Common Misconceptions About Investment Casting

17 3 月, 2020

At Impro, we are a premier manufacturer of high-quality engineered metal parts and components suitable for use in critical and demanding applications, such as those found in the aerospace, automotive, and construction industries. One of our core services offered is investment casting. Over the years, we have received various questions and encountered numerous misconceptions about the process. The following points aim to answer and address some of the most common ones.

1. Investment casting is only suitable for small and complex parts.

False. Investment casting is suitable for both large and small parts. Some of the greatest advantages of the investment casting process are reflected in the manufacture of large castings. 

2. Investment casting tolerance holds as ISO 8062 CT4-CT6.

False. At Impro, we use silica sol as our investment casting shell material to achieve a tighter tolerance range—CT4-CT6. However, depending on the part design and the process technology, the tolerance in the finished piece may not be as tight.

3. Investment casting is only suitable for certain steel alloys.

False. Investment casting accommodates a wide range of metals. In particular, aluminum, titanium, and steel alloys are well-suited for use in such process.

4. Investment casting is similar to the permanent mold casting process.

False. The wax patterns and ceramic molds used for investment casting are destroyed when the castings are produced and removed, respectively. As a result, new wax patterns and new ceramic molds must be created for each production run of an investment cast part. In contrast, the molds used in permanent molding casting operations are reusable, allowing industry professionals to use them for many production runs. 

5. Investment casting requires a draft for tooling release.

False. In an investment cast part design, it is not necessary to include a pattern taper. Since the process uses liquid slurry to create the part mold, the part design can feature almost any shape with a high degree of freedom regarding complex and intricate elements.

6. Investment casting has a parting surface.

False. Both the sand casting and investment casting processes have a parting stage. In sand casting, the stage refers to the process of splitting the mold to release the finished piece and, in investment casting, it refers to the process of melting the wax to create the ceramic mold for part production. While these processes occur at different stages during their respective casting operation, the key distinction lies in the surface finish achieved. 

  • In sand casting: The act of breaking the mold to remove the finished product creates seams—i.e., parting surfaces—on the piece. In addition to the rough texture left by the sand, this surface imperfection necessitates investment in additional finishing operations.
  • In investment casting: The use of hard ceramic molds allows for the production of smoother and more precise parts that require very little secondary processing.

7. Investment casting is more expensive than a machining-only process.

False. When used alongside machining processes, investment casting can lower production costs. For example, an investment cast part can be produced to reasonable part tolerances and/or combine individual assembly components into a single unit. Once cast, the part can then undergo machining for only the critical areas. Through this combined production process, industry professionals can reduce the overall time and labor required to produce the part. 

8. The lead time for investment casting is longer than other processes.

False. Lead time is largely determined based on the part. When a pattern tooling is made, simple parts can be completed with a lead time of 1–2 weeks, while more complex components can take 3–4 weeks. In general, investment casting lead times are competitive with those of other manufacturing processes as they can reduce the amount of labor needed by producing components that do not require additional assembly or finishing.

9. The cost of investment casting is always higher than sand casting.

False. Sand casting requires a greater wall thickness than investment casting, which translates to higher material usage and related costs. In addition to having lower material costs, the investment casting process can produce complex components as a single piece, reducing the need for investment in additional assembly and finishing. 

10. Investment cast parts have worse porosity performance than forged parts, so they aren’t appropriate for high-pressure applications.

False. The investment casting process can be optimized to improve porosity and meet the necessary pressure requirements. At Impro, we can produce investment castings with maximum pressure capacities up to 400 Bar. 

11. The thicker the wall, the lower the possibility of a casting defect.

False. The thickness of the component wall is determined based on the structure of the part. Thin walls will not exhibit unwanted porosity, provided they are at a sufficient distance from the pouring gate. Walls with uneven thickness pose a greater concern, as the different thicknesses affect the cooling rates for the various sections of the casting. 

12. A bigger transition radius is better.

False. A transition radius that is too great can cause porosity shrinkage or overheating in the finished part. 

13. The mechanical properties of investment cast parts are far inferior to those of rolled or forged parts.

False. While investment cast components do exhibit inferior mechanical properties when compared to rolled or forged parts, the differences between them are relatively insignificant and can be largely mitigated through hot isostatic pressing and heat treating operations. Compared to forging and rolling, the process also accommodates a wide range of ferrous and non-ferrous materials at lower production costs for low-volume runs. 

14. 3D printing technology will replace investment casting.

False. Although 3D technology is useful for producing investment casting patterns, it is unlikely to replace investment casting altogether. Additionally, the investment casting process is much cheaper than additive manufacturing processes and offers better surface quality and broader material accommodation. 

At Impro, we take pride in our exemplary investment casting services and outstanding customer service. To learn more about the investment casting process or our manufacturing services and capabilities, reach out to us today.

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