This case study describes improvements to the pin grinding and superfinishing processes for a 900-mm long, 60-kg forged crankshaft used in a six-cylinder diesel engine.
Machining vibrations caused by the eccentricity of the mass of the pins in relation to the journals increase the difficulty of achieving a stable and capable process. Through analysis of the crankshaft and connecting rod assembly, an opportunity is identified to improve the pin profile along its 30-mm length.
Based on measurements, it is found that, owing to variations of the order of 5 μm, the pin profile (nominally flat) may vary between a concave and a convex shape. Process improvements are focused on the grinding profile.
The amplitude of the grinding profile is established between 0 and 5 μm, tending toward a convex shape. The practical implementation of the proposed improvements involves the imposition of a greater restriction on the extent of the grinding profile to 3.5 μm.
The improvements are based on changes to the following crankshaft manufacturing processes: the steadiness of the journals in semifinish grinding, the dressing frequency and feed rate of the finishing grinding wheel, and the paper grit for superfinishing.
The results of this study and the implementation of the suggested improvements should bring benefits to crankshaft manufacturers and customers, reducing the number of product inspections needed and increasing product robustness.