Flexible Microfinishing System for Cylindrical Bearing Journals on Crankshafts

Microfinishing is a process that removes the microscopic amorphous surface material left from the grinding of a dimensionally finished part, such as a crankshaft, camshaft, or pump shaft, to permit a highly precise fit to a mating part. Microfinishing tolerances are unattainable with grinding. The Worldstar 1680 CNC microfinishing system from IMPCO Microfinishing (Lansing, MI) polishes the critical cylindrical bearing journals of a range of different size crankshafts to micron tolerances consistently and automatically, without the need to manually change and reposition the tooling, reducing changeover time from many hours to a few minutes. This is the first fully flexible microfinishing system for the automotive industry and was built in response to the requirements of a European automaker for installation in Brazil. It is used to generate the final functional surface texture required for friction reduction, higher performance, and greater reliability of the precision shafts.

“In today’s automotive engines, the surface texture on these functional key features on the internal engine components are microfinished to very fine tolerances that enable combustion engines to operate more efficiently and to meet emissions, horsepower and fuel economy goals,” explained Mark Hendel, the global sales director of IMPCO. In the Worldstar 1680, abrasive film is fed through a pair of opposed arms, each holding tooling that is shaped to fit over the part’s cylindrical bearing journals. During the process, the arms close around the journals, holding the film against the rotating part for a specified time to achieve the desired surface texture. The part may undergo several increasingly fine levels of finishing to produce the final finish. The machine processes a 4-cylinder crankshaft through three levels of microfinishing plus thrust face finishing. In the automotive industry, surface finish parameters used to evaluate the surfaces of the crankshafts include Ra, Rk, Rpk, and Rvk.

The flexibility of the machine to automatically position any of its 11 pairs of arms in any position to accommodate a range of crankshaft sizes saves the automaker time during changeover and avoids the need to retool the machine. The machine can produce any crankshaft in its matrix of part dimensions, including variation on bearing pitch (main bearing to pin bearing spacing), currently and into the future. Each microfinishing station in the 4-machine system is loaded and unloaded automatically with an overhead gantry. IMPCO has been pursuing development of the Worldstar 1680 for more than a year in response to a global need for flexibility to produce parts to a range of specifications and volumes with minimum changeover time and cost.

Industrial Metal Products Corporation, 3417 West St. Joseph Street, Lansing, MI 48917, 517-484-9411, Fax: 517-484-0502, www.impco.com.