Influences of Silicon Crystal Anisotropy in Nano-Machining Processes Using AFM

Atomic force microscope (AFM) machining has the potential to become an essential technology for manufacturing micro/nano-scale devices. In literature, this technique has been successfully employed to machine various types of materials, including semiconductor materials and metals. However, the effect of material anisotropy in terms of crystal direction is rarely considered in the existing studies. In this paper, we conduct nano-scratching experiments on the (1 0 0) plane of single crystal silicon surface with a diamond tip in an AFM machine. Three levels of crystal direction of nano-scratching are considered. Four levels of normal loading are applied. Machining performances are mainly evaluated by the groove morphology. Also, the wear coefficients and scratch ratio are calculated to the anti-wear performance. Based on the pile up volume and cutting volume respectively, the presence of the ploughing and cutting mechanisms is determined. The experiment results indicate that the applied normal load significantly affect the groove depth and debris morphology. The scratching direction has a pronounced effect on the friction coefficient and the calculated scratching hardness. By observing the debris morphology and cracks formation, the dependence of ductile to brittle transformation mechanism of silicon machining on the crystal direction is also discussed.

Surface and Subsurface Study on EDG and EDM Processing of Advanced Ceramic Composite Material

The advanced ceramic composites are made electrically conductive by doping with the conductive phase elements like TiN, TiC, TiB2 and TiCN. The doping of the naturally occurring nonconductive ceramic composite makes it suitable to be machined by unconventional machining processes where conductivity of the material plays prominent role. Though, the ceramic materials are fragile in nature, these are custom-tailored for the engineering applications. The machining of the ceramic material by conventional processes is quite difficult and leads to failure of the material under high cutting forces due to its fragile nature. In most of the cases deformities like surface and subsurface cracks, inclusion of pits and voids, deteriorates the functionality of the ceramic material. In our work, we have studied the surface and subsurface characteristics, while processing the material by electric discharge machining (EDM) and electric discharge grinding (EDG) processes. A setup has been designed, developed and mounted as an attachment on die-sinking EDM machining facility to carry out the EDG experiments. The conductive alumina ceramic has been chosen as workpiece material for processing. The surface characteristics has been observed by scanning electron microscopy (SEM) at the resolution of 1000X for EDG processed work pieces, and at 500X for EDM. In EDM machining, the surface contains the recast layer whereas in EDG, the recast layer is either removed or swept uniformly along the surface giving good glossy surface finish. It has been found that the components produced by EDM process contain prominent surface and subsurface cracks whereas such deformities are not visible in case of EDG processing. The best surface finish achieved is of the order of 0.04μm when processed by EDG.

Nanoparticle Reinforced Metal Composites Prepared by Electrocodeposition

Improving the physical and mechanical properties such as hardness and strength of metal thin films can be achieved by incorporating nanoparticles into the pure metals, for example via electrocodeposition. However, the agglomeration of nanoparticles during electrocodeposition of nanocomposite thin films is an unresolved issue. This paper presents the preliminary results of electrocodeposition thin nanocomposite films under different processing conditions. The microstructure and distribution of Al2O3 nanoparticles in electrocodeposited Cu matrix nanocomposite thin films on a pure Al plate were examined. In addition, the effect of electrolyte concentration on the agglomeration of nanoparticles was studied. Different stirring times were used for electrodepositing the alumina/Cu nanocomposite and the pure Cu control film. Under the constant stirring condition, different deposition times including 1, 4, 8, 12, and 24 hours were taken to study the differences between the agglomeration states of the alumina nanoparticles with the time change. We also examined the effect of turning the electromagnetic stirrer ON and OFF at different time intervals from as short as every 20 minutes to as long as ON and OFF every 2 hours on the nanoparticle agglomeration in the film. Optical and electron microscopic studies were made to reveal the microstructure of the nanocomposite. It is found that there is no significant difference in microstructures for the specimens that made under either intermittent stirring or constant stirring for the same length of time.

Investigating the Effect of Machining Parameters on Microdrilling of Titanium Grade 19 Alloy

Electrical Discharge Micro Drilling (EDMD) is considered as one of the most effective method for machining difficult to cut and hard materials like titanium alloy. However, selection of process parameters for achieving superior surface finish, higher machining rate and accuracy is a challenging task in drilling micro-holes. In this paper, an attempt is made to optimize micro-EDM process parameters for drilling micro holes on titanium grade 19 alloy. In order to verify the optimal micro-EDM process parameters settings, material removal rate (MRR), electrode wear rate (EWR) and over cut (OC) were chosen as the responses to be observed. Pulse on time, pulse off time, electrode diameter and current were selected as the governing process parameters for evaluation by Taguchi method. Nine micro holes of 300 μm, 400 μm and 500 μm were drilled using L9 orthogonal array (OA) design. Optimal combination of machining parameters were obtained through Signal-to-Noise (S/N) ratio analysis. It is seen that machining performances like material removal rate and overcut are affected by the peak current whereas electrode wear is affected by peak current and electrode diameter. Morphology of the micro holes has been studied through SEM micrographs of machined micro-hole.

Fabrication of Complex Micro Channels by Micro Electric Discharge Milling (µ-ED Milling)

Micro electric discharge milling (μ-ED milling) is an effective and economic process for the fabrication of micro channels. In the present work, the bulk approach of μ-ED milling is being attempted to make complex shaped micro channels. For a straight channel the bulk approach of μ-ED milling was found to be a successful approach. A tungsten tool of diameter 500 μm was used to fabricate semi-circular micro channels on EN-24 steel. Important machining parameters had earlier been optimized to make straight channels on EN-24 steel by the same method. The effect of geometrical parameters such as radius of curved channel and aspect ratio on MRR and TWR were studied by full factorial experimental design for single pass at optimized machining parameters. Finally complex shapes like T-type and serpentine channels were made by using optimized conditions of straight and curved channels by bulk approach with multiple passes of μ-ED milling.

Experimental Characterization and Multi-Objective Optimization of the Orbital Drilling Process of CFRP

Defects associated with drilling of Carbon Fiber-Reinforced Polymers (CFRPs) are of major economic and safety concerns for aerospace manufacturers. One of the most critical defects associated with drilling of CFRP laminates is delamination of layers which can be avoided by keeping the drilling forces below some threshold levels. Orbital Drilling (OD) is an emerging drilling process that exhibits lower cutting forces and temperatures, easier chip removal, higher produced surface quality, longer tool life, and a high possibility for dry machining. The OD process is featured by cyclic engagement and disengagement between the tool and the workpiece whereby a considerable part of the work done by the tool is directed towards the tangential direction while the work done in the axial direction is reduced. This reduces the risk of delamination at the exit. The objective of this research work is to investigate the effect of the OD process key parameters with respect to the produced hole attributes (surface roughness, delamination, and hole accuracy), as well as the cutting forces and temperatures. All the OD tests were performed under dry conditions using a four-flute 6.35 mm end-mill. The cutting forces were recorded using a 3-component dynamometer Kistler 9255B and cutting temperatures were measured using a FLIR ThermoVision A20M Infrared camera at the holes exit. A full factorial design of the experiment was used whereby the feeds varied from 60 to 360 mm/min and the speeds from 6,000 to 16,000 rpm. The test material used was a quasi-isotropic laminate comprising woven graphite epoxy prepreg. Analysis of the results showed 45% reduction in the axial force component in orbital drilling (OD), compared to conventional drilling. None of the holes produced by the entire set of experiments has experienced any entry or exit delamination. ANOVA was used to identify the significance of the controllable variables on the experimental outputs. To overcome the challenge of optimizing the competing parameters of the hole quality attributes while maximizing the productivity, an algorithm was applied by hybridizing Kriging as a meta-modeling technique with evolutionary multi-objective optimization to optimize the cutting parameters.

Chip Breaking Parameter Selection for Constant Surface Speed Machining

Modulated tool path (MTP) chip breaking is a lathe machining technique which produces chips of a predetermined length to reduce the risk of damage to the tool or the work piece caused by chip entanglement. Individual chips are formed by repeatedly interrupting chip formation through CNC commanded tool oscillations superimposed in the tool feed direction. Previous work has shown that the chip length and part surface finish quality are dependent on the tool oscillation frequency relative to the spindle speed (OPR), and the oscillation amplitude relative to the global feed per revolution (Raf). Apart from chip length and surface quality, the dynamic capabilities of the machine must be considered when selecting MTP parameters, OPR and Raf. The dynamic limitations of the machine will limit the available range of tool oscillation frequencies and amplitudes. In this paper, the factors which affect the MTP parameter selection process are discussed, and a process for selecting these parameters automatically based on multiple constraints and criteria is presented for constant surface speed MTP machining.

Numerical and Experimental Measurements of Die Swell for a LCP and an Amorphous Polymer

It is known that liquid crystalline polymer (LCP) melts have a high elasticity which can be measured from its effect on the rheology on the cessation of shear. On the other hand, LCPs show very limited die swell after extrusion. In this paper, the results of experimental measurements of the die swell for a liquid crystalline material and polypropylene (PP), an amorphous polymer, are presented. The extrudate thickness 5 cm below the die lip is optically measured and the results are analyzed using ImageJ software. A numerical simulation of the die swell based on the capillary rheometry data and oscillatory rheometry is performed for LCP materials using ANSYS ® POLYFLOW ®. Different viscoelastic properties are used to model the LCP and optimum properties to model the die swell for the base volume flow rate are determined. Results show similarity between die swell modeling for the LCP at the base volume flow rate but increasing the die swell results in some deviation from the experimental results.

Model-Based Simulation and Optimization of Cutting Operations in Sheet Metal Working

This paper presents method to calculate optimum punch entry inside the die block to avoid damage of the cutting edges. Experimentation is carried out on a hundred tonne capacity hydraulic press (AMINO, Japan make) with an inching facility. Piercing die with a hole size of 30 mm is used. Ten different materials are used with varying thicknesses. Punch entry was controlled by inching with 0.05 mm downward movement. Entry readings were noted at the point of fracture. Thickness and punch entry are correlated and a model is designed to compute percentage penetration with respect to thickness. Models are checked by simulation for various materials with varying thicknesses. These models we propose for all the industries to set the cutting dies at optimum entry to avoid damage of cutting edges.

Elasto-Plastic Stress Analysis of the Characteristics for T-Flange Bolted Joints Under External Loading

In designing bolted joints, it is necessary to know the contact stress distributions in bolted joints. Recently, high strength bolts have been used with a higher bolt preload. As the results, the permanent set occurs sometimes at the bearing surfaces of clamped parts in the bolted joint. In addition, when external loads such as tensile loads, transverse loads and bending moments are applied to the bolted joint, the permanent set can be extended at the bearing surfaces. As the permanent set increases, the reduction in the bolt preload increases. Thus, it is important to estimate the reduction in the bolt preload from the reliability stand point. However, no study on the permanent set at the bearing surface under the external loading taking into account the bending moment has been carried out. In this study, the stress distribution and the extension of the permanent set at the bearing surface of the T-flange bolted joint under the external tensile loading are examined using Finite Element Method (FEM), where two T-flanges are clamped with a hexagon bolt and a nut. Using the obtained results, an increment in the axial bolt force and the reduction in the bolt preload are estimated. For verification of the FEM stress analysis, the load factor of hexagon bolt was measured. The FEM results of the load factor (the ratio of the increment in the axial bolt force to the tensile load) and the axial bolt force are in a fairly good agreement with the experimental results.