Net shape manufacturing of plastic products through injection moulding, extrusion and other polymer forming processes has been limited by a lack of observability and controllability of the state of the polymer melt. For this reason, a self-regulating melt pressure valve has been developed that utilizes a valve pin to adjust the juncture loss to balance a provided control force with the force exerted by the melt pressure on an exposed surface of the valve pin. Since the valve pin position is adjusted in accordance with natural laws, an open-loop control system design is feasible without the need for any instrumentation or process feedback for closed-loop control. The process capability of a hot-runner injection moulding process with two self-regulating melt pressure valves is validated with respect to part weight consistency. A resolution four fractional factorial design characterized the main effects for conventional hot-runner injection moulding and injection moulding with the self-regulating valve operated in both open and closedloop control schemes. It was observed that the self-regulating valve operating in an open-loop control mode reduced the sensitivity of the part weight to changes in the moulding process by 73% compared with conventional injection moulding; short-term part-to-part variation was also reduced by 60%. While it might be expected that closed-loop control would provide even greater results, the relatively slow response of the pneumatic control valve actually tended to induce process variation compared with the open-loop control of the self-regulating valve.

A self-regulating melt pressure valve has been developed to proportion melt pressure relative to a control force without the need for a pressure transducer or a closed-loop controller. The lean and agile plastics injection moulding, realized through the use of multiple self-regulating melt pressure valves that provide independent zone-based control of the polymer melt pressure and flow rate, is characterized. The process productivity of a hot-runner injection moulding process with two selfregulating melt pressure valves is validated with respect to flexibility and clamp tonnage requirements. With respect to flexibility, the use of the two self-regulating valves provided the individual tuning of two cavities of varying geometry. The resulting mouldings could not be produced to specification without the self-regulating valves or changes in the mould design. Furthermore, the consistency (as measured by the standard deviation of part weights) of the moulded parts with the self-regulating melt pressure valves was at least twice the consistency of the moulded parts produced with conventional moulding. With respect to productivity, the independent profiling and time shifting of the melt pressure for each moulding zone with the selfregulating valves enabled a 20% reduction in clamp tonnage with no increase in cycle time and a 50% reduction in clamp tonnage requirement with an 8% increase in cycle time compared with conventional injection moulding.

Polymer process control is limited by a lack of observability of the distributed and transient polymer states. Three simulations of varying complexity are validated for on‐line simulation of an injection molding process with a two drop hot runner system to predict the state of the polymer melt in real time and thereby improve product quality in situ. The simplest simulation is a Newtonian model, which predicts flow rates given the inlet and outlet pressures. An intermediate non‐Newtonian and nonisothermal simulation utilizes a modified Ellis model that expresses the viscosity as a function of the shear stress in which the modeling of the heat transfer utilizes a Bessel series expansion to include effects of heat conduction, heat convection, and internal shear heating. A numerical simulation was also developed that utilizes a hybrid finite difference and finite element scheme to simultaneously solve the mass, momentum, and heat equations. Numerical verification indicates that the flow rate predictions of the described simulations compare well with the results from a commercial mold filling simulation. However, empirical validation utilizing a design of experiments indicates that the described analyses are qualitatively useful, but do not possess sufficient accuracy for quantitative process and quality control. Specifically, off‐line validation using optimal transducer calibration with well characterized materials provided a coefficient of regression, R2, of ∼0.8. However, blind validation with previously untested materials and no transducer re‐calibration provided a regression coefficient of ∼0.4. While the direction of the main effects was usually correct, the magnitudes of the effects were frequently outside the confidence interval of the observed behavior. Several sources of variance are discussed, including sensor calibration, constitutive modeling of the polymer melt, and numerical analysis. POLYM. ENG. SCI. 46:274–288, 2006. © 2006 Society of Plastics Engineers

Polymer process control is limited by a lack of observability of the distributed and transient polymer states. An analytical solution is presented for on-line simulation of non-Newtonian and nonisothermal viscous flow in real-time polymer processing. The modeling of the non-Newtonian viscous flow utilizes a modified Ellis model that expresses viscosity as a function of shear stress; the modeling of the heat transfer utilizes a Bessel series expansion to include effects of heat conduction, heat convection, and internal shear heating. The resulting simulation is suitable for inclusion in real-time process controllers requiring sub millisecond response. Numerical verification indicates that the flow rate predictions of the described analysis compare well with the results from a commercial molding simulation. However, empirical validation utilizing a design of experiments for an injection molding process indicates that the described analysis is qualitatively useful but does not possess sufficient accuracy for quantitative process and quality control.

Net shape manufacturing of plastic products through injection molding, extrusion, and other polymer processing methods has been limited by a lack of observability and controllability of the state of the polymer melt. A self-regulating valve is developed and validated that regulates the output melt pressure in proportion to an input control force. The valve relies on a valve pin that adjusts the juncture loss to balance the control force with the force exerted by the melt pressure on an exposed surface of the valve pin. Since the valve pin position is adjusted in accordance to natural laws, an open loop system design is feasible without need of any instrumentation or control system for closed loop feedback control. The design is analyzed using a three-dimensional flow analysis that utilizes independent shear and elongational viscosities for the polymer melt. Pressure drops and shear stresses through the valve are analyzed to estimate the steady state error in the output pressure when the valve pin is controlled in an open loop mode (i.e. without melt pressure feedback). Guidelines for the valve design are provided to achieve a reasonable tradeoff between flow and structural requirements. Finally, experimental validation indicates an excellent level of response and consistency given the simplicity of the design. POLYM. ENG. SCI., 46:549 -557, 2006.