Permanent Mold Gravity Casting

Permanent Mold Gravity Casting:

A solid choice for high quality casting

Permanent Mold Gravity casting may seem like a straightforward process, but a high level of skill is required to maintain the quality of products. As an experienced Gravity casting specialist, we follow a series of strict procedures to ensure our products can always meet your expectations.

Meticulous pre-casting preparations

We ensure smooth metal flow and minimal casting defects by pre-heating the casting mold to between 150°C (300°F) and 260°C (500°F). We then apply a ceramic coating to the mold cavities to extend the mold’s working life and make it easier to remove the casting parts.

Impeccable craftsmanship

It is worth noting that if the pouring process is not done evenly, it may leave visible flow marks on the finished parts. That is why we have our own casting specialists supervising the entire process, ensuring the molten metal is poured into the mold at the right speed. After the casting is done, all sprues and runners are accurately trimmed, then cleaned and painted (if required) by an experienced crew of workers.

Guaranteed quality for our casting processes

Our Gravity casting process can produce parts ranging from 50 grams to 70 kilograms with good dimensional repeatability and a smooth finish. All material specifications, dimensions and tolerances closely monitored and maintained by our QC specialists. Just as the other casting processes we offer, we guarantee no porosity in our Gravity casting parts. Learn more about our guarantee here.

Learn more about Permanent Mold Gravity Casting

Permanent Mold Gravity Casting is one of the oldest methods used for casting metals and alloys, dating all the way back to the earliest metal casting activities of mankind. As its name suggests, this process uses “permanent molds” that can be re-used many times, and the pouring process involves only the force of gravity (without the use of pressurized gases, vacuums, or centrifugal force).

The mold for this process is usually made of two halves of iron or steel tooling (male and female halves). Cores made from resin or sand can also be added to make hollow parts. The use of reusable molds makes this process ideal for mass production.

While the production cost can be reduced for repeating production, Permanent Mold Gravity casting is generally more expensive than sand casting, but still cheaper than Die Casting.

Check out our video on how the process works:

There are also other variations of the process developed to accommodate specific applications. These variations include:

Low Pressure Permanent Mold Casting

Instead of pouring the molten metal into the mold, the metal is instead forced into the mold by using low pressure air. This technique ensures the mold remain filled during casting, and helps in reducing shrinkage during the cooling process. It also allows the product to have finer details and thinner cast walls.

Vacuum Permanent Mold Casting

Similar to the low pressure technique, this technique uses a vacuum to force the material into the mold. It also allows thinner walls, finer details, and better mechanical properties on the product.

Slush Casting

In this process, molten metal is poured into the mold and allowed to cool and solidify at the cavity’s surface. When the solidified material reached the desired thickness, the remaining molten material is poured out of the mold. This technique is commonly used to cast hollow parts without the use of cores.

Pros and cons of Permanent Mold Gravity Casting:

Pros

Reusable molds
More precise control over dimensional attributes (compare to sand casting)
Can produce more complex shapes and designs (compare to sand casting)
Good as-cast surface finish (compare to sand casting)
Products have good mechanical properties
Highly repeatable process, well-suited for high volume production runs
Can be easily automated
Low shrinkage and low gas porosity

Cons

Materials with lower melting temperatures are more suited for this process
Materials with a high melting point such as cast iron may wear down the mold quickly (the higher the pouring temperature, the shorter lifespan the mold has)
Limited part geometry and size
Higher tooling cost and longer set-up time
Not a viable option for small volume production runs

Materials

The best materials for this process are non-ferrous alloys with lower melting points, including aluminium, magnesium, tin, zinc, copper and lead alloys. Materials with a higher melting point are not recommended, as they may wear down the mold more quickly. Common alloys used for this process includes:

Aluminum Alloys

Magnesium alloys

AM100A (10% aluminum, 0.10% manganese)
AZ81A (7.60% aluminum, 0.70% zinc, 0.13% manganese)
AZ91C (0.70% zinc, 8.70% aluminium, 0.13% manganese)
AZ92A (2.00% zinc, 9.00% aluminium, 0.10% manganese)

Copper based alloys

Due to the temperature and flowability requirements of the process, the use of copper based alloys is limited. These copper alloys can be divided into three groups:

Yellow Brasses
This group (more specifically C85500, C85800 and B-2) is widely used in the US and Europe for decorative faucets and sanitary fittings. This group is characterized by its conductivity to buffing, polishing and plating.
High Conductivity Coppers
This group of alloys are used for electrical components and are most difficult to cast. They have higher melting points and are susceptible to oxygen pickup.
Engineering Alloys
This group includes silicon brasses, aluminium bronzes and nickel silvers. This group of copper-based alloys are easier to cast using permanent mold processes, with fine finishes, excellent resistance to corrosion and good physical properties. They are widely used to cast cut-out hardware and water pump impellers.

Tolerances

Permanent Mold Gravity Casting can generally achieve tighter tolerances than conventional sand casting. The following section exhibits the tolerances of this process for your reference:

Our Products

Choose the appropriate casting process for your project

Gravity casting can produce parts with excellent mechanical properties and good surface finishes. This process is also known for its good dimensional repeatability and a reduced need for machining. It has many applications in the automotive industry and electrical industry, including engine components, gears, wheels, insulating flanges, brackets, hand levers and valve bodies, just to name a few.

If you need to produce relatively complex parts with finer surface finishes and tighter tolerances, you should probably consider permanent mold casting over conventional sand casting. It is also a good alternative for die casting, offering lower production costs and better ductility in the product.

Are you looking for a metal casting solution for your next project? Omnidex can help you assess your project and offer exceptional solution most-suited for your needs. Don’t forget to check out other casting processes on our website!

We are always ready to help with your latest project.

Contact our Customer Service and let us know how we can help to catapult your next project to success.

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