Pull and Foam

Foamed reinforcing ribs for thin-walled lightweight parts

Because of weight reasons and due to a low warpage, a lot of plastic components are produced by a foaming process. Yet, the foaming processes that are common up to now dispose of a limited application range. The biggest challenge related to the process of foaming injection moulding of thermoplastics consists in controlling the foaming degree. Thin-walled parts with partial thick places require a high injection pressure when filling the thin-walled areas. Consequently, the foaming degree in the whole part can be very low in most cases. However, the controlled foaming process of the newly developed procedure allows producing components with high-quality, thin-walled areas and partially foamed reinforcing ribs in one single process step.

Bild 1: Querschnitt vor und nach dem Aufschäumprozess

The new procedure is based on the idea that the foaming process does not start until the cavity expands – after the injection of the moulding compound that is loaded with the blowing agent and after the thin-walled areas of the component are freezed. Reducing the pressure in the enlarged cavity areas initialises the foaming and the following expansion of the supersaturated polymer. This is not about the already known mould techniques such as vertical flash face or core pulling procedure. The initialisation of the foaming process by enlarging the cavity is illustrated in the following schema.

Bild 2: Schematische Darstellung der Initiierung

The foaming degree of the reinforcing ribs can be controlled by the cavity enlargement. Consequently, rib structures that are extremely lightweight but stable can be produced. Thus, the result is a component that is lightweight and optically good, but for all that is has a hard strength, a low warpage and is rigid. The advantages of the new procedure can be summarised as follows:

  • thin-walled, compact and optically high-quality areas with large-volume rib structures can be produced,
  • structures that are locally very lightweight can be realised,
  • large-volume components can be generated on machines with low plasticising volume and little clamping pressure.

Numerous applications are conceivable. For instance, applications in the automotive industry, consumer electronic industry, furniture industry and medical engineering can be mentioned. The procedure does not require any additional process step. For further information, we are at your disposal. Please contact us, we are happy to advise you.

Our own preliminary works prove that the basic idea of the new procedure “pull and foam” can be realised in principle. Based on these works, the company 3 Pi Consulting & Management GmbH is planning a joint research project “pull and foam” in the near future. The main focus is on working out procedural fundamentals related to the specific characteristics of this new special technique of injection moulding. Further focal points and details about the planned joint research project can be learned from the following link.