Wetting Process during Laser Brazing of Aluminum Alloys with Aluminum-Based Braze Material

Authors: M.Sc. Till Leithäuser, Dr.-Ing. Peer Woizeschke, BIAS – Bremer Institut für angewandte Strahltechnik GmbH

1 Abstract

This application note is based on the authors’ article: “Influence of the Wire Feeding on the Wetting Process during Laser Brazing of Aluminum Alloys with Aluminum-Based Braze Material” published in the Journal of Manufacturing and Materials Processing 2019, 3(4), 83. The whole article can be found from: https://www.mdpi.com/2504-4494/3/4/83/htm. This document contains modifications and direct quotes from the article.

The wetting behavior in laser brazing can be designated as inconstant, caused largely by external process discontinuities such as the wire feeding. To reveal periodic melt pool propagation effects that occur during laser brazing of aluminum, and for a better understanding of those effects in laser brazing in general, the researchers analyzed high-speed recordings of the brazing process with aluminum alloy. It is demonstrated that two main effects of periodic melt pool behavior in different frequency scales occur during the process, both related directly to the wire feeding.

2 Setup

According to the article, the braze was done in a bead-on-plate configuration on a custom Power Automation CNC table with a moving specimen holder. An Nd:YAG laser was used as the laser source, emitting at a wavelength of 1064 nm. The filler wire was supplied to the workpiece laterally through a wire rope with a copper tip and argon was used to shield the braze from the surrounding atmosphere. The processing laser power of the Nd:YAG laser was 3 kW, the brazing speed was 2 m/min, and the wire angle was 30°. The wire feed rate was varied from 2.5 m/min to 3.5 m/min in 0.25 m/min increments.

The process was recorded with a Phantom VEO 410L high-speed camera, recording 768 × 312 px images at 18 kfps. CAVILUX HF illumination laser, emitting at 810 nm, was used as a light source for the recording together with an 810 ± 10 nm bandpass filter in front of the optics. This provided a controlled illumination of the process without disturbances from the surroundings.

The setup is visible in Figure 1. The created seam has a length of 100 mm.

Figure 1: Setup to visualize the laser brazing process.

The tracking of the wetting front, as well as the capturing of process parameters such as the wire feed rate and wire angle, was achieved with image processing in MATLAB. In Figure 2, a circular object is noticeable at the front of the wetting melt pool. This can be recognized as the reflection of the wire nozzle. The fact that the melt pool is forming a spherical geometry at the wetting front brings the reflection to the camera. This circular shape was used for tracking the wetting front with a circle detection algorithm that uses a circular Hough transform.

Figure 2: Image of the filler wire with reflection of the nozzle in the melt pool.

3 Results

During the imaging process all relevant process data were collected to study the wire feeding conditions during the brazing process.

Figure 3 demonstrates a representative sample of the wetting front deviation and the wire velocity signal. In the wetting front deviation, two periodicities are visible: one at 144 ± 3 Hz with an amplitude of 0.05 ± 0.01 mm, and superimposed a frequency of 13 ± 1 Hz with an amplitude of 0.12 ± 0.01 mm.

Figure 3. Section of the wetting front and the wire feed rate of a representative sample.

In Figure 4, periodic spikes of high velocity, of around twice the preset feed rate, are caused by a retained force that evolves when the wire is not sufficiently melted when it hits the base material. Due to a higher unmolten bottom edge of the wire in relation to the base material sheet, as shown in Figure 5, the load is smaller, resulting in a rather oscillating velocity signal. Finally, in Figure 6, the signal flattens when the bottom edge no longer touches the base material.

Figure 4. (Left) Wire velocity over time, when the wire hits the sheet and the retained force is released periodically. (Middle) Power spectral density (PSD) of the time signal. (Right) Snapshot of the high-speed recording during these events.

Figure 5. (Left) Wire velocity over time, when the wire feeding is hindered by the sheet. (Middle) PSD of the time signal. (Right) Snapshot of the high-speed recording during these events.

Figure 6. (Left) Wire velocity over time, when the wire feeding is uninfluenced by an interaction between the solid (unmolten) wire and the sheet. (Middle) PSD of the time signal. (Right) Snapshot of the high-speed recording during these events.

Based on the PSD (Power spectral density) of the feed rate velocity, each condition has a distinct amount of periodicity. During a strong interaction between the wire and the base material (Figure 4), the foremost frequency is at 106 Hz, accompanied by harmonics at 212 Hz and 318 Hz. In the second phenomenon (Figure 5), where there is less force between the wire and the sheet, there is no single dominating frequency but rather a range between 150 Hz and 400 Hz. When there is sufficient melting of the wire, and thereby no interaction in the wetting area, no frequencies are being noted, as in the PSD shown in Figure 6. It is feasible to classify the samples with dominant frequencies in the wire velocity as “noisy”, and those with a comparatively constant feed over the observed sequence as “smooth”.

More results from the measurements of the relation between wire velocity and wetting, as well as the influence of the wire feed rate on process frequencies, can be found in the original article.

4 Conclusions

The following conclusions can be drawn based on these studies:

Interactions between the unmolten wire and the base material cause oscillations in the wire feeding speed in the range of 160 Hz to 400 Hz and the oscillations being transferred to the wetting front movement with half of the frequency.

The oscillations of the wire velocity in the frequency range of 11 Hz to 15 Hz, caused by the wire feeder, affect the wetting front propagation with the same frequency.

5 References

M.Sc. Till Leithäuser, Dr.-Ing. Peer Woizeschke, BIAS – Bremer Institut für angewandte Strahltechnik GmbH, “Influence of the Wire Feeding on the Wetting Process during Laser Brazing of Aluminum Alloys with Aluminum-Based Braze Material” published in the Journal of Manufacturing and Materials Processing 2019, 3(4), 83 that can be found from: https://www.mdpi.com/2504-4494/3/4/83/htm.

Imaging Technology

Camera: Phantom VEO 410L
Illumination: CAVILUX HF System by Cavitar Ltd.

Authors

M.Sc. Till Leithäuser,
Dr.-Ing. Peer Woizeschke

BIAS – Bremer Institut für angewandte Strahltechnik GmbH
Klagenfurter Straße 5
28359 Bremen
Germany

Send me more information

Leave us your contact information and our expert will get back to you.

If you wish to further specify your question you can fill in more detailed information by using our general contact form.

Selective laser melting SLM – for 3D metal printing process

The video is of a selective laser melting (SLM) process, one technology for additive manufacturing. It shows a clear image of a powder bed in the 3D metal printing process. In addition to CAVILUX HF illumination laser system for high-speed imaging, high magnification with long focal length optics was used to capture the footage. CAVILUX HF totally eliminates the bright plasma light generated and enables the clear observation of what is going on under the plasma illumination.

Video courtesy of Nobby Tech Ltd.

Send me more information

Leave us your contact information and our expert will get back to you.

If you wish to further specify your question you can fill in more detailed information by using our general contact form.

Laser cutting

The video shows a laser cutting process of sheet metal captured with a high-speed camera and CAVILUX HF laser illumination at a frame rate of 10.000 fps.

With CAVILUX laser illumination one can see through the brightness of arc and laser welding, cladding or cutting processes.

Video courtesy of Nobby Tech Ltd.

Send me more information

Leave us your contact information and our expert will get back to you.

If you wish to further specify your question you can fill in more detailed information by using our general contact form.

Additive manufacturing with laser and powder-bed

additive manufacturing

One of the most applied additive manufacturing method for metals is based on a laser scanner and a powder-bed where the metal powder is distributed over a tray and the processing laser melts it according to the desired pattern. After the pattern is created, a new layer of powder is added and the process repeats. The process enables accurate processing and elimination of spatter is essential. High-speed imaging with CAVILUX laser illumination provides high-quality images of the process.

Video material is courtesy of Nobby Tech Ltd. In Japan.

Send me more information

Leave us your contact information and our expert will get back to you.

If you wish to further specify your question you can fill in more detailed information by using our general contact form.

Articles about shockwaves by CAVILUX customers

Shockwave

DLR, Germany

Authors: Klaus Hannemann, Jan Martinez Schramm, Sebastian Karl, Stuart J. Laurence
Title: “Enhancement of free flight force measurement technique for scramjet engine shock tunnel testing”
Published: 21st AIAA International Space Planes and Hypersonics Technologies Conference, International Space Planes and Hypersonic Systems and Technologies Conferences, (AIAA 2017-2235)
Application: Shockwave
Product: CAVILUX Smart

Authors: Stuart J. Laurence, Jan Martinez Schramm, Sebastian Karl and Klaus Hannemann
Title: “An experimental investigation of steady and unsteady combustion phenomena in the hyshot ii combustor”
Published: 17th AIAA International Space Planes and Hypersonic Systems and Technologies Conference 11 – 14 April 2011
Application: Shockwaves
Product: CAVILUX Smart

Authors: Stuart J. Laurence, Jan Martinez Schramm and Klaus Hannemann
Title: “Force and moment measurements on a free-flying capsule model in a high-enthalpy shock tunnel”
Published: 28th Aerodynamic Measurement Technology,Ground Testing, and Flight Testing Conference 25 – 28 June 2012
Application: Shockwaves
Product: CAVILUX Smart

Authors: Jan Martinez Schramm
Title: “Method of optical tracking to determine forces on free flying models in hypersonic flow”
Published: 10th Pacific Symposium on Flow Visualization and Image Processing Naples, Italy, 15-18 June, 2015
Application: Shockwaves
Product: CAVILUX Smart

Japan Aerospace Exploration Agency, Japan

Authors: H. Takayanagi, A. Lemal, S. Nomura and K. Fujita
Title: “Measurements of Carbon Dioxide Nonequilibrium Infrared Radiation in Shocked and Expanded Flows”
Published: Journal of Thermophysics and Heat Transfer, Volume 0, Issue 0
Application: Shockwave
Product: CAVILUX HF

Los Alamos National Laboratory, USA

Authors: M J Murphy and C E Johnson
Title: “Preliminary investigations of he performance characterization using swift”
Published: Journal of Physics: Conference Series 500 (2014) 142024
Application: Shockwaves
Product: SILUX

Military Unversity of Technology, Poland

Authors: Wojciech Napadáek
Title: “Laser percussive strengthening of the aluminum alloys”
Published: Journal of KONES Powertrain and Transport, Vol. 18, No. 1 2011
Application: Shockwaves
Product: CAVILUX HF

MIT – Massachusetts Institute of Technology, USA

Authors: D. Veysset, U. Gutierrez-Hernandez, L. Dresselhaus-Cooper, F. De Colle, S. Kooi, K. A. Nelson, P. A. Quinto-Su, T. Pezeril
Title: “Single-bubble and multi-bubble cavitation in water triggered by Laser-driven focusing shock waves”
Published: ARXIV
Application: Shockwave
Product: CAVILUX Smart

Nagoya University, Japan

Authors: Ducthuan Tran, Xie Chongfa, and Koichi Mori.
Title: “Experimental investigations of impulse generation and stabilization performance on spherical target irradiated by donut-mode beam”
Published: AIAA AVIATION Forum, (AIAA 2017-4160)
Application: Shockwave
Product: CAVILUX Smart

Authors: Ducthuan Tran, Xie Chongfa, and Koichi Mori
Title: “Experimental study of effect of ambient pressure to energy process of laser propulsion”
Published: AIAA AVIATION Forum, (AIAA 2017-4160)
Application: Shockwave
Product: CAVILUX Smart

Authors: Hoang Son Pham, Manabu Myokan, Takahiro Tamba, Akira Iwakawa, and Akihiro Sasoh.
Title: “Impacts of energy deposition on flow characteristics over an inlet”
Published: 47th AIAA Fluid Dynamics Conference, AIAA AVIATION Forum, (AIAA 2017-4305)
Application: Shockwave
Product: CAVILUX Smart

Authors: Hoang Son Pham, Tatsuro Shoda, Takahiro Tamba, Akira Iwakawa, and Akihiro Sasoh.
Title: “Impacts of laser energy deposition on flow instability over double-cone model”
Published: AIAA Journal, Vol. 55, No. 9 (2017), pp. 2992-3000.
Application: Shockwave
Product: CAVILUX Smart

Authors: Akira IWAKAWA, Tatsuro SHODA, Ryosuke MAJIMA, Son Hoang PHAM, Akihiro SASOH
Title: “Mach Number Effect on Supersonic Drag Reduction using Repetitive Laser Energy Depositions over a Blunt Body”
Published: TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, Nr. 60 (2017) 5 p. 303-311
Application: Shockwave
Product: CAVILUX Smart

Authors: Hoang Son Pham, Manabu Myokan, Takahiro Tamba, Akira Iwakawa and Akihiro Sasoh
Title: “Effects of Repetitive Laser Energy Deposition on Supersonic Duct Flows”
Published: AIAA Journal, Volume 56, Issue 2
Application: Shockwave
Product: CAVILUX Smart

Authors: DucThuan Tran, Akifumi Yogo, Hiroaki Nishimura, and Koichi Mori
Title: “Impulse and mass removal rate of aluminum target by nanosecond laser ablation in a wide range of ambient pressure”
Published: Journal of Applied Physics, Volume 122, Issue 23
Application: Shockwave
Product: CAVILUX Smart

Authors: Akira Iwakawa, Tatsuro Shoda, Hoang Son Pham, Takahiro Tamba and Akihiro Sasoh
Title: “Suppression of low-frequency shock oscillations over boundary layers by repetitive laser pulse energy deposition”
Published: AEROSPACE 2016, 3(2)
Application: Shockwaves
Product: CAVILUX Smart

Oxford University, UK

Authors: Phillip A. Anderson, M. R. Betney, H. W. Doyle, B. Tully, Y. Ventikos, N. A. Hawker, and Ronald A. Roy
Title: “Characterizing shock waves in hydrogel using high speed imaging and a fiber-optic probe hydrophone”
Published: Physics of Fluids, Volume 29, Issue 5, 10.1063/1.4982062
Application: Shockwaves
Product: CAVILUX Smart

Authors: MR Betney, PA Anderson, H Doyle, B Tully, NA Hawker, Y Ventikos
Title: “Numerical and experimental study of shock-driven cavity collapse”
Published: Journal of Physics: Conference Series 656 (2015)
Application: Shockwaves
Product: CAVILUX Smart

Saga University, Japan

Authors: Guang Zhang, Ik In Lee, Tokitada Hashimoto, Toshiaki Setoguchi, Heuy DongKima
Title: “Experimental studies on shock wave and particle dynamics in a needle-free drug delivery device”
Published: Journal of Drug Delivery Science and Technology
Volume 41, October 2017, Pages 390-400
Application: Shockwave
Product: CAVILUX HF

Stevens Institute of Technology, USA

Authors: Muhammad Mustafa, Matthew B. Hunt, Nick J. Parziale, Michael S. Smith, and Eric C. Marineau.
Title: “Two-dimensional krypton tagging velocimetry (ktv) investigation of shock wave/turbulent boundary-layer interaction”
Published: 55th AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, (AIAA 2017-0025)
Application: Shockwave
Product: CAVILUX HF

Tohoku University, Japan

Authors: Shin Yoshizawa, Ryo Takagi, Shin-ichiro Umemura
Title: “Enhancement of high-intensity focused ultrasound heating by short-pulse generated cavitation”
Published: Applied Sciences 2017, 7(3), 288
Application: Shockwave
Product: CAVILUX Smart

Authors: Kai Suzuki, Ryosuke Iwasaki, Ryo Takagi, Shin Yoshizawa and Shin-ichiro Umemura
Title: “Simultaneous observation of cavitation bubbles generated in biological tissue by high-speed optical and acoustic imaging methods”
Published: Japanese Journal of Applied Physics, Volume 56, Number 7S1
Application: Shockwave
Product: CAVILUX Smart

Authors: Hiroki Imaeda, Mingyu Sun
Title: “Dynamic Characteristics of Underwater Objects after Shock Wave loading”
Published: 2018 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, (AIAA 2018-0579)
Application: Shockwave
Product: CAVILUX HF

Authors: Jun Yasuda, Takuya Miyashita, Shin Yoshizawa and Shin-ichiro Umemura
Title: “Effects of rose bengal on cavitation generation in gel phantom investigated using high-speed camera”
Published: 23 June 2014, The Japan Society of Applied Physics
Application: Shockwaves
Product: CAVILUX Smart

Tokyo University of Agriculture and Technology, Japan

Authors: Shota Yamamoto, Yoshiyuki Tagawa, Masaharu Kameda
Title: “The evolution of a shock wave pressure induced by a laser pulse in a liquid filled thin tube using the background-oriented schlieren technique”
Published: 17th International Symposium on Applications of Laser Techniques to Fluid Mechanics, Lisbon, Portugal, 07-10 July, 2014
Application: Shockwaves
Product: CAVILUX Smart

Authors: Shota Yamamoto, Yoshiyuki Tagawa, Masaharu Kameda
Title: “Application of background-oriented schlieren (bos) technique to a laser-induced underwater shock wave”
Published: Experiments in Fluids, May 2015, 56:93
Application: Shockwaves
Product: CAVILUX Smart

Authors: Yoshiyuki Tagawa, Shota Yamamoto, Keisuke Hayasaka and Masaharu Kameda
Title: “On pressure impulse of a laser-induced underwater shock wave”
Published: Journal of Fluid Mechanics, Volume 808, Dec. 10th 2016, pp. 5 – 18
Application: Shockwaves
Product: CAVILUX Smart

Toyota Technological Institute – Department of Advanced Science and Technology, Japan

Authors: Taro Handa, Akira Urita
Title: “Experimental study of small supersonic circular jets actuated by a cavity”
Published: Experimental Thermal and Fluid Science, Volume 96, September 2018, Pages 419-429
Application: Shockwave
Product: CAVILUX Smart

University of Glasgow, UK

Authors: Kristoffer Johansen, Jae Hee Song, and Paul Prentice
Title: “Validity of the Keller-Miksis equation for ”non-stable” cavitation and the acoustic emissions generated”
Published: Researchgate
Application: Shockwave
Product: CAVILUX Smart

Authors: Kristoffer Johansen, Jae Hee Song, and Paul Prentice
Title: “Blind deconvolution of a hydrophone with a bubble-collapse shock wave”
Published: Researchgate
Application: Shockwave
Product: CAVILUX Smart

Authors: Kristoffer Johansen, Jae Hee Song, Paul Prentice
Title: “Performance characterisation of a passive cavitation detector optimised for subharmonic periodic shock waves from acoustic cavitation in MHz and sub-MHz ultrasound”
Published: Ultrasonics Sonochemistry Volume 43, May 2018, Pages 146-155
Application: Shockwave
Product: CAVILUX Smart

Authors: Phillip A. Anderson, Nicholas Hawker, Matthew Betney, Brett Tully, Yiannis Ventikos and Ronald A. Roy
Title: “Experimental characterisation of light emission during shock-driven cavity collapse”
Published: ICA 2013 Montral Proseedings, vol 19, 2013
Application: Shockwaves
Product: CAVILUX Smart

Authors: Jae Hee Song, Kristoffer Johansen, and Paul Prentice
Title: “Covert cavitation: spectral peak suppression in the acoustic emissions from spatially configured nucleations”
Published: The Journal of the Acoustical Society of America, Volume 141, Issue 3, 10.1121/1.4977236
Application: Shockwaves
Product: CAVILUX Smart

Authors: Kristoffer Johansen, Jae Hee Song, Keith Johnston, Paul Prentice
Title: “Deconvolution of acoustically detected bubble-collapse shock waves”
Published: Ultrasonics, Volume 73, January 2017, Pages 144-153
Application: Shockwaves
Product: CAVILUX Smart

Authors: Jae Hee Song, Kristoffer Johansen, and Paul Prentice
Title: “An analysis of the acoustic cavitation noise spectrum: the role of periodic shock waves”
Published: The Journal of the Acoustical Society of America 140, 2494 (2016)
Application: Shockwaves
Product: CAVILUX Smart

Authors: Kristoffer Johansen ; Jae Hee Song ; Paul Prentice
Title: “Characterising focused ultrasound via high speed shadowgraphic imaging at 10 million frames per second”
Published: 2016 IEEE International Ultrasonics Symposium (IUS), 18-21 Sept. 2016
Application: Shockwaves
Product: CAVILUX Smart

University of Maryland, College Park, USA

Authors: Richard E. Kennedy, Stuart J. Laurence, Michael S. Smith, and Eric C. Marineau
Title: “Hypersonic boundary-layer transition features from high-speed schlieren images”
Published: 55th AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, (AIAA 2017-1683)
Application: Shockwave
Product: CAVILUX HF

Authors: S.J. Laurence, C.S. Butler, J. Martinez Schramm, K. Hannemann
Title: “Force and Moment Measurements on a Free-Flying Capsule in a Shock Tunnel”
Published: Journal of Spacecraft and Rockets, Ahead of Print : pp. 1-12
Application: Shockwave
Product: CAVILUX Smart

Authors: Jason R. Burr and Ken H. Yu
Title: “Detonation propagation in a linear channel with discrete injectors and side relief”
Published: 26th ICDERS July 30th – August 4th, 2017
Application: Shockwaves
Product: CAVILUX Smart

Authors: Camilo Aguilera, Amardip Ghosh, Kyung-Hoon Shin, Kenneth H. Yu
Title: “Dynamic pressure characterization of a dual-mode scramjet”
Published: 26th ICDERS July 30th – August 4th, 2017
Application: Shockwaves
Product: CAVILUX Smart

Authors: Joseph S. Jewell, Richard E. Kennedy, Stuart J. Laurence, and Roger L. Kimmel.
Title: “Transition on a Variable Bluntness 7-Degree Cone at High Reynolds Number”
Published: 018 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, (AIAA 2018-1822)
Application: Shockwave
Product: CAVILUX HF

Authors: Jason R. Burr and Kenneth H. Yu.
Title: “Detonation Wave Propagation in Discretely Spaced Hydrocarbon Cross-Flow”
Published: AIAA SciTech Forum, (AIAA 2018-1420)
Application: Shockwave
Product: CAVILUX Smart

Authors: Richard E. Kennedy, Stuart J. Laurence, Michael S. Smith, and Eric C. Marineau
Title: “Visualization of the Second-Mode Instability on a Sharp Cone at Mach 14”
Published: 2018 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, (AIAA 2018-2083)
Application: Shockwave
Product: CAVILUX HF

University Paris Saclay, French

Authors: Sergey Stepanyan, Jun Hayashi, Sara Lovascio, Gabi D. Stancu, and Christophe O. Laux
Title: “Hydrodynamic effects induced by nanosecond sparks in air and air/fuel mixtures”
Published: 55th AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, (AIAA 2017-1581)
Application: Shockwave
Product: CAVILUX HF

University of Tokyo, Japan

Authors: Shinji Nakaya, Shingo Iseki, XiaoJing Gu, Yoshinari Kobayashi, Mitsuhiro Tsue
Title: “Flame kernel formation behaviors in close dual-point laser breakdown spark ignition for lean methane/air mixtures”
Published: Proceedings of the Combustion Institute, Volume 36, Issue 3, 2017, Pages 3441-3449
Application: Shockwave
Product: CAVILUX HF

 

Send me more information

Leave us your contact information and our expert will get back to you.

If you wish to further specify your question you can fill in more detailed information by using our general contact form.

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

Send me more information

Leave us your contact information and our expert will get back to you.

If you wish to further specify your question you can fill in more detailed information by using our general contact form.

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

Read more about CAVILUX HF

Send me more information

Leave us your contact information and our expert will get back to you.

If you wish to further specify your question you can fill in more detailed information by using our general contact form.

Measurements of hypersonic boundary-layer instabilities using a pulsed-laser schlieren technique

Author: Stuart Laurence, Department of Aerospace Engineering, University of Maryland, College Park

1 Introduction

When a hypersonic vehicle travels through the atmosphere, a boundary layer develops in the air close to the vehicle surface. Initially (close to the nose of the vehicle) this boundary layer is laminar, but typically will transition to turbulence at some point downstream. A turbulent boundary layer produces significantly larger heat flux and frictional drag at the vehicle surface than a laminar one, so to be able to accurately predict vehicle performance, knowledge of the laminar-to-turbulent transition process is important. There are a variety of boundary-layer instabilities whose growth and breakdown can lead to transition; for slender planar or axisymmetric bodies and small incidences, a key instability mechanism is the second or Mack mode, which can be thought of physically as acoustic waves that become trapped within the boundary layer. Second-mode waves typically exhibit very high frequencies – around 100 kHz or even higher – which makes their measurement very difficult with conventional techniques. Here I describe measurements of the second-mode instability using a schlieren system incorporating a CAVILUX pulsed-diode laser.

2 Experimental configuration

Experiments were performed at two hypersonic wind tunnels: the High Enthalpy Shock Tunnel Goettingen (HEG) of the German Aerospace Center (DLR), and Hypervelocity Tunnel 9 of the Arnold Engineering Development Center (AEDC) at White Oak, Maryland. HEG is capable of reproducing the extremely high flow velocities typical of atmospheric reentry (up to 7 km/s), though for very short test periods (~1 ms). In the present experiments, the flow velocity and density were 4.4 km/s and 0.0175 kg/m3. Tunnel 9, on the other hand, can produce high Mach numbers with longer test periods (around 1 s), but with lower flow velocities. In the present Tunnel 9 experiments, a variety of flow conditions were used, all having a Mach number of approximately 14 and a flow speed of 2 km/s.

In both cases the test article was a slender, 7° half-angle cone. The flow within the boundary layer over the cone was visualized using a conventional Z-fold schlieren arrangement, as shown in figure 1.

Figure 1: Z-fold schlieren visualization set-up used in the experiments described here.

Schlieren is a technique used to visualize flow features in compressible flows: a density gradient at some location in the imaging plane within the test section (in a direction normal to the knife edge placed in front of the camera) will result in a change in intensity at the corresponding location on the image taken by the imaging device (in this case a high-speed camera). In the HEG experiments the light source was a CAVILUX Smart pulsed-diode laser and the camera was a Vision Research Phantom v1210, recording at 200 kHz. The laser was run in ultra-high-speed mode, with a repeated 4-pulse pattern as shown in figure 2.

Figure 2: Laser pulse pattern used in the HEG experiments: Δt12 is 2 μs and Δt34 is 3 μs.

This pattern was necessary because the characteristic frequency of the second-mode disturbance in this case (~600 kHz) was significantly higher than the recording frequency, so closely spaced pulse pairs were used to unambiguously resolve the wave motion (further details to be provided shortly). In the Tunnel 9 experiments, a CAVILUX HF laser providing, uniformly spaced pulses at approximately 70 kHz, was used together with a Phantom v2512 camera. The laser pulse width in the two experiments varied between 20 ns and 50 ns; such short pulse widths were necessary to freeze the high-speed flow structures in images.

3 Results

The HEG experiments were particularly challenging because of the high flow velocity (meaning high second-mode frequencies) and low density (meaning weak intensity variations in the schlieren images). An example of a visualized second-mode wave packet, visible from its oblique “rope-like” structures close to the surface, is shown as it propagates within a sequence of schlieren images in figure 3. The propagation speed of the wave packet is constant – the apparently uneven motion is a result of the laser pulse pattern. By performing two-dimensional image correlations, it is possible to recover the propagation speed – in this case it is 3.8 km/s. The unequal spacing between the two pulse pairs in figure 2 avoids problems with aliasing in these correlations. By then taking the Fourier transform of rows of pixels parallel to the cone surface, wavenumber spectra can be constructed; these can subsequently be converted into frequency spectra using the propagation speed calculated earlier.

Figure 3: Sequence of reference-subtracted schlieren images showing the propagation of a second-mode wave packet (flow is left to right)

Plots of the averaged power spectral density (PSD) at three locations downstream are shown in the left plot of figure 4. Here we see a strong peak at approximately 600 kHz – this corresponds to the second-mode frequency at these conditions. The peak grows rapidly as we move downstream, showing strong amplification of the second mode. A more detailed picture of this growth is shown in the right plot of figure 4, which is a contour plot of the PSD versus distance downstream. Further details of these measurements can be found in Laurence et al. (2016).

Figure 4: (Left) Plots of the schlieren power spectral density (PSD) near the surface at three locations downstream (s is the distance along the cone from the nose); (right) contour plot of the PSD versus distance downstream.

An example of a propagating second-mode wave packet in one of the Tunnel 9 experiments is shown in figure 5. Again we see the characteristic “rope-like” structures, though now the disturbance energy appears to be less concentrated towards the cone surface than it was in the HEG experiments.

Figure 5: Propagation of a second-mode wave packet in a Tunnel 9 experiment

In the Tunnel 9 experiments, the schlieren system was calibrated by placing a long-focal-length lens in the imaging plane and recording images of it. This enabled a calibration curve relating image intensity to the density gradient to be established. From this calibration curve, one can then quantify the growth rate of the second-mode instability. A contour plot of the integrated growth rate, or N-factor, versus distance downstream and frequency is shown in figure 6.

Figure 6: Contour plot of N-factor versus distance downstream and frequency in Tunnel 9 experiment.

Again we see a strong second-mode contribution, but now at a much lower frequency of approximately 100 kHz. The decrease in this frequency moving downstream is associated with the thickening of the mean boundary layer. Such quantitative measurements are very important as they provide data against which numerical simulations and stability analysis computations can be compared. Further details of the Tunnel 9 experiments can be found in Kennedy et al. (2017).

4 Conclusions

The experiments described here demonstrate that it is possible to use high-speed schlieren techniques to perform quantitative measurements of extremely high-frequency instability waves in hypersonic boundary layers. The capabilities of CAVILUX pulsed-diode laser light sources proved instrumental in enabling these measurements.

5 References

Kennedy, R., Laurence, S., Smith, M., and Marineau, E. (2017), “Hypersonic Boundary-Layer Transition Features from High-Speed Schlieren Images”, 55th AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, AIAA Paper 2017-1683

Laurence S., Wagner, A., and Hannemann, K. (2016), “Experimental study of second-mode instability growth and breakdown in a hypersonic boundary layer using high-speed schlieren visualization”, Journal of Fluid Mechanics, vol. 797, pp. 471-503

About the author

Stuart Laurence (Ph.D) completed his graduate studies at the Graduate Aeronautical Laboratories, California Institute of Technology, in the area of hypersonic flows. He currently is Assistant Professor at the Department of Aerospace Engineering, University of Maryland, College Park

Send me more information

Leave us your contact information and our expert will get back to you.

If you wish to further specify your question you can fill in more detailed information by using our general contact form.

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

Send me more information

Leave us your contact information and our expert will get back to you.

If you wish to further specify your question you can fill in more detailed information by using our general contact form.

Spray diagnostics with CAVILUX HF

Author: Lukas Weiß

Description

The Institute of Engineering Thermodynamics at the Friedrich-Alexander University of Erlangen-Nürnberg is using CAVILUX HF laser illumination in various applications (Figure 1 – 3). The full potential of the laser lighting can be seen in shadowgraphy of fluid flows in injection nozzles. The camera, nozzle and illumination are aligned in this order at an optical rail. The laser illuminates through the transparent nozzle directly into the camera. Different phases of the liquid fuel lead to changes in the refractive index of the fluids. This can be captured by the camera. The field of view is 5 mm x 5 mm. The objective is a Navitar Long Distance Microscope. The depth of field can be adjusted with the aperture of the optics. However, this results in significant light losses. The high brightness of the CAVILUX laser illumination solves this challenge. The speed of the fluid stream in the nozzle is about 100 – 200 m/s which is captured by the camera with 200 kHz. Very short exposure times are needed to reduce motion blur. The camera does not provide short enough shutter times. Therefore the light source is the only option to reduce the motion blur. The pulsed mode of CAVILUX HF that creates short pulses at high frequencies allows to capture high quality images.

The visualization of fluid flows in the injection nozzles and the cavitation of the flows created in the nozzle would not be possible without CAVILUX HF laser illumination


Figure 1: Spray of fuel oil captured at 20.000 fps. Use of an effervescent nozzle. Field of view of 5 mm x 20 mm)


Figure 2: Video: Spray of fuel oil captured at 100.000 fps. Field of view 1,5 mm x 1,5 mm with nozzle size of 0,7 mm.


Figure 3: Fuel spray in engine


Figure 4: Flow in transparent nozzle.

About the author

Lukas Weiß, M. Sc.
Friedrich-Alexander Universität Erlangen-Nürnberg
Institute of Engineering Thermodynamics – LTT

Am Weichselgarten 8
91058 Erlangen
GERMANY

University of Erlangen logo

Send me more information

Leave us your contact information and our expert will get back to you.

If you wish to further specify your question you can fill in more detailed information by using our general contact form.