Numerical modelling of heat transfer and fluid flow in laser microwelding (original) (raw)
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Journal of Materials Processing Technology, 2012
This study is focused on numerical modeling analysis of laser-assisted micro-milling (LAMM) of difficultto-machine alloys, such as Ti6Al4V, Inconel 718, and stainless steel AISI 422. Multiple LAMM tests are performed on these materials in side cutting of bulk and fin workpiece configurations with 100-300 m diameter micro endmills. A 3D transient finite volume prismatic thermal model is used to quantitatively analyse the material temperature increase in the machined chamfer due to laser-assist during the LAMM process. Novel 2D finite element (FE) models are developed in ABAQUS to simulate the continuous chip formation with varying chip thickness with the strain gradient constitutive material models developed for the size effect in micro-milling. The steady-state workpiece and tool cutting temperatures after multiple milling cycles are analysed with a heat transfer model based on the chip formation analysis and the prismatic thermal model predictions. An empirical tool wear model is implemented in the finite element analysis to predict tool wear in the LAMM side cutting process. The FE model results are discussed in chip formation, flow stresses, temperatures and velocity fields to great details, which relate to the surface integrity analysis and built-up edge (BUE) formation in micro-milling.
International Journal of Machine Tools and Manufacture, 2008
Laser-assisted mechanical micromachining (LAMM) is a micro-cutting method that employs highly localized thermal softening of the material by continuous wave laser irradiation focused in front of a miniature cutting tool. However, since it is a heat-assisted process, it can induce a detrimental heat-affected zone (HAZ) in the part. This paper focuses on characterization and prediction of the HAZ produced in a LAMM-based micro-grooving process. The heat-affected zone generated by laser heating of H-13 mold steel (42 HRC) at different laser scanning speeds is analyzed for changes in microstructure and microhardness. A 3-D transient finite element model for a moving Gaussian laser heat source is developed to predict the temperature distribution in the workpiece material. The model prediction error is found to be in the 5-15% range with most values falling within 10% of the measured temperatures. The predicted temperature distribution is correlated with the HAZ and a critical temperature range (840-890 1C) corresponding to the maximum depth of the HAZ is identified using a combination of metallography, hardness testing, and thermal modeling.
onMelt-Pool Characteristics in LaserWelding of Metals
2018
Laser welding of metals involves with formation of a melt-pool and subsequent rapid solidification, resulting in alteration of properties and the microstructure of the welded metal. Understanding and predicting relationships between laser welding process parameters, such as laser speed and welding power, and melt-pool characteristics have been the subjects of many studies in literature because this knowledge is critical to controlling and improving laser welding. Recent advances in metal additive manufacturing processes have renewed interest in the melt-pool studies because in many of these processes, part fabrication involves small moving melt-pools. *e present work is a critical review of the literature on experimental and modeling studies on laser welding, with the focus being on the influence of process parameters on geometry, thermodynamics, fluid dynamics, microstructure, and porosity characteristics of the melt-pool. *ese data may inform future experimental laser welding stud...
Finite element modeling of transmission laser microjoining process
Journal of Materials Processing Technology, 2007
Use of laser beam in high precision joining of two dissimilar materials has become a very useful technique. It has potential application in biomedical implants and their encapsulation process. In this research, a numerical method is developed using finite element technique to determine the optimum condition of jointing two dissimilar materials namely titanium and polyimide. Non-uniform discretization with large number of elements in the areas of high temperature gradients were used. The accuracy of the current numerical model was verified by comparing sample results with experimental data and good match was found. This gave us the confidence that the current method can be used for other combination of materials. It was observed that for a particular value of the laser power, good bonding between the dissimilar materials is a function of laser scanning speed. Too high speed will not produce any significant increase in temperature at the bimaterial interface to have a good chemical bonding. On the other hand, too slow speed will cause excessive increase in temperature resulting in burnout condition for polyimide. For the ranges of parameters investigated in the current study, it was observed that for a leaser heat flux of 4.0 W, good bonding occurs for a laser scanning speed between 600 and 2000 mm/min. It was also observed that increased scanning speed causes the temperature contour to stretch in the horizontal direction.
Computer Methods in Applied Mechanics and Engineering, 2018
A 3D finite element model is developed to study heat exchange during metal selective laser melting (SLM). The approach is conducted on the scale of the part to be formed, using a level set framework to track the interface between the constructed workpiece and non-melted powder, and interface between the gas domain and the successive powder bed layers. In order to keep sustainable the computational efficiency, the powder bed deposition and the energy input are simplified by the scale of an entire layer or fractions of each layer. Layer fractions are identified directly from a description of the global laser scan plan of the part to be built. Each fraction is heated during a time interval corresponding to the exposure time to the laser beam, and then cooled down during a time interval equal to the scan time for the considered layer fraction. The global heat transfer through the part under additive construction and through the powder material non-exposed to the laser beam is simulated. To reduce the computational cost, a refining and de-refining mesh adaptation is carried out with a conform mesh strategy. Mesh sensitivity tests and validation of energy conservation are discussed. The proposed model is able to predict the temperature distribution and evolution in the constructed workpiece and non-melted powder during the SLM process at the macroscale, for parts of complex geometry. Application is shown for a nickel based alloy (IN718), but the numerical model can be easily extended to other materials by using their data sets.
Development and Modeling of Laser Micromachining Techniques
Laser micromachining has great potential as a MEMS (micro-electromechanical systems) fabrication technique because of its materials flexibility and 3D capabilities. The machining of deep polymer structures with complex, well-defined surface profiles is particularly relevant to micro-fluidics and micro-optics. This paper presents the use of projection ablation methods to fabricate structures and devices aimed at these application areas. A better understanding of the mechanisms of thermodynamics and heat transfer in MEMS is desired to improve the thermal performance of MEMS due to the importance of these physical processes. Ablation rate of the laser depends on temperature, the material properties and accumulation of heat in the work material. In consequence, to control the laser processing, thermal distribution of the sample has to be determined, which can be made by modeling of laser ablation. By using such modeling tool, proper laser parameters can be determined easier and faster. Geometry of the domain under investigation varies during the simulation, because laser pulses remove material from the sample, thermal effects, photochemical and other phenomena still exist and so the modeling of laser ablation is a specialised problem. A two dimensional finite element model is developed in this work for laser ablation of polymers. Model has been further modified for fabrication of curved sufaces utilized in MEMS applications.
The Open Automation and Control Systems Journal, 2012
The objectives of this work are to study Laser Engineered Net Shaping (LENS TM) produced materials and identify the microstructures. Numerical method was used to examine the influence of materials' type and LENS TM process parameters on the forming of the specific microstructures from thermodynamics and fluid dynamics point of view. Samples of 316L stainless steel were examined, microstructures of samples were used to estimate the corresponding cooling rate, and the cooling rate was compared with the results of three different levels of simplified models.
Modelling of Selective Laser Melting Process for Additive Manufacturing
Acta Metallurgica Slovaca, 2020
The proposed model is a numerical tool for designing processing windows suitable to metal alloy. The model is validated fitting experimental measures of track width, depth and cross sectional area from three literature sources. Effective liquid pool thermal conductivity laser absorptivity and depth of application of laser energy are here considered as fitting parameters. Laser absorptivity and depth of application of laser energy result to rise almost linearly with increasing specific energy.. The obtained results give confidence about the possibility of using the model as a predicting tool after further calibration on a wider range of metal alloys.
Laser micro-welding of aluminum alloys: experimental studies and numerical modeling
The International Journal of Advanced Manufacturing Technology, 2010
Experimental and numerical studies were conducted on the effects of the laser beam pulse shaping in the time domain on the quality of the welding seam in laser micro-welded AlMg3 with a thickness of 0.2 mm and 1 mm thick AlMg4.5 Mg foils, respectively. The pulse shaping was realized by a time sequence of three different rectangular pulses with different duration and power level. The first pulse was used to pre-heat the sample, welding occurred with the second pulse and the third pulse controlled the melt pool behavior. The power level and the duration of the single pulses were varied systematically and the resulting microstructure was analyzed by scanning electron microscope. The experiments were accompanied by numerical simulations based on a finite volume model which considers the transient heat flow, melt convection and the evolution of a gas capillary during the deep penetration welding process.