Surface-Coated Cutting Tool With Low-Oxygen Edge and Stress-Hard Coating
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Solution Overview
Problem
Surface-coated cutting tools with high compressive stress coatings tend to drop off easily, limiting their expected extended life due to low adhesiveness between the coating and the base material, primarily caused by unintended oxygen atoms entering the base material during machining.
Innovation Solution
Control the oxygen concentration at the cutting edge face to less than 1% at a depth of 0.4 μm and use a machining method that alternates between wet and dry grinding to prevent oxygen entry, while imparting a compressive stress of at least 1.5 GPa to the hard layer, enhancing adhesiveness and wear resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a coating with high compressive stress is formed on the base material to improve fracture resistance, then the toughness of the coating is improved, but the coating tends to drop off easily due to low adhesiveness
Solution Approach 1:
The patent applies preliminary action by controlling the oxygen concentration in the base material before coating formation. By pre-treating the base material to maintain oxygen concentration at ≤1 at.% at 0.4μm depth from the cutting edge face, the adhesion between the coating and base material is improved before the coating is applied, preventing the coating from dropping off even when high compressive stress is imparted to improve fracture resistance
Solution Approach 2:
The patent applies parameter changes by precisely controlling the oxygen concentration parameter in the base material. By maintaining the oxygen concentration at ≤1 at.% at a depth of 0.4μm from the cutting edge face, the material properties are optimized to achieve both high coating adhesion and high fracture resistance when compressive stress is applied to the coating
2Manufacturing precision
If wet grinding is performed to machine the base material, then the surface finish is improved, but oxygen atoms enter the base material reducing adhesiveness
Solution Approach 1:
The patent applies periodic action by alternating between wet grinding and dry grinding in a repeating sequence. This periodic alternation allows the surface finish to be improved during wet grinding phases while the subsequent dry grinding phases remove oxygen-contaminated surface layers, preventing oxygen accumulation in the base material and maintaining coating adhesion
3Reliability
If dry grinding is performed to prevent oxygen entry, then the oxygen concentration is reduced, but the surface finish and machining quality deteriorate
Solution Approach 1:
The patent applies periodic action by alternating between wet grinding and dry grinding. The wet grinding phases provide good surface finish and machining quality, while the dry grinding phases remove oxygen-contaminated surfaces. This periodic alternation ensures both good surface finish and low oxygen concentration are achieved
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method effectively suppresses coating drop-off, improves fracture resistance, and extends the life of the cutting tool by maintaining high adhesiveness and wear resistance, even with high compressive stress coatings.
Implementation Method 1
a first grinding process of alternately repeating wet grinding and dry grinding
Implementation Method 2
A topmost layer in the hard layer has a compressive stress of more than or equal to 1.5 GPa in absolute value
Data Source
AI summary
A surface-coated cutting tool includes a base material and a coating formed on the base material. The base material is a cemented carbide or a cermet. A surface of the base material includes a rake face, a flank face, and a cutting edge face connecting the rake face to the flank face. The base material has an oxygen concentration of less than or equal to 1 at. % at a depth position of 0.4 μm from the cutting edge face. The coating includes a hard layer. A topmost layer in the hard layer has a compressive stress of more than or equal to 1.5 GPa in absolute value.