Machining technology

Depending on the material, the machining technology for plastics can ensure extremely tight component tolerances. For this reason, injection-molded or pressed components are sometimes reworked by machining.

Another advantage of the machining technology is the ability to produce components with large wall thicknesses. Pieces with cross-section of several centimeters thickness can also be produced this way. Even undercuts, metal inserts and complex boreholes that are subsequently resealed are technically possible.

The extruded or pressed semi-finished products required for machining also have usually have better mechanical properties than the granulates used by injection molding. Due to the nature of the process, injection moldable plastics require an lower viscosity and generally have a lower degree of crystallization. Extruded semi-finished products often show significantly better properties here. Direct comparisons have shown that, for example, plain bearings turned from semi-finished products have a 30 to 40 percent longer service life than the comparable injection-molded version.

In the case of high-performance plastics, which often cost more than fifty euros per kilogram, a combination of machining and injection molding technology is also possible: in order to to save high material and tooling costs, a simple blank is produced using the injection molding process. The items is subsequently brought into shape and tolerance by machining so that the advantages of both processing methods are optimally combined.

Although the machining technology allows a relatively free design, there are also some restrictions to be observed here.

Basically, the surfaces achieved during machining are worse than with injection molding or compression molding technology. Roughness values from Rz 10 to 6.3 are possible. Particularly high-quality surfaces (less than Rz 6.3) are only possible through complex mechanical, partly manual processes (grinding, polishing, lapping etc.) to achieve, which significantly increase processing costs.

Machined plastic components must always be made from appropriately sized semi-finished pieces. There is a risk that the machining process may cause material stresses. In the worst case, the component will become extremely distorted. Even after weeks, strong dimensional changes in size and shape can occur, especially under the influence of temperature. Such stress-related changes can be reduced to a minimum through a complex machining process with idle times and/or thermal intermediate treatment.

Taking into account all aspects of component design is difficult and time-consuming and should therefore only be carried out by designers who are experienced with plastics. POLYTRON will help you with the plastic-compatible design of your components - just contact us!