Self-Regulating Melt Valves for Polymer Processing David Kazmer May 12, 2005 National Plastics Center

Agenda Introduction –Vision –Design Validation –Steady State Behavior –Consistency –Flexibility –Clamp Tonnage Reduction Current Status

Conventional Molding Barrel Heaters Reciprocating Screw Check valve Injection Cylinder Clamping Cylinder Operator Interface Stationary Platen Moving Platen Mold Pellets Polymer Melt Process Controller Hydraulic Power Supply Clamping Unit Injection Unit Tie Rods Uneven processing in conventional molding

Vision for Injection Molding Decouple the mold from the molding machine –To increase supply chain productivity Decouple the gates from each other –To increase part design flexibility –To increase manufacturing flexibility –To increase molded part consistency Decouple filling from the packing –Increased molded part quality

Enabler: Self-Regulating Valves Barrel Heaters Reciprocating Screw Check valve Injection Cylinder Clamping Cylinder Operator Interface Stationary Platen Moving Platen Mold Pellets Polymer Melt Process Controller Hydraulic Power Supply Clamping Unit Injection Unit Tie Rods Complete process control for each gate… …without pressure transducers or closed loop controllers

Valve Design Self-regulating valve –Two significant forces: Top: control force Bottom: pressure force Forces must balance –Pin moves to equilibrium position Melt pressure is proportional to control force –Intensification factor related to valve design

Valve Function No sensor or controller needed! Valve adjusts to reject input variation –Outlet pressure proportional to control force –Pin position determined by inlet pressure and required pressure drop F control time P out time P in time

Valve Deployment Advantages –Multi-axis melt control without cavity pressure transducers! –Compact with low actuation forces Disadvantages –Hot runner required Provides flexibility, consistency, and productivity

Performance Analysis: Flow Vectors Annular flow provides low shear rates & pressures

Performance Analysis: Effect of Position Pin will hover near 1mm with very fast response.

Performance Analysis: Effect of Size Higher melt flow with slightly larger valves

Performance Analysis: Open Loop Error Open loop error ~10N Correctable error of 1-2%

Agenda Introduction –Vision –Design Validation –Steady State Behavior –Consistency –Flexibility –Clamp Tonnage Reduction Conclusions

Validation All validation performed with a two cavity hot runner mold –Mold Masters Lts (Georgetown, Ontario) Mold produced binder separators –1.8 mm thick by 300 mm long –10 g weight Three control schemes investigated –Convention molding –Open loop control –Closed loop control with pressure feedback

Air Pressure vs. Melt Pressure Melt pressure proportional to air pressure

Melt Pressure vs. Part Weight Part weights adjusted with air pressure

Consistency Study: Design of Experiments Most significant parameters investigated

Process Sensitivities Conventional Valve Gating Open Loop Melt Valve Machine sensitivity greatly reduced Intra-run variation (whiskers) greatly reduced

Short and Long Run Consistency Short and long run consistency greatly increased

Quality Distributions

Flexibility Example Use mold inserts to make different cavities Use pressure valve to control weights & size

Control Actions The valve settings were optimized within 30 minutes, no retooling

Small Cavity Part Weights Small parts acceptable by third trial, optimal in sixth trial

Large Cavity Part Weights Large parts acceptable in second trial, optimal in sixth trial

Pressure Profile Phasing The processing of each cavity may be slightly offset in time By offsetting pressures, the moment of maximum clamp force is offset Slight extensions in cycle time can yield drastic reductions in clamp tonnage

Pressure Profile Phasing Black curve offset from green curve by 2 seconds.

Clamp Tonnage vs. Cycle Time 10% increase in cycle time allows 50% reduction in machine tonnage!

Current Status Intellectual property –UML has filed a utility application –Licenses under consideration Technology –Being validated for extrusion Extrusion of multi-layer nano-composites –New designs under development Valve gating Multiple materials