Clad Height Research Articles

Laser Cladding of Ti-6Al-4 V Powder on Ti-6Al-4 V Substrate: Effect of Laser Cladding Parameters on Microstructure

The laser cladding of Ti-6Al-4V powder on Ti-6Al-4V substrate has been investigated to determine laser parameters that could be used as a repair technology for Ti-6Al-4V components. The parameters chosen for the investigation were developed by an analytical laser cladding model. Holding clad height and melt pool depth constant, the traversing speed was varied between 300mm/min and 1500mm/min, an associated power for the given speed was calculated by the model. Two different melt pool depths were used in the calculation of laser power for a given process velocity. The resulting microstructures in the clad zone varied from a relatively thin martensitic structure to a dendritic/thick martensitic structure. The heat affected zone (HAZ) showed a refinement of the Widmanstatten microstructure with a decreasing laser traversing speed and a coarser martensitic structure for the sample prepared with a deeper melt pool.

Numerical simulation and experimental validation of powder flux distribution in coaxial laser cladding

In this research work a numerical model which simulates the powder flux distribution on a coaxial nozzle is presented. CFD fluent code was used to solve the model equations. The geometry of the domain was obtained using a reverse engineering process of a coaxial nozzle. The model required a deep study of the powder size distribution and feed rate because of their importance as input parameters. The simulation for the discrete phase model was carried out using both, the turbulence k– ɛ model and the Euler–Lagrange approximation. During the model validation a technique based on the selective weight measuring on planes perpendicular to the nozzle axis was used. The powder flux model validation results showed coherence between the estimated and measured particle flux values, particularly when the powder stream presents a Gaussian profile. A simple geometrical model was presented as an application example of the flux distribution model to estimate the clad height.

Height Control in Laser Cladding Using Adaptive Sliding Mode Technique: Theory and Experiment

A closed-loop control of the laser cladding process is desired due to difficulties encountered in depositing a layer with acceptable quality from both geometrical and metallurgical point of views. One of the main parameters to achieve the desired geometry in laser cladding process is the height of the deposited layers. In this paper, a real-time measurement and control of the clad height is presented. Due to complex nature of the process and presence of uncertainties, a robust and adaptive sliding mode control is proposed and implemented to control the clad height. The velocity of the substrate is used as a control input while the molten pool height, which is obtained using a charge-coupled device (CCD) camera and an image processing algorithm is used as a feedback signal. Stability of the controller is proven in the presence of time-varying uncertainties and the performance of the closed-loop system is validated by simulation and experiments. The experimental results are promising and show that the geometrical accuracy of the deposited layers can be improved significantly.

Modeling of Heat Transfer and Fluid Flow in the Laser Multilayered Cladding Process

The current work examines the heat-and-mass transfer process in the laser multilayered cladding of H13 tool steel powder by numerical modeling and experimental validation. A multiphase transient model is developed to investigate the evolution of the temperature field and flow velocity of the liquid phase in the molten pool. The solid region of the substrate and solidified clad, the liquid region of the melted clad material, and the gas region of the surrounding air are included. In this model, a level-set method is used to track the free surface motion of the molten pool with the powder material feeding and scanning of the laser beam. An enthalpy–porosity approach is applied to deal with the solidification and melting that occurs in the cladding process. Moreover, the laser heat input and heat losses from the forced convection and heat radiation that occurs on the top surface of the deposited layer are incorporated into the source term of the governing equations. The effects of the laser power, scanning speed, and powder-feed rate on the dilution and height of the multilayered clad are investigated based on the numerical model and experimental measurements. The results show that an increase of the laser power and powder feed rate, or a reduction of the scanning speed, can increase the clad height and directly influence the remelted depth of each layer of deposition. The numerical results have a qualitative agreement with the experimental measurements.

Development of an adaptive fuzzy logic-based inverse dynamic model for laser cladding process

The precision, performance, and robustness of model-based controllers depend, to a large extent, on the accuracy of the inverse dynamic model which is incorporated in the design of the controller. Due to complex nature of the laser cladding process and presence of time-varying uncertainties, derivation of an accurate mathematical inverse dynamic model of the process is very difficult, and involves many unknown parameters. The inverse dynamic model of the complex nonlinear laser cladding process, which is difficult to be described mathematically, can be described by a fuzzy logic-based inverse dynamic model constructed form input–output data. In this paper, the development of an adaptive fuzzy inverse dynamic model of the laser cladding process, using a systematic fuzzy modelling approach is presented. In a closed-loop laser cladding process, the scanning speed of the substrate is required to produce a clad with desired geometry and quality. In this paper, a fuzzy inverse dynamic model that describes the scanning speed as a function of the cladding parameters in particular the clad height is developed. The developed fuzzy model is validated by comparing the model output with experimental data. The results are very promising and show that fuzzy models can accurately describe the process dynamics.

Vision-based clad height measurement

The laser deposition process is useful for part creation, repair, and hard facing. To maintain consistent clad height in the presence of process uncertainties measurement and control is required. This work presents a vision-based clad height measurement technique that utilizes a CCD camera and a line laser to measure the complete clad profile. Unique line detection and spur trimming algorithms are presented that extract measurement data efficiently. The effectiveness of the measurement approach is validated through examples.

Three dimensional finite element modeling of laser solid freeform fabrication of cobalt alloy stellite 21 with 1.5% nano[formula omitted] on the low carbon steel 1015

Our purpose is to model the multilayer laser solid freeform fabrication (LSFF) process for the material properties of low carbon steel 1015 for workpiece and cobalt alloy stellite 21 with 1.5 wt.% nano CeO2 as the powder particles. In this paper, transient heat transfer and mass transfer equations in laser solid freeform fabrication process are solved by Finite Element Method (FEM). In this approach, the geometry of the deposited material, temperature and thermal stress fields across the process area are predicted. For each layer the clad height is computed and computations are done by the use of MATLAB and COMSOL software.

Laser Cladding Height Prediction Based on Neural Network

Real-time detection and closed-loop control of laser cladding height is necessary for forming high quality parts. Technological parameters are coupled and the forming process is a non-linear process. A large number of laser parameters affect the quality of the laser cladding surface. Based on the analysis of the influence of laser parameters on cladding height, the BP (Back propagation) neural network prediction model of cladding height is build. The neural network arithmetic is designed and the samples are acquired by laser forming experiment. The training samples are used to train the network to accomplish the mapping relation between input and output of the network. The test samples are used to verify the performance of the trained network. Simulation results indicate that the prediction model has sufficient accuracy. The BP neural network prediction model of cladding height is feasible and valid in theory and in practice. The laser cladding height BP neural network prediction model lays the foundation for real-time height prediction and closed-loop control in laser forming process, and it has great significance for improving the quality of formed parts.

Investigation of Hastelloy C Laser Clad Melt Pool Size and its Effect on Clad Formation

The melt pool size of a single-track clad in the laser cladding of Hastelloy C, a Nickel based alloy, on mild steel substrate has been investigated. The effect of laser processing parameters, such as laser power density, scan rate and powder mass flow rate on the melt pool size has been examined. It was found that the melt pool size is strictly controlled by the melt pool temperature which increases with laser power but decreases with increasing scan rate and powder mass flow rate. The melt pool size is critical for the clad formation in terms of clad height and dilution with the substrate. The clad height increases linearly with the ratio of melt pool size to powder stream diameter while the dilution is an exponential function of the ratio of melt pool size to laser spot size.

Adaptive Modeling of Laser Powder Deposition Process for Control and Monitoring Application

The laser powder deposition (LPD) process is an advanced material processing technique with many applications. Despite this fact, reliable and accurate control schemes have not yet been fully developed for the process. In this paper, identification of the LPD process is examined to find a more accurate model to predict and control the height of clad in real time. The model is adaptive single input—single output (SISO) and its structure is very similar to the Hammerstein model when the effective power (a function of laser power and velocity) is selected as the input and the clad height as the output. Weighted extended recursive least square (WERLS) is adopted to simultaneously estimate the model parameters using experimental data. Comparison of the results shows that this method can be used very efficiently in control of laser powder deposition process.

Transport phenomena during direct metal deposition

The evolution of temperature and velocity fields during direct metal deposition with coaxial powder injection was simulated using a self-consistent three-dimensional model based on the solution of the equations of mass, momentum, energy conservation, and solute transport in the liquid pool. The basic physical phenomena, including heat transfer, phase changes, mass addition, fluid flow, and interactions between the laser beam and the coaxial powder flow, were considered in the model. The level-set method was implemented to track the evolution of the liquid/gas interface. The temperature and velocity fields, liquid/gas interface, and energy distribution at liquid/gas interface at different times were simulated. For verification purposes, the cladding depth and height were compared with experimental results.

Prediction of laser solid freeform fabrication using neuro-fuzzy method

In this paper, a new application of a neuro-fuzzy method (ANFIS) to laser solid freeform fabrication (LSFF) is presented. The laser solid freeform fabrication process is a complex manufacturing technique that cannot be modeled analytically due to non-linear behaviours of the physical phenomena involved in the process. A neuro-fuzzy model is proposed to predict the clad height (coating thickness) as a function of laser pulse energy, laser pulse frequency, and traverse speed in a dynamic fashion. Four membership functions are assigned to be associated with each input of the model architecture. Experiments are performed to collect data for the training of the proposed network, and a set of unseen experimental data are also considered for the verification of the identified model. The effects of the assigned inputs on the clad height are discussed. The comparison between the experimental data and the model output shows promising results. The model can predict the process with an absolute error as low as 0.07%.

Predicting the geometric form of clad in laser cladding by powder using multiple regression analysis (MRA)

Currently, laser cladding by powder (LCP) is an emergent non-traditional process of components repair with potential application in several industries. This paper presents a study to evaluate the effect of the processing parameters (laser power, scanning velocity and powder mass flow rate) under the geometric form of clad. A plan of experiments was established considering laser cladding by powder with prefixed processing parameters in substrate 100 Mn Cr W4 (DIN) steel plates. The objective was to establish a model using multiple regression analysis (MRA) between processing parameters and the form of single-cladding layer (clad height, clad width and depth penetration into the substrate). In addition, confirmation tests were performed to make a comparison with the foreseen results from the mentioned model. Finally, two industrial applications of components repair are presented.

An image-based feature tracking algorithm for real-time measurement of clad height

This paper presents a novel algorithm for real-time detection of clad height in laser cladding which is known as a layered manufacturing technique. A real-time measurement of clad geometry is based on the use of a developed trinocular optical detector composed of three CCD cameras and the associated interference filters and lenses. The images grabbed by the trinocular optical detector are fed into an algorithm which combines an image-based tracking protocol and a recurrent neural network to extract the clad height in real-time. The image feature tracking strategy is a synergy between a simple image selecting protocol, a fuzzy thresholding technique, a boundary tracing method, a perspective transformation and an extraction of elliptical features of the projected melt pool’s images. The proposed algorithm and the trained network were utilized in the process resulting in excellent detection of the clad height at various working conditions in which SS303L was deposited on mild steel. It was concluded that the developed system can detect the clad height independent from clad paths with about 12% maximum error.

Prediction of clad angle in laser cladding by powder using response surface methodology and scatter search

Currently, laser cladding is an important process that allows the deposition of thick protective coatings on substrates. The article presents an experimental investigation of the influence of processing parameters on clad angle in laser cladding by powder (LCP). The clad angle is determined from the mathematical expression relating to the clad height and clad width. The cladding angle model was developed in terms of laser power, scanning speed, and powder mass flow rate by means of response surface methodology. A first-order equation covering a narrow range of the variables and a second-order equation covering a wide range of the variables are presented. An optimization technique, Scatter Search, is used to determine optimal processing parameters. The adequacy of the predictive model was tested by analysis of variance and found to be adequate.

Clad height control in laser solid freeform fabrication using a feedforward PID controller

In this paper, a feedforward proportional-integral-derivative (PID) controller is developed to effectively control the clad height in laser solid freeform fabrication (LSFF). The scanning velocity is selected as the input control variable and the clad height is chosen as the output. A novel knowledge-based Hammerstein model, including a linear dynamic and a nonlinear memoryless block, is developed, and its parameters are identified offline using experimental data. The architecture of the controller consists of a PID and a feedforward module, which is the inverse of the identified model. The advantage of adding a feedforward path to the PID controller is evaluated experimentally, in which the results show a lower overshoot and faster response times. Also, the performance of the controller is verified in the presence of geometrical disturbances, as well as in the fabrication of a nonplanar part.

Laser cladding: An experimental study of geometric form and hardness of coating using statistical analysis

Laser cladding is a technique in which a laser beam is used as the heating source to melt alloy powder to be clad on the surface of a substrate. This paper presents a study that evaluates the processing parameters (laser power, scanning velocity, and powder mass flowrate) under the form of single-cladding layer (clad height, clad width, and depth penetration into the substrate) and hardness of coating. A plan of experiments, based on orthogonal arrays, was established considering laser cladding with prefixed processing parameters. An analysis of variance (ANOVA) was preformed to investigate the influence of processing parameters in the form of a single-cladding layer and hardness of coating.

Prediction of melt pool depth and dilution in laser powder deposition

This paper presents a mathematical model of laser powder deposition (LPD) to predict temperature field, melt pool depth and dilution. The model validated by experiments is developed using the moving heat source method. In this method, the temperature distribution inside the clad and the substrate is obtained using the superposition principle and the solution of the heat diffusion due to a point heat source. The model, which can be used in real-time applications, predicts the melt pool depth and dilution as a function of clad height and clad width, which in practice can be measured by a vision system. Numerical and experimental analyses show a non-linear behaviour of the melt pool depth as a function of process speed. This indicates that the melt pool depth has a maximum at a certain process speed. The comparisons between the numerical and experimental results show that this model is capable of predicting the characteristics of the LPD process accurately. Using the model, some general curves that show the behaviours of the melt pool depth and dilution as a function of clad height, scanning speed and laser power are illustrated.

DEVELOPMENT OF AN IMAGE-BASED FEATURE TRACKING ALGORITHM FOR REAL-TIME CLAD HEIGHT DETECTION

This paper presents a novel algorithm for real-time detection of clad height in laser cladding. A real-time measurement of clad geometry is perfumed by a developed CCD-based optical detector comprised of three CCD cameras. The images grabbed by the CCD-based optical detectors are fed into the developed algorithm which combines an image feature tracking strategy with a recurrent neural network to extract the clad height in real-time. The image feature tracking strategy is a synergy between a simple image selection plan, a fuzzy thresholding technique, a boundary tracing method, a perspective transformation and an extraction of elliptical features of the projected melt pool's images. The proposed algorithm and the trained network are utilized in the process resulting in excellent detection of the clad height at various working conditions.

Parametric investigation of pulsed Nd: YAG laser cladding of stellite 6 on stainless steel

A systematic research into the cladding of stellite 6 on stainless steel by pulsed Nd:YAG laser has been carried out. The effects of pulse energy, pulse frequency, powder mass flow rate and spot overlap on the clad layer height, dilution and heat-affected zone (HAZ) have been examined. It was found that both the clad height and penetration into the substrate increase with the pulse energy, spot overlap and pulse frequency, but the effects of these parameters on dilution are complex. The dilution reaches the lowest value (4%) at the incident energy of 18 and 25 J/pulse, spot overlap of 89% and pulse frequency of 40 Hz. The powder mass flow rate of 22 g/min (for energy of 25 J/pulse and spot overlap of 83%) produces thick clad layer with low dilution but results in the formation of defects. The hardness of the clad layer decreases linearly with increasing dilution. No cracks have been found in single-track clad layers at a spot overlap of 89%, however, cracks occurred at lower spot overlap. These cracks were eliminated by the multi-track cladding when the track increment is less than 1/3 of the width of track, which is believed to be due to the remelting or heat treatment of the previous clad track by the subsequent track. The track bands in multi-track clad show coarser structure, higher element segregation and lower hardness.