Ball Screw Carburized Layer Design for Durability and Shaft Strength
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Solution Overview
Problem
Conventional ball screws face challenges in achieving optimal performance and durability due to differences in load distribution between the screw shaft and nut, requiring distinct hardness and strength profiles without excessive complexity or cost in manufacturing.
Innovation Solution
A ball screw design featuring a nut and screw shaft with carburized layers, where the nut has a higher carbon concentration in its carburized layer than the screw shaft, achieved through radio frequency carburization and induction hardening treatments, respectively, to enhance durability and strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the nut is made with higher surface hardness than the screw shaft to improve durability, then the durability of the ball screw is improved, but the screw shaft becomes more vulnerable to torsional and bending loads
Solution Approach 1:
The patent applies different surface treatments to different components: the nut receives carburization treatment to achieve high surface hardness (58-65 HRC) for durability, while the screw shaft receives induction hardening to achieve moderate surface hardness (45-55 HRC) that balances wear resistance with toughness for withstanding torsional and bending loads. This local differentiation of material properties resolves the contradiction between durability and strength requirements.
2Ease of manufacture
If conventional carburization treatment is used for both nut and screw shaft, then manufacturing process is simple, but the screw shaft lacks sufficient surface hardness for improved durability
Solution Approach 1:
The patent changes the surface hardness parameter of the screw shaft through induction hardening treatment, achieving a surface hardness of 45-55 HRC which is higher than conventional carburized screw shafts. This parameter change allows the screw shaft to have improved durability while maintaining manufacturing simplicity through the use of established heat treatment processes.
3Reliability
If the screw shaft is made as hard as the nut to improve durability, then the durability is improved, but the screw shaft becomes more susceptible to torsional and bending failures
Solution Approach 1:
The patent applies different surface treatments to different components: the nut receives carburization treatment to achieve high surface hardness (58-65 HRC) for durability, while the screw shaft receives induction hardening to achieve moderate surface hardness (45-55 HRC) that balances wear resistance with toughness for withstanding torsional and bending loads. This local differentiation of material properties resolves the contradiction between durability and strength requirements.
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 allows the ball screw to meet performance requirements with improved durability, reducing manufacturing complexity and cost while ensuring the screw shaft and nut have appropriate hardness and strength profiles.
Implementation Method 1
performing a radio frequency carburization treatment of heating a surface of the screw shaft in contact with the ball in a carburizing gas atmosphere while applying a radio frequency to form a carburized layer
Implementation Method 2
performing an induction hardening treatment of heating the screw shaft subjected to a radio frequency heating treatment while applying a radio frequency to the screw shaft to quench the screw shaft
Data Source
AI summary
An object of the present invention is to provide a ball screw having a structure in which a screw shaft and a nut satisfy required performance and having improved durability, a method for manufacturing the ball screw, a power steering device, and a method for manufacturing the power steering device.A ball screw according to the present invention includes: a nut made of a steel substrate having an inner peripheral surface on which a female screw is formed; a screw shaft that is combined with the nut and is made of a steel substrate having an outer peripheral surface on which a male screw facing the female screw is formed; and a plurality of balls arranged between the female screw and the male screw. A surface of the nut in contact with the ball and a surface of the screw shaft in contact with the ball each have carburized layers. A carbon concentration in the carburized layer of the nut is higher than a carbon concentration in the carburized layer of the screw shaft.