Process Control of 3D Welding as a Droplet-Based Rapid Prototyping Technique

Three-dimensional welding is investigated as a rapid prototyping technique for the production of real Inetallic parts using gas metal arc welding principles. A high speed machine vision system is used to study the correlation between droplet transfer parameters and resultant weld penetration characteristics. Experimental work is conducted to determine how droplet transfer frequency, droplet size, and number of passes affect the geometrical and Inetallurgical properties ofthe weld penetration. A finite element analysis is performed in order to study what influence additional layering has on the cooling characteristics and resultant penetration profile.Mechanical Engineerin

Techno-Economic Analysis of Hybrid Layered Manufacturing

Subtractive manufacturing (CNC machining) has high quality of geometric and material properties but is slow, costly and infeasible in some cases; additive manufacturing (RP) is just the opposite. Total automation and hence speed is achieved in RP by compromising on quality. Hybrid Layered Manufacturing (HLM) developed at IIT Bombay combines the best features of both these approaches. It uses arc welding for building near-net shapes which are finish machined to final dimensions. High speed of HLM surpasses all other processes for tool making by eliminating NC programming and rough machining. The techno-economic viability of HLM process has been proved through a real life case study. Time and cost of tool making using HLM promises to be substantially lower than that of CNC machining and other RP methods. Interestingly, the material cost in HLM was also found to be lower. HLM is a cheaper retrofitment to any 3 or 5 axis CNC milling machine or machining center.Mechanical Engineerin

Effect of Volume of Heat Sink on Process and Physical Properties of Parts Built by Welding Based SFF

A new numerical simulation of the effect of the volume of the heat sink on the welding–based deposition process is performed. For this purpose, the ANSYS parametric design language (APDL) is applied. Due to the complex internal and/or external shapes of the designed threedimensional (3D) part, different heat transfer conditions are met during the building process. The influences of the different heat transfer conditions on the physical part properties are also investigated. The influence of the volume of the heat sink on the process and on the physical properties is significant and can not be neglected. Extensive experiments are designed and executed in order to verify the conclusions derived from the finite elements model results and to investigate the material properties of the built part.Mechanical Engineerin

Nucleotides Regulate Secretion of the Inflammatory Chemokine CCL2 from Human Macrophages and Monocytes

CCL2 is an important inflammatory chemokine involved in monocyte recruitment to inflamed tissues. The extracellular nucleotide signalling molecules UTP and ATP acting via the P2Y2 receptor are known to induce CCL2 secretion in macrophages. We confirmed this in the human THP-1 monocytic cell line showing that UTP is as efficient as LPS at inducing CCL2 at early time points (2–6 hours). Expression and calcium mobilisation experiments confirmed the presence of functional P2Y2 receptors on THP-1 cells. UTP stimulation of human peripheral CD14+ monocytes showed low responses to LPS (4-hour stimulation) but a significant increase above background following 6 hours of treatment. The response to UTP in human monocytes was variable and required stimulation >6 hours. With such variability in response we looked for single nucleotide polymorphisms in P2RY2 that could affect the functional response. Sequencing of P2RY2 from THP-1 cells revealed the presence of a single nucleotide polymorphism altering amino acid 312 from arginine to serine (rs3741156). This polymorphism is relatively common at a frequency of 0.276 ( subjects). Finally, we investigated CCL2 secretion in response to LPS or UTP in human macrophages expressing 312Arg-P2Y2 or 312Ser-P2Y2 where only the latter exhibited significant UTP-induced CCL2 secretion ( donors per group)

Optimal Design of a Golf Club using Functionally Graded Porosity

The current work portrays a new concept of designing and manufacturing golf club heads with functionally graded porosity (FGP) by means of electron beam melting® (EBM®). In light of the advancement of additive manufacturing (AM) technologies and the consequent wide spread applications in the aerospace, automotive, and biomedical industries, the current work discusses a new application in sport technologies; for example, in the golf industry. EBM® makes it possible to print the designed porosity within a golf club head, to reduce the weight and optimize performance. The focus is to design the golf club head with FGP to improve performance and reduce weight. The dynamic properties of porous materials are investigated theoretically. The porosity in the club head was analyzed numerically by simulating the impact between the club head and a steel ball in order to determine the coefficient of restitution (COR) of the club head. The simulation’s parameters are in compliance with the U.S Golf Association’s (USGA) test procedure for measuring COR.Mechanical Engineerin

Induced gravitational collapse at extreme cosmological distances: the case of GRB 090423

CONTEXT: The induced gravitational collapse (IGC) scenario has been introduced in order to explain the most energetic gamma ray bursts (GRBs), Eiso=10^{52}-10^{54}erg, associated with type Ib/c supernovae (SNe). It has led to the concept of binary-driven hypernovae (BdHNe) originating in a tight binary system composed by a FeCO core on the verge of a SN explosion and a companion neutron star (NS). Their evolution is characterized by a rapid sequence of events: [...]. AIMS: We investigate whether GRB 090423, one of the farthest observed GRB at z=8.2, is a member of the BdHN family. METHODS: We compare and contrast the spectra, the luminosity evolution and the detectability in the observations by Swift of GRB 090423 with the corresponding ones of the best known BdHN case, GRB 090618. RESULTS: Identification of constant slope power-law behavior in the late X-ray emission of GRB 090423 and its overlapping with the corresponding one in GRB 090618, measured in a common rest frame, represents the main result of this article. This result represents a very significant step on the way to using the scaling law properties, proven in Episode 3 of this BdHN family, as a cosmological standard candle. CONCLUSIONS: Having identified GRB 090423 as a member of the BdHN family, we can conclude that SN events, leading to NS formation, can already occur already at z=8.2, namely at 650 Myr after the Big Bang. It is then possible that these BdHNe originate stem from 40-60 M_{\odot} binaries. They are probing the Population II stars after the completion and possible disappearance of Population III stars.Comment: 9 pages, 9 figures, to appear on A&

A microstructure-sensitive electro-chemo-mechanical phase-field model of pitting and stress corrosion cracking

An electro-chemo-mechanical phase-field formulation is developed to simulate pitting and stress corrosion in polycrystalline materials. The formulation incorporates dependencies of mechanical properties and corrosion potential on crystallographic orientation. The model considers the formation and charging dynamics of an electric double layer through a new general boundary condition for the solution potential. The potential of the model is demonstrated by simulating corrosion in polycrystalline materials with various grain morphology distributions. The results show that incorporating the underlying microstructure yields more extensive defects, faster defect kinetics, and irregular pit and crack shapes relative to a microstructurally-insensitive homogeneous material scenario