New CastingTechnology of Magnesium Alloys in the Automotive Industry: Part One

요약:

The last 10 years have seen a dramatic increase in the production and utilization of magnesium. This demand is primarily driven by the automobile industry and its desire to increase vehicle fuel efficiency.

Magnesium castings are traditionally produced either by high pressure die casting or precision sand casting. Each of these processes has its advantages as well as disadvantages for producing components.

The last 10 years have seen a dramatic increase in the production and utilization of magnesium. This demand is primarily driven by the automobile industry and its desire to increase vehicle fuel efficiency.

One way to improve vehicle fuel efficiency is to reduce vehicle weight by using alternative materials in vehicle components. Magnesium has found uses in several automotive components because of its low density and high strength-toweight ratio as compared to conventional automotive materials. The majority of magnesium components are produced using the high pressure die casting process.

This industry has shown significant growth as the automotive industry strives to reduce vehicular weight. Alternatively, low pressure and gravity fed magnesium casting processes have not achieved the same kind of growth in this industry sector. The key element missing is the lack of a technological base for foundry casting of magnesium alloys.

Magnesium castings are traditionally produced either by high pressure die casting or precision sand casting. Each of these processes has its advantages as well as disadvantages for producing components. Compared to lost foam casting processes, disadvantages of the conventional processes are that several casting design geometries cannot be produced by the steel die sections and are limited by moving cores of die cast tooling.

Other parts cannot be produced by means of high pressure die casting with acceptable levels of porosity. While precision sand casting can produce a wide range of part shapes with high levels of soundness, the process is expensive and generally limited to high value components such as those used in the aerospace industry.

Finding alternative casting processes, such as lost foam casting, to high pressure die casting and precision sand molding was the priority of scientists. One major advantage of the lost foam process over any of the other casting techniques is the ability to create one component to replace several fabricated components. Using the lost foam process is a major manufacturing cost saving.

The Lost Foam Casting Process utilizes unbonded sand and polymer foam patterns to produce highly complex metal castings without the need for cores or binders. The patterns are made by expanding polymer beads in a die and by assembling the pattern pieces and the gating system using adhesives. In order to achieve a good surface finish of the casting a refractory coating is applied to the pattern cluster. The coated and dried cluster is placed in a flask and sand is filled around the foam cluster.

Good vibration of the molding sand ensures that all cavities and undercuts in the pattern are completely filled with sand. When metal is poured into the mold, the foam is decomposed and the metal takes the shape of the pattern. Some of the advantages of the process are:

  • Highly complex parts can be made
  • Castings will not have any flash
  • No binder or cores are needed
  • Sand is reusable
  • Tooling will have very little wear
  • Machining operations may be eliminated

New materials have been developed, research has lead to a better understanding of the process, and the environmental impact has been reduced. Particularly in the USA Lost Foam casting has become generally accepted. It is gaining importance in China too. At the same time in Europe, particularly in Germany, this process only slowly finds acceptance. Some foundries have even discontinued their casting production in Lost Foam.

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