A method for adjusting operation of an injection molding machine so that the machine produces finished injected molded parts that are within a range of acceptable quality, wherein each production cycle performed by the machine includes in succession an injection phase in which a melt is injected under pressure into a cavity of an injection mold, a holding pressure phase during which the molten melt cools down and is solidified, and a residual cooling phase during which the solidified melt continues to cool down within the cavity prior to ejection from the cavity, the method comprising the steps of:
- using as a reference graph, an internal pressure graph of the cavity during a production cycle that produces a finished injection molded part having a characteristic that satisfies a predefined quality;
- defining in the reference graph, a first feature, a second feature, a third feature and a fourth feature, wherein each feature is readily identifiable in each production cycle of the injection molding machine;
- operating the injection molding machine during a first production cycle to produce a first finished part;
- representing in a form of a first internal pressure graph, a time variation of a detected internal pressure of the cavity during the first production cycle of the machine;
- upon determining that the first feature in the first internal pressure graph deviates from the first feature in the reference graph by at least a first quantitative deviation, then before beginning a second production cycle of the machine in immediate succession of the first production cycle of the machine, changing a first operating parameter of the machine by a first magnitude that tends to diminish the first quantitative deviation during the second production cycle of the machine;
- operating the injection molding machine during a second production cycle in immediate succession of the first production cycle of the machine;
- representing in the form of a second internal pressure graph, the time variation of the detected internal pressure of the cavity during the second production cycle of the machine;
- upon determining that the second feature in the second internal pressure graph deviates from the second feature in the reference graph by at least a second quantitative deviation, then before beginning a third production cycle of the machine in immediate succession of the second production cycle of the machine, changing a second operating parameter of the machine by a second magnitude that tends to diminish the second quantitative deviation during the third production cycle of the machine;
- operating the injection molding machine during a third production cycle in immediate succession of the second production cycle of the machine;
- representing in the form of a third internal pressure graph, the time variation of the detected internal pressure of the cavity during the third production cycle of the machine;
- upon determining that the third feature in the third internal pressure graph deviates from the third feature in the reference graph by at least a third quantitative deviation, then before beginning a fourth production cycle of the machine in immediate succession of the third production cycle of the machine, changing a third operating parameter of the machine by a third magnitude that tends to diminish the third quantitative deviation during the fourth production cycle of the machine;
- operating the injection molding machine during a fourth production cycle in immediate succession of the third production cycle of the machine;
- representing in the form of a fourth internal pressure graph, the time variation of the detected internal pressure of the cavity during the fourth production cycle of the machine;
- and
- upon determining that the fourth feature in the fourth internal pressure graph deviates from the fourth feature in the reference graph by at least a fourth quantitative deviation, then before beginning a fifth production cycle of the machine in immediate succession of the fourth production cycle of the machine, changing a fourth operating parameter of the machine by a fourth magnitude that tends to diminish the fourth quantitative deviation during the fifth production cycle of the machine.