Plastics are quite unique materials in that it has a decent toughness but extremely low stiffness (On relative terms). This characteristic makes plastics difficult to machine and it is really uncharacteristic to machine plastics. They melt too soon, their thermal coefficient of strength is too low, they have very low stiffness and at times too soft. Even different plastics feel different when machining. Despite all these things, machining plastics makes a lot of sense in a lot of different places.
Why plastic machining?
When we need a plastic prototype, we usually go for 3D printing. When we need to produce plastic parts at scale, we go for Injection moulding. But we need to produce medium-sized parts in a limited production run, machining plastics makes a lot of economic sense. Injection moulding involves precise machining of Dies and jigs, so it makes no economic sense make fifty parts in Injection moulding. At the same time, 3D printing being adding layer after layer to produce a part, is just too slow to make fifty parts. Plastic machining makes the most sense. Machining plastics is also a perk when you need to produce detailed features in our part (Like precise holes, undercuts, etc). Machining plastics also can help us make parts with tolerances better than a 3D printed part. The mechanical properties of a machined plastic part are also much better than a 3D printed part even when using the same material. This is as a result of the way 3D printing works (Creating a part slowly layer after layer) and its strength is limited to a single axis.
When should you go for plastic machining?
When you need to:
- Produce parts for a limited production run.
- Produce parts that are larger than what is possible on Injection Moulding.
- Produce Structural parts.
- Parts made of plastics which is not possible to make in a 3D printer.
- Different varieties of features in the part.
- Fairly tight tolerances.
Things you should consider when going for Plastic machining
The machines for Plastic machining are fairly the same as the Metal machining machines. But the process which goes through is barely the same. What makes this even harder is that there are several types of plastics and all of them have different machining characteristics. One thing is plastic is easier to cut; they are soft. But that does not mean we can machine plastics fast. In fact, metals can be cut several times faster than plastics. It all has to do with its thermal properties. Unlike metals, plastics don’t hold up well when the temperature rises. There is almost a linear reduction in the strength of plastics as temperature increases.
Along with this, plastics have a low melting point too. So, when the tool is fed too fast, the entire part’s temperature rises creating major distortions and at the point of tool and part, plastics melt and create a mess. So, the feed rate is super slow elongating the machining by several times that of steel. The only good thing with plastic, from a machining perspective, is that the tool wear is very low. But, as always, “time is money” in machining. So plastic machining will be expensive. Thermal regulation – a fancy way of telling cooling - during plastic machining is extremely crucial. As a matter of fact, plastics machining has a special coolant. As I already mentioned, plastic’s mechanical properties don’t hold up with temperature. Sometimes, Air blasting is also done as a cooling measure. The part cannot be too small too. Because plastics are less stiff and machining causes micro-vibrations on the blank. If parts are too small, the vibrations will be rampant making the part a tolerance nightmare. Along with it, less the part size means lesser the thermal mass, so the blank can get heated quickly. So, the part must be large enough. The plastic must also be stiff enough. Because in order to machine, one has to clamp the blank tightly on a chuck or a vice. If the plastic is not stiff enough, the clamping force can deform the part contorting the shape of it. The DFM for plastic machining is fairly similar to that of conventional machining but not exactly the same. For one thing, in plastics, you cannot reach the ultra-tight tolerances of 5 microns or anything close to that because there are just too many problems and irregularities when machining plastics. Our best machines can do 15 microns, but that’s it.
Types of plastics that can be machined
- Flame Tec
- PTFE. Etc
Contemporary applications of plastic machining
As mentioned earlier, plastic machining is done only for limited production runs and prototypes. And so, in the contemporary machining industry, plastic machining is considered a niche and the industries utilizing them also quite niche. Some of the industries using plastic machining in abundance includes,
- Biomedical and Pharmaceutical devices
- Chemical handling
- Food Handling
- Semiconductor components, etc
Plastic Machining capability of CUSTIV
We, at CUSTIV, have access to over 20 Plastic machining facilities and can help you manufacture your plastic parts in the quickest possible least time and lowest feasible cost, for prototyping or scale, with the highest quality standards you can expect. We also provide a free DFM check for your Plastic machining designs.