| Die casting is a very fast, efficient and economical manufacturing technique, which can produce near net shape castings with desired mechanical properties, dimensional tolerance and surface finish. The shot sleeve is the center of the molten metal injection system in the cold chamber die casting process. To achieve top quality die castings, desirable performance of the shot sleeve and plunger should be maintained during the molten metal injection phase of the process. Therefore, a systematic approach to minimize irregular, adverse conditions which prevent an optimal injection profile, is highly desirable. Shot sleeves deteriorate fast and sometimes fail catastrophically because of poor design and excessive operation parameters. Gross cracking, wear and washout are the leading causes to degrade quality, increase downtime, and thereby decrease productivity and profitability. To eliminate failures and minimize deterioration, their principle mechanisms have been investigated using failed shot sleeves collected from the industry.;As a result of this research, design criteria for robust shot sleeves were developed. They are design rules to prevent catastrophic fracture, accumulated fracture, and severe wear from friction. Stress analysis and calculation of deformation were discussed to obtain the design criteria. A case study confirmed the direct correlation between shot sleeve design and failures in the die casting industry. Variability in microstructure and mechanical properties of commercial shot sleeve material, were revealed to affect the robust design of shot sleeves. Appropriate quality assurance procedures and heat treatment would assist to avoid unexpected catastrophic failures of shot sleeves to a further extent. In addition, the different heat treatment of H13 hot work tool steel is expected to impart superior mechanical properties compared to the traditional martensitic microstructure. Probabilistic design concept was employed to statistically treat variability in materials and die casting process parameters. Thus, design of shot sleeves is specified in terms of probability of failure or acceptable reliability instead of a safety factor. In the future, the accuracy of the design rules would be tested in a real production environment. |
