Laser Forming Research Articles

An experimental investigation of underwater pulsed laser forming

Laser forming is a new forming technology, which deforms a metal sheet using laser-induced thermal stresses. This paper presents an experimental investigation of pulsed laser forming of stainless steel in water and air. The effects of cooling conditions on bending angle and morphology of the heat affected zone (HAZ) are studied. It is shown that the case of the top surface in air and the bottom surface immersed in water has the greatest bending angle based on the forming mechanism of TGM. The water layer above the sample decreases the coupling energy, leading to a small bending angle. For a thin water thickness (1mm), the water effects on the HAZ are limited. As water layer thickness increases (5mm), the concave shape of the HAZ is more remarkable and irregular because the shock waves by high laser energy heating water are fully developed. However, the area and the depth of the HAZ become less significant when water thickness is 10mm due to the long pathway that laser undergoes.

217 ステンレス線材へのレーザフォーミングメカニズムに関する研究(OS3 : アディティブ・マニュファクチャリングの生産システム(2))

It is easy for laser forming to control power and laser forming does not use a tool, so there is not wear of a tool. There are a lot of advantage in laser forming. But laser forming is not practical because of working difficulty. In this paper, I observed SUS304 wire after laser forming by SEM. I processed SUS304 wire and measured bending angle. Additionally l got temperature of SUS304 wire by simulation.

Optimization of Beam Mode for High Efficiency Laser Thermal Forming within Metallurgical Constraints

In the laser forming (LF) process, laser induced temperature distribution within the work-piece is of paramount importance. Through control of process parameters and depending on work-piece geometry, the temperature distribution can be altered to achieve either localized plastic compressive strains or elastic-plastic buckling. Conventionally, three process parameters are manipulated in order to control the temperature distribution within the work-piece; traverse speed, average power and spot size. Additionally, the intensity distribution and geometrical shape of the beam incident on the work-piece surface can be manipulated. The latter has the potential to be useful in maintaining bend angle per pass whilst working within strict metallurgical constraints. In this paper, the effect of beam intensity distribution and geometrical shape on the LF of automotive grade high strength DP 1000 steel sheet is investigated numerically and experimentally, with particular emphasis on optimization for minimal micro-structural transformation.

Laser forming of bi-layer Fe/Al sheet by Nd: YAG laser

Laser forming of bi-layer Fe/Al sheet by Nd: YAG laser

Bending Angle Characteristics of SPFC1180Y Steel by the Laser Irradiation Position

Laser forming is an advanced process in sheet metal forming in which a laser heat source is used to shape the metal sheet. This is a new manufacturing technique that forms the metal sheet only by thermal stress. Analyses of the temperature and stress fields are very important to identify the deformation mechanism in laser forming. In this experiment, the relationship between laser irradiation position and the bending angle, in terms of laser forming, has been tested and the result was compared and analyzed with respect to the theoretical bending moment and the elastic curve differential equation.

Numerical and experimental investigation on laser irradiated bending process of advanced high strength steel

Laser forming is an advanced process in sheet metal forming in which a laser heat source is used to shape the metal sheet. This is a new manufacturing technique that forms the metal sheet only by thermal stress. Analysing temperature and stress fields are very important to identify the deformation mechanism in laser forming. In this paper, temperature distributions and deformation behaviours of DP980 steel sheets are investigated numerically and experimentally. Coupled thermomechanical finite element simulations are firstly conducted to evaluate the response related to the bending angle of a square sheet part. The effects of process parameters such as laser power and scanning speed are analysed numerically. The thermomechanical behaviours during the straight line heating process are presented in terms of temperature, stress and strain. Experiments are then carried out to validate the simulation results. It is observed that the numerical results are in good agreement with the experimental results. Results also represent the relationship between line energy and bending angles for laser bending of DP980 steel sheets.

Investigation on the Microstructure and Segregation of Superalloy FGH96 by Direct Laser Forming

Direct laser forming directional solidification experiments were performed by using nickel-base superalloy as substrate and powder FGH96 as cladding material. The solidification microstructure of the cladding layer was investigated. Results showed that as-deposited microstructure was directionally solidified dendrites with the primary dendrite arm spacing of approximately 3μm and the secondary arm was small or even degenerated. According to the theory of columnar/equiaxed transition (CET) in front of the solid/liquid interface, it was found that in the single-path multi-layer cladding layers and multi-path multi-layer cladding layers, the microstructure with the same crystallographic orientation as the substrate was obtained by reasonably selecting the processing parameters. Composition segregation analysis showed a very uniform distribution of elements,and the segregation ratios were close to 1.

Advanced Powder Processing Techniques of Ti Alloy Powders for Medical and Aerospace Applications

In this paper, two kinds of advanced powder processing techniques Metal Injection Molding (MIM) and Direct Laser Forming (DLF) are introduced to fabricate complex shaped Ti alloy parts which are widely used for medical and aerospace applications. The MIM process is used to strengthen Ti-6Al-4V alloy compacts by addition of fine Mo, Fe or Cr powders. Enhanced tensile strength of 1030 MPa with 15.1% elongation was obtained by an addition of 4 mass%Cr because of the microstructural modification and also the solution strengthening in beta phase. However, their fatigue strength was lower compared to wrought materials, but was improved by HIP. Subsequently, the effect of feeding layer height (FLH) on the characteristics of the DLF compacts was investigated. In the case of 100 <TEX>${\mu}m$</TEX> FLH, surface roughness was improved and nearly full density (99.8%) was obtained. Also, tensile strength of 1080 MPa was obtained, which is higher than the ASTM value.

Laser forming of a dome shaped surface: Experimental investigations, statistical analysis and neural network modeling

Forming a 3D shape from a flat sheet metal using a laser beam requires multiple irradiations along different paths with necessary heating parameters. In this article, investigations on forming a dome shaped surface from a square metal sheet were carried out using laser forming under temperature gradient mechanism. Experiments were conducted to study the effects of various process parameters, considering laser power, scan speed and spot diameter as inputs and the dome height as the output. Statistical regression analysis was performed based on the experimental data collected according to a design of experiments. All the input variables were found to have significant effects on the dome height. Dome height increased with the laser power and decreased with the spot diameter, but it was found to initially increase and then decrease with the scan speed. Optimization was done to obtain the maximum dome height and the corresponding set of optimal input parameters. Neural network-based models were also developed to predict the dome height and carry out the process synthesis, i.e., to predict the process parameters for obtaining a particular dome height. These methods were able to predict the dome height and process parameters with reasonable accuracy. The effects of sample size, scan pitch, number of scans and Fourier number on dome height were further investigated experimentally. The dome height was found to increase with the increase of work piece size and number of laser scans, and decrease with the scan pitch and Fourier number.

Application of the CNC System Based on PMAC in Laser Forming Machine

With the research of the main structure of the CNC System, the design philosophy of the CNC System based on PMAC in Laser Forming Machine was put forward. This system takes PMAC as control model of CNC and PC as system supporting units, which is a double CPU CNC systemthe CNC system model of "PC+PMAC". A lot of experiments have proved that this system can work steadily and it can meet the demand of laser forming machine.

Evaluation of the Stability and Precision of Powder Delivery during Laser Additive Manufacturing

The fabrication of metal parts is the backbone of the modern manufacturing industry. Laser forming is combination of five common technologies: lasers, rapid prototyping (RP), computer-aided design (CAD), computer-aided manufacturing (CAM), and powder metallurgy. The resulting process creates part by focusing an industrial laser beam on the surface of processing work piece to create a molten pool of metal. A small stream of powdered alloy is then injected into the molten pool to build up the part gradually. By moving the laser beam back and forth and tracing out a pattern determined by a CAD, the solid metal part is fabricated line by line, one layer at a time. By this method, a material having a very fine microstructure due to rapid solidification process can be produced. In the present work, a type of direct laser deposition process, called Laser Metal Deposition Shaping (LMDS), has been employed and developed to fabricate metal parts. In the LMDS process, the powder delivery system is an important component to perform the powder transport from powder storage box to powder nozzle, which supplies the raw material for the as-deposited metal parts. Consequently, the stability and precision of powder delivery during LMDS is essential to achieve the metal parts with high quality, so it is critical to evaluate the main factors closely related to the stability and precision of powder delivery. The shielding gas flow and the powder feeding rate were ascertained through experimental measure and formula calculation. The results prove that the suitable shielding gas flow and powder feeding rate can promote the stability and precision of powder delivery, which is the basis for the fabrication of as-deposited metal parts with flying colors.

Forming treatment of metal plates and disks by local laser heating

The article is devoted to the study of thermal methods of forming. Namely, the laser forming, as the laser as a thermal source is stable, well defined, bases easily, and provides a locality heating. The mechanisms of laser forming were analyzed. The results of experimental studies were presented. It was found that the amount of deformation is proportional to the number of irradiation cycles for both carbon and austenitic stainless steels. When processing carbon steels the post-deformation occurs. It may or may not be coincident with the direction of the main deformation. The resistance of the laser formed constructions was studied. It was shown that the resistance of the constructions formed with the laser to force and thermal load is higher than of the constructions formed by the pressure treatment.This is explained by the fact that the pressure treatment in the processing zone causes wall thinning of an item, in turn, the laser forming causes the reverse process - thickening. Technological recommendations on the treatment of metal plates were worked out. The results of the forming of items of complex spatial configuration with the irradiation by the parallel and cross laser passages were presented.It was found that during the irradiation along the curvilinear trajectories it is appropriate to use a uniform heating, which can be achieved by rotating a workpiece with a frequency of 11000 rotations in a minute. The uniform heating of the workpiece in a closed curvilinear contour allows a uniform distribution of stresses and strains

Numerical Simulation of Laser Bending of Aluminum Foams

Laser forming of open-cell aluminum foams has been modeled by means of a 3D finite element model which is able to take into account the real foam geometry as well as the main process variables. A parametric procedure has been defined for the geometry construction and meshing, and the simulation run. In order to calibrate and validate numerical modeling, compression and flexure tests were performed on a closed-cell aluminum foam. The simulation of mechanical tests allowed a correct modeling of the aluminum alloy behavior under plastic deformation. The same material behavior was implemented in a complex thermo-mechanical model for laser bending simulation. The final model is able to predict the shape evolution during forming and the correlation between process variables and final bent angles.

A closed-form solution for thermal and deformation fields in laser bending process of different materials

An analytical solution for temperature and deformation fields produced by laser forming is derived. The effects of process parameters are investigated on samples of different materials and thicknesses. Experimental tests were carried out using a high-power diode laser on a poorly conductive material (AISI 304) and a highly conductive one (AA 6013) to evaluate the accuracy of the proposed model. A 2D FEM is developed to calibrate and validate the new model. The model predictions are in good agreement with experimental measurements even under low scanning speed due to the effect of conductive heat exchange of the irradiated zone with surrounding material. Based on the achieved results, a simple method for optimizing the process productivity is also discussed.

Modeling and reducing edge effects in laser bending

Laser forming of sheet metal offers the advantages of requiring no hard tooling, no spring back and no external force, thus this technology reduces cost, increases flexibility and accuracy. Laser forming is a complicated and transient thermo-mechanical process involving elastic and plastic strain depended on time history. How to control and enhance the accuracy of the laser forming attracts much attention. This paper delivered a deep insight into the mechanism of the edge effects in laser forming, improved an existing analytical model to approximately predict the edge effects, and based on this model a new strategy was put forward to reduce the edge effects. Numerical simulations and experiments were carried out to validate the model and the presented strategy.

Laser Forming of ERW Steel Square Tubes within Metallurgical Constraints

Laser forming (LF) is a non-contact method to shape metallic sheets and tubes by induced thermal stress without melting using a de-focused laser beam. Laser forming offers the industrial promise of controlled shaping of metallic and non-metallic components for prototyping, correction of design shape or distortion and precision adjustment applications. In order to fulfil this promise in a manufacturing environment the process must have a high degree of control, be repeatable and have a minimal impact on the material and mechanical properties of the part to be formed. In order to demonstrate the capability of the LF process a study is presented in this paper on the 3D Laser Forming of ERW steel square tubes SHS EN10305-5 E220 +CR2 (1.5x25x25mm and 1.5x50x50mm 300mm long tube) using a 1.5kW CO2 laser and industrial 5 axis gantry. Strategies have been developed for out of plane bending with specific emphasis on process throughput balanced with minimising adverse localised changes to material properties that could lead to stress concentration features in a component in service. Presented in this paper is empirical 3D LF shape data verified by a scanning laser profiler, a metallurgical study, hardness testing and a FEM model developed in Comsol Multi-Physics. The results of these studies were employed to develop optimised scan strategies for the controlled laser forming of the ERW steel square tubes within strict metallurgical constraints.

Simulation of Laser Shock Wave Propagation and Dispersion in SHPB

Laser shock wave oscillation caused by lateral inertia effects of Hopkinson bar in large-diameter SHPB apparatus, and the geometry dispersion effect, particularly, the rise time of the stress wave in different diameters and lengths of Hopkinson bar were investigated. The three-dimensional model of member bar is established by the finite element analysis software ABAQUS, and the different shapes pressure pulses including rectangular, triangular and Gaussian pulses induced by laser shock have been loaded on the end face of the bar, respectively. Results indicate that the triangle pressure pulse and Gaussian pressure pulse show less dispersion effect than rectangle stress pulse on wave shape, and Gaussian stress pulse can keep the morphology better and reduce the dispersion effect more effectively than triangle stress pulse in the propagation process. In addition, as the bar diameter increases and the distance of the propagating stress wave raises, wave oscillation enhances significantly in the bar, the same as the rise time of stress wave increases gradually and the maximum stress also has a certain degree of attenuation, which have influence on laser shock processing or forming.

Mechanics Study on Leveling Process by a Roller during Selective Laser Forming

Generally, pressures resulted from roller during leveling process in selective laser sintering has the effect of densification of powder materials. But extra frictions due to them become the forces which always deteriorate the surface of the part and mark it with several lines trace. Sometimes, the manufacturing can even not continue if these forces accumulate to a large extent to move the whole part. Therefore, the whole forming process will be obliged to stop owing to the displacement of part from above mentioned damage. In this work, the emerging reason and related variation factors of these forces were studied mathematically, the mathematical and physical model of friction force was also built to describe the connections between the leveling process parameters and them. How to control the influence factor of friction to abate their damages to surfaces and promote the forming quality were also discussed based on these models. This will provide a common reference for the application of selective laser sintering technology.

Investigation on multi-track multi-layer epitaxial growth of columnar crystal in direct laser forming

Direct laser forming has the advantage that the heat input is very much localized and it leads to large temperature gradient. Therefore, the solidification velocity can be controlled to stabilize the columnar crystal growth and to avoid the growth of equiaxed grains in the laser clad. Consequently, single crystal can be deposited onto a single crystal substrate. In this paper, DZ125L Ni based super-alloy was used for the experiment, the epitaxial growth of columnar crystal onto the substrate was characterized, and the epitaxial growth of columnar crystal in multi-track multi-layer deposition was obtained by analyzing the single cladding track characteristics and optimizing the technological parameters. The investigation is helpful for the approach to form 3D metal parts such as turbine blades, which require columnar crystal microstructure.

Basic Study on Laser Forming of Curved Surfaces with Simulation

Laser forming is a technology that produces plastic deformations in sheet materials by generating local heat stress. It is useful for prototype or small-quantity production because it does not require dies or molds. Although many studies on laser forming have been done, few have been on forming curved shapes. This paper deals with a method for generating the scanning paths and determining the scanning conditions for laser forming of a curved shape. The scanning paths are derived as the maximum and minimum curvature lines. Since the two curvature lines are orthogonal, they don’t affect each other in forming. The scanning speed is decided by an approximation equation derived from experiment and FEM analysis according to the angle of the bend at the irradiation point. The effectiveness of the scanning paths and the scanning speed determined by the proposed method are confirmed through experiments.