Figure 2.38 The situation for the 400 mm open machine

Figure 2.39 Three-dimensional view with gear

2.5.4 Toggle LeverA further possibility for the motion sequence of a stack mould is the toggle lever. It is installed in the middle of the central part. The two lever arms at the top and the bottom have the same length and are installed at the same distance from the centre. When turning the middle lever the two lever arms move simultaneously with it. As with the gear, half the distance is covered per side. The mould has been equipped with round guiding elements here due to lack of space. In Figure 2.40 the situation of the mould opened via a toggle lever is displayed. The distance is also halved here. In this version the central part is guided and supported through the round guides in the mould and the guide shoes on the machine base.

Figure 2.40 Mould with toggle leverTo better imagine this mould Figure 2.41 shows a three-dimensional view of the stack mould. The mould is moved via a toggle lever and the round guides are installed in the mould.

Figure 2.41 Three-dimensional view with toggle lever

2.5.5 EjectionThe plastic pieces are ejected centrally via an ejector retaining plate like for the classic mould. The ejectors in half 1 in Figure 2.40 can be controlled via the ejector unit in the machine. However, in half 2 an ejector unit must be installed which is moved hydraulically via cylinders.2.5.6„General Information on the Stack MouldThe closing force of the injection mould is deffned by the injection pressure and the projected area. If the plastic is injected in two stacks, the closing force is not higher despite the doubled number of plastic parts. The projected area does not add up. The closing force is an important criterion for purchasing an injection moulding machine. 

The total costs for a stack mould are only about 30 to 40 % higher in contrast to the doubled number of plastic parts. Nevertheless, a stack mould only makes sense when it is continuously used for high quantity production.

It should also be noted that the stack mould has a higher installation height than a normal, simple injection mould. Therefore the opening path of the machine for a stack mould can be much larger.