Welding Industry

Graphic

Welding processes typically emit very bright light that “blinds” the eye as well as machine vision camera systems. Without proper means the visual monitoring of a welding process is impossible.

Cavitar’s laser illumination enables the clear visualization of welding processes without any disturbances as if the process were cold. Our technology can be applied to all major arc welding processes such as GMAW (MIG, MAG) and TIG, as well as to all major beam welding processes including CO2 laser, fiber laser, diode laser, Nd:YAG laser and electron beam sources. In many cases we can also utilize structured laser illumination and provide information about seam or gap topography.

Business

  • Process observation from a safe distance and in an ergonomic manner
  • Welders can adjust the process in real-time based on the accurate live view
  • Images can be used for image analysis and automation
  • Images or videos can be stored for quality documentation

Research

  • Our laser illumination provides dramatically improved performance as compared e.g. to LED, flash lamp or halogen illumination
  • The illumination is highly uniform and bright which results in high-quality images with low speckle content and no motion blur
  • Our illumination is compatible with all high and low speed cameras that enable synchronization

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Articles about additive manufacturing by CAVILUX customers

Laser cladding

Dresden University of Technology, Germany

Authors: Johannes Trappa, Alexander M.Rubenchik, Gabe Guss, Manyalibo J.Matthews
Title: “In situ absorptivity measurements of metallic powders during laser powder-bed fusion additive manufacturing”
Published: Applied Materials Today, Volume 9, December 2017, Pages 341-349
Application: Additive Manufacturing
Product: CAVILUX HF

Lappeenranta University of Technology, Finland

Authors: Mehrnaz Modaresialam
Title: “Real-time monitoring of additive manufacturing
Published: Master Thesis, Lappeenranta University of Technology
Application: Additive Manufacturing
Product: CAVILUX HF

Lawrence Livermore National Laboratory, USA

Authors: Umberto Scipioni Bertoli, Gabe Guss, Sheldon Wu, Manyalibo J. Matthews, Julie M.Schoenung
Title: “In-situ characterization of laser-powder interaction and cooling rates through high-speed imaging of powder bed fusion additive manufacturing”
Published: Materials & Design, Volume 135, 5 December 2017, Pages 385-396
Application: Additive Manufacturing
Product: CAVILUX HF

Authors: M. J. Matthews
Title: “Physics of laser-assisted advanced manufacturing processes”
Published: Own publication
Application: Additive Manufacturing
Product: CAVILUX HF

Luleå University of Technology, Sweden

Authors: Jetro Pocorni, John Powell, Eckard Deichsel, Jan Frostevarg, Alexander F.H.Kaplan
Title: “Fibre laser cutting stainless steel: fluid dynamics and cut front morphology”
Published: Optics & Laser Technology, Volume 87, January 2017, Pages 87-93
Application: Additive Manufacturing
Product: CAVILUX HF

Authors: Ramiz S.M., Samarjy, Alexander F.H.Kaplan
Title: “Using laser cutting as a source of molten droplets for additive manufacturing: a new recycling technique”
Published: Materials & Design, Volume 125, 5 July 2017, Pages 76-84
Application: Additive Manufacturing
Product: CAVILUX HF

Stankin University, Russia

Authors: M. Doubenskaia, A. Domashenkov, I. Smurova
Title: “Study of the laser melting of pre-deposited intermetallic tial powder by comprehensive optical diagnostics”
Published: Surface and Coatings Technology, Volume 321, 15 July 2017, Pages 118-127
Application: Additive Manufacturing
Product: CAVILUX HF

University of Erlangen-Nuremberg, Germany

Authors: O. Hentschel, C. Scheitler, A. Fedorov
Title: “Experimental investigations of processing the high carbon cold-work tool steel 1.2358 by laser metal deposition for the additive manufacturing of cold forging tools”
Published: Journal of Laser Applications 29, 022307 (2017);
Application: Additive Manufacturing
Product: CAVILUX HF

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Articles about welding by CAVILUX customers

NdYag laser welding

Darmstadt University of Technology, Germany

Authors: P.Groche, M.Becker, C.Pabst
Title: “Process window acquisition for impact welding processes”
Published: Materials & Design, Volume 118, 15 March 2017, Pages 286-293
Application: Laser welding
Product: CAVILUX Smart

Dresden University of Technology, Germany

Authors: M. Dreher , U. Füssel, S. Rose, M. Häßler, M. Hertel, M. Schnick
Title: “Methods and results concerning the shielding gas flow in gmaw”
Published: Welding in the World May 2013, Volume 57, Issue 3, pp 391-410.
Application: Arc welding
Product: CAVILUX HF

Harbin Institute of Technology, China

Authors: Chuang Cai, Jiecai Feng, Liqun Li, Yanbin Chen
Title: “Influence of laser on the droplet behavior in short-circuiting, globular, and spray modes of hybrid fiber laser-mig welding”
Published: Optics & Laser Technology 83 (2016) 108–118
Application: Hybrid welding
Product: CAVILUX HF

Authors: Zhenguo Jiang, Wang Tao, Kun Yu, CaiwangTan, Yanbin Chen, Liqun Li, Zhijun Li
Title: “Comparative study on fiber laser welding of gh3535 superalloy in continuous and pulsed waves”
Published: Materials & Design, Volume 110, 15 November 2016, Pages 728-739
Application: Laser welding
Product: CAVILUX HF

Authors: Guolong Ma, Liqun Li, Yanbin Chen
Title: “Effects of beam configurations on wire melting and transfer behaviors in dual beam laser welding with filler wire”
Published: Optics & Laser Technology, Volume 91, 1 June 2017, Pages 138-148
Application: Laser welding
Product: CAVILUX HF

Authors: Zhibin Yang, Wang Tao, Liqun Li, Yanbin Chen, Chunyuan Shi
Title: “Numerical simulation of heat transfer and fluid flow during double-sided laser beam welding of t-joints for aluminum aircraft fuselage panels”
Published: Optics & Laser Technology, Volume 91, 1 June 2017, Pages 120-129
Application: Laser welding
Product: CAVILUX HF

Authors: Liqun Li Hongbo Xia, Guolong Ma, Genchen Peng
Title: “Flow dynamics during single- and dual-spot laser welding with one common keyhole of 321 stainless steel”
Published: Journal of Materials Processing Technology, Volume 255, May 2018, Pages 841-852
Application: Laser welding
Product: CAVILUX HF

Huazhong University of Science and Technology, China

Authors: Lei Wang, Xinwei Li, Ming Gao, Xiaoyan Zeng
Title: “Stabilization mechanism and weld morphological features of fiber laser-arc hybrid welding of pure copper”
Published: Journal of Manufacturing Processes, Volume 27, June 2017, Pages 207-213
Application: Hybrid welding
Product: CAVILUX HF

Authors: Zhang Chen, M. Gao, Ming Jiang, Xiaoyan Zeng
Title: “Effect of Weld Characteristic on Mechanical Strength of Laser-Arc Hybrid Welded Al-Mg-Si-Mn Aluminum Alloy.”
Published: Metallurgical and Materials Transactions A. 47A
Application: Hybrid welding
Product: CAVILUX HF

Authors: Jiajun Xu, Youmin Rong, Yu Huang, Pingjiang Wang, Chunming Wang
Title: “Keyhole-induced porosity formation during laser welding”
Published: Journal of Materials Processing Technology, Volume 252, February 2018, Pages 720-727
Application: Laser welding
Product: CAVILUX Smart

Ilmenau University of Technology, Germany

Authors: Karsten Günther, Jens Liefeith, Philipp Henckell, Yarop Ali, Jean Pierre Bergmann
Title: “Influence of processing conditions on the degradation kinetics of fused tungsten carbides in hardfacing”
Published: International Journal of Refractory Metals and Hard Materials Volume 70, January 2018, Pages 224-231
Application: Arc welding
Product: CAVILUX HF

Korea Advanced Institute of Science and Technology (KAIST), Korea

Authors: Kyungnam KimHyun Chung
Title: “Wire melting rate of alternating current gas metal arc welding”
Published: The International Journal of Advanced Manufacturing Technology, May 2017, Volume 90, Issue 5–8, pp 1253–1263
Application: Arc welding
Product: CAVILUX HF

LABSOLDA – Welding and Mechatronics Institute, Brazil

Authors: Régis Henrique Gonçalves e Silva, Kauê Correa Riffel, Marcelo Pompermaier Okuyama, Giovani Dalpiaz
Title: “Effect of dynamic wire in the GTAW process”
Published: Journal of Materials Processing Technology, Volume 269, July 2019, Pages 91-101
Application: Welding
Product: CAVILUX HF

Lappeenranta University of Technology, Finland

Authors: Heidi Piili, Antti Salminen, Petri Harkko and Janne Lehtinen
Title: “Study of phenomenon of fibre-laser-mig/mag-hybrid-welding”
Published: Paper 1006
Application: Arc welding
Product: CAVILUX HF

Authors: Antti Salminen, Janne Lehtinen and Petri Harkko
Title: “The effect of welding parameters on keyhole and melt pool behavior during laser welding with high power fiber laser”
Published: Proc. 27th Int. Conference on Applications of Lasers and Electro Optics ICALEO2008, Paper 703
Application: Arc welding
Product: CAVILUX HF

Authors: A. Salminen
Title: “The filler wire – laser beam interaction during laser welding with low alloyed steel filler wire”
Published: ISSN 1392 – 1207. MECHANIKA. 2010. Nr.4(84)
Application: Laser welding
Product: CAVILUX HF

Authors: Antti Lehti, Lauri Taimisto, Heidi Piili, Olli Nyrhilä, Antti Salminen
Title: “Correlation between pyrometer monitoring and active illuminaton imaging of laser assisted additive manufacturing of stainless steel”
Published: ICALEO 2011, PAPER 404.0
Application: Laser welding
Product: CAVILUX HF

Author: Zahra Rezaeisavadkohi
Title: “Real-Time monitoring of laser scribing process of CIGS solar panel utilizing integrated redundant sensory platform utilizing of high-speed camera and spectrometer solar”
Published: Master Thesis
Application: Laser scribing
Product: CAVILUX HF

Luleå University of Technology, Sweden

Authors: R. Olsson, I. Eriksson, J. Powell and A.F.H. Kaplan
Title: “Pulsed laser weld quality monitoring by the statistical analysis of reflected light.”
Published: Lasers in manufacturing 2009: proceedings of the Fifth International WLT-Conference Lasers in Manufacturing, LIM 2009 : Munich, Germany, June 15th – 18th, 2009
Application: Laser welding
Product: CAVILUX HF

Authors: Rickard Olsson
Title: “Signal processing and high speed imaging as monitoring tools for pulsed laser welding”
Published: Licentiate Thesis
Application: Laser welding
Product: CAVILUX HF

Authors: Ingemar Eriksson, John Powell, Alexander F. H. Kaplan
Title: “Ultra high speed camera investigations of laser beam welding”
Published: Congress proceedings ICALEO: 29th International Congress on Applications of Lasers & Electro-Optics : September 26 – 30, 2010, Anaheim, CA, USA, Paper 501
Application: Laser welding
Product: CAVILUX HF

Authors: E. A. I. Eriksson, P. Norman, A. F. H. Kaplan
Title: “Basic study of photodiode signals from laser welding emissions”
Published: NOLAMP proceeding 2009: Nordic Laser Materials Processing Conference ; 24th – 26th August 2009 in Copenhagen
Application: Laser welding
Product: CAVILUX HF

Authors: Ivan Bunaziv, Jan Frostevarg, Odd M. Akselsena, Alexander F.H. Kaplan
Title: “Process stability during fiber laser-arc hybrid welding of thick steel plates”
Published: Optics and Lasers in Engineering, Volume 102, March 2018, Pages 34-44
Application: Laser welding
Product: CAVILUX HF

Authors: Ivan Bunaziv, Odd M. Akselsen, Jan Frostevarg, Alexander F.H. Kaplan
Title: “Deep penetration fiber laser-arc hybrid welding of thick HSLA steel”
Published: Journal of Materials Processing Technology, Volume 256, June 2018, Pages 216-228
Application: Hybrid welding
Product: CAVILUX HF

Osaka University, Japan

Authors: Sarizam Bin Mamat, Shinichi Tashiro, Manabu Tanaka and Mahani Yusoff
Title: “Study on Factors Affecting the Droplet Temperature in Plasma MIG Welding Process”
Published: Journal of Physics D: Applied Physics
Application: Arc welding
Product: CAVILUX HF

Shanghai Jiao Tong University, China

Authors: Junhao Sun, Kai Feng, Ke Zhang, Baochao Guo, En Jiang, Pulin Nie, Jian Huang, Zhuguo Liab
Title: “Fiber laser welding of thick aisi 304 plate in a horizontal (2g) butt joint configuration”
Published: Materials & Design, Volume 118, 15 March 2017, Pages 53-65
Application: Laser welding
Product: CAVILUX HF

Authors: Junhao Sun, Pulin Nie, Fenggui Lu, Jian Huang, Kai Feng, Zhuguo Li, Baochao Guo, En Jiang, Wang Zhang
Title: “The characteristics and reduction of porosity in high-power laser welds of thick aisi 304 plate”
Published: The International Journal of Advanced Manufacturing Technology, December 2017, Volume 93, Issue 9–12, pp 3517–3530
Application: Laser welding
Product: CAVILUX HF

Authors: Junhao Sun, Pulin Nie, Kai Feng, Zhuguo Li, Baochao Guo, En Jiang
Title: “The elimination of pores in laser welds of aisi 304 plate using different shielding gases”
Published: Journal of Materials Processing Technology, Volume 248, October 2017, Pages 56-63
Application: Laser welding
Product: CAVILUX HF

University of Bourgogne, France

Authors: Issam Bendaoud, Simone Matteï, Eugen Cicala, Iryna Tomashchuk, Henri Andrzejewski, Pierre Sallamand, Alexandre Mathieu, Fréderic Bouchaud
Title: “The numerical simulation of heat transfer during a hybrid laser–mig welding using equivalent heat source approach”
Published: Optics & Laser Technology, Volume 56, March 2014, Pages 334-342
Application: Arc welding
Product: CAVILUX HF

University of Cambridge, UK

Authors: C. Earl a,b, J.R. Castrejón-Pitac, P.A. Hiltonb, W. O’Neill
Title: “The dynamics of laser surface modification a centre for industrial photonics”
Published: Journal of Manufacturing Processes 21 (2016) 214–223
Application: Laser welding
Product: CAVILUX Smart

University of Erlangen-Nuremberg, Germany

Authors: Christian Kägeler, Alexander Grimm, Andreas Otto, Michael Schmidt
Title: “Frequency-modulated zero-gap laser beam welding of zinc-coated steel sheets in an overlap joint configuration”
Published: Proceedings of the Fifth International WLT-Conference on Lasers in Manufacturing 2009
Application: Laser welding
Product: CAVILUX HF

University of Stuttgart, Germany

Authors: Daniel J.Förster, Sebastian Faas, Stefan Gröninger, Franziska Bauer, Andreas Michalowski, Rudolf Weber, Thomas Graf
Title: “Shielding effects and re-deposition of material during processing of metals with bursts of ultra-short laser pulses”
Published: Applied Surface Science, Volume 440, 15 May 2018, Pages 926-931
Application: Laser welding
Product: CAVILUX Smart

Wuhan Institute of Technology, China

Authors: Chen Zhang, Ming Gao, Ming Jiang, Xiaoyan Zeng
Title: “Effect of weld characteristic on mechanical strength of laser-arc hybrid-welded al-mg-si-mn aluminum alloy”
Published: Metallurgical and Materials Transactions A, November 2016, Volume 47, Issue 11, pp 5438–5449
Application: Hybrid welding
Product: CAVILUX HF

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Guide to high-quality welding imaging

The imaging of welding is often challenging since the camera can easily be blinded by the large amount of light emitted by the welding process. Cavitar presents guidelines for achieving high-quality images of welding.

1 Filtering and illumination

If a welding process is visualized without active lighting the only illumination source is the process light itself. Main source of radiation is the electric arc with temperature between 6 000 – 20 000 °C depending on the process. In addition to thermal radiation (Planck) there are emission peaks specific to process elements. For most camera sensors this process light is so strong that the image gets saturated and one does not see much of the process features i.e. “hot” and “cold” areas simultaneously.

Fig. 1a. Thermal process radiation

Fig. 1b. Emission peaks of process elements

With e.g. neutral density filters one can reduce the amount of process light but at the same time areas with less process light become darker and darker.  Such filtering thus merely makes it possible to “select” which features can be seen and which not.

In order to be able to see both the “hot” and the “cold” regions of the object at the same time, the following conditions have to be fulfilled:

  1. apply a filter which prevents the saturation of the image by reducing the amount of process light in the image
  2. apply illumination which can illuminate the object appropriately and fits with the applied filter transmission band

Since welding processes itself is typically acting as an extremely strong broadband light source, one would need to have an even more powerful broadband light source in order to be able to see all details properly. Such a starting point is obviously highly impractical.

On the other hand, if the object is illuminated with essentially monochromatic laser illumination, highly efficient narrow band pass filters can be applied. Such filters block practically all process light except for the process light emitted at the narrow transmission band of the filter. Therefore the active laser illumination has to be more powerful than the process light only within the narrow transmission band of the filter. In practice this can be accomplished with a laser power of a few hundred watts.  As a result, both “hot” and “cold” regions can be clearly seen at the same time.

Comparisson of filters for welding

2 Camera properties

In industrial environment customers often want to observe the welding process continuously in real-time and therefore the frame rates are low. When studying welding processes for research and development purpose the use of high-speed cameras becomes more common.

Independent of the frame rate, a camera should preferably have a short exposure time, and ideally, a monochrome sensor if it is intended to be used together with laser illumination.

Short exposure times help to reduce the amount of process light that will pass through the narrow band pass filter. Equally important is that the process can be illuminated with a short laser pulse (preferably in the microsecond scale) instead of e.g. a continuous wave light source. Short laser pulses don’t cause any thermal effects on the object and also simplify laser safety management.

In combination with laser illumination, monochrome cameras are preferable to color cameras due to improved sensitivity and image quality.

3 Properties of camera optics

Main criteria for selecting camera optics include the field of view and the working distance. Also the physical dimensions of the camera optics need to be taken into account.  In addition, it is often useful to have an adjustable iris which enables the overall adjustment of the image brightness. A smaller iris enables also larger depth-of-view.

4  Positioning of camera and illumination

One can highlight different features of the welding process by modifying the relative angle between camera and illumination and also avoid unwanted specular reflections from the metal surface.

Common visualization geometries include:

  1. Camera and illumination looking from essentially the same direction towards the process. The surface of the object, welding wire etc. can be seen clearly. Specular reflections might be disturbing
  2. Side illumination (camera and illumination at around 90 degree angle). This setup often reduces specular reflections and can improve the visibility of the melt pool
  3. Direct back illumination (object between camera and illumination). This setup generates sharp silhouette images which can be suitable e.g. for drop formation studies
  4. Indirect back illumination (illumination not directed directly to the camera). This setup can improve the visibility of the melt pool as compared to direct back illumination
  5. Application of diffusing elements or multiple illumination sources (distributed illumination like light delivery via multiple illumination fibers) in order to reduce the amount of specular reflections from the object
  6. Combination of techniques described above

In many cases the best configuration can be found by testing different angles between camera and illumination.


Direct illumination of arc welding from front


Direct illumination of tee-joint arc welding from front


Indirect illumination using a reflective plate to highlight melt pool dynamics


Direct illumination of laser welding from font

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Flux coated electrode hand welding – CAVILUX laser illumination

Flux core welding

Visualization of flux coated electrode hand welding with Cavitar’s CAVILUX illumination laser – front illumination. Video taken at 7.000 frames per second by Leibniz Universität Hannover.

Read the application note

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Spatter behavior in laser beam welding process

Authors: M.Sc. Falk Nagel, Prof. Dr.-Ing. Jean Pierre Bergmann,  Ilmenau University of Technology, Fakultät für Maschinenbau, Fachgebiet Fertigungstechnik, Lasermaterialbearbeitung

1 Description of process

The group of production technology at Ilmenau University of Technology investigates the spatter behavior in laser beam welding process. Spatter is the formation of metal droplets that leave the melt pool as the result of the flow conditions in the capillary and in the melt pool. It is known that the spatter formation depends strongly on the welding speed, but the industry requires high welding speed to increase output. The escaping droplets cause lack of material in the weld seam this leading to reduction of their mechanical properties. Furthermore, the droplets deposit on the work piece reducing the surface quality. The spatter can also deposit on the protective window of the laser optic which then needs to be replaced causing downtime that has to be avoided.

Hence, the task of the group is to understand the physical mechanisms of spattering and how it can be reduced.

The research group observes the formation of the capillary as well as the melt pool behavior around the capillary using a high-speed camera. Due to the high demands in terms of high frames rates and short shutter times, an external lighting source is needed. Here the group uses Cavitar’s CAVILUX HF illumination laser for lighting the area of interest. The reason for choosing CAVILUX HF lies in its ability to produce high qualitative and homogeneous illumination to the melt pool. The robust design of the CAVILUX system enables also easy handling. Furthermore, an integrated green laser pointer in the illumination laser unit permits a simple alignment of the focusing optic in relation to the area of interest. The involved operators welcome the comfort of easy configuration of the laser parameters and the simple synchronization of the lighting with the used Photron SAX 2 high-speed camera.

For observing the spatter behavior, the best illumination results were achieved using the transmitting light setup. Therefore, the optic of the illumination system was placed on the opposite side of the high-speed camera using the same angle of incidence like the camera.

Video 1 shows the formation of the capillary and the melt pool. Moreover, the development of a column of material on the back side of the capillary can be observed. The column increases in vertical direction with further time steps and disintegrates into several droplets. The droplets leave the melt pool resulting in the lack of material and reduction of mechanical properties of the weld.


Video 1: Formation of capillary in melt pool of laser welding. Captured at 20.000 fps.

Video 2 shows the influence of the superimposed diode laser on melt pool behavior using the same welding speed. It is clearly visible that the size of the melt pool is increased, whereby the dynamics of the melt flow is reduced. Particularly the last mentioned effect leads to a distinctive decrease of spattering.


Video 2: Influence of superimposed diode laser on melt pool. Captured at 20.000 fps.

The use of the CAVILUX illumination system in combination with the high-speed camera enables the possibility to visualize the impact of the superimposed laser spots on the weld pool behavior and hence, the formation of spatter. The observations are necessary in order to extend the knowledge of spatter formation and their reduction.

The investigations are carried out within the project ”Spatter reduction due to adapted laser intensity for high-speed welding” (01.07.2016 – 30.06.2018). The research project (IGF-18582 BR/2) is supported by the Federal Ministry of Economic Affairs and Energy within the Allianz Industrielle Forschung (AIF), which is based on a resolution of the German Parliament.

2 Imaging technology

Camera: Photron SAX 2

Objective: Navitar 12 x zoom

Illumination: Cavitar Ltd’s CAVILUX HF

Authors

M.Sc. Falk Nagel, Prof. Dr.-Ing. Jean Pierre Bergmann
Ilmenau University of Technology
Fakultät für Maschinenbau
Fachgebiet Fertigungstechnik
Lasermaterialbearbeitung
Gustav-Kirchhoff-Platz 2
98693 Ilmenau
GERMANY

 

Fakultät für Maschinenbau

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High-Speed Visualization of Electromagnetic Pulse Welding

Impact welding

Author: Christian Pabst, Darmstadt University of Technology – Institute for Production Engineering and Forming Machines (PtU)

1 Introduction

Impact welding is a process which enables metallurgical bonds even between dissimilar metals. Electromagnetic pulse welding has been developed as one method for impact welding. It draws its energy from charged high-voltage capacitors. The accelerating force on the workpiece is generated by a coil, through which the current is driven by discharging the capacitors.

The main applications of electromagnetic pulse welding are the construction of hybrid space frames, the gas-tight sealing of high-pressure containers or low-ohmic joints between aluminum to copper for the electromobility. The joints produced with impact welding are very tough, because the joint area is not weakened by thermal influences but exhibits fine grains.

The basic mechanisms are understood and illustrated in Figure 1: One workpiece has to impact another at velocities in the range of roughly about 250 m/s and above. The impact has to occur under a certain impact angle. This leads to a collision point (or line) travelling across the surface. Figure 1: Schematic illustration of impact welding. The impact is accompanied by a bright flash which is characteristic for this process. The metallically pure surfaces are then pressed together by the immense pressure of the impact, which finally evokes the metallurgical joint.

Figure 1: Schematic illustration of impact welding.

2 Experimental Configuration

For the basic investigations, a special test rig has been developed at the PtU. It avoids the drawbacks of explosion welding and electromagnetic pulse welding by colliding and welding flat sheets mechanically. The buildup consists of two rotors which are driven by one motor each. Each rotor holds an aluminum tube with a welding specimen mounted at one side. Figure 2 shows the test rig without housing.

Figure 2: Left: Test rig without housing. Right: Rotors with specimens in collision position.


Both rotors have the same sense of rotation, so the specimens’ velocity adds when they meet in the center. When the specimens are welded successfully, they rip off their clamped rest with the help of a predetermined breaking point. The welded specimens and the clamped parts are shown in Figure 3.

Figure 3: Welded specimens (center) with the clamped parts.

3 Imaging Setup

As the actual impact and the joint formation take place in only few microseconds, the process is hard to capture with a conventional high-speed camera. Hence for these research works, an image intensifier camera is used. It allows exposure times and frame delays in the range of nanoseconds at still remarkable spatial resolutions of up to more than 1000 pixels. Filming the impact is accompanied by two more obstacles in addition to the high speeds: During the impact, a bright flash covers the actual joint area. Its formation will be discussed in the following chapter. Exact triggering is the second challenge, because the camera technique does not allow pre-triggering. Due to the fast turning rotors, the exact measurement of the momentary angle is hardly possible. The bright process glare can be suppressed by a trick which is also used when conventional welding processes are investigated. As the glare is usually white, it can be concluded that its intensity is spread almost constantly across all (visible) wavelengths. The light source that is mandatory for high-quality high-speed images only emits light in a small wavelength range. Thus, its intensity is much greater than the process glare, even if the latter appears to be brighter to the human eye. Figure 4 illustrates this issue.

Figure 4: Emitted wavelength range of the light source and the wavelength distribution of the process light.


To suppress all other wavelengths, an optical bandpass filter is fitted to the camera in addition to the special light source. In the experiments, CAVILUX Smart laser illumination system with a nominal wavelength of 640 nm ± 10 nm is used together with a filter for 640 nm ± 5 nm. The laser light is comparably easy to handle, because the light is visible and the emitted beam itself is neither coherent nor collimated which prevents speckling. The laser pulses are synchronized with the camera because their length is limited to a few microseconds only due to the limited duty cycle which prevents a constant illumination. Triggering is realized by using the two rotors as a kind of switch for the trigger circuit.

The following Figure 5 shows the process in two independent experiments immediately after the finished impact with and without bandpass filter. It can be clearly seen that it is almost impossible to investigate the impact in detail without the filter.

Figure 5: Propagation of the jet 20 µs after the impact with (left) and without (right) optical bandpass filter.

Figure 6: Image series taken from the side the process with 2 mm aluminum plates at 3 Mio fps.

Figure 7: Image series taken from the side of the process with 0.74 mm steel plates at 2 Mio fps. The process creates also shockwaves which can be seen in the images.

 

4 Jet Formation and Process Glare

A common explanation for the process glare is that it is caused by the jet. The jet does not only consist of oxides, but also of parent material. The theory states that this parent material burns whilst being emitted and thus causes the intense light. However, it is generally accepted at the same time that high temperatures or even melting do not occur during the impact and welding process. Thus, a sufficient energy source which is capable of initiating the oxidation should actually not exist. In order to examine jetting and glare in more detail, the electromagnetic pulse welding process is investigated under different atmospheres. The complete housing of the test rig has a volume of approximately 1 m³ and is not gas-tight. For the experiments, the coil is covered by an acrylic glass box, which is filled with an inert welding gas. When the enclosure is completely filled with the inert gas, the pulse generator is charged and the weld is established after only few seconds. The following images show the welding of two aluminum sheets with a thickness of 2 mm by a peak current of 300 kA at 20 kHz. Figure 8 shows the welding process with the inert gas atmosphere (left) and with the surrounding air (right). The inert gas does not only significantly decrease the emitted light, but also strongly weakens the emitted pressure wave during the impact.

Figure 8: Electromagnetic pulse welding of two aluminum sheets with (left) and without (right) inert gas atmosphere.


Welds between two copper sheets (Cu-ETP, thickness 1 mm) show a different behavior: Neither the light emission nor the pressure wave is significantly influenced by the surrounding atmosphere. In both cases, it is comparable to aluminum welds with inert gas. These experimental results suggest that an oxidation proceeds during the impact. Aluminum burns with a bright white flame and the oxidation is a highly exothermal reaction. As it can be seen in Figure 5, the emitted jet looks like a cloud of dust. If this dust does not only consist of superficial oxides but also of pure aluminum from the base material, a huge surface is created. Thus, if an appropriate energy source is available, a strong exothermal reaction can occur. This theory is supported by the experiments with the test rig: The extent of the glare and the extent of the jet are almost identical as highlighted in Figure 8. This indicates that jetting and glare are the same phenomenon or at least correlate closely.

Figure 9: Electromagnetic pulse welding of two aluminum sheets with (left) and without (right) inert gas atmosphere.

 

The auto ignition temperature of aluminum strongly depends on the particle size. The past research work in this field shows that the auto ignition of aluminum powder with a particle size of under 10 µm can already happen at about 600 °C. As burning aluminum is even capable of splitting water molecules, a hydrogen explosion due to the atmospheric humidity might occur as well. Copper on the other hand does not burn, which explains why the surrounding atmosphere does not change the light emission.

 

5 Conclusions

Through ultra-high-speed imaging employing a CAVILUX Smart laser illumination and image intensifier camera, it was possible to investigate the jet formation and the process glare in electromagnetic pulse welding. The laser illumination enabled the efficient removal of the thermal light emitted by the process. This provided a detailed view behind the bright process light. With back illumination and short pulse duration it is also possible to observe shockwaves.

The high image quality enabled the verification of the theoretical models and to validate research in that area. More information about the theoretical models and considerations for the source of the temperature that is created for the ignition that creates the process glare can be found from: https://eldorado.tu-ortmund.de/bitstream/2003/33500/1/C.Pabst_Electromagnetic%20pulse%20welding.pdf

 

 

About the author

 

Mr. Christian Pabst (M.Sc.)
Darmstadt University of Technology
Institute for Production Engineering and Forming Machines
Otto-Berndt-Straße 2
64287 Darmstadt
Germany 

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Research and Development of Modern Variants of Classical Arc Welding Technologies with High-Speed Videography with Laser Illumination

Author: Prof. Regis Henrique Goncalves e Silva, Dr. Eng.

Over the last years a profusion of new versions of arc welding processes has overwhelmed the international welding scenario in the industry and academia. Innovations have been made possible not only by means of electronics and software developments, but also through new concepts in mechanical design and mechanisms.

With respect to the TIG process, one example is Dynamic Feed (Wire Oscillation). Low productivity is often a disadvantage attributed to conventional TIG, when compared to other arc welding processes. In order to manage this drawback, as well to better deal with hard wetting materials (Ni-Cr alloys for example), a forward and backward wire oscillation movement has been implemented in TIG systems and it finds good acceptability in the industry as well as great interest within the scientific community. A further benefit of reducing porosity may also be expected from the technique. For the study and development of such techniques, high-speed filming has been a powerful tool for observation and stability evaluation of the metal fusion and transfer, arc behavior and weld pool behavior. Main objectives are scientific investigations on parameters influence over the resulting physical phenomena and development of parameterization for different welding conditions (position of wire feeding, torch geometry, wire dynamics).


Video 1: Dynamic Feed TIG Welding imaged at 1.000 fps

With respect to MIG/MAG welding, new technologies aim at developing adaptive control methods, innovative current waveforms and mechanization techniques in order to improve arc stability, metal transfer regularity, process reliability and expansion of the application range. Here, examples are the rotary arc and the pulsed arc mode, which are promising in achieving outstanding results for cladding and thick walled narrow gap joints. In these cases, high-speed filming is applied for metal transfer phenomena observation, arc movement patterns and respective influences over the weld pool, arc geometry and generation of the weld bead. Also, high-speed filming has been being applied to evaluation of consumables and peripherals (like wire-electrodes, contact tips and wire feeders).


Video 2: Rotary Arc Pulsed MIG/MAG Welding imaged at 5.000 fps


Video 3: MIG/MAG Welding with forward/backward movement of the wire electrode imaged at 4.166 fps

For the videos shown above a CMOS, 1.0 megapixel array size color camera was applied with 105mm and 180mm macro lenses. Acquisition rates were adjusted in synchronization with electric welding data monitoring via a Data Acquisition System.

In the scope of these investigations and developments, CAVILUX HF has been intensively applied. The laser  illumination system allows us to finely adjust the arc intensity of the high-speed images produced, thus enabling the selection and isolation of specific welding process features (wire, arc, droplet, pool, etc.) which are goal sensitively, specifically meant to be monitored, analyzed and investigated.

About the author

Prof. Regis Henrique Goncalves e Silva, Dr. Eng.
Director of R&D
LABSOLDA – Welding and Mechatronics Institute
Mechanical Engineering Department – EMC
Federal University of Santa Catarina – UFSC – BRAZIL
www.labsolda.ufsc.br
regis.silva@labsolda.ufsc.br

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Welding PIV measurement of protective gas flows

PIV GMAW welding

Studying the flow of the protection gas of a Gas Metal Arc Welding (GMAW) process by applying welding PIV imaging method.By the Institute of Surface and Manufacturing Technology, Dresden University of Technology, Germany. Illumination is provided by CAVILUX HF with light sheet optics.

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Schlieren imaging of TIG welding

TIG Schlieren

Visualization of TIG welding with Schlieren imaging method using Cavitar’s CAVILUX illumination laser. Video taken at 2.000 frames per second. The method enables the observation of protective gas flow with a high level of detail.

Read more about different Schlieren setups.

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