CV Joint Cage Austempering for Uniform Hardness and Ductility
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Solution Overview
Problem
Existing methods for manufacturing cages for constant velocity joints face issues with non-uniform hardness and ductility between the surface and core parts, leading to high differences in hardening degrees, potential cracks, and increased manufacturing time.
Innovation Solution
A method involving cutting, turning, punching, broaching, and austempering of medium carbon steel cylindrical pipes to achieve full hardening, with a heat treatment process that includes heating to 860-900°C, followed by slow cooling in a salt bath, eliminating the need for quenching and tempering, and using methanol gas to prevent decarburization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If quenching and tempering process is used to harden the surface of the cage, then the surface hardness is improved, but the ductility of the surface decreases and there is a high difference in hardening degree between the surface and the core part
Solution Approach 1:
The patent applies austempering heat treatment at controlled temperatures (200-270°C) to transform the microstructure of medium carbon steel (0.3-0.5% C) into ausferrite, achieving uniform hardness (HRC 48-59) throughout the cage while maintaining ductility. This temperature parameter control prevents the surface-core hardening degree difference caused by conventional quenching.
Solution Approach 2:
The patent utilizes the phase transition of medium carbon steel during austempering, where austenite transforms to ausferrite (a mixture of ferrite and cementite) at controlled temperatures. This phase transition produces a uniform microstructure throughout the cage, eliminating the surface high-carbon martensite/core low-carbon martensite differentiation caused by conventional quenching.
2Strength
If quenching process is used to harden the cage, then the hardness is improved, but the possibility of cracks or deformation increases
Solution Approach 1:
The patent replaces rapid quenching with controlled austempering at 200-270°C, changing the cooling rate parameter from rapid to controlled. This produces ausferrite microstructure uniformly throughout the cage without thermal shock, eliminating cracks and deformation while achieving the required hardness (HRC 48-59).
Solution Approach 2:
The patent utilizes the austempering phase transition where austenite transforms to ausferrite at controlled temperatures without rapid cooling. This phase transition occurs uniformly throughout the cage structure, preventing the localized stress concentrations that cause cracks and deformation in conventional quenching.
3Strength
If case hardening is used on low carbon steel to harden the surface, then the surface hardness is improved, but the process time increases due to required carburizing and diffusion processes
Solution Approach 1:
The patent changes the base material from low carbon steel (0.18-0.22% C) to medium carbon steel (0.3-0.5% C), which has sufficient carbon content to form ausferrite directly during austempering. This eliminates the need for time-consuming carburizing and diffusion processes required for case hardening low carbon steel, reducing total manufacturing time while achieving uniform hardness throughout.
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 results in a cage with uniform hardness and strength across the surface and core, reduced manufacturing time, improved tensile and compressive strength, and enhanced durability, while preventing deformation and grain boundary oxide formation.
Implementation Method 1
a heat treatment operation of fully hardening the completely broached cage via austempering
Implementation Method 2
the structure of the surface is lower bainite, and the structure of the core part is tempered martensite
Implementation Method 3
followed by slow cooling in a salt bath, eliminating the need for quenching and tempering
Implementation Method 4
using methanol gas to prevent decarburization
Data Source
AI summary
Disclosed are a method of manufacturing cage for a constant velocity joint and a cage for a constant velocity joint manufactured using the same for providing a cage having improved hardness, strength, and elongation while having a structure with a uniform core part and surface and for ensuring economic feasibility by reducing manufacturing time. The method includes a cutting operation of forming a structure having an outer shape by cutting a cylindrical pipe, forming an outer circumference of the cut structure to have a curved surface thereon, performing a turning operation on a surface of the formed structure, a punching operation of forming a window in the surface of the structure on which the turning operation is performed, a broaching operation of processing an edge of the window formed via punching, and a heat treatment operation of fully hardening the completely broached cage via austempering.