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West Lafayette, IN, United States

Mann J.B.,M4 Sciences LLC | Saldana C.,Pennsylvania State University
Transactions of the North American Manufacturing Research Institution of SME | Year: 2013

The present study characterizes the effects of modulation amplitude on forces and specific energies in machining of AA6061-T6. These effects are correlated with tool load duty cycles that vary directly with modulation amplitude. Closed-form expressions were derived to evaluate fraction of time spent cutting in the presence of modulation. The duty cycle ratio ranges from 1 to 0.5 depending on the modulation amplitude used for a specific modulation frequency and spindle frequency combination. When the duty cycle decreased, average machining forces rise while the apparent average machining forces and specific energies both decrease. Use of apparent average machining forces for describing tool load profiles was found to be tenuous as maximum load on the tool actually increases in the presence of modulation. The ability to modify the fraction of time spent cutting has direct implications for affecting changes in thermal dissipation and interface lubrication, which are important in characterizing the effects of machining conditions on surface integrity and cutting tool performance. Source

Mahato A.,Purdue University | Guo Y.,M4 Sciences LLC | Sundaram N.K.,Indian Institute of Science | Chandrasekar S.,Purdue University
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2014

Using high-resolution, in situ imaging of a hard, wedge-shaped model asperity sliding against a metal surface, we demonstrate a newmechanism for particle formation and delamination wear. Damage to the residual surface is caused by the occurrence of folds on the free surface of the prow-shaped region ahead of the wedge. This damage manifests itself as shallow crack-like features and surface tears, which are inclined at very acute angles to the surface. The transformation of folds into cracks, tears and particles is directly captured. Notably, a single sliding pass is sufficient to damage the surface, and subsequent passes result in the generation of platelet-like wear particles. Tracking the folding process at every stage from surface bumps to folds to cracks/tears/particles ensures that there is no ambiguity in capturing the mechanism of wear. Because fold formation and consequent delamination are quite general, our findings have broad applicability beyond wear itself, including implications for design of surface generation and conditioning processes. © 2014 The Author(s) Published by the Royal Society. All rights reserved. Source

Sagapuram D.,Purdue University | Yeung H.,Purdue University | Guo Y.,M4 Sciences LLC | Mahato A.,Purdue University | And 4 more authors.
CIRP Annals - Manufacturing Technology | Year: 2015

Large strain plastic flow in cutting of metals is studied at multiple length scales using high-speed imaging and marker techniques, complemented by particle image velocimetry and electron microscopy. Quantitative analysis of streak-lines, strain fields and microstructure, shows the flow to be often unsteady. Instabilities such as segmentation driven by ductile fracture, vortex-like flow in ductile metals, and shear banding in low-thermal diffusivity systems are elucidated using direct observations. A constrained-cutting process is demonstrated for suppressing the instabilities and unsteady flow. © 2015 CIRP. Source

Guo Y.,M4 Sciences LLC | Compton W.D.,Purdue University | Chandrasekar S.,Purdue University
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2015

The flow dynamics, deformation fields and chip-particle formation in cutting and sliding of metals are analysed, in situ, using high-speed imaging and particle image velocimetry. The model system is a brass workpiece loaded against a wedge indenter at low speeds. At large negative rake angles, the flow is steady with a prow of material forming ahead of the indenter. There is no material removal and a uniformly strained layer develops on the workpiece surface - the pure sliding regime. When the rake angle is less negative, the flow becomes unsteady, triggered by formation of a crack on the prow free surface and material removal ensuing - the cutting regime. The strain on the prow surface at crack initiation is found to be constant. Chip morphologies, such as discrete particle, segmented chip and continuous chip with mesoscale roughness, are shown to arise from a universal mechanism involving propagation of the prow crack, but to different distances towards the indenter tip. The simple shear deformation in continuous chip formation shows small-angle oscillations also linked to the prow crack. Implications for material removal processes and ductile failure are discussed. © 2015 The Author(s) Published by the Royal Society. All rights reserved. Source

Agency: Department of Defense | Branch: Army | Program: STTR | Phase: Phase I | Award Amount: 99.89K | Year: 2010

This STTR project seeks to develop a new manufacturing system for large-scale, low-cost production of bulk ultrafine grained (UFG) or nanostructured metals in plate, sheet or bar forms. These capabilities will be based on scale-up of a new class of machining-based processes called large strain extrusion machining (LSEM) that has been effective at creating high strength, nanoscale microstructures in a variety of alloy systems. Combining the strengths of M4 Sciences and Purdue University, the project will build on findings that hybrid machining-extrusion processes, based on LSEM constrained chip formation, offer a transformative approach for overcoming the limitations to large-scale production of UFG alloys by Severe Plastic Deformation (SPD) processing. The new hybrid machining processes can impart the large levels of plastic strain needed to effect grain refinement under controlled conditions, while simultaneously providing unprecedented control of the resulting bulk form (size and shape). Based on a strong foundation of preliminary work and intellectual property development, the project seeks to demonstrate LSEM of 4340 steel alloy, integrating systematic processing studies, material characterization, and analysis of energy, cost and equipment requirements.

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