Tip of the Day 29: What is Injection Forward?

What is “Injection Forward”?

That part of the machine cycle in which the ram is being pushed forward. It starts when the injection unit begins pushing plastic into the mold and ends when it stops applying pressure (in preparation for the screw running).

What is it used for in the eDART?

This is the king of Machine Sequence signals. The eDART uses this as a sort of “Master Start” of the cycle. Without some sort of Machine Sequence / Injection Forward signal the eDART assumes the machine has stopped.

The eDART also computes Injection Integrals while Inj. Fwd is ON, ignores peaks in cavity pressures after injection forward is off (a selectable setting), figures out hold time, hold pressure and a number of other items (detailed below). Furthermore it is used by controls such as V->P Transfer, Shuttle, Basic 3-Stage and Valve Gate to cause the eDART to take certain actions.

Where does the Machine Sequence signal come from?

The most robust way to tell the eDART that the machine is injecting is to wire the sequence module input to the signal on the machine that is ON during the injection portion of the cycle.

If this signal is not available the eDART uses several techniques to try to figure out when Injection Forward is on. In descending order of quality (some depending on other signals being there):

·         First Stage or Second Stage sequence input signals, if available

·         Screw motion forward / falling edge of injection pressure

·         Screw motion forward / screw motion backward for a time

·         Injection pressure thresholds

         Mold Clamped plus a time to turn on and a set injection forward on time.

Details to follow

Key Point in Sequencing:

If you do not supply the eDART with a good Seq. Module Input / Injection Forward signal then you, the user, will have to tweak some settings to get a good Machine Sequence / Injection Forward for proper computation. But if the eDART is interfaced to the machine with the REDI kit then the user does not need to know about or adjust anything for proper sequencing.

The good news is that once you have it set up to work the settings are memorized for that machine and should work every time. So this should be a one time only startup problem (unless you need thresholds that can change with the process).

Tomorrow: How to Deal with No Injection Forward Signal

Some Summary Values that use Machine Sequence / Injection Forward

  • Every computation needs Injection Forward to start the cycle

  • Injection Integral / pressures and volume

  • Sequence Time / Hold Time and Injection Forward Time

  • Average Value / Hold Pressure

  • Average Value / Stable Hold Pressure