What is Compression Moulding?
Compression moulding is the process where a heated rubber material is placed in one side of a mould, then the other side of the mould is clamped down, and the rubber material is compressed into the desired shape. The mould must also be heated, as the combined compression and heat is what causes the rubber to take its new shape. The mould also has to be designed to meet certain accommodations. For example, the mould needs to have overflow grooves built into it. Since it is difficult to accurately predict the amount of rubber material needed without any overflow, it is better to error on the safe side and use a little extra material to ensure the mould is filled and the piece is moulded correctly. This means that every piece will have flash that needs to be trimmed.
Benefits of Compression Moulding
One of the biggest benefits of compression moulding is cost. Compared to other processes like plastic injection moulding, creating a mould is a lot cheaper. (Obviously this is a comparison of a rubber manufacturing process to a plastic manufacturing process – not apples-to-apples – but it’s just for the relative comparison). When creating a mould for compression moulding, you don’t have to worry about creating gates and runners. You also won’t need to complete a mould flow analysis.
Second, it is cheaper and easier to create larger parts. Generally, with other manufacturing processes, it gets significantly more expensive as part size increases. For example, with plastic injection moulding, not only do you need to create a larger mould, but you also need to increase the total clamp force a machine can produce. With compression moulding, you don’t need to significantly increase the pressure of the machine when you make larger parts.
The thickness of parts can vary quite a bit – you can easily produce parts that are between 1.3 mm thick to 1 inch. You are also able to get seamless design features with compression moulding – you don’t have to worry about the flow lines or knit lines that may appear in injection moulding.
Disadvantages of Compression Moulding
One of the issues with compression moulding is the long cycle times. One cycle can take up to several minutes as a technician has to manually place the material into the mould, heat it up, apply pressure and then wait for the mould to cool off enough to remove the part.Parts require additional work after they are moulded. By the very nature of compression moulding, parts will have flash, so there is an additional step of removing the flash.
Another issue is that compression moulding isn’t the best choice for complex designs. Simple designs can be easily filled, but complex designs can leave sections underfilled.
Process for Compression Moulding
Our instant plastic injection moulding quotation team and mould frame sharing technology enables us to simplify and shorten both the quoting and tooling manufacturing process for custom plastic injection moulding.
1. Load your 3D CAD file to get your mould and part quote.
2. Add your requirements for inserts in the comments, and your project manager will contact you.
3. Upon order confirmation, we start the mould and part order process
4. Tooling design review by our engineers
5. Upon design approval, we begins building your injection mould
6. Customer examines samples for approval
7. Part production begins