Parting Line Steel Preload Calculation for Multi Cavity Injection Moulds
Calculate multi cavity parting line preload by balancing machine clamp force against internal hydraulic separation force to maintain positive shut-off land sealing stress.
Mould Plate Flexure
Meaning
Structural plate deformation occurs when the high pressure of the injected plastic forces the mould halves apart. Minimizing mould plate flexure is essential for maintaining the dimensional accuracy of the part and preventing flash. This bending happens most often in the center of the tool where the support is the weakest.
Designers add support pillars and increase plate thickness to counteract this movement.
Support Geometry
Adding solid steel columns between the back plate and the cavity plate reduces the amount of bending. A mould plate flexure of even 0.05 millimeters can cause the part wall thickness to vary beyond the allowed tolerance. Correct placement of these pillars depends on the location of the injection gates and the part geometry.
Wall Deviation
Parts with large surface areas exert a tremendous force against the steel during the packing phase. If mould plate flexure is too high, the center of the part will be thicker than the edges. This variation can lead to assembly problems or functional failures in the finished product.
Clamping Pressure
Increasing the tonnage of the injection press can help hold the mould together but it also increases the stress on the machine. When mould plate flexure is identified as the cause of a defect, it is better to stiffen the tool than to simply turn up the pressure. Overloading the press leads to broken tie bars or damaged platens.