Are Investment Castings Expensive?

Due to the costs and labor with the molds, investment castings generally have higher costs than forged parts or sand and permanent mold casting methods. However, they make up for the higher cost through the reduction of machining achieved through as-cast near-net-shape tolerances. One example of this is innovations in automotive rocker arms, which can be cast with virtually no machining necessary. Many parts that require milling, turning, drilling and grinding to finish can be investment cast with only 0.020-0.030 finish stock.

Further, investment castings do not need taper to remove the components because the ceramic shells are cracked off the part. This can allow castings with 90-degree angles to be designed with no shrink build included and no additional machining to obtain those angles.

How Many Parts Are Needed to Make Investment Casting Practical?

This number depends on how many casting runs will occur. If there is a run size of 50 that will be produced 10 times per year, the tooling costs for the wax patterns likely will be well paid off after the 10th run. Further, no additional repairs need to be made to the tool because wax does little to cause wear defects to the tool material. Generally, machine toolmakers say that the logical part count to pay off a tool is at least 25 castings. Once a tool is purchased, it likely needs only one or two pieces at a time for replacements.

There are a number of investment casting facilities, mainly in the automotive industry, that produce more than 100,000 parts per month. The high part numbers are dependent on how much a metalcasting facility is willing to expand its capacity to produce such high volumes. For standard orders, the bulk of investment castings produced fall in the range of 100-10,000 pieces per year.

What Tooling and Pattern Equipment Is Necessary?

To produce the wax mold patterns, a split-cavity aluminum die (with the counter shape of the final casting) will need to be made. Depending on the complexity of the casting, various combinations of aluminum, ceramic or soluble cores may be employed to allow for the desired configuration. Most tooling for investment casting falls between $1,000-$10,000.

Rapid prototyping methods allowed for the delivery of this investment cast part in less than two months while also achieving the required mechanical properties.

Are There Porosity and/or Shrinkage Defects with Investment Castings?

This depends on how well a metalcasting facility degasses a melt and how fast the parts solidify. As mentioned earlier, a properly built tree will allow porosities to be trapped in the tree, not the casting, and a high-heat ceramic shell allows for better cooling. Also, vacuum-investment cast components rid the molten metal of gassing defects as air is eliminated. Investment castings are used for many critical applications that require x-ray and must meet definite soundness criteria. The integrity of an investment casting can be far superior to parts produced by other methods.

What Are the Typical Leadtimes?

Like most casting processes, leadtimes with investment casting vary due to part complexity and casting plant capacity. Generally 6-8 weeks is typical for tooling and sample castings and 8-10 weeks for production. Once a wax pattern is created, a component can be produced in seven days; much of this time is spent with the coating and drying of the ceramic slurry. Several investment casting facilities have quick drying capabilities for ceramic molds to produce parts in 24 hrs. In addition, by using RP processes, engineered cast metal components can be delivered only days after accepting a final CAD model.  MetalcastingDesign.com