Injection moulding method

A method of injection moulding an article having a base and a sidewall, the method including the steps of:

• (a) providing an injection mould comprising first and second mould parts;
• (b) disposing the first and second mould parts in a fully closed configuration so as to define a mould cavity therebetween, in the fully closed configuration the first and second mould parts defining a cavity outer surface which defines the outer shape of the article to be moulded in the mould cavity, the mould cavity having a base-forming portion and a sidewall-forming portion for respectively forming a base and a sidewall of an article to be moulded;
• (c) injecting molten material into the cavity at an injection inlet of the cavity;
• and
• (d) moving at least one portion of one of the first and second mould parts away from the injection inlet during the injection thereby to vary the volume of the mould cavity in the fully closed configuration,
• wherein in step (d) the moving of the at least one portion of one of the first and second mould parts away from the injection inlet during the injection controls the filling pressure of the molten material in the cavity according to a predetermined pressure characteristic in an injection moulding cycle, wherein the volume of the cavity is enlarged in a first phase of the injection moulding cycle and reduced in a second phase of the injection moulding cycle, in both of which phases the molten material is injected into the mould cavity, wherein in a third phase, following the second phase, of the injection moulding cycle the volume of the cavity is continued to be reduced, in which third phase the injection of molten material into the mould cavity has been terminated, and wherein at the end of the second phase the mould cavity is overfilled with the molten material and in the third phase any excess molten material in the mould cavity is urged back through the injection inlet against a controlled injection pressure.