Showing papers by "Yung C. Shin published in 2007"
TL;DR: In this article, a new hybrid burnishing process, laser-assisted burnishing (LAB), is proposed and investigated experimentally in the present study, where the workpiece surface layer is temporarily and locally softened by a controllable laser beam, and then immediately processed by a conventional burnishing tool.
Abstract: Burnishing has been widely used to produce excellent surface finish, work hardening and compressive residual stress by plastically deforming the workpiece surface layer. However, conventional burnishing is difficult on hard materials, because an excessive burnishing force might be required. A new hybrid burnishing process, laser-assisted burnishing (LAB), is proposed and investigated experimentally in the present study. During LAB, the workpiece surface layer is temporarily and locally softened by a controllable laser beam, and then immediately processed by a conventional burnishing tool. LAB and conventional burnishing experiments were conducted on MP35N, annealed and hardened AISI 4140, respectively, to evaluate the effect of laser power on the burnishing results. Because more plastic deformation occurs in LAB than in conventional burnishing, thanks to the temporary softening of workpiece material prior to burnishing, it is shown by these experiments that LAB can produce much better surface finish, higher surface hardness and similar compressive residual stress compared to its conventional counterpart.
70 citations
TL;DR: In this paper, an accurate predictive modeling of the laser hardening process in terms of laser operating parameters and initial microstructure without the need of any experimental data is presented. But the model does not provide the diagrams that are useful for predicting hardness profiles, optimizing practical process parameters and assessing the potential of laser hardens for different steels.
Abstract: This paper presents accurate predictive modeling of the laser hardening process in terms of laser operating parameters and initial microstructure without the need of any experimental data. The model provides the diagrams that are useful for predicting hardness profiles, optimizing practical process parameters and assessing the potential of laser hardening for different steels. It is shown that the hardness and depth of the hardened layer in hypoeutectoid steels (carbon wt% The model combines a three-dimensional transient numerical solution for a rotating cylinder undergoing laser heating by a translating laser beam with a kinetic model describing pearlite dissolution, carbon redistribution in austenite and subsequent transformation to martensite by utilizing the feedback from the CCT diagram. In order to validate the thermal model and assert the accuracy of temperature predictions the temperature was measured using an infrared camera and a good agreement between the predicted and measured temperatures is shown. Results are presented as processing maps, which show how the case depth and hardness depend on input operating parameters. The good agreement between the measured and predicted hardness profiles ascertains the accuracy of the thermal-kinetic model developed for AISI5150H steels.
56 citations
TL;DR: It is shown that for nanosecond laser metal ablation in air at sufficiently high intensity, the dominant physical mechanism for mass transfer from the condensed phase to the plasma plume is hydrodynamic expansion instead of surface evaporation.
Abstract: It has been generally believed in literature that in nanosecond laser ablation, the condensed substrate phase contributes mass to the plasma plume through surface evaporation across the sharp interface between the condensed phase and the vapor or plasma phase. However, this will not be true when laser intensity is sufficiently high. In this case, the target temperature can be greater than the critical temperature, so that the sharp interface between the condensed and gaseous phases disappears and is smeared into a macroscopic transition layer. The substrate should contribute mass to the plasma region mainly through hydrodynamic expansion instead of surface evaporation. Based on this physical mechanism, a numerical model has been developed by solving the one-dimensional hydrodynamic equations over the entire physical domain supplemented by wide-range equations of state. It has been found that model predictions have good agreements with experimental measurement for plasma front location, temperature, and electron number density. This has provided further evidence (at least in the indirect sense), besides the above theoretical analysis, that for nanosecond laser metal ablation in air at sufficiently high intensity, the dominant physical mechanism for mass transfer from the condensed phase to the plasma plume is hydrodynamic expansion instead of surface evaporation. The developed and verified numerical model provides useful means for the investigation of nanosecond laser-induced plasma at high intensities.
46 citations
TL;DR: In this paper, a multiscale finite element model is developed to simulate the chip formation in laser-assisted machining of silicon nitride ceramics, which reveals that discontinuous chips form by the propagation of cracks in the shear zone while the machined surface is generated by plastic deformation of the workpiece material under high pressure.
Abstract: A multiscale finite element model is developed to simulate the chip formation in laser-assisted machining of silicon nitride ceramics. To consider the workpiece heterogeneous microstructure and crack evolution in silicon nitride machining, the workpiece material is modeled with continuum elements imbedded in thin interfacial cohesive elements. The continuum elements simulate the deformation of the bulk workpiece while the interfacial cohesive elements account for the initiation and propagation of intergranular cracks. The model reveals that discontinuous chips form by the propagation of cracks in the shear zone while the machined surface is generated by plastic deformation of the workpiece material under confined high pressure. The simulated cutting forces, chip morphology and subsurface integrity are compared with corresponding experimental observations and the validity of the present model is shown by the good agreements in the comparisons.
45 citations
TL;DR: In this article, a 2D axisymmetric model is developed by numerically solving the hydrodynamic equations, supplemented with appropriate equations of state of water and the coating material.
Abstract: In laser shock peening (LSP) under a water-confinement regime, laser-matter interaction near the coating-water interface can induce very high pressures in the order of gigapascals, which can impart compressive residual stresses into metal workpieces to improve fatigue and corrosion properties. For axisymmetric laser spots with finite size, the pressure generation near the water-coating interface is a two dimensional process in nature. This is in particular the case for microscale LSP performed with very small laser spots, which is a very promising technique to improve the reliability performance of microdevices. However, models capable of predicting two dimensional (2D) spatial distributions of the induced pressures near the coating-water interface in LSP have rarely been reported in literature. In this paper, a predictive 2D axisymmetric model is developed by numerically solving the hydrodynamic equations, supplemented with appropriate equations of state of water and the coating material. The model can p...
39 citations
TL;DR: In this paper, a simplified model that is easy to apply but at the same time can also provide reasonably accurate predictions of ablation depth is presented, which has been found to be applicable for laser pulse duration up to 10 ps based on comparisons of model predictions with experimental measurements.
37 citations
TL;DR: In this paper, a self-closed model is developed by numerically solving the one-dimensional hydrodynamic equations, supplemented with appropriate equations of state of water and the coating material.
Abstract: In laser shock peening (LSP) under a water-confinement regime, laser-matter interaction near the coating-water interface can induce very high pressures in the order of gigapascal, which can impart compressive residual stresses into metal workpieces to improve fatigue and corrosion properties. However, self-closed models with spatial distribution considerations for the induced pressures near the coating-water interface in LSP are rarely reported in literature. In this paper, a self-closed model is developed by numerically solving the one-dimensional hydrodynamic equations, supplemented with appropriate equations of state of water and the coating material. The model can produce the one-dimensional spatial distributions of the material responses near the water-coating interface in LSP. The model-predicted pressures have been compared with experimental measurements under a variety of conditions typical for LSP, and good agreements have been found for both the transient pressure history and the peak pressure magnitude.
34 citations
TL;DR: Li et al. as discussed by the authors presented a systematic study on the chatter characteristics of cylindrical plunge grinding processes, and the unique transient chatter behaviors during spark-in and spark-out of plunge grinding are also studied; and the transient chatter occurrence is separated from the steady-state chatter occurrence, which is used to define the chatter boundaries.
Abstract: This paper presents a systematic study on the chatter characteristics of cylindrical plunge grinding processes. Chatter occurrence under a wide range of operating conditions is experimentally identified. The unique transient chatter behaviors during spark-in and spark-out of plunge grinding are also studied; and the transient chatter occurrence is separated from the steady-state chatter occurrence, which is used to define the chatter boundaries. It is shown that the measured structure dynamics of the wheel/workpiece exhibit strong dependency on grinding conditions. The dynamic/chatter model of cylindrical plunge grinding [H. Li, Y.C. Shin, A time-domain dynamic model for chatter prediction of cylindrical plunge grinding processes, ASME Journal of Manufacturing Science and Engineering 128(2) (2006) 404–415] is improved to handle the grinding force-dependent structure dynamics, and the modified model is validated by comparing the predicted chatter boundaries with experimental chatter conditions.
30 citations
TL;DR: The applicability of the proposed method is suggested as an alternative way to derive the system multivariable interaction when the system mathematical model is not available.
25 citations
TL;DR: In this article, a multi-level fuzzy control (MLFC) technique is developed and implemented for a creep-feed grinding process, where the grinding force is maintained at the maximum allowable level under varying depth of cut, so that the highest metal removal rate is achieved with a good workpiece surface quality.
Abstract: In this paper, a multi-level fuzzy control (MLFC) technique is developed and implemented for a creep-feed grinding process. The grinding force is maintained at the maximum allowable level under varying depth of cut, so that the highest metal removal rate is achieved with a good workpiece surface quality. The control rules are generated heuristically without any analytical model of the grinding process. Based on the real-time force measurement, the control parameters are adapted automatically within a stable range. A National Instrument real-time control computer is implemented in an open architecture control system for the grinding machine. Experimental results show that the cycle time has been reduced by up to 25% over those without force control and by 10-20% compared with the conventional fuzzy logic controller, which indicates its effectiveness in improving the productivity of actual manufacturing processes. The effect of grinding wheel wear is also considered in the creep-feed grinding process, where the grinding force/power can be maintained around the specified value by the proposed MLFC controller as the wheel dulls gradually.
22 citations
TL;DR: In this paper, the authors present the current development of the Generalized Intelligent Grinding Advisory System (GIGAS), which provides a systematic way of modelling complex grinding processes and finding optimal process conditions while meeting the general class of process requirements.
Abstract: The paper presents the current development of the Generalized Intelligent Grinding Advisory System (GIGAS), which provides a systematic way of modelling complex grinding processes and finding optimal process conditions while meeting the general class of process requirements. GIGAS provides a way of incorporating three different types of knowledge, including analytical models, experimental data and heuristic knowledge from experts, to describe complex grinding processes. The developed optimization algorithm can handle various optimization problems including different grinding processes and optimization objectives. Case studies are presented for surface grinding and cylindrical plunge-grinding with various optimization objectives to demonstrate its capability of performing optimization. The overall architecture and the developed software with the graphical user interface are described.
TL;DR: Laser transformation hardening in the solid state is shown to successfully provide a surface hardness increase of almost 40% for Ti-6Al-4V with a case depth over 2.5 mm while reducing surface damag...
Abstract: Laser transformation hardening in the solid state is shown to successfully provide a surface hardness increase of almost 40% for Ti–6Al–4V with a case depth over 2.5 mm while reducing surface damag...
TL;DR: In this paper, the authors presented a comprehensive dynamic model that simulates infeed centerless grinding processes and predicts their instability-related characteristics by considering the complete two-dimensional kinematics, dynamics, surface profiles and geometrical interactions of the workpiece with the grinding wheel, regulating wheel, and supporting blade.
Abstract: This paper presents a comprehensive dynamic model that simulates infeed centerless grinding processes and predicts their instability-related characteristics. The new model has the unique ability of accurately predicting the coupled chatter and lobing process of a multi-degree of freedom and two-dimensional centerless grinding system by considering its critical issues. First, the model considers the complete two-dimensional kinematics, dynamics, surface profiles, and the geometrical interactions of the workpiece with the grinding wheel, regulating wheel, and supporting blade. Second, a two-dimensional distributed grinding force model along the contact length is adopted and modified for centerless grinding processes as a function of normalized uncut chip thickness. The forces of the work holding system are determined by balancing the grinding force and accordingly the work holding instability can be identified as well. Third, a two-dimensional contact deformation model under the condition of general surface profiles or pressure distributions is developed for the contacts of the workpiece with the grinding wheel, regulating wheel, and supporting blade. The new model is validated by comparing the predicted chatter and lobing occurrences with experimental results.
Patent•
12 Oct 2007TL;DR: An integrated laser material processing cell as mentioned in this paper allows laser-assisted machining to be used in conjunction with directed material deposition in a single setup, achieving greater geometric accuracy and better surface finish than currently possible in existing laser freeform fabrication techniques.
Abstract: An integrated laser material processing cell allowing laser-assisted machining to be used in conjunction with directed material deposition in a single setup, achieving greater geometric accuracy and better surface finish than currently possible in existing laser freeform fabrication techniques. The integration of these two processes takes advantage of their common use of laser beam heat to process materials. The cell involves a multi-axis laser-assisted milling machine having a work spindle, a laser emitter, and means for positioning the emitter with respect to the spindle so as to direct a laser beam onto a localized area of a workpiece in proximity to a cutting tool mounted in the spindle. A powder delivery nozzle mounted on the machine and positioned adjacent to the emitter delivers powder to a deposition zone in the path of the beam, such that material deposition and laser-assisted milling may be performed substantially simultaneously in a single workspace.
01 Apr 2007
TL;DR: In this paper, a transient, three-dimensional heat transfer model is presented for LAD of superabrasive grinding wheels, where the effective thermophysical properties of the porous heterogeneous wheel are calculated and applied to the thermal model.
Abstract: Laser-assisted dressing (LAD) has been proposed to prepare efficiently superabrasive grinding wheels by significantly reducing dressing forces and dresser wear. In this paper, a transient, three-dimensional heat transfer model is presented for LAD of superabrasive grinding wheels, where the effective thermophysical properties of the porous heterogeneous wheel are calculated and applied to the thermal model. Temperature measurements are conducted with an infrared camera and the excellent agreement between the measured and predicted temperatures show the validation of the present model for LAD of grinding wheels or, generally, laser-assisted machining of composite materials. To evaluate the influence of LAD on superabrasive wheels, grinding tests were carried out using a CBN wheel prepared by conventional and laser-assisted dressing respectively. The grinding tests show that LAD under proper conditions could improve the performance of CBN wheels.
TL;DR: In this article, a simple two-stage model for the formation and expansion of the plasma induced by high intensity nanosecond laser metal ablation in vacuum has been developed, which is easy to apply and has very small computational cost.
01 Jan 2007
TL;DR: In this article, a 4.0 kW HPDDL was used to perform blown-powder cladding on AISI 4140 and aISI 5150 steel shafts.
Abstract: Blown-powder laser cladding is an efficient method for enhancing the surface properties of engineering components while preserving the properties of the base material. High power direct diode lasers (HPDDLs) offer wide beams with nearly uniform intensity distribution, allowing the deposition of wide clad tracks with flatter profiles than those produced with a Gaussian beam. In this work, a 4.0 kW HPDDL is used to perform blown-powder cladding on AISI 4140 and AISI 5150 steel shafts. The first part of the experiments concerns two-layer circumferential tracks created from two commonly used hardfacing alloys: Stellite 6 (Co-Cr alloy) and Nistelle 625 (Ni-Cr alloy). The effects of laser power and powder feed rate on the clad geometry are assessed. Increasing the powder feed rate and holding constant all other parameters decreases the track width-to-thickness aspect ratio. All tracks exhibit dendrite microstructures that are characteristic of powder-based clad tracks. The tracks exhibit no cracks or porosity. Energy dispersive X-ray (EDX) analysis reveals dilution of five percent or less between the clad and substrate materials. The second part of the experiments concerns overlapping of single-layer clad tracks in a continuous helical pattern on the substrate to form a layer that covers a large area. Clad layer thickness and inter-track porosity are measured to determine the optimum degree of overlap for producing a high-quality clad layer. The thickness of the resulting Stellite 6 and Nistelle 625 clad layers decreases as the overlap percentage decreases. No inter-track, interfacial, or bulk pores are present for any tests, comprising overlap percentages of 50% and lower.© 2007 ASME
24 Jun 2007
TL;DR: A novel method of systematically constructing the fuzzy inverse model for a general multi-input single-output (MISO) system represented with triangular input membership functions, singleton output membership function and fuzzy-mean defuzzification is presented.
Abstract: This paper presents a novel method of systematically constructing the fuzzy inverse model for a general multi-input single-output (MISO) system represented with triangular input membership functions, singleton output membership function and fuzzy-mean defuzzification. The fuzzy inverse model construction method has the ability of uniquely determining the inverse relationship for each input-output pair. It is derived in a straightforward way and the required input variables can be simultaneously obtained by the fuzzy inferencing calculation to realize the desired output value. Simulation examples are provided to demonstrate the effectiveness of the proposed method to find the inverse kinematics solutions for complex industrial robot manipulators.