The advantages of the fluid injection technique (gas and water injection technique) lie in the significantly greater design freedom compared with other moulding techniques and in the considerably lower costs compared with the melting core technique with an equivalent design freedom. This special form of injection moulding allows tubular components with a high degree of integration to be produced very cost effectively as one-piece solutions. Further¬more, the process results in components characterised by a very low intrinsic stress level, low part distortion and reduced process-specific sink marks.

The gas injection technique was initially used only to save material and cycle time during the production of thick-walled plastic parts (e.g. handles, structural parts). The excess material was pressed out of the mould using nitrogen. Three process variants can be distinguished here:

• Short shot method in which the mould cavity is only partly filled with plastic melt and then the plastic is pressed against the mould wall by means of a fluid.
• Full shot method in which the whole cavity is filled with plastic melt before the liquid plastic melt centre is pressed out of the cavity into the open branch cavity by means of a fluid.
• The full shot back into the barrel method functions in the same way as the full shot method, but with the difference that the excess plastic melt is returned to the barrel of the injection moulding machine instead of being pressed in a branch cavity.