Laser-Smoothed Glass Substrates for Magnetic Disks

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Solution Overview

Problem

Conventional laser-based end face smoothing and chamfering of magnetic-disk glass substrates can lead to deteriorated roundness, which may cause air flow disturbances and fluttering during high-speed rotation.

Innovation Solution

The method involves irradiating the glass substrate end faces with a laser beam to create regions of differing roughness, specifically a low-roughness and high-roughness regions, and extending the irradiation path beyond a single lap to maintain or improve roundness, with a preferred roundness of 15 μm or less.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If laser beam irradiation is performed along a distance of one lap of the inner circumferential end face and outer circumferential end face, then the end faces are smoothed and chamfered surfaces are formed, but the roundness of the end faces deteriorates (increases)

Engineering Contradiction:

Improveroundness of end faceVSAvoidend face smoothing and chamfering

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The end face surface is divided into multiple regions with different roughness levels (first region with higher roughness, second region with lower roughness). This segmentation allows different portions of the end face to have different laser irradiation characteristics, enabling simultaneous achievement of smooth surfaces and maintained roundness by controlling the irradiation pattern across different zones.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the end face are given different surface qualities (roughness levels) through controlled laser irradiation. The first region receives irradiation conditions that create higher roughness, while the second region receives irradiation that creates lower roughness. This local differentiation resolves the contradiction by allowing the overall surface to be smooth while specific local regions maintain characteristics that preserve roundness.

Inventive Principle:

Principle #3Local quality

2Manufacturing precision

If end faces are smoothed and chamfered by laser irradiation, then surface quality is improved, but roundness deterioration causes air flow disturbance and fluttering during high-speed rotation

Engineering Contradiction:

Improvesurface smoothness and chamfer qualityVSAvoidair flow stability during rotation

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The end face is segmented into regions with different roughness characteristics, where the second region has lower roughness to minimize air flow disturbance, while the first region has higher roughness to maintain manufacturing feasibility. This segmentation ensures that the surface is sufficiently smooth for reliable high-speed rotation while remaining manufacturable through laser processing.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Specific local regions of the end face are optimized for different functions: the second region is optimized for low roughness to ensure stable air flow during rotation, while the first region is optimized for higher roughness that is easier to manufacture. This local quality differentiation resolves the contradiction between surface smoothness and rotational reliability.

Inventive Principle:

Principle #3Local quality

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 smooths and chamfers the end faces without deteriorating roundness, ensuring stable air flow and reducing the risk of fluttering during high-speed rotation.

Implementation Method 1

the inner and outer circumferential end faces of the annular glass blank are irradiated with a laser beam to heat them to a temperature higher than or equal to the softening point of the glass, thereby melting the inner and outer circumferential end faces

Methodology Applied

Scientific EffectLaser heating: Laser

Implementation Method 2

heating them to a temperature higher than or equal to the softening point of the glass, thereby melting the inner and outer circumferential end faces

Methodology Applied

Scientific EffectMelting: Melting

Data Source

PatentUS12406694B2Magnetic disk-use glass substrate manufacturing method, discoidal glass substrate, glass substrate, and magnetic disk-use glass substrate

Publication Date: 2025.09.02 HOYA CORPORATION

AI summary

A disk-shaped glass substrate manufacturing method for manufacturing a glass substrate (1) includes preparing a disk-shaped glass blank having main surfaces (11a, 11b) and an outer circumferential end face (12), and irradiating the disk-shaped glass blank with a laser beam (L) along a distance longer than one lap of the outer circumferential end face (12) of the disk-shaped glass blank.