OPTIMIZATION OF THE ONE-STEP-SANDWICH-SMC PROCESS

摘要

Long fiber reinforced plastics like the thermoset material SMC (sheet molding compound) arernestablished in all ranges of the electrical and the automotive industry. The advantages of thisrnmaterial are good mechanical properties as well as freedom of design and temperature resistance.rnActual requirements for SMC parts are the optimization of the surface quality and the reductionrnof weight. The weight reduction can be achieved either by optimization of the material viarnreduction of density (e.g. Light SMC) or the use of materials with higher strength (AdvancedrnSMC). Another option is the improvement of the fabrication process with the objective ofrnrealizing a sandwich structure of SMC parts.rnThe one-step-sandwich-SMC (OSS-SMC) process can realize a SMC part with a sandwichrnstructure. A blowing agent will be added to the SMC material in the center layer. After closingrnthe mold the agent decomposes and the SMC foams.rnTo realize parts with reproducible qualities it is necessary to know the influence of the processrnparameters on the foaming process. Furthermore the time to start the foaming process influencesrnthe quality strongly and has to be defined during the OSS-SMC process.rnIn this paper the results of investigations on these subjects are presented. The first part describesrnthe foaming process of SMC depending on the mold temperature, the acting pressure, the typernand the content of different blowing agents.rnIn the second part, the application of an online ultrasonic measuring device to define the startingrnpoint of foaming is mentioned. The ultrasonic signal, especially the sound velocity, is principallyrnable to control the OSS-SMC process.