Gas assisted moulding (GAM) became available commercially as a process for the shaping of plastics in the mid 1980s. It is estimated that there are now approximately 1500 GAM installations worldwide, and the rate of acceptance of the process has accelerated considerably in the last three years. Based on the controlled injection of gas to form continuous hollow channels in the thicker sections of a moulding, the process offers many advantages over other moulding processes.

In a thick section moulding such as a handle, the weight of plastic used can be reduced by as much as 45 by the incorporation of hollow sections. In more conventional plate-like mouldings weight reduction can still be achieved by combining thicker ribs with reduced general wall thickness. Reduced material thicknesses also allow moulding times to be reduced. Furthermore, the presence of gas within the hollow channels of a moulding provides a means of pressurising the plastic during cooling and solidification. This allows a substantial reduction in moulding pressure, and hence press lock force, in comparison with traditional injection moulding.

Television housings provided the first major application for GAM. Diverse automotive applications followed, and many uses in domestic appliances. Other applications of GAM have included air conditioning cabinets, furniture and sanitary ware. Terry Pearson was involved in the early development and commercial introduction of GAM. He is now Chairman of Gas Injection Limited, which he founded in the UK in 1993, and President of Gas Injection Corporation in the USA. The two companies offer GAM equipment, training, consultancy and documentation.

In this Rapra Review Report he examines the current state of the art in GAM technology and applications. He outlines the fundamental principles and discusses the benefits and limitations of the process. He describes the choice of equipment, including aspects such as nitrogen gas preparation and the position and timing of gas injection. He also provides design guidelines for thin and thick section mouldings and the dimensions and location of gas channels. External gas moulding is also briefly described.

More than 50 diagrams are included, together with a number of tables, providing the reader with the clearest possible description of the practical implementation of GAM. The report is completed by an indexed section, containing some 300 references and abstracts from the Polymer Library, which provides much additional information on equipment, suppliers and end products.

The abstracts also provide access to the academic research which is underway in a number of countries, which may lead to further advances in the simulation and practical application of GAM.

Gas assisted moulding is a relatively new process. It is intended that this report will contribute to the dissemination of information about the process, and encourage product designers and moulders to examine the technical and economic benefits that GAM can offer in an expanding range of applications.