Sensitivity Analysis of Process Parameters in Laser Deposition

In laser cladding with powder injection process, process output parameters, including melt pool temperature and melt pool dimensions, are critical for part quality. This paper uses simulation and experiments to investigate the effect of the process input parameters: laser power, powder mass flow rate, and scanning speed on the output parameters. Numerical simulations and experiments are conducted using a factorial design. The results are statistically analyzed to determine the significant factors and their interactions. The simulation results are compared to experimental results. The quantitative agreement/disagreement is discussed and further research is outlined.Mechanical Engineerin

Numerical modeling of heat transfer and fluid flow in laser metal deposition by powder injection

Laser metal deposition is an additive manufacturing technique which allows quick fabrication of fully-dense metallic components directly from Computer Aided Design (CAD) solid models. A self-consistent three-dimensional model was developed for the laser metal deposition process by powder injection, which simulates heat transfer, phase changes, and fluid flow in the melt pool, The governing equations for solid, liquid and gas phases in the calculation domain have been formulated using the continuum model. The free surface in the melt pool has been tracked by the Volume of Fluid (VOF) method, while the VOF transport equation was solved using the Piecewise Linear Interface Calculation (PLIC) method. Surface tension was modeled by taking the Continuum Surface Force (CSF) model combined with a force-balance flow algorithm. Laser-powder interaction was modeled to account for the effects of laser power attenuation and powder temperature rise during the laser metal deposition process. The governing equations were discretized in the physical space using the finite volume method. The advection terms were approximated using the MUSCL flux limiter scheme. The fluid flow and energy equations were solved in a coupled manner. The incompressible flow equations were solved using a two-step projection method, which requires a solution of a Poisson equation for the pressure field. The discretized pressure Poisson equation was solved using the ICCG (Incomplete Cholesky Conjugate Gradient) solution technique. The energy equation was solved by an enthalpy-based method. Temperature-dependent thermal-physical material properties were considered in the numerical implementation. The numerical model was validated by comparing simulations with experimental measurements --Abstract, page iv

Numerical Modeling of the Additive Manufacturing (AM) Processes of Titanium Alloy

It is easy to understand why industry and, especially, aerospace engineers love titanium. Titanium parts weigh roughly half as much as steel parts, but its strength is far greater than the strength of many alloy steels giving it an extremely high strength-to-weight ratio. Most titanium alloys are poor thermal conductors, thus heat generated during cutting does not dissipate through the part and machine structure, but concentrates in the cutting area. The high temperature generated during the cutting process also causes a work hardening phenomenon that affects the surface integrity of titanium, and could lead to geometric inaccuracies in the part and severe reduction in its fatigue strength [Benes, 2007]. On the contrary, additive manufacturing (AM) is an effective way to process titanium alloys as AM is principally thermal based, the effectiveness of AM processes depends on the material\u27s thermal properties and its absorption of laser energy rather than on its mechanical properties. Therefore, brittle and hard materials can be processed easily if their thermal properties (e.g., conductivity, heat of fusion, etc.) are favorable, such as titanium. Cost effectiveness is also an important consideration for using additive manufacturing for titanium processing. Parts or products cast and/or machined from titanium and its alloys are very expensive, due to the processing difficulties and complexities during machining and casting. AM processes however, have been found to be very cost effective because they can produce near-net shape parts from these high performance metals with little or no machining [Liou & Kinsella, 2009]. In the aerospace industry, titanium and its alloys are used for many large structural components. When traditional machining/cast routines are adopted, conversion costs for these heavy section components can be prohibitive due to long lead time and low-yield material utilization [Eylon & Froes, 1984]. AM processes have the potential to shorten lead time and increase material utilization in these applications. The following sections 1.1, 1.2 and 1.3 summarize the fundamental knowledge for the modeling of additive manufacturing processes

A Review of Layer Based Manufacturing Processes for Metals

The metal layered manufacturing processes have provided industries with a fast method to build functional parts directly from CAD models. This paper compares current metal layered manufacturing technologies from including powder based metal deposition, selective laser sinstering (SLS), wire feed deposition etc. The characteristics of each process, including its industrial applications, advantages/disadvantages, costs etc are discussed. In addition, the comparison between each process in terms of build rate, suitable metal etc. is presented in this paper.Mechanical Engineerin

Genome-wide identification and functional analysis of lincRNAs acting as miRNA targets or decoys in maize

LincRNA information derived from three articles. (XLS 20 kb

Co-Emergence of Specialized Endothelial Cells from Embryonic Stem Cells.

A well-formed and robust vasculature is critical to the health of most organ systems in the body. However, the endothelial cells (ECs) forming the vasculature can exhibit a number of distinct functional subphenotypes like arterial or venous ECs, as well as angiogenic tip and stalk ECs. In this study, we investigate the in vitro differentiation of EC subphenotypes from embryonic stem cells (ESCs). Using our staged induction methods and chemically defined mediums, highly angiogenic EC subpopulations, as well as less proliferative and less migratory EC subpopulations, are derived. Furthermore, the EC subphenotypes exhibit distinct surface markers, gene expression profiles, and positional affinities during sprouting. While both subpopulations contained greater than 80% VE-cad+/CD31+ cells, the tip/stalk-like EC contained predominantly Flt4+/Dll4+/CXCR4+/Flt-1- cells, while the phalanx-like EC was composed of higher numbers of Flt-1+ cells. These studies suggest that the tip-specific EC can be derived in vitro from stem cells as a distinct and relatively stable EC subphenotype without the benefit of its morphological positioning in the sprouting vessel

Enabling VNA Based Channel Sounder for 6G Research: Challenges and Solutions

To support research and development for sixthgeneration(6G) communication, it is imperative to understandthe application needs and develop accurate and realistic channelmodels to meet the application needs. Several key radio technologiesare identified for 6G research, including utilization offrequency bands ranging from sub-6 GHz to THz, antenna configurationcovering simple single antenna to complicated giganticmultiple-input and multiple-output (MIMO) systems, and diversedeployment scenarios requiring various measurement ranges.This paper summarizes latest strategies to significantly extendthe capabilities of current vector network analyzer (VNA)-basedchannel sounder, mainly radio-over-fiber (RoF) to enable longrangechannel measurements, phase compensation to achieveaccurate and coherent phase measurement, frequency extensionto extend the carrier frequency and frequency bandwidth,and virtual antenna array (VAA) schemes to enable multiantenna/link channel measurements

Measurement-Based Multi-Link Massive MIMO Channel Characterization at Millimeter-Wave Bands

This paper presents a multi-user channel measurement campaign using a recently developed VNA-based multi-link channel sounder in an indoor hall scenario. The channel sounder architecture and comparison with the conventional multi-linkchannel sounder are firstly demonstrated, with a focus on the cost-effectiveness of the developed channel sounder. The two multi-user location combinations are considered in these channel measurements. The empirical channel data for the multi-user is then processed using the calibration procedure. By using the classical beamforming algorithm, the power-angle-delay-profiles (PADPs) are obtained from the calibrated channel response. The channel characteristics of the two links, i.e., PADP, delay and angular spread, are analyzed and compared