Patent Publication Number: US-2021170525-A1

Title: Systems and methods for laser-welding a workpiece with a laser beam that reaches inaccessible areas of the workpiece using multiple reflecting parts

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation-in-Part of U.S. patent application Ser. No. 16/352,104, filed on Mar. 13, 2019, which claims priority to and the benefit of U.S. Provisional Patent Application No. 62/801,269, titled “Systems and Methods for Laser-Welding Tubular Components Using a Single, Fixed Optical Reflector with Multiple Reflecting Surfaces,” filed Feb. 5, 2019, both of which are hereby incorporated by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     Aspects of the present disclosure relate generally to laser-welding systems and, more particularly, to systems and methods for welding tubular components using a laser beam and a single, fixed optical reflector having multiple optically reflecting surfaces. 
     BACKGROUND 
     Most medication delivery devices incorporate plastic tubing that connects different parts of the device and those through which the medicine is delivered to the patient. A joint between various tubular components, such as tube-to-port, or tube-to-tube type is one of the most common sub-assembly and can be found in most medication delivery devices. 
     A laser-welding process is currently the most advanced assembly technique, and has a number of proven benefits for a high-volume manufacturing. However, utilizing a laser-welding process for joining tubular components between themselves and to other parts presents a technical challenge, as it requires a 360° circumferential weld around the mating surfaces. Because rotating the laser source around the assembly, or spinning the assembly (which may have a container or other components attached to it) under a stationary laser head are not always feasible for a manufacturing process, a number of methods have been proposed to address this challenge. 
     For example, a tubular workpiece can be disposed longitudinally at a center of a concave circular mirror surrounding the workpiece. Then, the laser beam is swiveled or circled around the mirror above the workpiece, directing the laser beam around the entire circumferential outer surface of the workpiece. This conventional technique is not suitable in a manufacturing environment because manipulation of the workpiece through the center of the circular mirror is very difficult and burdensome particularly in a high-production setting. 
     By way of another example, a complex set of optical reflectors are used to redirect the laser beam onto an opposite side of the workpiece. A combination of multiple concave and flat mirrors, such as conical, spherical, and plane mirrors, is used for deflecting the laser beam toward the opposite and lateral sides of the workpiece during welding. However, such intricate and convoluted optical systems are very expensive and difficult to repair during maintenance. 
     Another conventional approach is proposed in US Patent Application Publication No. 20170182592A1, which describes a pair of adjustable optical reflectors positioned under the tubular assembly, whose angles, as well as lateral and vertical positions can be adjusted, so the beam reflected from these reflectors could cover both sides of the bottom part of the assembly, while the upper part of the assembly is being exposed to the direct beam, which scans the assembly in lateral direction. The stated aim of this method is to deliver a “simpler, more space-saving technique.” However, in order for the reflected beam to heat uniformly the whole bottom part of the assembly, and generate an even melting of the material, this method requires a time-consuming adjustment of each of the reflector pairs to find the correct angle and lateral and vertical position of the two reflectors in relation to the assembly. 
     If the angle between the two reflectors, or their lateral or vertical position are not correct, this error would result in uneven heating of different portions of the bottom part (workpiece). For example, a wider angle between the reflectors or a larger distance in the Z-axis (vertical relative to ground) between the two reflectors&#39; base and the position of the assembly would lead to overheating of the very bottom of the workpiece part and under-heating of its sides. A larger lateral distance between the reflectors, a smaller angle, or a shorter Z axis separation, would result in excessive heating of the sides of the bottom part of the assembly, and under-heating of the center of the bottom (the lowest portion), which would cause an inadequate heating and potential leak path at that location. In order to heat both sides of the bottom part of the workpiece in the assembly uniformly, the angle between the Z axis (vertical) and the surface of both reflectors needs to be exactly the same, and while adjusting the angular position of one reflector is easy, measuring the angle between the reflectors in the fixture is very awkward, time-consuming, and challenging. As this adjustment needs to be iterated a number of times to find the correct angle corresponding to a specific position of the assembly, and to ensure that the position of both reflectors is identical. This need for a precise angular alignment of both reflectors relative to one another significantly contributes to the difficulty of the setup. 
     In other words, the approach proposed in US Patent Application Publication No. 20170182592A1 provides too many opportunities for setup error or a prolonged setup time because of the numerous adjustment combinations that have to be made to multiple operating components of the assembly for each workpiece part. 
     Another need exists for an arrangement in which the laser can reach areas of a workpiece that are not in the direct path of the laser. For example, the area of a workpiece directly behind a laser cannot be accessed by the energy unless the workpiece is turned or the laser is moved, which requires careful calibration and movement coordination and a bulky setup that would be difficult to apply to multiple workpiece types and form factors. 
     Therefore, what is needed are systems and methods for more accurately laser-welding tubular components that yields more consistent and higher quality weld results without requiring extensive, error-prone, or time-consuming pre-adjustment or calibration of the assembly prior to welding in a high-production manufacturing setting. 
     SUMMARY OF THE INVENTION 
     Aspects of the present invention reflect improvements to the disclosure set forth in US Patent Application Publication No. 20170182592A1. A key difference is that instead of using a pair of optical reflectors, the present disclosure proposes to use a single, unitary, fixed optical reflector having multiple optically reflecting side surfaces (configured to reflect a laser beam) that are angled at an obtuse angle (greater than 90 degrees and less than 180 degrees) relative to each other. Another key difference is that the only pre-welding setup required for the welding assembly is a Z-axis adjustment (vertical direction) of the workpiece relative to the optical reflector before initiating the laser weld. No adjustment of the respective lateral positions or angles of the reflecting surfaces relative to one another is required relative to the workpiece. Indeed, because the optical reflector of the present disclosure is a fixed, unitary piece, no such adjustment is even possible. Thus, the optical reflector remains fixed at all times, both pre-weld during setup of the equipment, and during welding itself in which laser energy is imparted to the workpiece. Furthermore, the laser source does not need to be rotated around the workpiece during welding, but rather remains at a stationary distance relative to the workpiece both pre-weld during setup and during the weld. These aspects produce a consistently high quality 360-degree circumferential weld with high repeatability and very low variability, and very minimal setup time and effort (only adjustment of the vertical distance between the workpiece and the bottom or center of the optical reflector), in a high-production setting where setup time needs to be minimized, but the weld must be consistent and of high quality from part to part without requiring micro-adjustments to the setup while the same parts are being welded during a manufacturing process. The present disclosure promotes a “set it and forget it” configuration of a laser-welding setup for circumferential welding of tubular parts (workpieces), with only one adjustment needed during setup before welding is initiated for the same parts without requiring any further adjustments for the same part in a high-production setting. Not only is weld quality overall improved and remarkably consistent from part to part, but throughput is significantly increased due to the quick setup time (vertical adjustment of one part of the assembly) and elimination of any adjustments needed once the setup has been completed. 
     A laser welding system for welding around all or most of a circumference of a workpiece is provided. The system includes a laser beam source configured to direct a laser beam; and an assembly including a first angled reflector and an optical reflector assembly, the first angled reflector being arranged at a fixed angle to change a direction of the laser beam so that the laser beam irradiates a front area of the workpiece, the optical reflector assembly having at least two angled mirrors positioned to direct the laser beam passing around the workpiece to reach areas of the workpiece that are not directly in the path of the laser beam. The first angled reflector can be angled relative to the laser beam at 45 degrees such that the laser beam changes direction orthogonally relative to its direction emanating from the laser beam source. The at least two angled mirrors can include a first mirror and a second mirror. The first mirror and the second mirror can be arranged on a curved surface of the optical reflector assembly such that they change a direction of the laser beam by 45 degrees, thereby allowing the laser beam to reach the areas of the workpiece that are not directly in the path of the laser beam. The laser beam source can be fixed, and the workpiece can be fixed relative to the assembly as the laser beam is presented to the workpiece. The workpiece can have a generally cylindrical cross section at an area where a weld is to be created. The laser beam can reach an entire circumference of the workpiece in response to its direction being changed by the first angled reflector and the optical reflector assembly. The optical reflector assembly can include a third mirror positioned to change a direction of at least a portion of the laser beam toward an area of the workpiece that is not directly in the path of the laser beam after being reflected by the first angled reflector. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood from the following description of preferred embodiments together with reference to the accompanying drawings, in which: 
         FIG. 1  is an example laser assembly and workpiece assembly with a fixed U-shaped optical reflector with stationary reflecting surfaces fixed at an obtuse angle; 
         FIG. 2  is a perspective view of the workpiece assembly shown in  FIG. 1 ; 
         FIG. 3  is an example photograph of a laser weld achieved using the optical reflector according to the present disclosure; 
         FIG. 4  is a further example photograph of a laser weld achieved using the optical reflector according to the present disclosure; 
         FIG. 5  is a perspective view of an adjustable vertical distance between the workpiece and the bottom or lowest point of the top surface of the optical reflector; and 
         FIG. 6  is a perspective view of an example laser assembly and workpiece assembly with an optical reflector arranged to irradiate a workpiece along directions orthogonal to the laser beam direction, including areas behind the direct path of the laser. 
     
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
     A laser assembly  200  shown in  FIG. 1  includes a conventional laser source  210 , which generates a laser beam  120  of radiation. A mount  212   a  is coupled to orthogonal gantries  214   a  and  214   b.  One or more scanner mirrors within a scan head  212  are controlled by a processor-controlled drive unit  213  to direct a laser beam  120  downwardly onto an assembly  250  that includes a thermoplastic workpiece  110  having a tubular part to be joined by welding. The drive unit  213  is controlled to adjust the positions of the scanner mirrors to move the laser beam  120  in a manner required to illuminate a prescribed weld zone on the top surface of the workpiece  110  fixed within the assembly  110 . 
     Based on the experimentation it has been established that using a single, unitary V- or U-shaped reflector  260  having two flat side surfaces  262   a,    262   b  fixed at approximately 110-135 degrees (e.g., plus or minus 15%) to each other and a continuous reflecting surface from end-to-end  264   a,    264   b,  allows the setup for a tubular workpiece  110  placed equidistant to the sides  262   a,    262   b  of the optical reflector  260  to be greatly simplified compared to conventional approaches, and limits the required setup effort to only the vertical adjustment (Z-axis) of the part position. Moving the workpiece  110  and the optical reflector  260  closer together (decreasing distance D labeled in  FIG. 5 ) allows to direct more laser energy from the laser source  210  to the very bottom of the workpiece part  110 , whereas moving the workpiece  110  and the optical reflector  260  farther apart (along the Z-axis or increasing distance D shown in  FIG. 5 ) increases the illumination of the sides of the lower portion of the workpiece  110 . Once the Z value which provides an even illumination of the bottom portion of the part is found, the workpiece  110  and the optical reflector  260  are locked to that Z-value distance D ( FIG. 5 ), and the setup is complete. Scanning the workpiece  110  with the laser beam  120  in a lateral direction (no rotation, see X and/or Y axis labeled in  FIG. 1 ) by the weld head  212  positioned above the assembly  250 , will illuminate the upper portion of the workpiece  110  by direct exposure to the laser beam  120 , and the bottom portion of the workpiece  110  by the laser beam  120  reflected by the V- or U-shaped reflector  260 , thus allowing a 360° circumferential weld around the tubular workpiece  110 . 
     The optical reflecting surface(s)  262   a,    262   b  of the optical reflector  260  can be a gold-plated mirror, which is configured to reflect laser energy  120  received. The angle of the surfaces  262   a,    262   b  direct the laser energy  120  into surfaces of the workpiece  110  that are not directly accessible to the laser beam  120 , which is fixed above the workpiece  110 . Those of ordinary skill in the welding art will appreciate that the entire surface  262   a,    262   b  does not have to be coated with an optically reflecting material. As a practical matter, it is convenient to plate the entire surface of the optical reflector  260  with gold or other optically reflecting material, but of course only the surface portions of the optical reflector  260  where the laser beam  120  will be directed need to have an optically reflecting material. The other portions do not have to optically reflecting, such as the bottom or lowest portion  270  (best seen in  FIGS. 2 and 5 ) directly below the workpiece  110  where no laser energy will be received. The portion  270  ( FIG. 2 ) directly underneath the workpiece  110  receive the reflected laser energy that bounce off of the optically reflecting surfaces  262   a,    262   b  of the optical reflector  260 . All this is to say that those skilled in the art will appreciate that only those surface portions where laser energy  120  will be directed need to be optically reflecting on the optical reflector  260 . The key point here is that the optical reflector  260  is non-moving and stationary at all times, including during setup of the assembly when the vertical distance, D, along the Z-axis between the underside of the workpiece  110  and the bottom or lowest point  270  of the optical reflector  260  directly below the underside of the workpiece  110  is being optimized. 
     The first  262   a  and second  262   b  side surfaces of the fixed optical reflector  260  are arranged at a fixed obtuse angle α relative to each other. By fixed it is meant that the angle α is unchanged even during setup before the laser weld is initiated. The assembly  250  has a height adjustment mechanism (not shown) that is configured to adjust a vertical distance D between the lowest point  270  of the optical reflector  260  and the underside of the workpiece  110  along a Z-axis that is transverse to a longitudinal axis (e.g., Y-axis) of the workpiece  110 . Preferably, the workpiece  110  is the adjustable part of the assembly  250 , such that the workpiece  110  is moved up or down relative to the optical reflector  260  to change the vertical distance D (shown in  FIG. 5 ). Alternately, the workpiece  110  can be fixed, and the optical reflector  260  is adjusted up or down to change the vertical distance D; however, at all times the angle α between the reflecting surfaces  262   a,    262   b  is constant and fixed. In yet another alternative, both the workpiece  110  and the optical reflector  260  can be adjusted along the Z-axis to change the distance D, for example, in an assembly  250  that has been retrofitted or modified to be configured according to the present disclosure. 
     The first and second side surfaces  262   a,    262   b  define a curve that is transverse to the longitudinal axis (e.g., Y-axis), and this curve forms the V- or U-shape of the optical reflector  260 . Note that this portion does not have to be strictly curved, because no laser energy will be directed to this portion, so its shape plays no role and therefore has no impact on optical reflection. Rather, it can be relatively flat or notched, depending on the design parameters and the angle of the reflecting surfaces  262   a,    262   b.  It also does not have to be coated with an optically reflecting material, but for ease of manufacturability, coating the entire surface of the optical reflector  260  is desirable from that standpoint. 
     While in one aspect the reflecting surface on the optical reflector  260  can be continuous, those skilled in the art will appreciate that the portion of the optical reflector  260  that sits directly underneath or below (relative to the incoming laser beam  120 ) the workpiece  110  does not directly receive the laser beam  120 , and thus it is not necessary to render that part of the surface optically reflecting. While it is easier to manufacture a continuous surface, the present disclosure is not limited to a continuous surface. The flat side surfaces  262   a,    262   b  of the optical reflector  260  can receive a reflective optical coating, whereas the portion  270  of the optical reflector  260  that sits directly beneath the workpiece  110  can lack a reflective optical coating. Moreover, while a single, unitary optical reflector  260  is also described, in other aspects, the optical reflector  260  can be composed of multiple parts, but all such parts being fixed and stationary to one another so that their angle α cannot be adjusted during setup of the assembly  250 . The point is that there are at least two reflecting surfaces  262   a,    262   b  that are fixed and stationary during the setup of the assembly  250 , such that only a vertical adjustment of the distance D between the workpiece  110  and those reflecting surfaces  262   a,    262   b  is necessary during setup. This differs from conventional approaches that allowed too much freedom of adjustment of the lateral distance and angular displacement of the reflectors and distance between workpiece and the reflectors, but this freedom leads to longer setup times and more complex setup parameters, iterative adjustments of the setup parameters, and other problems indicated above. 
       FIGS. 3-4  illustrate photographs of cross-sections of thermoplastic sample workpieces joined by the welding apparatus and method disclosed herein, showing the high quality and consistently uniform weld circumferentially around the joined interfaces. The reflecting surfaces  262   a,    262   b  were angled at an angle α of 133 degrees. 
       FIG. 6  illustrates another example workpiece assembly  600  with a fixed laser source omitted for ease of illustration. This assembly  600  uses an extra conversion: a fixed laser source (not shown) is above shining vertically down (along the Z-axis direction  620 ), then the beam is reflected horizontally (X-Y plane or X-direction) on a cylindrical part or workpiece  610 . The front  612  of the workpiece part  610  is exposed to the laser beam  622  directly and the back  614  of the workpiece  610  is illuminated due to reflection from a semi-circular mirror  606  of an optical reflector  604 . Put another way, the fixed laser source directs a laser beam  620  in a vertical (Z-axis) direction toward a first angled reflector  602 , which in this example, changes the direction of the laser beam by 90 degrees so that it runs in a direction orthogonal to the original direction of the laser beam  620  (along the X-axis or X-Y plane). 
     The main advantage of the extra conversion is the ability to redirect the laser beam to be perpendicular to the weld while the laser source remains (preferably in a fixed position) above the workpiece  610 . This gives the ability to reach an otherwise inaccessible weld surface when the workpiece  610  is constrained to a vertical orientation. 
     In the illustrated assembly  600 , the mirror design is a basic example having a first mirror  608   a  angled at 45 degrees to project the beam onto the next mirror  608   b  (and optionally additional mirrors, not shown), which is also angled at 45 degrees to reach the back side  614  of the workpiece  610 , which in this example has a generally cylindrical shape. Those skilled in the art will appreciate that the mirror angles do not necessarily have to be constrained to 45 degrees; rather the angles can be tailored specifically to the needs to the application to deliver the beam precisely to an otherwise inaccessible weld surface, without requiring turning, moving, or rotation of the workpiece  610 . The workpiece  610  can remain fixed relative to the workpiece assembly  600 , and the laser source can also remain fixed. There can also be additional mirrors besides  608   a,    608   b  to gain the ability to reach the weld area to accommodate space or clearance constraints. 
     This concept would also work for workpiece parts having a shape other than cylindrical. Odd-shaped parts can also be welded as long as the sides are similar in length and space allows for the mirror design. Likewise, the angle of the first angled reflector  602 , which is shown as 45 degrees, can also be modified to direct the laser energy in a direction to directly reach a weld surface of the workpiece part  610 . The angle of the first angled reflector  602  will determine where the laser energy directly reaches the front part  612  of the workpiece  610 , whereas the mirrors  608   a,    608   b  and their respective angles will determine where the laser energy reaches the inaccessible areas  614  (i.e., inaccessible to direct irradiation by the laser beam) of the workpiece  610 . Odd-shaped workpieces are particularly well-suited for this application, and any workpiece where the weld needs to be reach all or substantially all of a circumferential area of a part. 
     Although the inventions and other aspects will be described in connection with certain preferred embodiments or examples, it will be understood that the present disclosure is not limited to those particular embodiments or examples. On the contrary, the present disclosure is intended to cover all alternatives, modifications, and equivalent arrangements as may be included within the spirit and scope of the invention as defined by the appended claims.