| Summary: | 碩士 === 崑山科技大學 === 機械工程研究所 === 98 === This thesis aims to study the thermal stresses during a precision casting process with plastic patterns and investigate the key material properties of plastics that increase the chance of cracking the ceramic.
Numerical analyses of transient heat transfer coupled with structural mechanics were conducted in order to study the thermal stresses inside a ceramic shell in both de-waxing and burnout temperatures in an Investment Casting process. During the study, 2D analyses are considered.
The thermal stress distributions during the de-waxing process are higher than in the burnout process. This fact, exacerbated by the low MOR during de-waxing, makes the ceramic shell prone to crack in the initial stage of investment casting.
Moreover, the sensibility of thermal stresses to the non-linear thermal and mechanical properties of three different plastics are reviewed and discussed.
It is found that the thermal stress is most sensitive to the glass transition temperature Tg, followed by the coefficient of thermal expansion, α, of plastic patterns. The results may serve as the guidelines for introducing plastic injection molding to investment casting manufacturing due to wide range of plastics available.
These results will make investment casting process more successful providing high temperature metal and metal alloy parts with; more precision, more repeatability, lowered production cost and labor in high volume production for small or mini metal parts.
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