CBN Coated Cutting Tool Surface Roughness for Peel-Off Resistance
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Solution Overview
Problem
Existing cutting tools with cubic boron nitride sintered bodies face issues with chipping, peeling, and wear resistance, especially under high-load and high-efficiency machining conditions, due to insufficient surface roughness and adhesion between the base material and coating.
Innovation Solution
A cutting tool with a sintered body containing 30-80% cubic boron nitride and a binder, featuring a coating composition of M1 x L1 y, where x ≤ 1.2 and y = 1, with specific surface roughness ratios and convex/concave portions, enhancing adhesion and wear resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the surface roughness of the coating is reduced to 0.2 μm or less by polishing, then the surface smoothness is improved, but chipping and peeling occur under high-load machining conditions due to insufficient adhesion
Solution Approach 1:
The invention applies different surface roughness requirements to different regions: the negative land face and flank are polished to Ra≤0.2μm for smoothness, while the rake face maintains higher roughness (Ra>0.2μm) to promote coating adhesion through mechanical interlocking. This local differentiation resolves the contradiction between smoothness and adhesion.
Solution Approach 2:
The base material surface is pre-treated with specific roughness characteristics before coating application. The rake face is intentionally left with higher roughness to create anchor points for the coating, ensuring strong adhesion before the coating process occurs.
2Strength
If a coating is applied to improve wear resistance, then the coating provides better protection, but the coating peels off under high-load conditions due to poor adhesion to the cubic boron nitride sintered body
Solution Approach 1:
Different surface treatments are applied to different faces: the rake face maintains higher roughness for coating adhesion, while the negative land face and flank are polished smooth. This ensures the coating adheres well where needed without compromising overall surface quality.
Solution Approach 2:
The invention uses a composite structure combining cubic boron nitride sintered body with a multi-layer coating system (TiAlN, TiCN, AlCrN). The controlled surface roughness creates a gradient structure that enhances interfacial bonding between the ceramic base material and the metallic coating layers.
3Reliability
If the surface roughness of the base material is increased to improve coating adhesion, then adhesion is enhanced, but melting and adhering occur on the negative land face and flank due to insufficient smoothness
Solution Approach 1:
The invention applies opposite surface roughness strategies to different faces: the rake face is kept rough (Ra>0.2μm) to enhance adhesion, while the negative land face and flank are polished smooth (Ra≤0.2μm) to prevent melting and adhering during high-load machining.
4Strength
If the total film thickness of the coating is increased to improve protection, then wear resistance is enhanced, but the coating becomes more prone to peeling due to insufficient adhesion
Solution Approach 1:
The base material surface is pre-treated with optimized roughness characteristics before coating application. The rake face is intentionally maintained with higher roughness to create mechanical interlocking anchors, ensuring strong adhesion foundation before the coating layers are deposited.
Data Source
AI summary
A cutting tool according to this invention is a cutting tool including a base material and a coating formed on the base material. The base material is a sintered body containing 30 to 80 % by volume of cubic boron nitride, and a binder. The surface in contact with the coating, of the base material, has a plurality of convex portions made of the cubic boron nitride and a plurality of concave portions made of the binder. A surface roughness Rsub of the surface in contact with the base material, is 0.1 to 0.4 µm. A surface roughness Rsurf of an outermost surface of the coating is 0 to 0.15 µm. A surface roughness Rasurf of the outermost surface of the coating is 0 to 0.1 µm. The surface roughness Rsub of the surface in contact with the coating, of the base material, is greater than the surface roughness Rsurf of the outermost surface of the coating.