Tip of the Day 35: Machine Sequence / Fill

The second most important sequence signal from the machine side is Machine Sequence / Fill. This signal is supposed to go on as plastic begins flowing into the mold. It must go off at the point where the ram slows down to begin packing (with either speed (D3) or pressure (D2) ). In decoupled processes this will be before the cavity is actually full. If the eDART can create a good signal for Machine Sequence / Fill then it can accurately calculate viscosity, fill rates, fill time, shear (for rheology study) and more.

Best Start of Fill:

The very best signal for start of fill is the “zero crossing” of the stroke / volume sensor. This is the point at which the ram was located when the screw stopped turning (loading plastic into the shot). To avoid drool the machine often is set to “suck back” after the screw stops. As it begins injecting again we do not count that “suck-back” distance as actually flowing plastic. Hence “fill start” is when the screw passes through the point at where the shot was full (usually called “shot size” on the machine). While not strictly precise this is much better than using start of injection for start of fill.

On the eDART this is easily done by having the screw position (volume) automatically zeroed when the Machine Sequence / Screw Run signal goes off (motor stops). Then the sequencer sets the Machine Sequence / Fill signal to On when it sees the position (volume) cross through zero going from negative to positive.

Best End of Fill:

Since one of the prime reasons for the Fill signal is to figure out the start and end of viscosity and flow calculations we want to know when the machine slows down to begin packing. This causes injection pressure to drop, the melt to decompress and so on. So the best computation of viscosity is done while the machine is running at fill speed. We need to know when that ends.

In a Decoupled 2 process fill ends at transfer to hold. If you provide the eDART with a Seq. Module Input / First Stage then the sequencer assumes that transfer (end of First Stage) is the end of fill.

In Decoupled 3 we would like to know when the machine slows down for packing; i.e. when it changes speeds from the faster filling speed to the slower controlled velocity packing speed. Unfortunately no machines yet provide us this signal directly to us as a sequence signal. So we need to find a way to tell the eDART when this event occurs.

The best way to do this is to set a number for the volume of material injected at the point that the machine slows down. You can do this by making a short shot and pressing a button on the “Sequence Settings” “Fill” tab. Or you can type the volume in on the “Sequence Settings” “Fill” tab. Or you can do it on cycle using the “Set Fill Volume at Cursor”. Place the cursor just at or before the sudden kink in the volume curve and click the right mouse then “Set Fill Volume at Cursor”.