High Pressure Die Casting of Zamak Alloys

Steven Richard Pires de Oliveira
Dissertação de Mestrado
Orientador na FEUP: Prof. Doutor Rui Jorge de Lemos Neto
Orientador no INEGI: Doutora Inês Vieira de Oliveira

Abstract

The high pressure die casting process has undergone major advances in recent years, due to its increasing use in the automotive sector. Although aluminum alloys are the most widely used, the use of zinc alloys has been increasing, mainly due to their excellent characteristics of surface quality and production cycles.

These characteristics make zinc alloys widely used in small applications, where surface quality and low cost are an indispensable requirement. In this study, more attention will be given to the high pressure die casting of zinc alloys, more precisely the Zamak alloys. During the injection process, a turbulent molten metal flow is generated, as a result of the high injection velocities. For this reason, large amounts of air porosity are produced during the injection process.

This causes the air to become trapped in the parts, which deteriorates the mechanical properties. Heat treatments cannot be applied to components with air porosity, since they will expand and cause blistering. An optimized gating system is a solution to minimize the occurrence of these defects. A major concern, is that this process is not valued enough, because many times only the designers experience is used for the dessign process of a gating system.

For these reasons, a good practice manual for designing a gating systems is presented and then applied in a real case, where the lack of an otimized gating system results in production rejection rate of more than 40 %. This solution is later validated using a die casting simulator, ProCAST, where the occurrence of defects will be analyzed. It has been found that an optimized gating system resulted in a more uniform filling pattern, which resulted in less air entrapments.

Even with an optimized gating system, it is not always possible to completely reduce air entrapments during the filling process. The application of vacuum in the cavity arises from the need to reduce/minimize this problem. This technology is widely applied in aluminum and magnesium alloys. However, in zinc alloys it is not common practice.

This is due to the fact that the zinc alloy market is not very demanding in terms of mechanical properties and is reserved for parts with a lower added value. However, it may be necessary to use vacuum in cases where an optimized system is not sufficient. A designing vacuum system method is proposed, where it is applied in a real case. This design is based on the use of the Esco Engineering App, which is a tool that calculates a number of parameters of the vacuum system. This program also enables the validation of the design based on the desired vacuum efficiency.

고압 다이캐스팅 공정은 자동차 부문에서의 사용 증가로 인해 최근 몇 년 동안 큰 발전을 이루었습니다. 알루미늄 합금이 가장 널리 사용되지만 아연 합금은 표면 품질 및 생산 주기 특성이 우수하기 때문에 그 사용이 증가하고 있습니다. 이러한 특성으로 인해 아연 합금은 표면 품질과 저렴한 비용이 필수 요건인 소규모 응용 분야에 널리 사용됩니다.

본 연구에서는 아연 합금, 보다 정확하게는 Zamak 합금의 고압 다이캐스팅에 더 많은 관심을 기울일 것입니다. 사출 공정 중에 높은 사출 속도로 인해 난류 용융 금속 흐름이 생성됩니다. 이러한 이유로 사출 공정 중에 많은 양의 기공이 생성됩니다. 이로 인해 공기가 부품에 갇히게 되어 기계적 특성이 저하됩니다. 공기 다공성이 있는 구성 요소에는 열 처리를 적용할 수 없습니다. 팽창하여 기포가 발생하기 때문입니다. 최적화된 게이팅 시스템은 이러한 결함 발생을 최소화하기 위한 솔루션입니다.

주요 관심사는 게이팅 시스템의 설계 프로세스에 설계자 경험만 사용되는 경우가 많기 때문에 이 프로세스의 가치가 충분하지 않다는 것입니다. 이러한 이유로 게이팅 시스템 설계를 위한 모범 사례 매뉴얼을 제시하고 최적화된 게이팅 시스템이 부족하여 40% 이상의 생산 거부율이 발생하는 실제 사례에 적용합니다.

이 솔루션은 나중에 다이캐스팅 시뮬레이터인 ProCAST를 사용하여 검증되며 결함 발생이 분석됩니다. 최적화된 게이팅 시스템은 보다 균일한 충전 패턴을 제공하여 공기 포획을 줄인다는 사실이 밝혀졌습니다. 최적화된 게이팅 시스템을 사용하더라도 충진 공정 중 공기 포집을 완전히 줄이는 것이 항상 가능한 것은 아닙니다. 캐비티에 진공을 적용하는 것은 이 문제를 줄이거나 최소화할 필요가 있기 때문입니다.

이 기술은 알루미늄 및 마그네슘 합금에 널리 적용됩니다. 그러나 아연 합금에서는 일반적이지 않습니다. 이는 아연 합금 시장이 기계적 특성 측면에서 그다지 까다롭지 않고 부가가치가 낮은 부품에 국한되어 있기 때문입니다. 그러나 최적화된 시스템이 충분하지 않은 경우 진공을 사용해야 할 수도 있습니다. 실제 사례에 적용되는 설계 진공 시스템 방법을 제안합니다.

이 설계는 진공 시스템의 여러 매개변수를 계산하는 도구인 Esco Engineering 앱의 사용을 기반으로 합니다. 이 프로그램은 또한 원하는 진공 효율성을 기반으로 설계를 검증할 수 있습니다.

KeyWords

High pressure die casting; Zamak alloys; Gating system; ProCAST; SolidWorks; Vacuum;
Exco Engineering

Figure 9- Left: Schematics of a conventional HPDC cold chamber machine [14]; Right: Typical layout of a component produced by a cold chamber machine [15].
Figure 9- Left: Schematics of a conventional HPDC cold chamber machine [14]; Right: Typical layout of a component produced by a cold chamber machine [15].
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