The Complete Buying Guide: Investment Casting

What is investment casting?

Investment casting is also known as lost wax casting or precision casting. This is a manufacturing technique in which wax patterns are used to mold disposable ceramic molds. The wax pattern takes the shape of the desired product (the casting). The wax pattern is often coated using a refractory material, primarily a ceramic slurry. Once this material dries to harden, it is heated to remove the wax. The hard ceramic shell obtained is then filled up with molten metal and left to solidify. After solidification, the casting is broken out from the shell, and it is called an investment casting product. 

Generally, the term investment casting came from the process itself, which is investing or surrounding the wax pattern with a refractory material. Precision investment casting is often preferred over other casting techniques because it guarantees fine surface finishes on every product manufactured. Investment casting products can be produced with thin walls and complex designs. 

When you compare investment casting vs. sand casting, you realize that investment casting is far superior and less costly because it does not require drafts.  The investment casting process steps may be a bit complex to follow. However, the entire process is cost-effective, since it does not require final post-processes, such as machining. Additionally, lost wax investment casting can be used with almost every metal and metal alloy, making it very convenient. 

Investment casting applications are vast. Investment casting is used for the manufacture of medical equipment, firearm parts, golf products, turbine blades, jet engine components, and other parts with complex geometry. 

What is lost wax investment casting?

Investment casting is considered a solution to manufacturing parts with complex geometry and in large quantities. This is achieved by injecting wax into permanent dies to create the wax pattern. Investment casting manufacturers can also produce investment castings in lost wax patterns. These are economically viable products when produced in low volumes using manual tooling or high volumes using automatic systems. 

The history of investment casting, also known as the lost wax investment casting process, can be traced back to 1700BC. During this period, products were mainly hand-sculptured using wax patterns with fine detail. After the Second World War, the technique evolved and expanded into almost every industry to what it is today. 

The investment casting process

The investment casting process consists of many steps. Even though every manufacturer may have a different way of producing investment casting products, these steps are often the same throughout. 

Constructing metal die

The wax patterns and ceramic molds are always destroyed to remove the casting in precision investment casting. Therefore, every production cycle ion investment casting requires the creation of a new wax pattern. Adie or mold is created to construct the wax pattern. This may not be the case when the process is used to make products in small volumes.  

The size of the die or mold is predetermined after considering factors such as shrinkage to ensure it fits well. 

Manufacturing wax patterns 

Creating molds

At this phase, a gating system is attached to the mold. Smaller products may need several wax patterns attached to form a tree assembly. 

The resulting assembly is dipped in a refractory material several times to achieve the required thickness. The mold is then left to dry and harden. Upon solidification, the ceramic mold is heated to dewax, leaving a hollow ceramic shell. 

Pouring 

Molten metal is poured into the mold cavity through the gating system. The mold shapes the molten metal to achieve every detail of the desired product. 

Cooling 

The metal in the mold is left to cool and solidify. The time taken to solidify depends on the size and thickness of the mold and the product. 

Shakeout 

After the casting has cooled and solidified, the ceramic mold is broken to remove the product. The mold can be broken manually or using water jets. 

Finishing 

Post-processes may be applied, though not necessary since precision investment casting produces parts with fine surface finishes. 

Advantages and disadvantages of Investment casting

Advantages of investment casting

• Investment casting can be used to manufacture parts with complex geometry and intricate features. 
• Precision investment casting can guarantee the production of products without cold shut defects when the length is kept short and the depth shallow.  
• The lost wax investment casting process guarantees excellent dimensional precision and tighter tolerance. 
• Compared to other casting techniques, investment casting achieves an excellent surface finish, eliminating the need for post-processes. 
• Lost wax investment casting offers freedom inters of investment casting materials used. Investment casting manufacturers can use both ferrous and non-ferrous metals and metal alloys.
• The wax used in investment casting can be reused, making it cost-effective. 
• The process eliminates the need for additional machining.
•  The manufactured parts do not have flash since the process does not have parting lines.

Disadvantages of investment casting 

• The investment casting process is very complex, with many steps that require training. This aspect makes the technique more expensive compared to other casting methods. 
• Dies used in investment casting to make wax patterns are expensive. This aspect limits precision casting to large production volumes.
• The process requires specialized equipment. It also involves a high cost of labor and refractory materials.
• Parts that require a core with holes smaller than 1.6 mm or deeper than 1.5 times the diameter are challenging to manufacture. 

Conclusion

In precision investment casting, wax patterns are dipped in refractory material, mainly ceramic slurry. Once the pattern is coated and hardened, the process is repeated to achieve the desired thickness and strength. The resulting coating is dewaxed by heating to make the mold. Molten metal is poured into the mold and left to solidify. 

The mold is then broken away to reveal the final product. 

Investment casting has been applied in almost every industry due to its vast benefits. This article is generated to help you understand every aspect of the investment casting process. You can get similar resources in the forms of investment casting process pdf or investment casting ppt.

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