Lasers Based Manufacturing

Laser bending is a process of bending a sheet by the irradiation of laser beam on the surface of the sheet. A number of analytical and numerical methods have been proposed for the estimation of bend angle. A brief review of these methods is presented. A finite element analysis of laser bending process is carried out with ABAQUS package for the purpose of understanding the physics of the laser bending. Afterwards, a simple analytical model is developed to evaluate the bending angle in laser bending of metal sheet. The model is based on the elastic-plastic bending of sheet. It is ascertained from the experimental results available in literature that the model provides reasonably good prediction of bend angle. It is also shown that the model can be used for the quick estimation of yield stress of the material during laser bending process.

Laser forming is a comparatively recent technique which has been developed to shape metal components. It has also been applied to the forming of composite materials. In this process, thermal stresses are produced in the sheet metal by irradiating the surface of the sheet using a controlled defocused laser beam. This causes the sheet to bend, usually, towards the side of the sheet which is exposed to laser irradiation. The laser beam power, scan speed, beam size, and number of laser passes determine the shape of the final product. Laser forming is different when compared to the traditional forming techniques like bending, drawing, pressing, stamping, etc. in the sense that it is a non-contact technique. Hence, the advantage of the laser forming process for a small batch of components is its flexibility and reduction in cost and time. Research to-date on laser forming has been done theoretically, experimentally, and numerically. Effect of almost all the parameters—geometric, material and energy—affecting the shape of final product have been studied at length. Some experimental studies have been carried out using surface coating like graphite on the face of the sheet where the laser is passed. However, there are limited studies on the effect of different surface coatings on laser forming of sheets. Hence, the objective of the present work is to investigate the effect of different surface coatings on the laser forming of metal sheets. In the present work, mild steel is selected as the work material. Two different coatings, viz., commercial lime and cement are selected. First, the effect of the coatings is studied on simple line bending operation. The experiments are carried out at different values of laser power and laser scan speed for each coating. The results are compared with the results obtained from line bending of uncoated specimen. It is found that the cement coating performs better than the lime coating. Next, the effect of coatings is investigated on laser forming of complex shapes like dome and bowl shaped surfaces. For each coating the experiments are carried out at different values of laser power. It is found that the cement coated specimens can undergo more deformation than the lime coated specimens.

Recently, laser bending has received the attention for a wide variety of applications in industries due to its excellent bend quality with high productivity and flexibility. In this work, finite element simulations of bending of small sized sheets are carried out using ABAQUS package. The temperature and strain-rate dependent material properties of D36 shipbuilding steel sheet are considered. Simulation results throw light on the bending behavior of small sized sheet components.

Pulsed laser forming is a non-contact thermal forming process, where sheet metal gets plastically deformed by thermal residual stresses induced by controlled discontinuous laser irradiations. The temperature and deformation fields have been determined using finite element analysis under different processing conditions. Two types of pulsed laser forming processes, i.e., overlapped and discrete spot forming have been identified depending on the combinations of process parameters. Bending angle is found to increase with the degree of overlap and decrease with the increase of gap in case of the two types of spot forming processes. A comparative study between pulsed and continuous laser forming has also been performed using both finite element simulations and experiments. Bending angle in case of discrete spot pulsed laser forming is found to be more compared to the continuous laser forming. The results of finite element simulations have been found to be in good agreement with the experimental results.

During Laser bending process, the worksheet bends by means of thermal stresses induced by the laser beam irradiation. It can be achieved by various mechanisms viz. temperature gradient mechanism (TGM), buckling mechanism (BM) and upsetting mechanism (UM). The interactive effect of process parameters viz. laser power, scanning speed, beam diameter and absorption coefficient decide the occurrence of bending mechanism during a laser bending operation. Literature reports experimental as well numerical studies on the effect of process parameters viz. laser power, scan speed, beam diameter on the process mechanism and process performance. However, a very few attempts have been made on the study of shape of laser irradiation path on the quality and productivity of laser bending operation. Curvilinear laser bending is generally used to produce complex shapes using lasers. In this chapter an experimental study on the curvilinear laser bending of aluminum sheets for TGM and BM mechanisms has been presented. Initially the basic principle of the laser bending process and TGM and BM are discussed. Then the experimental procedure, plans are presented. The results are discussed in terms of the effect of laser power and scan speed on the bend angle and edge effect during parabolic irradiation. The experiments are carried out for both thick as well as thin worksheets. It was found that, in thin sheets, the scanning path curvature does not have significant effect on the bend angle however, in thick sheets the bend angle increases with decrease in scanning path curvature. The deformation behavior of curvilinear laser bending was found to be different from that of straight line laser bending process. The presented results may be used as guidelines to generate complex shapes in aluminum and its alloys using lasers.

Line heating assisted with laser as a heat source is a flexible forming process that forms sheet metal by means of stresses induced by external heat instead of by means of external force. The process has the potential to be applied as a primary forming method for forming accurate shapes. However successful application of this process in industry is limited due to high equipment costs and safety requirements. The production of complex shapes requires the understanding of laser-material interaction. The chapter presents the mathematical formulation of development of smooth continuous curved surface. It is developed by deformation of sheet under plane stress condition by taking into account the strain distribution and the coefficient of first fundamental form of curve surface. Surface development is carried out along principal curvature direction along with the procedure for suitable determination of heating line pattern for the desired engineering surfaces.

Aluminium and its alloys have high demand in manufacturing and service industries due to their high specific strength. Addition of different metals like Cu, Mg, Ni, Cr, and Zn provides enhanced service life. In this work, commercially available 99 % pure aluminium was alloyed with copper powder of 10 μm particles size, which was melted by CO₂ laser. Three different methods were used for uniform placing of 95 % copper powder and 5 % aluminium powder on the aluminium substrate. The result was examined by Vickers hardness test. SEM and FESEM were used for studying surface and subsurface defects. Defect free aluminium alloy with improved microstructure and enhanced mechanical properties was obtained.

In this chapter basic mechanism of laser surface modification technique has been discussed. Based on the process mechanism laser surface modification techniques are classified and discussed in brief. Specific advantages, disadvantages and applications of these processes are also explained. A brief review on laser surface modification of Aluminium substrate using different coating materials, surface modification of various engineering materials with TiC and surface modification of metallic substrate by utilizing pulse type low power laser have been presented. Finally, experimental details of TiC coating on pure Aluminium substrate using a pulsed Nd:YAG laser has been discussed. Effect of laser peak power and pulse overlapping on the Aluminium substrate by pre-placing TiC powder has been analyzed experimentally. Optical images of the cross-sectional view of the laser irradiated samples show successful formation of coating. Experimental results also show that, increase in laser peak power and pulse overlapping increases the coating thickness. High peak power results in removal of coating material but produces TiC mixed Aluminium layer at the top surface of substrate. Micro-hardness profile on the coating shows improvement in hardness up to 20 times than that of as received Aluminium substrate.

Laser cladding is a coating technique, wherein several layers of clad materials are deposited over a substrate so as to enhance the physical properties of the work-piece such as wear resistance, corrosion resistance etc. Strong interfacial bond with minimum dilution between the material layers is a pre-requisite of the process. This technique also finds widespread applications in repair and restoration of aerospace, naval, automobile components. A thermomechanical finite element models is developed wherein the Gaussian moving heat source is modelled along with element birth and death technique to simulate powder injection laser cladding of CPM9V over H13 tool steel, which is extensively used for repair of dies. The present work focuses on predicting the clad geometry and other clad characteristics such as the heat affected zone, dilution region and the subsequent residual stress evolution. It is expected that this knowledge can be used for repair of structures subjected to cyclic thermomechanical loads.

Non-conventional, non-contact type advanced machining process like laser based micro machining process is widely used in modern industries for producing components with geometrically complex profiles. Though laser based micro machining of polymer, by and large, is a cold ablation process, photo thermal process associated with the laser heating may affect the surface characteristics. This chapter starts with an introduction to various excimer laser sources and proceeds to micromachining application areas with specific reference to polymers. The study of excimer laser micromachining in different gaseous media, conducted by the authors is elaborated further. This study was conducted to ascertain the impact of purging with gases such as air, argon, nitrogen, helium and hydrogen during the laser ablation process. A negative photo resist, E-1020 obtained from M/s Cadmosil Chemical Pvt. Ltd, India was studied using 248 nm KrF excimer laser. The effect of gas purging on the ablation rate and surface characteristics of the polymer was studied. Amongst the gases used, hydrogen gas showed distinct results with respect to ablation rate and surface characteristics. It has been observed that hydrogen gas has enhanced both the ablation rate and the surface quality significantly. The role of hydrogen gas in enhancing the laser ablation rate may be attributed to the possible involvement of hydrogen gas in the laser assisted chemical reaction with polymer. Eximer laser micromachining process is characterized by a number of process parameters that determines efficiency, economy and quality of the whole process. In this chapter, the details of the experiment along with the results and observations, with areas for future study have been presented.

Laser-Induced Micromachining (LIMM) is a non-conventional machining process in which a high power laser beam is focused over the work surface in order to remove the material selectively. The material is removed through melting, evaporation and plasma formation. LIMM offers better machining efficiency than other non-conventional machining processes in terms of the machining rate, efficient debris removal, better surface morphology and capability to machine wide range of materials irrespective of its hardness and electrical conductivity. Further precision can be obtained by confining the laser induced plasma plume from the surface using an external magnetic field or electric field. This chapter deals with a brief introduction and basic principle of laser induced micromachining. This is followed by a discussion on various configurations of LIMM. Further, a review on numerical and experimental studies of the laser induced micromachining is presented. At the end of the chapter, preliminary experimental work on laser induced micromachining of mild steel has been reported.

Micro Lens arrays are widely used in optical devices such as photo-sensors, digital projectors, photovoltaic cells, 3D imaging etc. These have traditionally been fabricated by photolithography, moulding and embossing, reactive ion etching and electroforming. These processes are wet processes and require expensive setup and running cost. A novel method is presented in this work that allows fabrication of micro lens array using excimer laser micromachining. The fabrication has been done using mask projection with work piece scanning. A KrF excimer laser has been used to micro machine lenses on a poly (methyl methacrylate) substrate. The surface profile of the lens array is measured and then related to the laser-material coupling and the energy of the laser pulses. Using this method, it is possible to fabricate micro lenses down to a diameter of 5 µm over a considerably large area.

Microfluidic devices are highly commonplace in the field of biomedical technology, point of care diagnostics and chemical analysis. The rapid and low cost manufacturing of these devices have always been a challenge. CO₂ laser micromachining has played an important role in micro-machining of devices at a scale similar to the microfluidic devices although it renders the machined surfaces with high surface roughness. The chapter reports an initiative to do process optimization of laser micromachining technique for producing smooth machined surfaces in the micro scale devices. The chapter discusses the impact of process parameters like raster speed, laser power, print resolution etc. and its optimization using two target functions of dimensional precision and surface roughness on micro-channels made in PMMA (Poly methyl metha acrylate) substrates. The laser machined PMMA samples are analyzed using 3D-profilometry and Field emission scanning electron microscope (FESEM) for surface quality and dimensional precision. To investigate optimum process parameters of CO₂ laser for fabricating the micro-channel on PMMA with dimensional accuracy and good surface quality, Analysis of variance (ANOVA) and regression analysis is conducted. It is found that optimum surface roughness of this process is around 7.1 µm at the optimum value of the process parameters 7.5 mm/s (50 % of maximum machine limit) raster speed, 17.9 W (51 % of maximum machine limit) laser power and 1200 DPI (100 % of maximum machine limit) printing resolution. The static contact angle of the micro-machined surface has also been observed for analyzing the amenability of these channels to flow of water like fluids for micro-fluidic applications. The chapter also covers a review of work done by various researchers in which they developed different methodology for successful manufacturing of microfluidic devices by employing CO₂ laser micromachining.

CO₂ laser micromachining provides low cost machining solution for fabrication of three dimensional microfluidic channels on poly-methyl-methacrylate(PMMA). In this research work CO₂ laser microchanneling process has been analyzed from the first principle. Considering the Gaussian distribution of laser beam, an energy based model has been proposed to predict the microchannel depth and channel profile. For fabricating microfluidic devices, PMMA has emerged as a cheap alternative to many other costly materials like silicon, quartz etc. Its material properties like absorptivity and thermal properties have been investigated. In order to physically verify the proposed model, experiments have been performed on a 3 mm thick PMMA sheet and actual and predicted results have been compared. Simultaneous TGA/DSC tests have been conducted to determine various thermal properties of PMMA. Since thermal conductivity of the PMMA is very low, the conduction loss has been neglected while developing the model. The proposed model successfully predicts the channel depth and profile without much loss of accuracy. energy based analysis has been found to be simple yet powerful method to predict the channel dimensions for low thermal conductivity materials.

Progress of laser micro-machining i.e. micro-cutting, micro-drilling, Micro-channeling, micro-grooving, micro-turning etc. in the field of aeronautic, automobile, semiconductor and biomedical industries such as turbine blades of aircraft engine, automotive fuel filters, combustion chambers, surgical needles and micro-fluidic devices have emerged extensively in the present era. The prime contributor to the success of laser micro-machining in the recent years is fiber laser technology that involves the combination of diode pumped solid state lasers and fiber technology. This is the most promising substitute to the high-power, bulk solid-state lasers and some gas lasers owing to its simplicity, ruggedness, cost effectiveness, low maintenance, higher efficiency, higher reliability and smaller spot size. Fiber lasers are mainly characterized by short pulse lengths which range from millisecond to picosecond and even femtosecond for precise micro-machining of different materials. Titanium alloys play crucial roles in the areas of advanced structures and technologies for aerospace and power industry, medicine, automatics and mechatronics and various measurement equipments, because of their high strength and stiffness at elevated temperatures, high corrosion resistance, fatigue resistance, high strength to weight ratio and ability to withstand moderately high temperatures without creeping. The conventional machining methods intended for cutting these alloys not only suffer due to poor thermal conductivity, low elastic modulus and high chemical affinity at elevated temperatures but also have to undergo higher cost associated with the machining of Ti-6Al-4V caused by lower cutting speeds and shorter tool life. Numerous research works have been conducted with laser beam micro-machining approaches on titanium alloys mainly on Ti-6Al-4V, in order to establish the optimal experimental conditions that are to be used in different applications. However, the physical mechanism which leads to the observed geometry and surface roughness of the micro-machined surface is still behind the veil. The aim of the present chapter is to make an in depth study of the fiber laser micro-grooving of Ti-6Al-4V, discussing vividly the fiber laser machining system, the occurring physical processes and machining strategy and influence of various process parameters. Experimental results of present research work along with the work of various researchers are discussed so as to validate and run down hypotheses on the mechanisms involved.

Laser marking is one of the well-developed technologies of materials processing. Laser marking is the best and most applied permanent marking method. Ceramic is a difficult material to be processed by conventional marking techniques due to its high hardness and brittleness. This chapter deals with the artificial neural network (ANN) and the response surface methodology (RSM) based mathematical modelling and also an optimization analysis on marking characteristics i.e., mark width, mark depth and mark intensity on zirconia ceramic. The experiments have been planned and carried out based on Design of Experiment (DOE). The major influencing laser marking process parameter considered are pulse frequency, lamp current, pulse width, scanning speed and air pressure. The experiments have been planned and carried out based on RSM based modelling with 32 runs. ANN modelling is performed and the results are compared. The average percentage of prediction errors of the developed ANN model for mark width, mark depth and mark intensity are 2.52, 2.58 and 2.58 respectively and the overall percentage of prediction error is 2.6. The output of the RSM optimal data is validated through experimentation and ANN predictive model. A good agreement is observed between the results based on ANN predictive model of 82.8 μm, 46.3 μm and 0.605 for mark width, mark depth and mark intensity respectively and actual experimental observations.

Nd:YAG laser microdrilling of SiC30BN nanocomposite material is studied here. Taguchi based grey relational analysis is used to simultaneously determine the optimum setting for minimum hole taper and HAZ width. Grey relation analysis is adopted for combining multiple quality characteristics into one integrated numerical value called Grey relational grade. A L27 orthogonal array has been used for conducting experiments. Lamp current, pulse frequency, pulse width, assist gas pressure and focal distance are considered as input process parameters whereas hole taper and HAZ width are considered as machining responses. It is observed that the quality characteristics of drilled micro holes are improved markedly at the optimized parameter settings as compared to quality levels achieved for initial machine parameter settings.

Laser micro-turning process is one of the new and emerging technologies in the area of laser material processing (LMP) of engineering materials. It is employed for generation of micro-turning surface of particular surface profile and dimensional accuracy on cylindrical workpiece with specific length and depth of turn within tight tolerance. As the process is recently developed micro manufacturing technique, a well planned research study and experimental investigation should be conducted considering various laser micro-turning process parameters. Therefore, various experimental schemes are adapted to study and analysis of significant process parameters on response criteria such as surface roughness and machining depth. A servo controller based fixture is designed and developed indigenously to hold and rotate the cylindrical shaped work samples at various workpiece rotating speed. Overlap between two successive spots (i.e. spot overlap) and overlap between two successive micro-groove widths (i.e. circumferential overlap) play major role for generating quality surface features during laser micro-turning process. Therefore, mathematical formulations of spot overlap and circumferential overlap are developed for better understanding of the laser micro-turning process and also to study the effects of these overlap factors on performance characteristics. Moreover, attempt has been made to carry out experimental investigation to micro-turn cylindrical shaped engineering ceramics at laser defocus conditions of laser beam. Moreover, comparative study and analyse is performed to explore the effect of focused and defocused conditions of laser beam on surface roughness criteria. SEM micrographs of the laser turned surface captured at various parametric combinations have also been studied for qualitative analysis of the process.

Laser welding is a sophisticated, high accuracy and high speed welding process. Laser welding is a process of joining components where laser beam used as a heat source. In this present study a literature review on welding by laser as a heat source has been addressed. In the present review, emphasis has been given especially on the laser welding numerical and experimental temperature field analysis, thermo-mechanical analysis. The time frame of the review is 1992–2013.

In fusion welding, thermo-chemical reactions may take place among surrounding atmosphere particles and molten weld pool at high temperature gradients. The atmosphere particles such as oxygen, hydrogen and nitrogen may become part of final weld joint that severely affects the weld joint quality and weld metal properties. Therefore, the welding atmosphere and protection of weld pool plays a noticeable role on the quality of the final weld joint. Henceforth, in this chapter, fiber laser welding of austenitic stainless steel plates have been examined in two different ambient atmospheres. Firstly, the experiments are conducted in open atmosphere and in argon ambient atmosphere to study the characteristic difference between them. The experimental investigation specifies that the weld bead dimensions and aspect ratio are higher in case of argon atmosphere as compared to open atmosphere. The microstructures of heat affected zone (HAZ) and fusion zone (FZ) at both atmospheric conditions are analyzed. It is obvious from the experimental results that the top surface profile is smoother and very clear in case of welds at argon atmosphere. Moreover, in this work, the authors also reported an efficient conduction mode finite element based heat transfer model of linear fiber laser welding process using a volumetric heat source. The calculated weld bead dimensions using finite element model are compared with the experimentally measured results at similar process variables. Relatively fair agreement of the experimental results with model results entitles the robustness of the modeling approach followed here and reported in this work.

In this work, a numerical investigation of transient temperature profile of Laser beam welding process is carried out. A 3-D finite element modelling is developed considering combined double-ellipsoidal heat source model for both spot and moving heat sources. The temperature dependent thermo-physical material properties of Ti-6Al-4V alloy are incorporated. The effect of latent heat of fusion and convective and radiative boundary conditions are considered. The effect of laser beam power on the transient temperature profile and the dimensions of the heat affected zone are analysed. From finite element simulation, it is observed that the peak temperature in the fusion zone increases with increased laser beam power. Also, the size of the heat affected zone strongly depends on the power of the laser beam.

In the present study, tungsten carbide (WC) and cobalt (Co) powder mixture was sintered through selective laser sintering process using a pulsed Nd:YAG laser. Two different compositions of the powder mixture having 85 wt% WC + 15 wt%Co and 80 wt% WC + 20 wt% Co were used in the experiments. The optimum level of parameters, such as, composition of powder, layer thickness, hatching distance, pulse energy, pulse width and distance from focal plane were obtained by using the Taguchi method for achieving higher density, higher micro-hardness and minimum porosity. The Taguchi design of experiments involving an L-18 orthogonal array was followed. The effects of various sintering parameters were investigated on various responses like density, microhardness and porosity. The composition of the powder mixture and the pulse energy were found to have significant role on the microhardness. Hatching distance and cobalt percentage were the main influencing parameters on density and porosity. Surface morphology and formation of intermetallic compounds were analyzed through scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques.