1993-03-01

SMC Molding Cycle-Time Reduction Through Real-Time Control of Part-To-Part Variation 930171

Many factors influence SMC cure behavior including mold temperature, SMC temperature, formulation, and aging. Although most of these factors are controlled to some extent, small uncontrollable variations will always cause some degree of fluctuation in cure behavior. The recent development of in- mold cure sensors allows the analysis and control of these variations from part to part and from batch to batch. In this study, SMC molding was monitored for thousands of parts and analyzed using Statistical Process Control (SPC) methods. The standard deviation in part to part cure times was found to be on the order of 1 to 5 seconds depending on factory conditions. A strong correlation of cure time with mold surface temperature was found, however, other uncontrolled parameters were found to have an additional significant influence. The cure sensor and monitoring system was connected to the press controller thus implementing closed loop control. Average cycle times were reduced by more than 10% through early mold opening, automatically triggered by real time cure state information, while part quality standards were met or surpassed. Cure state as a function of the thickness of the part was also investigated and will be reported.

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