Plastic machining is not an easy task. Plastic as a material is known for being easy to change its shape, its size, a whole lot more when you try to work with it. It can chip or melt while you are trying to cut it, it can crack if you try to decrease it, a whole lot of things can go wrong. There is a large range of problems and strange behaviours that can come with nylon machining. Each plastic has it’s own unique way of which you must work with it, so below is a brief guide on things you should know if you are already or considering working with plastic.
The first factor is thermal expansion. This is basically the term used for something that grows when heat is applied to it. This is not something you will see when machining metals, plastics on the other hand, can expand a lot. Some plastics can expand five times the rate of metals and more. A great example of this is aluminum and UHMW. UHMW otherwise known as ultra high molecular weight polyethylene will expand up to 10 times the amount that aluminum would when exposed to the same temperature.
Another thing you may not is that some plastic absorbs moisture. This is another factor that could affect your plastic as it can make it grow larger in size. People in the nylon machining industry know about this. Machining plastic nylon can be tricky and if you don’t know about the moisture absorption properties, all your efforts can go to waste. The best way to avoid this is to keep your products in an air conditioned room or you can seal them in a plastic bag that gives a little moisture transfer.
The process that is machining plastic can produce residual stress on your product. The cooling process is difficult as the outside cools much faster than the inside which can really stress the surface. You can easily deform your material when you try to remove it. You can easily avoid this by using a stress-relived plastic stock or by using an annealing oven.
Some plastics can also have a reaction to chemicals which you may or may not be aware of. Most materials can resist chemicals at room temperature but if you raise the temperature even a little bit, this can cause the material to easily crack. One very common reaction that happens is when you have a product made from acrylic or poly-carbonate plastic and you try to clean it using acetone this can cause the plastic to crack.
Like with any plastic material you have to be careful when it comes to work-holding as plastic is much softer than most other materials. It can easily be deformed if it is clamped down on too hard. Most manufacturers will usually make their own soft jaws from softer plastic materials which you can also adjust according to your needs. The most important tip to remember is that you don’t use the same cutting forces that you use with metal so you don’t need to clamp down as hard.
Plastics do not work the same way as metals, that is why most people who come from a metal industry background are so against working with plastics. They are challenging and the process can change a lot. One lot of material can work out perfectly fine, but the next batch might not turn out quite the same. There is a lot of cleaning machines in between use and a lot of trail and error. One thing is for sure, plastics are part of our everyday life, we use them for so many different things and every day we find a new and innovative way to use it.