Validation of moulding consistency with a self-regulating melt pressure valve

Abstract

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.

Design and performance analysis of a self‐regulating melt pressure valve

“…Compared to earlier systems [3,4] and machine-based cavity pressure controllers [8], the valve provides the capability to control the melt at multiple locations and with faster response. The increase in polymer processing consistency and productivity has been validated [9,10]. Given the simplicity of the valve design, it is expected that the self-regulating valves will be used in many molding, extrusion, blow molding, and other applications where increased process flexibility and consistency are required.…”

“…⌬P ϭ 690 4.5 (10) where is the valve pin diameter in mm, the pressure drop is measured in MPa, and the value in the numerator is related to the apparent viscosity of the material and the geometry of the valve. This result occurs for two reasons.…”

Validation of moulding productivity with two self-regulating melt pressure valves

“…1 for efficiently exploiting the process flexibility afforded through the use of multiple self-regulating valves. Given the compactness of the valve design and low actuation forces previously described 1 , it is possible to use a large number of valves in a single injection mould. Several applications are immediately apparent, including the use of different valves corresponding to different cavities in a family mould, or the use of multiple valves to control the flow rates and/or cavity pressure distribution in a complex multi-gated part, or the use of multiple valves to increase the process consistency and fine tuning of multiple precision parts.…”

“…A standard two-drop, valve-gated hot-runner system (Mold-Masters, Georgetown, Ontario) was retrofitted with two self-regulating valves as previously described. 1 The mould, which was used to produce binder separators, Q!DP :…”

“…Recognizing the need for improved control of the polymer melt, a self-regulating valve design was developed and shown to provide excellent polymer processing consistency. 1 A focus on consistency is necessary to satisfy today's myopic focus on Six Sigma, [2][3] but is insufficient to ensure competitiveness. Specifically, increased polymer processing controllability should lead to flexibility, i.e.…”