Jyotirmoy Mazumder

Closed loop direct metal deposition: art to part

Abstract The direct metal deposition (DMD) process is drawing considerable contemporary interest due to its capability to deliver “Art to Part”. DMD can reduce the lead time for a concept to product by eliminating several intermediate steps. The most attractive feature of the process is that not only can it produce functional parts but it can also be interfaced with the homogenization design method, heterogeneous solid model and computer aided design software to produce “Designed Material” with desired properties generally not observed in nature. Closed loop DMD is a synthesis of multiple technologies including lasers, sensors, computer numerical controlled work handling stage, CAD/CAM software and cladding metallurgy. This paper describes the methodology used to produce a designed macro- and microstructure and reviews the state of the art for closed loop DMD.

Numerical simulation of heat transfer and fluid flow in coaxial laser cladding process for direct metal deposition

The coaxial laser cladding process is the heart of direct metal deposition (DMD). Rapid materials processing, such as DMD, is steadily becoming a tool for synthesis of materials, as well as rapid manufacturing. Mathematical models to develop the fundamental understanding of the physical phenomena associated with the coaxial laser cladding process are essential to further develop the science base. A three-dimensional transient model was developed for a coaxial powder injection laser cladding process. Physical phenomena including heat transfer, melting and solidification phase changes, mass addition, and fluid flow in the melt pool, were modeled in a self-consistent manner. Interactions between the laser beam and the coaxial powder flow, including the attenuation of beam intensity and temperature rise of powder particles before reaching the melt pool were modeled with a simple heat balance equation. The level-set method was implemented to track the free surface movement of the melt pool, in a continuous las...

Fabrication of microfluidic mixers and artificial vasculatures using a high-brightness diode-pumped Nd:YAG laser direct write method

This paper describes a direct write laser technology, which is fast and flexible, for fabricating multiple-level microfluidic channels. A high brightness diode-pumped Nd-YAG laser with slab geometry was used for its excellent beam quality. Channels with flat walls and staggered herringbone ridges on the floor have been successfully fabricated and their ability to perform passive mixing of liquid is discussed. Also, a multi-width multi-depth microchannel has been fabricated to generate biomimetic vasculatures whose channel diameters change according to Murrays law, which states that the cube of the radius of a parent vessel equals the sum of the cubes of the radii of the daughters. The multi-depth architecture allows for flow patterns to resemble physiological vascular systems with lower overall resistance and more uniform flow velocities throughout the network compared to planar patterning techniques which generate uniformly thin channels. The ability to directly fabricate multiple level structures using relatively straightforward laser technology enhances our ability to rapidly prototype complex lab-on-a-chip systems and to develop physiological microfluidic structures for tissue engineering and investigations in biomedical fluidics problems.

A method for the design and fabrication of heterogeneous objects

Layered Manufacturing (LM), also referred to as Solid Freeform Fabrication (SFF), is emerging as a new technology that enables the fabrication of three-dimensional heterogeneous objects. To take full advantage of this capability, a new method to design and fabricate heterogeneous components has to be developed. This paper introduces an integrated design and fabrication system for heterogeneous objects, especially Functionally Graded Materials (FGMs). We first describe the variant design paradigm and a constructive representation scheme for heterogeneous objects. A discretization-based process planning method, which converts continuous material variation into stepwise variation, is then described. Next, Direct Metal Deposition (DMD), a laser-based LM method that can take advantage of the proposed process planning method, is described in detail. Finally, examples are shown to illustrate the entire design-fabrication cycle for heterogeneous objects.

Modelling of high-density laser-material interaction using fast level set method

A high-energy-density laser beam-material interaction process has been simulated considering a self-evolving liquid-vapour interface profile. A mathematical scheme called the level-set technique has been adopted to capture the transient liquid-vapour interface. Inherent to this technique are: the ability to simulate merger and splitting of the liquid-vapour interface and the simultaneous updating of the surface normal and the curvature. Unsteady heat transfer and fluid flow phenomena are modelled, considering the thermo-capillary effect and the recoil pressure. A kinetic Knudsen layer has been considered to simulate evaporation phenomena at the liquid-vapour interface. Also, the homogeneous boiling phenomenon near the critical point is implemented. Energy distribution inside the vapour cavity is computed considering multiple reflection phenomena. The effect of laser power on the material removal mode, liquid layer thickness, surface temperature and the evaporation speed are presented and discussed.

Multiple reflection and its influence on keyhole evolution

In laser drilling and keyhole welding, multiple reflection phenomena determine how the energy is transferred from the laser beam to the workpiece, and, most importantly, all other physics such as fluid flow, heat transfer, and the cavity shape itself depend on these phenomena. In this study, a multiple reflection model inside a self-consistent (or self-evolving) cavity has been developed based on the level set method and ray tracing technique. In the case of drilling, it is observed that the laser energy tends to concentrate near the center, where the effective intensity reaches a value two orders of magnitude higher than the original distribution. In keyhole welding, however, the maximum laser intensity is only around five times higher than the original during the entire process. Combined with the strong keyhole fluctuation, the redistributed intensity patterns are very dynamic. The intensity fluctuation drives the keyhole fluctuation, and the keyhole fluctuation, in turn, affects the intensity fluctuati...

Role of preheating and specific energy input on the evolution of microstructure and wear properties of laser clad Fe-Cr-C-W alloys

Synthesis of Fe-Cr-C-W alloy (10 : 4 : 1 : 1, wt(%)) was carried out on AISI 1016 steel substrate using laser cladding technique which lead to the development of a suitable alternate for cobalt bearing wear resistant alloys. This study involved understanding of process variables like preheating temperature and specific energy input on the evolution of microstructures and their effect on wear resistance properties. The microstructure was examined with a scanning electron microscope and various types of complex carbides were identified using both energy dispersive x-ray and auger spectroscopy facilities. A combination of MC, M7C3 and M6C types of carbides of certain proportions (formed at a preheating temperature of 484°C with specific energy input of 9.447 KJ/cm2) has been found to be most attractive for achieving an optimum combination of microhardness and steady state friction coefficient values. A similar advantage may be derived at a lower level of specific energy input of 8.995 KJ/cm2 but with a higher preheating temperature of 694°C. However, increasing the specific energy input to 12.376 KJ/cm2 can significantly soften the matrix.

Physics of zinc vaporization and plasma absorption during CO2 laser welding

A number of mathematical models have been developed earlier for single-material laser welding processes considering one-, two-, and three-dimensional heat and mass transfers. However, modeling of laser welding of materials with multiple compositions has been a difficult problem. This paper addresses a specific case of this problem where CO2 laser welding of zinc-coated steel, commonly used in automobile body manufacturing, is mathematically modeled. The physics of a low boiling point material, zinc, is combined with a single-material (steel) welding model, considering multiple physical phenomena such as keyhole formation, capillary and thermocapillary forces, recoil and vapor pressures, etc. The physics of laser beam–plasma interaction is modeled to understand the effect on the quality of laser processing. Also, an adaptive meshing scheme is incorporated in the model for improving the overall computational efficiency. The model, whose results are found to be in close agreement with the experimental observ...

Microstructural Characterization of Laser-Deposited Al 4047 Alloy

Direct metal deposition (DMD) technology is a laser-aided rapid prototyping method that can be used to fabricate near net shape components from their CAD files. In the present study, a series of Al-Si samples have been deposited by DMD in order to optimize the laser deposition parameters to produce high quality deposit with minimum porosity and maximum deposition rate. This paper presents the microstructural evolution of the as-deposited Al 4047 sample produced with optimized process parameters. Optical, scanning, and transmission electron microscopes have been employed to characterize the microstructure of the deposit. The electron backscattered diffraction method was used to investigate the grain size distribution, grain boundary misorientation, and texture of the deposits. Metallographic investigation revealed that the microstructural morphology strongly varies with the location of the deposit. The layer boundaries consist of equiaxed Si particles distributed in the Al matrix. However, a systematic transition from columnar Al dendrites to equiaxed dendrites has been observed in each layer. The observed variation of the microstructure was correlated with the thermal history and local cooling rate of the melt pool.

Effects of laser beam spatial distribution on laser-material interaction

The efficiency of any laser materials processing depends on the efficient energy transfer from the laser to a substrate. One of the critical factors in the process is the spatial distribution or the “mode” of the laser beam. Although an inverse Bremsstrahlung initiates the photon to electron energy transfer, a major part of the process is transport phenomena created by the absorbed energy. A mathematical model for transport phenomena during laser materials interaction is developed that includes multiple reflections, capillary and thermocapillary forces, recoil pressure, temperature distribution, melt pool flow, and phase changes. This model simulates interaction between a CO2 laser (λ = 10.6 μm) with four different spatial distributions and iron. The results of a simulation for fundamental understanding of this laser-material interaction are presented in this paper. First, overall keyhole behaviors are compared in terms of response time, penetration hole geometry, and absorptivity. Furthermore, a dimensionless parameter is developed to examine keyhole collapse quantitatively. Finally, velocity, temperature, and, intensity fields are analyzed.