Plastic machining services

Plastic as an industrial material has first appeared in our lives in the 1800s, when first Industrial Revolutions began to happen. Due to its convenience, it has rapidly spread and developed. Nowadays, we do not spend a single day without touching or using something made of plastic. Same things can be said about designing or manufacturing any product. You will definitely have parts that are made of plastic. Some product prototypes are wholly machined from a solid piece of plastic due to the fact that it is softer than metal and thus can be machined faster. That is why it is really worth it to know some nuances about plastic machining.

 Things you have to know about machining plastics

Plastics are valued because they have a bunch of useful properties: they are very lightweight, they are good insulators, they have a really good corrosion resistance, good surface finish is easily obtainable with them. That is the reason why they are so important in modern-day industry.

There are lots of different types of plastics and not all of them are good for machining. The main parameter here is viscosity. The more viscous a plastic is, the worse it is to machine it. It is quite logical if you think about it. As the material gets heated by the friction from the cutting tool, it gets even more viscous. As a result, cutting chips stick to the tool and cover its sharp cutting edges. So, if you want a machined plastic part, first of all, choose a harder type of plastic. Typically, all plastics are divided into three groups:

1. Soft plastics (polyethylene, polypropylene). Those are the worst to be machined as they are soft and get stuck on the tool;

2.Hard plastics (ABS, Polycarbonate, PPSF). Machining them is easier since they produce harder chips that are easily deleted from the cutting area;

3.Reinforced plastics. (They are composite materials, basically) Those are the hardest and the strongest among others. They are better than soft plastics but worse than hard ones because they are usually reinforced by some abrasive particles which dull the cutting tool really fast

Another important factor when we talk about polymers is its thermal expansion. It is 10 times that of a metal, which brings certain constrains in machining processes. Plastics have bad heat conductivity too. And, to add to the previous problems, they have a much lower melting temperature. All of that leads to a possibility of melting your stock while trying to machine it. You either have to use coolants and those are not always compatible with some plastic types or you have to modify the process. Some ways to avoid thermal expansion will be described later because they differ with the machining process.

Plastic milling

Polymers are usually milled on conventional metal milling centres. However, there are some nuances due to the plastics properties. They mostly concern fixtures and cutting tools. First of all, fixtures have to be adapted to have a larger contact area with the material since any plastic is much softer than metal and fixtures may leave considerable dents in the stock.   Now, the Cutting Tools  also have some peculiarities. First of all, it has to be much sharper than a conventional metal tool because plastics are much softer and if the tool is dull, you will basically deform the surface rather than cut it. Then, the tool has to be sharpened much more often because abrasive particles used for reinforcing engineering plastics dull the instrument that much faster than metals. You also have to use higher speeds because of the viscosity and to prevent overheating, use smaller tool feeds. That way chip size is smaller, as are cutting forces and friction. In some cases, gaseous coolants can be used to carry the heat away. 

Plastic turning

As it was with milling, you can turn plastics on a conventional Lathe that was designed for metal. The differences are all about the technological systems. First of all, the cutter is quite different. If you look at metal cutters, they are more like a sharpened block and that is understandable since cutting forces are large and it has to withstand them and be very rigid. When we cut plastic, the situation is different. The forces are much smaller and you have to make them so that the stock does not bend under the influence of the tool, and so is the hardness of the material. That is why the cutter has to be sharper and thinner. Plastic cutters look much more like knives compared to metal cutters. The tool for cutting the part off is different too. It has a sharp pointed edge in the center, whereas metal cut-off tool was just broad there because it would have broken right away otherwise. Now, as it was with the milling, cutting speeds are much higher, again, because of viscosity and feeds are smaller due to low heat conductivity and high thermal expansion. If you want to use a coolant, best of all, use something neutral like compressed air because that way your stock won’t form a chemical reaction with the oils in the coolant fluid.

 Plastic Drilling

Drilling plastics can be a hassle due to the fact that heat generation happens inside the stock and the contact area is much higher than when milling or turning. Internal heating may lead to additional stresses inside the part which in turn may cause warping and deformations. That is why in case of drilling, cooling is most important. If you have a drill with internal cooling passages, it will greatly ease the process. In any case, you should choose a drill with a thin bridge (its diameter in the middle) and sharpen it because dull instrument increases internal stress as well, a dull drill has an increased friction parameter as well, which is bad for the process as it builds up more heat. It is recommended to withdraw the drill as often as possible to cool it and to withdraw chip. It is recommended to avoid manual feed because any instability in the process may result in the drill being caught inside the stock and cracking it.

Conclusion

As you can see, machining plastic has a lot of nuances. And if you are not well acquainted with manufacturing technology, it is recommended that you use professional Plastic Machining Services  which are numerous everywhere due to the widespread use of plastic everywhere and the fact that they can be united with metal machining.