Permanent mold gravity casting (known as Gravity Die Casting) is a process that enables you to produce a large number of castings using a single reusable mold. The casting process simply involves pouring molten metal into a mold, where it cools and solidifies. Afterwards, the mold is opened, the casting is removed, and the mold is reused.
A high-temperature metallic material is used to make the mold, such as cast iron or hot work die steel; both can withstand the repeated heating and cooling typically involved with large volume production.
Gravity Die Casting have relatively high strength, toughness, and ductility – this is due to the metallic mold walls rapidly removing heat from the liquid metal. This generates a fast solidification rate which produces a fine grain structure in the cast metal.
Permanent mold gravity casting produces metal with greater dimensional tolerance, superior surface finish, and higher and more uniform mechanical properties when compared with metal that is solidified using sand casting.
A variety of different metals and alloys can be used for this process, particularly those with lower melting points. Aluminium Gravity Die Casting is the most commonly-used metal casting method by the aerospace industry;
After the permanent molds (e.g. ingots) are produced, which are then processed by working operations (e.g., forging, cnc rolling, etc.) into aerospace structural components.
First, the mold is preheated to around 150-260°C to allow for better metal flow, and to reduce defects. Then, a ceramic coating is applied to the mold cavity surfaces to facilitate part removal and to increase the lifespan of the mold.
The mold consists of at least two parts – the two mold halves, and any cores that are used to form complex features. Such cores are typically made from iron or steel. In this step, the cores are inserted and the mold halves are clamped together.
The molten metal is poured at a slow rate from a ladle into the mold, through a sprue at the top. The metal flows through a runner system and enters the mold cavity.
The molten metal is left to cool and solidify in the mold.
After the metal has solidified, the two mold halves are opened and the casting is removed.
During cooling, the metal in the runner system and sprue solidifies while it is attached to the casting. This excess material is now cut away.
Typical | Feasible | |
|---|---|---|
Materials | Magnesium Copper Aluminium | Zinc Lead Tin Cast iron |
Quantity | 1000-100000 | 1000-100000 |
Tolerance | ±0.015 in | ±0.01 in |
Surface Finish | 120-250 µin | 30-400 µin |
Max. Wall Thickness | 0.08-8 in | 0.08-8 in |
Part Size | 2 oz-300 kg | 2 oz-300 kg |
Shapes | Thin-walled: Complex Solid: Cylindrical, cubic, complex | Thin-walled: Complex Solid: Cylindrical, cubic, complex |
To ensure smooth metal flow and minimal casting defects, we must first pre-heat 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.
You may find more information about the details of the common alloys used in gravity casting process here.
It is worth noting that unskilled pouring 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.
Our gravity casting process can produce porosity-free parts ranging from 50 grams to 70 kilograms with good dimensional repeatability and a smooth finish. All material specifications, dimensions and tolerances are closely monitored and maintained by our QC specialists.
You may also provide us any quality control requirements together with drawings and regulatory documentation if required.
We are able to meet all the customer demands and specifications with our Permanent Mold Gravity Casting techniques. To receive expertise throughout the gravity casting projects and discuss how our advanced industrial engineering and manufacturing capabilities can transform your casting project, please contact our team or submit an enquiry form for more information.
Contact our Customer Service and let us know how we can help to catapult your next project to success.
If you are looking for metal casting services, our brochure is a great way to discover what Omnidex has to offer. You can download HERE to learn more.
