Type of Document Dissertation Author Li, Jing Author's Email Address firstname.lastname@example.org URN etd-07012006-135801 Title Modeling, Design and Control of Vacuum Assisted Resin transfer Molding (VARTM) for Thickness Variation Reduction Degree Doctor of Philosophy Department Industrial and Manufacturing Engineering, Department of Advisory Committee
Advisor Name Title Chuck Zhang Committee Chair Ben Wang Committee Co-Chair Max Gunzburger Committee Member Okenwa Okoli Committee Member Zhiyong Liang Committee Member Keywords
- Variation Reduction
- Stochastic Process
Date of Defense 2006-05-26 Availability unrestricted AbstractIn general, composite manufacturing processes have more variations compared to the metal manufacturing processes due to the larger raw material and manufacturing processes variations. Vacuum-assisted resin transfer molding (VARTM), one of a commonly used composite manufacturing processes, is becoming more popular due to its low cost tooling and environmental friendly operating conditions. Currently, most commercial products manufactured by VARTM are developed based on the userís experience and involve repeated experiments. To optimize the process, reduce manufacturing costs, and maintain consistent part quality, knowledge of mold filling, especially flow through thickness direction is required.
This dissertation investigates the mechanism of the thickness variation and quantifies the magnitudes of the thickness distribution. Typically, thickness gradient and variations of VARTMed parts result from material variations and the infusion pressure gradient during the process. After infusion, certain amount of pressure gradient is frozen into the preform, which primarily contributes to the thickness variation. This research investigates the mechanism of the thickness variation dynamic change during the infusion and curing/relaxing processes. A numerical model was developed to track the thickness change of the bagging film free surface. A time-dependent permeability model as a function of compaction pressure was incorporated into an existing resin transfer molding code for obtaining the initial conditions of curing/relaxing process. Control volume (CV) and volume of fluid (VOF) methods were combined to solve the free surface problem.
In addition, this dissertation analyzes the sources of the uncertainties and quantifies the magnitudes of the uncertainties by error propagation theory to characterize the statistical properties of the permeability values. Normal distribution and Weibull distribution were utilized as the statistical models for representing the average permeability values and race-tracking effects, respectively.
Factors related to the part thickness variation were identified with design of experiments method and a better tooling design was obtained by configuring the different flow media. With the help of the simulation program, a process model-based tooling design optimization was formulated. However, the parameter uncertainty made the deterministic optimization unreliable. To address the issue of part-to-part thickness variation, a stochastic process simulation coupled with optimization was proposed and demonstrated.
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