Manufacture of Functionally Gradient Materials Using Weld-Deposition

When the inherent inhomogeneity of Additive Manufacturing techniques is carefully exploited, the anisotropy transforms into the desired distribution of the properties paving the way for manufacture of Functionally Gradient Materials. The present work focuses on using welddeposition based Additive Manufacturing techniques to realize the same. Mechanical properties like hardness and tensile strength can be controlled by a smaller degree through control of process parameters like current, layer thickness etc. A wider control of material properties can be obtained with the help of tandem weld-deposition setup like twin-wire. In tandem twin-wire weld-deposition, two filler wires (electrodes) are guided separately and it is possible to control each filler wire separately. The investigations done on these two approaches are presented in pape

Numerical Simulation of Spin Coating Process for Circular Disc

The process of applying a uniform thin film on a horizontal substrate is called spin coating. Spin coating relatively used in several industrial and scientific applications. In this study an attempted was made to numerically study the various factors affecting the spin coating process. CFD simulations were performed on 2D axisymetric geometry, VOF multiphase model was used to its work the liquid/gas interface, results from isothermal CFD simulation were first validated against theoretical values. Subsequently, CFD simulations were performed to determine the effects of flow important parameters. Parametric study was a alone to see the effect of spin, thermo viscosity and thermo capillary on spin coating process

MANUFACTURE OF FUNCTIONALLY GRADIENT OBJECTS THROUGH WELD-DEPOSITION

Functionally Gradient Material (FGM) may have a controlled variation of the material matrix so as to obtain the desired distribution of the properties such as color, density, porosity, hardness, toughness etc. There is a growing interest in FGMs due to their ability to offer high toughness, high strength, machinability, better resistance to corrosion and oxidation effects, and facilitating bonding of metals without severe internal thermal stresses. However, actual realization of FGMs still remains a challenge. Most naturally occurring objects are gradient in nature; examples are bamboo, bone, stone etc. Most man-made objects on the other hand are uniform. This is mainly due to the complexity involved in their design and subsequent manufacturing. The objects built through Additive Manufacturing techniques are inhomogeneous or non-uniform, i.e., they are inherently anisotropic. When this inherent nature is carefully exploited, the anisotropy transforms into the desired distribution of the properties. Weld-deposition based Additive Manufacturing techniques offer unique advantages on that front due to their ability to control the properties of the deposited matrix by controlling the process parameters like current, layer thickness etc. Preliminary experiments carried out this subject have shown that the hardness of the material is dependent on the weld-deposition current. Hence, online control of the same will help in manufacturing a metal matrix with variable hardness value. The variation possible through this method however will be limited in nature. A wider control of material properties can be obtained with the help of tandem weld-deposition setup like twin-wire. In twin-wire weld-deposition, two filler wires (electrodes) are guided separately and it is possible to control each filler wire individually. The present work focuses on obtaining a wide range of material properties by selecting filler wires with complementary properties and controlling the deposition rate of each of them separately. The experimental setup of Twin-wire Weld-deposition based Additive Manufacturing (TWAM) are discussed in detail. Working principle of twin-wire weld-deposition process along with the individual attachments viz. welding torch, wire feeder and power source are also presented. ER70S-6 and ER110S-G are the two filler wires used for the study; the former has lower hardness than the latter. The range of process parameter for different combinations of these filler wires was determined and the operating range of the same was identified. A second order regression equation for predicting weld bead geometry of width and height as a function of wire speed and torch speed was generated based on a series of experiments and subsequently validated. Subsequently, the criterion for adapting the twin-wire welding from joining to weld-deposition of a complete layer like thermal steady-state condition, effect of torch direction and effect of overlapping beads have also been studied. Having established the primary process parameters and the secondary operating condition for the TWAM process, various experiments carried out to identify the suitable process parameters at a given location for a desired variation of hardness have been presented. A predictive model for obtaining the wire speed of the filler wires required for a desired value of hardness was also created. The following four sample layers were fabricated to demonstrate the concept of realizing FGMs through TWAM (1) gradient in stepover direction (2) gradient in weld-deposition direction and (3) gradient in both the directions (4) gradient in three dimensions. The latter two as the hardness variation is occurring in every weld-bead, a given weld-bead has to be divided into multiple sub-programs and each sub-program representing the particular set of process parameters has to be called from the robot controller. The fabricated parts showed good match with the desired hardness values for a given location. Furthermore, to demonstrate the possible applications of TWAM, two illustrative examples were fabricated. Once the methodology for fabrication of FGMs has been established, characterization of objects fabricated through TWAM have been undertaken. Specimen made with five different combinations of filler wires {100:0, 75:25, 50:50, 25:75, 0:100} were used for the analysis. These specimen were examined further by subjecting them to micro hardness, microstructural, X-Ray Fluorescence (XRF), Energy Dispersive X-ray analysis (EDAX) and X-Ray diffraction (XRD) analysis. Further on, the width of the transition region while switching over from one set of parameters to another was also investigated. That will help in assessing the best possible resolution of the gradient matrix possible. Modelling of the welding process is felt necessary to understand the evolution of the material properties and to better control the thermal and structural characteristics like residual stresses resulting from the process. With the help of Finite Element Analysis (FEA) and experimental methods, the effect of area filling paths on the residual stresses developed during weld-deposition have been investigated. Three area-filling patterns viz. raster, spiral-in and spiral-out were chosen. FEA for these three patterns was done using ANSYS Mechanical APDL. The twin-wire arc weld-deposition was modeled as a set of two moving heat sources separated at a fixed distance. The deposited material was activated by element birth method once the arc passes over a location, simulating the weld material deposition. The temperature gradient induced residual stresses produced during and post material deposition were predicted using passively coupled thermo-mechanical simulations. For validation, the residual stresses in the weld-deposition specimen were measured using an X-ray diffraction (XRD) system. Temperature distribution plays a critical role in the evolution of the residual stresses during weld-deposition. Hence, two metrics viz., thermal mismatch profile and secant-temperature rate were introduced to quantify preheat and conduction. It was observed that raster patterns had the lowest thermal mismatch and secant-rates resulting in lowest residual stresses of the three area-fill patterns. Residual stresses from experiments are of the same order as those obtained from elastic-FE simulations, however, with a low accuracy of the prediction. Hence, these cannot be directly used for investigating the residual stresses developed. Nevertheless, for comparing the various area-fill patterns, these simulations can provide preliminary insights. With a combination of (1) process parameter study of twin wire deposition, (2) manufacturing of gradient objects, (3) characterization of gradient layers, (4) modelling of twin wire deposition process, this research attempt tries to establish twinwire weld-deposition based additive manufacturing as the viable method for the manufacture of functionally gradient materials

Determination of Process Parameter for Twin-Wire Weld-Deposition Based Additive Manufacturing

Various energy sources are available for sintering and/or depositing the material in additive manufacturing for metallic objects. These can be mainly categorized as laser based, electron beam based and arc based. While laser and electron offer better surface finish, it is possible to achieve high deposition rates in arc based weld-deposition. The inferior surface finish can be compensated by going for a hybrid system, combining deposition and machining. Twin-wire based weld-deposition, used in the present work, makes it possible to even realize functionally gradient material matrix; the use of two different filler materials into a single weld-pool makes this possible. Wire speed, torch speed and filler material are important factors that effect the composition of the deposited volume. Determination of the operating range and effect of these process parameters therefore is important to control the properties of the weld-deposited gradient objects. The current work presents the material composition of two filler materials ER70S6 and ER110SG with different wire speed and torch speed. Deposited material elemental compositions were analyzed using ED-XRF machine

Studies on Dissimilar Twin-Wire Weld-Deposition for Additive Manufacturing Applications

Due to its high deposition rate, low cost and simple setup, weld-deposition based additive manufacturing is slowly evolving into a viable alternative for creating meso-scale applications. There is also an increasing demand for creating functionally gradient objects with varying properties. Gas metal arc welding based twin-wire weld-deposition presented here makes it possible to create functionally gradient objects with varying mechanical properties like hardness. This is achieved by using separate filler wires of different composition and controlling the proportion of each wire separately. The current work presents a proof of concept of the twin-wire weld-deposition and also the primary experiments carried out for understanding the effect of weld-deposition process parameter on bead geometry. Two filler wires viz., ER70S-6 and ER110S-G, the former having lower hardness than the latter, were used for the experimentation. The range of process parameter for different combinations of these filler wires was determined and the operating range of the same was identified. Subsequently, the criterion for adapting the twin-wire welding from joining to weld-deposition of a complete layer like thermal steady-state condition, effect of torch direction and effect of overlapping beads have also been studied

Determination of Process Parameter for Twin-Wire Weld-Deposition Based Additive Manufacturing

Various energy sources are available for sintering and/or depositing the material in additive manufacturing for metallic objects. These can be mainly categorized as laser based, electron beam based and arc based. While laser and electron offer better surface finish, it is possible to achieve high deposition rates in arc based weld-deposition. The inferior surface finish can be compensated by going for a hybrid system, combining deposition and machining. Twin-wire based weld-deposition, used in the present work, makes it possible to even realize functionally gradient material matrix; the use of two different filler materials into a single weld-pool makes this possible. Wire speed, torch speed and filler material are important factors that effect the composition of the deposited volume. Determination of the operating range and effect of these process parameters therefore is important to control the properties of the weld-deposited gradient objects. The current work presents the material composition of two filler materials ER70S6 and ER110SG with different wire speed and torch speed. Deposited material elemental compositions were analyzed using ED-XRF machine

Investigations into effect of weld-deposition pattern on residual stress evolution for metallic additive manufacturing

Twin-wire welding based additive manufacturing (TWAM) is a novel additive manufacturing (AM) process for creating metallic objects using gas metal arc welding (GMAW). The twin-wire welding, apart from offering higher deposition rates, also makes it possible to create gradient objects by the use of dissimilar filler wires. However, there is necessity to manage the thermal stresses while depositing multiple layers on the substrate plate; this is one of the major challenges to be addressed. With the help of finite element analysis (FEA) and experimental methods, this paper studies the effect of area-filling paths on the residual stresses developed during weld-deposition. Three area-filling patterns viz. raster, spiral-in, and spiral-out were chosen. FEA for these three patterns was done using ANSYS Mechanical APDL. The twin-wire arc weld-deposition was modeled as a set of two moving heat sources separated at a fixed distance. The deposited material was activated by element birth method once the arc passes over a location, simulating the weld material deposition. The temperature gradient induced residual stresses produced during and post material deposition was predicted using passively coupled thermo-mechanical simulations. For validation, the weld-deposition experiments were done using twin-wire GMAW welding set up, and residual stresses were measured using an X-ray diffraction (XRD) system. Temperature distribution plays a critical role in the evolution of the residual stresses during weld-deposition. Hence, two metrics viz., thermal mismatch profile, and secant-temperature rate were introduced to quantify preheat and conduction. It was observed that raster patterns had the lowest thermal mismatch and secant rates resulting in the lowest residual stresses of the three area-fill patterns. Residual stresses from experiments has reasonable correlation with those obtained from elastic-FE simulations in order as well as trend and provide valuable insights into the evolution of the stresses for various area-fill patterns in TWAM

Functionalizing magnet additive manufacturing with in-situ magnetic field source

Additive manufacturing via 3-D printing technologies have become a frontier in materials research, including its application in the development and recycling of permanent magnets. This work addresses the opportunity to integrate magnetic field sources into 3-D printing process in order to enable printing, alignment of anisotropic permanent magnets or magnetizing of magnetic filler materials, without requiring further processing. A non-axisymmetric electromagnet-type field source architecture was designed, modelled, constructed, installed to a fused filament commercial 3-D printer, and tested. The testing was performed by applying magnetic field while printing composite anisotropic Nd-Fe-B + Sm-Fe-N powders bonded in Nylon12 (65 vol.%) and recycled Sm-Co powder bonded in PLA (15 vol.%). Magnetic characterization indicated that the degree-of-alignment of the magnet powders increased both with alignment field strength (controlled by the electric current applied to the magnetizing system) and the printing temperature. Both coercivity and remanence were found to be strongly dependent on the degree-of-alignment, except for printing performed below but near the Curie temperature of Nd-Fe-B (310 degrees C). At applied field of 0.15 kOe, Sm-Co and hybrid Nd-Fe-B/Sm-Fe-N printed samples showed degrees-of-alignment of 83 % and 65 %, respectively. The variations in coercivity were consistent with previous observations in bonded magnet materials. This work verifies that integration of magnetic field sources into 3-D printing processes will result in magnetic alignment of particles while ensuring that other advantages of 3-D printing are retained.</p

Functionalizing magnet additive manufacturing with in-situ magnetic field source

Additive manufacturing via 3-D printing technologies have become a frontier in materials research, including its application in the development and recycling of permanent magnets. This work addresses the opportunity to integrate magnetic field sources into 3-D printing process in order to enable printing, alignment of anisotropic permanent magnets or magnetizing of magnetic filler materials, without requiring further processing. A non-axisymmetric electromagnet-type field source architecture was designed, modelled, constructed, installed to a fused filament commercial 3-D printer, and tested. The testing was performed by applying magnetic field while printing composite anisotropic Nd-Fe-B + Sm-Fe-N powders bonded in Nylon12 (65 vol.%) and recycled Sm-Co powder bonded in PLA (15 vol.%). Magnetic characterization indicated that the degree-of-alignment of the magnet powders increased both with alignment field strength (controlled by the electric current applied to the magnetizing system) and the printing temperature. Both coercivity and remanence were found to be strongly dependent on the degree-of-alignment, except for printing performed below but near the Curie temperature of Nd-Fe-B (310 degrees C). At applied field of 0.15 kOe, Sm-Co and hybrid Nd-Fe-B/Sm-Fe-N printed samples showed degrees-of-alignment of 83 % and 65 %, respectively. The variations in coercivity were consistent with previous observations in bonded magnet materials. This work verifies that integration of magnetic field sources into 3-D printing processes will result in magnetic alignment of particles while ensuring that other advantages of 3-D printing are retained