Not only injection mold temperature determines melt temperature as it moves quickly through the mold. The melt temperature itself as it starts its journey through the injection mold (self-evidently) is the reference point. Speed of injection, particularly in thin sections, is of huge influence, as it will determine the degree of shear heating. Fighting against this will be the loss of heat to the injection mold. Forget the idea of notional mold temperature. In other words, it is a fantasy to imagine that coolant (water usually) set temperature is what the material encounters at each point in its journey.
It is a cyclically fluctuating parameter with each injection cycle and will vary from point-to-point over the entire pair of injection mold surfaces. This is why mold-filling and cooling simulation is such a great tool and does give a fantastically useful insight into what actually happens throughout each cycle. Only by measuring at/near injection mold surfaces dynamically (thermocouple) can anyone know what the REAL (not SET) conditions are actually being encountered by the highly compressible fluid we know as plastic. It never ceases to fascinate me.
Flow simulation alone (HH) always assumes a completely uniform mold surface temperature, geometrically and temporally. Only by using the results of the part flow simulation as input to a cooling simulation will you approach correlation of simulation and reality, as the location and duration of heat loads through the entire cycle, versus the injection mold's capacity to remove them, at all locations on the part's surfaces conspire to create a constantly changing and moving "target". A good flow/cooling simulation will most certainly indicate the effect on the injection mold surface of cooling lines below it.
Set and actual conditions (i.e., as experienced by every one of the millions/billions of molecules that constitute each molded part) will never and ever remain in synchronicity throughout a cycle. The ambient temperature surrounding the injection mold and machine are bound to change the actual temperature profiles experienced by the part, unless and until someone manages to change fundamental Laws of the Universe. Ambient humidity variations must also cause transient differences within the air space inside a plastic injection mold, as the advancing melt fronts compress it, the changing degree of compression (and therefore heating) being dependent upon the rate of air volume reduction versus the ability for the air to escape to atmosphere. I am not aware of any flow simulation packages that include R.H. and heating effects of the compressed air as variables, but they most certainly are.
The article comes from China injection mold manufacturer - Mold Best Assurance Company Limited, website is www.mbamoldanddesign.com
