Steering Rack Machining for Uniform Compressive Tooth Stress
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Solution Overview
Problem
Current methods for manufacturing steering racks fail to achieve a uniform stress distribution, leading to 'chaotic' stress profiles with tensile and compressive stresses, which compromises fatigue strength and weight optimization without altering the microstructure.
Innovation Solution
Integrating X-ray diffraction measurements and shot peening or inductive heating into a continuous machining sequence to introduce defined compressive stresses, ensuring a uniform stress distribution in the gear teeth without changing the microstructure, using techniques like steel wire shot blasting to control stress peaks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional hardening and straightening operations are performed on racks, then the rack structure is strengthened, but a chaotic stress profile with tensile and compressive stresses is created that compromises fatigue strength
Solution Approach 1:
The patent converts the harmful chaotic stress profile created by conventional hardening and straightening into a beneficial uniform compressive stress profile through shot peening treatment. The shot peening process intentionally introduces compressive stresses that counterbalance the tensile stresses from previous operations, transforming the problematic stress state into a favorable one that enhances fatigue strength and reliability
Solution Approach 2:
The patent changes the stress state parameters by applying shot peening treatment with controlled parameters (shot size, shot velocity, treatment duration) to transform the stress profile from chaotic and non-uniform to uniform and predominantly compressive. This parameter control allows optimization of both strength and stress distribution uniformity
2Weight of moving object
If the rack diameter is reduced to save weight, then weight economy improves, but the structural strength and stress distribution become compromised
Solution Approach 1:
The patent changes the material's stress state parameters through shot peening, introducing compressive residual stresses that effectively increase the rack's load-bearing capacity. This allows the use of smaller diameter racks with reduced weight while maintaining or even improving structural strength through the enhanced stress profile
3Reliability
If advanced stress control methods are implemented, then stress distribution uniformity improves, but manufacturing complexity and costs increase
Solution Approach 1:
The patent employs shot peening treatment, a well-established and widely available surface treatment process, to achieve uniform stress distribution. This self-service approach uses conventional equipment and methods rather than requiring complex new systems, thereby improving stress uniformity without significantly increasing manufacturing complexity
Solution Approach 2:
The patent achieves improved stress distribution by optimizing parameters of existing shot peening processes rather than introducing fundamentally new manufacturing methods. By controlling shot peening parameters (media type, velocity, duration), uniform compressive stress profiles are obtained using conventional equipment
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 achieves a uniform stress plane in the gear teeth, enhancing fatigue strength and allowing for diameter minimization while maintaining material quality, thus meeting weight-saving and safety requirements for automotive steering systems at reduced technological costs.
Implementation Method 1
measured by X-ray diffraction
Implementation Method 2
X-ray diffraction measurements
Implementation Method 3
introducing compressive stresses by shot peening
Implementation Method 4
or inductive heating into a continuous machining sequence
Data Source
AI summary
The invention relates to a method for machining a rack and to a rack (1) machined according to said method, for example a steering rack. In said method, the stress pattern that is present after hardening and/or straightening the rack and that has a chaotic internal stress distribution of tensile and compressive stresses is converted into a stress pattern that optimizes the strength and the use of the material and also the diameter of the rack, such that, without altering the structure, at least the region of the gear teeth (2) is pre-stressed, in a functionally combined series of steps of a machining pass, with a deliberately introduced internal compressive stress without tensile stress and with a predominantly uniform stress distribution or stress plane.