Best metals and practices for achieving optimum functioning in automobile castings

The need of the hour today is to provide the automobile industry with fuel-efficient vehicles, which reduce energy consumption and air pollution. This can be possible only if the vehicle is in top operating condition, and requires minimal maintenance due to optimal functioning. In order to ensure the optimum functioning of automobiles, the parts used in their manufacturing should be of the highest quality.

The automobile industry relies heavily on components made from aluminum and zinc. Carbon steel is also used in sections that require weld ability. If the manufacturing processes of these components are state-of-art, the automobile industry will reap the benefits in terms of reduced breakdowns, fuel consumption and air pollution.

Automobile casting materials

1. Zinc
It is mostly used in die casting and requires a hot chamber machine to pour it into the die. Zinc is preferred for its high strength, excellent electrical conductivity, high thermal conductivity, full recyclability, high dimensional accuracy and stability, corrosion resistance, thin wall capability, and low cost of raw material.

Automobile casting using zinc is the most preferable and superior alternative to fabricated, pressed, stamped, and machined components. The high strength and hardness of zinc makes it ideal for rugged, corrosion resistant, highly complex, multi-faceted shapes that are required in the automobile industry.

2. Aluminum
It is used in both die casting and sand casting. Aluminum is preferred for its high operating temperatures, full recyclability, lightweight composition, RMI and EMI shielding properties, thermal conductivity, strength-to-weight ratio, and high electrical conductivity.

Aluminum is used to cast extremely lightweight and thin walled components that can withstand extremely high operating temperatures. The above properties also lead to aluminum having the smoothest surface finishings.

Automobile casting methods

1. Die Casting
This process makes molten metal (aluminum or zinc – in case of automobile casting) fill a steel die under pressure. Either direct pouring or vacuum enabled pouring is used for filling the die. The output is a precisely formed component that requires minimal or no machining/finishing.

Die castings have smoother surface and uniform wall thickness, whereas wall thickness varies greatly in sand casting according to the speed of pouring. Die casting machines are either hot chamber machines (for alloys with low melting temperatures, like zinc) or cold chamber machines (for alloys with high melting temperatures, like aluminum).

The die casting cycle involves 5 steps:

  • Clamping – The metal die is opened, cleaned and lubricated before each automobile casting cycle. It is then held together by pressure.
  • Injection – The molten metal is injected at a pressure of 1000 to 20000 psi into the die within 0.1 second to ensure filling all cavities in the die.
  • Cooling – The metal is allowed to solidify until the specified cooling time.
  • Ejection - After the specified cooling time, the die is opened.
  • Trimming – The excess material adhering to the component is burned, sawed or trimmed to derive a smooth finished automobile part.

2. Sand Casting
Sand casting is one of the oldest methods of casting aluminum. Earlier a niche method only for automotive parts, it is now widely adopted across industry verticals. It offers freedom of design, process reliability and quality, and is relatively low costing compared to other casting methods.

Low-pressure sand casting has made it possible to manufacture highly resilient aluminum components like gearbox cross members, anti-roll bars, trapezoidal links, wheel carriers, engine bracket, consoles, auxiliary frame, and intake manifolds and oil sumps. The die is made from pressed sand.

This process is a combination of traditional aluminum sand casting and low-pressure chill casting. Both these processes have the molten metal rising up from below leading to elimination of swirling while the die is being filled. This helps the automobile castings components develop high mechanical strength, which is a must for drivetrain and chassis components of cars and commercial vehicles.

Sand casting is used when the parts to be manufactured are hollow and have intricate designs or conversely, very large patterns. It is a slow process economical only for small quantity of production.

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