Cavity pressure control

Another fundamental state variable that can be regulated during the cycle is cavity pressure. Closed loop control of cavity pressure could automatically compensate for variations in melt viscosity and injection pressure to achieve a consistent process and consistency of molded products. Adaptive control methods have been developed to track the cavity pressure profile at one location in the mold. In these earlier works, cavity pressure control was handicapped by the absence of actuators for distributed pressure control, as conventional molding machines are equipped with only one actuator (the screw), which prevents the simultaneous cavity pressure control at multiple points in the mold. This problem has been solved with the development of dynamic melt flow regulators that allow control of the flow and pressure of the polymer melt at multiple points in the mold.[ °l... 

Gao, F. Patterson, I.A.N. Kamal, M.R. Selftuning cavity pressure control of injection molding filling. Adv. Polym. Technol. 1994,13, 111-120. 

Nunn, R.E. Grolman, C.P. Closed loop cavity pressure control in injection molding. J. Reinforced Plastics Composites 1991, 9, 2121. 

Kazmer, D.O. Barkan, P. Multi-cavity pressure control in the filling and packing stages of the injection molding process. Polym. Eng. Sci. 1997, 37, 1865-1879. 

In order to judge performance capabilities that exist within the controlled variabilities, there must be a reference to measure performance against. As an example, the injection mold cavity pressure profile is a parameter that is easily influenced by variations in the materials. Related to this parameter are four groups of variables that when put together influences the profile (1) melt viscosity and fill rate, (2) boost time, (3) pack and hold pressures, and (4) recovery of plastica-tor. TTius material variations may be directly related to the cavity pressure variation. Details on EQUIPMENT/PROCESSING VARIABLE are in Chapter 8. 

Wan and Isayev (1996) examined a hybrid approach of control-volume finite-element and finite-difference modelling of injection moulding of rubber compounds. The effect of vulcanization on viscosity and yield stress during cavity filling is reported. On comparing two versions of the modified Cross viscosity models - with and without the effect of cure - the use of a viscosity model that accounts for the cure was found to improve the accuracy of the cavity-pressure-prediction models. When the modified Cross model was further extended to include the yield stress and was implemented in the simulation program a significant improvement in the prediction of cavity pressure was obtained in the case of low injection speed. 

ECDL External Cavity Diode Laser OI Optical Isolator L Lens AOS Acousto-Optic Switch PZT Piezo-Electric actuator Me Cavity mirror APD Avalanche Photodiode PC Pressure Controller P Pump... 

Unbalanced cavity pressure buildup, mold distortion, dimensional variation/poor shrinkage control, stresses, flash, etc. 

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