Technical Articles

Minor oversights during the design phase of a casting can lead to unintended downstream costs.  Let us consider two case studies we have encountered recently as examples of how overlooking the requirements of specifications on your drawing can lead to extraneous manufacturing steps. 

As it is with other hard alloys such as inconel or even stainless steel, the secondary machining of MMC castings is a significant cost component of their manufacture.   The near-net-shape advantage and the greater freedom of design that is inherent with the Investment Casting process provides opportunities to greatly reduce or eliminate machining content of MMC castings. 

Aluminum alloy / Silicon Carbide MMC castings can be produced in 20%, 30% & 40% concentrations of Silicon Carbide by volume and heat treatable, commonly being furnished to a T77P heat treatment.

With its unique set of properties MMC alloys have been employed in diverse applications such as moving structures in high speed equipment for manufacturing, brake rotors for vehicles, heat sinks for electronics and as housings & mirrors for optics.

OFC invests heavily with its Customers to forward our mutual success.  O’Fallon Casting represents so much more value in a supply chain than simply “good parts on time, every time”.

Investment Casting-201 is a three day class taught at O’Fallon Casting on the basics of Investment Casting manufacture.  An IC-201 class provides an introduction to all of the investment casting manufacturing operations and includes hands-on experience with pattern injection, sprue assembly, gate grinding, straightening, radiography and penetrant inspection.  In addition IC-201 “students” receive 3-hours of classroom work, participate in a collaborative engineering workshop and are exposed to toolmaking, solidification modeling and defect analysis.

For most foundry processes the commonly accepted standard for the nondestructive testing is SAE International specification AMS 2175.  Although better known for delineating the frequency and inspection criteria for Radiography, Magnetic Particle and Penetrant Inspection, AMS 2175 also devotes substantial sections to quantifying the standards for Visual inspection. 

Slots and fins are common features that appear often on Investment Cast parts and typical of configuration that can be incorporated into a design with minimal impact on the cost.  There are, however, some basic rules-of-thumb for the design of slots and grooves to help keep them from becoming cost drivers.

One of the special capabilities of the investment casting process is the production of castings with internalized features, passageways or undercuts.  O’Fallon Casting has four techniques available to produce internal detail:  mechanical tooling, soluble wax cores, pre-formed ceramic cores and imbedded pre-formed tubing.  We’ll expand here on each of these four techniques.

Blind holes and pockets are common features of investment casting designs. They serve to lighten the part, provide designed clearances and are examples of the type of detail that can often be provided by the investment casting process at negligible cost to a customer.

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