CBN Inserts Improve Hardened Steel CV Joint Bore Finishing Consistency

Automotive Parts Machining Case Study

Comparison Under the Same Machining Conditions

Project Background and Challenge

The customer machines CV joints for automotive transmission applications on automated CNC turning lines. The S55C workpiece, hardened to HRC 58–62, required inner-diameter finishing with a small allowance of approximately 0.2 mm. In the original process, visible tool marks, dimensional variation, frequent insert changes, and inconsistent unattended operation affected production rhythm and quality control.

CBN Bore Finishing Solution

UHD recommended the UPN312/860 CBN insert in TNGA160416 geometry for dry, continuous finishing. The solution focused on maintaining a stable cutting load during small-allowance machining, while supporting predictable wear behavior for automated production.

• Small-depth cutting control: optimized the cutting path and parameter window to reduce edge micro-vibration and surface marks.
• Insert consistency: the CBN composite brazed structure supported more consistent tool-to-tool performance and reduced the influence of setup variation.
• Production rhythm planning: tool-life verification enabled more structured insert-change intervals for continuous machining.

Application Results and Manufacturing Value

After process validation, cutting speed increased from 160 m/min to 180 m/min, while single-part machining time decreased from 30 seconds to 25 seconds. Tool life increased from 400 to 600 pieces per edge. In addition to the measured results, the customer observed fewer surface tool marks, more stable batch-to-batch dimensions, lower insert-change frequency, and improved suitability for unattended automated turning.

This case demonstrates that hardened steel bore finishing is not only a tool-material selection issue. For CV joints and similar automotive parts, stable CBN insert structure, controlled small-allowance parameters, and standardized tool-life management work together to make finishing quality and line efficiency more manageable. Henan UHD Ultrahard Tools Co., Ltd provides CBN insert and custom ultrahard cutting-tool solutions for comparable hardened steel precision turning applications.