Rolling Bearing Raceway Machining for Inclusion-Induced Flaking
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Solution Overview
Problem
Inclusions present in the surface layer of a rolling bearing's raceway surface can cause cracks and early flaking, even without structural changes, leading to inadequate prevention of flaking effects.
Innovation Solution
Implementing a machining process on the raceway surface to introduce compressive residual stress and retain austenite, with specific conditions of a machining amount of 0.03 or more and 70% or more retained austenite, and compressive residual stress 500 MPa higher than in the unmachined region, to prevent crack progression and flaking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a machining process is applied to the raceway surface to introduce compressive residual stress, then flaking resistance is improved, but the amount of retained austenite decreases
Solution Approach 1:
The invention optimizes machining parameters (contact surface pressure between 3.9-7.2 GPa, machining amount between 0.03-0.3 mm) to achieve the desired balance between compressive residual stress and retained austenite. By precisely controlling these parameters, the machining process introduces sufficient compressive stress to prevent crack initiation while preserving adequate retained austenite to maintain material toughness and prevent flaking.
Solution Approach 2:
The invention employs dynamic machining conditions including specific feed rates (0.05-0.5 mm/rev) and rotational speeds to control the machining process. The dynamic interaction between the machining tool and raceway surface allows for optimal introduction of compressive residual stress while controlling the transformation of retained austenite, achieving a balance between the two competing requirements.
2Strength
If the contact surface pressure during machining is increased to introduce more compressive residual stress, then crack resistance is improved, but excessive martensite transformation occurs reducing retained austenite
Solution Approach 1:
The invention establishes an optimal contact surface pressure range (3.9-7.2 GPa) that balances crack resistance and retained austenite preservation. Within this range, sufficient compressive residual stress is introduced to prevent crack initiation and propagation from inclusions, while the pressure remains below the threshold that would cause excessive martensite transformation and deplete retained austenite below beneficial levels.
3Reliability
If inclusions are present in the surface layer of the raceway, then flaking occurs from crack initiation at the inclusions, but machining to compress the surface may transform retained austenite to martensite reducing protection
Solution Approach 1:
The invention optimizes the combination of machining amount (0.03-0.3 mm) and contact surface pressure (3.9-7.2 GPa) to achieve sufficient compressive residual stress that prevents crack initiation at inclusions, while preserving adequate retained austenite (5-20% in the surface layer) to maintain material toughness. This parameter optimization ensures that the compressive stress field extends deep enough to counteract inclusion-induced stresses without causing excessive phase transformation.
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
This approach effectively prevents inclusion-induced flaking at different internal depths from the surface layer, particularly in rolling bearings like HUBs and electric motor bearings, by managing the machining amount, retained austenite, and compressive residual stress.
Implementation Method 1
a region, which has: (a) a machining amount of 0.03 or more; (b) an amount of retained austenite being 70% or more of an amount of retained austenite in the first region; and (c) a compressive residual stress being higher by 500 MPa or more than a compressive residual stress in the first region
Implementation Method 2
an amount of retained austenite being 70% or more of an amount of retained austenite in the first region
Data Source
AI summary
In a raceway surface of at least one of an inner ring and an outer ring, a region not affected by machining is set as a first region, and a region, which has (a) a machining amount of 0.03 or more, (b) an amount of residual austenite being 70% or more of an amount of retained austenite in the first region, and (c) a compressive residual stress being higher by 500 MPa or more than a compressive residual stress in the first region, is set as a second region.