Casting is an old and versatile manufacturing process, which enables to produce complex metal components with diverse shapes and sizes. Among those various casting processes, investment casting (also known as lost-wax casting) stands out for its precision and flexibility. However, other methods such as sand casting, die casting, and permanent mold casting dominate specific industry. This article mainly explores how investment casting compares to other casting methods in terms of process complexity, cost, accuracy, material compatibility, and applications.
Investment Casting
Investment casting involves creating a wax or 3D-printed pattern, coating it with a ceramic shell, melting out the wax, and pouring molten metal into the cavity. After solidification, the ceramic shell will be broken away to reveal the final part. This method is known for producing intricate geometries with tight tolerances and smooth surface treatment. Investment casting is widely used in aerospace, medical devices, automotive industries and more.
Comparison with Other Casting Methods
1. Sand Casting
Sand casting uses expendable sand molds formed around a pattern. After pouring metal, the mold is destroyed to retrieve the part.
Advantages:
- Low cost the large parts and production quantity can be from low to medium.
- Suitable for various large parts (e.g., engine parts, pump housings).
- Can be fused with most of metals, such as iron, steel,aluminum and so on.
Limitations:
- Surface finish and dimensional accuracy are poor.
- The design is limited due to mold constraints.
Comparison:
Investment casting performs better than sand casting in precision and surface quality but is not for simple and large parts. But sand casting is still ideal for heavy industry applications as precision requirement is secondary.
2. Die Casting
Die casting forces molten metal under high pressure into reusable steel molds ,which is commonly used for non-ferrous metals like zinc, aluminum, and magnesium.
Advantages of die casting:
- High production speed.
- Excellent dimensional consistency and smooth surfaces.
- Minimal post-processing required.
Limitations:
- High tooling costs at early stage making it viable only for mass production.
- Restricted to those metals with low melting points.
- It will cause air hole problems due to air entrapment.
Comparison:
Compared with investment casting, die casting is faster and cheaper in mass production,but lacks the design flexibility of investment casting. Investment casting supports more complex shape and high-temperature alloys (such as titanium, high-temperature alloys), making it inevitable for aviation turbines.
3. Permanent Mold Casting
Similar to die casting but the permanent mold casting uses gravity or low pressure to fill reusable metal molds. It's often suitable for aluminum and copper alloys.
Advantages:
- Permanent mold casting has better surface finish and accuracy than sand casting.
- The cost of permanent mold casting is lower than that of investment casting in medium production.
Limitations:
- Permanent mold casting is limited to simpler shape compared to investment casting.
- Tooling costs of permanent mold casting is higher than sand casting.
Permanent mold casting keeps a balance between sand and investment casting but cannot achieve the same level of detail. Investment casting still has an advantage in producing thin-wall or complex core parts.
4. Centrifugal Casting
In the centrifugal casting process,molten metal is poured into a rotating mold, using centrifugal force to fill the cavity. It's ideal for making cylindrical parts like pipes and rings.
Advantages:
- Centrifugal casting has high-density, defect-free structures.
- Centrifugal casting is suitable for symmetrical parts.
Limitations:
- Centrifugal casting is limited to axisymmetric shapes.
- Less design flexibility compared to investment casting.
Compared to investment casting, centrifugal casting performs well in specific shapes but lacks the versatility of investment casting in complex, asymmetrical parts.
Key Standard for Method Selection
- Complexity: Investment casting can produce complex near net shaped parts with fine details.
- Surface Finish: Die casting and investment casting support the best appearance, but investment casting can avoids air hole problem seen in die casting.
- Material Flexibility: Investment casting supports high-performance alloys such as inconel, titanium), while die casting and permanent mold casting are limited to lower-melting-point metals.
- Cost:
a.Tooling: Tooling cost of sand casting is the lowest,while die casting the highest.
b.Per Unit: Investment casting is economical for small quantity (<1,000 units), but die casting is cheaper in mass production.
c.Lead Time: Investment casting requires pattern and shell creation, resulting in longer lead times than sand or die casting.
Future Trends
The advancement in 3D printing is completely changing investment casting. Printed wax or resin patterns eliminate the need for physical molds, reducing costs and lead times for prototyping. The hybrid method combining investment casting and additive manufacturing expands the possibilities of design while maintaining metallurgical benefits.
Conclusion of different casting
Investment casting's unparalleled precision and versatility make it the preferred method for high-value parts in demanding industries. However, sand casting, die casting, and permanent mold casting retain advantages in cost-effectiveness for simpler, high-volume parts. The decision ultimately depends on the part's complexity, material requirements, production volume, and budget. With the development of technology, the integration of digital tools with traditional casting methods promises to further blur the boundaries between these casting processes, offering manufacturers greater flexibility than ever before.