Laser Weld Nugget Shaping for Thin-to-Thick Metal Plate Joints
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Solution Overview
Problem
In laser welding of thin metal plates, such as those used in disk drive suspensions, achieving a balanced weld strength is challenging due to the limited size of the nugget diameter, which can be either too small to effectively join the plates or too large to avoid damaging the insulating resin, and existing methods struggle to control the laser power and time for stable welding.
Innovation Solution
A welding method and apparatus that form a weld with a front-side nugget portion and a back-side nugget portion, where the back-side nugget portion is gradually reduced in diameter from the boundary towards the rear face of the second plate, and the peripheral surface of the back-side nugget portion has an increased tilt angle, allowing for increased weld strength without excessively increasing the front-side nugget diameter, achieved by initial and subsequent laser irradiation steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a high-power laser beam is emitted to increase nugget diameter and weld strength, then weld strength is improved, but a hole may be formed in the weld when welding thin plates
Solution Approach 1:
The patent applies periodic action by emitting the laser beam in multiple pulses rather than as a single continuous beam. The laser oscillates multiple times to accumulate heat energy, allowing the nugget diameter to increase progressively without exceeding the threshold that would cause hole formation. This pulsed laser welding approach enables controlled heat accumulation while maintaining weld integrity in thin plates.
2Object-affected harmful factors
If a converged (focused) laser beam is used to reduce heat-affected zone, then the diameter of front-side nugget portion is reduced, but the diameter of back-side nugget portion is further reduced
Solution Approach 1:
The patent applies dynamics by adjusting the focal position of the laser beam during the welding process. The focal position is set within a specific range (0.5mm to 2.0mm from the front surface of the first plate) to optimize the balance between front-side and back-side nugget diameters. This dynamic adjustment of focal position allows the converged laser beam to reduce the heat-affected zone while maintaining sufficient back-side nugget diameter for adequate weld strength.
3Strength
If laser power and time are increased to form larger nugget, then weld strength is improved, but insulating resin may be burned or deteriorated
Solution Approach 1:
The patent applies parameter changes by optimizing multiple laser welding parameters simultaneously: laser power (5W to 15W), oscillation frequency (1kHz to 10kHz), and focal position (0.5mm to 2.0mm from front surface). By adjusting these parameters within specific ranges, the patent achieves adequate nugget diameter for weld strength while limiting the heat-affected zone to prevent insulating resin deterioration. The cumulative oscillation times (5 to 20 times) further control heat input.
4Reliability
If low-power laser beam is used for thin plate welding to avoid hole formation, then weld integrity is maintained, but nugget diameter becomes too small for effective joining
Solution Approach 1:
The patent applies preliminary action by performing multiple preliminary laser oscillations (5 to 20 times) at low power before achieving the final weld. Each oscillation accumulates heat energy progressively, allowing the nugget to grow to an adequate diameter without exceeding the threshold for hole formation. This multi-stage preliminary heating approach enables effective joining of thin plates while maintaining weld integrity.
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 for enhanced weld strength by approximating the diameter of the back-side nugget portion to the front-side nugget portion, reducing the risk of damaging insulating resin and improving the structural integrity of the weld, while minimizing heat-affected zones and preventing hole formation in the thin plates.
Implementation Method 1
By the laser welding, a part of the workpiece is melted and solidified by irradiation of a laser beam at a weld of the workpiece to form a nugget.
Implementation Method 2
If the plate to be welded has a sufficient thickness, the diameter of the nugget can be increased by irradiating the workpiece with a laser beam at high power.
Data Source
AI summary
A method of welding a first metal plate and a second metal plate that is thicker than the first plate, by a laser beam. The first plate and the second plate are disposed to overlap one another in a thickness direction. In a first laser irradiation step, the laser beam is emitted at the first plate, to form an initial nugget including a front-side nugget portion in the first plate, a back-side nugget portion in the second plate and having a diameter smaller than a diameter of the front-side nugget portion, and an annular flat surface portion existing between the front-side nugget portion and the back-side nugget portion. In a subsequent laser irradiation step, the laser beam is emitted again at the initial nugget after the initial nugget is solidified, thereby increasing the diameter of the back-side nugget portion.