3 plate mold designs are used in multi cavity cold runner mold
tooling when a 2 plate mold design does not permit a suitable gate location.
Figure 1 shows an assembly section of a three plate mold producing a 47mm cap. This design allows the gate to be placed on the top of each cap. The caps and cold runner are ejected by their own individual stripper plates during mold opening.
Right click here to download Figure 1 in PDF format.
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During the opening sequence the first split is between the cavity plate and the stripper plate (for runner) due to spring pressure (see spring in figure 3) for the distance defined by limit screws (A) in figure 2. At this stage the runner is exposed but held firmly to the mold by the sucker pins (the sucker pins are labelled in Figure 1) .Right click here to download Figure 2 in PDF format.
As the mold continues to open, the 2nd split is between the cavity plate and the stripper plate (for cap) for a distance defined by limit screws B in figure 3.Right click here to download Figure 3 in PDF format.
The 3rd stage opening is between the back plate on the fixed side and the stripper plate (for runner) for a distance defined by limit screw (C) in Figure 4 which ejects the runner off the sucker pins. The runner falls to the ground.
At this stage the mould is fully opened, so the KO bar must be initiated by the machine ejector to remove the caps from the mold tool which is the 4th.
When designing a cold runner mold tool a 2 plate mold design should be considered first because it is easier and cheaper to make.
One potential limitation of a 2 plate design is that the gate must come from the side of the part which has the potential to cause the following quality issues in some parts: weld lines, jetting, unfavourable shrinkage rates and wall thickness variation due to core shift in tall parts. Longer flow paths may also be required which can place higher demands on the injection molding machine and consume a lot more energy.
Having said that, the 2 plate mold is suitable for many types of plastic parts.
The advantage of a three plate mold design is that it permits the gates to be located on top or bottom of the part at any point on the surface. Well placed gates will produce quality parts every cycle.
Figures 5 & 6 are an example of a 2 plate & a 3 plate mold design respectively for the same 47mm alcohol cap. Notice the different gate locations.
Right click here to download Figure 5 in PDF format.
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