A method of selecting thermoplastic materials for use with an injection molding apparatus that adjusts viscosity of a thermoplastic material based on an interpreted viscosity is provided. The method includes determining a target MFI for an identified plastic article based on performance properties. A thermoplastic material supply chain is analyzed and a first thermoplastic material having a first starting MFI and a first MFI range is identified and a second thermoplastic material having a second starting MFI and a second MFI range that is greater than the first MFI range is identified and is priced less than the first thermoplastic material. The second thermoplastic material is purchased. The second thermoplastic material is tested by providing the second thermoplastic material to the injection molding apparatus for multiple shot molding cycles with the second thermoplastic material in a molten state. The step of testing includes monitoring melt pressure of the molten second thermoplastic material using a sensor and providing a signal to a controller indicative of melt pressure. The controller controls introduction of an additive to the second thermoplastic material thereby changing a viscosity of the molten second thermoplastic material based on the signal. A molded article is formed by reducing a mold temperature of the second thermoplastic material within the at least one mold cavity.

Injection molding at substantially constant pressure and utilizing sequential coining to produce molded parts substantially free of cosmetic and mechanical defects.

In order to injection mold parts at a constant flow front velocity in a mold cavity of an injection molding system, particularly where the mold cavity has a varying thickness along its length, mold modeling software is used to calculate the cross-sectional area as a function of the distance from the gate, percentage of fill, or length of the mold cavity. Based on that cross-sectional area, the mold modeling software determines an appropriate recommended ram force profile and/or melt pressure profile that would result in filling the mold cavity at a constant flow rate. An injection molding system is then operated according to the recommended ram force profile and/or melt pressure profile.