Multi-Layer Coated cBN Tool for Hardened Steel Wear Resistance
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Solution Overview
Problem
Conventional cutting tools fail to achieve sufficient surface roughness life during high precision processing of hardened steel, particularly due to inadequate wear resistance, which limits their dimensional precision and tool life.
Innovation Solution
A surface-coated boron nitride sintered tool with a specific multi-layer coating configuration, including an A layer and a B layer, is developed, where the B layer is formed by alternately stacking compound layers with varying compositions and thickness ratios to enhance crater and boundary wear resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a coating film containing Si is formed on the surface of a cBN sintered body, then wear resistance is improved, but surface roughness life is insufficient for high precision processing of hardened steel
Solution Approach 1:
The coating film is segmented into multiple layers with different compositions and functions. The lower layer (first coating layer) contains Si for wear resistance, while the upper layer (second coating layer) has different composition for surface quality. This segmentation allows each layer to perform its specific function optimally, resolving the contradiction between wear resistance and surface roughness life.
Solution Approach 2:
Different regions of the coating film have different local qualities. The lower layer near the substrate has high Si content for wear resistance, while the upper layer has optimized composition for maintaining surface roughness. This local quality differentiation allows the coating to simultaneously achieve both wear resistance and surface quality requirements.
2Device complexity
If a single-layer coating film is formed on the cBN sintered body, then the coating structure is simple, but insufficient wear resistance and surface roughness life are achieved
Solution Approach 1:
The coating is divided into multiple functional layers, each with specific composition and thickness. The first coating layer contains Si for wear resistance, while the second coating layer provides surface quality enhancement. This segmentation enables the coating to achieve superior wear resistance and surface roughness life compared to single-layer coatings.
Solution Approach 2:
The coating film uses composite material structure with different layers having different compositions. The lower layer uses Si-containing compounds for wear resistance, while the upper layer uses different compounds for surface quality. This composite structure resolves the contradiction between structural simplicity and performance requirements.
3Duration of action of stationary object
If boundary wear occurs in the front boundary portion of the wear zone, then tool life is significantly reduced, but conventional coating structures cannot prevent this type of wear
Solution Approach 1:
The upper coating layer is specifically designed with composition and properties optimized for protecting the front boundary portion where boundary wear occurs. This local quality enhancement at the critical region prevents boundary wear and extends tool life.
Solution Approach 2:
The coating structure preliminarily protects against boundary wear by providing a resistant upper layer before the wear process begins. This preliminary anti-action prevents the harmful boundary wear from occurring, thereby extending tool life.
Data Source
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AI summary
A surface-coated boron nitride sintered body tool is provided, in which at least a cutting edge portion includes a cubic boron nitride sintered body and a coating film formed on a surface of the cubic boron nitride sintered body. The coating film contains Si and includes a B layer formed by alternately stacking one or more of each of a B1 compound layer and a B2 compound layer that are different in composition. A ratio between an average thickness t 1 of the B 1 compound layers and an average thickness t2 of the B2 compound layers is defined as t2/t1 that satisfies a relation of 0.5 < t2/t1 ≤ 10