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.
Elastic Deformation
Meaning
Temporary change in the shape or dimensions of a material that reverses completely once the applied load is removed. In injection moulding, elastic deformation occurs in both the tool steel and the polymer part during the high-pressure phases of the cycle. Spring-like behavior in the metal and plastic allows for the storage of energy that is released when the clamping or injection pressure drops.
Tooling Mechanics
Steel mould plates flex slightly when the cavity pressure reaches its peak during the packing stage. This movement is often invisible to the eye but can be measured in microns and is sufficient to cause flash if the tool is not stiff enough. Large parts with high projected areas are most susceptible to this phenomenon.
Polymer Recovery
Parts compressed inside the cavity expand slightly as they are ejected and the internal stresses are relieved. This behavior determines the final dimensions of the part and must be accounted for in the mould design. The amount of recovery depends on the modulus of the resin and the temperature at which the pressure is released.
Design Constraint
Engineers calculate the expected deflection to ensure that the tool stays within the elastic limit of the steel. If the stress exceeds the yield strength, the deformation becomes permanent and the tool is ruined. Proper support pillars and thick backup plates are the primary defenses against excessive movement during the moulding cycle.