Laser powder bed fusion (LPBF) has the ability to produce three-dimensional lightweight metal parts with complex shapes. Extensive investigations have been conducted to tackle build accuracy problems caused by shape complexity. For metal parts with stringent requirements, surface roughness, laser beam positioning error, and part location effects can all affect the shape accuracy of LPBF built products. This study develops a data-driven predictive approach as a promising solution for geometric accuracy improvement in LPBF processes. To address the shape complexity issue, a prescriptive modeling approach is adopted to minimize geometrical deviations of built products through compensating computer aided design models, as opposed to changing process parameters. It allows us to predict and control a wide range of shapes starting from a limited set of measurements on basic benchmark geometries. An error decomposition and compensation scheme is developed to decouple the influence from different error components and to reduce the shape deviations caused by part geometrical deviation, laser beam positioning error, and other location effects simultaneously via an integrated modeling and compensation framework. Experimentation and data collection are conducted to investigate error sources and to validate the developed modeling and accuracy control methods.

The advance in computational science and engineering allows people to simulate the additive manufacturing (AM) process at high fidelity, which has turned out to be a valid way to model, predict, and even design the AM processes. In this paper, we propose a new method to simulate the melting process of metal powder-based AM. The governing physics is described using partial differential equations for heat transfer and Laminar flow. Level set methods are applied to track the free surface motion of the molten metal flow. Some fundamental issues in the metal-based AM process, including free surface evolution, phase transitions, and velocity field calculation, are explored, which help us gain insight into the metal-based AM process. The convergence problem is also examined to improve the efficiency in solving this multiphysics problem.

Laser cladding (LC) is a material deposition technique, in which a laser beam is used to deposit one or several layers of a certain clad material onto a substrate to improve its wear or corrosion resistance. It can also be used for structural repair. Consequently, it is of interest to characterize the residual stresses and the microstructure along with the clad geometry as a function of process parameters. A 100 W fiber laser and focusing optics capable of producing very small spot sizes (∼10 μm) have been integrated with a micromachining center. This paper focuses on providing a comprehensive metallurgical and mechanical characterization of microscale LC of preplaced powdered mixture of cobalt and titanium on IS 2062 (ASTM A36) substrate. Parametric studies were conducted by varying the scanning velocity, laser power, and spot size to produce clad layers well bonded to the substrate. The results show that the width and height of the cladding increases up to 28% and 36%, respectively, due to the variation in the laser parameters. An increase of up to 85% in the microhardness is observed in the cladded layer with presence of Ti–Co intermetallic compounds at the interface, highlighting the application of the process in improving subsurface properties of existing components. The residual stresses obtained in the cladded layer are compressive in nature, indicating the potential application of this technique for repair of structures. In addition, a finite element model has been developed for predicting the clad geometry using a moving Gaussian heat source. Molten region is determined from the thermal model and Tanner's law has been used to account for spreading of the molten layer to accurately predict the clad geometry. The model predicts clad geometry with reasonable prediction errors less than 10% for most cases with stronger dependence on scan velocities in comparison to laser power.

Selective laser melting (SLM) is a technique for the additive manufacturing (AM) of metals, plastics, and even ceramics. This paper explores using SLM for depositing glass structures. A CO2 laser is used to locally melt portions of a powder bed to study the effects of process parameters on stationary particle formation as well as continuous line quality. Numerical modeling is also applied to gain insight into the physical process. The experimental and numerical results indicate that the absorptivity of the glass powder is nearly constant with respect to the processing parameters. These results are used to deposit layered single-track wide walls to demonstrate the potential of using the SLM process for building transparent parts. Finally, the powder bed process is compared to a wire-fed approach. AM of glass is relevant for gradient index optics, systems with embedded optics, and the formation of hermetic seals.

Laser bending of silicon sheet is a process to form three-dimensional microstructural silicon elements in an ambient environment. This study aims to investigate the process mechanism with the aid of both experimental and numerical analyses. To this end, a thin-film thermocouple was prepared to capture the temperature field within the heating zone of the laser beam. A new method was then developed to precisely determine the absorption factor by coupling numerical simulation of the laser bending results with the experimental results. It was found that each laser pulse causes a cycle of sharp temperature rise-drop in a silicon sheet. When the temperature in the heating zone is low, the sheet deforms elastically. When it is beyond the brittle–ductile transition temperature of silicon, however, plastic deformation in the sheet takes place and bending occurs. The bending angle becomes larger with increasing the number of laser beam scanning, once the temperature gradient in the scanning area is large enough.

This article illustrates the development of a complete and exhaustive mathematical model for the simulation of laser transformation hardening of hypo-eutectoid carbon steels. The authors propose an integrated approach aimed at taking into consideration all the phenomena involved in this manufacturing process, with particular attention to implementing easy mathematical models in order to optimize the trade-off between the accuracy of the predicted results and the computational times. The proposed models involve the calculation of the 3D thermal field occurring into the workpiece and predict the microstructural evolution of the target material exploiting an original approach based on the definition of thermodynamic thresholds, which can be considered as a physical constant of the material itself. Several parameters and phenomena are taken into consideration in order to accurately simulate the process: laser beam characteristics, fast austenization of the steel, and tempering effect due to mutually interacting beam trajectories. The accuracy of the model is presented by means of hardness comparisons between hardness predictions and measurements in single and double paths surface treating of AISI 1040.

This work presents an experimental and numerical analysis of a low output power single-pass laser forming process applied to thin stainless steel sheets. To this end, the proposed methodology consists in four stages respectively devoted to material characterization via tensile testing, estimation of thermal boundary conditions present in laser forming, realization of laser bending tests for two sets of operating variables, and finally, numerical simulation of this process carried out with a coupled thermomechanical finite element formulation accounting for large plastic strains, temperature-dependent material properties and convection–radiation phenomena. The numerical analysis, focused on the description of the evolution of the thermomechanical material response, is found to provide a satisfactory experimental validation of the final bending angle for two laser forming cases with different operating variables. In both cases, the predicted high temperature gradients occurring across the sample thickness show that the deformation process is mainly governed by the thermal gradient mechanism.

A novel methodology of laser coating of mixture of bioceramic and titanium nanoparticles onto metal implants is developed in this work. Feasibility of this approach is demonstrated via both multiphysics simulation and experiments. Treating incident laser as an electromagnetic wave, an electromagnetic (EM) module is coupled with a heat transfer (HT) module. The EM-HT model analyzes the interaction between laser and nanoparticles and ends up with a temperature rise in the system. Hydroxyapatite (HAp) and titanium nanoparticles are coated on the Ti–6Al–4V substrate. Processing parameters such as laser power, beam radius, scan speed, and layer thickness are studied, and correlation between these parameters and the final temperature is presented. The effect of the HAp/Ti mixing ratio to the generated temperature is also examined. Experiments are carried out to verify the model. Good agreements have been found between the EM-HT model and experiments.

In this study, nylon tubes were welded to nylon plaques using laser transmission welding. A conical mirror inserted inside the tube was used to guide the laser beam along the weld path around the inner circumference of the tube. The effect of beam location with respect to the tip of conical mirror on beam distortion was modeled and assessed experimentally. The effects of the laser power, the angular speed, and the number of passes on the joint shear strength were examined. Process parameters that gave good joint strengths were identified.

In laser cleaving of brittle materials using the controlled fracture technique, thermal stresses are used to induce a single crack and the material is separated along the cutting path by extending the crack. One of the problems in laser cutting of glass with the controlled fracture technique is the cut deviation at the leading and the trailing edges of the glass sheet. This work is about minimizing this deviation through an optimization process, which includes laser beam geometry. It has been established that the thermal stresses generated during laser scanning are strongly dependent upon laser beam geometry. Experimental techniques are used to quantify cut deviation for soda-lime glass sheets under a set of conditions while finite element modeling is used to optimize the process and reduce (or eliminate) cut deviation. The experimental results of the effect of different laser beam geometries on cut path deviation have been presented in this study, along with the finite element modeling of the cutting process to simulate the transient effects of the moving beam and predict thermal fields and stress distribution. These predictions are compared with the experimental data. In comparison to other beam geometries, the triangular-forward beam at the leading edge and triangular-reverse and circular beam geometry at the trailing edge produces lower tensile stresses ( σ x x ) and hence minimizes the cut path deviation. The work also shows that beam divergence inside the glass plays a significant role in changing the cut path deviation at the bottom leading and trailing edges of the glass.

This paper discusses the development of a model of laser transmission welding that can be used as an analytical design tool. Currently the majority of laser transmission welding (LTW) applications rely on trial and error to develop appropriate process parameters. A more rigorous design approach is not commonly used primarily due to the complexity of laser welding, where small material or process parameter changes can greatly affect the weld quality. The model developed in this paper also enables optimizing operating parameters while providing monetary and time saving benefits. The model is created from first principles of heat transfer and utilizes contact conduction that is a function of temperature and pressure, Gaussian laser distribution, and many material properties that vary with temperature including the absorption coefficient. The model is demonstrated through a design example of a joint between two polyvinyl chloride parts. The model is then validated with samples welded with a diode laser system using the operating parameters developed in a design example. Using the weld width as the primary output, the error between the model and the experimental results is 4.3%, demonstrating the accuracy of the model.

A three-dimensional model of selective laser sintering of a two-component loose metal powder layer on top of previously sintered layers by a single-line laser scanning is presented. A temperature-transforming model is employed to model melting and resolidification accompanied by partial shrinkage during laser sintering. The heat losses at the top surface due to natural convection and radiation are taken into account. The liquid flow of the molten low-melting-point metal powders, which is driven by capillary and gravity forces, is also considered and formulated by using Darcy’s law. The effects of the dominant processing parameters, such as laser-beam intensity, scanning velocity, and number of the existing sintered layers underneath, are investigated.

Laser forming is a spring-back-free noncontact forming method that has received considerable attention in recent years. Compared to mechanical bending, no hard tooling, dies, or external force is used. Within laser forming, tube bending is an important industrial activity with applications in critical engineering systems such as heat exchangers, hydraulic systems, boilers, etc. Laser tube bending utilizes the thermal stresses generated during laser scanning to achieve the desired bends. The parameters varied to control the process are usually laser power, beam diameter, scanning velocity, and the number of scans. The thermal stresses generated during laser scanning are strongly dependent upon laser beam geometry. The existing laser bending methods use either circular or rectangular beams. These beam geometries sometimes lead to undesirable effects such as buckling and distortion in tube bending. This paper investigates the effects for various laser beam geometries on laser tube bending. Finite element modeling has been used for the study of the process with some results also validated by experiments.

The transverse motion of a saw-wire affects the cutting surface geometry in wire-saw slicing. To evaluate the magnitude of the wire transverse motion under no-slurry and no-workpiece conditions, which should be minimized before starting the slicing process, a high accuracy, noncontact device has been developed. The measuring head of the device is composed of a laser diode module and a dual-element photodiode between which a saw-wire is placed for measurement. This paper elucidates the appropriate positional configurations of the photosensitive surface of the dual-element photodiode and the laser beam focal point with respect to the 160 μ m diameter wire in the laser beam direction. Furthermore, a measurement experiment is carried out on a wire-saw machine under no-slurry and no-workpiece conditions. The paper reports and discusses the critical issues, such as measurement sensitivity, linearity, and accuracy.

The effect of transformation hardening depends upon both heating and cooling rates. It is desirable to have a slow heating rate and a rapid cooling rate to achieve full transformation. To date laser transformation hardening has been carried out using circular or rectangular beams which result in rapid heating and cooling. Although the use of different beam intensity distributions within the circular or rectangular laser beams has been studied to improve the process, no other beam geometries have been investigated so far for transformation hardening. This paper presents an investigation into the effects of different laser beam geometries in transformation hardening. Finite element modeling technique has been used to simulate the steady state and transient effects of moving beams in transformation hardening of EN 43A steel. The results are compared with experimental data. The work shows that neither of the two commonly used beams, circular and rectangular, are optimum beam shapes for transformation hardening. The homogenization temperature exceeds the melting point for these beam shapes for the usual laser scanning speeds and power density. Triangular beam geometry has been shown to produce the best thermal history to achieve better transformation and highest hardness due to slower heating without sacrificing the processing rate and hardening depths.

Laser sintering of a metal powder mixture that contains two kinds of metal powders with significantly different melting points under a moving Gaussian laser beam is investigated numerically. The continuous-wave laser-induced melting accompanied by shrinkage and resolidification of the metal powder layer are modeled using a temperature-transforming model. The liquid flow of the melted low-melting-point metal driven by capillary and gravity forces is also included in the physical model. The numerical results are validated by experimental results, and a detailed parametric study is performed. The effects of the moving heat source intensity, the scanning velocity, and the thickness of the powder layer on the sintering depth, the configuration of the heat affected zone, and the temperature distribution are discussed.

A modified triangular laser displacement sensor having a resolution of 1.0 μ m was used to measure the diameter of a turned workpiece with curvatures. This sensor was attached to a specially designed stage mounted on a precision slide unit and operated by three drive motors. In the measurement, the laser sensor was controlled by a θ motor depending on workpiece curvatures so that the illuminating laser beam is always normal to the part surface and can measure the workpiece diameter in an on-line fashion. This sensor positioning control was found to be effective for measuring the diameter of a curved workpiece with an accuracy of several micrometers.

Four laser scanning schemes for tube bending, including point-source circumferential scanning, pulsed line-source axial procession, and line-source axial scanning without and with water cooling are investigated in numerical simulation. The coupled thermomechanical model established using the finite element method is validated and applied to predict the bending deformation and help better understand bending mechanisms under different schemes. The influence of important parameters such as beam coverage, scanning velocity and cooling offset on the deformation is investigated in detail. Parametric studies are carried out to determine proper processing windows at which the largest bending can be obtained. The deformation characteristics, including the wall thickness variation and the cross-section distortion produced by different scanning schemes are analyzed, along with the processing efficiency.

A new direct laser patterning system for improving the quality of the pattern on the glass substrate of large Flat Panel Displays (FPD) was developed, which consists of the laser machining center, the laser measurement system, and the adaptive rotational mirror system. The new system is distinguished from the existing system by its control mechanism which compensates for the laser beam error caused by the volumetric error of the multi-axis machine. The new system, in comparison with existing systems which control each stage of multi-axis, uses a fast steering mirror (FSM) and adaptive laser optics to compensate for the error of the laser beam on the substrate. Through this study, a mathematical model of the volumetric error of the multi-axis laser machining center was developed to quantify the geometric and the kinematic errors of each machine axis and their contributing effect on the substrate. The information contained in the mathematical model was expressed in a volumetric error matrix. Further, a mathematical model of the beam delivery was developed to measure the beam delivery on the substrate and its effect on the quality of the patterning. The patterning errors were corrected by using an FSM, which has two rotational angles. The viability of the proposed scheme was demonstrated through simulations and experiments.

This paper presents the development of a six-degree-of-freedom (DOF) geometric error measurement (6GEM) system that can be applied to the simultaneous measurement of six geometric error components of the moving axes of a meso-scale machine tool (mMT). The system consists of a laser module constructed by a cube beam splitter and a pigtailed laser diode, three two-dimensional position sensitive detectors (PSDs), and an additional cube beam splitter. The laser module moving with the positioning system of the developed mMT testbed generates two perpendicular laser beams, one of which is further divided into two laser beams at the second cube beam splitter. These three laser beams are detected by the three PSDs, and the full pose of the laser module is then calculated simultaneously by forward and inverse kinematic computations. The calculated full pose of the laser module is translated into six-DOF geometric errors of the mMT testbed. A series of experiments are performed to demonstrate the effectiveness and accuracy of the proposed 6GEM system. The experimental results show that the measurement accuracy of the 6GEM system was better than ± 0.6 μ m for translational error components and ± 0.6 arcsec for angular error components.