The basics of CNC plastic machining tips
Why are plastics so popular? Ever since the invention of industrial-grade polymers, the invasion of plastics in all branches of modern industry has been unstoppable. There are many reasons for this. I will only list three main reasons. Plastic parts are cheap, lightweight and durable. Let’s talk about the first point here. Cheap means that the cost of making them is much lower than that of metal parts.
There are many ways to produce high-precision plastic parts. Modern industrial-grade plastics are cast, injection molded, printed or machined. The first three options are well suited for making parts with complex geometries with excellent surface finish. However, when you need to achieve tight tolerances or produce a mirror-like surface finish on almost any type of part, nothing is better than machining. About 80% of plastic parts are CNC milled. This is the most widespread method used to make parts without rotating axes. All the rest are usually turned on lathes. To achieve an excellent surface finish, CNC-machined parts are polished or chemically treated.
Plastic Processing Tips
1.Machinery and Equipment
First, let’s make something clear. There are no plastic CNC machines. Virtually all machine tools used to cut plastics are metalworking tools. Their precise rigidity and power output allow them to easily machine even hardened plastics. I would like to point out that woodworking machines are less rigid and therefore do not work as well.
2.Machining tools
Choosing the best cutting tool for plastic parts is a complex task. The reason for this is that the composition of plastics, as well as composite materials, varies greatly. Some plastics are reinforced with hard carbide particles or have some additives that increase flexibility, heat resistance or other parameters. All this changes the way the plastic reacts to machinery. Even the colorant of the material is important, because depending on its type, during machining, due to a lot of heating, the hue may change.
Having said that, it is obvious that it is necessary to choose the right cutting tool geometry for the plastic parts being machined. For example, a milling cutter is similar to an aluminum milling cutter with two grooves, however, the sharp edges have a sharper angle. The same can be said about drills. Their main angle (120 degrees for metal) becomes only 60 degrees. In this way, the chips are smaller and can be removed more easily. However, you cannot use such a drill on metal. It will break in a few minutes.
3.Clamping of parts
When clamping plastic blocks, it is important to remember. Plastic is not metal. If you clamp the blank with too much force, it is easy to leave large marks on the surface. In fact, if you use too much force, the part may break. If you want to avoid leaving marks 100%, it is recommended to use special spacers made of softer materials between the fixture and the part. Another issue is the rigidity of the part. For example, if you are drilling a fairly large part (think of a laptop case). You need to pay close attention to the distance of the drilling position from the fixture. During this process, the drill will try to pull the part up along its slot, and if the fixture is too far away, the drill will succeed. It will bend the part, or it may actually tear the part from the fixture.
4.Cutting parameters
Let’s take the example of CNC milling a plastic shell to look at the selection of plastic cutting processes. The main problem you must pay attention to is excessive friction and plastic deformation of the part, not cutting. To avoid the second problem, always keep the cutter sharp, and if the material you are using is not strong enough, freeze it. Plastics become hard and brittle at low temperatures.
To prevent chips from melting into the CNC machined part, you need to keep the tool moving and prevent it from staying in one position for too long, remove the chips as soon as possible. When the feed rate is large, the spindle speed must also be fast. A rough estimate is about 3 times the aluminum feed rate, with corresponding cutting speeds.
Plastic processing services are closely related to CNC prototype making technology. Polymer materials are very suitable for prototype making and engineering verification. The reason is that plastics are actually very easy to process. If you don’t have any heating or forming equipment, then making parts from CNC plastic blocks is a good way to get these prototypes conveniently and quickly. You can use the same widely used equipment as you do for processing metals, so you have great flexibility. Cutting speeds and feed rates will be faster, so delivery times are shorter, and there is an opportunity to test your product samples faster and bring them to market earlier than your competitors.