MACHINING PROCESS ACCURACY IMPROVEMENT TO ELIMINATE THE QUALITY REJECTION OF OVERSIZED HOLE DIAMETER OF CRANKSHAFT

Abstract

This study focuses on precision machining, specifically the dimensional accuracy of crankshaft hole diameters produced through fine boring operations. A recurring quality issue, that is “NG Hole Diameter” defects—was identified as a major contributor to reduced product quality and process instability. Traditional problem-solving approaches often rely on assumptions or managerial decisions, which tend to overlook key process-driven variations. To address this, a hybrid methodology combining the Taguchi method, Shainin Red X root cause analysis, Six Sigma principles, and data analysis was applied. This integrated approach enabled a thorough investigation of variation sources and the identification of critical machining parameters. By “asking the parts,” or directly analyzing defective components, the study uncovered that inconsistent tool offset input was the primary root cause, with secondary factors including clamper wear and misalignment of part positioning sensors. Depth of cut was found to have the greatest influence on hole diameter, while spindle speed had minimal impact. Implementing optimized machining parameters improved process capability, reduced rejection rates, and enhanced production stability. Academically, the study contributes to machining process improvement through a structured, data-driven methodology, while practically offering industries actionable strategies to improve dimensional consistency, extend tool life, and boost operational efficiency.