Melt Temperature and Density…

I received this excellent question last week…

In one of your videos, you state that higher melt temperatures will increase part weight. To my understanding, a less viscous material is pumped in the cavity with a relative ease thus increasing the part weight. Could you please guide me as to whether or not a decrease in density negates the above?

My Response
You are correct that you will be injecting a less dense material in this scenario… but the higher melt temperature causes many things to occur, but the 2 major factors increasing the part weight and density are listed below:
1) There will be a higher amount of material flow and in-mold pressure during packing resulting in more material entering the mold during both 1st and 2nd stage.
2) A higher melt temperature promotes an increase in part shrinkage resulting in a higher overall part density.
Additional Thoughts
This question points out how complex the interactions between the mold, machine, material, and  injection molding process can become.

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