Sequential and cascade moulding

Two special injection moulding methods have been developed to get around this problem, both based on HR systems with multiple gating sequential moulding and cascade moulding. Both methods require the use of shut-off nozzles with independent control. 

Sequential moulding is based on mutually independent opening and closing of the nozzles in the mould cavity in such a way as to allow the weld lines to be shifted until they reach an optimum position. This technique is used for products of large area and with numerous apertures which cause weld lines to appear. The use of simulation clearly provides a good starting point for optimisation of nozzle control. 

Nozzle control takes place using one of the following methods  

Correcting the line shift by changing the size of the gates would make for a difference in filling conditions, and would thus lead to different shrinkage of both parts of the piece. 

With sequential control of the nozzles it is possible to fill the lid and hinge before beginning to fill the box. The weld line will be located on the bottom of the box, and its position may easily be adjusted. 

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A shut-off nozzle is the only type of nozzle that allows HR to be used for injection moulding of structural foam, and for sequential and cascade moulding. 

Mould filling control. An HR system with hydraulically or pneumatically closed nozzles has given rise to a new potential for controlling the mould filling process. These techniques are known as sequential and cascade moulding (see Chapter 8.1). 

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