Understanding the Gravity Die Casting Process

Gravity die casting is a commonly used method of casting whereby a hallow mold is filled with molten metal under the forces of gravity. Unlike pressure die casting, where in external forces are applied to the molten metal to push it inside the mold, in gravity die casting, the molten metal is allowed to flow into the mold as a result of its own weight. This process is popular in automotive and aerospace industries because it yields parts of good mechanical properties of high dimensional and geometrical precision.

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What is Gravity Die Casting?

In the gravity die casting process, molten metal is introduced into a reusable metallic mold (referred to as die as well) via gravitational force. The mold is manufactured of steel or cast iron and is made for multiple usages making the cost of the manufacturing process for medium to high quantity casting runs very economically efficient. Molds are manufactured in a way that they are quite complicated geometrically and built with fine details opening doors for mass production of accurate parts.

Benefits of Gravity Die Casting

Exceptional Quality of Castings

High quality gravity die casting services involve producing high quality castings with very high dimensional accuracy and surface quality. This means that it is appropriate for parts which have close fittings and need a fine finish.

Economical for Medium to Large Scale Production

The fabrication of a recoverable metal mold has a relatively high initial cost, however as gravity die casting can be carried out repeatedly, this makes it‘s cost beneficial for medium to large runs. Also reduces the amount of materials that are wasted when compared to other casting techniques.

Improved Mechanical Properties

Parts achieved by gravity die casting are usually of better mechanical properties than those attained through sand casting. The solidification process is enhanced through cooling, which increases the cast components mechanical strength and toughness.

Different Types of Materials

Gravity die casting can use various metals such as aluminum, or zinc and copper alloyed with magnesium. Each one presents a different property magnifying the opportunity of the manufacturer to pick the right one for the desired use.

Key Steps in the Gravity Die Casting Process

Preparation of the Mold

To achieve correct and continued flow of metals within the mold, it is essential to preheat the mold before casting. The required temperature depends on the alloy type being cast. Also, usually a core release agent is coated to the mold so as to reduce metal bonding and enhance the quality of the final product.

Pouring the Molten Metal

When the mold is ready, molten metal, aluminum alloys, zinc alloys, or copper alloys usually contained in a ladle is poured into the mold cavity. The filling of the mold with the metal occurs purely through the activity of highly accelerated gravity which effectively reaches every corner of the mold’s geometry.

Solidification and Cooling

Casts are formed whenever the mold has been filled by the molten metal and the metal cools within the internal section of the mold. The new cast part can be susceptible to changes depending on the cooling speed, so uniform cooling can be done to eradicate chances of deformities like shrinkage or even pores. After sufficient cooling processes have occurred until the metal is fully solidified, the mold is taken apart and the casting removed.

Finishing and Trimming

When the cast is taken from the mold any extra material such as runners and risers will be cut off. Sometimes, it is also necessary to use some finishing operation, for example, machining, polishing, heat treatment, etc. for the surface or mechanical properties of the final part.

Common Applications of Gravity Die Casting

• Automotive Industry

Gravity die casting technology is widely applied for manufacturing engine components, transmission cases, cylinder heads and other structural parts in the automobile industry. Because of this feature, it also allows increasing the general performance and reducing the fuel consumption of the automobile.

• Aerospace Industry

Components used in the aerospace industry are often fabricated using gravity die casting due to the strength to weight ratio required of aircraft engine parts, landing gear components and supporting structures.

• Consumer Goods and Electronics

A large number of appliances and electronic devices contain gravity die adjustable parts: light and strong aluminum covers and brackets.

Challenges of Gravity Die Casting

Limited to Simple Geometries

Even though gravity die casting may incorporate certain technological intricacies it isn’t quite as flexible when it comes to designing detailed models with cut-outs as pressure die casting. More geometrically complex components may require secondary operation of machining or assembly following casting.

Initial Investments for Tooling May be Costly

The fabrication of intermediate and last metal dies and other reusable metal forms can be expensive which will discourage some lower production runs. However, for medium to high volume batch production, it will be cost effective because of the reusability of the molds.

Coming About the Risk of Shrinkage

Subsequent to the cooling down and solidification stages, the metal could possibly undergo shrinkage, which may compromise the dimensions and cause some defects. Poor design of the molds and not controlling the cooling process effectively imposes risks of such nature.