Rockwell Automation 1771-QDC, D17716.5.93(Passport) PLASTIC MOLDING MODULE - Manual (Page 241)

Tune Your Machine
Chapter 10
10-13
Cushion, Shot Size, and Transition Setpoints
Shot Size is the amount of molten plastic injected into the mold. Cushion is
the amount of molten plastic that remains in the barrel after injection.The
sum of shot size (PPC61) plus cushion (PPC62) tells the QDC module
where to terminate the Plastication profile.
During injection, the QDC module does NOT terminate the shot at
cushion, but continues injecting until one of the three injection transition
conditions occurs. These three conditions during the injection profile are:
elapsed time exceeds a preset limit
ram (screw) pressure exceeds a preset limit
ram (screw) position exceeds a preset limit
Shot Size
(PPC61)
Shot size (measured from cushion) is the amount of molten plastic needed
to fill the mold (figure 10.3). Determine it with these general steps:
1. Start with a shot size you know will NOT fill the mold.
2. Enter a ram(screw) transition position about 1/2” from ram bottom.
3. Run a shot with transition on position.
The end-of-hold position will be at ram bottom, because mold
cavities continue to fill during pack and hold.
4. While continuing to transition on position, slowly increase the shot
size until the end-of-hold position is
above ram bottom
approximately equal to cushion
5. The shot size is correct for the mold/part you are tuning when:
the end-of-hold position is approximately equal to cushion
all cavities on the mold are being fully filled
Cushion
(PPC62)
Cushion (measured from mold end) is the length of molten plastic you
want remaining in the barrel after filling mold cavities (figure 10.3). The
QDC module adds this length to shot size length to determine where to
terminate plastication.