In the field of high-hardness material machining, CBN inserts are widely used due to their excellent wear resistance and thermal stability, especially suitable for turning materials like cast iron and hardened steel.

However, in practical applications, if CBN inserts are used improperly, abnormal wear phenomena may still occur, seriously affecting tool life and machining quality.

This article by Zhengzhou Berlt analyzes the main causes of abnormal wear in CBN inserts from various aspects and provides countermeasures based on practical applications.

I. Common Abnormal Wear Conditions of CBN Inserts

· Abnormal wear on the flank face. Manifested as obvious pits, grooves, or crescent-shaped wear marks on the contact surface between the insert's rear edge and the workpiece, often accompanied by reduced tool life, increased surface roughness of the machined part, and larger dimensional errors.

· Cratering on the rake face. Manifested as localized deep corrosion, such as "pit-shaped" or "bowl-shaped" marks, on the rake face of the cutting edge or the chip flow surface. This is usually caused by chemical reactions, metal diffusion, or the effects of high-speed cutting heat.

· Cutting edge chipping, micro-chipping, or fracture. Manifested as chipping, flaking, or breakage at the cutting edge, potentially accompanied by signs of vibration or impact. This is typically caused by mechanical shock, unstable fixture, excessive overhang, or insufficient structural strength of the insert.

· Thermal cracks / thermal fatigue cracks. Manifested as one or multiple cracks visible at the cutting edge or insert periphery, usually perpendicular to the cutting direction. Crack propagation can lead to insert fracture. This is a typical thermal fatigue phenomenon caused by thermal cycling, sudden changes in cutting temperature, or improper cooling conditions.

II. Main Causes of Abnormal Wear in CBN Inserts

The occurrence of abnormal wear in CBN inserts is often the result of the combined effects of multiple factors such as cutting parameters, workpiece material, tool selection, and machine tool system. Specific analysis is required based on the actual cause.

· Improper cutting parameters. Excessively high cutting speed causes a sharp rise in edge temperature, accelerating thermal diffusion/chemical diffusion mechanisms, leading to crater wear on the rake face or plastic deformation. Excessive feed rate/depth of cut increases vibration and load, thereby accelerating edge chipping or flank wear.

· Workpiece material and structural factors: Hard inclusions or abrasive particles in the workpiece cause localized high wear on the CBN insert's cutting edge. Elements like Ni, Co, Cr in the workpiece material can chemically react with CBN during high-temperature cutting, inducing crater wear. Poor chip control, chip tangling, or clogging leads to increased temperature and friction, thereby accelerating wear.

· Unreasonable tool selection or structural design. Improper selection of CBN insert grade, such as using a grade with poor chipping resistance for interrupted cutting, cannot withstand the actual machining conditions. Inadequate edge structure or insert connection strength can lead to micro-cracking, grain pull-out, developing into edge chipping. An overly small or unreasonable cutting edge hone radius easily causes stress concentration and heat concentration, thereby accelerating abnormal wear.

· Machine tool system and machining environment factors. Poor machine tool rigidity, excessive tool overhang, unstable fixture, etc., can easily cause vibration and impact loads, leading to edge breakage or chipping.

III. Monitoring and Optimization Suggestions for Abnormal Wear

To delay or avoid the aforementioned abnormal wear, it is recommended to implement inspection and optimization from the following dimensions:

· Establish an insert wear inspection system, regularly checking the cutting edge morphology, wear on the rake and flank faces, and for cracks or chipping on the cutting edge.

· Select the appropriate CBN insert material grade based on the workpiece material and machining conditions.

· Optimize cutting parameters, control cutting speed, feed rate, and depth of cut to maintain stable machining conditions.

· Strengthen machine tool rigidity and the tool clamping system to ensure a stable machining environment.

Abnormal wear not only directly leads to a shortened service life of CBN inserts but may also cause decreased part accuracy, deteriorated surface quality, and increased production costs. If you encounter specific cases of abnormal wear while using CBN inserts, please feel free to contact the Zhengzhou Berlt technical service team. We will provide personalized diagnosis and optimization solutions based on your workpiece material, machining conditions, tool grade, etc.