Numerical modelling of heat transfer and fluid flow in laser microwelding (original) (raw)
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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.
Journal of Engineering Materials and Technology, 2010
Detailed analysis of a residual stress profile due to laser microjoining of two dissimilar biocompatible materials, polyimide (PI) and titanium (Ti), is vital for the long-term application of bio-implants. In this work, a comprehensive three-dimensional (3D) transient model for sequentially coupled thermal/mechanical analysis of transmission laser (laser beam with wavelength of 1100 nm and diameter of 0.2 mm) microjoining of two dissimilar materials has been developed by using the finite element code ABAQUS, along with a moving Gaussian laser heat source. First the model has been used to optimize the laser parameters like laser traveling speed and power to obtain good bonding (burnout temperature of PI>maximum temperature of PI achieved during heating>melting temperature of PI) and a good combination has been found to be 100 mm/min and 3.14 W for a joint-length of 6.5 mm as supported by the experiment. The developed computational model has been observed to generate a bonding z...
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.
International Journal of Materials and Product Technology, 2015
A three-dimensional transient simulation for thermal and thermal stress analysis of transmission laser microjoining of dissimilar materials is performed. The laser beam moving at a velocity passes through the transparent glass (Gl), gets absorbed by the absorbing silicon (Si), and eventually softens/melts the Gl to form the bond. A good comparison is observed between the computational and experimental bond widths. Through computational optimisation of process parameters, it is observed that at a laser velocity of 30 mm/min with an initial dwell time of about four seconds good bonding was obtained with increasing bond widths. Acceleration is added which results in a uniform bond width. Subsequently, room temperature residual stress profiles of the microjoint are calculated. Stress profiles on both the Gl and Si surfaces show similar trend. At room temperature both the surfaces show low stresses which do not cross the tensile or the compressive strengths of the respective materials.
Laser-assisted micromachining techniques: an overview of principles, processes, and applications
Laser-assisted micro-machining (LAMM) has emerged as a transformative technology in precision manufacturing, enabling the creation of highly intricate micro-features on various materials. This paper provides a foundational overview of LAMM technology, exploring its fundamentals, methods, and applications. The construction of the LAMM temperature field is examined because it is crucial to improve its efficiency and cost-effectiveness. The study delves into the development of industrial femtosecond laser micromachining systems, explores fabrication techniques using LAMM, and discusses its role in the production of ceramics and semiconductors. Furthermore, it examines the capabilities of LAMM in creating 3D microstructures and explores the materials commonly used in laser micromachining. Overall, this paper gives valuable insights into the possible uses of laser-based micromachining technologies in various domains, such as the semiconductor industry, microfluidics, optics, etc. and emphasises the need for additional research to overcome its limitations and increase efficiency and cost-effectiveness.
Effect of Process Parameters and Material Properties on Laser Micromachining of Microchannels
Micromachines, 2019
Laser micromachining has emerged as a promising technique for mass production of microfluidic devices. However, control and optimization of process parameters, and design of substrate materials are still ongoing challenges for the widespread application of laser micromachining. This article reports a systematic study on the effect of laser system parameters and thermo-physical properties of substrate materials on laser micromachining. Three dimensional transient heat conduction equation with a Gaussian laser heat source was solved using finite element based Multiphysics software COMSOL 5.2a. Large heat convection coefficients were used to consider the rapid phase transition of the material during the laser treatment. The depth of the laser cut was measured by removing material at a pre-set temperature. The grid independent analysis was performed for ensuring the accuracy of the model. The results show that laser power and scanning speed have a strong effect on the channel depth, whi...
Technology and Properties of Peripheral Laser-Welded Micro-Joints
Materials, 2021
This article presents the results of research on the technology and peripheral properties of laser-welded micro-couplings. The aim of this research was to determine the characteristics of properly made joints and to indicate the range of optimal parameters of the welding process. Thin-walled AISI 316L steel pipes with diameters of 1.5 and 2 mm used in medical equipment were tested. The micro-welding process was carried out on a SISMA LM-D210 Nd:YAG laser. The research methods used were macroscopic and microscopic analyses of the samples, and assessment of the distribution of elements in the weld, the distribution of microhardness and the tear strength of the joint. As a result of the tests, the following welding parameters are recommended: a pulse energy of 2.05 J, pulse duration of 4 ms and frequency of 2 Hz, beam focusing to a diameter of 0.4 mm and a rotation speed of 0.157 rad/s. In addition, the tests show good joint properties with a strength of more than 75% of the thinner pi...
Micromanufacturing: A review—part II
Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture
This article discusses an overview of microforming, microcasting and microwelding processes. In the case of microforming, the processes reviewed are micro deep drawing, microforging, microextrusion, microrolling, microstamping, microhydroforming and incremental microforming. This section also throws some light on how the lasers have been used for microbending and micropunching purposes. The work done in the area of physics of microforming processes has also been discussed briefly. This article also deals with different types of microcasting processes particularly permanent mold and investment microcasting processes. The applications of these microcasting processes have been specified in different fields of engineering, biomedical and so on. Some areas in which further research work is needed have been identified. It includes both theoretical and experimental works which need attention. The last part of this article deals with microjoining in general and laser microjoining in particular. This section discusses the types of the lasers that are being used for microjoining purposes. The process parameters (laser, optics, system and material) have been explained, and some work done on the parametric analysis has been reported briefly. Various applications of laser microjoining have been elaborated before the last section on concluding remarks. This last section presents, in very brief, the areas in which further work is required in microjoining processes.
Pulsed Laser Assisted Micromilling for Die/Mold Manufacturing
ASME 2007 International Manufacturing Science and Engineering Conference, 2007
Laser assisted machining is an alternative to conventional machining of hard and/or difficult-to-process materials which involves pre-heating of a focused area with a laser beam over the surface of the workpiece to cause localized thermal softening along the path of the cutting action. The main advantage that laser assisted machining has over conventional machining is the increased material removal rate and productivity. Laser assisted micromilling is a scaled down derivative of laser assisted machining assuming that the process effectiveness potentially exists at the meso/micro scale. It is well-known that continuous-wave (c.w.) lasers generate a wide and deep heat affected zone, and can cause microstructure alterations, potentially making laser assistance counter-productive at the meso/micro scale. The novel use of a pulsed laser in assisting micromilling enables processing of die/mold metal alloys that are typically hard and/or difficult-to-process in micro scale, while reducing the heat affected zone. A fairly innovative technique is introduced by thermally softening only the focused microscale area of the work material with induced heat from a pulsed laser, and material removal is performed immediately with micro mechanical end milling. The focus of this paper is to present a fundamental understanding of the pulsed laser assisted micromilling (PLAM), in particular, to investigate the influence of pulsing on microscale localized thermal softening by coupling with the finite element simulation of the micromilling process. Experiments and Finite element method-based process simulations for micromilling of AISI 4340 steel with and without the laser assistance are conducted to study the influence of the pulsed laser thermal softening on the reduction in cutting forces and its influence on the temperature rise in the cutting tool.
Modification of an ophthalmic laser for micro-joining on MEMS
SPIE Proceedings, 2008
The requirement to make low profile ohmic contacts to a piezo-resistive MEMS pressure sensor has highlighted limitations of ultrasonic wire bonding technology. Wire bonding typically uses 25-50 m diameter gold or aluminium wire and ultrasonic welding to the contact pads of micro-electronic devices results in a contact wire proud of the pad surface. If the application involves the MEMS pressure sensor and contacts being encapsulated, then repetitive changes in pressure flexing the contact wires can lead to fracture. A possible solution is to scale down laser welding technology to fuse materials at the micron scale. For this purpose a precision ophthalmic surgical laser system has been modified to investigate optimum conditions for laser welding, both at the micron scale and for the typical geometries involved. Typical requirements involve a cylindrical contact wire to be bonded to a thin contact pad on the MEMS device. Since the pad size is of similar dimension to the wire, and the requirement for a low profile stable configuration, a keyhole welding strategy is required. The Nd:YAG based ophthalmic laser has been modified, the Q-switch removed and the output pulse width and energy controlled principally via control of the flashlamp.