EP1945400A1

EP1945400A1 - Apparatus for dynamic control of laser beam profile

Info

Publication number: EP1945400A1
Application number: EP05819011A
Authority: EP
Inventors: designation of the inventor has not yet been filed The
Original assignee: Quintessence Photonics Corp
Current assignee: Quintessence Photonics Corp
Priority date: 2005-11-10
Filing date: 2005-11-10
Publication date: 2008-07-23
Also published as: WO2007055691A1; EP1945400A4

Abstract

A laser system that can be used to perform manufacturing process such as welding, cutting, drilling and marking a work piece. The laser system includes an array of laser diodes (12) that each generate a laser beam. The laser beams (16) may collectively create a beam that is directed onto the work piece (20). The system also includes a control circuit (28) that can select and control the laser diodes to vary a characteristic(s) and/or profile of the beam. The control circuit may control the laser diodes so that an outer area of the beam has a higher intensity than an inner area of the beam.

Description

APPARATUS FOR DYNAMIC CONTROL OF LASER BEAM PROFILE

BACKGROUND OF THE INVENTION

1. Field of the Invention

The subject matter disclosed generally relates to the

field of semiconductor lasers and a process of using an

array of semiconductor lasers to perform work.

2. Background Information

Lasers are frequently used to perform work on

different work pieces. For example, lasers are used to

weld, cut, drill or mark a work piece such as a sheet of

metal . The laser must be a high powered device such as a

CO₂ or a YAG:Nd laser to perform such manufacturing

process. Such high powered lasers typically generate a

laser beam profile that has a uniform intensity profile

across the diameter of the beam. A uniform intensity does

not always provide the most desired result.

For example, referring to Figure 1, a laser beam 2

may be directed onto a work piece 4 to weld the same. A laser beam with a uniform intensity distribution will

create a thermal gradient across the weld. The center of

the weld will be hotter than the outer weld areas. The

higher temperatures in the center of the weld area create

depression as shown in Fig. 1. The result is a less than

robust weld.

Conventional laser systems used in manufacturing

processes typically do not have the ability to vary the

profile of the beam. Additionally, conventional high

powered lasers are large in size and costs. It would be

desirable to provide a relatively small, low cost, high

powered laser system that can perform various

manufacturing processes such as welding, cutting, drilling

and marking.

BRIEF SUMMARY OF THE INVENTION

A laser system that is used to perform work on a work

piece. The laser system includes an array of laser diodes

that each generate a laser beam. The system also includes

a control circuit that can individually select and the

laser diodes to create and define a beam that performs a

selected process on the work piece.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures 1 is an illustration showing a laser weld of

the prior art;

Figure 2 is a schematic of a laser system;

Figure 3A-C are illustrations showing an intensity

profile of a beam during different times of a welding

process;

Figure 4 is a timing diagram showing pulse intensities

of the beam during the welding process;

Figure 5 is an illustration of a welded work piece;

Figure 6 is an illustration of a work piece being

welded;

Figure 7 is an illustration of the work piece at a

later time in the weld process;

Figure 8 is an illustration showing two welded work

pieces; Figure 9 is a graph showing power intensities versus

time and work piece locations;

Figure 10 is an illustration showing an embodiment of a

laser diode array.

^■ DETAILED DESCRIPTION

Disclosed is a laser system that can be used to perform

manufacturing process such as welding, cutting, drilling

and marking a work -piece. The laser system includes an

array of laser diodes that each generate a laser beam. The

laser beams may collectively create a beam that is directed

onto the work piece. The system also includes a control

circuit that can select and control the laser diodes to

vary a characteristic (s) and/or profile of the beam. The

control circuit may control the laser diodes so that an

outer area of the beam has a higher intensity than an inner

area of the beam.

Referring to the drawings more particularly by

reference numbers, Figure 2 shows an embodiment of a laser

system 10. The system 10 includes an array of laser diodes

12. The array 12 includes a plurality of individual laser

diodes 14. Each laser diode 14 generates a laser beam 16.

The beams 16 can be focused by a lens 18 onto a work piece

20. The lens 18 may contain a plurality of lenses and

other optical components. The system may include a fiber

optic cable (not shown) in lieu of or in addition to the lens 18 to direct the beams onto the work piece. The laser

beams 16 may be focused and/or directed onto the work piece

20 collectively as a single beam 22.

The system 10 may include a control circuit 24 that

selects and controls the operation of the laser diodes 14.

The circuit 24 may include a plurality of driver circuits

26 that provide power to the laser diodes 14. The driver

circuits 26 may be controlled by a controller 28. The

controller 28 may be a microprocessor. The controller 28

may be connected to memory 30. The controller 28 may be

operated in accordance with operations and data stored in

memory. The operations and data may cause the laser diodes

14 to operate in various modes and/or routines. The modes

and/or routines may include varying the timing of laser

beam generation, and/or changing the profile and/or certain

characteristics of the laser beams 16 and beam 22.

Figures 3A-C, 4 and 5, show a technique for varying the

timing and intensity gradient of the beam 22 to weld two

work pieces 4OA and 40B. The controller 28 may initially

cause the generation of a high intensity precursor pulse as

shown in Fig. 4. The precursor pulse creates a "keyhole" in the work pieces 4OA and 4OB. The keyhole is a

depression in the surface of the work piece that is

partially filled with molten metal. The depression causes

the beam to be reflected from its sidewalls to enhance the

absorption of the beam. The increase in absorption

improves the overall efficiency of energy transfer in the

process .

At time Tl the controller 28 may select and control the

laser diodes to create a non-uniform intensity gradient

across the beam 22 as shown in Fig. 3A. For example, the

controller 28 can control the driver circuits 26 so that

laser diodes in an inner portion of the array generate

laser beams with less intensity than laser beams generated

in an outer area of the array. The result may be a more

uniform temperature gradient across the weld area of the

work piece .

At time T2 the controller varies the output of the

laser diodes to obtain a more uniform intensity gradient

across the beam 22 as shown in Fig. 3B. At time T3 the

controller 28 causes the generation of a beam with an

essentially uniform intensity gradient as shown in Fig. 3C. As shown in Fig. 5 the result is a robust weld 42 (compare

Fig. 5 to Fig. 1) .

By way of example, to spot weld a work piece

constructed of 304 stainless steel with a weld diameter of

0.4 mm, the total pulse energy delivered may be

approximately 1 Joule. The total length of the welding

pulse may be approximately 1 ms . The times Tl, T2 and T3

may range between 0.01-0.2 ms, 0.2-0.8 ms, and 0.5-1.0 ms,

respectively. The peak power of the precursor pulse may

range between 2-10 kW.

Figures 6-8 show a welding process wherein the profile

of the beam 50 is varied to match the weld pattern 52 on a

work piece 54A welded to another work piece 54B. In this

process there is relative movement between the beam and the

work piece. This process is preferably performed with a

two-dimensional array of laser diodes.

In general it is desirable to decrease the cooling rate

of the work piece as it is being welded. Cracking is

inversely proportional to the cooling rate. As show in

Fig. 6 the beam 50 may have an elongated shape to extend

the cooling period as the beam moves along the weld line 52. The controller may cause an initial precursor pulse to

create a keyhole in the work piece. The beam intensity may

be reduced as the work piece moves relative to the beam.

An example of an intensity profile relative to time and

work piece location is shown in Figure 9.

Referring to Fig. 7, the weld pattern may have a bend.

As the work piece moves relative to the beam 50 the

controller 28 may select certain laser diodes from the two-

dimensional array to create an L-shaped beam 50 that

corresponds to the L-shape of the weld line 52. This

creates an elongated beam that can reduce the cooling time

of the weld along the entire weld line. Fig. 8 shows the

resultant weld 54.

By way of example, the process may weld two galvanized

steel sheets each having a thickness between 0.7-2.0 mm.

The weld speed may be 1-4 meters per minute. The elongated

beam may have a length of 3 mm and a width of 0.5 mm. At

the initial work piece location (i.e. X = 0) the intensity

may range between 1-4 MW/cm². Pulses may be separated by

200-600 μs, with pulse widths between 50-200 μs . The

average power density may be gradually reduced by a factor of 4. There may be negligible pulsing at X = 800 μm and

pulsing again at X = 1600 μm. The power densities may

range between 0.5-0.1 MW/cm².

The system 10 may be a station or part of a station

that can perform different processes such as welding,

cutting, drilling, marking etc. The controller 28 can

control the laser diodes to obtain a beam for each type of

process. Thus the system 10 may provide a single station

that can weld, cut, drill, mark, etc., by creating

different beam profiles. By way of example, the station

may create a beam with a non-uniform profile for welding

and a uniform profile for cutting. The station may include

a screen with a keyboard (not shown) that allows an

operator to select a process. The types of profiles can be

stored in memory in a look-up table or other manner.

Figure 10 discloses an embodiment of an array 112. The

array may be fabricated as a semiconductive die 112 that

contains a plurality of laser stripes 114 and one or more

reflective elements 116. There is typically a reflective

element 116 associated with a group of laser stripes 114.

The laser strips 114 generate a plurality of laser beams 118 that travel toward an edge 120 of the die 112. The

reflective element 116 reflects the laser beam 118 so that

the beam 118 is emitted from a top surface 122 of the die

112. Each array 112 may include lenses 124 to focus the

beams 118.

Although a vertical emitting laser diode array is shown

and described, it is to be understood that the array can be

constructed in variety of manners, including the assembly

of horizontal emitting laser diodes or with an array of

vertical cavity surface emitting lasers (VCSEL¹ s) .

While certain exemplary embodiments have been described

and shown in the accompanying drawings, it is to be

understood that such embodiments are merely illustrative of

and not restrictive on the broad invention, and that this

invention not be limited to the specific constructions and

arrangements shown and described, since various other

modifications may occur to those ordinarily skilled in the

art.

Claims

CLAIMSWhat is claimed is:

1. A laser system used to perform work on a work

piece, comprising:

an array of laser diodes, each said laser diode

generates a laser beam,- and,

a control circuit that can individually select and

control said laser diodes to create and define a beam that

performs a selected process on the work piece .

2. The system of claim 1, wherein said control

circuit includes a plurality of driver circuits coupled to

said laser diodes, and a controller coupled to said driver

circuits.

3. The system of claim 1, wherein the process

includes welding.

4. The system of claim 1, wherein said laser diodes

are of a vertically emitting type.

5. The system of claim 1, wherein said laser diodes

include at least one inner laser diode and at least one

outer laser diode and said control circuit controls said

laser diodes such that a laser beam generated by said inner

laser diode has a lower intensity than a laser beam

generated by said outer laser diode.

6. The system of claim 1, wherein said laser diodes

collectively create a beam that has a length greater than a

width.

7. The system of claim 1, wherein said control

circuit controls said laser diodes to change a shape of

said beam.

8. The system of claim 1, wherein said control

circuit controls said laser diodes to vary an intensity

gradient of said beam.

9. A laser system used to perform work on a work

piece, comprising:

laser diode array means for generating a beam,- and, control circuit for controlling said laser diode

control means to create and define a beam that performs a

selected process on the work piece.

10. The system of claim 9, wherein said control

circuit means includes a plurality of driver circuits

coupled to said laser diode array means, and a controller

coupled to said driver circuits.

11. The system of claim 9, wherein the process

includes welding.

12. The system of claim 9, wherein said laser diode

array means includes a plurality of laser diodes of a

vertically emitting type.

13. The system of claim 9, wherein said laser diode

array means includes a plurality of laser diodes that each

generate a laser beam, said laser diode array means

includes at least one inner laser diode and at least one

outer laser diode and said control circuit means controls

said laser diodes such that a laser beam generated by said inner laser diode has a lower intensity than a laser beam

generated by said outer laser diode.

14. The system of claim 9, wherein said laser diode

array means includes a plurality of laser diodes that each

generate a laser beam, said laser diodes collectively

create a beam that has a length greater than a width.

15. The system of claim 9, wherein said control

circuit means controls said laser diodes to change a shape

of said beam.

16. The system of claim 9, wherein said control

circuit means controls said laser diodes to vary an

intensity gradient of said beam.

17. A method for performing work on a work piece with

an array of laser diodes, comprising:

selecting and controlling one or more laser diodes of a

laser diode array to generate a plurality of laser beams

that collectively create a beam; and,

directing the beam onto a work piece to perform the

process.

1 18. The method of claim 17 further comprising varying

2 a shape of the beam during the process.

1 19. The method of claim 17, wherein the laser diode

2 array includes at least one inner laser diode and at least

3 one outer laser diode and the laser beam generated by the

4 inner laser diode has a lower intensity than a laser beam

5 generated by the outer laser diode.

1 20. The method of claim 17, wherein the beam that has

2 a length greater than a width.

1 21. The method of claim 17, further comprising

2 changing a shape of the beam.

1 22. The method of claim 17, further comprising

2 changing an intensity gradient of the beam.

1 23. The method of claim 17, wherein the beam welds the

2 work piece .

L

24. The method of claim 17, wherein the beam cuts the

I work piece.

25. The method of claim 22, wherein the beam cuts the

work piece.