Recently, MoreSuperHard received feedback from a customer experiencing severe edge chipping on a solid CBN insert while machining a cast iron roll.
Photographic evidence showed cbn tool damage and corresponding edge breakout marks on the roll surface. This article analyzes the root cause and provides actionable recommendations.
Initial Assessment: Material Compatibility & Process Parameters
The customer confirmed the roll’s material and hardness fell within the operational range of our recommended CBN grade. Initial checks of machining parameters (via machine panel photos) also appeared normal.
Critical Oversight:
While basic settings seemed correct, the cutting depth (0.5mm) and the chamfer width (1.5mm) of the selected insert (RCGX120700VS15015) created a critical mismatch.
Root Cause: Cutting Depth vs. Chamfer Width Mismatch
Key Technical Insight:
A wider chamfer enhances edge strength for heavy cuts but becomes counterproductive in shallow-depth applications.
Why Edge Chipping Occurred:
- Insufficient Cutting Depth (0.5mm):
The 1.5mm chamfer increased edge-workpiece contact area, reducing localized cutting force distribution. This caused edge rubbing instead of clean material removal, generating cyclic stress peaks.
- Stress Concentration:
Shallow cuts directed uneven forces toward the tool’s side, exceeding the CBN edge’s impact resistance.
Recommended Solutions
Option 1: Adjust Cutting Depth
Increase cutting depth to 1–2mm to align with the chamfer’s load-bearing capacity.
Option 2: Optimize Insert Geometry
For fixed cutting depths (≤0.5mm), use inserts with narrower chamfers like RCGX120700VS05020 (0.5mm chamfer width) to minimize rubbing and stress concentration.
Practical Example: Machining Hardened Surfaces
When turning heat-treated D80 round steel with ovality (82mm max/78mm min dimensions):
- First-pass depth must stay below 78mm.
- Continuous cutting ensures stable tool engagement, preventing edge chipping.
Need Help Selecting CBN Inserts for Roll Machining?
Contact MoreSuperHard’s engineers for customized insert recommendations based on your:
- Workpiece material & hardness
- Machine power & rigidity
- Required cutting parameters
