Injection moulding process
 

When technical components are required in large quantities, injection moulding technology is of considerable economic advantage. Particularly in the case of high-performance plastics, injection moulding can also be economical for smaller quantities (from 500 to 1000 units) due to the potential material savings.

Another advantage of injection moulding technology is the possibility of flow path design, which can be used to align the material properties under certain conditions. In addition, a complex geometry, for example, can be produced economically in larger quantities using an appropriate mould.

However, there are some restrictions that need to be taken into account. Firstly, only thermoplastically processable plastics can be used in injection moulding; the injection moulding of PTFE, PI and PBI is therefore not possible. We only process selected high-performance plastics and offer injection moulded parts made of Victrex® PEEK™ and Torlon® and. In particular, we specialise in the processing of Torlon® (PAI).

When selecting the injection moulding technology, it should be borne in mind that a mould is always required that can cost several tens of thousands of euros, depending on its complexity. With such values, a certain minimum production quantity is required in order to be able to distribute the costs reasonably.

In addition, there are some technical restrictions regarding the component design. Certain wall cross-section and flow path length ratios are required for injection moulding.

Due to the high viscosity, injection moulded parts made of Torlon® should not have a wall thickness of less than 1.5 mm. When using unreinforced Victrex® PEEK™, wall thicknesses of one millimetre are also possible. For wall thicknesses of more than 10 mm, ribs must be provided to avoid sink marks.

Due to their generally high thermal expansion, injection-moulded plastics sometimes shrink (shrink) considerably when they cool down. High-performance plastics, however, exhibit only minimal shrinkage. Victrex® PEEK™ has shrinkage values of less than 2.5% Torlon® even only one per cent or less. Shrinkage is generally slightly lower in the direction of flow than at right angles to it. Sufficient bevels (approx. 2°) must therefore be provided in the design so that the component can be removed from the mould without any problems.undercuts, inserts, clips and other design elements are generally possible with appropriate moulds. However, the actual feasibility depends on various factors and should therefore be checked on a case-by-case basis.

Due to the poorer viscosity of high-performance plastics, especially Torlon®, it is essential to ensure that the melt flows together in the cavity. The flow fronts that form during injection often bond poorly and therefore represent potential breakage points.

These few notes make it clear that the special features and requirements of the processing method must be taken into account when designing injection moulded components. It is generally not possible to switch between processing methods without making design changes.