GITBlow I und II

Combination of two procedures for producing extremely thin-walled functional elements

In recent years, the gas assised injection moulding technique (GAIM) has emerged as a widespread large-scale procedure in the field of special procedures of injection moulding. This technique reduces shrinkage effects typical for plastics and improves visible surfaces as well as the dimensional stability of the parts. However, the procedure reaches its limits as soon as functional cavities with high volume or big diameters are required, as the cross-sectional area of the gas bubble cannot be produced arbitrarily big. According to the geometry of the gas guidance channel, a certain residual wall thickness of the standard GAIM part cannot be under-run. In order to cut the production costs of plastic articles, plastic processors have two aims:

  • on the one hand, the cooling time and the material consumption are to be reduced by wall thicknesses as thin as possible,
  • on the other hand, the production process chain for a component part or a module is to be shortened.

This difficulty led to the idea to combine the GAIM with a blowing process in order to produce complexly formed plastic parts with a cavity of a big diameter and thin walls. By increasing the tool cavity and a subsequent, second gas injection, this so-called GITBlow procedure generates wall thicknesses that are far below the residual wall thickness of a standard GAIM part.

Bild 1: Maximale Gaskanalquerschnitte und minimale Wanddicken GIT-Blow Verfahren

For inflating the components, the part temperature has to be in the thermoelastic or thermoplastic range. This condition can be achieved by two process options. 
The so-called one-stage process utilises the residual heat existing in the closed tool. By essentially enlarging the cavity and re-applying the gas pressure, the standard GAIM part which is still warm is stretched to a functional channel with extremely thin walls.

Bild 2: Beispielanwendung von GIT-Blow

The two-stage process enlarges the cavity by converting the part into a second, enlarged cavity. Before the tool is closed again and the second gas injection takes place, radiant heaters heat the part up to the moulding temperature specific to the material. This two-stage process is mainly characterised by more variation possibilities with regard to the reachable geometries.

Bild 3: GIT-Blow Prototypen

Preliminary tests proved that the process idea GITBlow can basically be realised from the technical point of view. The combination of GAIM with a blowing process allows for the production of functional elements. In fact, the particular method separately could not produce them at all or only with great effort. The advantages of the GITBlow procedure can be outlined as follows:

  • big hollow cross-sections
  • equal distribution of the (low) residual wall thickness
  • extremely thin-walled functional channels
  • connection to filigree areas
  • production of complex geometries that cannot be generated by core puller technique
  • broad application range

In order to use the above mentioned advantages in practice, further analyses with different material, process parameters and geometries have to be conducted. The temperature distribution in the initial geometry - resulting from the wall thickness distribution of the standard GIT part before the blowing up - constitutes an essential parameter to be optimised.

Currently, the GITBlow procedure is analysed in the context of a BMBF project under the support code 01RI05174. The project management is realised by the company 3 Pi Consulting & Management GmbH in cooperation with the Institut für Kunststofftechnik Paderborn (KTP).

First test results can be learned from the following link:

GITBlow prototype components (PDF 302KB) 

Next to the aspects related to the process, new approaches also have to be found for the layout of injection moulding machines and tools. For this reason, the 3 Pi Consulting & Management GmbH offers interested companies from the fields of tool construction and injection moulding machine construction a joint project focusing on the layout of tools.