibre-reinforced thermoset composites:
- Thermosets are widely used because once they cure, they can’t be remelted. This permanent chemical change gives them excellent heat resistance, rigidity and dimensional stability, even under long-term load or high temperatures. Common thermoset resins include epoxy, phenolic, polyester, melamine, urea-formaldehyde, polyurethane and vinyl ester.
- Reinforced composites combine a thermoset resin (discussed above) with strengthening glass or carbon fibres. These fibres add stiffness, strength and impact resistance while keeping the weight relatively low. Typical compression-moulded composites include SMC ( fibre reinforced sheet) and BMC (fibre reinforced paste).
In some applications, you can also use elastomers in compression moulding to form rubber or rubber-based seals and gaskets. This depends on the manufacturer’s setup.
Why choose compression moulding?
Some of the key benefits of using compression moulding include the following:
- Dimensional stability – your finished parts resist warping, shrinking, or expanding under heat or stress.
- High strength and durability – compression-moulded components can withstand heavy use and harsh environments.
- Lower tooling cost – moulds are typically simpler and cheaper than those used in injection moulding, which can make the process cost-effective for certain production volumes.
- Material efficiency – because the material is placed directly into the mould, there’s less waste than processes that use runners or gates.
- Metal replacement potential – compression moulding can produce high-strength parts capable of replacing some metal components in structural applications.
Although compression moulding is a great option, it isn’t the best choice for every product or application. In general, it’s often the best option when your part needs one or more of the following:
- Heat resistance
- Mechanical strength
- Fire performance compliance
- Dimensional stability
- Large or thick geometries
These properties are why it’s widely used for applications such as electrical housings, rail components and structural parts. It’s also particularly useful for large or complex shapes.
Limitations to consider
Compression moulding is excellent for the applications we’ve mentioned so far. However, it’s important to consider its trade-offs, too. It might be that other production methods, such as injection moulding, are more appropriate.
Compression moulding cycles tend to be slower than other moulding methods. As such, it isn’t always suitable for very large production runs, which may be better suited to injection moulding.
The moulding process itself is often better suited to simpler geometries rather than highly intricate designs. Injection moulding may be able to produce a more detailed plastic component.
In general, if you need very high volumes of small plastic parts, injection moulding might be the best options. But, if you need large, strong, heat-resistant components, compression moulding is the way to go.
Choosing the right compression moulding partner
Even when it’s obvious that compression moulding is the right production method, it’s still important to find the best production partner. You need a company with material expertise, tooling quality, precise process control and scalable production capability.
That’s where Talisman Group comes in. We operate multiple UK facilities and offer moulding capacity ranging from small precision parts through to large components weighing over 10 kg each. With advanced presses and in-house tooling, we can make sure you get consistent, repeatable results across multiple production runs.
To learn more about how we’ve aided clients in the electronics, fluid transfer, rail, automotive and other specialist engineering sectors, or to book a consultation, get in touch with our expert team today.