Cryogenic Mechanical Working of Austenitic Stainless Steel Substrates
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for forming magnetic substrates for encoder scales do not effectively enhance the magnetic permeability difference between scale markings and the substrate, leading to suboptimal magnetic encoder performance.
Innovation Solution
A method combining mechanical working and cooling of an austenitic stainless steel substrate, followed by laser marking to create non-magnetic regions, which increases the martensite phase content and improves magnetic permeability differences, using techniques such as cryogenic cooling and surface hardening like pulsed plasma nitriding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If mechanical working is performed on the substrate, then the magnetic content increases, but the substrate temperature increases which may reduce magnetic permeability difference
Solution Approach 1:
The substrate is pre-cooled to cryogenic temperatures (e.g., -196°C using liquid nitrogen) before mechanical working is applied. This preliminary cooling ensures that even though mechanical working generates heat, the substrate remains at low temperatures throughout the process, maintaining high magnetic permeability difference while still achieving increased magnetic content through the mechanical working.
2Quantity of substance
If multiple working operations are performed to reduce substrate thickness, then the magnetic content increases, but the process time increases
Solution Approach 1:
Multiple working operations are performed in continuous succession without interrupting the cryogenic cooling. The substrate remains continuously cooled throughout the entire sequence of working operations, allowing maximum magnetic content to be achieved in minimum time by eliminating idle cooling periods between operations.
3Strength
If the substrate is heated after mechanical working, then the magnetic content may be reduced, but the mechanical strength increases
Solution Approach 1:
The substrate undergoes controlled heating to specific temperature ranges (e.g., 150-250°C) for defined periods to achieve the desired balance between mechanical strength and magnetic content. By precisely controlling the heating parameters, the substrate gains improved mechanical strength while retaining sufficient magnetic content for encoder scale applications.
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 significantly increases the magnetic content of the substrate, enhancing the magnetic permeability difference between scale markings and the substrate, resulting in improved magnetic encoder performance and mechanical robustness.
Implementation Method 1
The combination of mechanical working (also termed cold forming) and cooling of the substrate has been found to increase the amount of magnetic material formed during substrate processing. This improves the magnetic permeability difference between subsequently formed scale markings and the substrate
Implementation Method 2
The mechanical working step is performed on a substrate that has been cooled to a temperature below 0° Celsius. In a preferred embodiment, the mechanical working step is performed on a cryogenically cooled substrate. Such cryogenic cooling may be provided by immersion of the substrate in a bath of liquid nitrogen.
Implementation Method 3
The combination of mechanical working (also termed cold forming) and cooling of the substrate has been found to increase the amount of magnetic material formed during substrate processing.
Implementation Method 4
It has been described previously in JP63098501 how encoder scale marking can be formed in magnetic material by using a laser beam to heat small regions of material. These heated regions are converted from a magnetic material to a non-magnetic material.
Implementation Method 5
The method may comprise a step of heating the substrate after completion of the mechanical working step. The heating step may comprise heating the substrate to an elevated temperature for a prolonged period. For example, the substrate may be heated above 100°C, above 200°C or above 300°C. Advantageously, the substrate may be heated to around 450°C.
Implementation Method 6
The method may comprise the additional step of applying a surface hardening step after the step of mechanically working the substrate. For example, the surface hardening step may conveniently comprise pulsed plasma nitriding.
Data Source
Figure 1
AI summary
The present invention relates to a method for producing a magnetic substrate for an encoder scale. The method comprising the step of mechanically working the substrate, wherein the substrate is cooled prior to the mechanical working step. In one embodiment, a stainless steel substrate is used. The stainless steel may comprise an austenite (non-magnetic) phase and a martensite (magnetic) phase. Mechanically working and cooling in this manner increases the amount of magnetic (martensite) phase material that is formed, thereby improving the magnetic contrast when non-magnetic (austenite) marking are subsequently formed on the substrate by laser marking.