(1)Mold design

The basic principle of mold design for GAI molding is the same as that for ordinary injection molding, but the injection pressure can possibly be reduced and so smaller injection molding machines can be used. However, it is safer to assume higher pressure in the course of the design and the production of molds.
It is recommended to design and produce molds taking following points into account.

1. It is recommended to induce the fountain flow, instead of the jetting, of molten resin in the cavity by selecting gate positions other than thick-walled portions, and by designing proper shapes and cross sections.
   In some cases, the wrinkles caused by jetting are ruptured by the pressure of gas.
2. The expansion of gas can not cope with the sudden change in wall thickness and the complicated shapes. This results in the formation of resin masses which cause the deformation of moldings.
3. The bends of right angle should be radiused as generously as possible, without causing uneven wall thickness distribution.
4. In the case of multi-cavity molds, the length of runners from the sprue to each cavity must strictly be the same. Otherwise each cavity must be equipped with its own gas-control unit, because all the cavities can not be filled at the same time.
5. In GAI molding the effect of mold temperature on the dimension is more significant in comparison to ordinary molding. Therefore it is sometimes preferable to install an independent mold-temperature controller for each cavity, in the case of multi-cavity molds.
6. When gas is directly injected into molded products, pin gates seem to be preferable in order to prevent the back flow of pressurized gas through the gate to the runner. However, pingates which directly reach molded products are not so desirable since they may cause jetting. Therefore the best way is to feed the molten resin through a pin gate to a tab which is attached to the molded product, and then from the tab to the molded product where the tab plays a role of a side gate.
7. Be aware of the hole which remains on the surface of the molded product.
8. When a sub-cavity is installed, the thickness of the gate for it should be thinner than that of the molded product itself, so that the molten resin can flow into the sub-cavity only after the cavity for the molded products is fully filled, in order to make its function more effective.

(3)Concentricity

As can be seen in the figures shown below, the concentricity of the products made by GAI molding is far superior to that of ordinary moldings.

(4)Molding cycle time with the trial mold for a roller

In ordinary injection molding, concentricity could be reduced from 1700 to 900 by extending the molding cycle time. In GAI molding, however, the concentricity of 300 could be achieved which could never have been reached in ordinary injection molding as shown below.