The part is a thin wall (OD to ID) flanged sleeve previously manufactured from a solid L605 bar. The ID is coated with Triballoy and requires precision grinding to final dimensions. The OEM, for cost saving purposes (reducing material and machining costs), elects to have the part made from cast L605 in a near net-shape form.
Gas turbine combustion chamber part
Thermally coated Triballoy
Takes place ID
Out of round parts can be difficult to coat and grind without compromising the thickness of the coating. This particular part is a thin walled (OD to ID) flanged sleeve. It had been previously manufactured from a solid L605 bar. To reduce material and machining costs, the OEM decided to make the part from cast L605 in a near net-shape form. The part was to be coated with a finish grind on the ID.
The out of roundness of diameters from the cast part create challenges for the machining source in achieving a round OD for locating with work-holding during grinding. While the required part print OD and ID roundness is achieved during machining, the variables of diameter tolerances and out of roundness presented risks of grinding through the coated ID.
Early in the part process development, the variables from dimensional results, including OD and ID out of roundness, out of flatness of the flange face surface and OD to ID runout resulted in grinding through the coating in areas of the ID. IPG’s engineering staff documented the impact each variable had on the unacceptable results. Working in collaboration with engineers from the part OEM, the machining source and the coating source, IPG proposed a part work holding design for the grinding process that required a slight change to the OEM product design and an added control for the machining operation of the non-critical flange diameter. This allowed IPG to work hold off the robust flange eliminating the OD out of roundness from impacting the grinding process, resulting in a controlled and uniform coating thickness after grinding. Analysis, collaboration, total process design and creative work holding resulted in an acceptable and controlled process.