Systems and methods for monitoring and / or controlling wobble processing using inline coherence imaging (ICI)

Abstract

Systems and methods can be used to monitor and / or control material processing that moves a process beam in a wobble pattern, such as a wobble welding process. As at least one process beam is moved according to a wobble pattern over a processing site (e.g., a weld site) of a workpiece, an inline coherent imaging (ICI) system moves an imaging beam to one or more measurement locations on the wobble pattern at least partially independently of the process beam and obtains ICI measurements (e.g., depth measurements) at those locations. The ICI measurements can be used, for example, to evaluate keyhole and / or melt pool characteristics during a welding process. Although this application describes a wobble welding process, the systems and methods described herein can also be used with other material processing applications in which a laser or other energy beam is wobbled or dithered during processing including, but not limited to, additive manufacturing, marking, and material removal.

Description

[0001] This application is a divisional application of IPG Photonics Co., Ltd., with application number 201980048317.3, entitled "System and method for monitoring and / or controlling swing processing using inline coherent imaging (ICI)," which entered the Chinese national phase on January 19, 2021 (international application date: July 18, 2019, international application number: PCT / US2019 / 042436).

[0002] Related applications

[0003] This application claims the benefit of U.S. Provisional Application Serial No. 62 / 853,368, filed May 28, 2019, entitled “System and Method for Monitoring and / or Controlling Oscillating Welding Using Inline Coherence Imaging (ICI),” and U.S. Provisional Application Serial No. 62 / 700,606, filed July 19, 2018, entitled “Oscillating Welding of Copper and Aluminum Alloys Using Inline Coherence Imaging,” both of which are incorporated herein by reference in their entirety. Technical Field

[0004] This disclosure relates to monitoring and / or controlling material handling, and more specifically to systems and methods for monitoring and / or controlling material handling (e.g., oscillating welding) using inline coherence imaging (ICI) to monitor and / or control a process beam moving in an oscillating pattern. Background Technology

[0005] While laser welding of non-ferrous alloys for industrial applications is expanding, it also presents several challenges. For example, the low absorption of near-infrared industrial laser wavelengths in aluminum and copper alloys prevents the initial formation of keyholes, which may be necessary for effectively bonding energy into the workpiece. Once a keyhole is established, the low viscosity of the melt (e.g., compared to ferrous alloys) can lead to reduced process stability and an increased likelihood of defects.

[0006] For challenging materials such as aluminum, copper, and other nonferrous alloys, combining a high-brightness fiber laser source (e.g., single-mode / low-mode) with dynamic beam deflection (or beam wobbling) can be an effective method to maintain high levels of radiation intensity at the sites of photomatter interaction while precisely controlling the laser power distribution on the material surface. One “wobbling welding” technique for faster and more precise beam movement involves using movable mirrors to provide the beam for a wobbling pattern, as disclosed, for example, in more detail in U.S. Patent Application Publication No. 2016 / 0368089, which is common to and fully incorporated herein by reference. This wobbling welding process can improve process stability, particularly when welding copper and aluminum, and also provides reduced spatter and porosity, as well as a greater degree of control over the finished weld geometry. Therefore, stable, repeatable, and controllable results have demonstrated broad potential for industrial applications.

[0007] A more detailed study of the orifice and melt pool dynamics that produce these industrially advantageous end results is invaluable for further leveraging the value of oscillating welding technology. However, the additional degrees of freedom introduced by oscillating welding may make the task of recording orifice dynamics using process monitoring via photodiode-based sensors or high-speed cameras more challenging. Summary of the Invention

[0008] According to one aspect, a laser material processing system includes: a material-modifying beam source for generating a process beam; and a processing head coupled to the material-modifying beam source and including at least one process beam scanning actuator for guiding and moving the process beam along at least one axis according to an oscillation pattern at a processing location on a workpiece. An inline coherent imaging (ICI) system is optically coupled to the processing head and includes at least one imaging beam scanning actuator for positioning an imaging beam at least partially independent of the process beam. A control system controls at least the material-modifying beam source, the process beam scanning actuator, and the imaging beam scanning actuator. The control system is programmed to cause the processing head to scan the process beam in an oscillation pattern and to cause the imaging beam scanning actuator to move the imaging beam cooperatively with the oscillation pattern to multiple measurement positions on the processing location.

[0009] According to another aspect, a method for monitoring an oscillating welding process is provided. The method includes: guiding a process beam and at least one imaging beam from an inline coherent imaging (ICI) system to a welding location on a workpiece; moving the process beam within an oscillation pattern on the welding location of the workpiece; moving at least one imaging beam at least partially independently of the process beam to multiple measurement locations on the welding location; and obtaining ICI measurements from the multiple measurement locations as the process beam moves within the oscillation pattern. Attached Figure Description

[0010] These and other features and advantages will be better understood by reading the following detailed description in conjunction with the accompanying drawings:

[0011] Figure 1 This is a schematic block diagram of a laser welding system consistent with embodiments of the present disclosure, which provides an oscillating welding pattern and is monitored by using inline coherence imaging (ICI).

[0012] Figure 1A This is a schematic diagram of a focused laser beam with a relatively small range of motion provided by two reflecting mirrors for oscillation purposes, consistent with embodiments of this disclosure.

[0013] Figures 2A to 2D This is a schematic diagram showing different oscillation patterns consistent with embodiments of the present disclosure and sample welds formed by those oscillation patterns.

[0014] Figure 3A These are micrographs of standard welds consistent with embodiments of this disclosure.

[0015] Figure 3B These are micrographs of welds formed using oscillating patterns.

[0016] Figure 4 and Figure 5 This is a perspective view of a laser welding head having a collimator module, a oscillator module and a core module assembled together and emitting a focused beam, consistent with embodiments of this disclosure.

[0017] Figure 6 This is a schematic block diagram of an ICI system that can be used to monitor wobbling welding, consistent with embodiments of this disclosure.

[0018] Figure 7 This is a flowchart illustrating a method for monitoring oscillating welding using ICI, consistent with embodiments of this disclosure.

[0019] Figure 8 This is an illustration of an example of using ICI to monitor oscillating welding by moving an imaging beam across the welding area using a grating scanning pattern and by including a oscillating pattern of the process beam.

[0020] Figure 9 This diagram shows the average depth of a stainless steel weld with a circular oscillation pattern and a variable oscillation diameter, which is obtained by raster scanning. Figure 8 The imaging beam shown is formed.

[0021] Figure 10 This is an illustration of another example of using ICI to monitor oscillating welding by moving the imaging beam to multiple fixed measurement positions along the oscillation pattern of the process beam.

[0022] Figure 11 Is Figure 10 The graph shows the relationship between the penetration depth and the weld distance measured at a fixed measurement location.

[0023] Figure 12 In such Figure 10 The bar graph shows the average melt depth measured at a fixed measurement location.

[0024] Figure 13 This is an illustration of another example of using ICI to monitor oscillating welding by moving the imaging beam along the oscillation pattern in the opposite direction to the process beam.

[0025] Figure 14 When the imaging beam is like Figure 13 The graph shows the relationship between the penetration depth measured when moving as shown and the distance along the weld.

[0026] Figure 15 This shows that when the imaging beam is like Figure 13 The graph shows the relationship between the average penetration depth and the rotation angle at different welding speeds when moving as shown. Detailed Implementation

[0027] Systems and methods consistent with embodiments of this disclosure use inline coherent imaging (ICI) to monitor and / or control material handling, such as oscillating welding processes, where a process beam moves within an oscillating pattern. As at least one process beam moves according to the oscillating pattern over a processing location (e.g., a welding position) on the workpiece, the ICI system moves an imaging beam, at least partially independent of the process beam, to one or more measurement locations on the oscillating pattern and obtains ICI measurements (e.g., depth measurements) at these locations. These ICI measurements can be used, for example, to evaluate keyhole and / or melt pool characteristics during the welding process. Although this application describes oscillating welding processes, the systems and methods described herein can also be used with other material handling applications where laser or other energy beams are oscillated or jittered during processes including, but not limited to, additive manufacturing, marking, and material removal.

[0028] In one embodiment, an imaging beam is moved to scan the weld joint in a scanning pattern (e.g., raster scan) at multiple measurement locations surrounding the oscillation pattern to form a depth map of the weld joint. In another embodiment, one or more imaging beams are moved to one or more fixed measurement locations on the oscillation pattern. In yet another embodiment, the imaging beam moves along the oscillation pattern in a direction opposite to the movement of the process beam. In still another embodiment, the imaging beam moves along the oscillation pattern in the direction of the process beam but independently of the process beam to, for example, provide dynamic offset control and / or cyclic alignment correction.

[0029] As used herein, “oscillation” refers to the reciprocating movement of a laser beam within a relatively small field of view defined by a scan angle of less than 10° or a maximum beam angular displacement of ±5° (e.g., reciprocating movement on at least one axis). In one example, an ICI system may be used with a laser welding head having one or more scanning actuators (e.g., movable mirrors) that perform welding operations using an oscillation pattern, as described in more detail, for example, in U.S. Patent Application Publication No. 2016 / 0368089, which is common to and fully incorporated herein by reference. The scanning actuator provides oscillating movement of one or more beams within a relatively small field of view defined, for example, by a scan angle of 1° to 2°. The scanning actuator may include, but is not limited to, galvanometer scanning mirrors, polygonal scanning mirrors, MEMS-based scanning mirrors, piezoelectric scanning mirrors, diffraction-based beam scanners, rotating prisms, potassium tantalum niobium oxide (KTN) crystals, and other types of scanning mirrors or optics. The laser welding head may also include diffractive optics to shape the moving one or more beams.

[0030] As used herein, inline coherent imaging (ICI) refers to a process in which an imaging beam is guided, together with or “inlined” with a process beam, to a workpiece for the purpose of measuring process and / or workpiece characteristics. The term “inline” does not require the imaging beam and the process beam to be coaxial. The imaging beam may be coaxial with the process beam, or it may be offset or angled relative to the process beam. The embodiments described in this disclosure can be used with any ICI system, for example, as described in more detail in U.S. Patent Nos. 8,822,875, 9,757,817, and 10,124,410, which are common to and are fully incorporated herein by reference. An ICI system may be coupled downstream of a process beam scanning actuator to a welding head and may include an imaging beam scanning actuator to move the imaging beam independently of the process beam, as described in more detail below. The scanning actuator may include, but is not limited to, galvanometer scanning mirrors, polygonal scanning mirrors, MEMS-based scanning mirrors, piezoelectric scanning mirrors, diffraction-based beam scanners, rotating prisms, and other types of scanning mirrors or optics.

[0031] ICI can be used to monitor oscillating welding in copper and aluminum alloys, as well as other non-ferrous alloys. In particular, ICI allows for direct geometrical pinhole measurements and can be used to perform pinhole depth mapping within the oscillation pattern to reveal periodic fluctuations within the pinhole corresponding to its position, which are not always observable in finished welds. Pinhole and melt pool dynamics under rotating pinhole oscillation welding conditions and common pinhole oscillation welding conditions can be examined. ICI measurements can provide a unique window into the welding process dynamics using dynamic beam deflection. ICI measurements, such as weld penetration or profile and / or part measurements for pre- or post-processing, can also be used to control processing parameters such as laser power or oscillation patterns.

[0032] When applied to measuring laser pinhole welding processes, ICI offers advantages over traditional photodiode-based sensors or high-speed cameras. As will be described in more detail below, ICI uses process optics to deliver an auxiliary imaging beam (e.g., an infrared beam) to enable direct geometric measurements of the pinhole, melt pool, and surrounding material during welding. ICI offers the advantage of not being obscured by process light from blackbody radiation or backscattering, and it allows for direct measurement of the pinhole penetration during laser welding. ICI measurements achieve micrometer-level accuracy and microsecond-level temporal resolution. Using ICI to examine pinhole behavior during oscillating welding has provided new insights into the behavior of this welding process.

[0033] Reference Figure 1 Consistent with embodiments of this disclosure, an ICI system 150 can be used to monitor and / or control the laser welding system 100 for oscillating welding. The ICI system 150 can be used to monitor and / or control oscillating welding by performing one or more ICI measurements at one or more locations at the weld site and along an oscillation pattern, as will be described in more detail below. Although the ICI system 150 is described in the context of a specific embodiment of the laser welding system 100, the ICI system 150 can be used with any type of laser welding system for oscillating welding or with other material handling systems in which a laser or energy beam is oscillated or jittered.

[0034] In the illustrated embodiment, the laser welding system 100 includes a laser welding head 110 coupled to the output fiber 111 of a fiber laser 112 (e.g., an output fiber with connector 111a). The laser welding head 110 can be used, for example, to perform welding on a workpiece 102 through a weld seam 104 to form a weld bead 106. An ICI system 150 can be coupled to the laser welding head 110, for example, to a camera port or other optical port on the welding head 110.

[0035] The laser welding head 110 and / or workpiece 102 can move or translate relative to each other along the direction of the seam 104. The laser welding head 110 can be located on a motion table 114 for translating the welding head 110 relative to the workpiece 102 along at least one axis (e.g., along the length of the seam 104). In one example, the motion table 114 is a multi-axis robot such as an ABB IRB-4400 six-axis robot, and the material or workpiece is clamped in a static fixture. Additionally or alternatively, the workpiece 102 can be located on a motion table 108 for moving or translating the workpiece 102 relative to the laser welding head 110.

[0036] Fiber laser 112 may include a ytterbium fiber laser capable of generating laser light in the near-infrared spectral range (e.g., 1060 to 1080 nm). The ytterbium fiber laser may be a single-mode or multi-mode continuous-wave ytterbium fiber laser, capable in some embodiments of generating laser beams with power up to 1 kW and in other embodiments of generating higher power up to 50 kW. Examples of fiber laser 112 include lasers from IPG Optoelectronics' YLR SM or YLR HP series, such as the YLS-6000 fiber laser (wavelength 1070 nm) provided using 100 μm core fiber laser technology. Fiber laser 112 may also include a multi-beam fiber laser, such as the type disclosed in International Application No. PCT / US2015 / 45037, filed August 13, 2015, entitled "Multi-beam Fiber Laser System," capable of selectively transmitting one or more laser beams through multiple optical fibers.

[0037] In the illustrated embodiment, the laser welding head 110 typically includes: a collimator 122 for collimating a laser beam from an output fiber 111; at least a first movable mirror 132 and a second movable mirror 134 for reflecting and moving the collimated beam 116; and a focusing lens 142 for focusing and delivering a focused beam 118 to the workpiece 102. In one example, the welding head 110 is an IPG D50 oscillating welding head with a 150mm collimator and a 300mm final focusing optics (nominal focusing diameter of 200μm). The ICI system 150 can be coupled downstream of the movable mirrors 132, 134 to the welding head 110. In the illustrated embodiment, the fixed mirror 144 is also used to guide the collimated laser beam 116 from the second movable mirror 134 to the focusing lens 142. Collimator 122, movable mirrors 132, 134, focusing lens 142, and fixed mirror 144 can be housed in separate modules 120, 130, 140 that can be connected together, as will be described in more detail below.

[0038] Movable mirrors 132 and 134 can pivot about different axes 131 and 133 to move the collimated beam 116 and thus move the focused beam 118 relative to the workpiece 102 on at least two different vertical axes 2 and 4. Movable mirrors 132 and 134 can be galvanometer mirrors movable by a galvanometer motor, capable of rapidly reversing direction. In other embodiments, other mechanisms (e.g., stepper motors) can be used to move the mirrors. The use of movable mirrors 132 and 134 in the laser welding head 110 allows for precise, controllable, and rapid movement of the laser beam 118 for beam oscillation purposes without having to move the entire welding head 110 and without using a rotating prism.

[0039] In one embodiment of the welding head 110, the movable reflectors 132, 134 pivot the beam 118 within a relatively small field of view (e.g., a maximum beam displacement of ±30 mm at the workpiece) by means of a scanning angle α of less than 10° (or with a maximum beam angular displacement of ±5°) and especially within a scanning angle of about 1° to 2°. Figure 1A As shown, this allows the beam to oscillate. In contrast, conventional laser scanning heads typically provide laser beam movement within a larger field of view (e.g., greater than 50mm × 50mm and up to 250mm × 250mm) and are designed to accommodate a larger field of view and scanning angle. Therefore, it is counterintuitive to provide only a relatively small field of view in the laser welding head 110 using movable mirrors 132, 134, and contrary to the conventional view that a wider field of view is provided when using a galvanometer scanner. For example, the limitation on the field of view and scanning angle is advantageous when using a galvanometer mirror in the welding head 110 by achieving faster speeds, allowing the use of lower-cost components (e.g., lenses), and allowing the use of accessories (e.g., air knives and / or gas-assisted accessories).

[0040] Due to the smaller field of view and scanning angle in the exemplary embodiment of the welding head 110, the size of the second reflector 134 can be substantially the same as that of the first reflector 132. In contrast, conventional galvanometer scanners typically use a larger second reflector to provide a larger field of view and scanning angle, and a larger second reflector may limit the movement speed on at least one axis. Therefore, the smaller size of the second reflector 134 in the welding head 110 (e.g., substantially the same size as the first reflector 132) compared to the larger reflector in a conventional galvanometer scanner that provides a large scanning angle allows the reflector 134 to move at a faster speed.

[0041] The focusing lens 142 may include focusing lenses known for use in laser welding heads and having a range of focal lengths, for example, from 100 mm to 1000 mm. Conventional laser scanning heads use multi-element scanning lenses (e.g., F-θ lenses, field-planar lenses, or telecentric lenses) with much larger diameters (e.g., a 300 mm diameter lens for a 33 mm diameter beam) to focus the beam within a larger field of view. Because the movable mirrors 132, 134 move the beam within a relatively small field of view, a large multi-element scanning lens (e.g., an F-θ lens) is unnecessary and not used. In an exemplary embodiment of the welding head 110 consistent with this disclosure, a plano-convex F300 focusing lens with a diameter of 50 mm can be used to focus a beam with a diameter of about 40 mm to move within a field of view of about 15 mm × 5 mm. The use of a smaller focusing lens 142 also allows for the use of additional accessories, such as air knives and / or gas-assisted accessories, at the end of the welding head 110. The larger scanning lenses required by conventional laser scanning heads limit the use of such accessories.

[0042] Although the exemplary embodiment of the laser welding head 110 includes two movable mirrors 132, 134, other types and numbers of scanning actuators may also be used to provide an oscillating pattern. Other optical components may also be used in the laser welding head 110, such as beam splitters for separating the laser beam to provide at least two beam points for welding (e.g., on either side of the weld). Additional optical components may also include diffractive optics and may be located between the collimator 122 and the mirrors 132, 134.

[0043] A protective window 146 can be provided in front of the lens 142 to protect the lens and other optics from debris generated during the welding process. The laser welding head 110 may also include a welding head accessory (e.g., an air knife) for providing a high-speed airflow through the protective window 146 or the focusing lens 142 to remove debris and / or a gas-assisted accessory to deliver shielding gas to the welding site in a coaxial or off-axis manner to suppress weld plume. Therefore, the laser welding head 110 with a movable reflector can be used with existing welding head accessories.

[0044] In the illustrated embodiment, the ICI system 150 is optically coupled to the laser welding head 110, for example, downstream of reflectors 132, 134. The ICI system 150 generates an imaging beam 152 that is aligned with the process beam 118. The fixed reflector 144 may be a dichroic mirror that reflects the process beam 118 and allows the imaging beam 152 to pass through. The ICI system 150 includes one or more scanning actuators (not shown) to move the imaging beam 152 to one or more measurement locations on the weld site and oscillation pattern, which will be described in more detail below. In one example, the ICI system 150 includes an IPG LDD-700 ICI system that includes a second pair of galvanometer scanning mirrors, thereby positioning the imaging beam independently of the process beam. In other embodiments, the ICI system 150 may be optically coupled upstream of reflectors 132, 134.

[0045] The illustrated embodiment of the laser welding system 100 also includes a control system 160, which controls, for example, the position of the fiber laser 112, the movable mirrors 132, 134, and / or the motion stages 108, 114 in response to sensing conditions in the welding head 110, the detection position of the joint 104, and / or the movement and / or position of the laser beam 118. The control system 160 can also monitor and / or control the welding operation by receiving data from the ICI system 150, such as measurements of depth along the weld area.

[0046] The control system 160 can control the fiber laser 112, for example, by turning off the laser, changing the laser power, or adjusting any other adjustable laser parameters. The control system 160 can also control laser parameters (e.g., laser power) in response to the movement or position of the beam 118 without turning off the laser 112. If one of the movable mirrors 132, 134 moves the beam 118 out of range or moves it too slowly, the control system 160 can reduce the laser power to dynamically control the energy of the beam spot to avoid damage to the laser. The control system 160 can further control the selection of the laser beam in a multi-beam fiber laser.

[0047] The control system 160 can control one or both of the movable reflectors 132, 134 to provide oscillating movement during welding, as described in more detail below. The control system 160 can also control the scanning actuator in the ICI system 150 to control the movement and / or positioning of the imaging beam 152 at the welding location as described below. The control system 160 may also include a data processing system for calibrating ICI measurements. The control system 160 may also include a record generator for generating records of ICI measurements and a quality judgment system for performing quality analysis of the welded parts.

[0048] Therefore, the control system 160 includes laser control, oscillation control, motion control, and ICI control, which work together to control the oscillation welding process and monitor the oscillation welding process. The control system 160 may include, for example, hardware (e.g., a general-purpose computer or microcontroller) and software known for controlling fiber lasers and galvanometer mirrors. For example, existing galvanometer control software can be used and modified to allow control of the galvanometer mirror as described herein.

[0049] The laser welding system 100 may also include an auxiliary measurement system 170, which includes auxiliary sensors and / or cameras such as visible light and / or IR-sensitive photodiodes, some of which may be coupled to the welding head 110 via optical fibers. The auxiliary measurement system 170 may be configured to measure process radiation, for example, within a spectral band from 100 nm to 20 μm. The auxiliary measurement system 170 may include optical elements such as apertures, lenses, scanning mirrors, and optical fibers (some of which may be coupled to the process laser or the ICI system itself) to perform spatially localized measurements relative to the process beam and / or the measurement beam. Examples of auxiliary sensors are described in more detail in U.S. Patent No. 10,124,410, which is incorporated herein by reference. One or more outputs of the auxiliary measurement system 170 may be used to dynamically deflect an imaging beam from the process beam at the workpiece surface based on the position of the process beam within an oscillation pattern during the welding process. The auxiliary measurement system 170 may be configured to perform spatially localized measurements at measurement locations dynamically deviated from the process beam based on at least one output from the ICI system.

[0050] Figures 2A to 2D An example of a periodic or repeating oscillating pattern is shown, which can be used to perform stir welding on butt joints and the resulting sample welds. Figure 2A and 2B A clockwise circular pattern is shown. Figure 2B A linear pattern is shown. Figure 2C It shows a figure-eight pattern, and Figure 2D An infinity symbol pattern is shown. Although some oscillating patterns are shown, other oscillating patterns are also within the scope of this disclosure, including but not limited to spiral patterns. One advantage of using a movable mirror in the laser welding head 110 is the ability to move the beam according to a variety of different oscillating patterns.

[0051] Figure 3A and Figure 3B A comparison of a standard weld and a weld formed by an oscillating pattern is shown. The laser welding system and method described herein can be used to improve welding to materials that are typically difficult to weld, such as titanium.

[0052] Figure 4 and Figure 5 An exemplary embodiment of the scanning laser welding head 410 is shown in more detail. Although one specific embodiment is shown, other embodiments of the laser welding heads, systems, and methods described herein are also within the scope of this disclosure. Figure 4 and Figure 5 As shown, the laser welding head 410 includes a collimator module 420, a oscillator module 430, and a core module 440. The oscillator module 430 includes a scanning actuator (e.g., a first movable mirror and a second movable mirror as described above) and is coupled between the collimator module 420 and the core module 440.

[0053] Collimator module 420 may include a collimator (not shown) having a pair of fixed collimator lenses, such as those known for use in laser welding heads. In other embodiments, the collimator may include other lens configurations, such as movable lenses, capable of adjusting the beam spot size and / or focus. Oscillator module 430 may include a first galvanometer and a second galvanometer (not shown) for moving a galvanometer mirror (not shown) about different vertical axes. Galvanometers known for use in laser scanning heads may be used. The galvanometers may be connected to a galvanometer controller (not shown). The galvanometer controller may include hardware and / or software for controlling the galvanometers to control the movement of the mirror and thus the movement and / or positioning of the laser beam. Known galvanometer control software may be used and may be modified to provide the functions described herein, such as seam detection, oscillation patterning, and communication with the laser. Chip module 440 may include a fixed mirror (not shown) that redirects the beam received from oscillator module 430 to a focusing lens and then to the workpiece. The ICI system can, for example, be coupled to the chip module 440, and the fixed mirror in the chip module 440 can be a dichroic mirror that allows the reflected imaging beam to return through the ICI system, as will be described in more detail below.

[0054] Figure 4 and Figure 5 The assembled laser welding head 410 is shown, wherein each module 420, 430, 440 is connected together and emits a focused beam 418. The laser beam connected to the collimator module 420 is collimated, and the collimated beam is guided to the oscillator module 430. The oscillator module 430 uses a mirror to move the collimated beam and guides the moved collimated beam to the core module 440. The core module 440 then focuses the moved beam, and the focused beam 418 is guided to the workpiece (not shown).

[0055] Figure 6An example of an ICI system 650 is shown, which includes an interferometer configuration and uses low-coherence interferometry to monitor the wobbling welding system as described above. The illustrated embodiment uses a Michelson interferometer; however, ICI systems with other interferometric configurations, such as Mach-Zehnder, can also be used with wobbling welding systems and are within the scope of this disclosure.

[0056] The ICI system 650 includes an imaging beam source 651 and a beam splitter / combiner 654. The imaging beam source generates one or more imaging beams 652, and the beam splitter / combiner 654 separates the imaging beams 652 such that at least one imaging beam component 652a is directed to the workpiece 602 (i.e., applied to the sample arm 656) and at least one imaging beam component 652b is directed to a reference mirror 657 (i.e., applied to the reference arm 658). In the illustrated embodiment, the imaging beam component 652a directed to the workpiece 602 passes through a dichroic mirror 644, which reflects the process beam 618 used to perform wobbling welding. Other combining optics may also be used to combine the imaging beam component 652a with the process beam 618 while allowing the reflected imaging beam component 652a to return toward the beam combiner 654.

[0057] The reflected imaging beam components from the workpiece 602 and the reference mirror 657 are then combined by a beam splitter / combiner 654 to provide a combined signal as the interferometric measurement output. The ICI system 650 also includes a signal detector 655, such as a high-speed spectrum detector, to receive and detect the combined signal formed by the reflected imaging beam components 652a and 652b, thereby generating an interferogram from the interferometric measurement output. The interferogram can be provided to an interferogram processor 661 to process the interferogram and calculate measurements (e.g., depth measurements) from it. The interferogram processor 661 may be... Figure 1 This is part of the ICI system 650 or control system 160 shown.

[0058] In this embodiment, the ICI system 650 also includes one or more imaging beam scanning actuators 659 (e.g., a 2-axis galvanometer scanner or other active deflection device) for scanning the imaging beam component 652a independently of the process beam 618. The scanning actuator 659 may be used, for example, to scan the imaging beam component 652a to maintain substantially aligned with the process beam 618 as it moves through the oscillating pattern. The scanning actuator 659 may also be used to scan the imaging beam component 652a in various scanning patterns surrounding the oscillating pattern of the process beam 618, as will be described in more detail below. In other embodiments, the ICI system 650 may include a plurality of sample arms 656 and / or a plurality of reference arms 658. For example, when scanning the imaging beam component 652a, a plurality of reference arms 658 with different optical path lengths may be used to illustrate variations in the optical path length.

[0059] Reference Figure 7 A method for monitoring oscillating welding using ICI is shown and described. The method includes: 710 - guiding at least one process beam (e.g., process beams 118, 618) and at least one imaging beam (e.g., imaging beams 152, 652a) from an ICI system to the weld site. 712 - moving the process beam within an oscillation pattern on the weld site, for example, as described above. 714 - moving the imaging beam at least partially independently of the process beam to one or more measurement locations on the weld site (including, for example, measurement locations on the oscillation pattern). 716 - obtaining ICI measurements from one or more measurement locations as the process beam moves within the oscillation pattern. The imaging beam can be moved to obtain ICI measurements at different locations, thereby allowing evaluation of various aspects of the oscillation welding, including, for example, keyhole and / or melt pool characteristics, as described in more detail below. The imaging beam can also be moved along the same oscillation path and substantially aligned with the process beam. The imaging beam can also be locally jittered or oscillated at one or more measurement locations.

[0060] ICI measurements can also be used, for example, to control the oscillating welding process by adjusting one or more processing parameters and / or the oscillating movement of the process beam. Examples of control include feedback control, such as that described in U.S. Patent Nos. 8,822,875, 9,757,817, and 10,124,410, which are common to this patent and are incorporated herein by reference in their entirety.

[0061] Reference Figure 8 and Figure 9One embodiment of using ICI to monitor an oscillating welding process includes moving an imaging beam 152 to raster scan the weld site in a scanning pattern covering multiple measurement locations surrounding the oscillation pattern to form a depth map of the weld site. In one example, a process beam 118 oscillates using a circular pattern and moves in welding direction 3 to perform linear plate bead welding on a stainless steel (304) specimen. During each weld, the ICI measurement beam or imaging beam raster scans through a 1.5 mm × 1.5 mm square grid pattern centered on the process beam axis (in static condition). Depth measurements at each point in the grid pattern are combined to form an asynchronous three-dimensional image of the weld site. According to Table 1 below, the process parameters remain constant except for the oscillation pattern diameter, which varies from 0 μm (equivalent to a fixed optical weld) to 500 μm. The three-dimensional images of the continuous weld are combined by calculating the average depth at each location in (x, y) to create a representative depth map of the material surface, including the original steel, keyholes, and melt pool.

[0062] Table 1: Process parameters for the orifice shape experiment

[0063]

[0064] Figure 9 Average depth maps of stainless steel welds with different oscillation diameters (e.g., no oscillation, 100 μm, 200 μm, 300 μm, 400 μm, and 500 μm) are shown, where the welding direction is from right to left in the images. Each map is a combination of five consecutive 3D images acquired during different welding processes with the same parameters. A qualitative change in depth map is observed between 100 μm and 200 μm oscillation diameters. For fixed-beam welding, and for the case of 100 μm beam oscillation, the process produces localized pinholes located deep in the center of the image.

[0065] With diameters of 200 μm and above, the melt pool begins to encroach on the center of the oscillating pattern (e.g., as indicated by a measurement depth similar to the material surface). If this diameter is exceeded, the deeper measurements of the aperture fall into a ring-shaped distribution. In this case, the aperture traces a circular pattern in a larger melt pool after the process beam passes through it. In other words, increasing the oscillation diameter to the focusing diameter of the process beam causes the aperture depth distribution to transition from a single local aperture region to a rotating aperture with a high melt center region flush with the material surface.

[0066] These results are intuitive when considering the diameter of the process beam. For these experiments, the nominal 1 / e² beam diameter at the focal point was 200 μm. When the oscillation diameter is increased to match the beam diameter, there is no longer a significant intensity overlap region at the center of each rotation of the process beam. This results in insufficient evaporation backpressure on the process axis compared to oscillation patterns with smaller diameters, leading to a unique orifice transition to a circumferential motion. For oscillation diameters smaller than the beam diameter, the orifice depth distribution appears more similar to that of a fixed-beam orifice. In this case, the orifice can still have some small-scale circumference after the process beam, which... Figure 9 This is not visible in the image shown. When using a large-diameter beam with an equal time-averaged intensity distribution, this can affect melt pool dynamics and overall process stability in ways that are impossible to achieve.

[0067] Reference Figures 10 to 12 Another embodiment of using ICI to monitor the oscillating welding process involves moving the ICI imaging beam 152 along an oscillation pattern to one or more fixed locations to obtain fixed ICI measurements at those locations. In one example, the process beam 118 oscillates using a circular oscillation pattern and moves in the welding direction 3 to produce a linear on-plate bead weld in copper (110), with the aim of observing and comparing the oscillation stability of the pinhole depth at specific fixed points in the oscillation pattern. Pinhole measurements are continuously acquired at fixed locations in the oscillation pattern throughout the entire duration of each weld. Different measurement locations were examined during continuous welding with the same parameters, according to Table 2 below.

[0068] Table 2: Process parameters for the stability of the pinhole at the fixed point

[0069]

[0070] In this example, static ICI depth measurements were obtained at four base points (e.g., 152a to 152d) around the circular oscillation pattern. Two points along an axis parallel to the welding direction (e.g., 152a, 152b) will be referred to as front (152a) and rear (152b), and two points along an axis perpendicular to welding direction 3 (e.g., 152c, 152d) will be referred to as fast (152c) and slow (152d). The motion of the process beam, combined with the head's movement speed relative to the part, results in a localized asymmetry in the beam's travel speed between the fast and slow sides of the oscillation pattern. Based on the oscillation parameters, the circumferential velocity of the process beam in the processing head's reference frame is 785 mm / s. On the fast side of the oscillation pattern, the process beam travels at 835 mm / s in the forward welding direction 3 (relative to the material), while on the slow side, the process beam travels towards the rear of the weld at 735 mm / s.

[0071] The depth data acquired in this manner includes measurements from the bottom of the aperture when the process beam 11 8 passes through the measurement beams (152a to 152d), and measurements from the surface of the melt pool at other times. The depth data is reduced to a set of aperture minima by searching for local minima within each expected intersection interval of the two beams. Figure 11 The results show the pinhole depths obtained at all four measurement locations (i.e., the front, back, slow, and fast sides of the oscillation pattern) during bead soldering on different copper plates with the same parameters. Figure 12 The mean depth and standard deviation at each of these measurement locations on the base point of the circular oscillating pattern are shown.

[0072] Figure 11 Each of the four depth measurement sets exhibits its own characteristic depth and stability features. The front and rear measurements show a significant difference in melt depth (e.g., approximately 400 μm). The melt depth reached as the orifice moves along the rear edge of the oscillating pattern (closest to the majority of the melt volume) is greater than that reached at the front edge of the pattern. The slow and fast edges of the pattern exhibit differences in both depth and stability. The slow edge of the oscillating pattern is observed to reach a greater depth on average than the fast edge. This increased melt depth at the slow edge is accompanied by greater variability in depth measurements compared to other measurement locations. The deeper “peak” observed in the fast edge data coincides with the most unstable region of the orifice trajectory for the test parameters here. Besides the difference in surface velocity of the process beam between the slow and fast edges of the oscillating pattern, this asymmetry may also be partly attributed to melt dynamics caused by the stirring effect of the moving orifice.

[0073] Reference Figures 13 to 15 Another embodiment of using ICI to monitor the oscillating welding process involves moving the imaging beam 152 along the oscillation pattern in the opposite direction to the movement of the process beam 118 and in sync with the oscillation cycle. In one example, the process beam 118 oscillates using a circular pattern and moves in welding direction 3 to produce linear on-plate bead welds in copper (110) and aluminum (6061) to evaluate variations in the keyhole depth within the oscillation pattern. Except for varying welding speeds, welding parameters for each material remain constant, as shown in Table 3 below. The ICI measurement beam or imaging beam 152 rotates counter-clockwise relative to the process beam 118, resulting in multiple intersections of the keyhole and measurement beams per oscillation cycle.

[0074] Table 3: Process parameters for the variation of the hole depth within the oscillating pattern

[0075]

[0076] The resulting depth information includes measurements of the orifice (when the beam is aligned) and measurements of the melt pool surface (when the beam is at different locations around the oscillating path). The measurement beam and the process beam meet at regular intervals (referred to herein as "cross intervals") determined by their respective rotation frequencies. A set of orifice minima is extracted from each set of depth data by searching for local minima within each expected cross interval. Figure 14 The hole depths measured from the front, back, left, and right points of an oscillating pattern during bead soldering on a copper plate are shown, where each position in the oscillating pattern exhibits different depth and stability characteristics.

[0077] These orifice minimums are then plotted as a function of the polar angle around the process axis. Depth values ​​are merged at 10-degree intervals around the circular oscillation pattern, and the mean and standard deviation of each merge are calculated. To help characterize the magnitude of orifice variation and the orientation of orifice depth extrema relative to the welding direction, sine curves are fitted to each depth group using only phase and amplitude as free variables. Figure 15 This diagram illustrates the relationship between the average penetration depth of the pinhole minimum in copper and aluminum welding and the rotation angle around the oscillation pattern at different welding speeds. In each case, the average penetration depth is fitted with a sine curve to help assess the amount of depth variation and the orientation of penetration extremes relative to the weld travel direction. In each figure, the back direction is marked by a dashed line at 180 degrees, the slow side of the oscillation pattern is marked at 90 degrees, and the fast side is marked at 270 degrees.

[0078] based on Figure 15 The results show that two distinct effects can influence the orifice depth at different locations around the oscillating pattern. The first effect assumes that the orifice depth varies with the travel speed of the process beam across the material surface. In isolation, this effect would tend to bias the orifice depth extrema towards the slow and fast edges of the oscillating pattern, where the maximum and minimum process beam travel speeds occur. The second effect assumes that the orifice depth varies with the material temperature, influenced by the proximity of most of the melt volume (lagging behind the process). Theoretically, once the weld has been made long enough to fully establish the melt pool, the material at the rear edge of the oscillating pattern where the process beam is incident should be at a higher temperature than at the front edge.

[0079] based on Figure 15The results show that, for both aluminum and copper, the depth extrema appear to align towards the front / back axis of the oscillating pattern. This is consistent with the approximate size of the back melt volume, which plays a major role in the orifice depth within the oscillating pattern. One would still expect some skew to the slow or fast side of the oscillating pattern based on the surface velocity. This trend appears to be observed in copper welds, with all welds exhibiting a maximum depth offset of approximately 20 degrees towards the slow side of the oscillating pattern. The results for aluminum do not show a consistent trend towards either the slow or fast edge, but the depth data for aluminum are significantly noisier than that for copper, which could lead to inconsistent placement of the fitted depth extrema. In this particular process for aluminum, the dominant orifice depth variation appears to occur between the front and back edges of the oscillating pattern.

[0080] Although examples of imaging beam scanning patterns have been described above, other imaging beam scanning patterns are possible and within the scope of this application.

[0081] In another embodiment, the oscillating welding process can be monitored by moving the imaging beam in the direction of the process beam and using an ICI system synchronized with the oscillation cycle. While the imaging beam can be moved in the direction of the process beam, it can be independent of the process beam to, for example, provide dynamic offset control and / or allow cyclic alignment correction. The imaging beam can be aligned substantially coaxially with the process beam, or it can be aligned to lag the process beam to monitor, for example, a characteristic of the amount of process beam lag related to the processing speed. As mentioned above, in some oscillation patterns, the processing speed varies periodically around the oscillation pattern. For example, in a circular oscillation pattern, the oscillation pattern has a slow side and a fast side, so the desired alignment of the imaging beam may be affected as the beam moves along the circular oscillation pattern.

[0082] To provide cyclic alignment correction, the control system can be programmed to cause the imaging beam scanning actuator to move the imaging beam relative to the process beam, correcting the alignment of the imaging beam relative to the process beam based at least in part on the beam's position on the oscillation pattern. For example, in a circular oscillation pattern, the alignment can be periodically changed for the slow and fast sides. Cyclic alignment correction can also be based on other parameters, such as processing speed, material type, and material thickness.

[0083] In some embodiments, the control system of the laser welding system described herein can be programmed to provide dynamic offset control of the imaging beam based on one or more other factors or parameters. These factors or parameters include, but are not limited to: the position of the process beam within its oscillation pattern; the process beam oscillation pattern (e.g., oscillation geometry, oscillation amplitude, and / or oscillation period); the workpiece geometry; a lookup table consisting of offset parameters based on material and welding process parameters; a thermomechanical welding model; ICI measurements from previous welding processes; previous ICI measurements from the same welding process; at least one component of the instantaneous velocity vector of the process beam relative to the material; a curved welding path through the material; and one or more corrections to the laser beam transmission system (e.g., chromatic aberration field correction, focal plane field correction, spot size field correction, and / or beam shaping correction). Alternatively or additionally, ICI measurements can also be corrected based on one or more of these factors or parameters (e.g., using a data processing system) to, for example, smooth the ICI measurements and ensure uniformity in the welding process.

[0084] The systems and methods described herein can be used to monitor weld penetration profiles. In one example, the ICI system can scan (e.g., using raster scanning) an imaging beam transverse to the welding direction at various points along the weld to generate an indication of the weld penetration profile transverse to the weld direction at those locations. In another example, the ICI system can scan the imaging beam along the welding direction to generate an indication of the weld penetration profile along the welding direction at various points along the weld. In yet another example, the ICI system can scan the imaging beam to generate an indication of the weld penetration profile along a virtual cross-section defined by an arbitrary geometric surface. The control system can be configured to adjust the laser power based on weld penetration measurements from the ICI system at multiple locations during the oscillation cycle. In particular, the control system can be configured to adjust the laser power to reduce weld penetration variation throughout the oscillation cycle. As described above, the ICI measurements can be corrected based on one or more additional factors or parameters to, for example, ensure that the oscillating weld depth produces a uniform depth to guarantee quality and / or ensure that the oscillating weld bead does not move.

[0085] In another embodiment, the control system can adjust the processing based on part measurement outputs from the ICI system. The control system can be configured to adjust the process beam oscillation pattern, for example, based on pre-processed part measurement outputs and / or post-processed part measurement outputs from the ICI system.

[0086] The welding system can also control the measurement beam relative to the process beam in other ways. For example, when the ICI system is connected upstream of the scanning actuator in the oscillating head, the control system can be programmed to move the imaging beam scanning actuator, which is complementary to the process beam scanning actuator, in a synchronous manner, such that the imaging beam is effectively separated from the process beam oscillation pattern on the workpiece surface. Alternatively or additionally, the control system can be programmed to trigger the process beam scanning actuator between its oscillation pattern and a fixed position to achieve ICI measurements of the workpiece surface separated from the oscillation pattern. The control system can also be programmed to trigger ICI system measurements such that they are time-synchronized with the oscillation cycle.

[0087] One of the main advantages of oscillation welding is its beneficial effect on the quality bonding of dissimilar metals (such as common engineering alloys of copper, aluminum, steel, stainless steel, and titanium, with various coating or plating versions). The bonding of dissimilar metals is used in a wide range of applications, including but not limited to electrified transportation systems (such as automobiles, trains, and airplanes).

[0088] Once an effective means of measuring weld penetration and / or process kinetics is configured using a wobbling head and ICI system, ICI measurements can be used specifically as an alternative to assess the amount of mixing between materials in the weld joint. For example, when overlapping copper and aluminum, insufficient mixing can lead to poor mechanical and electrical connections. Excessive mixing, due to the large presence of intermetallic phases, can cause brittle fracture. These aspects of weld metallurgy can be monitored through ICI observation and / or ICI-based control of the bonding process to ensure quality and / or to compensate for variations in manufacturing processes, raw materials, and the environment. Pre-start calibration and comparison with metallurgical analysis are helpful for this process.

[0089] Therefore, even with complex wobbling patterns formed by process lasers, inline coherent imaging (ICI) can be advantageously used to monitor wobbling welds. By using various techniques to move the imaging beam to different measurement positions, various aspects of the wobbling weld can be monitored, including keyhole depth and stability, as well as the formation of the melt pool.

[0090] While the principles of the invention have been described herein, those skilled in the art will understand that this description is by way of example only and is not intended to limit the scope of the invention. Other embodiments besides the exemplary embodiments shown and described herein are also within the scope of the invention. Modifications and substitutions by those skilled in the art are considered to be within the scope of the invention, which is limited only by the appended claims.

Claims

1. A laser material processing system, comprising: A material-modified beam source, wherein the material-modified beam source is used to generate a process beam; A processing head, connected to the material modification beam source and including at least one process beam scanning actuator for guiding and moving the process beam along at least one axis according to an oscillation pattern at the processing location of the workpiece. An inline coherent imaging system, optically coupled to the processing head, and comprising at least one imaging beam scanning actuator configured to position an imaging beam at least partially independent of the process beam; and A control system is provided for controlling at least the material modification beam source, the process beam scanning actuator, and the imaging beam scanning actuator, wherein the control system is programmed to cause the processing head to scan the process beam in the oscillation pattern, and the control system is programmed to cause the imaging beam scanning actuator to move the imaging beam in coordination with the oscillation pattern to multiple measurement positions on the processing site. The control system is further programmed to cause the imaging beam scanning actuator to move the imaging beam relative to the process beam to correct the alignment of the imaging beam relative to the process beam, at least in part, based on the position of the process beam on the oscillation pattern, thereby providing cyclic alignment correction.

2. The laser material processing system according to claim 1, wherein, The processing head is a welding head used to guide and move the process beam according to the oscillation pattern on the welding site.

3. The laser material processing system according to claim 1, wherein, The material modification beam source is a fiber laser.

4. The laser material processing system according to claim 1 further includes at least one motion stage, the at least one motion stage being used to translate at least one of the processing head and the workpiece relative to each other while the process beam moves in the oscillation pattern on the workpiece.

5. The laser material processing system according to claim 1, wherein, The inline coherent imaging system is optically coupled to the processing head downstream of at least one process beam scanning actuator.

6. The laser material processing system according to claim 5, wherein, The control system is programmed such that the imaging beam scanning actuator causes the imaging beam to move along the oscillation pattern in the opposite direction to the movement of the process beam and in sync with the oscillation pattern.

7. The laser material processing system according to claim 5, wherein, The control system is programmed such that the imaging beam scanning actuator causes the imaging beam to move along the oscillation pattern in the direction of the process beam and in sync with the oscillation pattern.

8. The laser material processing system according to claim 1, wherein, The inline coherent imaging system is optically coupled to the welding head upstream of at least one process beam scanning actuator.

9. The laser material processing system according to claim 1, wherein, The control system is programmed to move the imaging beam using the imaging beam scanning actuator, such that the imaging beam scans the processing area within a scanning pattern that at least partially surrounds the oscillating pattern.

10. The laser material processing system according to claim 1, wherein, The control system is configured to control the process beam scanning actuator in response to measurements from the inline coherent imaging system to adjust at least one of the oscillation geometry, oscillation period, oscillation speed, and oscillation amplitude.

11. The laser material processing system according to claim 1, wherein, The control system is configured to control the power of the process beam in response to measurements from the inline coherent imaging system.

12. The laser material processing system according to claim 1, wherein, The process beam scanning actuator is configured to move the process beam, with a maximum beam displacement of ±30 mm at the workpiece.

13. The laser material processing system according to claim 1, wherein, The process beam scanning actuator is configured to move the process beam by a maximum beam angular displacement of ±5° to provide an oscillation amplitude.

14. The laser material processing system according to claim 1, wherein, The at least one process beam scanning actuator and the at least one imaging beam scanning actuator are selected from the group consisting of a galvanometer scanning mirror, a polygonal scanning mirror, a MEMS-based scanning mirror, a piezoelectric scanning mirror, and a diffraction-based beam scanner.

15. The laser material processing system according to claim 1 further includes an auxiliary measurement system configured to measure process radiation.

16. The laser material processing system according to claim 15, wherein, The auxiliary measurement system measures process radiation within a spectral band from 100 nm to 1 mm.

17. The laser material processing system according to claim 15, wherein, The auxiliary measurement system includes optical elements to perform spatial local measurements relative to the process beam.

18. The laser material processing system according to claim 17, wherein, The auxiliary measurement system is configured to perform the spatial local measurement at a measurement location dynamically offset from the process beam, based on at least one output from the inline coherent imaging system.

19. The laser material processing system according to claim 15, wherein, The auxiliary measurement system includes optical elements to perform spatial local measurements relative to the imaging beam.

20. The laser material processing system according to claim 15, wherein, The control system is programmed to move the imaging beam using the imaging beam actuator, such that the imaging beam is dynamically deflected from the process beam based on at least one output of the auxiliary measurement system.

21. A method for monitoring an oscillating welding process using a laser material processing system according to any one of claims 1 to 20, the method comprising: Guide the process beam and at least one imaging beam from the inline coherent imaging system to the welding area of ​​the workpiece. The process beam is moved within an oscillating pattern on the welding area of ​​the workpiece; The at least one imaging beam is moved, at least partially independently of the process beam, to multiple measurement positions on the welding site; as well as As the process beam moves within the oscillating pattern, inline coherent imaging measurements are obtained from the plurality of measurement locations. The imaging beam is moved relative to the process beam to correct the alignment of the imaging beam relative to the process beam, at least in part, based on the position of the process beam on the oscillation pattern, thereby providing cyclic alignment correction.

22. The method of claim 21, further comprising: As the process beam moves within the oscillation pattern at the welding site, at least one of the process beam and the workpiece is translated relative to each other.

23. The method according to claim 21, wherein, Moving the imaging beam includes scanning the imaging beam independently of the process beam in an inline coherent imaging scan pattern covering the welded portion of the workpiece, wherein the inline coherent imaging scan pattern at least partially surrounds the oscillation pattern.

24. The method according to claim 23, wherein, Obtaining inline coherent imaging measurements includes: obtaining depth measurements at points in the inline coherent imaging scan pattern; and obtaining inline coherent imaging measurements also includes: combining the depth measurements to form a three-dimensional image of the welded area.

25. The method according to claim 23, wherein, Scanning includes raster scanning.

26. The method according to claim 21, wherein, Moving the imaging beam includes locally jittering the measurement beam around at least a portion of the oscillation pattern.

27. The method according to claim 21, wherein, Moving the imaging beam includes: moving the imaging beam independently of the process beam to a plurality of fixed measurement positions on the oscillating pattern, and wherein obtaining inline coherent imaging measurements includes: obtaining depth measurements at the fixed measurement positions as the process beam moves in the oscillating pattern.

28. The method according to claim 27, wherein, At least one of the fixed measurement positions includes four measurement positions around the oscillating pattern, the four measurement positions including a front measurement position, a rear measurement position, a fast measurement position, and a slow measurement position.

29. The method according to claim 21, wherein, Moving the imaging beam includes: moving the imaging beam independently of the process beam in a direction opposite to the movement of the process beam along the oscillation pattern, wherein the imaging beam passes through the process beam at intersecting intervals, and wherein obtaining inline coherent imaging measurements includes: obtaining depth measurements at points along the oscillation pattern using the inline coherent imaging system.

30. The method according to claim 29, wherein, The depth measurement is obtained from the bottom of the aperture when the process beam and the imaging beam intersect, and from the surface of the melt pool at other times.

31. The method of claim 29, further comprising: When the process beam and the imaging beam intersect, the aperture depth is determined based on the depth measurement value obtained from the bottom of the aperture.

32. The method according to claim 31, wherein, Determining the aperture depth includes searching for a local minimum depth within a range around each intersection interval of the process beam and the imaging beam.

33. The method according to claim 21, wherein, Moving the imaging beam includes: moving the imaging beam independently of the process beam and along the oscillation pattern, wherein inline coherent imaging measurements are obtained as the imaging beam moves along the oscillation pattern.

34. The method according to claim 33, wherein, The imaging beam is moved such that it dynamically deflects from the process beam at the surface of the workpiece according to the position of the process beam within the oscillation pattern.

35. The method according to claim 33, wherein, The imaging beam is moved so that it dynamically deflects from the process beam at the surface of the workpiece to compensate for changes in the position of the pinholes within the oscillating pattern.

36. The method according to claim 33, wherein, The oscillation pattern is a periodic pattern.

37. The method of claim 21, further comprising: The welding head is moved relative to the workpiece to translate the process beam relative to the workpiece.

38. The method of claim 21, further comprising: The workpiece is moved relative to the welding head to translate it relative to the process beam.

39. The method according to claim 21, wherein, The workpiece comprises dissimilar metals, and wherein the inline coherent imaging measurement indicates the amount of mixing between the dissimilar metals.

40. The method according to claim 21, wherein, The workpiece comprises a material selected from at least one of copper and aluminum.

41. The method according to claim 21, wherein, The workpiece includes non-ferrous alloys.

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