Browsing by Subject "Cutting"

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    Investigating flank face friction during precision micro cutting of commercially pure titanium via plunging tests with diamond grooving tools
    (Elsevier, 2022-01) Karpat, Yiğit
    This study investigates flank face friction while micro machining commercially pure titanium (cp-Ti grade 2) work material considering size effects. It is important to understand friction phenomena at the tool flank and work material surface since they affect the surface integrity of the machined parts. A single crystal diamond grooving tool is used in machining experiments to reduce the influence of cutting edge radius. In addition, plunging type of cutting experiments were performed to investigate the influence of flank face contact on the machined surface. A friction model which is based on work and tool material properties is proposed to model the contribution of adhesion and deformation of the flank face coefficient of friction. The results show that for the cp-Ti and diamond tool pair, adhesion seems to be the dominant model of friction and also contributes to the size effect. The deformation friction becomes more dominant during the chip formation stage. When cutting edge effect is eliminated, the influences of flank and rake face friction on the size effect are shown.
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    Investigating the influence of built-up edge on forces and surface roughness in micro scale orthogonal machining of titanium alloy Ti6Al4V
    (Elsevier, 2016) Oliaei, S. N. B.; Karpat, Y.
    The edge geometry of cutting tools directly influences the chip formation mechanism in micro-mechanical machining, where the edge radius and uncut chip thickness are in the same order of magnitude. An uncut chip thickness that is smaller than the cutting edge radius results in a large negative rake angle during machining, and built-up edge formation then affects the mechanics of the process. In this study, micro-scale orthogonal cutting tests on titanium alloy Ti6Al4V were conducted to investigate the influence of built-up edge formation on the machining forces and surface roughness. Cutting edges in these tests are engineered using wire EDM technique to have an edge radius of around 2 μm and clearance angles of 7° and 14°. It is observed that machining process inputs (uncut chip thickness, cutting speed, and clearance angle) affect the size of the built-up edge, which in turn affect the process outputs. It is observed that built-up edge formation protects the cutting edge from flank and crater wear under micro machining conditions and the influence of built-up edge on the surface roughness varies depending on the cutting speed and uncut chip thickness. Our findings also indicate a close relationship between the minimum uncut chip thickness and the mean roughness depth (Rz) of the machined surface. The minimum uncut chip thickness is found to be around 10% of the edge radius in the presence of built-up edge.
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    Investigating the influence of friction conditions on finite element simulation of microscale machining with the presence of built-up edge
    (Springer, 2017) Oliaei, S. N. B.; Karpat, Y.
    In micromachining, the uncut chip thickness is less than the cutting tool edge radius, which results in a large negative effective rake angle. Depending on the material properties, this large negative rake angle promotes built-up edge (BUE) formation. A stable BUE acts like a cutting edge and affects the mechanics of the process. The size of the BUE increases with increasing uncut chip thickness and cutting speed. It also creates a positive rake angle, but it decreases the clearance angle of the tool. A method of including BUE formation in finite element simulations is to use sticking friction conditions at the tip of the tool. However, this approach is shown to be insufficient to simulate BUE formation in microscale machining. Therefore, the cutting edge is modified with the experimental BUE size in the finite element simulations based on experimental measurements. The influence of friction models between BUE and the work material has been investigated, and the study identifies friction coefficients that yield good agreements with experimental results. The finite element model is shown to be capable of simulating process forces and chip shapes for uncut chip thickness values larger than minimum uncut chip thickness.
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    Milling force modelling of multidirectional carbon fiber reinforced polymer laminates
    (Elsevier, 2012) Karpat, Yiğit; Bahtiyar, O.; Deger, B.
    Carbon fiber reinforced polymer (CFRP) usage in the aerospace industry has been steadily increasing due to its superior material properties such as high strength, low weight, high resistance to corrosion, and a low thermal expansion coefficient. In addition, CFRP parts are produced near-net-shape, a process that eliminates rough machining operations. However, machining operations such as drilling, side milling, and slotting are still necessary to give the CFRP parts their final shape. A majority of the studies on machining of CFRP laminates are on drilling. The number of studies on milling of CFRPs is quite limited. In this study, a mechanistic cutting force model for milling CFRPs is proposed based on experimentally collected cutting force data during slot milling of unidirectional CFRP laminates using a polycrystalline diamond cutter. Cutting force coefficients in radial and tangential directions are calculated as a function of fiber cutting angle. The mechanistic model is shown to be capable of predicting cutting forces during milling of multidirectional CFRP laminates and capable of investigating stability of machining. © 2012 The Authors.
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    Unraveling the complex interplay between elastic recovery, contact pressure, and friction on the flank face of the micro tools via plunging-type testing
    (Elsevier Inc., 2024-07-06) Karpat, Yiğit; Güven, Can
    A good understanding of the interplay between the cutting tool edge radius, elastic recovery, friction, and contact pressure is essential for better modeling of ploughing forces during micro-scale cutting. This study conducts plunging tests on an ultra-precision CNC with engineered tungsten carbide cutting tools on commercially pure titanium alloy. The cutting tool edge radius is prepared to be around 3.5-4 mu m, which resembles those cutting tools used in micro scale machining. During plunging tests, the micro cutting tool is given a sinusoidal movement with an amplitude close to edge radius of the tool as the work material is rotated at a constant speed. The residual depth profiles of the webs corresponding to the commanded depths were investigated in detail to identify elastic recovery rate. The cutting and thrust force measurements during plunging experiments together with identified elastic recovery rate was employed in an analytical model of micro scale machining to obtain the variations of contact pressure and coefficient of friction as a function of commanded depth. Due to the scale of the experiments that were performed, the effects of surface topography of the cutting tool and possible alignment errors are also considered in the analytical model. A linear relationship between the contact pressure and elastic recovery has been identified during ploughing-dominated machining conditions for the work material and the cutting tool pair considered in this study. The proposed experimental technique is shown to be promising in terms of modeling ploughing forces during micro-scale cutting.