Injection molding process-control variable

This module, called Production Xpert, graphically monitors variables specific to the injection-molding process and can automatically determine the quality control limits. The key advantage of the Production Xpert is its ability to automatically detect process variations and drift and it can either suggest how to correct the process or make the necessary changes itself... 

FIGURE A.2 Process control variables for injection molding. 

The differences in the injection molding processing seem to be a significant variable in controlling the construction of the polymer... 

The melt temperature is known to be a key variable in the injection molding process that directly affects the materials viscosity, flow behavior, shrinkage, and the resulting part quality. Accurate melt temperature sensors and careful interpretation of the data are critical both for the control and the simulation of the injection molding process. The melt temperature in the machines nozzle is of special interest because it helps characterize the polymers state just prior to entering the mold and is independent of the part and mold geometry. 

Both theoretical and experimental results have emphasized the importance of the repeatability of molding variables such as mold temperature, melt temperature, and cavity pressure. These process parameters have been investigated as controlled variables for the injection molding process [1] demonstrating that good contfol performance on some of these parameters is essential in order to achieve high product quality. 

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. 

An example of successful use of SPC comes from the injection molding industry where part counts are high and part values are generally low. The material in reject parts can sometimes be recycled. The process is very rapid, with few control variables and the major, often the only, criteria for quality is reproducible shape. For this situation, SPC is an excellent... 

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