Method and Apparatus for Joining Workpieces at a Lap Joint

Abstract

A method and an apparatus for joining two workpieces by means of a processing beam by forming a weld seam along a lap joint, wherein a gap formed at the lap joint between the two workpieces is filled during welding. The processing beam performs a spatial oscillatory movement parallel and/or perpendicular to the joint during welding. The oscillation parameters of said oscillation, the feed rate, the power of the processing beam and the angle of incidence of the processing beam onto the surfaces of the workpieces are adjusted dynamically during the welding process such that the upper sheet is fused in line with demand and the melt flows from the upper sheet down to the lower sheet thus closing the gap. The gap height is measured permanently during welding and the process parameters are adjusted such that a reliable closing of the gap is made possible.

Claims

1. A method for joining workpieces by means of a processing beam (2) of a joining apparatus, comprising processing optics with actively driven deflection units for guiding the processing beam (2) and with at least partially movable optical elements for focusing the processing beam (2) onto a surface of a first (6) and/or a second (7) of said workpieces to be joined, said method comprising a joining of the first (6) to the second (7) workpiece at a lap joint by generating a spatially confined weld pool (17) using said processing beam (2), wherein the processing beam (2) performs during joining a spatially oscillating movement defined by oscillation parameter, one or more height positions with respect to the plumb line are captured for both, the first (6) and the second (7) workpiece, each at a top surface section of said workpieces (6, 7) adjacent to a processing position at the lap joint to be processed by the processing beam (2), said height positions are evaluated with regard to determining a height difference between the top surface sections of the first (6) and the second (7) workpiece adjacent to the processing position at the lap joint, and an energy input of the processing beam (2) into the top surface section of the workpiece, which is located at a higher position at the processing position, is increased with an increasing height difference at the lap joint and is decreased with a decreasing height difference said method for joining being characterized in that a determination of a position of the lap joint, of the first (6) and of the second (7) workpiece is carried out; setting of a plurality of process parameter, including the oscillation parameter of the spatially oscillating movement as well as a defocusing of the processing beam (2), occurs based on a programmed process model, which at least depends on a material composition of the workpieces (6, 7) to be joined, the thicknesses of the workpieces (6, 7) as well as a continuously during joining determined height of the gap (16) and positioning of the workpieces (6, 7) in space and relative to each other, wherein at least one oscillation parameter of the oscillating movement of the processing beam (2) is set in such a way that the oscillations of the processing beam (2) couple into melt waves formed on the surface of the weld pool (17) so that molten material flows from the weld pool (17) at the processing position into a gap (16) formed between the two workpieces (6, 7) at the lap joint.

2. The method as claimed in claim 1, characterized in that said height positions are measured using a light-slit method, wherein at least one measuring line projected onto the component is recorded by means of a camera and the distortion of the measuring line with respect to a determination of the height positions of the top surface sections of the first (6) and the second (7) workpiece adjacent to the processing position is evaluated.

3. The method as claimed in claim 1, characterized in that said height positions are measured based on a runtime measurement of laser light, wherein a running time of said laser light from a laser light emitter to the respective measuring position is detected for a plurality of measuring positions on the top surface sections of the first (6) and the second (7) workpiece, and the orientation of the top sections in space and the height difference between the top surface sections of the first (6) and the second (7) workpiece adjacent to the processing position are determined by evaluating runtime differences.

4. The method as claimed in claim 1, characterized in that said process parameter comprise oscillation parameter of the oscillating movement of the processing beam (2), a feed rate (Vs), a power of the processing beam (2), oscillations of the power of the processing beam (2), an angle of the beam axis of the processing beam (2) with respect to the plumb line (z), a geometric shape and a size of a focal spot (8) of the processing beam (2) on the workpiece surfaces.

5. The method as claimed in claim 1, characterized in that the oscillation parameter to be adjusted comprise an amplitude of the spatial oscillations of the processing beam (2) and/or a frequency of oscillation and/or a shape of the oscillations.

6. The method as claimed in claim 1, characterized in that quality values, which characterize the quality of the weld seam formed, are detected in the feed direction (x) immediately behind the processing beam (2) by means of an optically operating seam quality detection sensor system (18) and are evaluated with regard to a deteriorating quality, wherein a deteriorating quality is compensated by adjusting individual or several process parameter.

7. A joining apparatus for joining a first workpiece (6) to a second (7) workpiece at a lap joint by means of a processing beam (2) according to the method as claimed in claim 1, comprising a processing beam generation unit (1), a remote processing optics with scanning devices (4a, 4b ) for guiding the processing beam (2) and with at least partially movable optical elements (3, 5) for focusing the processing beam (2) onto the surface of the first (6) and/or the second (7) of the workpieces to be joined, sensor systems to determine a respective position of the lap joint, of the first (6) and of the second (7) workpiece, and an evaluation and control unit (15), which is connected to the sensor systems, the processing beam generation unit (1) and the remote processing optics, wherein said evaluation and control unit (15) is configured in such a way that the remote processing optics and the processing beam generation unit (1) are controllable on the basis of a programmed process model stored in the evaluation and control unit (15), wherein said programmed process model at least depends on a material composition of the workpieces (6, 7) to be joined and the thicknesses of the workpieces (6, 7) to be entered before starting the process, as well as a height of the gap (16) at the lap joint between the first (6) and the second (7) workpiece and a positioning of the workpieces (6, 7) in space and relative to each other, said height of the gap (16) and positioning of the workpieces (6, 7) being determined by the use of measurement values gathered by the sensor systems.

8. A joining apparatus as claimed in claim 7, characterized in that a database containing a plurality of default values of process parameter is stored in the evaluation and control unit (15), wherein each process parameter is assigned an input parameter or a combination of said input parameter, said input parameter comprising a material composition of the workpieces (6, 7) to be joined, a height of the gap (16), a thickness of the workpieces (6, 7) and a positioning of the workpieces (6, 7) relative to each other and/or in space defined by six degrees of freedom.

9. A joining apparatus as claimed in claim 7, characterized in that said joining apparatus comprises angle sensors for determination of a tilt of the top surface sides of the first (6) and/or the second (7) workpiece with respect to a processing head of the joining apparatus, said processing head comprising the remote processing optics.

10. A joining apparatus as claimed in claim 7, characterized in that said joining apparatus comprises a seam quality detection sensor system (18) connected to the evaluation and control unit (15), said seam quality detection sensor system (18) being capable of detecting in real time the weld seam behind the weld pool (17) with respect to the feed direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0054] An exemplary embodiment of the invention will be described in more detail below on the basis of the drawings. Shown therein are:

[0055] FIG. 1 a schematic representation of a joining apparatus in a cross-sectional view with the lap joint in longitudinal-sectional view;

[0056] FIG. 2 a schematic representation of the lap joint in cross-sectional view with the processing beam oscillating perpendicular to the lap joint; and

[0057] FIG. 3 an intensity distribution of the processing beam at the position of the focal spot oscillating perpendicular to the lap joint.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058] In FIG. 1 a laser beam welding apparatus with remote laser processing optics is represented; thus, the processing beam is a laser beam. The laser beam generation unit 1 generates the laser beam 2, which collimates from the collimation unit 3, which can be moved along the beam axis, onto the deflection units 4a, which oscillate about their respective cross axes, and the deflection units 4b, which oscillate about their longitudinal axis. Eventually, the focusing unit 5 generates the laser focal spot 8 on the surface of the workpieces 6 (upper sheet) and 7 (lower sheet), said focal spot 8 being moved along the lap joint at a feed rate V.sub.s.

[0059] A projector 10 projects on the surface of the workpieces by means of the measurement light 11 a light line, which is running perpendicular across the lap joint. Sensors 13 detect the light line, wherein a sensor focusing 12 unit may be connected ahead of the sensor 13. An evaluation and control unit 15 connected to the sensors calculates from their collected data an exact position of the joint, a position of the workpieces 6 and 7 with respect to each other (and which of the two workpieces is the upper sheet 6) as well as a height of a gap 16 between the two workpieces 6 and 7 at the joint.

[0060] A seam quality detection sensor system 18 generates a snapshot of the weld seam behind the laser focal spot 8 with respect to the direction of the feed motion (x). These snapshots are processed by the evaluation and control unit 15, wherein upon first signs of a deteriorating quality of the weld seam the process parameter are adjusted according to a process model stored in the evaluation and control unit 15 specifically to the detected signs.

[0061] The deflection units 4a, represented schematically in FIG. 2, of the remote laser processing optics allow—driven by the evaluation and control unit 15—for an oscillatory movement of the laser beam 12 across the lap joint in a way that the upper sheet 6, which consists from the material aluminum, is fused, so as to form the weld pool 17. Additionally, the oscillation parameter are adjusted in such a way that at least a part of the pasty weld pool 17 is flowing down onto the lower sheet 7 and thus closing the gap 16.

[0062] An intensity distribution of the laser focal spot 8 created on the surfaces of the workpieces is represented in FIG. 3. The oscillations of the laser beam 2 (and accordingly the laser focal spot 8) are set such that the maximum I.sub.2 of the intensity I, which is introduced into the surfaces of the workpieces by the laser beam 2 in a direction perpendicular to the joint, is located on the upper sheet 6. A secondary local maximum I.sub.1 of the intensity I is located on the lower sheet 7.

LIST OF REFERENCE NUMERALS

[0063] 1 Processing laser [0064] 2 Laser beam [0065] 3 Collimation unit [0066] 4a Deflection unit, oscillating about its cross axis [0067] 4b Deflection unit, oscillating about its longitudinal axis [0068] 5 Focusing unit [0069] 6 Workpiece (upper sheet) [0070] 7 Workpiece (lower sheet) [0071] 8 Laser focal spot [0072] 10 Projector [0073] 11 Measurement light [0074] 12 Sensor-focusing unit [0075] 13 Sensor [0076] 15 Evaluation and control unit [0077] 16 Gap [0078] 17 Weld pool [0079] 18 Seam quality detection sensor system [0080] vs Feed rate [0081] I Intensity [0082] x x-direction/direction of the feed motion [0083] y y-direction/direction perpendicular to the feed motion [0084] z z-direction/plumb line