When talking about machining most people think about milling steel or turning wood blocks. On the other hand, the development of material sciences and technologies of polymers/plastics leads to situations when those materials can be used in place of metal in many applications.
Polymers are taking the place of alloys in applications that require low mass and cost of manufacturing but not high mechanical rigidity. That is why milling – traditional and CNC – of polymers and plastics allows faster production of high-quality parts for many industries.
What is polymer milling?
Plastics (also called 'polymers') milling is a method of machining used to manufacture parts out of blocks of a vast variety of polymer types. Just like in machining alloys (steel, aluminum) or other materials – such processing can be performed with traditional and CNC mills (to deliver very tight tolerances of machine plastic parts).
Polymers milling is a type of removal treatment – the final part or element is lighter than the initial block of material. On the contrary 3D printing or injection molding – is focused on additive processing.Although the technology of polymer milling is similar to alloy machining, plastics require the usage of different tools and machining techniques.
First of all: plastics have very low thermal dispersion during processing. That is why the machining of these materials requires high-efficiency heat removal systems and a good suction hood for chips and shavings.
High temperatures during machining plastics can lead to sticking chips to the cutting tool and as a result – decrease the quality of the machined surface, especially due to thermal deformations.
For these reasons, to machine polymers the most efficient technique is up-cut milling – chips are removed by cutters away from the processed surface, in the direction of not yet milled parts. The reason for that type of processing is simple: hot chips can transfer heat to the machined surface and cause thermal deformations on the surface of plastic material. It is not as important in the roughing cuts, but in the finishing milling can cause mentioned problems.
In some applications, when up-cut milling is impossible, the alternatives are the usage of specialized cutters (with proper geometry) or a very efficient chip removal system. On the other hand – technique and cutting tools should be tailored to the selected type of polymer.
Head cutters for the polymers and plastics milling are usually made of carbide monolith and work with geometry tailored for the machined material. Such combinations can improve the quality of shaping polymers and chip removal (especially for cutters with big chip holes).
Technology-wise the best effects of that process can be delivered by a combination of high routing speeds of the milling machine spindle and medium feed rate. It is worth mentioning the flat surfaces of plastics are best to machine with frontal milling than the cylindrical ones – contrary to wood.
Such parameters can help to deliver the best effects of work and increase the manufacturing of precision parts. They are even more important in CNC plastic milling (numerically controlled) – the automatization of that process allows to speed up parts manufacturing. On the other hand: requires from the operator more attention to details and programming devices.
Polymers and plastics machining: what are applications?
When discussing applications of polymers in industries as a material for parts production it is crucial to focus on the mechanical parameters of that material. Contemporary technologies of polymer manufacturing allow the production of material with good enough rigidity, thermal, and wear resistance to replace – in some applications – some of the alloy parts.
Combined with other advantages of plastic components like lower mass and price of manufacturing make that material perfect for many applications, especially less demanding.
Especially when a high strength or very high chemical resistance is not crucial.
On top of that – the usage of milled polymer parts can lead to real savings.
The advantages mentioned above are connected to the strong sides of contemporary plastics, like:
- low mass,
- decent mechanical and thermal rigidity,
- good enough impact resistance,
- ease of machining,
- good dimensional stability,
- high resistance to many chemicals,
- low electrical conductivity,
- relatively low price of material,
- vast selection of many types of polymers that differ in properties and can be easily fitted to many applications.
Of course – polymers and plastics are not flawless, perfect for any application.
It is worth mentioning the disadvantages of these materials:
- lover mechanical rigidity and higher susceptibility to wear,
- lover stiffness,
- lover resistance to high temperatures.
What is important: these are features of modern polymers.
Particular types can and will differ in parameters (eg. polyoxymethylene has very good thermal and mechanical resistance; similar, but not identical polycaprolactam – not). That is why the selection of the right polymer should be combined with in-depth knowledge of the environment in which the part made will be placed.
As mentioned – the vast variety of polymer types makes plastics machining easier and their advantages make them a perfect material to produce parts like:
- lightweight gears, often monolithic,
- wide range of pins and bushings,
- parts of devices housings,
- a vast variety of racks and grilles.
Parts milled from plastics and polymers are often used in many industries – from toys and smaller construction elements to bigger and smaller elements in the automotive industries or medical devices.
Milling polymers, especially numerically controlled, allows speed up the production, delivers higher quality parts due to lover tolerances, and decreases the unit cost.
Types of plastics for the CNC machining
The development of the material sciences and industrial chemistry created many new possibilities for the usage of plastics. The vast range of polymers with different properties and features makes the selection of the right material for a particular application easier.
Many types of polymers will suit better in different applications – finding the perfect material for the job can be (sometimes) problematic.In some applications more important will be abrasive resistance and the best possible stiffness; in others – flexibility with good high-temperature tolerances.
Among many types of polymers, it is worth mentioning the most often used in CNC plastics machining are:
- high-performance polymers (e.g. PEI – polyetherimide or PAI – polyamideimide), with very good mechanical properties and high abrasion resistance,
- polyoxymethylene (POM) is – a very popular polymer for construction and less exposed frames, with good stiffness and abrasion resistance is often used in the automotive industry,
- polycaprolactam (PA-6) – material very easy in machining, but with less than average mechanical properties. On the other hand – electrically insulative. Very often used in manufacturing small parts for electrical devices,
- acrylic glass (PMMA, often called 'plexiglass') – transparent polymer, often used as a cheaper alternative for a sheet of glass (eg. as covers or front for frames) with good enough mechanical parameters and very good UV resistance,
- Teflon PTFE (polytetrafluoroethylene) – good mechanical parameters, high melting point, or good temperature resistance make that material popular for machining shops and plants.
Selection of the right polymer to mill parts can be challenging, yet is very important. Propper plastic can help to decrease the cost of production and produce parts with parameters much more appropriate for the application. For example – not every transparent cover should be made out of glass or expensive polycarbonate; in many applications, cheaper acrylic glass will be enough.
In the process of selecting the right material for plastic milling, it is worth contacting a team of professional CNC machining plants. Their knowledge of the material science and CNC machining process will help to find the right material for the job and deliver the highest quality parts.
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At RADMOT, we can offer CNC milling services, CNC turning services as well as many additional services, including washing, aluminum anodizing, laser marking and assembly.
Contact us and tell us what you need. We have been providing CNC services for almost 40 years. Our quote is completely free. And if you are in doubt about which technology will work best for you, we are able to advise customers from many industries on machining and quickly determine the price of machining the parts you order - our expertise is at your disposal.