Injection mold temperature

Not only the injection mold temperature determines the melt temperature, as it moves quickly in the mold. The temperature at which the melt begins to pass through the injection mold is (self-evident) the reference point. The injection speed, especially on thin sections, has a huge impact because it will determine the degree of shear heating. The counterbalance is the heat loss of the injection mold. Forget the concept of mold temperature. In other words, it is a fantasy to imagine that the set temperature of a coolant (usually water) is the temperature that the substance encounters at every point in its journey.

It is a periodically fluctuating parameter that changes from point to point on the surface of the entire injection mold as each injection cycle changes. This is why mold filling and cooling simulation is such a great tool and provides a very useful insight into what is actually happening at each cycle. Only by dynamically measuring the surface/vicinity of the injection mold (thermocouple) can anyone know the actual (unset) conditions that highly compressible fluids we call plastics actually encounter. It has always fascinated me.

Separate flow simulations (HH) always assume a completely uniform die surface temperature in geometry and time. Only when the results of the part flow simulation are used as inputs to the cooling simulation can the simulation be close to the real correlation, that is, the position and duration of the heat load throughout the cycle, in relation to the ability of the injection mold to eliminate the heat load, at all locations on the part surface, conspiring to create a constantly changing and moving "target". A good flow/cooling simulation will definitely show the effect of the cooling line below it on the injection mold surface.

The set and actual conditions (i.e., experienced by each of the millions/billions of molecules that make up each molded part) never remain synchronized throughout the cycle. The ambient temperature around injection molds and injection molding machines will necessarily change the actual temperature distribution experienced by the part unless or until someone manages to change the fundamental laws of the universe. Changes in ambient humidity must also cause transient differences within the air space inside the plastic injection mold, as the advancing melt front compresses it, and the degree of change in compression (and heating) depends on the rate at which the air volume is reduced and the ability of the air to escape into the atmosphere. I'm not aware of any flow simulation packages that include R.H. and the heating effect of compressed air as variables, but they certainly are.