Unlike aluminum pressure die casting, gravity die casting is the casting technique that utilizing gravity to fill the mould with liquid aluminum alloy. Such gravity die casting can also be called as aluminum gravity casting in China.
Aluminum Gravity Die Casting Process
Like other casting processes, aluminum gravity die casting process starts from the developping of mold by CNC machines. Then, melt aluminum ingots into liquid status, and pour the aluminum liquid water into the permanent molds to fill the cavity by handwork or by gravity casting machines. Next, cool the poured aluminum alloy for a while for solidification. Finally, take the aluminum gravity die casting blanks from the mould, and remove the flash and carry out necessary post operations like shot blasting, machining and others. Below is a video showing the aluminum gravity die casting process in our foundry:
Aluminum Gravity Die Casting Alloy: A356-T6
A356 is a type of aluminum alloy especially for gravity die casting. A356 cast aluminum alloy has good casting and machining performance, suitable for use in aircraft, pump housings, impellers, high-velocity blowers, and other structural castings that require high strength. This light alloy is often used to manufacture intricate and complex aluminum castings, which provides lightweight, pressure tightness and great mechanical properties. Sometimes, A356 used as an alternative for 6061 aluminum.
Chemical Compositions
| A356 Aluminum Alloy | Elements | ||||||||
| Cu | Mg | Mn | Si | Fe | Zn | Ti | Others | Al | |
| ≤0.2% | 0.25%-0.45% | ≤0.10% | 6.5%-7.5% | ≤0.2% | ≤0.1% | ≤0.2% | ≤0.15% | balance | |
Mechanical Properties
- Elongation at Break: 3-6%
- Fatigua Strength: 50-90 MPa
- Shear Modulus: 26 GPa
- Ultimate Tensile Strength: 160-270 MPa
- Yield Tensile Strength: 83-200 MPa
- Melting Onset: 570℃
- Density: 2.6 g/cm³
After gravity die casting, T6 heat treatment is suggested to improve the mechanical properties of A356 aluminum castings. The hardness, tensile strength and ductility of A356 castings could be improved by 106%, 106% and 214% respectively.
Benefits of Aluminum Gravity Die Casting
- The tolerances and surface finish are good.
- Gravity die casting method is competitive casting method when production quantity is relatively small or when heat treatment is needed to improve the mechanical properties.
- This casting method gives better tolerances and surface finish than sand casting. But the tooling costs are a bit higher than by sand casting.
- Using sand cores in gravity die casting makes it possible to manufacture items with complicated inner shapes in a cost effective way in small and medium quantities.
Surface Finishing Options
| Surface Finish | Images | Process | Advantages |
| Shot Blasted Finish |  |
High-speed steel shots are propelled at the surface to remove imperfections and improve surface quality. |
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| Powder Coated Finish |  |
A dry powder is applied electrostatically to the surface, which is then cured under heat to form a hard, durable coating. |
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| Anodized Finish |  |
An electrochemical process that converts the metal surface into a decorative, durable, and corrosion-resistant oxide layer. |
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| As Machined Finish |  |
Computer numerical control (CNC) machines remove material from the die-cast part to achieve the desired shape and finish. |
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When to Choose Aluminum Gravity Die Casting
Choosing the right casting process depends on various factors such as production volume, part complexity, material requirements, and surface finish requirement. Aluminum gravity die casting is particularly well-suited for specific components. Here are some situations where you might choose this method:
High Production Volume
Gravity die casting is a good option when you have a high production volume, as the molds can be used multiple times, making the cost per unit more economical in the long run.
Complexity and Dimensional Accuracy
For complex geometries that require high dimensional accuracy, aluminum gravity die casting offers superior results compared to other casting methods like sand casting.
Material Requirements
If your project requires a lightweight material with a good strength-to-weight ratio, as well as good thermal and electrical conductivity, then aluminum is an excellent choice.
Surface Finish Quality
This process typically provides a better surface finish than sand casting, reducing the need for additional surface treatments.
Rapid Production
Once the mold is prepared, the gravity die casting process is relatively quick, making it a good choice for projects with tight deadlines.
Mechanical Properties
Aluminum gravity die cast parts often have better mechanical properties compared to parts made from other casting methods due to the faster cooling rates, which result in a finer microstructure.
Aluminum Gravity Die Casting vs. Aluminum Sand Casting
| Aspect | Aluminum Gravity Die Casting | Aluminum Sand Casting |
| Process | Molten aluminum is poured into a metallic mold, relying on gravity for filling. | Molten aluminum is poured into a sand mold, created using a pattern. |
| Precision | High precision; good dimensional accuracy and repeatability. | Moderate precision; can accommodate larger tolerances. |
| Surface Finish | Smooth and fine surface finish. | Rougher surface finish, often requires additional finishing processes. |
| Tooling Costs | Higher due to metallic molds, which are more expensive to produce. | Lower, as sand molds are generally less expensive to make. |
| Production Speed | Faster, suitable for medium to high volume production. | Slower, more suitable for low to medium volume production. |
| Complexity of Parts | Suitable for complex geometries but may have limitations for very intricate parts. | More flexible with complex shapes and internal geometries. |
| Material Waste | Minimal waste, efficient use of material. | Can result in more material waste and requires proper sand management. |
| Mechanical Properties | Consistent mechanical properties due to controlled process. | Can have varied mechanical properties depending on sand quality and process. |
| Economic Considerations | More cost-effective for larger production runs due to mold reusability. | Often more cost-effective for smaller batches and prototypes. |
| Environmental Impact | Less waste and efficient energy consumption, but requires proper handling of molds. | Use of sand can lead to waste management concerns and potential emissions. |
Aluminum Gravity Die Casting in CFS Foundry
CFS Foundry has been involved in aluminum gravity die casting since 1998. During these years, we have been continuously introducing much advanced gravity die casting machines to improve the production efficiency. For large quantity orders, such machines greatly shorten the production cycle and offer our customers in a much lower price. However, for some small orders, we also reserve our handwork gravity casting processin a cost effective manner.
Currently, our aluminum gravity die cast products are supplied to a wide range of industries, such as automobile industry, oil field industry, agriculture implements, furniture parts, housing appliance, etc. Typical products produced this way are e.g. air intake components for diesel engines, valves for flow systems, tanks for air conditioning systems, etc. Those gravity die casting parts are mostly exported to American and Eourpean countries. We can provide custom aluminum gravity die casting with different aluminum alloys with value added services such as heat treatments, surface treatments (including electroplating, powder coating, painting), assembly, etc.
If you have RFQs for aluminum gravity die castings or other aluminum castings from China, just pls feel free to contact us. We are always waiting online for your service.