Meaning
Boundary conditions at the interface between the molten plastic and the tool surface are controlled by a circulating fluid. The mould wall temperature determines the rate at which the part cools, which directly influences the surface finish and the degree of crystallinity in the polymer. Maintaining a stable temperature across the entire cavity is necessary to prevent part warping.
Surface Cooling
Heat is removed from the plastic through the steel of the tool and carried away by water or oil channels. A higher mould wall temperature allows the material to stay in a liquid state longer, which improves the replication of the tool surface for high-gloss parts. This also reduces the visibility of weld lines where two flow fronts meet.
The design of the cooling circuit must ensure that the heat is pulled away evenly from thick and thin sections to avoid internal stresses.
Crystalline Growth
Semi-crystalline resins like polypropylene or nylon require a specific cooling rate to develop their internal structure. If the mould wall temperature is too low, the surface of the part may cool so quickly that it remains amorphous, leading to inconsistent mechanical properties. Proper thermal management ensures that the part reaches its target density.
Finish Quality
Achieving a consistent appearance across a production run requires precise control of the tool surface. When the mould wall temperature fluctuates, the part dimensions and the surface texture can vary between shots. This leads to aesthetic defects that are visible to the naked eye.
