Injection molding apparatus and method for automatic cycle to cycle cavity injection

A method of operating an injection molding system for initiating flow of a fluid material into multiple gates of a mold cavity during an injection cycle, wherein the system includes:

• a first selected valve comprising a first fluid flow passage having a first gate to the cavity, a first valve pin driven reciprocally along an axial upstream downstream path of travel through the first flow passage by a first actuator between gate open and gate closed positions,
• one or more downstream valves, each downstream valve comprising a downstream fluid flow passage having a downstream gate to the cavity disposed downstream of the first gate, a downstream valve pin driven reciprocally along an axial upstream downstream path of travel through the downstream fluid flow passage by a downstream actuator between a gate open and a gate closed position the method comprising:
• detecting, at a downstream detection time, a select property of a flow front of the fluid material flowing downstream at a trigger position within the cavity disposed between the first gate and at least one selected downstream gate wherein,
• instructing the actuator of the valve associated with the at least one selected downstream gate, or a control valve for that actuator, to withdraw the valve pin from the gate closed position at an instruction time (X) comprising a predetermined open gate target time (X) following the downstream detection time,
• detecting, at an actual open gate time, withdrawal of the valve pin from the at least one selected downstream gate,
• determining an adjusted instruction time (X′), for use on a subsequent injection cycle, wherein the determining step comprises decreasing the time of instruction to the valve pin to open on a subsequent injection cycle by an adjustment time equal to any delay in time (Y) between the predetermined open gate target time (X) and the actual open gate time (A).