Systems and approaches for manufacturing parts

A method for controlling a molding machine having a mold forming a mold cavity, a nozzle, and a screw that moves from a first position to a second position toward the nozzle, the molding machine being controlled by a controller according to a mold cycle, the method comprising:

• injecting a molten polymer into the mold cavity;
• obtaining, using a first sensor positioned at or near the screw, a first measurement of a variable during the mold cycle, the variable comprising a compressibility of the molten polymer;
• obtaining, using a second sensor positioned at or near the nozzle, a second measurement of the variable during the mold cycle;
• determining a measured compressibility ratio value, the measured compressibility ratio value being a difference between the measured variable obtained by the first sensor and the measured variable obtained by the second sensor;
• comparing the measured compressibility ratio value with a reference compressibility ratio value;
• adjusting at least one control parameter based on a difference between the reference compressibility ratio value and the measured compressibility ratio value;
• and the compressibility of the molten polymer is used to determine a density value thereof, wherein the adjusting of the at least one control parameter occurs within 10% a mold cycle time and 40% of the mold cycle time.