Cost Considerations

The cost on any project can vary, but there are elements under your control which you should consider before the start of a project if you are looking to control costs.

Number of parts per assembly

There are several reasons why the number of parts you use could affect the cost of your project, including:

  • A lower yield. Yield is the ratio of total part weight to assembly weight. A lower yield means more metal is poured per saleable casting, more ceramic material is used, and more handling is required per part.
  • Lower yield also reduces the number of parts that can be placed on one hanger or in the burnout oven – this reduces the throughput of the process in these critical areas.
  • All of these issues reduce efficiency and increase the number of raw materials required to produce a casting.

Additional Processes

Occasionally, due to other requirements related to alloy performance, or for the inspection of highly critical applications, there can be a need for further processes. These are usually related to heat treatments, machining, and non-destructive testing (such as fluorescent penetrant inspection and radiographic inspection).

Inspection Requirements

There is sometimes a tendency to over-inspect investment castings, which can add a high cost to a project. Some elements such as cold shuts, hot tears, and linear shrink cannot be allowed, but less critical things are:

  • Positives
  • Porosity
  • Parting lines

We can limit the critical dimension and gauging to reduce costs on a project, without any loss of quality.

Ease of Shelling

The complexity of a design is a common impact on the cost of a project. The main areas of impact are:

  • Complex geometries with deep pockets will reduce airflow during drying in between ceramic dipping sequences.
  • This reduced airflow will increase the amount of time required for the part dry and allow the binder in the ceramic slurry to set; this reduces the throughput in the shelling process and in turn, adds cost.
  • Other complex geometries require the use of cores with additional expensive raw material as well as a further process, by way of leaching, to remove the core.

The best way to limit these problems is to limit the number of complex geometries used in casting. By only using these when necessary to the function of the casting, you can cut the cost of your investment casting.

Other Factors

Aside from the most common elements above, other factors which are likely to influence the cost of your investment castings are:

    • Cut off time. Cut off time reduces the amount of labor required to remove the parts.
    • Ease of casting. The geometry of the parts dictates how easy casting will be. Multiple hot spots created by multiple thick to thin sections can cause porosity rates to increase or require additional gates; causing scrap rates and labor requirements to increase.
    • Ease of injection. Ease of injection is also influenced by part geometry. Undercuts in the part geometry require moving cores that significantly increase the complexity of the tooling. While this may not increase the piece price of the castings, it can dramatically increase the initial cost of the tooling.
    • Alloy selection. The more expensive the alloy, the more expensive the cost of the casting. Certain materials can also require additional processes such as canning to prevent the formation of chrome oxide during solidification. Other alloy properties can also increase or reduce scrap rates due to varying levels of fluidity, solidification profiles, and hardness (for material removal).