Soundarapandian Santhanakrishnan

Laser assisted crystallization of ferromagnetic amorphous ribbons: A multimodal characterization and thermal model study

This paper focuses on laser-based de-vitrification of amorphous soft magnetic Fe-Si-B ribbons and its consequent influence on the magnetic properties. Laser processing resulted in a finer scale of crystallites due to rapid heating and cooling during laser annealing compared to conventional furnace annealing process. A significant increase in saturation magnetization is observed for laser-annealed ribbons compared to both as-received and furnace annealed samples coupled with an increase in coercivity compared to the as received samples. The combined effect of thermal histories and stresses developed during laser annealing results in the formation of nano-crystalline phase along the laser track. The phase evolution is studied by micro-XRD and TEM analysis. Solute partitioning and compositional variation within the phases are obtained by Local Electrode Atom probe analysis. The evolution of microstructure is rationalized using a Finite Element based heat transfer multi-physics model.

Stress-induced selective nano-crystallization in laser-processed amorphous Fe–Si–B alloys

It is shown that laser processing results in localized compressive stresses in amorphous Fe–Si–B, leading to homogeneous nano-crystallization at the edges of the laser track. The mechanism can be attributed to enhanced diffusivity at these edges, resulting from a reduced diffusion activation barrier, which has been calculated by coupling the results of a thermal model with microstructural characterization.

Laser coating of hydroxyapatite on Mg for enhanced physiological corrosion resistance and biodegradability

Abstract This paper addresses the critical issues associated with using conventional bioimplants (stainless steel, cobalt–chromium and titanium alloy), and it emphasises on Mg as a potential material for fabricating load bearing bioimplants (hip, knee, shoulder and elbow). Hydroxyapatite (HAp) is a well established biodegradable coating material, while its combination with Mg enhances its corrosion resistance and biodegradability, thereby extending its longevity as a bioimplant material. A laser (2 kW IPG ytterbium of 1064 nm) coating of HAp on Mg alloy (AZ31B) was achieved under different processing conditions, and its corrosion behaviour and biodegradability were studied in simulated body fluid. Preliminary results indicate an improved corrosion resistance (48%) and biodegradability (180%) of AZ31B coated with HAp for selected laser process variables (power, scanning speed and beam indexing). Further, a detailed investigation is in progress in efforts to address many critical issues related to the fabrication and longevity of load bearing bioimplants.

Process parameters analysis of high power direct diode laser cladding

The one-step cladding by using a high power direct diode laser (HPDDL) compared to a CO2 or a Nd:YAG laser is found to be a cost-effective process for repairing or building valued components and tools that are used in an automotive, aerospace, nuclear, and defense industries. Whereas, number of processing parameters such as laser power, scanning speed, powder feed rate, laser focal spot, and thermo-physical properties of the materials are involved in the process to achieve the desired geometrical features (size and shape) of the clad, and the surface properties (hardness, resistance to heat, wear, and corrosion). Numerical simulation is a cost-effective technique to predict the effect of processing parameters on the variation of geometry of the clad and the surface properties.In this study, an experimentally-based finite element (FE) thermal model coupled with thermo-kinetic equations is developed to predict the temperature history and hardness of the cladding process. The temperature-dependent material properties and phase change kinetics are taken into account in this model. As-used experimental boundary conditions are adopted in this model.A 2-kW direct diode laser of 808 nm in wavelength, rectangular-shaped laser spot of 12 mm×1 mm with uniform distribution (top-hat) of laser power is used to carry out the experiments. An off-axis powder injection system is used to deposit tool steel H13 on the AISI 4140 steel substrate. Metallurgical characterization and hardness measurements are performed to quantify the effect of processing parameters on the variation of geometrical features of the clad and its hardness.The one-step cladding by using a high power direct diode laser (HPDDL) compared to a CO2 or a Nd:YAG laser is found to be a cost-effective process for repairing or building valued components and tools that are used in an automotive, aerospace, nuclear, and defense industries. Whereas, number of processing parameters such as laser power, scanning speed, powder feed rate, laser focal spot, and thermo-physical properties of the materials are involved in the process to achieve the desired geometrical features (size and shape) of the clad, and the surface properties (hardness, resistance to heat, wear, and corrosion). Numerical simulation is a cost-effective technique to predict the effect of processing parameters on the variation of geometry of the clad and the surface properties.In this study, an experimentally-based finite element (FE) thermal model coupled with thermo-kinetic equations is developed to predict the temperature history and hardness of the cladding process. The temperature-dependent material p...

A thermo-kinetic phase transformation model for multi-pass laser heat treatment by using high power direct diode laser

When a larger surface area is heat treated, multiple scans by laser beam with slightly overlaps are applied. Under this condition, a tempered zone is formed in overlapped regions that will affect the uniformity of heat treated depth of material. In this study, an experimentally-based finite element (FE) thermal model coupled with thermo-kinetic equations is developed to predict the cross-sectional as well as surface temperature history, phase transformations, and hardness of multi-pass laser heat treatment (MPLHT) process. The temperature-dependent material properties and phase change kinetics are taken into account in the model. As-used experimental boundary conditions are incorporated in this model. A tool steel AISI S7 is heat treated by changing the laser power (1400-1800 W) and scanning speeds (15-25 mm/s) while keeping a constant size of overlap (25% of length of laser beam). The tempering effect of the MPLHT process is studied for different lengths of scan (10-35 mm). The thermo-kinetic phase transformation model results are verified with experimental ones to optimize the processing parameters. The optimized processing parameters, including laser power, scanning speed, size of overlap, and the length of scan are used to achieve a uniform hardness distribution and an even depth of heat treatment in the multi-pass laser heat treated area.When a larger surface area is heat treated, multiple scans by laser beam with slightly overlaps are applied. Under this condition, a tempered zone is formed in overlapped regions that will affect the uniformity of heat treated depth of material. In this study, an experimentally-based finite element (FE) thermal model coupled with thermo-kinetic equations is developed to predict the cross-sectional as well as surface temperature history, phase transformations, and hardness of multi-pass laser heat treatment (MPLHT) process. The temperature-dependent material properties and phase change kinetics are taken into account in the model. As-used experimental boundary conditions are incorporated in this model. A tool steel AISI S7 is heat treated by changing the laser power (1400-1800 W) and scanning speeds (15-25 mm/s) while keeping a constant size of overlap (25% of length of laser beam). The tempering effect of the MPLHT process is studied for different lengths of scan (10-35 mm). The thermo-kinetic phase trans...

A Three-Dimensional Transient Modeling and Experimental Analysis of Laser Transformation Hardening by Using High Power Direct Diode Laser

Laser transformation hardening (LTH) based on rapid heating and cooling cycles produce hard and wear-resistant layers of the metallic component. A high intensity moving laser beam heats up the thin layer of the external surface of the component without damaging the bulk of material. The metallurgical transformations taking place in the material during the thermo-kinetic cycles could effectively improve the mechanical properties of its surface. Nowadays, a high power direct diode laser (HPDDL) has been accepted by industry as a valuable tool to carry out this process. A three-dimensional (3-D) transient thermo-kinetic model has been developed to predict the temperature profile of the hardened layers of the material surface. The temperature-dependence of the thermal properties of the material is taken into account in the model. The laser beam is considered as a moving line heat source with a uniform distribution of laser power. The numerical solution is obtained by using a transient 3-D heat conduction equation with convection boundary conditions at the surfaces of the workpiece. A number of experiments have been carried out to harden components of AISI S7 tool steel by a continuous wave (CW) HPDDL at different power levels (1200 W – 2000 W) and different scanning speeds (5 mm/s – 20 mm/s). The main processing parameters such as laser power and scanning speed are optimized based on the numerical analysis of the heat conduction involved in this process. The numerical simulation results are compared with results produced experimentally by a HPDDL laser operating in CW, showing good agreement.Copyright

Orthopaedic surgical robot manipulator

Nowadays robotic-based surgery is most promising one in medical field. Since the Total Knee Replacement (TKR) and Total Hip Replacement (THR) are increasing in numbers therefore it is a need for using the robots in these types of surgeries. Also, more precise bone removal rate is required in TKR and THR to fix the implants; therefore robots are needed to incorporate to remove the bone precisely. Lot of existing systems are based on industrial manipulators and also having high cost. Hence, there is a need for exclusively designing a robot for orthopaedic-related surgery with low cost and also by analyzing all the parameters involved in bone removal. So, this paper aims to design an orthopaedic surgical robot arm manipulator. The modeling results are presented and it showed reasonable matched outcome with the phantom models. Also the results are showing an encouraging trend in furthering this research.

Modeling and experimental approaches of laser system for lasik eye surgery

LASIK is one of the most common refractive eye surgeries for correcting vision problems. Refractive eye surgery is used to change the refractive state of the eye in order to let people enjoy a good vision. Refractive errors result from the inability of the eye to focus the light from the objects clearly on the retina causing blurred or in some cases zero vision. This paper deals with the development of laser system for LASIK eye surgery. Experiments were carried out on preserved cow-eyes samples with a different set of processing conditions. The ablation patches created on the cow’s corneal layer, due to laser irradiation were observed. The image of the corneal patches was acquired, and was compared with the other patches obtained from different laser energy densities. The heat transfer model was built using COMSOL, and based on the processing conditions that were supplied, the simulation was run. The results obtained from this model were the corneal peak temperature, the temperature along the line through the center of the cornea, and the ablation depth.LASIK is one of the most common refractive eye surgeries for correcting vision problems. Refractive eye surgery is used to change the refractive state of the eye in order to let people enjoy a good vision. Refractive errors result from the inability of the eye to focus the light from the objects clearly on the retina causing blurred or in some cases zero vision. This paper deals with the development of laser system for LASIK eye surgery. Experiments were carried out on preserved cow-eyes samples with a different set of processing conditions. The ablation patches created on the cow’s corneal layer, due to laser irradiation were observed. The image of the corneal patches was acquired, and was compared with the other patches obtained from different laser energy densities. The heat transfer model was built using COMSOL, and based on the processing conditions that were supplied, the simulation was run. The results obtained from this model were the corneal peak temperature, the temperature along the line throug...

Laser processing of preplaced hydroxyapatite on electron beam melted titanium alloy

Laser deposition of Hydroxyapatite, HAp biomaterial preplaced by spray coating on the coupons made of electron beam melted Ti-6Al-4V is investigated using two types of high power diode laser systems. A 2 kW, continuous wave, top hat profile, rectangular beam, High Power Direct Diode laser (HPDL) is used to compare with a 1kW power, Gaussian profile, circular beam, Fiber Coupled Diode Laser (FCDL) on the effect and efficiency of cladding, its composition and homogeneity. Evolution of microstructure and microhardness of melt and heat affected zone formed during HAp cladding of Ti6Al4V alloy are evaluated.Laser deposition of Hydroxyapatite, HAp biomaterial preplaced by spray coating on the coupons made of electron beam melted Ti-6Al-4V is investigated using two types of high power diode laser systems. A 2 kW, continuous wave, top hat profile, rectangular beam, High Power Direct Diode laser (HPDL) is used to compare with a 1kW power, Gaussian profile, circular beam, Fiber Coupled Diode Laser (FCDL) on the effect and efficiency of cladding, its composition and homogeneity. Evolution of microstructure and microhardness of melt and heat affected zone formed during HAp cladding of Ti6Al4V alloy are evaluated.