Masoud Alimardani

Three-dimensional numerical approach for geometrical prediction of multilayer laser solid freeform fabrication process

This article presents the development of a three-dimensional numerical method for predicting transient geometrical and thermal characteristics of multilayer laser solid freeform fabrication as a function of process parameters and material properties. In the proposed method, the thermal domain is numerically obtained, assuming the interaction between the laser beam and powder stream is to be decoupled. Once the melt pool boundary is obtained, the physical domain is discretized in a cross-sectional direction. Based on the powder feed rate, elapsed time, and intersection of the melt pool and powder stream area substrate, layers of additive material are then added onto the nonplanar domain. A standard object is fit to each added layer to facilitate the numerical analysis of successive layers. Variations in physical parameters due to formation of nonplanar surfaces are incorporated into the model to increase the accuracy and reliability of the simulated results. The developed model was used to predict the geometrical and thermal properties of a four-layer thin wall of AISI 4340 steel. The results show that the temperature and the thickness of the deposited layers sensibly increase at the end point of layers 2, 3, and 4. Also, the powder catchment efficiency for the first layer is significantly lower than those of successive layers. The experimental results demonstrate the validity of the developed numerical methodology.This article presents the development of a three-dimensional numerical method for predicting transient geometrical and thermal characteristics of multilayer laser solid freeform fabrication as a function of process parameters and material properties. In the proposed method, the thermal domain is numerically obtained, assuming the interaction between the laser beam and powder stream is to be decoupled. Once the melt pool boundary is obtained, the physical domain is discretized in a cross-sectional direction. Based on the powder feed rate, elapsed time, and intersection of the melt pool and powder stream area substrate, layers of additive material are then added onto the nonplanar domain. A standard object is fit to each added layer to facilitate the numerical analysis of successive layers. Variations in physical parameters due to formation of nonplanar surfaces are incorporated into the model to increase the accuracy and reliability of the simulated results. The developed model was used to predict the geom...

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%.

Effect of Thermal and Stress Fields on the Microstructure of a Thin Wall Built Using Laser Solid Freeform Fabrication Process

Temperature distribution and consequent rapid cooling determine the microstructure and final physical properties of a part fabricated using laser solid freeform fabrication (LSFF). As well, in this technique, thermal stresses are the main cause of any possible delamination and crack formation across deposited layers. In this paper, the temperature distribution and the stress field induced during the LSFF process are studied throughout the fabrication of a thin wall up to four layers. The thin wall is fabricated of stainless steel AISI 304L using a 1 kW Nd:YAG pulsed laser. Variations of the microstructure and geometry of the wall are studied. A 3D dynamic numerical model of the multilayer LSFF process is used to interpret the experimental results in terms of the temperature distribution, stress field and microstructure. The experimental results show that the stress concentrations at the end points of the wall, which are due to the higher temperature gradient at these regions, are the locations for possible delaminations and crack formations. Different types of microstructures are observed at the various locations within the same layer due to the different cooling rate. While numerical results confirm the experimental findings, they also show that it is possible to reduce the maximum stress by preheating the substrate.Copyright

On the microstructure of a thin wall formed under thermal and stress fields induced in laser solid freeform fabrication process

In laser solid freeform fabrication (LSFF), the final microstructures and consequently the physical properties of the successive deposited layers of additive materials are determined through melting, solidification and solid state transformations caused by a moving laser beam. In this paper, temperature distribution and stress field induced during the multilayer LSFF process and their correlation with the local microstructure formation are studied throughout the fabrication of a four-layer thin wall of SS304L. For this purpose, parallel to the experimental investigation, a coupled 3D time-dependent numerical model is employed to simulate the process. The numerical and experimental results show that stress concentrations formed at the end points of the wall are the locations prone to potential delaminations and crack formations. Different types of microstructures, such as dendritic with and without secondary arm spacings, are observed at various locations within the same layer due to different cooling rates.

Correlation between temperature distribution and formed microstructure of in-situ laser cladding of Fe-TiC on carbon steel

One of the unique aspects of in-situ laser cladding is to create a uniform clad by melting the powder and a thin layer of the substrate to form a composite of pure powder components with minimal dilution. Therefore, this technique can be an excellent candidate for hardfacing process by deposition of multiple clad beads side by side on a low cost base material. Since TiC has desirable properties such as hardness, wear and corrosion resistance, in this work, the hardfacing process of AISI 1030 carbon steel using titanium (Ti) and graphite (C) as a composite coating material (i.e., Fe(Ti)-TiC) is investigated using a numerical and experimental analysis. In order to study the microstructure of the TiC morphology and distribution in the clad, a 3D time-dependent numerical model and ternary phase diagram are used to interpret the experimental results along with the temperature distributions formed throughout the deposition process. The morphology and distribution of TiC particles are studied by means of SEM, XRD.One of the unique aspects of in-situ laser cladding is to create a uniform clad by melting the powder and a thin layer of the substrate to form a composite of pure powder components with minimal dilution. Therefore, this technique can be an excellent candidate for hardfacing process by deposition of multiple clad beads side by side on a low cost base material. Since TiC has desirable properties such as hardness, wear and corrosion resistance, in this work, the hardfacing process of AISI 1030 carbon steel using titanium (Ti) and graphite (C) as a composite coating material (i.e., Fe(Ti)-TiC) is investigated using a numerical and experimental analysis. In order to study the microstructure of the TiC morphology and distribution in the clad, a 3D time-dependent numerical model and ternary phase diagram are used to interpret the experimental results along with the temperature distributions formed throughout the deposition process. The morphology and distribution of TiC particles are studied by means of SEM, XRD.

Chapter 22 – Multiphysics Modelling of Laser Solid Freeform Fabrication Techniques

Laser solid freeform fabrication is a flexible layered/additive manufacturing technique with the potential for various applications including rapid prototyping, coating, and high-value- component repair. This chapter first describes the importance of the modelling of this multifaceted technique and then outlines the underlying physics of the process. After introducing a basic lumped model, a 3D numerical modelling approach is described by which the geometry of the deposited material as well as coupled temperature and thermal stress fields across the process domain can be dynamically predicted. The chapter concludes with the multiphysics simulation of a thin wall as a case study.

The Effect of Thermal Field on the Deposition of Fe-TiC on Carbon Steel Using Laser Cladding

In this paper, a numerical and experimental method is used to investigate the effect of thermal fields on the deposition of Fe-TiC using the laser cladding process. Since in laser cladding temperature distributions and consequent rapid cooling rates determine the microstructure and final physical properties of the deposited layers, a 3D time-dependent numerical model is used to simulate the cladding process parallel to experimental analysis. The numerical results are used to study the temperature distributions and their evolutions throughout the deposition process. The experimental and verified numerical outcomes are then employed to study the variations of the microstructures of the deposited material as well as correlation between the formed microstructures and temperature distributions across the deposition domain. The numerical and experimental investigations are conducted through the deposition of Fe-TiC on the substrate of AISI 1030 carbon steel using a 1.1 kW fiber laser. The experimental results confirm that by increasing the substrate temperature throughout the process the distribution of the TiC particles changes along with the deposited tracks and the TiC particles start forming clusters at the top of the clad.Copyright

On the temperature distributions and thermal stresses induced in laser solid freeform fabrication of multi-material structures

In this paper, the effects of the material properties and their variations on the temperature distribution and thermal stress field, which have determining roles on the final qualities of a part fabricated using laser solid freeform fabrication process, are studied. This is achieved by numerical and experimental fabrications of a thin wall of two Stellite 6 layers and two Ti layers on a SS304L substrate. A 3D time-dependent numerical approach is used to simulate the process. Using this model, the geometry of the additive material in a layer-by-layer fashion as well as temperature distribution and thermal stress field are dynamically obtained throughout the process domain. The experimental and numerical results are used to characterize the build-up and also identify an optimum laser power for each layer deposition in order to reduce the thermal stresses.In this paper, the effects of the material properties and their variations on the temperature distribution and thermal stress field, which have determining roles on the final qualities of a part fabricated using laser solid freeform fabrication process, are studied. This is achieved by numerical and experimental fabrications of a thin wall of two Stellite 6 layers and two Ti layers on a SS304L substrate. A 3D time-dependent numerical approach is used to simulate the process. Using this model, the geometry of the additive material in a layer-by-layer fashion as well as temperature distribution and thermal stress field are dynamically obtained throughout the process domain. The experimental and numerical results are used to characterize the build-up and also identify an optimum laser power for each layer deposition in order to reduce the thermal stresses.

Effects of Process Parameters on Surface Finish in Laser Solid Freeform Fabrication

Laser Solid Freeform Fabrication (LSFF) is a flexible rapid prototyping technique in which a laser beam is used to melt and deposit the injected powder in a layer-by-layer fashion to form 3D components. In this paper, the effects of the main process parameters such as laser power and traverse speed on the surface finish of the parts fabricated using the LSFF process are investigated. Since these process parameters and their variations determine the microstructure and other resultant physical qualities of the fabricated parts, they should carefully be selected to increase the surface quality without compromising other quality aspects of the outcomes. For this purpose, along with the experimental analyses, an experimentally verified 3D time-dependent numerical model is employed to comprehensively study the temperature distributions, thermal stress fields, and their variations resulted from different process parameters and consequently different surface finishes. The experimental investigations are conducted through the fabrications of several thin walls of AISI 303L stainless steel using a fiber laser with a maximum power of 1100 W. The numerical and experimental results show under a constant power feed rate by increasing the process speed while optimizing the laser power, the surface finish of the fabricated parts can improve without compromising the melt pool conditions.Copyright

Effect of Preheating on the Delamination and Crack Formation in Laser Solid Freeform Fabrication Process

This paper presents a numerical-experimental investigation on the effects of preheating the substrate on the potential delamination and crack formation across the parts fabricated using the Laser Solid Freeform Fabrication (LSFF) process. For this purpose, the temperature distributions and stress fields induced during the multilayer LSFF process, and their correlation with the delamination and crack formation are studied throughout the numerical analysis and the experimental fabrication of a four-layer thin wall of SS304L. A 3D time-dependent numerical approach is used to simulate the LSFF process, and also interpret the experimental results in terms of the temperature distribution and the thermal stress fields. The numerical results show that by preheating the substrate prior to the fabrication process, the thermal stresses throughout the process domain substantially reduce. Accordingly, this can result in the reduction of potential micro-cracks formation across the fabricated part. Preheating also decreases the transient time for the development of a proper melt pool which is an important factor to prevent poor bonding between deposited layers. The experimental results are used to verify the numerical findings as well as the feasibility of preheating on the reduction of the micro-cracks formed throughout the fabrication process.Copyright