3000W CW diode laser cladding systemcn.laser.focuslight.com/upload/3000W CW diode laser... · 2017. 5. 17. · 3000W CW diode laser cladding system Lingling Xiong a, Min Wang b, Xiaobiao

3000W CW diode laser cladding system Lingling Xiong1a, Min Wangb, Xiaobiao Wangb,Yanfang Zhengb, Di Wub, Pu Zhanga, Xiaoning Lia,c,

Zhenfu Wanga, Xingsheng Liua,b

a State Key Laboratory of Transient Optics and Photonics, Xi'an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, No. 17 Xinxi Road, New Industrial Park, Xi'an Hi-Tech Industrial Development

Zone, Xi'an, Shaanxi, 710119, P.R. China b Xi’an Focuslight Technologies Co., LTD, No. 60 Xibu Road, New Industrial Park, Xi'an Hi-Tech Industrial

Development Zone, Xi'an, Shaanxi, 710119, P.R. China c Key Laboratory for Physical Electronics and Devices of the Ministry of Education & Shaanxi Key Lab of

Information Photonic Technique, Xi’an Jiaotong University, No.28, Xianning West Road, Xi'an, Shaanxi, 710049, P.R. China

ABSTRACT

Laser cladding has become a useful tool in material processing for improving the surface properties of the substrate material, and has been widely used in industry in recent years. In this paper, we studied the 3000W CW laser cladding system based on the high power diode lasers. The beam control method was proposed to reduce the collimated beam pointing errors caused during the packaging of the laser stack. At an input current of 84A, the output power and the optical coupling efficiency of this laser cladding system were 3738W and 93.7%, respectively, and at work face the beam spot size was 2.5mm*7.9mm with symmetry intensity distribution. The laser cladding system was also used in cladding the nickel powder onto the iron substrate and the nickel powder can be clothed onto steel plate uniformly.

Key words: High power; Semiconductor laser stacks; Laser cladding system; Collimated beam pointing error

1. INTRODUCTION

The CO2 and solid state lasers have been widely used in the industry process field for many years.[1-3] With the development of the packaging and beam shaping technologies, diode laser stacks as light sources have been directly applied in industry processing, such as laser cladding, laser welding and laser hardening.[4-9] The diode laser stack is composed of multiple diode laser bars arranged in a row along vertical direction, the continuous-wave output power of the laser stack can extend from 1000W to 3000W.[8,9] However, due to the large divergence angles and beam size on output facet, the direct applications of the stack in laser cladding are limited. In addition, the beam quality of the laser stack is reduced sharply by the collimated beam pointing error generated during laser packaging. Hence, it is necessary to improve the beam quality of the diode laser stack before applications. In this paper the beam shaping and the whole machine design of the diode laser cladding system were proposed.

Based on the beam combination technique of the polarization multiplexing, the 976nm 3000W CW laser cladding system was designed. The collimated beam pointing error of the laser stack was analyzed in detail and the control method was proposed to correct the beam error. The laser cladding system is composed of the temperature controlling system, the 1 [email protected], Phone: (86)-29-88880786; Fax: (86)-29-88887075.

High-Power Diode Laser Technology and Applications X, edited by Mark S. Zediker, Proc. of SPIE Vol. 8241, 824106 · © 2012 SPIE · CCC code: 0277-786X/12/$18 · doi: 10.1117/12.909599

Proc. of SPIE Vol. 8241 824106-1

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laser head, the work platform, the power and cooling devices. The 3000W CW laser cladding system was used in cladding the nickel powder onto the iron substrate and the nickel powder can be clothed onto steel plate uniformly.

2. THE OPTICAL DESIGN OF THE CLADDING SYSTEM

The diode lasers stacks are chosen as the typically laser source for the laser cladding application. The output power of the diode laser stack fabricated by numerous laser bars can reach several thousand watts. Two 976nm diode laser stacks were used in this system and each stack is consisted of 20 diode laser bars. The maximum output power of each stack is 2000W. The beam combination technique of polarization multiplexing was adopted in the optical design of the laser cladding system. The incident beams from the two diode laser stacks are combined by a polarization combiner at first, and then the combined beams are focused by a focus optical system. As a result, the satisfied beam spot is obtained at the work face.

combinerHalf wave plate

Stack 1

Stack 2

Fig.1 Optical design for diode laser cladding system

The optical design of the diode laser cladding system is shown in Fig.1, and the polarization combiner and the focus system are marked by blue rectangles. However, before the beams pass through the polarization combiner, other preparation works should be done. Due to the large divergence angles, the diode laser bars of the laser stack should be collimated in slow and fast axis. As shown in Fig.1, the fast axis beam collimators (FACs) is in front of and much close to the bars. The FACs are aspheric micro lenses. The slow axis collimator is a convex and concave lens group which is placed behind the FAC. Owing to the same polarizations state of the two laser stacks in the cladding system, a half-wave plate is used to change the polarization of the laser stack 1.



Fig.2 Simulation of the rectangle spot intensity distribution on work plane

According to the optical design, the simulation results in Fig.2 show that at the work face with the distance of 150mm the theoretical beam size of 90% energy is 2mm*9mm and the intensity distribution is a symmetrical rectangle. Figure 3 (a) and (b) show the actual optical system and the laser head, respectively. The position of the laser stacks is marked in the Fig.3 (a). The laser head used in cladding system has a small size of 340mm*180mm*138mm and light weight of below 15kg.

(a) The optical system of the laser head (b) The laser head

Fig.3 Inner optical system and laser head

The performances of the laser head were tested at the temperature of 25�. When the current and voltage were set as 84A and 79V, respectively, the output power of the laser head on the working face can reach to 3738W and the conversion efficiency is 93.7%. The LIV test result is shown in Fig.4, and the laser head has a low input current threshold of 6.8A, a high slope efficiency of 56.9(W/A) and an electro-optical conversion efficiency of 62.4%. As shown in Fig.5, the actual beam size on working place was. 2.5mm*7.9mm.



Fig.4 The test result of LIV 3000W laser head

Fig.5 The test beam size on work plane for the laser head

3. THE BEAM DIRECTION CONTROL METHOD

The laser stack has the beam error which is called the collimated beam pointing error (CBPE), which reduces the beam quality of the laser stack greatly. The typical CBPEs marked with red rectangle are shown in Fig.6 and 7, respectively. The ideal far field intensity and beam pattern with CBPEs are compared in Fig.8. Figure 8 (a) shows the ideal far field intensity pattern of the laser stack, while three typical CBPEs are shown in Fig. 8 (b). As shown in Fig.8 (b), the first one is CBPE along fast axis which is measured with ΔD, the second one is the CBPE rotated along slow axis measured by rotation angle δ, and the last one is the CBPE along slow axis measured with moving distance b.

Fig.6 The typical tested CBPE 1 Fig.7 The typical tested CBPE 2



b

(a) The ideal beam (b) The typical collimated beam pointing errors

Fig.8 The collimated beam point error

The laser stack is composed of the collimated laser bars with FACs. The CBPE of the laser stack is caused by three factors. The first is the large smile of the laser bars. The laser bars used in the laser stack are made by Xi'an Focuslight Technologies Co., Ltd and the smile is less than 1μm [10]. Hence, the smile of the bars cannot reduce the collimated beam quality of the laser bars and can be ignored in applications.

Fig.9 The laser bar with a FAC

The second factor is the installation error of FAC, and figure 9 shows the laser bar with a FAC. The FAC is a micro aspheric lens and the far field intensity distribution of the laser bar is very sensitive to the position of the lens. The collimated beam quality of the laser bar is reduced greatly for the tiny installation errors of the FAC. The laser stack with 7 laser bars is used as an example, and the FACs on the laser bars are arranged by “1, 2, 3, 4, 5, 6, 7”, as shown in Fig.10. The ideal far field intensity distribution without any installation error of the FAC is shown in Fig. 10 (a). Several typical installation errors of the FACs are discussed below. six typical installation errors of the FACs are shown in the left of the Fig.10 (b) and measured with parameters of angles –δ’ and δ’, horizontal distance -Δz’ and Δz’, and vertical distance ΔD’ and -ΔD’, respectively. In Fig.10 (b), the first and last lenses are rotated around z axis by the angles of δ’ and –δ’, respectively. Here δ’=0.1°. The second and sixth lenses are off fast axis with the distances of ΔD’ and -ΔD’, respectively. Here ΔD’=0.01mm. The positions of the third and fifth lenses are off the focus spot of the FACs with the distances of Δz’ and -Δz’, respective. Here Δz’=0.2mm. On the right side of Fig.10 (b), the stimulated far field intensity of the laser bars with installation errors is shown, and the collimated beam pointing errors caused by the installation errors of the FACs can be observed obviously. Therefore, reducing the installation error of each laser bar with the FAC lens is an important step to reduce the collimated beam point error of the laser stack.



xll

高亮

ΔD’

-ΔD’

δ’

-δ’

Δz

-Δz

Fast axis

(a) The ideal beam with no installation error (b) Typical installation and collimated beam errors

Fig.10 The collimated beam error of the stack due to the installation error of FAC

During the laser stack packaging, the CBPE can also generate by the installation error of the stack. It means that during the packaging there are position deviations between each laser bar of the laser stack, such as the tilting or displacement of laser bars along fast or slow axes. Hence, reducing the installation error during the stack packaging is also a significant step. To reduce the CBPE, the beam control method has been proposed, and the main steps are shown in Fig.11. Fast-axis collimation components are added to keep each bar pointing direction consistent, and then advanced real-time monitoring equipment is applied. The position of each bar is fine-tuned from multi-dimension orientations to ensure accurate positioning. [11]

Fig. 11 The process of pointing direction control [11]

Based on the method, the laser stack with 20 laser bars was taken as an example and the beam pointing error was successfully corrected. As shown in Fig. 12, the value of parameter δ is below 0.1 degree, ΔD and b can be ignored mostly in applications.

z



xll

高亮

xll

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Fig.12 The corrected result

4. THE CLADDING SYSTEM AND APPLICATION

The 976nm 3000W CW diode laser cladding system product has been made and the output power is continuously adjustable from 0 to 3000W. The whole system is composed of the laser processing platform, the laser head, the temperature control system, the delivering power system and cooler device. The power and cooler devices are the common devices in the laser systems. The control system shown in Fig.13 has three functions. The first function is to control the power and cooling system to ensure the laser head to work normally. The second is the protection function. When the abnormal states appear, such as that cooling system suddenly shuts down or the speed of the work piece is too fast, the control system will cut off the power and protect the cladding system. The third is temperature monitoring. The power will be cut off automatically if the temperature of the laser head is too high.

Fig.13 The control system of the cladding system

Various materials can be used in the cladding process by this cladding system, such as aluminium, iron and nickel. The nickel powder was chosen as the cladding material in the experiment. A laser processing platform was built and includes the laser head and the auto moving platform, as shown in Fig.14 (a). The processes of the laser cladding are introduced as follows: firstly, the nickel powder was spread onto a steel plate uniformly, and the thickness of the powder was chosen as 1.5 and 2.5 mm in the experiment, respectively; the second is to choose the output power of the laser head and the



moving speed of the work platform; at last the steel plate moved under the laser head and the nickel powder was clothe onto the plate.

However, the matched output power and running speed of the platform are difficult to obtain. When the output power of the laser head is fixed, the matched running speed of the platform can be achieved after multiple tests. In the experiment, the output power was chosen as 3000W. By repeatedly tests, the speed is 30mm/s for 1.5mm thickness of the powder and 20mm/s for 2.5mm thickness. The cladding results of the nickel powder onto the steel plate were also tested, and the cladding results of nickel powder with 1.5mm and 2.5mm are shown in Fig.15 (a) and (b), respectively. After analysis, when the moving speed of work piece is 30mm/s for 1.5mm nickel powder, the hot influence depth is 0.3mm and the cladding height is 1.6mm.

Laser head

Steel plateAuto moving platform

(a) The simple laser processing platform (b) The work procedure Fig.14 The 3000W diode laser cladding system

Cladding surface (a) The thickness of 1.5mm (b) The thickness of 2.5mm

Fig.15 The tested results

5. CONCLUSION

In conclusion, the optical design for 3000W diode laser system was proposed. In order to obtain high beam quality, the collimated beam pointing error was studied, and it was well corrected by the beam controlling method. According to the shaping method, the 3000W laser cladding system, which is composed of two diode laser stacks with the wavelength of 976nm, was produced. The system has high optical coupling efficiency of 93.7% and the small beam spot of 2.5mm*7.9mm with symmetry intensity distribution at the work face. The maximum output power of the system was 3738W at the current of 84A. In order to obtain good laser cladding, the output power and the running speed of the laser head of the system should be matched well. The cladding application was successfully performed when the output power and the speed of the laser head are 3000W and 30mm/s, respectively, and the nickel powder with 1.5mm can be clothed



onto steel plate uniformly. The cladding system can realize the surface treating of various materials and will be wildly used in laser processing.

REFERENCES

[1]J.C. Ion, Laser Processing of Engineering materials: principles, procedure and industry application [M], Great Britain, Biiddle Ltd, 2005.

[2] S.V. Alekseev, OA. Novodvorsky, Application of diffractive beam coupler in industrial CW CO2 laser resonator [S], Proc. SPIE, 1994, 193, 2257.

[3]A. Pascu, R. Iovanas, D. Petre, I.C. Roata, Industrial Application of High Power Diode Pumped Solid State Laser for Welding Technology Laser for Welding Technology [J], Bulletin of the Transilvania University of Brasov, 2009, 2(5), 175-181.

[4]F. Lusquin˜os , J.C. Conde, S. Bonss, A. Riveiro, F. Quintero, R. Comesan˜a, J. Pou, Theoretical and experimental analysis of high power diode laser (HPDL) hardening of AISI 1045 steel [J], applied surface science, 2007, 254, 948-954.

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[6]M.J. Balart1, A. Bouzina, L. Edwards, M.E. Fitzpatrick, The onset of tensile residual stresses in grinding of hardened steels [J], Materials Science and Engineering, 2004,367,132-142.

[7]P. M. Beckett, A. R. Fleming, R. J. Foster, J. M. Gilbert, D. G. Whitehead, The application of semiconductor diode lasers to the soldering of electronic components [J], Optical and Quantum Electronics, 1995, 27,1303-1311.

[8]http://www.coherent.com/Products/index.cfm?807/Diode-Laser-Systems.

[9]http://www.dilas.com/gdresources/downloads/DILAS_ThinMetal.

[10]J.W. Wang, Z.B. Yuan, Study of the mechanism of "smile" in high power diode laser arrays and strategies in improving near-field linearity, IEEE Proceedings of 59th Electronic Components and Technology Conference (ECTC), 2009, 837-842.

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3000W CW diode laser cladding systemcn.laser.focuslight.com/upload/3000W CW diode laser... · 2017. 5. 17. · 3000W CW diode laser cladding system Lingling Xiong a, Min Wang b, Xiaobiao