Updated: Jul 10, 2020
My goal is to help you understand the investment casting process. So, what exactly is
the investment in “investment” casting? The term “invested” historically carries the
meaning of “surround.” Investment casting process starts with pouring wax into a pattern of the desired part. This pattern is attached to a hanger (tree) which is submerged in a slurry of ceramic, plaster, or plastic that coats (surrouds) the wax pattern. The coating is allowed to dry, then it is fired in a furnace melting away the wax (“lost wax”) leaving a hard shell to pour the base metal into. Once the part has been cooled, the shell is mechanically removed and the parts are cut from the tree for finishing process such as machining, heat treat, coating, or polishing.
The stainless-steel motor bearing carrier in the picture is an example of a part made by investment casting. This process was ideal for the bearing carrier because fine details, precision tolerances, and polishing were required.
The bearing required a transition fit and had to be concentric with the machined pilot on the outside diameter within 0.0015"; otherwise, the motor performance and life would be compromised.
We chose the investment casting process because this was the best way to meet the part requirements in stainless steel without a lot of machining. The machining is critical for the function of the part and the polish provides a uniform decorative look. Since investment castings and polishing are both labor intensive, this part was made in a Low-Cost Country to keep the overall part cost down.
As with most materials and design decisions, a discussion with a metals expert can help