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Yayın Effects of turn-milling conditions on chip formation and surface finish(Elsevier Science BV, 2019-04-24) Rahimzadeh Berenji, Kaveh; Karagüzel, Umut; Özlü, Emre; Budak, ErhanTurn-milling operations performed on mill-turn machines offer significant advantages provided that appropriate conditions are used. Compared to conventional machining processes, kinematics and geometry of turn-milling are more complicated due to additional parameters such as speed and diameter ratios of the tool and workpiece as well as eccentricity between them. In this study, the effects of process conditions on chip formation and surface generation are investigated. A novel approach is presented in order to select turn-milling conditions and related machine tool parameters using the relationship between the process and the machine tool.Yayın Effect of scanning strategies and laser parameters on metal-composite joining(Bellwether Publishing, 2021-07-27) Kuzu, Ali Taner; Karagüzel, Umut; Erbay, Batıray; Bakkal, MustafaThis study presents an investigation on the effectiveness, automation characteristics, and mechanics of joints between different material types namely glass ?ber reinforced plastics (GFRPs) and SS304 stainless steel using an industrial Nd: YAG continuous-wave laser welder and a 2-axis custom design jig. The custom design jig includes computer-controlled (CNC) step motors, which provide high accuracy position control of the selected laser patterns. Four different patterns (Linear Curve, Hilbert Curve, Triangle Weave, and Curlique Weave) are investigated under different process parameters (laser power, lap joint length, and traveling speed) to obtain more robust joints. The strength of the joint is examined by variance analysis and found that the laser power and the pattern are the most important factors. Tensile shear tests present that the best-resulted joint carried around 4000 N before fracture. Polymer vaporization resulted in sub-millimeter sized bubbles that are widely formed inside the molten zone of the GFRP specimen. Therefore, a strong joint between GFRP and SS304 stainless steel could be obtained by a direct laser joining process at low power, with load adaptable space-filling curve patterns and without needing surface pretreatment, sophisticated clamps or high clamping forces.Yayın Experimental analysis on drilling of Al/Ti/CFRP hybrid composites(Bellwether Publishing, 2021-01-25) Kayihan, Mete; Karagüzel, Umut; Bakkal, MustafaCarbon fiber reinforced composites (CFRP) have superior mechanical properties such as high strength/density ratio, and good damping ability. CFRP which is frequently used in parts in the aviation industry can also be single or stacked together with titanium and aluminum alloys. However, delamination could occur on the CFRP surfaces after drilling which leads to deterioration in mechanical properties. Therefore, in this paper, the effect of process parameters and stack order on cutting force, torque are investigated. The tests were carried out at three different drilling speeds and feed rates on a CNC vertical machine tool by using a solid carbide cutting tool. The results of hole quality indicate that the process outputs are significantly affected by process parameters and stack order. The force and torque values obtained at high drilling speeds and low feed rates are independent of the stack order. However, the stacking order is determined to be the most effective parameter for the thrust force and torque values. The force generated during the Ti/CFRP/Al stack in which the highest force value is approximately 50% higher than the lowest force which occurs on Al/Ti/CFRP stack. The surface roughness value measured during the Al/Ti/CFRP stack is approximately half of the other stack order.Yayın Investigating effects of milling conditions on cutting temperatures through analytical and experimental methods(Elsevier Science SA, 2018-12) Karagüzel, Umut; Budak, ErhanCutting temperatures in milling operations have a significant impact on tool wear, size and shape tolerances and residual stresses of the machined part. Prediction and measurement of cutting temperatures in milling, on the other hand, have some challenges due to the rotary tools resulting in an intermittent process and transient thermal loadings. In this study, novel approaches are presented to model and measure the cutting tool temperature variations during milling. The model is used to predict effects of milling conditions on cutting temperatures particularly to determine a relationship between tool temperature and radial depth of cut. The model predictions are verified by measurements obtained from the developed measurement technique and the literature data.Yayın Transient multi-domain thermal modeling of interrupted cutting with coated tools(Springer Science and Business Media Deutschland GmbH, 2021-09) Karagüzel, UmutInterrupted cutting operations, such as milling, produce fluctuating tool temperatures which directly affect the process outputs. Thus, prediction of cutting tool temperatures enables process planning, selection of materials for tool substrate and coating layers, and tool geometric design for improved productivity in machining operations. Theoretical analysis of temperature is a cost effective way to predict the tool temperatures. Considering the industrial needs, a theoretical model should be fast, easy to implement, and reliable. To that end, a novel hybrid model, which assembles analytical and numerical methods, is proposed in this study. This novel transient thermal model simulates the interrupted cutting with coated cutting tools. The proposed model includes an analytical heat flux calculation at the tool-chip interface considering the sticking-sliding contact behavior. The determined heat flux is, then, used to perform a numerical solution of the transient heat conduction problem in the cutting tool geometry with temperature-dependent thermal properties. The developed model is validated with experimental results found in literature under different cutting conditions. The results show that the model can predict the maximum temperatures generated in a thermal cycle with an accuracy of 2–10%. Thus, the proposed model can be further used to determine the process parameters, properties of coating layers, and tool geometric design.
