Master Thesis

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Eidgenössische Technische Hochschule Zürich Swiss Federal Institute of Technology Zurich

Institut für Werkzeugmaschinen und Fertigung Institute of Machine Tools and Manufacturing

Eidgenössische Technische Hochschule Zürich Swiss Federal Institute of Technology Zurich

Institut für Werkzeugmaschinen und Fertigung Institute of Machine Tools and Manufacturing

1. Motivation

Well-known benefits of Additive Manufacturing (AM) as reduction in process steps, possible increase in geometrical complexity of products and an accelerated development process have led to intensified efforts in process understanding and process control of the different AM technologies. One of these rapidly growing technologies is laser cladding. Due to the variety of physical effects and their interaction, such as the dynamics of the powder-injection, coating formation and powder stream-laser beam interaction, the laser cladding process is very complex. Thus, online monitoring and simulation become important tools to understand physical phenomena in order to gain the ability to control the process and meet quality and micro-dimensional requirements in the manufacturing industry. A fundamental problem in the field of laser cladding is the lack of appropriate theoretical concepts describing process phenomena such as powder stream-laser beam interaction, powder consolidation, particle deflection from the powder consolidation zone and geometrical instability of the fused bead. The temperature in the melt pool is one of the key factors during the process due to its strong dependence on the basic assessable parameters, such as laser power, scanning speed and powder feed rate. Therefore, the temperature dynamics during the entire thermal cycle of the cladding process is of great practical interest. The total radiation from the working zone, as is known consists of reflection of the laser beam, plasma radiation and thermal radiation of the melt pool. Aggregation and interpretation of the measured signals hence represents a major difficulty. Furthermore, the wide spatial, temporal and temperature ranges of the laser cladding process in addition to the complexity of process parameters complicate the applicability of optical monitoring methods. Modelling distinct parts of the process can help overcome these difficulties in monitoring and assist in gaining a deeper understanding as well as control of the process. Simulations regarding the laser cladding process have mainly been focusing on the powder consolidation zone. The areas of interest were modelling the residual stress resulting from the fast changing thermal conditions in the substrate and the clad as well as the uncovering of the relationship between process parameters and clad geometry for different materials. Only few models have tried to simulate the interaction between powder stream and laser beam and the influence of shifting focusses has never been investigated before.

Author: Sebastian Freihse (10-922-508)

Issue date:

Submission date:

Supervisor: Dimitry Kotoban

Professor: Konrad Wegener, Sergey N. Grigoryev

Title:

Study of high temperature heat and mass transfer during laser cladding by means of optical diagnostics

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2. Task definition

Several experiments are to be conducted in order to understand the physical phenomena and the influences of certain process parameters. The interaction of laser beam and powder stream, as well as the temperature in the melting pool are to be investigated. The following monitoring devices should be used: pyrometer, infrared camera and high speed camera. Various materials such as Steel, Bronze, Nickel super alloy and Cobalt super alloy are to be compared. Furthermore, the relation between changes in process parameters and the corresponding physical phenomena should be revealed and discussed in detail. The focus of this work should be on the laser beam-powder stream interaction, where the effect of shifting focuses of laser beam as well as powder stream are to be investigated. Using optical monitoring of the process plus examination of the clad geometry all occurring influences may be analysed. Using the high speed camera, the changes in interaction of laser beam and powder stream are to be observed. To fully understand the heat and mass transfers during this part of the process, a model should be developed. Objective of the model is to reveal changes in the particles temperatures and their phase states before entering the melting pool. The infrared camera and the pyrometer are to be used in order to analyse the continuous development of the melt pool and the thermal cycle of the substrate in different cladding conditions. Relevant literature has stated that modelling the transition of particles in flight and their entry in the melt pool has rarely been done due to its complexity. In this work an extension of the model including the transition phenomena is considered as optional.

3. Potential approach

3.1 Literature and equipment

The literature listed in the bibliography section include thermal and hydrodynamic

effects during the laser cladding process. Additionally, some analytical and

numerical approaches for modelling the process are presented. An introduction to

optical monitoring and systematic experiments in laser cladding is included as

well. Further literature will be added throughout the project.

3.2 Simulation / Matlab-Comsol Model

- Learning of Comsol software and needed physics interfaces

- Understanding of previous models/simulations

- Modelling of the laser beam-powder stream interaction including the following

phenomena (amongst others):

Particles dynamic behaviour

Particle heating

Laser power distribution

Wall conditions (nozzle, substrate, adjacent track)

Laser beam attenuation

Shielding of process by gas stream

- Integration of algorithms to improve efficiency and stability of the simulation

- Extend model to transition phase (particles entering melt pool) [optional]

3.3 Experimental setup and measurements

- Substrate and powder preparation

- Powder stream behaviour and interaction with laser beam (high speed camera,

possibly infrared camera)

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- Melt pool temperature analysis (pyrometer, infrared camera)

- Powder particles coinciding with melt pool (high speed camera, possibly infrared

camera)

- Recording of thermal cycle of surface [substrate + clad] (pyrometer)

- Clad track characterisation and cross section analysis: optical microscope,

hardness testing

3.4 Material and parameter variations

- Materials to test: Stainless steel (AISI 321), Nickel super alloy, Cobalt super alloy,

Copper (9% Al)

- Material specification (Particle size, distribution) will be determined with

respective equipment (Occhio 500nano)

- Experiment 1: Investigation of the powder heated by the laser beam in flight

Experimental parameters: Laser power, scanning speed, powder feed

rate

Equipment: high speed camera, infrared camera, pyrometer

Expected results: thermal maps (temperature distribution) in the

stationary and non-stationary states (heating and cooling) of the

melt pool, video and images of particles stream-laser beam

interaction, information on the thermal cycle based on pyrometer

signal

- Experiment 2: Influence of focus/defocus of powder stream and laser beam

Experimental parameters: optimal cladding parameters, focus point

laser beam, focus plane powder stream

Equipment: high speed camera, infrared camera, pyrometer

Expected results: influence of focusses shifting on particle heating,

powder stream-laser beam interaction, melt pool and thermal cycle

- Experiment 3: Influence of hatch distance [optional]

Experimental parameters: optimal cladding parameters, hatch

distance

Equipment: high speed camera, infrared camera, pyrometer

Expected results: influence of adjacent tracks on hydrodynamics,

melt pool and thermal cycle

3.5 Simulations

- Verification of developed model i.e., sensitivity and reliability check

- Simulation of different parameter settings

- Optimization of input parameters and verification of target range

- Validation of results with experiments

3.6 Summarization & Documentation

- Experimental results

- Simulation program

- Results interpretation

- Thesis report

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Required Resources: - Comsol 5.1 with MATLAB Livelink, Matlab R2016a

- Laptop (simulation server if necessary)

- Powder materials and substrates

- High Speed Camera, Infrared Camera, Pyrometer

- Trumpf Laser TruDisk 2001 + CNC machine TruCell 3008

4. Literature [1] U. de Oliveira, V. Ocelík, and J. T. M. De Hosson, “Analysis of coaxial laser cladding processing

conditions,” Surf. Coat. Technol., vol. 197, no. 2–3, pp. 127–136, Jul. 2005. [2] J. Lin, “A simple model of powder catchment in coaxial laser cladding,” Opt. Laser Technol., vol. 31,

no. 3, pp. 233–238, Apr. 1999. [3] Y. Fu, A. Loredo, B. Martin, and A. B. Vannes, “A theoretical model for laser and powder particles

interaction during laser cladding,” J. Mater. Process. Technol., vol. 128, no. 1–3, pp. 106–112, Oct. 2002.

[4] J. F. Li, L. Li, and F. H. Stott, “A three-dimensional numerical model for a convection–diffusion phase change process during laser melting of ceramic materials,” Int. J. Heat Mass Transf., vol. 47, no. 25, pp. 5523–5539, Dec. 2004.

[5] G. Bi, A. Gasser, K. Wissenbach, A. Drenker, and R. Poprawe, “Identification and qualification of temperature signal for monitoring and control in laser cladding,” Opt. Lasers Eng., vol. 44, no. 12, pp. 1348–1359, Dec. 2006.

[7] H. Qi, J. Mazumder, and H. Ki, “Numerical simulation of heat transfer and fluid flow in coaxial laser cladding process for direct metal deposition,” J. Appl. Phys., vol. 100, no. 2, p. 24903, Jul. 2006.

[8] Maria Doubenskaia, Sergey Grigoriev, Ivan Zhirnov, and Igor Smurov, “Parametric analysis of SLM using comprehensive optical monitoring,” Rapid Prototyp. J., vol. 22, no. 1, pp. 40–50, Jan. 2016.

[9] O. B. Kovalev, A. V. Zaitsev, D. Novichenko, and I. Smurov, “Theoretical and Experimental Investigation of Gas Flows, Powder Transport and Heating in Coaxial Laser Direct Metal Deposition (DMD) Process,” J. Therm. Spray Technol., vol. 20, no. 3, pp. 465–478, Aug. 2010.

[10] M. Ignatiev, I. Y. Smurov, G. Flamant, V. Senchenko, and V. Dozhdikov, “Two-dimensional resolution pyrometer for real-time monitoring of temperature image in laser materials processing,” Appl. Surf. Sci., vol. 109–110, pp. 498–508, Feb. 1997.

[11] M. A. Doubenskaia, I. V. Zhirnov, V. I. Teleshevskiy, P. Bertrand, and I. Y. Smurov, “Determination of True Temperature in Selective Laser Melting of Metal Powder Using Infrared Camera,” Mater. Sci. Forum, vol. 834, pp. 93–102, 2015.

[12] M. Doubenskaia, M. Pavlov, S. Grigoriev, E. Tikhonova, and I. Smurov, “Comprehensive optical monitoring of selective laser melting.”

[13] A. V. Gusarov, I. Yadroitsev, P. Bertrand, and I. Smurov, “Heat transfer modelling and stability analysis of selective laser melting,” Appl. Surf. Sci., vol. 254, no. 4, pp. 975–979, Dec. 2007.

[14] M. Doubenskaia, P. Bertrand, and I. Smurov, “Optical monitoring of Nd:YAG laser cladding,” Thin Solid Films, vol. 453–454, pp. 477–485, Apr. 2004.

[15] G. G. Gladush and I. Smurov, Physics of laser materials processing: theory and experiment, vol. 146. Springer Science & Business Media, 2011.

[16] I. Smurov and M. Doubenskaia, “Temperature Monitoring by Optical Methods in Laser Processing,” in Laser-Assisted Fabrication of Materials, J. D. Majumdar and I. Manna, Eds. Springer Berlin Heidelberg, 2013, pp. 375–422.

[17] M. Ignatiev, I. Smurov, and G. Flamant, “Real-time optical pyrometer in laser machining,” Meas. Sci. Technol., vol. 5, no. 5, p. 563, 1994.

[18] F. Vásquez, J. A. Ramos-Grez, and M. Walczak, “Multiphysics simulation of laser–material interaction during laser powder depositon,” Int. J. Adv. Manuf. Technol., vol. 59, no. 9–12, pp. 1037–1045, Aug. 2011.

[19] P. Peyre, P. Aubry, R. Fabbro, R. Neveu, and A. Longuet, “Analytical and numerical modelling of the direct metal deposition laser process,” J. Phys. Appl. Phys., vol. 41, no. 2, p. 25403, 2008.

[20] I. Smurov, M. Doubenskaia, and A. Zaitsev, “Comprehensive analysis of laser cladding by means of optical diagnostics and numerical simulation,” Surf. Coat. Technol., vol. 220, pp. 112–121, Apr. 2013.

[21]S. Morvielle, M. Carin, D. Carron, P. Le Masson, M. Gharbi, P. Peyre, and Fabbro, R, "Numerical

Modeling of Powder Flow During Coaxial Laser Direct Metal Deposition: Comparison Between Ti-

6Al-4V Alloy and 3161 Stainless Steel," Excerpt Proc. 2AL2 COMSOL Conf. Milan,2012.

t22lW. Devesse, D. D. Baere, and P. Guillaume, "Modeling of laser beam and powderflow interaction in

laser cladding using ray-tracing," J. Loser Appl., vol.27, no. s2, p. s29208, Feb. 2015.

[23]J, tbarra-Medina, M. Vogel, and A. J. Pinkerton, "A CFD modelof laser cladding:from deposition

head to melt pool dynamics," Proc ICALEO'2011, pp.23-27 ,20IL[24]1. Tabernero, A. Lamikiz, S. Martinez, E. Ukar, and L. N. L6pez de Lacalle, "Modelling of energy

attenuation due to powder flow-laser beam interaction during laser cladding process," J. Moter'

Process. Technol.,vol.2t2, no. 2, pp' 516-522,Feb'2012.

t25lE, Toyserkani, A. Khajepour, and s. F. corbin, Loser cladding. cRC Press, 2004.

Moscow,

Moscow, , /ay'l 20/6Dimitry Kotoban

Zurich,Prof. Dr. K. Wegener

Approval

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