The water injection technique (WIT) opportunities and challenges

The water injection technique, developed at the Institute of Plastics Processing (IKV), Aachen, Germany, is an innovative specialty injection molding process that is closely related to the well-known gas-assisted injection molding (GAIM) technique. The primary aim of the development was to reduce cooling times in the material-saving production of rod-shaped hollow plastics articles and also in the production of plastics parts with integrated thick-walled sections. The melt displacement is generated by means of water in its liquid phase (inexpensive, available everywhere, re-usable, good cooling effect). For this purpose, the realization of a sufficiently high volume flow rate and the formation of a melt displacing flow front is a basic requirement. Therefore, the injector technology represents the centerpiece of the water injection technique, since it is the most crucial link between the WIT plant and the mold. With WIT, cooling times can thus be reduced by up to 70 % compared with GAIM, depending on the part size and geometry and on the specified product properties. With WIT, it is generally possible to achieve larger part dimensions with a lower residual wall thickness than with GRIM. In addition, smoother inner surfaces can be achieved. Studies of a wide range of unfilled and filled materials show that WIT constitutes an attractive alternative and supplement to GAIM.