소형 Zn-합금제품의 최적 다이캐스팅 조건과 대형트럭 브레이크 부품의 냉간단조를 위한 금형 설계에 관한 연구 = Effect of Die Casting Condition on the Mechanical Property of Zn-alloy and Die design of Cold Forging making large truck brake parts

다국어 초록 (Multilingual Abstract)

This dissertation investigates process optimization and die design principles for metal forming processes by focusing on two representative manufacturing technologies: high-pressure die casting (HPDC) of Zn alloys and cold forging of large steel fasteners. Although these processes differ in material systems and deformation mechanisms, they share common engineering challenges related to defect control, mechanical performance, and die durability under severe processing conditions. The primary objective of this study is to establish an integrated framework linking process parameters, material behavior, and die response, and to provide practical design guidelines applicable to industrial production. In the HPDC study, the effects of melt temperature (420–440 °C) and melt speed on porosity formation, microstructure, and mechanical properties of a Zn–Al based alloy were systematically examined. The results showed that variations in melt temperature and speed within the investigated range did not significantly influence grain size or tensile and yield strengths. However, porosity exhibited a strong dependence on melt temperature, decreasing with increasing superheat, while increased porosity led to a pronounced reduction in elongation. These findings indicate that ductility degradation in Zn alloy die castings is governed primarily by porosity rather than grain refinement, and that an appropriate process window is required to suppress defect formation while maintaining mechanical performance. In the cold forging study, the die design for manufacturing large-sized flange bolts—traditionally produced by hot forging—was evaluated to enable cold forging as an alternative process for improved energy efficiency and cost reduction. Finite element method (FEM) analysis was employed to assess stress distributions in preform dies with different geometric configurations. The results revealed that conventional upsetting-based die designs were unsuitable due to excessive principal stresses, whereas trimming-based die configurations provided favorable stress states for cold forging. Optimization of the die outer diameter through FEM analysis led to a significant reduction in stress concentration and an extension of die service life, which was successfully validated through application in actual manufacturing. Overall, this study proposes a unified die–process–defect (or stress) optimization approach applicable to both casting and forging processes. The results contribute to manufacturing engineering by extending conventional process-specific optimization toward a generalized framework for improving product quality, process stability, and die durability in metal component production.

목차 (Table of Contents)

• 제1장 서론 1
• 제2장 Zn-합금의 인장 특성에 미치는 다이캐스팅 조건의 영향 6
• 2-1. 이론적 배경 6
• 2-1-1. 아연의 개요 6
• 2-1-2. 아연 합금의 연구 동향 8
• 2-1-3. 아연 합금 die casting에 관한 연구 동향 및 문제점 10
• 2-1-4 Zn 합금의 개요 및 분류 13
• 2-1-5. Zn 합금의 기계적 물리적 특성 16
• 2-1-6. Zn 합금 다이캐스팅 17
• 2-1-7. 다이캐스팅 기계 및 금형 22
• 2-1-7-1. 다이캐스팅 기계 22
• 2-1-7-2. 다이캐스팅 금형 24
• 2-1-8. Zn 합금의 인장 특성 31
• 2-1-9. Zn 합금 다이캐스팅 주공과 주조 조건 34
• 2-2. 재료 및 시험방법 36
• 2-3. 결과 및 고찰 41
• 2-3-1. Microstructure 41
• 2-3-2. Porosity according to the die-casting condition 48
• 2-3-3. Tensile property according to the die-casting condition 53
• 2-4. 결론 58
• 제3장 대형트럭 브레이크 오일커버를 냉간단조 공법으로 제조하기 위한 금형 설계에 관한 연구 59
• 3-1. 이론적 배경 59
• 3-2. 재료 및 시험방법 61
• 3-3. 결과 및 고찰 63
• 3-3-1. 소재의 미세조직과 기계적 특성 63
• 3-3-2. 압출 핀 입구 각도에 따른 성형하중 해석 69
• 3-3-3. 보강링 압입각에 따른 응력해석 73
• 3-3-4. 소성유동 해석 및 금형 수명 80
• 3-4. 결론 83
• 참고문헌 85