Today's KNOWLEDGE Share:Actual shortshots

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Today's KNOWLEDGE Share

So, let's say you "do" Flow Analysis and want to compare it to actual shortshots...


Most people would look at "isochrone" lines, a representation of flow front position vs. time, as "shortshots". But have you ever thought about what really happens when you experimentally produce a shortshot ? You essentially partly fill the cavity and just...stop there, with no packing. Sure..

But when you stop, you might have 1000 bars at the gate, so depending on how you exactly control your screw, your flow front will keep moving due to the expansion flow, producing a shortshot possibly very different from the transient front position at the very moment you stopped. This expansion flow is not velocity controlled and may produce a very strange end of flow, possibly showing fake weldlines, when thickness distribution is complex. So simulation doesn't show a weldline where, possibly, experiment does. The key to correctly simulating a shortshot is to switch over to pack with zero pressure for a few seconds letting the computation go on and include the expansion flow. Note that that weldline you found may only exist in the shortshot but not in the full part ! Just make sure you don't look at your filling isochrone lines as precise shortshots, because they are NOT !


source:Vito leo


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