What is Gravity Die Casting|Echofast

What is Gravity Die Casting?

Gravity die casting, also known as permanent mold casting, is one of the oldest processes used to produce complex parts. In the process, the molten metal is poured into a reusable metal mold under only the force of gravity rather than external pressure. Gravity die casting is different from other casting methods in that only the force of gravity is used to fill the mold cavity.

How does Gravity Die Casting Work?

Gravity die casting relies on the force of gravity to pour the molten metal directly from a ladle into a semi-permanent or permanent die. The gasses can escape and the mold can be filled completely due to the vents and risers. This results in minimal porosity and inclusions, making the process suitable for the creation of high-quality metal parts with complex shapes.

Step-by-Step Process of Gravity Die Casting

1.Pattern creation

A permanent metal mold usually made of steel or cast iron should be created at first in the process. It is designed with the shape of the final part, and consists of two halves.

2.Preheating

The die is preheated to a specific temperature, which helps to reduce likelihood of defects like cold spots and improve the flow and solidification of the molten metal.

Metal mold illustration. https://www.open.edu/openlearn/science-maths-technology/engineering-technology/manupedia/gravity-die-casting

3.Coating

The inner surfaces of the mold cavity are coated with a refractory material or a release agent to help prevent casting sticking and remove the solidified part.

4.Closing the mold

After being preheated and coated, the mold is closed with the two halves aligned precisely. This creates a sealed cavity in line with the desired shape of the part.

5.Pouring

Molten metal is poured into the mold under the force of gravity alone. It reduces turbulence and air entrapment, which prevents defects in the casting.

Pouring molten metal into a mold. https://www.open.edu/openlearn/science-maths-technology/engineering-technology/manupedia/gravity-die-casting

6.Cooling and solidification

As the molten metal is introduced into the mold cavity, it comes to cooling and solidification. Then , it takes on the shape of the mold cavity. The solidification rate varies with the type of metal being cast and the design of the part.

7.Mold opening

Once the molten metal is solidified, the die is opened and the part can be removed.

8.Finishing

Further finishing processes are sometimes required to achieve the desired shape and precision level. They include shot blasting,trimming, and machining.

Common Materials Used for Gravity Die Casting

1.Steels

2.Magnesium

3.Aluminum alloys

4.Cast irons

5.Copper alloys

6.Zinc

Advantages of Gravity Die Casting

Gravity die casting has various advantages, including:

A variety of material options

Gravity die casting can be used to produce parts with a variety of materials, such as aluminum, brass, bronze, zinc, magnesium, and copper,etc.

Less scrap

Less scrap is made in the gravity die casting process, because it can create non-ferrous castings with minimal defects and porosity.

Cost-effective

It is more cost-effective for small and medium volume production of metal parts with consistent quality.

Excellent mechanical properties

Gravity die casting produces parts with excellent mechanical properties like strength and stiffness, which are also suitable for heat treatment.

Good quality

The molds used in the process are often made of steel, which results in moderate dimensional accuracy. This contributes to the creation of high-quality parts with smooth surface finish and precision.

Disadvantages of Gravity Die Casting

There are some disadvantages of gravity die casting, including:

Longer lead times

The process has longer lead times in comparison to other casting methods. It usually takes up to several months for the creation of permanent molds.

Less suitable for the fabrication of larger components

It is less suitable for the fabrication of larger components due to the high cost.

High initial investment

The initial investment in tooling and equipment, between $10,000 and $100,000, is much higher than sand casting.

Limited design flexibility

There are some limitations on design flexibility.The molten metal is poured into the mold cavity by solely utilizing gravity in the process. This makes it difficulty to achieve certain design features like thin walls and intricate geometries.

Applications of Gravity Die Casting

Gravity die casting can be used to manufacture premium parts across multiple industries.Some common gravity die cast applications include:

Automotive

Turbos, brake calipers, knuckles,engine blocks, cylinder heads, pistons, intake manifolds, and transmission housings

Aerospace

Aircraft engine parts, brackets, and housings

Industrial machinery

Valve bodies, gearboxes and pump housings

Decorative and functional lighting fixtures

Ornamental components, housings and lamp bases

Kitchen tools

Pots and spoons

FAQs

1.What are the alternatives to gravity die casting?

High-pressure casting, low-pressure casting, sand casting, investment casting, centrifugal casting, and squeeze casting.

2.What is the minimum wall thickness for gravity die casting?

In general , the minimum wall thickness for gravity die casting ranges from 3 mm to 5mm.

3.How long does gravity die casting take?

It depends on some factors, such as die design , material selection, and the size of the casting. As for simpler castings, it takes up to a few minutes. As for larger or more complex parts, it takes up to several hours.

4.Is gravity die casting suitable for the casting of connecting rods and pistons of the automobile?

Yes, it is. This is because gravity die casting can be used to produce a simple shape of the casting.

5.What’s the difference between gravity die casting and pressure die casting?

Gravity die casting uses only gravity to fill the mold whereas die casting requires additional pressure.

Gravity die casting is slower than pressure die casting, but it can produce stronger parts.

Gravity die casting is more suited to small production runs, while pressure die casting is more suitable for large volume.