Dynamically controlled laser drilling system and method for generating holes - Patents.com

Abstract

The laser drilling system is configured with a combination of system components including a fiber laser source, a laser processing head, a dynamic compensator configured with one or more galvanometers, and a stage supporting a workpiece to be laser drilled. All of the system components are operatively connected to each other to provide a plurality of trepanned holes in the workpiece, each having a desired shape. The laser head and the stage are continuously displaceable relative to each other, while the dynamic compensator pivots to keep the laser spot and the predetermined drilling location fixed relative to each other for a predetermined period of time sufficient to drill a hole. The laser source is selected from a solid-state laser configured with a single-core or multi-core delivery fiber. The multi-core delivery fiber is associated with an adjustable mode beam (AMB) laser to provide annular holes, polygonal holes, or irregular holes.

Description

[Technical field]

[0001] The present disclosure relates to a laser drilling system, and more particularly, to a laser drilling system configured with a dynamic compensator configured to controllably generate a variety of hole geometries. [Background technology]

[0002] In particular, countless industries, including industrial machining, aerospace, industrial recycling, food processing, waste management, water treatment, and air and gas filtration, use parts that are manufactured with various perforations or holes. The manufacturing process for creating perforations has unique challenges and limitations when, for example, in metals, the holes are punched, mechanically drilled, or created by a workpiece drawing process. Each of these processes can create residual mechanical stresses that can result in warping (twisting or cupping) of the workpiece. Typically, these undesirable effects are corrected by secondary operations.

[0003] An alternative method of drilling holes in a workpiece involves the use of lasers in general, and fiber lasers in particular. The fiber laser can produce holes with precision and speed while minimizing residual stresses in the laser-produced filter workpiece. The fiber laser drilling process dramatically expands the hole design options. Holes can be round, square, oval, tapered, angled, or have custom shapes. The workpiece surface can be flat, circular, or have complex 3D shapes. Because the laser is an integral part of the multi-axis machine, different perforations can be applied to different 3D surfaces. This allows the perforations to be positioned and shaped as needed which helps optimize the laser drilling process.

[0004] There are various drilling techniques: single shot, multi-shot, or percussion and trepanning. Figures 1, 2A and 2B show an exemplary single shot technique whereby a single pulse 26 creates a hole. This technique allows for very high drilling frequencies (holes per second) and therefore high throughput. Furthermore, the single shot technique allows for "drilling on the fly", including continuous hole creation without disturbing the displacement of the workpiece 26 (Figure 2A) and the laser head 14 relative to each other, dramatically reducing the inertia-related time waste associated with starting and stopping. It is important that the "laser on" time (or laser pulse width) is short enough so that the movement of the workpiece support or stage during the laser pulse width does not include deformations in the roundness of the hole due to the relative movement between the laser head and therefore the laser beam and the workpiece, as described below.

[0005] A laser drilling system 10 typically includes a laser source 12 (FIG. 1), a processing laser head 14, a processor 16, an interface 18 between the processor 16 and a workpiece support stage 38 (FIG. 2A), and, if required by the particular drilling process, a transport and gas supply system, respectively (not shown). The desired speed, maximum power, pulse duration, and pulse repetition rate of the laser head are predetermined and stored. All of the above individual elements or any combination of them (laser source 12, laser head 14, interface board 18, processor 16), and the workpiece support stage 38 are housed within a laser cube or housing 20 (FIG. 1), which may function as both a system controller and a laser head processor and may be referred to as a central processing unit (CPU). Alternatively, the system 10 is provided with a CPU 22 attached to the laser cube 20 and configured to control a number of parameters of the system 10, including, for example, the speed at which the laser head 14 and / or the stage supporting the workpiece to be laser processed are displaced relative to each other. In this configuration, processor 16 is designated to control only laser head 14 and to be in communication with CPU 22 .

[0006] One of the most typical drilling operations involves drilling holes in workpieces used to manufacture various filters. To start the operation of the system 10, the laser parameters, including the maximum power Pp, pulse duration, and pulse repetition rate or drilling speed, are empirically or theoretically predetermined and stored in the memory of the CPU 22. In response to a signal from the CPU 22, either the stage 38 (FIGS. 2A and 2B) supporting the target workpiece or the laser head 14, or both the stage and the laser head, are actuated to achieve a continuous displacement of the laser head 14 and the workpiece 26 relative to each other. Assuming that the laser head 14 is movable, at some point it will reach a predetermined position corresponding to one of the positions 28 to be drilled. At this point, in response to a control signal from the processor 16 (or CPU 22) coupled into the laser source 12, the laser source outputs a laser beam including a pulse 25 (FIG. 2A) that is incident on the beam guiding lens 24 fixed to the laser head 14. The beam guiding lens 24 further deflects the laser beam toward one of the positions 28. Quite by chance, the laser head continues its displacement and the beam spot inevitably drags in the direction of laser head displacement D. Correspondingly, assuming that pulse 25 is characterized by the desired maximum power, it will drill a hole at position 28.

[0007] During a time corresponding to the pulse duration, the laser head 14 is displaced in a direction D (FIG. 2A) from position 25a (FIG. 2B) through intermediate positions 25b and 25c before it arrives at position 25d corresponding to the end of the pulse duration. The continuous displacement of the laser head 14 with the beam guiding lens 24 (FIG. 2A) during a time interval corresponding to the duration of a single pulse 25 results in an elongated or oval hole 28 drilled in the target workpiece 26. The elongation of the hole 28 is the result of the beam lens 24 after the displacement of the laser head 14 and thus the dragging of the beam spot along a linear path. Once the current hole is generated, the laser source 12 (FIG. 1) is de-energized, while the laser head 14 and / or the stage 38 continue to move towards the next position. The aforementioned operation continues until each of the marked positions has been laser processed.

[0008] The hole characteristics (inner diameter, outer diameter, conicity) are directly dependent on the laser parameters such as maximum power, pulse width, process gas pressure, and system characteristics such as nozzle width. The physical relationship between hole volume and energy density can be found experimentally. Larger holes and thicker workpieces require more energy input to create holes. Two laser parameters are directly correlated with pulse energy: maximum power and pulse width. The product of these two parameters results in the total pulse energy. To increase the pulse energy (for larger holes and / or thicker workpieces), either the maximum power needs to be increased if the pulse width remains unchanged, or the pulse width needs to be increased while the maximum power remains unchanged. The increase in the maximum power requires a laser source with a higher overall power, which entails higher manufacturing and maintenance costs, while the increase in pulse width results in a deformation of the hole, known as "hole ovalization" as disclosed above. The "hole ovalization" is problematic for many applications. For example, if the workpiece being laser drilled is a filter, ovalization destroys the uniformity of the drilling. Hole asymmetry adversely affects the filtering characteristics and therefore reduces the efficiency of the filter. To avoid ovalization, the speed at which the workpiece and the laser head are displaced relative to each other must be reduced. This reduction in speed leads to a reduction in the drilling frequency, which in turn leads to a reduction in the machine's throughput. As has been experimentally determined, to prevent hole asymmetry, the drilling frequency must be reduced to 5-7 Hz, which is too low to make production economically sustainable.

[0009] Filters for plastic recycling machines can have up to 3 million holes (depending on the size and pitch of the holes (the smaller the hole size, the higher the total number of holes)). For such a filter to be competitive, its entire manufacturing process should not exceed 6-7 hours. Beyond this time limit, the filter manufacturing costs are economically unjustified.

[0010] With hole diameters varying between about 80 and 100 μm and stainless steel thicknesses up to 1 mm, a drilling frequency of 250 Hz may be sufficient to generate 3 million holes in about 6 hours at a maximum power of 2-3 kW. For larger holes, such as 1000 μm diameter holes drilled in 2 mm thick stainless steel, obviously the maximum power needs to be increased to complete the process in 6 hours. In the example with a 1000 μm hole diameter, the filter typically has about 250,000 holes, which means that the total process time to complete a single filter at a frequency of 5 Hz (a frequency required to prevent hole ovalization) exceeds 15 hours. It is possible to increase the maximum power and reduce the pulse width to obtain the same pulse energy required to efficiently drill 1000 μm holes, but it requires a drilling frequency of at least 40 Hz for sustainable production. At a drilling frequency of 40 Hz, the pulse width does not need to exceed 3 ms to avoid hole ovalization, which would require a maximum power of 47 kW to have the same pulse energy, but which would require a 50 kW laser source, which is too costly and also economically unjustifiable. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] International Publication No. 2020 / 117816 (WO '816) Summary of the Invention [Problem to be solved by the invention]

[0012] Therefore, there is a need for a laser drilling system that operates at a power and drilling frequency that produces a desired large number of uniform round holes while meeting throughput and manufacturing costs according to market demands.

[0013] Additionally, there is another need for such a laser drilling system that is configured to controllably drill holes having a variety of shapes. [Means for solving the problem]

[0014] These needs are met by the disclosed laser drilling system, characterized by a laser source, a laser head, a transport system, or a multi-axis stage, and in some embodiments, a delivery fiber system. The laser source may include various solid-state lasers, such as fiber lasers operating in a quasi-continuous wave (QCW) or pulsed regime. The laser outputs a train of pulses, each of which is characterized by a maximum power and pulse duration that achieves a desired high drilling frequency that meets market demands for throughput and manufacturing costs. However, in contrast to known prior art, the holes / perforations drilled in the workpiece do not have ellipticity or non-circularity, which is the amount of roundness of the hole. In addition to the laser drilling system disclosed above, a beam delivery system configured to controllably adjust the mode / shape of the beam expands the capabilities of the system of the present invention by enabling the system to generate a variety of hole shapes.

[0015] According to one prominent feature, the roundness of the hole is maintained by continuously displacing the laser head relative to the target workpiece along a path while simultaneously adjusting a fixed beam spot at each of the predetermined hole locations on the target workpiece for a period of time sufficient to drill a round hole. Technically, a single or multiple galvo mirrors are mounted in the laser head and operated to guide the laser beam so that it is incident on the desired location of the workpiece for a predetermined period of time, while the laser head continues to move continuously, or the workpiece on the stage is moving, or both the laser head and the workpiece are moving. In other words, the beam spot and the illuminated location are fixed in space and time relative to each other during the drilling of the hole. In summary, in a system including a laser, a laser head, a workpiece support / stage, and a galvo mirror, the position between the beam spot and the illuminated workpiece is fixed for a predetermined period of time sufficient to drill the desired round hole to be provided, and of course the maximum power is properly determined.

[0016] In accordance with another prominent feature of the present invention, the hole drilling system disclosed above is further configured with a fiber delivery system that is constructed to controllably output beams of different shapes. Combined with the galvo mirror of the present disclosure, this configuration allows for the creation of an infinite number of hole shapes, including round holes.

[0017] The above-mentioned and other structurally and conceptually complementary features will become more apparent with reference to the attached figures, which are not drawn to scale. The features provide illustrations and provide a further understanding of the various associated embodiments and diagrams, which form part of this specification, but do not imply any limitation of any particular diagram and embodiment. In the drawings, each identical or nearly identical component that appears in various figures is represented by a similar numeral. For the purpose of clarity, all components may not have the same reference numerals. [Brief description of the drawings]

[0018] [Figure 1]FIG. 1 is a general design drawing of a laser drilling system. [Figure 2A] FIG. 2 is an optical diagram of the known laser drilling system of FIG. 1. [Figure 2B] 2 is an illustration of the operation of the known laser drilling system of FIG. 1. [Figure 3A] FIG. 2 is an optical diagram of the inventive principle of the laser drilling system of FIG. 1. [Figure 3B] 2 is a diagram of the operation of the inventive principle of the laser drilling system of FIG. 1; [Figure 4A] FIG. 1 is an optical schematic showing the first drilling step. [Figure 4B] FIG. 2 is an optical schematic diagram of the final drilling step according to the known technique. [Figure 4C] FIG. 13 is an optical schematic diagram of the final drilling step according to the concepts of the present invention. [Figure 5A] FIG. 4D is a diagram of a cylindrical hole produced by the fiber laser system of the present invention of FIG. 4C, which outputs a laser beam having a fixed beam diameter. [Figure 5B] FIG. 4D is a diagram of a tapered hole produced by the fiber laser system of the present invention of FIG. 4C, which outputs a laser beam with an adjustable beam diameter. [Figure 6A] FIG. 1 is a diagram of an exemplary adjustable mode beam (AMB) laser system. [Figure 6B] FIG. 1 is a diagram of an exemplary adjustable mode beam (AMB) laser system. [Figure 6C] FIG. 1 is a diagram of an exemplary adjustable mode beam (AMB) laser system. [Figure 7A] 1, 3A-3B, and 4C are diagrams of exemplary hole shapes that can be produced by the laser systems of the present invention. [Figure 7B] 1, 3A-3B, and 4C are diagrams of exemplary hole shapes that can be produced by the laser systems of the present invention. [Figure 7C] 1, 3A-3B, and 4C are diagrams of exemplary hole shapes that can be produced by the laser systems of the present invention. [Figure 7D] 1, 3A-3B, and 4C are diagrams of exemplary hole shapes that can be produced by the laser systems of the present invention. [Figure 7E] 1, 3A-3B, and 4C are diagrams of exemplary hole shapes that can be produced by the laser systems of the present invention. [Figure 7F] 1, 3A-3B, and 4C are diagrams of exemplary hole shapes that can be produced by the laser systems of the present invention. [Figure 7G] 1, 3A-3B, and 4C are diagrams of exemplary hole shapes that can be produced by the laser systems of the present invention. [Figure 7H] 1, 3A-3B, and 4C are diagrams of exemplary hole shapes that can be produced by the laser systems of the present invention. [Figure 7I] 1, 3A-3B, and 4C are diagrams of exemplary hole shapes that can be produced by the laser systems of the present invention. [Figure 7J] 1, 3A-3B, and 4C are diagrams of exemplary hole shapes that can be produced by the laser systems of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The inventive concept relates to a laser system for processing a workpiece, comprising at least three elements displaceable relative to each other such that a laser beam is incident on the workpiece at a controllable angle of incidence. In particular, the inventive laser drilling system implements a drill-on-the-fly technique to generate an unlimited number of substantially uniform round holes at a drilling speed that meets market demands. In relation to the known prior art, the hole elongation problem is solved by a dynamic compensator attached to the laser head of the inventive system. The dynamic compensator is configured to controllably guide the laser beam in a direction opposite to the direction of continuous displacement of the laser head and / or the stage supporting the workpiece. The beam is directed to the desired location of the workpiece to be drilled. According to the inventive concept, each time a pulse is generated at a predetermined maximum power, the beam spot and the irradiation location are in a fixed spatial and temporal relationship for a pulse duration sufficient to generate a round hole. Based on the above, the inventive system utilizes a drill-on-the-fly technique that enables a high throughput of round holes in a cost-effective manner that meets and exceeds market demands.

[0020] With reference to FIG. 1 and FIG. 3A and 3B, the laser drilling system 10 of FIG. 1 disclosed above is improved by incorporating a single-axis or multi-axis galvo mirror system 34 (FIG. 3A) in the wobble laser head 44. Gyroscopes are key rotating elements incorporated in various beam guiding, navigation, and other systems. Similar to the beam guiding lens 24 of the known art (FIG. 2A), the galvo mirror system 34 is displaceable along a linear path together with the wobble laser head 44 relative to the XYZ stage 38 that supports and guides the workpiece 26. Unlike the beam guiding lens 24 of FIG. 2A, the galvo mirror system 34 controllably pivots about an axis A that extends transversely to the horizontal and vertical (with respect to the sheet) propagation planes of the laser beam 25. The angular displacement of the galvo mirror system 34 is indicated by a double-headed arrow and is characterized by two fixed spaced apart positions (the initial or first position shown in solid line and the final or second position shown in dashed double-dot line). The linear distance between the initial and final positions corresponds to the distance traveled by the wobble laser head 44 during the pulse duration. When the laser head 14 reaches a predetermined position, which corresponds in the time domain to the initial position of the mirror 34, the galvo mirror system 34 begins to pivot. At the end of the single pulse duration, the galvo mirror 34 reaches its final angular position. During the pulse duration, the beam spot and the position / hole 30 are spatially fixed relative to each other. The maximum power, pulse duration, drilling frequency, laser head speed, angular velocity ω of the mirror 34 (where ω=θt, θ is the rotation angle), and other parameters are selected to generate a round hole. However, as one skilled in the mechanical arts will appreciate, the parameters can be controlled to generate holes having various shapes. For example, controlling these parameters can generate various types of annular holes. Using various beam shapers, other hole shapes can include polygonal holes or square holes.

[0021] As the wobble laser head 44 continues to move in the direction D during the pulse duration, the galvo mirror system 34 continuously pivots the beam 25 about the axis A in a direction opposite to the displacement D of the wobble laser head 44, thus controllably changing the incidence angle of the beam. As a result, the beam spot and the location / hole 30 larger than the beam spot remain fixed relative to each other. Correspondingly, the hole 30 has no elongation and is substantially circular. At the end of the pulse, the galvo mirror system 34 pivots back to its initial position, while the wobble laser head 44 continues its displacement towards the next location to be drilled, and the above disclosed operations are repeated for each of the predetermined locations. It should be noted here that the displacement of the laser head 44 can be stopped and the above disclosed operations can be based on the displacement of the stage with the workpiece 26 in a direction opposite to that shown by the arrow D.

[0022] 4A-4C provide a visual comparison between the drilling operation of the prior art drilling system (FIG. 4B) and the system of the present invention (FIG. 4C), respectively. In both the known laser drilling system and the laser drilling system of the present invention, the beam 25 is incident on a mirror while the wobble laser head 44 and the stage supporting the workpiece 26 move relative to each other during the pulse duration, as shown in FIG. 4A. In the known system of FIG. 4B, the beam 25 and the workpiece 26 are also displaced relative to each other (a movement resulting in an oval hole) by a distance Δx (corresponding to the length of the displacement between the laser head and the workpiece). The reason for such relative movement between the beam 25 and the workpiece 26 is the fixed angular position between the beam guiding lens 24 and the wobble laser head 44, which drags the beam spot along a linear path that illuminates the length of the workpiece 26. The hole is therefore oval. The above description is based on a laser source selected to output the maximum pulse power believed to make the system of the present invention economically appealing to the relevant market.

[0023] In contrast, as shown in Figure 4C, angular displacement of the galvo mirror system 34 of the present invention changes the angle of incidence pivoting the laser beam 25 in a direction opposite to the direction of displacement of the laser head 44 for the entire duration of the pulse. However, the beam spot and workpiece 26 remain fixed relative to one another, resulting in a round hole because the beam spot illuminates exactly the same location on the workpiece for the entire pulse duration.

[0024] The above description primarily refers to a movable laser head. However, as one skilled in the art will appreciate, having a fixed laser head and a movable stage / workpiece does not change the relationship between the galvo mirror system 34 and the workpiece 26. In particular, during the pulse duration, the galvo mirror system 34 pivots the beam 25 in the opposite direction to the stage movement and at the same axial velocity. With this parameter, during the same pulse width / pulse duration, the interaction point between the laser beam 25 and the workpiece surface is always the same, and the relative velocity between the beam spot and the position is strictly equal to zero.

[0025] Alternatively, both the laser head and the workpiece can move simultaneously, subject to the direction and the desired speed ratio between the laser head 44 and the workpiece 26, and the angular velocity of the galvo system and the angle at which it pivots along with the preset drilling frequency are appropriately selected and controlled, which can be realized by one skilled in the art of machine / laser / software combination. Furthermore, while the present disclosure is directed to round holes, one skilled in the art will readily appreciate that all of the parameters disclosed above can be controlled to generate various hole shapes, such as figure-eight holes. Furthermore, the diagrammatically illustrated example of the system of the present disclosure is configured with a galvo mirror system 34 that pivots the beam 25 against the direction of the laser head displacement D, which can be reconfigured to pivot the beam 25 in the opposite direction.

[0026] Thus, dynamic compensation is performed by a single or multiple galvanometer mirrors 34 mounted in the drilling wobble head 44. During the pulse duration, the galvo mirrors 34 make a linear trajectory in the opposite direction to the axial movement at the same axial speed. The length of the line is directly related to the pulse width, so that the time required for the galvo mirrors 34 to make a line at a certain speed is exactly the same as the laser pulse width. This means that the interaction point between the laser beam 25 and the workpiece surface is always the same during the pulse duration, and the relative speed (between the beam spot and the workpiece) is exactly equal to zero. In this way, the hole is drilled as if the process / laser head 44 and the workpiece 26 were immobile and fixed. The laser source 12 of FIG. 1 can be operated in a QCW state or a pulsed state and can be configured as a solid-state laser, including a fiber laser. As mentioned above, the firing of the laser beam is controlled by the wobble head controller 16 or the CPU 22, so that the laser emission is activated at the pivot start point and stopped at its very end. Once the hole is completed and the laser emission is turned off, the galvanometer returns to its original position and is only activated when it is time to drill the next hole. The process is repeated for each hole to be created.

[0027] Based on the above, the use of the wobble head of the present invention increases the overall throughput of drilling holes with diameters ranging from the beam size to approximately the nozzle size, which generally matches the 0.1-3 mm hole diameter range produced in material up to 5 mm thick. Testing also demonstrated good dimensional accuracy / repeatability and reduced spatter with minimal laser cost. Testing also demonstrated high throughput of 10 holes / sec. Several tests resulted in 15-20 1 mm holes per second in 3 mm thick stainless steel. Based on results obtained during numerous tests, wobble drilling is approximately 5-10 times faster than gantry trepanning of 3 mm thick stainless steel. More than 50 holes per second can be produced with reduced hole dimensions and material thicknesses less than 2 mm. Wobble drilling has been observed to have minimal dross at the exit and virtually no spatter on top. Also, cutting off-center with the nozzle does not adversely affect the roundness of the holes.

[0028] 5A and 5B generally illustrate another salient feature of the laser system of the present invention shown in FIGS. 1, 3A, and 3B. In particular, the laser drilling system 10 of FIG. 1 is configured with an AMB laser source characterized by a propagation system that changes the beam shape / mode of the system's output. As previously described, the high power laser 12 of the system 10 for trepanning holes can operate in a QCW state and in a pulsed state with a duty cycle ranging from 1 to 99%. Typically, the laser 12 outputs a beam 25 characterized by a single beam shape or profile, such as an annular beam having a Gaussian-shaped intensity distribution profile. The laser system 10 typically has a delivery fiber that guides the laser beam 25 of FIG. 3A through its core such that the laser beam irradiates a single spot on the surface of the workpiece. As a result, the system output beam 25 drills holes 30, which typically pass through the web of the workpiece 26. Each hole 30 is defined by a perimeter wall that is substantially circular, as shown in FIG. 5A. As a result, the holes 30 are each circular. Some applications benefit from the round, uniformly sized holes thus produced. Other applications do not.

[0029] For example, a filtering application requires a tapered round hole as shown in FIG. 5B. To meet this need, the system of the present invention includes a combination of a wobble head 44 (FIG. 3A) and a double-clad delivery fiber 60 of FIG. 6A and FIG. 6C, which allows the output system beam to have at least two or more different modes. Tests have shown that such a combination allows the creation of the tapered hole of FIG. 5B. AMB laser systems, such as those manufactured by IPG Photonics Corporation, are configured to switch between annular and donut-shaped beam modes.

[0030] An exemplary AMB laser is disclosed in International Publication No. 2020 / 117816 (WO '816), commonly owned by the same applicant and incorporated herein by reference in its entirety, and is generally illustrated in Figures 6A-6C. The disclosed AMB laser includes a power source configured with a single or multiple central lasers 52 (Figure 6A) and multiple peripheral lasers 54. The output fibers 56 and 58 of the central and peripheral lasers are combined in a coupler 62 (Figure 6B) that is fused to a double-clad delivery fiber 60 of Figure 6C. The double-clad delivery fiber may have a uniformly sized cross-section, but more often it has a double-bottleneck cross-section, including fiber ends each having a respective diameter smaller than the diameter of the central fiber region extending between the fiber ends. The delivery fiber 60 thus has two waveguiding double-bottleneck cores 66 and 64, respectively. The central core 66 outputs an annular beam received from the central output fiber 56 of the coupler 62 and generated by the laser or lasers 52 located at the center of FIG. 6A. The outer core 64 receives light generated by the peripheral lasers 54 via the output fibers 58 of the respective peripheral couplers. When the peripheral lasers 54 are operated, the output beam has a doughnut shape, while when only the central laser or lasers 52 are operated, the output beam is annular. Obviously, another mode of operation includes the simultaneous operation of all lasers 52 and 54. Different numbers of lasers and respective powers of the central laser 52 and the peripheral lasers 54, respectively, and different power ratios of the respective annular beams and doughnut beams are easily accommodated.

[0031] To create a tapered hole using the AMB laser, the displacement of the galvo mirror unit 44 is first preprogrammed to follow a predetermined displacement trajectory corresponding to a selected hole shape. To facilitate the formation of the selected hole shape, the laser is controlled to output light that is propagated through the core, metal cladding, or core and metal cladding of the delivery fiber 60 of FIG. 6C to the workpiece. For example, by adjusting the power of the central laser 52 while gradually decreasing the power of the peripheral lasers 54, the workpiece can be trepanned to form the tapered annular wall 50 that defines the tapered hole 30 of FIG. 5B as well as to control the taper angle. Alternatively, the peripheral lasers 54 can be completely de-energized after the initial large diameter portion of the tapered hole 30 on the illuminated surface of the workpiece has been drilled. The remaining portion of the tapered hole 30 is completed by controlling the power of the central laser 52. Of course, the trepanning system of the present invention configured with an AMB laser can create a completely cylindrical hole if desired.

[0032] In fact, the system 10 of the present invention provided with the AMB structure allows for a multitude of hole shapes to be obtained, including but not limited to those shown in Figures 7A-7J. Virtually any desired hole shape can be trepanned by the laser drilling system 10 of the present invention, which requires programming the operation of the galvo mirror system 34 of Figure 3A and controlling the power of the central laser and the peripheral lasers of Figure 6A. Of course, the pulse frequency and other pulse parameters should be carefully selected to meet industrial product demands. As shown in the figures, the hole shape can be annular, and can include circular, oval, and oblong holes, as shown in Figures 7A, 7B, and 7C, respectively. The hole shape can be polygonal, and can include octagonal, hexagonal, rectangular, square, and other polygonal hole shapes, as shown in Figures 7D, 7G, and 7J, respectively. Irregular hole shapes are also obtainable, as illustrated by the Marietta, Grecian, and cloverleaf hole shapes shown in Figures 7F, 7H, and 7I, respectively. Other hole shapes, such as elliptical holes, are also easily realized by the inventive system provided with the AMB structure. The drilled holes can be arranged in various patterns based on the preprogrammed relative displacement between the wobble head 44 and the stage 38 of Figure 3A. For example, Figures 7A and 7B show a straight round hole pattern and a staggered round hole pattern, respectively.

[0033] As those skilled in the art will appreciate, the structures discussed above are exemplary, and alternative optical structures that operate to adjust the beam mode may be successfully used within the scope of the present invention.

[0034] In this method, the throughput of the process machine is in line with market demands, up to 10 times higher than the throughput of the standard process without compensation shown in Figures 2A-2B and 4B. The overall investment cost of the system 10 of the present invention is in line with market demands, with laser power levels not exceeding a few kilowatts.

[0035] The aspects disclosed herein according to the present invention are not limited in their application to the details of construction and the arrangement of components as described in the following description or illustrated in the accompanying drawings. These aspects are capable of other embodiments and of being practiced or carried out in various ways. Examples of specific implementations are provided herein for illustrative purposes only and are not intended to be limiting. In particular, operations, components, elements, and features discussed in connection with any one or more embodiments are not intended to be excluded from a similar role in any other embodiment.

[0036] Additionally, the phraseology and terminology used herein are for descriptive purposes and should not be considered limiting. Reference to the singular or plural is not intended to limit the presently disclosed systems or methods, their components, operations, or elements. Furthermore, in the event of inconsistent terminology usage between this document and any document incorporated herein by reference, the terminology usage in the incorporated reference is supplementary to the terminology usage in this document, and in the event of irreconcilable discrepancies, the terminology usage in this document will control.

[0037] Although some aspects of at least one example have been thus described, those skilled in the art will readily appreciate that various changes, modifications, and improvements will readily occur to those skilled in the art. For example, the examples disclosed herein may be applicable in other contexts. Such changes, modifications, and improvements are part of this disclosure. Accordingly, the foregoing description and drawings are merely examples. [Explanation of symbols]

[0038] 10 Laser Drilling System 12 Laser light source, high power laser 14 Laser head, processing laser head 16 Processor, Wobble Head Controller 18 Interface, interface board 20 Laser cube, housing 22 Central Processing Unit, CPU 24 Beam Guiding Lens 25 Single pulse, laser beam, system output beam 25a position 25b, 25c intermediate position 25d Position corresponding to the end of the pulse duration 26 Workpieces 28 Hole Drilling Location 30 positions / holes 34 Multi-axis galvo mirror system, galvanometer mirror 38 Workpiece support stage, XYZ stage 44 Wobble Laser Head 50 Circular Wall 52 Central Laser 54 Ambient Laser 56 (of the central laser) output fiber, central output fiber 58 (Output fiber of ambient laser), (Output fiber of ambient coupler) 60 Double-clad delivery fiber 62 Combiner 64 Waveguide double bottleneck core, outer core 66 Waveguide double bottleneck core, central core A-axis D (Laser head) displacement direction, arrow Pp Maximum output Δx distance θ Rotation angle ω angular velocity

Claims

1. 1. A laser drilling system for trepanning a plurality of holes in a workpiece, comprising: a laser source that outputs a pulsed laser beam controllably incident on a plurality of locations on a surface of the workpiece corresponding to each hole to be drilled, each pulse having a predetermined maximum power and pulse duration for drilling the hole; the laser head comprising a galvo mirror unit disposed between the laser source and the workpiece, the galvo mirror unit being fixed to the laser head and configured to guide the pulsed beam such that the pulsed beam forms a beam spot at each position during the pulse duration; a stage supporting the workpiece to provide continuous displacement between the workpiece and the laser head as the galvo mirror unit controllably pivots between a first position and a second position at each position during the pulse duration such that an angle of incidence of the beam on the surface of the workpiece is controllably changed to drill the hole having a desired hole shape; A laser drilling system comprising:

2. 2. The laser drilling system of claim 1, wherein the laser head, the stage, and the galvo mirror unit are controlled such that the beam spot and the position are in a fixed spatial relationship during the pulse duration of the laser beam during continuous relative displacement between the stage and the laser head.

3. 3. The laser drilling system of claim 2, wherein the laser source comprises a delivery fiber having a uniform single core that guides and outputs the laser beam to drill a plurality of round, uniformly sized holes in the workpiece, each hole being defined by a cylindrical perimeter.

4. The laser light source is at least one central laser outputting a first beam and a plurality of surrounding lasers surrounding the central laser outputting respective second beams; a double-clad delivery fiber having a central core for guiding the first beam and outputting an annular beam incident on the surface of the workpiece, and an outer core for receiving the second beam and outputting a donut-shaped beam spot incident on the surface, the central laser and the peripheral lasers being controllably operable to output the laser beam comprising only an annular beam or only a donut-shaped beam, or both annular and donut-shaped beams; The laser drilling system of claim 2 , comprising:

5. The laser drilling system of claim 4 , wherein the laser beam trepans a plurality of round holes in the workpiece.

6. 6. The laser drilling system of claim 5, wherein a ratio between the power of the central laser and the power of the peripheral lasers is controllably adjusted to have peripheral walls each defining the round hole tapered at a desired taper angle.

7. 5. The laser drilling system of claim 4, wherein the double-clad delivery fiber has a uniformly sized or double-bottlenecked cross-section along the fiber axis, the bottleneck cross-section flanking a central fiber region and having spaced-apart fiber ends, each having a respective diameter smaller than a diameter of the central fiber region.

8. 2. The laser drilling system of claim 1, wherein the laser head is continuously displaceable while the stage is stationary, thereby preventing relative displacement between the workpiece and the beam spot formed thereon as the galvo mirror unit pivots between the first position and the second position.

9. 2. The laser drilling system of claim 1, wherein the stage is actuated to continuously displace the workpiece while the laser head remains stationary, thereby preventing relative displacement between the workpiece and the beam spot formed thereon as the galvo mirror unit pivots between the first position and the second position.

10. 2. The laser drilling system of claim 1, wherein both the laser head and the stage are actuated to provide continuous displacement between the laser head and the workpiece, while the beam spot and the workpiece are displaceably fixed relative to one another at each position as the galvo mirror unit pivots between the first position and the second position.

11. 10. The laser drilling system of claim 1, wherein the galvo mirror unit is preprogrammed to effect drilling of a plurality of holes, each of the holes being defined by a peripheral wall, each of the peripheral walls having a regular or irregular cross-section.

12. The laser drilling system of claim 11 , wherein the regular cross-section comprises a circular cross-section or a polygonal cross-section.

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