Process and apparatus for spot welding with a laser beam

• US 20040226923A1
• Filed: 05/07/2004
• Published: 11/18/2004
• Est. Priority Date: 05/13/2003
• Status: Active Grant

• Current Assignee: Coherent Switzerland AG (Coherent Corp.)
• Original Assignee: Lasag AG (Coherent Corp.)
• Inventors: Sidler, Thomas, Wissing, Christian, Amorosi, Simone, Schwob, Hans Peter, Gianotti, Ronald
• Granted Patent: US 8,304,687 B2
• Time in Patent Office: Days
• US Class Current: 219/121.64
• CPC Class Codes: B23K 26/032 using optical means
• CPC Class Codes: B23K 26/034 Observing the temperature of the workpiece
• CPC Class Codes: B23K 26/22 Spot welding
• CPC Class Codes: B23K 26/60 Preliminary treatment

Abstract

The invention relates to a laser spot welding process for executing a spot weld in two successive steps, namely a first step of preparing the surface state of the material to be welded and a second step of welding as such. The luminous energy (BR) reflected by the weld region of the material is measured in real time during the first step and then processed by a controller circuit (37) connected to a control circuit (30) of the laser source (31). In this way, the characteristics (LM) of the laser beam are adjusted in real time as a function of the measurements effected to allow effective control of the quality of the weld obtained, and in particular of its dimensions.

The invention also relates to a welding device for implementing this process.

Claims

1. A spot welding process using a laser beam in which the welding of at least one spot comprises at least a first step of preparation of the material to be welded followed by a second step of welding during which said laser beam is maintained at least partly operational, said first step being adapted to modify the surface state at least in a weld region of said material to be welded to obtain predefined conditions suited to the implementation of said second step, said first step comprising the following operations:

a) directing a laser beam onto said weld region of the material to be welded,

b) measuring the value of at least one physical parameter that is characteristic of the surface state of the material to be welded in said weld region to monitor the evolution thereof, and

c) adjusting the characteristics of the laser beam as a function of the evolution of the value of said physical parameter determined in operation b), in order to obtain said predefined conditions before implementing said second step.

2. The welding process according to claim 1, wherein, during said first step, the operation b) is preceded by a calibration phase during which an initial value of said physical parameter is determined, the operation b) further comprising a step of processing each value of said measured physical parameter in relation to said initial value in particular, in order to define a parameter whose evolution during said first step is related to the evolution of the value of said physical parameter, the characteristics of the laser beam being adjusted during the operation c) as a function of the evolution of said parameter.

3. The welding process according to claim 2, wherein said predefined conditions comprise the dimension, at the level of the surface of said material to be welded in the weld region, of a region of said material brought to a molten state at the end of said first step, said dimension being a function of the value of said calculated parameter at the end of said first step.

4. The welding process according to claim 3, wherein, after said calibration phase, the power emitted by the laser beam onto said weld region is increased, preferably in a substantially linear manner as a function of time.

5. The welding process according to claim 3, wherein said physical parameter whose value is measured evolves during said first step in a manner that is related to the evolution of the level of light reflected by the material to be welded.

6. The welding process according to claim 5, wherein said physical parameter is measured in a direction substantially normal to the surface of said weld region.

7. The welding process according to claim 5, wherein said characteristics of the laser beam adjusted during the operation c) of claim 1 comprise its power.

8. The welding process according to claim 3, wherein the power of the laser beam is reduced by at least 10% in response to obtaining a predefined value of the defined parameter in said processing step, said predefined value corresponding to the end of said first step.

9. The welding process according to claim 3, wherein the value of an additional physical parameter, the evolution of which is related to the evolution of the temperature of said weld region, is also measured during the operation b) and taken into account to improve the setting of the characteristics of the laser beam in the operation c) of claim 1.

10. The welding process according to claim 3, wherein the operations a) to c) of claim 1 are effected continuously throughout said first step.

11. The welding process according to claim 1 applied to welding metal or metal alloy parts.

12. The welding process according to claim 11, said metal and said metal alloy being respectively chosen in the groups respectively comprising copper, silver, gold, aluminium and cuproberyllium, brass, bronze.

13. A spot welding device employing a laser beam and comprising a source controlled by a control circuit and capable of emitting a laser beam in the direction of at least one weld region of a material to be welded, the device further comprising control means for executing a spot weld in two successive steps, including a first or preparation step adapted to modify the surface state of said material to be welded in said weld region to obtain predefined conditions suited to the implementation of a second step comprising welding as such, said control means comprising means for measuring at least the value of a physical parameter characteristic of the surface state of the material to be welded in said weld region and producing a first signal representative of said measured value sent to a control circuit able to monitor the evolution of the value of said physical parameter, the control circuit being also adapted to produce a second signal that is a function of the evolution of the value of said physical parameter and is sent to the control circuit of the laser source in order to adjust the characteristics of the laser beam emitted during said first step to obtain said predefined conditions.

14. The welding device according to claim 13, wherein said regulation means are further adapted to execute a preliminary calibration phase during which the characteristics of the laser beam are substantially constant to enable the determination of an initial value of said physical parameter, said control circuit being adapted to take account of said initial value in order to process measured values of said physical parameter and to define a parameter whose evolution is related to the evolution of the value of said physical parameter, said second signal produced by the control circuit and sent to the control circuit of the laser source being a function of the value of said parameter.

15. The device according to claim 14, wherein said regulation means comprise a first optical sensor for measuring the value of a physical parameter whose evolution is related to the evolution of the level of light reflected by the material to be welded.

16. The device according to claim 15, wherein said regulation means further comprise a second optical sensor for measuring the power of the laser beam emitted on the optical path thereof between the laser source and the weld region.

17. The device according to claim 15, wherein said regulation means comprise an infrared radiation sensor for measuring the evolution of the temperature in said weld region.

18. The device according to claim 17, wherein it comprises a machining head from which said laser beam is emitted out of the device and in which all of said sensors are arranged.

19. The device according to claim 14, wherein it is connected to a computer for controlling it via a suitable interface.