DE-112024002120-T5 - Identification and correction of sweat paths using optical coherence tomography

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Abstract

A method and a system for laser welding a workpiece. The system may comprise: a laser source emitting processing laser radiation, an OCT system comprising an imaging light source emitting imaging light and designed to generate interferometric output, a laser head designed to direct the processing laser radiation and a beam of imaging light onto the workpiece, at least one scanning device designed to direct the beam of imaging light along at least one measurement welding path on the workpiece, and at least one control unit designed to: receive data corresponding to the reference welding path on the workpiece, generate a corrected welding path based at least partially on a comparison between the interferometric output of the at least one measurement welding path and the reference welding path, and control the laser head to direct the processing laser radiation along the corrected welding path on the workpiece.

Inventors

SCHWENGER NICHOLAS D
BECKER KODIE D
WEBSTER PAUL J L

Assignees

IPG PHOTONICS CORP

Dates

Publication Date: 20260507
Application Date: 20240517
Priority Date: 20230517

Claims (20)

A laser welding system for welding a workpiece, comprising: a laser source designed to emit processing laser radiation; an optical coherence tomography (OCT) system comprising an imaging light source designed to emit imaging light, wherein the OCT system is designed to receive reflected imaging light from the workpiece and to generate an interferometric output based at least partially on the reflected imaging light; a laser head designed to direct the processing laser radiation and a beam of imaging light onto the workpiece; at least one scanning device designed to direct the beam of imaging light along at least one measurement welding path on the workpiece, wherein the at least one measurement welding path is based at least partially on a reference welding path on the workpiece; and at least one control unit designed to: receive data corresponding to the reference welding path on the workpiece; Generating a corrected welding path, based at least partially on a comparison between the interferometric output of the at least one measurement welding path and the reference welding path; and controlling the laser head so that the processing laser radiation is directed along the corrected welding path on the workpiece.
Laser welding system according to Claim 1 , wherein the interferometric output of the at least one measurement welding path is used by the at least one control unit to generate multidimensional geometric data which is used to generate the corrected welding path.
Laser welding system according to Claim 1 , wherein the at least one control unit is further designed to apply a curve adaptation algorithm to generate the corrected welding path.
Laser welding system according to Claim 1 , wherein the OCT system and a scanning device of the at least one scanning device are designed to obtain transverse measurements along the at least one measuring welding path.
Laser welding system according to Claim 1 , where the reference welding path, the measuring welding path and the corrected welding path are elliptical paths.
Laser welding system according to Claim 5 , where the workpiece is a battery cell.
Laser welding system according to Claim 1 , wherein the at least one control unit controls the at least one scanning device such that the beam of imaging light is directed along the corrected welding path at the same time as the processing laser radiation is directed along the corrected welding path, and wherein the at least one control unit is designed to calculate weld depth measurements based on an interferometric output that is generated at least partially from the beam of imaging light directed along the corrected welding path.
Laser welding system according to Claim 7 , wherein the at least one scanning device comprises a scanning device designed to direct the processing laser radiation along the corrected welding path on the workpiece.
Laser welding system according to Claim 1 , wherein the at least one control unit controls the at least one scanning device such that the beam of imaging light is directed along a post-welding scanning path along the corrected welding path after the processing laser radiation has been directed along the corrected welding path, and wherein the at least one control unit is designed to calculate at least one post-welding measurement based on an interferometric output that is generated at least partially from the beam of imaging light directed along the post-welding scanning path.
Laser welding system according to Claim 1 , wherein the control unit is further designed to: capture multiple corrected welding paths; and process the multiple corrected welding paths using one or more trained machine learning models to predict the corrected welding path.
Laser welding system according to Claim 10 , wherein one or more trained machine learning models are further trained using the multiple corrected welding paths.
Laser welding system according to Claim 1 , wherein the laser head is designed to be stationary, and the workpiece is designed to be stationary during at least one section of a Period in which the processing laser radiation and/or the beam of imaging light is directed onto the workpiece, moved relative to the laser head.
A method for welding a workpiece, comprising: Receiving a reference welding path for the workpiece; Directing a beam of imaging light along at least one measurement welding path on the workpiece, wherein the at least one measurement welding path is based at least partially on the reference welding path; Determining an interferometric output based at least partially on the imaging light reflected by the workpiece along the at least one measurement welding path; Generating a corrected welding path based at least partially on a comparison between the interferometric output of the at least one measurement welding path and the reference welding path; and Directing processing laser radiation along the corrected welding path on the workpiece.
Procedure according to Claim 13 , which further includes using the interferometric output of the at least one measurement welding path to generate multidimensional geometric data that can be used to generate the corrected welding path.
Procedure according to Claim 13 , wherein generating the corrected welding path further includes applying a curve fitting algorithm.
Procedure according to Claim 13 , which further includes obtaining transverse measurements with the beam of imaging light along the at least one measuring welding path.
Procedure according to Claim 13 , which further includes: guiding the beam of imaging light along the corrected welding path while the processing laser radiation is guided along the corrected welding path; determining the interferometric output at least partially based on the imaging light reflected by the workpiece along the corrected welding path; and calculating weld depth measurements based on the interferometric output generated at least partially from the beam of imaging light guided along the corrected welding path.
Procedure according to Claim 13 , which further comprises: directing the beam of imaging light along a post-weld scanning path after the processing laser radiation has been directed along the corrected welding path; determining the interferometric output at least partially based on the imaging light reflected by the workpiece along the post-weld scanning path; and calculating at least one post-weld measurement based on the interferometric output generated at least partially from the beam of imaging light directed along the post-weld scanning path.
Procedure according to Claim 13 , where the reference welding path, the measuring welding path and the corrected welding path are elliptical paths.
Procedure according to Claim 19 , wherein the workpiece is a battery cell and the method further comprises: comparing the geometric coordinate values of the corrected welding path with a target threshold; and in response to a determination that the geometric coordinate values are within the target threshold, accepting the battery cell, or in response to a determination that the geometric coordinate values are not within the target threshold, rejecting the battery cell.

Description

Related registrations The present application claims priority over the preliminary US application with serial number [number]. 63/467036 entitled “IDENTIFICATION AND CORRECTION OF WELD PATHS USING OPTICAL COHERENCE TOMOGRAPHY”, which was submitted on May 17, 2023 and whose content is fully incorporated here by reference. background Technical field The technical field generally refers to the use of optical coherence tomography (OCT) in laser welding applications and, in particular, to the use of OCT for adapting welding paths in laser welding applications. Discussion of the background Manufacturing batteries for electric vehicles presents many unique challenges. For safety and economic viability, the battery manufacturing process must meet strict criteria regarding speed and quality. Quality criteria can include precise weld positioning, weld depth, weld strength, and consistency of the welding process. Laser welding has emerged as a technology that can address some of these challenges, but the success of laser welding batteries depends on the accuracy and precision of the welding path. Welding path accuracy problems can occur even when battery components are manufactured within specified tolerances (using forming techniques such as stamping and pressing). Welding path accuracy is further compromised by variations due to part fixtures and irregularities in system movement and positioning (e.g., linear axes and robot arms). The result is a workpiece shape so irregular that a welding path positioned without feedback control would lead to substandard weld quality. Poorly positioned welds can cause immediate failure or sudden failure after some time. In either case, a battery weld failure can have catastrophic consequences, as it compromises the battery assembly system if errors occur during assembly and endangers the public if a poor weld can make its way into a finished product. A number of camera-based machine vision technologies have been used to improve the accuracy of weld paths and, in some cases, to measure quality. However, these approaches have several shortcomings. One is that the contrast generated in a camera-based vision solution is highly dependent on the lighting, which complicates their implementation. Camera-based solutions can be affected by external light sources, which may not be uniform across the entire field of view of a welding probe. This results in a limited field of view of the probe and, consequently, its productivity. In some cases, elements of the fixture or the workpiece itself can cast shadows, further complicating the contrast of the camera-based view. Camera-based methods are also often unable to measure during welding (due to blurring of their field of view and/or overexposure by the light generated during welding) or to capture critical quality aspects such as penetration. Therefore, a method for quickly correcting the weld positioning and creating highly precise weld paths for each individual battery cell before welding is of great value to battery manufacturers. This problem exists for any batteries or cells that are laser-welded, which includes, without limitation, 46XX cells (such as 4680), 21XXX cells (such as 21700), and prismatic batteries. Beyond weld quality, any weld misalignment on the part can complicate subsequent quality assurance (QA) measurements. This could lead to difficulties in tracing and identifying poor welds, which in turn results in compromised battery cells entering later production stages and generating significant amounts of waste when the defect is eventually discovered. Conventional methods for defining and correcting weld paths involve the use of optical or camera-based systems to detect the edge, seam, or geometry of an object. Such systems are highly dependent on the quality and consistency of lighting, the material's reflectivity, and the component's fit. The disadvantages of these systems include increased costs and mechanical complexity due to the additional equipment requirements. They can increase the complexity and integration complexity of a system. Furthermore, they do not allow for direct measurement of the weld depth and other weld characteristics, such as the seam and the fit of the parts before welding, as well as the solidified weld bead after welding. Summary Aspects and embodiments relate to a method and a system for laser welding a workpiece. According to certain embodiments, a laser welding system for welding a workpiece is disclosed. According to an exemplary embodiment, a laser welding system for welding a workpiece is provided, comprising: a laser source designed to emit processing laser radiation; an optical coherence tomography (OCT) system comprising an imaging light source designed to emit imaging light, wherein the OCT system is designed to receive reflected imaging light from the workpiece and generate an interferometric output based at least partially on the reflected imaging light; a laser head designed to direct th