Process Spotlight: Compression Molding
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When it comes to manufacturing a product or component, you will normally have a number of different options available to you regarding how you want to go forward. This is particularly true with plastics, for which there are a number of different molding options – each with their own pros and cons. You have transfer molding, injection molding and compression molding.
In this post, we’ll be shining our spotlight on compression molding to see precisely how this process works, and which scenarios it is best for specifically.
The Process
Compression molding, as the name suggests, is a molding process that utilizes the power of compression to create a certain shape or design from plastic. It involves the use of two halves of a mold which are pressed together with enough pressure to force the thermostat resins inside to take on their shape.
Basically then, the thermostat resins – in the form of granules, sheets or ‘preforms’ – will be placed into a preheated mold, which will then be heated further as pressure is applied to force the material into all the corners and contours of the mold. The resin is then left to cool and harden and once this process is complete, it can be removed from the mold. A durometer can be used to measure the durability of the finished product.
To imagine how this might work, imagine taking some playdough and then squashing it against the table with a small egg cup. The playdough would of course take on the domed shape of the inside of the egg cup, and this is essentially how the process of compression molding works too. This is in contrast to injection molding, which works by piping the resin into a closed mold for it to fill out all the internal space.
There are many applications for compression molding which is mostly suited to making large and relatively intricate parts. It can be seen used commonly in soft plastic and rubber products such as bottle caps, mechanical parts, rubber car mats, wellington boots, buckets, plastic crockery, knobs and handles.
Advantages and Disadvantages
There are many benefits to using compression molding, the first being that the lower cost of the molds makes compression molding suitable for producing shorter runs and for lower budgets. This is further aided by the minimal amount of waste material created by the process and by its simplicity, which can help to keep labor costs down.
Unfortunately though there are also downsides that prevent compression molding from being suitable in every situation. For one, compression molding is only possible with certain materials meaning that it can’t be used unless you want to create something with a soft plastic/rubber-like appearance and feel.
Compression molding is also considerably slower than injection molding and other techniques, and results in lower product consistency. If it is very important that your end product have high dimensional tolerance – then this may not be the right method for you. This can be improved by using more expensive sheet molding compounds versus bulk molding compounds, but it will still be less accurate than other common processes.
Compression molding can be used for fairly intricate parts, but particularly small and delicate elements may be troublesome and the mold can’t include undercuts. For very small parts the deflashing process may be difficult and require specific techniques such as ‘cryogenic’ deflashing.
Conclusion
Obviously, compression molding is not for everyone, but as an affordable and simple method for creating high volumes of products at low cost, it is a great option. As a hardware startup, it’s your job to assess these pros and cons and to consider how they relate to your specific requirements and specifications. Remember that you can always use different techniques for different components of your product.
Let us know what you think of compression molding and of your own experiences, if any, in the comments. And of course, subscribe to the email newsletters if you want to learn more about other manufacturing processes.
