Which is the control Chart (SPC chart) you suggest for monitoring PROCESS parameters of Injection molding (Like melt cussion, Dosing time, Injection pressure etc..). I am not a Injection Molding expert but as a Quality professional , I am interested to know how to measure the stability of process parameters

As you may know SPC in injection molding usually means part control and not process control, just the nature of the beast. Your right we need to start looking at the process up stream the problem is what to you monitor in the machine so you don't have to monitor your parts. What I've done in the past is set up process or run sheets that allow a certain level of changes for 4 or 5 key parameters so long as they don't deviate to far from the original settings. I would also set up a change log so that any changes to the process had to be documented if a change was made then the parts would have to be verified by quality and then the process sheet would be changed to reflect he new parameters. Even with all this I was never able to get away from checking the parts I don't think our business is ready for that let.
My key parameters are, cycle time, transfer pressure, mold temperature, hold pressure. Cycle time because its what make the company money, if it wrong then you need to look at fill time, hold time and cooling or cure time.
Transfer pressure tells me a lot about material, melt temp, transfer positions and so on.
mold temp is key to maintaining the same dimensional part as well as hold pressures.
I'm one that believes that molding process are dynamic they will change there are so many noise factors involved that you can't monitor everything and in molding everything effects everything else. So allow for a certain amount of variation allow you processors to be processors monitor the process and investigate why things change. The worse kind of processor is one that's a knob turner without expectation of why he turned it and what result they expected to see.

Cushion volume at the end of holding pressure, mínimum cushion volume during holding pressure, maximal injection pressure , filling time, pressure in swicht over phase, moulding cavity pressure, etc.

Are you familiar with what the Molex plants in Lincoln Nebraska and Chengdu China are using? They've done a very nice job with their realtime process monitoring strategy. I can get you contact information if it would help.

Mike, Id be interested. I'm working on a similar project now.

that's the key i believe to ensure process stability as well as repetitiveness. common machines are equipped with a process control page where you can set in parameters you like to keep under control then set a range variability, over that machine can stops if you like. It depends on what machine type you work with, but actually you should be able to print out a process report too. i am used to control repetitivenss from cycle time,hydraulic pressure peak,injection time,cuscion,dosing time, (obviously deviation ranges depends on how many cavities, material grade, thickness) ... all these mentioned parameters are the Key to control any changing may occurs to the melt index, tool temperatures, % of rigrinded resin perhaps, blocked cavity for a multicavity tool that may prevents unexpected dimensional changing on molded parts.

It is very interesting one since i am also in the same field of PET Preforms where i am using SPC software to calculate the same.