INJECTION MOLDING
Injection molding
When technical components are required in large quantities, the injection molding technology is economically of considerable advantage. Particularly in the case of high-performance plastics, the injection molding process can also be economical for smaller quantities (from 500 to 1000 pieces) due to the possible material savings.
Another advantage of the injection molding technology is the possibility of designing the flow path with which the material properties can be aligned under certain conditions. In addition, a complex geometry, for example, can be manufactured economically with an appropriate tool in larger quantities.
However, there are some restrictions that need to be considered. First, only thermoplastics can be used in injection molding; the injection molding of PTFE, PI and PBI is therefore not possible. We only process selected high-performance plastics, and offer injection molded parts made of Victrex® PEEK and Torlon®. In particular, we are specialized in the processing of Torlon® (PAI).
When selecting the injection molding technique, it should be taken into account that a tool is generally required that, depending on its complexity, can cost thousands of euros. Regarding such expenses a certain minimum production volume is required in order to be able to distribute the costs in a reasonable manner.
In addition, there are some technical limitation regarding the component design. For injection molding, certain wall cross-section and flow path length ratios are needed.
Due to the high viscosity, injection molded components made of Torlon® should have a wall thickness of at least 1.5 mm. When using non-reinforced Victrex® PEEK, wall thicknesses of one millimeter are possible. For wall thicknesses of more than 10 mm, ribs must be provided to avoid sink marks.
Because of their generally high thermal expansion, injection-molded plastics sometimes shrink significantly when they cool down. High-performance plastics, however, show only a slight shrinkage. Victrex® PEEK has shrinkage values of less than 2.5%, Torlon® even only of one percent and less. The shrinkage is usually somewhat less in the direction of flow than transverse to it. That means that sufficient bevels (approx. 2°) should be provided during construction so that the component can be removed from the tool without any problems.
Undercuts, inserts, clips and other construction elements are basically possible with the appropriate tool. The actual feasibility depends on various factors and should therefore be checked on a case-by-case basis.
Due to the poorer viscosity of the high-performance plastics, especially of Torlon® , it is essential to pay attention to the confluence of the melt in the cavity. The flow fronts that are built during injection often combine poorly and therefore represent potential breaking points.
The few indications make clear that when designing injection-molded components attention must be paid to the special features and requirements of the processing method. Switching between processing methods without design changes is usually not possible.
POLYTRON offers support with the plastic-compatible design of the components! You can find your contact person here!