Adaptive process control for injection molding

A method of controlling certain parameters of an injection molding cycle applying PVT optimization wherein the molding cycle comprises plasticating a material by means of a rotating screw, injecting a shot of the plasticated material into a closed mold by axially advancing the screw, applying holding pressure on the material in the mold for a holding period, permitting the molded part to cool in the closed mold, and then opening the mold at the end of the cooling period, said control method comprising:

• performing at least one qualifying molding cycle to produce a first part having acceptable quality wherein the qualifying cycle cooling period has a selected length,
• in the qualifying cycle, measuring the injection velocity and injection pressure at at least one selected axial position of the screw during injection,
• calculating the viscosity of the plasticated material as a function of the measured injection velocity and pressure,
• performing a subsequent second molding cycle to produce a second part,
• measuring the injection velocity and injection pressure during said second cycle at said selected position of the screw,
• calculating the viscosity of the plasticated material in the second cycle as a function of said measured injection velocity and pressure in the second cycle, and
• adjusting the cooling period time in the second cycle in proportion to the ratio of said calculated viscosities in the qualifying and second cycles.

A method of controlling certain parameters of an injection molding cycle applying PVT optimization wherein the molding cycle comprises plasticating a material by means of a rotating screw, injecting a shot of the plasticated material into a closed mold by axially advancing the screw, applying holding pressure on the material in the mold for a holding period, permitting the molded part to cool in the closed mold, and then opening the mold at the end of the cooling period, said control method comprising:

• performing at least one qualifying molding cycle to produce a first part having acceptable quality wherein the qualifying cycle holding period and cooling period have respective selected lengths,
• in the qualifying cycle, measuring the injection velocity and injection pressure at a plurality of selected axial positions of the screw during injection,
• calculating the average viscosity of the plasticated material as a function of the measured injection velocities and pressures,
• performing a subsequent second molding cycle to produce a second part,
• measuring the injection velocity and injection pressure during said second cycle at said selected positions of the screw,
• calculating the average viscosity of the plasticated material in the second cycle as a function of said measured injection velocities and pressures in the second cycle, and
• adjusting the holding period time and cooling period time in the second cycle as a function of the ratio of said calculated average viscosities in the qualifying and second cycles.