Systems and methods for laser-welding tubular components using a single, fixed optical reflector with multiple reflecting surfaces

Abstract

Device and method for laser welding around a circumference of a workpiece. A fixed, non-movable unitary optical reflector is provided, which has a pair of optical reflecting surface portions on a first side surface and a second side surface, respectively, arranged at an obtuse angle relative to each other. A workpiece is positioned and fixed in an assembly that includes the unitary optical reflector. During setup, the vertical distance is adjusted between the unitary optical reflector and the workpiece along an axis that is transverse to a longitudinal axis of the workpiece without any adjustment of the reflecting surfaces, which remain fixed during setup. The first and second side surfaces define a curve that is transverse to the longitudinal axis. Once setup has been completed, a laser beam is directed so that it moves along the optical reflector to thereby produce a 360 degree circumferential weld around the workpiece.

Claims

1. A laser welding system for welding around a circumference of a workpiece, the system comprising: a laser beam source configured to direct a laser beam; an assembly including a unitary optical reflector having at least two optical reflecting surface portions on a first side surface and a second side surface, respectively, of the optical reflector, the first and second side surfaces of the optical reflector being arranged at a fixed obtuse angle relative to each other, the workpiece being moveable relative to the optical reflector, which is fixed relative to workpiece, along an axis that is transverse to a longitudinal axis of the workpiece to adjust a vertical distance between the optical reflector and the workpiece, the first and second side surfaces defining a curve that is transverse to the longitudinal axis; and a scan head configured to move relative to the workpiece to move the laser beam along the optical reflector to thereby produce a 360 degree circumferential weld around the workpiece.

2. The system of claim 1, wherein the optical reflector has an approximately V- or U-shape such that the first and second side surfaces are flat and converge to a curved surface.

3. The system of claim 2, wherein the continuous reflecting surface extends continuously from an end portion of the first side surface to a corresponding end portion of the second side surface.

4. The system of claim 1, wherein the at least two optical reflecting surface portions are part of a single, continuous reflecting surface that extends from an end of the first side surface to an end of the second side surface.

5. The system of claim 1, wherein the unitary optical reflector is a single part.

6. The system of claim 1, wherein the scan head is coupled to a mount and a pair of orthogonal gantries.

7. The system of claim 1, wherein the optical reflector is non-movable and fixed relative to the scan head.

8. A laser welding method for welding around a circumference of a workpiece, the method comprising the steps of: providing a fixed, non-movable unitary optical reflector having at least two optical reflecting surface portions on a first side surface and a second side surface, respectively, arranged at an obtuse angle relative to each other; positioning and fixing a workpiece in an assembly that includes the unitary optical reflector; responsive to the fixing the workpiece, adjusting the vertical distance between the unitary optical reflector and the workpiece by moving the workpiece relative to the fixed, non-movable optical reflector along an axis that is transverse to a longitudinal axis of the workpiece, the first and second side surfaces defining a curve that is transverse to the longitudinal axis; and responsive to the adjusting, directing a laser beam so that it moves along the optical reflector to thereby produce a 360 degree circumferential weld around the workpiece.

9. The method of claim 8, wherein the optical reflector has an approximately V- or U-shape such that the first and second side surfaces are flat and converge to a curved surface.

10. The method of claim 9, wherein the continuous reflecting surface extends continuously from an end portion of the first side surface to a corresponding end portion of the second side surface.

11. The method of claim 8, wherein the at least two optical reflecting surface portions are part of a single, continuous reflecting surface that extends from an end of the first side surface to an end of the second side surface.

12. The method of claim 8, wherein the unitary optical reflector is a single part.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood from the following description of preferred embodiments together with reference to the accompanying drawings, in which:

(2) 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;

(3) FIG. 2 is a perspective view of the workpiece assembly shown in FIG. 1;

(4) FIG. 3 is an example photograph of a laser weld achieved using the optical reflector according to the present disclosure;

(5) FIG. 4 is a further example photograph of a laser weld achieved using the optical reflector according to the present disclosure; and

(6) 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.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

(7) A laser assembly 200 shown in FIG. 1 includes a conventional laser source 210, which generates a laser beam 120 of radiation. A mount 212a is coupled to orthogonal gantries 214a and 214b. 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.

(8) Based on the experimentation it has been established that using a single, unitary V- or U-shaped reflector 260 having two flat side surfaces 262a, 262b fixed at approximately 110-135 degrees (e.g., plus or minus 15%) to each other and a continuous reflecting surface from end-to-end 264a, 264b, allows the setup for a tubular workpiece 110 placed equidistant to the sides 262a, 262b 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.

(9) The optical reflecting surface(s) 262a, 262b 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 262a, 262b 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 262a, 262b 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 262a, 262b 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.

(10) The first 262a and second 262b side surfaces of the fixed optical reflector 260 are arranged at a fixed obtuse angle relative to each other. By fixed it is meant that the angle 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 between the reflecting surfaces 262a, 262b 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.

(11) The first and second side surfaces 262a, 262b 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 262a, 262b. 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.

(12) 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 262a, 262b 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 cannot be adjusted during setup of the assembly 250. The point is that there are at least two reflecting surfaces 262a, 262b 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 262a, 262b 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.

(13) 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 262a, 262b were angled at an angle of 133 degrees.

(14) 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.