Improving spur gear microgeometry and surface finish by AFF process

This paper describes improving microgeometry and surface finish of spur gears by abrasive flow finishing (AFF) by experimentally identifying optimum values of finishing time and AFF medium viscosity. An experimental apparatus was developed for gear finishing by AFF using a medium of silicon carbide as abrasives, silly putty and silicone oil as blending agents. A special fixture was developed comprising of two metalon cylindrical disks having circumferential holes for back and forth movements of AFF medium between two adjacent flanks of 20MnCr5 alloy steel spur gear teeth. Twenty experiments were conducted varying AFF medium viscosity at four levels and finishing time at five levels to study their influence on error reduction in total profile, total lead, total pitch, runout, and average surface roughness. Results showed considerable reduction in the microgeometry deviation and surface roughness with AFF medium viscosity increase and existence of optimum finishing time for attaining maximum improvement in microgeometry and surface finish. Consequently, 25?min and 135?kPa.?s were identified as optimum values and corresponding gear’s microgeometry and microstructure were studied. It revealed that AFF-finished gear flank surfaces are free from cracks, cutter marks, thermal distortions. This proves AFF as economical and productive alternative for gear finishing.     

Investigations on surface quality of WEDM-manufactured meso bevel and helical gears

This article presents investigations on and analysis of surface finish of meso bevel and helical gears made of stainless steel (SS 304) manufactured by wire electric discharge machining (WEDM) process using thin soft plain brass wire of 0.25?mm diameter. Effects of eight WEDM process parameters, namely, peak current, pulse-on time, pulse-off time, wire feed rate, wire tension, servo-gap voltage, dielectric pressure, and cutting speed on average and maximum surface roughness of the meso bevel and helical gears have been studied by conducting 31 experiments using one-factor-at-a-time approach to identify their optimum ranges/values for further experiments. Tooth profile, microstructure, microhardness, and topography of tooth flank surface have been studied for the best quality meso gears. Average and maximum surface roughness of tooth flank surfaces of meso bevel and helical gears increase with increase in peak current, servo-gap voltage, pulse-on time, wire feed rate, wire tension and cutting speed, and decrease with increase in pulse-off time while dielectric pressure does not significantly influence surface roughness. This work establishes that WEDM process can be an economic and sustainable manufacturing alternative for net-shaped meso-sized bevel and helical gears having better surface finish which will eliminate need of any subsequent finishing processes.     

Experimental investigations of ceramic machining using µ-grinding and µ-rotary ultrasonic machining processes: A comparative study

Comparative experimental investigations of µ-grinding and µ-rotary ultrasonic machining (µ-RUM) were made on borosilicate and Zerodur materials to know the efficacy of the processes for micro electro mechanical system (MEMS) application. The electroplated diamond tool of Ø 300 µm for drilling operation and Ø 300 µm to Ø 6 mm for milling operation has been tried in the computer numerical control (CNC) machine with an HSK63 ultrasonic actuator. A suitable interface has been developed to hold the micro tool with the ER11 taper in the existing ER20 collet ultrasonic tool holder. Cutting force, edge-chipping area, and taper in drilling operation; and surface finish, material removal mode, specific energy and un-deformed chip thickness in milling operation were evaluated for both processes under the same material removal rate conditions. The experimental results showed that µ-RUM could perform in a less spindle speed machine as compared to µ-grinding. It was inferred that the maximum and minimum amount of reduction in cutting force, edge chipping, and taper were found to be (49.3%, 10.8%), (87%, 40%), and (95.56%, 4.76%), respectively, in µ-RUM compared to µ-grinding for drilling operation. It was also concluded that surface finish and ductile mode of fracture were higher in µ-RUM compared to µ-grinding for the milling operations. These effects were more pronounced as tool size decreased.     

Surface integrity and removal mechanism in grinding sapphire wafers with novel vitrified bond diamond plates

In order to improve machining efficiency of sapphire wafer machining using the conventional loose abrasive process, fixed-abrasive diamond plates are investigated in this study for sapphire wafer grinding. Four vitrified bond diamond plates of different grain sizes (40?µm, 20?µm, 7?µm, and 2.5?µm) are developed and evaluated for grinding performance including surface roughness, surface topography, surface and subsurface damage, and material removal rate (MRR) of sapphire wafers. The material removal mechanisms, wafer surface finish, and quality of the diamond plates are also compared and discussed. The experiment results demonstrate that the surface material is removed in brittle mode when sapphire wafers are ground by the diamond plates with a grain size of 40?µm and 20?µm, and in ductile mode when that are ground by the diamond plates of grain sizes of 7?µm and 2.5?µm. The highest MRR value of 145.7?µm/min is acquired with the diamond plate with an abrasive size of 40?µm and the lowest surface roughness values of 3.5?nm in Ra is achieved with the 2.5?µm size.     

Failure analysis of a petrochemical plant reducing gear

This study aims to investigate the cause of failure of an 845 mm external diameter reducing gear that operated during 30 months in a petrochemical plant. The failure analysis procedure included material characterisation (microstructure, chemical composition and microhardness), fracture surface evaluation, and stress distribution by finite elements on critical regions of the gear. Fracture mechanics and fatigue crack growth were also used to develop a da/dN–ΔK curve and then determine the gear material crack growth resistance. Results indicate that the gear was not properly manufactured and failure occurred as a result of a fatigue process facilitated by a manufacturing defect.     

Structure and properties of attrition-milled aluminium powder

Aluminium powder has been attrition milled in the presence of 1.5 wt% of a wax. The aim was to achieve a mechanically alloyed powder amenable to powder metallurgy processing. Changes in particle size and form, microstructure, hardness and other properties of powders with milling time has been studied. Under the experimental conditions employed, a process time of 10 h was selected for the mechanical alloying of Al powder. The powder milled in this way shows a Vickers microhardness (127 HV) more than six times higher than the starting powder (20 HV), a coarser particle size (mean particle size is doubled) and a better flowability.     

High-energy ball milling of saquinavir increases permeability across the buccal mucosa

Saquinavir (SQV), a candidate for buccal drug delivery, is limited by poor solubility. This study identified the effects of high-energy ball milling on the buccal permeability of SQV and compared it to the effects of chemical enhancers, i.e. ethylenediaminetetraacetic acid (EDTA), sodium lauryl sulfate (SLS), polyethylene glycol (PEG) and beta cyclodextrin (β-cyclodextrin). SQV was ball milled using a high energy planetary mill (1, 3, 15 and 30?h) and permeation studies across porcine buccal mucosa were performed using franz diffusion cells. Drug was quantified by UV spectrophotometry. Both unmilled and milled SQV samples were able to permeate the buccal mucosa. Milled samples of 15?h displayed the greatest flux of 10.40?±?1.24?µg/cm^2?h and an enhancement ratio of 2.61. All enhancers were able to increase the buccal permeability of unmilled SQV, with SLS achieving the greatest flux (6.99?±?0.7?µg/cm²) and an enhancement ratio of 1.75. However, all the milled SQV samples displayed greater permeability than SLS, the best chemical enhancer for unmilled SQV. Enhanced permeability by ball milling was attributed to reduction in particle size, formation of solid dispersions and an increase in solubility of milled samples. Microscopical evaluation revealed no significant loss in mucosal cellular integrity treated with either unmilled or milled SQV. Histological studies suggest that SQV uses both the paracellular and transcellular route of transport across the mucosa, with drug treatment having no permanent affects. High-energy ball milling was superior to the chemical enhancers studied for enhancement of SQV buccal permeation.     

Empirical approach to develop a multilayer icebonded abrasive polishing tool for ultrafine finishing of Ti-6Al-4V alloy

This paper covers the development of a multilayer icebonded abrasive polishing (IBAP) tool for multistage polishing of Ti-6Al-4V alloy specimens based on a systematic study that determined the number of layers, thickness of each layer, and the type, size and concentration of abrasives in each layer. Based on this study, a three-layered IBAP tool with the bottom layer consisting of soft aluminum oxide abrasives of 3?µm size with 5% concentration, the middle layer with moderately hard silicon carbide abrasives of 8?µm size with 10% concentration and the top layer with hard boron carbide abrasives of 15?µm size with 30% concentration was formulated for ultrafine finishing of Ti-6Al-4V alloy specimen in a single setup. The performance of the three-layered IBAP tool assessed in terms of finish and morphology over the work surface showed 81% improvement in surface finish, showing its effectiveness over a single-layered IBAP tool. Polishing studies have clearly demonstrated the generation of ultrafine surfaces, yielding a finish of 37?nm while the morphological studies on the polished surface have shown a nearly scratch-free surface on the Ti-6Al-4V alloy.     

Surface Roughness and Microhardness Evaluation for EDM with Cu–Mn Powder Metallurgy Tool

In the present research, composite electrode (Cu–Mn) manufactured through powder metallurgy has been used to machine hot die steel (H11) by electrical discharge machining (EDM) process with the aim of inducing manganese and carbon into the machined surface. Such alloying is expected to improve the microhardness and other surface characteristics. Best level of process parameters for better surface finish and high microhardness are found using Taguchi method. Six processing parameters are considered and their significance is investigated by analysis of variance. Techniques like energy dispersive spectroscopy, scanning electron microscopy, and X-ray diffraction are used to ascertain the surface characteristics. Surface machined at optimum process conditions for microhardness shows 93.7% improvement due to formation of cementite, ferrite and manganese carbide phases. Surface roughness having Ra value of 3.11 µm has been achieved.     

Surface integrity in high speed end milling of titanium alloy Ti–6Al–4V

Abstract

Machined titanium components, such as medical prosthesis, require the greatest reliability, which is determined by process induced surface integrity. However, surface integrity of milled titanium components easily deteriorates due to the poor machinability of titanium alloys and cyclic chip loading during milling. Milling induced surface integrity, including anisotropic surface roughness, residual stress, surface microstructure alterations and microhardness, has received little attention. In the present study, a series of end milling experiments were conducted to comprehensively characterise surface integrity at various milling conditions of titanium alloy Ti–6Al–4V with TiAlN coated carbide cutting tools. The experiments were carried out under dry cutting conditions. For a range of cutting speeds, feeds and depths of cut, analyses of machined surface roughness, residual stress, microhardness and the microstructural observations were carried out. The present work aims to evaluate the influence of different milling conditions on workpiece surface integrity.     

Comparative study on sintering behavior of Al86Ni6Y4.5Co2La1.5 mechanically alloyed amorphous powder and melt-spun ribbon

In this research work, the sintering characteristics of Al₈₆Ni₆Y_4.5Co₂La_1.5 mechanically alloyed amorphous powders and milled melt spun ribbon have been compared. Mechanically alloyed amorphous powders were synthesized via 200?h high energy ball milling. Melt spun ribbons were synthesized by single roller melt spinning technique and grounded to powder form by ball milling. Mechanically induced partial crystallization occurred in the ribbons during milling. Significantly higher amount of contaminations such as carbon, oxygen and iron were observed in the mechanically alloyed amorphous powders compared to the milled ribbons. Both powders were consolidated via spark plasma sintering. Superior particle bonding was found in the sample consolidated from milled ribbons, ascribed to the lower amount of contamination that could not effectively restrict the viscous flow and diffusion of atoms. Various complex crystalline phases evolved in the sample consolidated from milled ribbon particles due to the presence of crystalline phases in the powders which acted as nucleation sites, whereas the amorphous phase was mostly retained in its counterpart. Vickers microhardness of the consolidated alloys from milled ribbon and mechanically alloyed amorphous powders were 3.60?±?0.13?GPa and 2.53?±?0.09?GPa, respectively. The higher hardness in the former case was attributed to the superior particle bonding and distribution of hard intermetallic phases in the amorphous matrix.     

Production of high-precision micro metallic components by electroforming process

In this study, nickel (Ni) micro components with high precision were produced by electroforming using a soft mold produced by soft lithography and photolithography techniques. The effects of current densities on the microstructures and mechanical properties of the fabricated micro components were studied. It is found that a high-precision soft mold was successfully fabricated and micro Ni gears with sharp walls and fine features were produced. A feature size as small as approximately 70?µm, a height of 380?µm, and a pitch diameter of 3?mm were achieved for the gear. The densities of the gears electroformed are found to be within the range of 5.24–2.95?g/cm³ when current densities utilized vary between 50 and 10?mA/cm². A lower current density leads to a finer microstructure and a larger value of microhardness. Meanwhile, by changing the current density from 50 to 10?mA/cm², the grain size decreases from around 50 to 30?nm while the microhardness increases from 220 to 410. In addition, the preferred orientation of the Ni matrix changes from (111) to (200) or (220) with the decreasing current density.     

Material and Energy Interactions between Milling Bodies,Milled Particles,and Milling Environment

Changes in particle size, surface state, and composition brought about by planetary and vibration milling of silicon and quartz in various permittivity liquids were investigated. Using a variety of spectroscopic techniques (IRS, XPS, and Mössbauer spectroscopy) the changes in quality of the superficial layers of milled particles have been determined. During energy-intensive milling, the material being milled intensively interacts with the media and milling environment. The nature of the interaction and quality of the surface shell covering the milled particles depend on the reactivity and hardness of the interacting solids and of the milling environment. During planetary milling of silicon with tungsten carbide media, the superficial layers are formed by silicon suboxides and silicon oxide. The thickness of the superficial layer and the share of SiO₂ increase with increasing permittivity of liquids. Milling with steel media results in a more complicated composition of the superficial layer. According to Mössbauer spectra, the iron is present in two main forms: as a magnetically ordered form identical with basic material of balls and in a paramagnetic form as a product of a mechanically stimulated surface reaction between Si and Fe. The presence of the superficial layers on the milled particles of silicon and quartz markedly influences the values of the specific surface area. This influence should be taken into consideration when calculating the specific contamination of the milled powder.     

UV-TiO2 photocatalysis-assisted chemical mechanical polishing 4H-SiC wafer

The objective of this study is to propose a photocatalysis-assisted chemical mechanical polishing (PCMP) method for atomic smoothing SiC wafer based on the powerful oxidability of UV photo-excited hydroxyl radical on nano-TiO₂ particles. The study identifies five slurries of different photocatalyst, electron capturer, UV light, and pH value by measuring oxidation reduction potential and static oxidation experiment. After PCMP process, a SiC wafer is examined with optical microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy for information on surface finish and quality, material removal and mechanisms. The study demonstrates that photocatalyst, UV light, electron capturer, and acid environment are necessaries for PCMP process. Among the five PCMP slurries, the one with 1?g of TiO₂, 0.3?g of (NaPO₃)₆, 10?ml H₂O₂, 5?g SiO₂ abrasives under UV light irradiation provides the highest material removal rate of 0.95?µm/h and the best surface finish (Ra?=?0.35?nm) and surface quality. It then discusses how UV light irradiation promotes the chemical oxidation of hydroxyl radical with SiC by forming “Si–C–O,” “Si–O,” “C–O,” and “C?O” on SiC surface. The study concludes that the proposed PCMP is effective and clean manufacturing method for SiC wafer without releasing toxic chemicals to environment and human health.     

Surface integrity of Inconel 718 by hybrid selective laser melting and milling

ABSTRACT

While selective laser melting (SLM) offers design freedom of metal parts with much less material consumption, there exist several limitations, including high surface roughness, low-dimensional accuracy, and high tensile residual stresses. To make functional parts with high form accuracy and superior surface integrity, an as-SLM part needs finishing to remove the deposited surface material. The integration of machining and SLM creates a hybrid manufacturing route to overcome the inherited limitations of SLM. However, little study has been done to characterise surface integrity of an as-SLM part followed by machining (e.g. hybrid SLM-milling). In this paper, surface, integrity including surface roughness, microstructure, and microhardness, have been characterised for IN718 samples processed by the hybrid process. It has been found that microhardness varies with the scan direction and the use of coolant in the subsequent milling, and surface integrity can be significantly improved by the hybrid SLM-milling route.     

Surface alloying of miniature components by micro-electrical discharge process

Surface alloying is necessary to enhance the surface features of machine elements. In the present study, feasibility of micro-electric discharge machining (micro-EDM) process for surface alloying has been investigated. Experiments are conducted on Nickel sheets using tool of Ti6Al4V with EDM oil and kerosene as dielectric. The surface modification takes place by spark discharges on localized regions of the work piece and the tool surface causing melting of tool and work piece, disassociation of dielectric, alloying, and quenching in the electrolyte. The samples were analyzed by field emission scanning electron microscope equipped with energy-dispersive X-ray spectroscopy, microhardness testing machine, and X-ray diffraction. Recast layers obtained have distinct structure and composition as compared to the work piece. Average recast layer thickness varied from 10.72 to 69.8?µm in case of EDM oil and from 13.5 to 31.6?µm in case of kerosene by varying voltage, pulse duration (on time) and frequency during the experiment. The microhardness of the machined surfaces was obtained in a wide range of 161.61–338.25 HV whereas the microhardness of unaffected base metal was 132.25 HV. Titanium carbide (TiC) was deposited and consequently there was improvement in the hardness of the work piece.     

Role of preplaced silicon on a TIG processed SiC incorporated microalloyed steel

ABSTRACT

Research aimed at enhancing the surface properties of carbon steels by incorporating fine silicon carbide particulates has had limited success because the dissolution of the ceramic occurred. This research considers a method of reducing SiC dissolution by generating a high Fe–Si liquid which protects the ceramic. Three particulate groups were investigated, (1) ～ 5?µm SiC, (2) ～45?µm Si +～ 5?µm SiC, and (3) ～45?µm Si, all incorporated into a microalloyed steel using a tungsten inert gas process. Detailed microhardness of the melt zones together with microstructural analysis showed that the addition of Si resulted in a cracked hard layer containing SiC. However, in Specimen 1, a thicker, hardcrack-free layer resulted from the microstructure developed by the dissolution of SiC.     

Optimum milling parameters for production of highly uniform metal-matrix nanocomposites with improved mechanical properties

In the present paper, a system dynamic model is presented to predict the final particle size of milled powder during ball milling process. The presented model is used to obtain the optimum ball size, milling speed and milling time that achieve the best particle size reduction of metal-matrix nanocomposites. Parametric study is performed using the presented analytical model to study the influence of ball size and milling speed on the milling efficiency. The predictions of the presented model are validated with experimental results done during this work for Cu-5%ZrO₂ nanocomposite and others available in the literature. The results show that the milling time required to achieve the steady state condition for Cu-5%ZrO₂ nanocomposite is 15?h. At 15?h of milling, ZrO₂ particles are highly uniform distributed in Cu matrix and the microhardness is increased from 75.4 HV for Cu to 197.6 HV for Cu-5%ZrO₂ nanocomposite. After 15?h, the particle size reduction rate is too low and the hardness improvement rate is too low as well (204.1 HV after 20?h milling) which make the milling process after 15?h is not appreciable.     

Virtual manufacturing of various types of gears and validation of the technique using rapid prototype

Virtual manufacturing of gears is carried out to illustrate the fairly complicated gear generation process and the associated simultaneous motions being provided to the gear blank and the gear cutter. An attempt has been made to capture the phenomenon of chip formation as well. Generation of various types of gears are shown employing two types of operation, one being use of a gear hobbing cutter having multiple cutting edges. As such validation of the virtual manufacturing technique is always a difficult task. Using rapid prototype technology, a novel approach is proposed to ascertain the efficacy of the virtual manufacturing process being followed. The methodology is quite general and can be used for validation of any other virtual manufacturing process as well.     

Influence of inner-spraying rotating tool during electrochemical milling of Nimonic-263 alloy

Electrochemical milling (EC milling) has great possibility in consequence of its flexibility and applications in the various manufacturing industries, especially in defense and biomedical industry. In future, it is likely to be one of the most capable, successful, and commercially used unconventional machining processes in the up-to-date manufacturing industries. In this research work, an attempt has been made to develop a versatile in-house EC milling setup to study the impact of inner-spraying rotating tool on the different responses of EC milling. Experiments have been performed on a special type of nickel-based (nickel–cobalt–chromium–molybdenum) superalloy commonly known as Nimonic-263 alloy specially developed for high-temperature and high-strength applications to identify the impact of major process parameters, e.g., feed rate and milling layer depth with and without tool rotation, on the responses like machining depth, side angle, surface roughness, and quality of machined profile. During EC milling of Nimonic-263 alloy, excellent surface finish ranging from 0.06 to 0.08 μm has been attained by employing mixed electrolyte, i.e., NaCl (1 M) and NaNO₃(1 M). With the incorporation of inner-spraying rotating tool, flushing can be improved to a large extent which improves the accuracy of machining.