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Title:Development of meso-scale flexible cutting tool for micro-groove cutting in steel
Author(s):Rajagopalan Hari, Raghavendra
Advisor(s):Kapoor, Shiv G.
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Atomic Force Microscopy
Cubic Boron Nitride
Flow Stress
Finite Element Analysis
Side Burr
Tool Wear
Abstract:One of the key challenges in product miniaturization technologies is the creation of micro-grooves in devices for mechanical, electronic, photonic and bio-medical applications, such as production of hot embossing molds, micro-heat exchangers, optical lithography masks, micro-forming dies, engineered surface textures, etc. Processes such as micro-endmilling, laser scribing, μ-EDM, micro-fly cutting, AFM microscribing, photolithography, etc. have shown capability in producing micro-scale grooves in a range of materials. However, they were found to have limitations in producing grooves in hard materials that are less than a few microns wide and a few microns deep, several millimeters long, and that have arbitrary cross-sectional shapes with high relative accuracy, good material removal rates and superior surface finish at reasonable machining cost. To meet these requirements, a strain-gauge sensor-integrated meso-scale CBN flexible cutting tool is developed that is capable of machining micro-grooves in steel. A MEMS process-based approach has been employed to fabricate the meso-scale flexible cutting tool with the integrated stain-gauge sensors. The strain-gauge sensor integrated on the meso-scale flexible cutting tool is responsible for controlling the tool deflection during the cutting process. Novel approaches for mounting and modifying the single CBN crystal on the flexible cutting tool blank and a suitable method for packaging the tool are demonstrated. The process was implemented on a 5-axis mMT with a retrofitted micro-groove cutting assembly. The initial study of the meso-scale CBN flexible cutting tool has demonstrated the ability of the new tool to cut well-defined rectangular micro-grooves up to 1 μm deep, in stainless steel samples using a single tool pass, cutting at a speed of 100mm/min. Micro-groove characterization studies have been carried out to evaluate the outcome of the machined micro-grooves based on its expected geometry, floor surface profile, repeatability and consistency. Side burr formed during the cutting process were assessed through a series of experiments to arrive at the most suitable machining parameters for burr minimization. Multiple tool passes and high cutting speed yielded the lowest side burrs. Tool wear studies revealed that low applied loads and low cutting speeds gave the longest tool life. The ability of the flexible cutting tool to machine various micro-groove patterns has also been demonstrated. To understand the process mechanics of micro-groove cutting in steel, the 3D finite element model for aluminum groove machining developed previously has been enhanced to include an thermo-elastic-plastic model of steel workpiece using Lagrangian formulation material and its related mechanical and thermal properties, and suitable remeshing scheme, damage governing laws and different cutting edge geometries. Various inherent process mechanics including the stress and strain distribution, chip formation and development, cutting force predictions, side burr formation, and temperature distributions at the size scale involved were studied. Validation with experimental results in AISI 4340 steel showed that the model predicted side burr height to within 1.8% and chip thickness to within 28 % error. The influence of cutting edge geometry and machining conditions on the outcome of the process mechanics were observed thorough a series of planned simulation trials. It was found that the cutting geometry with a small edge radius experienced lower stresses and cutting forces on its rake face, while the geometry with a larger edge radius enabled better heat conduction through the workpiece.
Issue Date:2013-02-03
Rights Information:Copyright 2012 Raghavendra Rajagopalan Hari
Date Available in IDEALS:2013-02-03
Date Deposited:2012-12

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