프레스 온도와 금형 온도 차이에 따른 대형 금형의 열변형 특성에 관한 연구

Abstract

The press-forming process of large molds is significantly influenced by thermal conditions such as press slide temperature, upper and lower mold temperature, and bolster temperature. These temperature differences induce non-uniform thermal deformation of the mold, leading to dimensional instability in the final product. In this study, thermal deformation of a 3,300-mm core mold was measured under two real operating conditions: (1) after natural cooling following press installation, and (2) during reheating as the mold was re-mounted and brought into contact with the press slide in a high-speed press. Experimental results showed that a 3.8 °C decrease in the upper mold temperature produced 0.1 mm of thermal contraction, while a 1.5 °C temperature increase resulted in approximately 0.05 mm of thermal expansion. The measured values closely matched the theoretical linear expansion calculated from the mold material’s thermal expansion coefficient. Furthermore, a comparison between a standard press and a large press equipped with an upper oil-circulation cooling system revealed that the latter maintained temperature fluctuations within ±1 °C, significantly reducing mold deformation. These findings confirm that temperature differences between the press and mold are a primary factor affecting clearance variation, and that controlling these temperature differences is essential for precision mold operations.