Milling Plexiglas – Recommendations for optimum processing

1. origin and fields of application of Plexiglas

The plastic polymethyl methacrylate (PMMA) was first produced around 1933 and is considered to be the first acrylic glass in the world and was subsequently given the brand name Plexiglas. Plexiglas or acrylic glass sheets are available from us in colourless and coloured versions and are characterised by either a glossy, structured or matt surface of the material. Due to our wide range of designs, Plexiglas offers many processing possibilities, especially for creative users. In the industrial sector, our Plexiglas products are used for applications such as building glazing, advertising, trade fair construction, furniture manufacturing and many other areas. But also in the craft industry and among private craftsmen our Plexiglas blanks are a popular material for many applications – from simple handicrafts to complex terrace roofing.

2. characteristics of different types of Plexiglas

We distinguish between two different types of production of plexiglass and acrylic glass. The Plexiglas version GS (cast production) is mainly used for the production of solid plates, blocks, tubes or rods. The XT variant of Plexiglas is produced by our teams using an extrusion process and is also available in the form of solid sheets, tubes, rods, as well as structural sheets, mirror sheets, corrugated sheets and multi-skin sheets. The two Plexiglas types differ particularly in the material thickness, whereby we attribute a much greater thickness tolerance to the XT model than to the alternative product GS. However, our plastic sheets of the Plexiglas type GS compensate for the lower thickness with a much better surface quality and a lower risk of stress cracking.

3. our processing of plexiglas/acrylic glass by CNC milling

Plexiglas can be processed industrially as well as for private use in many different ways. In addition to the professional CNC milling of Plexiglas or acrylic glass, the plastics turning shop K&B also processes the corresponding material by turning, drilling or injection moulding. However, our most frequently used method is CNC milling of Plexiglas, as the plastic is excellently suited for this type of processing and almost any contour can be achieved with our CNC milling machines. The material products of our milling cutters are extremely precise and are highly attractive in terms of price, especially in higher quantities. If complex shapes and low tolerances are required, our CNC milling cutters for the processing of plexiglass or acrylic glass are currently the ultimate. Before the actual machining process, we write an appropriate program for the milling cutter, whereby the subsequent computer-aided shaping is carried out by the CNC milling cutter with maximum precision. Our plastic turning shop uses various milling cutters with special grindings for the versatile CNC milling of plastic.

4. recommendations for action and criteria for milling Plexiglas

Plexiglas is not always the same, especially when it comes to further processing with a milling machine. With Plexiglas or acrylic glass, there are only a few plastics that can be milled without cooling, for example. Here price and quality correlate very strongly with each other, since the milling of the cheapest Plexiglas usually also involves the greatest loss of quality. It is important for a reasonable result when milling not to buy the cheapest Plexiglas product on the market.

4.1 Criteria for milling without cooling

As already mentioned, there are only a few Plexiglas grades that can be machined without cooling in contact with CNC milling. The worst thing that can happen when milling plexiglass or acrylic glass is that the material is heated too much, caused by a milling machine that has become too hot. As a result, the plastics can melt and Plexiglas bonding can occur on the tool due to the contact between the plastics and the cutting edges of the milling cutter. A tool breakage within the CNC-milling can be the bitter consequence in case of non-observance. Only the right choice of milling cutter, feed rate, infeed and speed makes it possible for us not to have to use an additional Plexiglas cooling system.

4.2 Milling Plexiglas using cooling

In order to completely eliminate the risk of tool breakage during CNC milling, we usually use spray mist cooling for milling. The cooling prevents excessive heat development on the milling cutter during the processing of plexiglass or acrylic glass and also increases the service life of our milling cutters. By increasing the feed and speed as well as the depth of feed, we can save a lot of time, especially with coarse milling of plexiglass or acrylic glass. To achieve this, it is necessary to use additional cooling to avoid excessive heat stress on the CNC milling machines. Compared to frequent quality losses of Plexiglas as well as tool breakages within the milling cutters, it is also much more efficient to consider the use of professional spray mist cooling for the processing of such materials.

4.3 Review: Important aspects for milling Plexiglas and similar plastics

When processing plastic by milling, a number of criteria must be observed which have a significant effect on the quality and optical properties of the Plexiglas products.
First of all, when clamping the Plexiglas sheets, we make sure that the material is as stress-free as possible so that subsequent products are also free of distortion. In addition, the following applies to the cutting edges of our CNC milling cutters: the sharper, the better! Especially when milling soft plastics, it is difficult to achieve an immaculate result if the CNC milling cutters do not work with the highest degree of sharpness. In addition to the already mentioned cooling of the milling cutter, we use the lowest possible speeds for CNC milling of plastics, so that the temperature at the infeed point is kept additionally low. Finally, we recommend deburring the material after milling, as sharp edges often appear on the plexiglass or acrylic glass in contact with the CNC milling machine, which pose a risk of injury to employees.
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