Advanced Materials Research Vols. 264-265

Abstract: The finite element method (FEM) has been used to model high speed turning processes with orthogonal cutting conditions. In most of the situations, continuous chip formation is used to analyze the turning process due to its stability and allowing many conditions to simplify the process. However with the increasing applications of high speed turning, serrated chip formation is becoming a more common phenomenon in metal cutting. Serrated chips usually occur in machining of difficult to cut materials at or above a threshold speed. An updated Lagrangian formulation has been used in this study which works with element deletion technique based on a failure criterion. The Johnson Cook strain-hardening thermal-softening material model is used to model serrated chip formation. In addition high speed turning experiments were conducted on AISI H13 tubes using PCBN to analyze serrated chip phenomenon. The chips were analyzed after surface treatment using scanning electron microscope. It has been found that the length of cuts in the chip increases with the cutting speed and the chip changes from serrated to discontinuous. Different process variables like cutting forces, chip morphology, stress, strain and temperature distributions are predicted at different process parameters using FEM. The results show cyclic variation in the cutting forces at high cutting speeds due to varying chip load.

Abstract: Warpage on the backside of silicon wafer after thinning process is examined. The thinning process includes back-grinding (BG) and wet chemical etching (WCE). Results of wafer warpage were compared to sub-surface damage from Transmission Electron Microscopy (TEM) analysis and showed that sub-surface damage on the backside of the silicon 100 would induce high wafer warpage, and reduced wafer strength. Further studies from surface roughness and topography of each surface finish is obtained by Atomic Force Microscopy (AFM) and SEM show that low surface roughness is in accordance with smooth surface condition, which comes after the wet etching process.

Abstract: The two biggest problems that often experienced in machining cast iron are poor machinability and high hardness. Up to now, many researchers have investigated machining performance and how to find optimum condition in machining ductile cast iron. This study aims to investigate the machining performance of ductile cast iron and carbide cutting tool using FEM. Performances were evaluated by changing the cutting tool geometries on the machining responses of cutting force, stress, strain, and generated temperature on the workpiece. Deform-3D commercial finite element software was used in this study. Ductile cast iron FCD 500 grade was used as the work piece material and carbide insert DNMA432 type with WC (Tungsten) was used for the cutting tool. The effects of rake and clearance angles were investigated by designing various tool geometries. Various combination of carbide insert geometries were designed using Solid Work to produce +15, +20 and +30 deg for rake angle and 5, 7, 8 and 9 deg for clearance angle. Machining condition for the simulations were remained constant at cutting speed of 200 m/min, feed rate of 0.35 mm/rev, and depth of cut of 0.3 mm. The results of effective-stress, strain and generated temperature on both chip and material surface were analysed. The results show that by increasing the rake angle (α), it will improves the machining performance by reducing the cutting force, stress, strain and generated temperature on surface of workpiece. But, by increasing the clearance angle (γ), it will not affect much to the cutting force, stress, strain and generated temperature on chip.

Abstract: Obtaining the resonance frequency of cutting tools is necessary for dynamic modelling and instability study in milling process. In this paper, two geometrically different endmills are modelled by analytical and Finite Element (FE) approaches and their natural frequencies are calculated. For evaluation of the results, modal testing is carried out. The discrepancies of the analytical results compared to the modal experiments are approximately 25% for both tools. FE results differ 18% and 22% from experimental values for respectively tool 1 and 2. FE values are closer to those of experiment in comparison with analytical results.

Abstract: Industries are forced to seriously evaluate their design and manufacturing of their products due to the competition in the marketplace. Product characteristics such as tolerance specification, appearance, and service life now become a major concern for machined components. One of the most important aspects in machined components is surface integrity. It involves mainly the surface roughness and micro hardness changes during machining operation, which should be controlled and monitored to fulfill the product functions and customer needs. This paper presents the comparison effect of the end milling and EDM parameters on the surface integrity of AISI H13 tool steel (HRC50 3). The parameters studied were the cutting speed (224 m/min – 280 m/min), feed rate (0.25 mm/tooth) and depth of cut (0.3 mm-0.8 mm for end milling process. Whereas for EDM, the parameters studied were the peak current (1 and 4 A), pulse ON-time (6 and 12 μs), and pulse OFF-time (2 μs). The electrodes used were graphite and copper. In this study, the workpiece surface and recast layer were examined using an optical microscope. The observation revealed that both processes of end milling and EDM had cause the formation of three layers structure, i.e. white, martensite quenched and bulk material layers. The subsurface alteration for EDM process is considered rigorous as compared with the end milling process. Damages beneath the machined surface such as micro cracks and void were observed for EDM process, and microscopic pitting and surface roughning for end milling process. The measurement of the microhardness beneath the machined surface of AISI H13 was carried out using Vickers microhardness tester to characterize its mechanical properties. It was found that the highest hardness of 1010 Hv was in the white layer, and hardness of martensite quench layer was 423 Hv, which was lower than the bulk material layer of 430 Hv in EDM process. Whereas, a maximum of 550 Hv was measured directly underneath the generated surface, i.e. 30% more as compared to the hardness of the basic material in the end milling process.

Abstract: The great advancement in the development of carbide cutting tool with super-hard coating layers taken place in recent few decades, can improve the performance of cutting tool and machinability of titanium alloy. The turning parameters evaluated are cutting speed (55, 75, 95 m/min), feed rate (0.15, 0.25, 0.35 mm/rev), depth of cut (0.10, 0.15, 0.20 mm) and tool grade of PVD carbide tool. The results that tool life shows patterns of rapidly increase at the initial stage and gradually increased at the second stage and extremely increased at the final stage. The trend lines of surface roughness have are the surface roughness value is high at first machining after that regularly decreases. Work hardening of the deformed layer beneath machined surface caused higher hardness than the average hardness of the base material. However, the softening effect also occurred below the machined surface. Segmentation or serration at the chip edge was caused by high strain and pressure during machining.

Abstract: Present study introduces low-frequency workpiece vibration during micro-EDM drilling of difficult-to-cut tungsten carbide with an objective to overcome the difficulty in flushing of debris and machining instability in deep-hole machining. The effects of vibration frequency, amplitude and electrical parameters on the machining performance, as well as surface quality and accuracy of the micro-holes have been investigated. It is found that the overall machining performance improves significantly with significant reduction of machining time, increase in material removal rate (MRR), and decrease in electrode wear ratio (EWR). The surface quality improves and the overcut and taper angle of the micro-holes reduces after applying the workpiece vibration in micro-EDM. The frequency and amplitude of 750 Hz and 1.5 μm were found to provide optimum performance.

Abstract: First, a 2D orthogonal cutting model for titanium alloy is constructed by finite element method in this study. The cutting tool is incrementally advanced forward from an incipient stage of tool-workpiece engagement to a steady state of chip formation. Cockroft and Latham fracture criterion [1] is adopted as a chip separation criterion. By changing the settings of cutting variables such as cutting speed, depth of cut and tool rake angle to investigate the chip formation process and the variation of cutting performance during titanium cutting simulation. The changes of chip type, cutting force, effective stress/strain and cutting temperature with different cutting condition combinations are thus analyzed. The result demonstrates that the serrated chip type is obviously produced when cutting titanium alloy. Next, water-based and oil-based cutting fluids are employed in conjunction with proper cutting parameter arrangements to perform up-milling experiments. By measuring the cutting force, surface roughness and tool wear to investigate the effect of these combinations of milling variables on the variation of cutting performance for Ti-6Al-4V. The chip shape and cutting force obtained from the experiment are compared with those calculated from simulation. It is shown that there is a good agreement between simulation and experimental results.

Abstract: EDM is a nontraditional method of removing material by a series of rapidly recurring electric discharges between an electrode (the cutting tool) and the workpiece, in a medium of a dielectric fluid. EDM is a precision machining technique and is used in making dies and molds of extremely hard materials that cannot be machined by conventional techniques. The present work was conducted in order to investigate the surface finish, material removal rate and the surface damage during EDM. Copper and carbide were taken as the electrode and the work materials for the present study. The influence of current and pulse-on time on the responses were studied. Design of Experiment (DOE) was used to conduct the investigation. It was found that MRR and surface roughness increases with both current and pulse on time. Tool wear, work surface damage and materials migration between the electrode and the workpiece was found to be increased with current.

Abstract: The elastic compliance of a work-piece under machining forces during machining operation and its subsequent spring back causes dimensional error. This phenomenon is more critical in turning process especially when long work-pieces are machined between chuck and center or between centers. Ultrasonic vibration assisted turning (UAT) where the cutting tool is put into an ultrasonicfrequency vibration during the ordinary cutting process leads to considerable improvement of the machined work-piece including increase in the dimensional accuracy. This is partly attributable to the noticeable decrease of the machining force in UAT compared with those occurring in conventional turning (CT). It is noteworthy that UAT is regarded as an advanced machining technique which is especially suitable for machining of brittle and hard-to-cut materials such as glass, ceramics and super alloys. In the present study, the diametrical error due to the spring back of work-piece being machined between chuck and center in turning operation is first analyzed. A model is then presented for prediction of this error in UAT by statistical analysis of extant experimental results. All influencing parameters are thus taken into consideration when deriving the predicting model. This model is verified by FEM simulation.