Mechanics, Materials Science & Engineering, December 2017 ISSN 2412-5954
MMSE Journal. Open Access www.mmse.xyz
Laser Welding of Secondary Cell made of Aluminium and Nickel
1
Heeshin Kang
1, a
, Jiwhan Noh
1
, Byunghoon Seo
1
1 Korea Institute of Machinery and Materials, Daejeon, Korea
a khs@kimm.re.kr
DOI 10.2412/mmse.39.73.113 provided by Seo4U.link
Keywords: laser, welding, metal, aluminium, nickel, process.
ABSTRACT. The purpose of this study is to make the experimental basis for the development of the laser-assisted micro
welding technology. The basic experiments are carried out on the melting of the thin aluminium and nickel sheets in order
to secure the micro laser welding process technology for manufacturing the secondary cell. The micro laser welding joints
are lap joints. The welding specimens are made from the aluminium and nickel foil. The thickness of metal sheet is 0.1
mm and 0.15 mm. The quality of welding specimens is tested by observing the shape of the beads on the plate after the
laser welding and the cross-section of the welded parts is observed by using metallography method. The mechanical
tensile test is carried out for analyzing the performance of welding strength. The monitoring method by using ultraviolet
and infrared light sensors are used for finding the correlation with the results of the mechanical and metallurgical test.
Introduction. Laser welding is one of the important technologies used in the manufacturing of
lighter, safer product at a high level of productivity; to that end, the leading manufacturers have
replaced spot welding with laser welding in the process of the secondary cell assembly. Korean
manufacturers are developing and applying the laser welding technology using the Nd:YAG laser.
The conventional spot resistance welding used in the secondary cell assembly process has been an
obstacle to cell design and manufacturing due to the limited applicability and lower welding
efficiency resulting from the geometry and welding characteristics of spot welding machines. As
such, the industry has been trying to develop new welding and joining technologies. This study was
conducted to develop a laser welding technology for the secondary cell, a welding quality inspection
technique, and a robot control. In particular, due to the characteristics of laser welding - where the
laser beams have to be directed perpendicularly to the welding surface - it is very difficult to instruct
the robot to direct the laser beam perpendicularly on to a curved surface. Indeed, many studies have
been performed to improve the speed of the laser welding process and the quality of welding parts
[1-3]. In this study, these problems were addressed by applying the laser welding method and the
quality monitoring method [4-7].
Experimental equipment. Figure 1 shows a schematic block diagram and the developed system of
the entire remote laser welding control system. The beam from the laser generator is transmitter via
an optical fiber to the welding head at the end of the robot's arm. The laser welding can be achieved
by manipulating the axes of the robot system. The laser generator used was 1.6 kW fiber laser system
and the robot system was the 6 axes Industrial robot of payload 130 kg. To conduct a basic study of
the weldability of the remote laser welding system, the lap welding were conducted with the common
aluminium and nickel foils. The weld joints were inspected and tested for tensile strength to determine
the optimal welding parameters. In order to devise a technique of measuring the quality of the laser
welding on a real-time-basis, basic experiments were conducted with a technique capable of deter-
mining the quality of welding by monitoring plasma and temperature. The pattern welding tests were
conducted to examine the accuracy of the entire remote laser welding system.
1
© 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license
http://creativecommons.org/licenses/by-nc-nd/4.0/
Mechanics, Materials Science & Engineering, December 2017 ISSN 2412-5954
MMSE Journal. Open Access www.mmse.xyz
Fig. 1. The laser welding system.
Table 1. Core units of remote laser welding system
Laser source
1.6 kW high-power fiber laser
Focusing unit
Collimation, Bean expander, Image transfer
optics, F-theta lens
Scanning unit
XY 2 axes scanner
Handling system
6 axes industrial robot (payload: 130kg)
Workpiece device
Jig, Clamping
Position sensing, process monitoring
CCD vision, Optical emission monitoring
Main control
PC-based controller
Figure 2 shows the process sequence of quality monitoring system for the laser welding. During the
laser welding on a real-time-basis, the basic tests were conducted to develop a technique which facil-
itates the evaluation of weld quality by monitoring plasma and temperature. The tests were conducted
using the fiber laser. To monitor weld quality using plasma flux intensity, the initial criteria of plasma
intensity - which itself determines the critical weld quality - needs to be determined. When the plasma
intensity lies between the maximum and minimum values of the standard range as Figure 3 (a), the
weld quality can be judged to be acceptable.
Mechanics, Materials Science & Engineering, December 2017 ISSN 2412-5954
MMSE Journal. Open Access www.mmse.xyz
Fig. 2. Process sequence of quality monitoring system.
Fig. 3. The results of fiber laser welding quality monitoring by using reference curves.
Test results. Figure 4 shows the size of laser welding specimens. In the fiber laser tests, dissimilar
light metals of the nickel and aluminium foils were welded at a laser powers of 165W and a welding
speed of 1 m/min. The diameter of laser beam is about 0.3 mm and the focal length of laser objective
Mechanics, Materials Science & Engineering, December 2017 ISSN 2412-5954
MMSE Journal. Open Access www.mmse.xyz
lens is 490 mm. The fiber laser was tested at from 100 W to 500 W power using an ultraviolet light
and infrared light sensors. The results were obtained by scanning the specimens by using the laser
scanner of the laser welding system.
Figure 5 shows the results of laser welding plasma monitoring test. An ultraviolet light and infrared
light sensors were used in the tests conducted to detect plasma intensity. The plasma and temperature
signals could be detected at the appropriate values, confirming that real-time-based quality monitor-
ing can be implemented. Table 2 shows the results of the welding test to find the optimal welding
conditions by using a fiber laser. Table 2 show the strength average value after peel test for laser
welding specimens. The strength average value of spot welding is about 0.5 kgf in peel test. The
strength average value of the laser welding is 2.414 kgf and better than the conventional spot welding.
(a)
(b)
Fig. 4. The size of the specimens; (a) nickel, (b) aluminum.
Mechanics, Materials Science & Engineering, December 2017 ISSN 2412-5954
MMSE Journal. Open Access www.mmse.xyz
(a)
(b)
Fig. 5. The results of the laser welding test using the fiber laser. (a) welding specimens, (b) the
wavelength graph by spectrometer.
Table 2. The strength average value after peel test for laser welding specimens.
Mechanics, Materials Science & Engineering, December 2017 ISSN 2412-5954
MMSE Journal. Open Access www.mmse.xyz
Summary. The laser welding system was built on the basis of the interfacing between the laser system
and the industrial robot system. Using the laser welding system, the lap welding of aluminium and
nickel foils were conducted and the tensile strength of the samples was tested to determine the optimal
welding parameters. The weld joints and defects were analyzed after the laser welding tests. During
the laser welding, the plasma intensity signals were measured and analyzed to assist the development
of a technique, which enables evaluation of the quality of laser welding in real time. On the basis of
the laser welding quality tests, the lap welding of dissimilar metals and the algorithms for evaluating
the quality of laser welding will be tested in further studies.
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