Surendar Marya

SERRATED CHIP PREDICTION IN FINITE ELEMENT MODELING OF THE CHIP FORMATION PROCESS

A 2D Finite Element Model set up using the Arbitrary Lagrangian Eulerian (A.L.E) formulation proposed in Abaqus/Explicit (v6.4) is employed to predict serrated chip formation during cutting process. No artificial criterion is employed to create the chip or to initiate serrated chip formation. The sensitivity of serrated chip prediction to numerical and process parameters is analyzed in this paper. Experimental tests in orthogonal cutting conditions on machining of AISI-4140 with coated and uncoated cemented-carbide inserts were carried out to validate numerical results. They showed significant influence of cutting speed and rake angle on the serrated chip phenomena. The comparison between numerical and experimental results showed a good qualitative agreement and underlined the outstanding influence of the element dimensions employed in Finite Element Modeling (F.E.M.) tests.

Steel-to-Aluminum Joining by Control of Interface Microstructures - Laser-Roll Bonding and Magnetic Pulse Welding -

Laser-roll bonding and magnetic pulse welding are two relatively new processes that greatly minimize problems of metallurgical incompatibilities between dissimilar metals and alloys. These two processes, though technologically apart and invented for components with distinct geometries, utilize to various extents high pressures to facilitate rapid and localized interfacial heating and create reliable joints. In this paper, relations between process parameters, microstructures, and properties are discussed for aluminum-to-steel joints made by laser-roll bonding and magnetic pulse welding.

Tolerances of joint gaps in Nd:YAG laser welded Ti-6Al-4V alloy with the addition of filler wire

The effect of joint gap on the butt joint quality of Ti-6Al-4V alloy welded using a 4 kW Nd:yttrium aluminum garnet laser was evaluated in terms of the welding defects, microstructure, hardness, and tensile properties. The joint gap was proportionally filled using the filler wire with the compositions of the parent alloy. Fully penetrated welds without cracking were obtained up to a joint gap of 0.5 mm. The main defects observed in the welds were porosity and underfill. Specifically, the porosity area increased with increasing joint gap but remained less than 1% of the fusion zone area. Large underfill defects appeared in the weldments in the absence of a joint gap, but filler wire addition was observed to reduce this defect in the presence of a joint gap. The weld hardness decreased slightly with increasing joint gap, but the tensile properties were optimized at an intermediary gap size, probably due to the compromise between the low underfill (after the use of a filler wire) and a limited amount of poro...

Effect of Post-Weld Heat Treatment on Nd: YAG Laser Welded Ti-6Al-4V Alloy Quality

The effects of post-weld heat treatment on 3.05-mm thick Ti-6Al-4V alloy were investigated using a 4 kW Nd:YAG laser. Two main defects, underfill and porosity, were observed. The use of filler wire reduced underfill defects but slightly increased porosity. No cracks were detected. The as-welded and stress-relief annealed welds had very similar microstructures, hardness, and tensile properties. However, the post-weld solution heat treatment and aging transformed the martensite in the fusion zone into a coarse interlamellar α-β structure, causing a decrease in ductility but a more homogeneous distribution in the hardness of the welds.

On the Forming of Metallic Parts through Electromagnetic and Electrohydraulic Processing

Forming of metallic parts by the application of high intensity transitory magnetic pulses or shock waves is a challenge task from industrial perspectives as this offers extended scope of forming highly precise parts that result from material behavior at high deformation rates. Electromagnetic forming requires that the part must be intrinsically very conducting. The electrohydraulic forming is exempt from this material constraint as the deformation is generated by a shock wave in a fluid through electric discharge in between the electrodes. The application of a static pressure during forming is used to reduce the discharge energy for a given deformation. Work has been conducted to form different parts through these two techniques involving aluminum, copper and steels. The paper presents the technical obstacles still facing the electromagnetic techniques and gives examples of formed parts and joints in relation with microstructures.

Material Flow Stress Sensitivity Analysis in Numerical Cutting Modeling

Numerical cutting modeling provides understanding and prediction of chip formation process variables such as stress, temperature, cutting forces… . Thus, it could help to improve several areas related to the cutting process as cutting tool development, machining parameter set up, material development and so on. However, several aspects as numerical model definition, validation of numerical results and identification of entry parameters should be improved prior to offering it as a robust and reliable tool to the industry. This paper deals with workpiece material flow stress identification. Several aspects are pointed out : the difficulty to validate numerical results, the influence of the material flow stress, the need to establish tolerances during parameter identification and the difficulty to properly identify by inverse simulation material flow stress coefficients.

3D construction and repair from welding and material science perspectives

Additive manufacturing, based on layer-by-layer deposition of a feedstock material from a 3D data, can be mechanistically associated to welding. With feedstock fusion based processes, both additive manufacturing and welding implement similar heat sources, feedstock materials and translation mechanisms. From material science perspectives, additive manufacturing can take clue from lessons learned by millennium old welding technology to rapidly advance in its quest to generate fit for service metallic parts. This paper illustrates material science highlights extracted from the fabrication of a 316 L air vent and the functional repair of a Monel K500 (UNS N0500) with Inconel 625.

Enhanced Weld Penetrations In GTA Welding with Activating Fluxes Case studies: Plain Carbon & Stainless Steels, Titanium and Aluminum

Flux applications prior to the convention Gas Tungsten Arc Welding (GTAW) is known to improve weld penetrations and improve process competitiveness. This paper summarizes the investigations on aluminum, plain carbon steels, stainless steels and titanium. The importance of flux composition, homogeneity and profile of its application are shown to be primordial in determining the weld depth to width ratio of weld pools. The mechanisms that lead to improved penetrations along with some industrial case studies are presented.Key Words: ATIG, Weld penetrations, Steels, Titanium, Aluminum

Additive Manufacturing Viewed from Material Science: State of the Art & Fundamentals

Additive Manufacturing (AM), also designated as 3D Printing (3DP), is one of the most visionary and friendly approaches for flexible manufacturing with conservation of energy and material resources. It is a factory in a box that can generate multiple objects. It requires little manpower to bring virtual innovations into the real world. AM for metals can be mechanistically associated with welding. The technique employs a variety of energy sources (laser, electron beam, electric Arc, ...), feed stocks (powder, wire and ribbon) and motion kinematics & control (articulated robot and 3-5 axes CNC machine ). From the materials perspectives, akin to fusion welding in many respects, AM involves a multitude of complex and interacting physical phenomena such as heat transfer, fluid flow, discrete and continuum mechanics, sintering, melting, solidification, solid state transformations, grain growth, diffusion, textures etc. The desired process performance can be achieved by controlling the parameters of energy, feed stock and motion. The effect of successive thermal cycles along with the epitaxial relations between substratum and deposits constitute some of the challenging tasks for developing optimized parts. This paper reviews the state of the art and presents some challenges facing metal product development for service applications.

Research and development of laser technology in materials processing

Laser Materials Processing is no longer a scientific curiosity but a common day Industrial reality. Lasers in manufacturing sector are currently used in welding, cutting, drilling, cladding, marking, cleaning, micro-machining and forming. Recently, high power laser diode, LD pumped YAG laser, 10 kW lamp pumped YAG laser, 700 W fiber laser and excimer laser have been developed in the industrialized countries, which had their own big national projects. As a result of large numbers of research and developments, the modern laser materials processing has been realized and used in all kinds of industries now. At the beginning of 20th century, the price of laser system has become lower competitive to the conventional lasers. Lower the price of laser diode systems is, wider is the field of their applications. In the present paper, the researches and developments in laser materials processing in US, EU and Japan are outlined and metallurgical aspects are described on the base of laboratory researches.