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The Ewald method for evaluating the free-space 1-D periodic Green’s function is extended to leaky waves by allowing for complex wavenumbers. It is shown that care must be taken when choosing the path of integration in the complex plane in the derivation of the Ewald method in order to obtain solutions that correspond to physical leaky-wave solutions. The use of different paths results in an evaluation of the Ewald method using an analytical continuation of the exponential integral function previously used when the wavenumber is real. The extension of the Ewald method to complex wavenumbers allows for the treatment of practical periodic leaky-wave antennas and periodic guiding structures with losses, as well as metamaterials, including 1-D chains of plasmonic nanoparticles.

Surface-wave excitation from microstrip antennas is of major concern in many practical antenna applications. In this paper, the challenge of reducing the surface-wave excitation from microstrip antennas in a general way is addressed. The proposed approach is based on a theorem called the reduced surface wave (RSW) theorem. The RSW theorem suggests that by properly selecting the permittivity of the filling material inside the patch cavity, the patch will not excite the dominant TM0 surface-wave mode. A validation of this theorem is demonstrated here for the first time by comparing the mutual coupling between a pair of RSW antennas and a pair of conventional antennas.

The input impedance and radiation pattern of the inset-fed rectangular microstrip patch antenna are investigated. It is concluded that a shifted cosine-squared function describes well the variation of the resonant input resistance with the feed location (point of contact between the microstrip feed line and the notch) for a given patch and substrate geometry. The parameters of the shifted cosine-squared function depend on the notch width for a given patch and substrate geometry. The cross-polarization level is seen to increase as either the notch width or depth increases. However, for a fixed input resistance level, the notch depth decreases as the width increases, so that the cross-polarization level is not very sensitive to the notch width for a fixed input resistance.

Precision abrasive finishing is a key technology in the manufacture of thin-film magnetic heads (TFH) for rigid disc drives. The read and write microdevices of the recording heads are fabricated on ceramic substrates (“wafers”) using thin-film processing technology. After wafer processing, the substrates are sliced to individual bars (containing 46 heads per bar) using a diamond dicing wheel. They are then finished using an advanced lapping process with individual head close-loop control (sensor height control for the control of the material removal as well as for the end point detection). Finally, the bars are diced into individual heads (called “sliders”) using a diamond dicing wheel. The slider abrasive finishing process critically affects the magnetic, electrical and mechanical performance of the recording heads. This paper presents the results of some experimental studies based on the state-of-the-art abrasive finishing of recording heads, taking into account the critical challenges involved, namely the sensor height control, pole-tip recession (PTR) (metal dishing), alumina recession (AluR) (oxide erosion), trailing-edge profile, polishing uniformity, smearing, surface roughness (scratches) and air-bearing surface (ABS) flatness. The relative advantages of the fixed- versus free-abrasive processes are also discussed. The results of chemical-mechanical fixed-abrasive lapping/nanogrinding to achieve near-zero PTR (to minimize magnetic space loss) and low AluR (to reduce flying height variation) to meet the high areal density head requirements are also presented.

Nanometric uniaxial tension tests have been conducted on four fcc metals, namely, Al, Cu, Ag and Ni using combined Monte Carlo (MC)-damped trajectory (DT) simulations and the results compared with conventional MD simulations employing the same potential-energy surface and identical testing conditions. The MC-DT method combines DTs or steepest-descent methods with MC-Markov chains to converge the lattice atom coordinates rapidly to those that characterize the equilibrium state for a given extension of the workpiece in the tensile test. The computational times required for the MC-DT method are significantly less than the corresponding times for pure MD simulations; they are nearly a linear function of the number of lattice atoms for the MC-DT calculation, but exponential for the MD studies. This differential becomes significant as the number of atoms under consideration increases. Ultimate strengths and the corresponding strains, Young's modulus, and the strain at fracture are nearly in the same ranking ord...

Molecular dynamics (MD) simulation, like other simulation techniques, such as the finite difference method (FDM), or the finite element method (FEM) can play a significant role in addressing a number of machining problems at the atomic scale. It may be noted that atomic simulations are providing new data and exciting insights into various manufacturing processes and tribological phenomenon that cannot be obtained readily in any other way—theory, or experiment. In this paper, the principles of MD simulation, relative advantages and current limitations, and its application to a range of machining problems are reviewed. Machining problems addressed include: (a) the mechanics of nanometric cutting of non-ferrous materials, such as copper and aluminium; (b) the mechanics of nanometric cutting of semiconductor materials, such as silicon and germanium; (c) the effect of various process parameters, including rake angle, edge radius and depth of cut on cutting and thrust forces, specific force ratio, energy, and subsurface deformation of the machined surface; the objective is the development of a process that is more efficient and effective in minimizing the surface or subsurface damage; (d) modelling of the exit failures in various work materials which cause burr formation in machining; (e) simulation of work materials with known defect structure, such as voids, grain boundaries, second phase particles; shape, size and density of these defects can be varied using MD simulation as well as statistical mechanical or Monte Carlo approaches; (f) nanometric cutting of nanostructures; (g) investigation of the nanometric cutting of work materials of known crystallographic orientation; (h) relative hardness of the tool material with respect to the work material in cutting; a range of hardness values from the tool being softer than the work material to the tool being several times harder than the work material is considered; and (i) the tool wear in nanometric cutting of iron with a diamond tool. The nature of deformation in the work material ahead of the tool, subsurface deformation, nature of variation of the forces and their ratio, and specific energy with cutting conditions are investigated by this method.

Diamond coatings were deposited on commercial silicon nitride (Si 3 N 4 ) cutting tools by low pressure microwave plasma assisted chemical vapor deposition (MPCVD) at various processing conditions to assess the quality and adhesion of diamond coatings. A four-factor, three-level fractional factorial experimental design methodology was used to determine the significance of the process variables, such as the microwave chamber pressure, substrate temperature, microwave power and % CH 4 concentration in the hydrocarbon–hydrogen mixture. The reactor pressure was found to have the strongest influence on nucleation followed by the temperature and the % CH 4 concentration. Microwave power was found to have a minimum influence on nucleation. It was also found that nucleation density decreases with increase in pressure, while it increases with increase in the % CH 4 concentration. Substrate temperature and % CH 4 concentration were found to be the most crucial parameters dictating the overall growth rate as well as the quality of the diamond films. Diamond-coated Si 3 N 4 tools were characterized by μ-Raman spectroscopy and scanning electron microscopy. The former was used to assess the quality of the diamond coatings (phase purity as well as the amount of amorphous carbon associated with the sp 2 structure) as well as the residual stresses on the tools. The relative intensity of the non-diamond to the crystalline diamond was found to decrease with increase in the microwave chamber pressure. Higher microwave power was found to increase the intensity of the crystalline diamond and decrease the non-diamond peak intensity. The morphology of diamond coatings was assessed using an SEM. The diamond films deposited were qualitatively assessed for adhesion using the Rockwell hardness tester with a Brale indenter and an abrasion wear tester. A chamber pressure of ∼20 torr (2.65 kPa); a microwave power of ∼1000 W; a CH 4 concentration of 0.5–1%; and a substrate temperature in the range of 850–900°C, were identified as the optimum deposition conditions for producing good quality diamond coatings on Si 3 N 4 substrate.

The role of hydrostatic pressure in the ductile machining of silicon is demonstrated experimentally using a single crystal diamond tool with a large negative rake (40°) and a high side cutting edge angle (SCEA) ( 88°) and undeformed chip thickness in the nanometric range (50 nm) using an ultraprecision machine tool and a special machining stage inside a high external hydrostatic pressure (400 MPa) apparatus. © 2001 Elsevier Science B.V. All rights reserved.

The role of transition-metal substrates on the deposition of polycrystalline diamond was investigated using a microwave—plasma-assisted chemical vapour deposition process. Diamond deposition was carried out on the transition elements of the first series (3d block) and on the elements belonging to groups VB and VIB. It was found that the chemical nature of the transition metals plays an important role in the formation of diamond. Similarity in morphological features was observed on the diamond films grown on the substrates belonging to the same group. Micro-Raman (μ-Raman) spectroscopy indicated that diamond films on substrates belonging to groups VB and VIB have lower internal stresses than those deposited on group VIII. An attempt was made to relate the trends observed from the μ-Raman spectroscopy to the chemical properties of the transition elements. The mechanism of diamond growth seem to vary across the period. Elements belonging to the first half of the transition series, namely Ti, V. Nb, ...

A hybrid process for the synthesis of diamond using a low pressure chemical vapor deposition (CVD) technique (microwave assisted CVD) in conjunction with the use of graphite powder and a ‘catalyst-solvent’ as the starting materials is reported. Graphite is partially converted into diamond by the low pressure synthesis in the presence of nickel, a commonly considered ‘catalyst-solvent’ in the high pressure-high temperature (HP-HT) process. The resulting product is examined in the SEM, low-angle X-ray diffraction, and μ-Raman spectroscopy to show evidence of the conversion to diamond. The hybrid process is compared with the traditional HP-HT process for diamond synthesis to propose possible similarities of the ‘catalyst-solvent’ action present at HP-HT conditions and that at LP-HT conditions.

A thermal model for magnetic field assisted polishing of ceramic balls/rollers is presented. The heat source at the area of contact between the balls and the abrasives where material removal takes place is approximated to a disk. The disk heat source is considered as a combination of a series of concentric circular ring heat sources with different radii. Each ring in turn is considered as a combination of a series of infinitely small arc segments and each arc segment as a point heat source. Jaeger’s classical moving heat source theory (Jaeger, 1942; Carslaw and Jaeger, 1959) is used in the development of the model, starting from an instantaneous point heat source, to obtain the general solution (transient and steady-state) of the moving circular ring heat source problem and finally the moving disc heat source problem. Due to the formation of fine scratches during polishing (on the order of a few micrometers long), the conditions are found to be largely transient in nature. Calculation of the minimum flash temperatures and minimum flash times during polishing enables the determination if adequate temperatures can be generated for chemo-mechanical polishing or not. This model is applied in Part II for magnetic float polishing (MFP) of ceramic balls and in Part III for magnetic abrasive finishing (MAF) of ceramic rollers.

Conditions during finishing of advanced ceramics by magnetic abrasive finishing (MAF) processes are found to be, by and large, transient. Consequently, the available quasi-steady-state solutions for the moving heat sources are not directly applicable for this case. Hence, the general solution for a moving disk heat source, developed in Part I of this three-part series, is applied to determine the minimum flash temperatures and flash times generated at the contact points between the workmaterial (Si3N4 roller) and the abrasive (Cr2O3)). Since chemo-mechanical action between the abrasive—the workmaterial—the environment depends on both the thermodynamics and kinetics of the process, it is important to determine the flash temperatures as well as flash times during polishing. These were determined as a function of the polishing pressure and the rotational speed of the work material in this investigation. Thermodynamic considerations (not covered in this paper) indicate that even the minimum flash temperatures generated under the conditions of lower pressure, lower sliding velocity, and transient state would be adequate to initiate chemo-mechanical action, and experimental results confirmed the formation of chemo-mechanical reaction products during polishing (Bhagavatula and Komanduri, 1996).

The thermal model developed in Part I of this three-part series is applied in this paper to magnetic float polishing (MFP) of ceramic (Si3N4) balls. Using this method, the flash temperatures, flash times, and temperature distribution at the interface between the balls and the shaft of the MFP apparatus are calculated. Examination of the polished surfaces (scratch lengths) of the balls showed that the length of most scratches during the final stage of polishing is

Chromium oxide abrasive has been reported in the literature to provide efficient chemo-mechanical polishing action for silicon nitride ceramic. Since aluminum oxide and chromium oxide abrasives are nearly of the same hardness, magnetic float polishing tests were conducted on silicon nitride balls with these two abrasives to investigate mechanical versus chemo-mechanical aspects of polishing. Tests results show higher removal rates and smoother surface texture (with fewer pits) with chromium oxide abrasive compared to aluminum oxide abrasive. Formation of pits due to brittle fracture seems to be the more predominant mode of material removal with aluminum oxide abrasive than with chromium oxide abrasive. While there may be some mechanical action (abrasion) with chromium oxide abrasive initially, subsequent removal is believed to be due to chemo-mechanical action. This could be due to degeneration of the chromium oxide abrasive (both mechanical and chemical) during polishing. Various hypotheses for the material removal mechanism (both mechanical and chemo-mechanical) were considered. Based on that, the higher removal rates and smoother surface texture on the silicon nitride balls with chromium oxide abrasive in semifinish polishing is interpreted here as possibly due to chemo-mechanical action. Higher chemical stability of aluminum oxide abrasive (compared to chromium oxide abrasive) and the known role of chromium oxide as a catalyst for the oxidation of silicon nitride are some of the reasons attributed for this action.

Diamond films were synthesized using an oxyacetylene flame on a molybdenum substrate mounted on a water-cooled copper block. The morphology and quality of the synthetic diamond films produced depend on several factors including the substrate temperature, gas flow rates and their ratio, and substrate position. The substrate temperature profile was shown to be influenced by the coolant flow rate, nozzle size, substrate position on the heat sink, substrate position in the combustion flame, and the total flow rate of mixed gas (acetylene and oxygen). In this paper, the effects of substrate temperature and nozzle size on the morphology and quality of diamond films are discussed. Fine-gage thermocouples were used to measure the temperature distribution in the substrate during the process. Scanning electron microscopy of the produced diamond films is used to show the variation of crystal morphology.

Summary An experimental study of the effect of single crystal diamond tool edge geometry on the resulting cutting and thrust forces and specific energy in the ultraprecision orthogonal flycutting of Te-Cu was made. The effects of both the nominal rake angle and tool edge profile were investigated over uncut chip thicknesses from 20μm down to 10 nm. Characterization of the tool edge was performed with the use of atomic force microscopy. Both the nominal rake angle and tool edge profile were found to have significant effects on he resulting forces and energies.

Leaky-wave antennas can be classified into two basic types [1], depending on whether the geometry of the guiding structure is uniform or is periodically modulated along its length. In a uniform leaky-wave antenna, the fundamental mode is a fast-wave (meaning that the phase velocity is greater than that of the light in free space) and therefore radiates whenever the structure is open. In the second type of leaky-wave antenna, the periodic leaky-wave antenna, a periodic modulation of the guiding structure is introduced, and it is this periodicity that produces the leakage. In a periodic leaky-wave antenna the fundamental mode is a slow-wave that does not radiate, with radiation occurring from one of the space harmonics.

Low-pressure synthesis of diamond by activated chemical vapour deposition processes is attractive for producing diamond films for optical and electronic (i.e. non-abrasive) applications because of the ability of these processes to produce these films in large dimensions. The low growth rate (about 1 μm h−1) has, however, precluded these processes for abrasive grain production on simple economic grounds. With the introduction of combustion synthesis of diamond at growth rates exceeding 100μmh−1, this barrier seems less formidable than it once did. The synthesis of large (about 200 μm) well formed single crystals of diamond by the combustion process with growth rates of about 100μm h−1, reported here, offers an opportunity to explore the potential of this process for abrasive grain production.

A theorem for designing planar microstrip antennas with reduced surface-wave excitation has been given and validated by using patches printed on multi-layered substrates. The theorem states that the excitation of the TM0 surface wave is eliminated if the patch cavity is filled with a material having an effective relative permittivity that satisfies.

This research proposes a low-profile dual-band UHF antenna that can be integrated into a multi-band antenna system for public safety vehicles to cover the Ultra High Frequency (UHF), Global Positioning System (LI-GPS), and Wireless Fidelity (Wi-Fi) bands. The antenna system is designed to be small enough to fit on the roof of the vehicle (about 30 cm in diameter), while being only about 3 cm in height.

This paper deals with the fundamental considerations on the interactions between the abrasive and the work material as well as the micro-mechanisms of material removal and surface generation process in ‘gentle’ grinding and polishing (surface roughness in the range of a few nanometers rms) of advanced ceramics and glasses. In developing plausible mechanisms, an attempt is made to delineate the failure mechanisms operable in polycrystalline ceramics and glasses versus the metals. This is necessary because of the significant differences in the nature of bonding, microstructure and the tribochemistry, and, flaws generated during processing of these materials and their consequent effect on the failure mechanisms associated. For example, metals are fully dense crystalline materials with an orderly arrangement (both long and short range) of atoms in all directions. Plastic deformation, instead of brittle fracture, is by far the predominant mode of failure in these materials. Glasses, in contrast, are non-crystalline (or amorphous) and respond intermediate between a liquid and a solid, i.e. at room temperature they behave in a brittle manner but above the glass transition temperature in a viscous manner. Ceramics, though mostly crystalline, are different in the nature of bonding. For example, metallic bonding in the case of metals, no long range order in the case of glasses, and ionic and/or covalent bonding in ceramics. Since ceramics are processed from powders using sintering, hot-pressing, or hot-isostatic pressing, they are less than theoretically dense. This results in some inherent porosity in the microstructure. Also, the grain boundaries generally consist of a weak, glassy phase. All these factors affect the strength and failure (deformation/fracture) behavior of these materials. Grain dislodgement, viscous flow at the grain boundaries, and microfracture of the crystals may be the predominant modes of failure than plastic deformation in this case. Also, under the high pressures and temperatures generated at the contacting points during polishing, mechano-chemical effects can play an important role in the material removal. In this investigation, effect of these factors are carefully considered in the development of a mechanistic model of the process. While plastic deformation is feasible at high temperatures and/or under high hydrostatic pressures, the wide range of defect structures present at various levels in most ceramics tend to favor microfracture, grain dislodgement etc. Further, in ceramics containing a glassy phase at temperatures higher than the glass transition temperature, viscous flow of the glassy phase takes place. Since the glassy phase is present at the grain boundaries, this can cause grain boundary sliding.

Micron-sized spherical particles in sliding contact are found to reduce the static coefficient of friction, as with the case of larger-sized balls and rollers in bearings.

Manual adaptive control (MAC) is a system under development at Carnegie Mellon University in which a programmable calculator is used to adjust a machine tool to operate under optimum conditions (usually minimum cost per part). The machine operator is the sensor and is part of the control loop. This paper illustrates how the system is applied to axial feed centreless grinding operations.

Results of a four-year Advanced Machining Research Program (AMRP) to provide a science base for faster metal removal through high-speed machining (HSM), high-throughput machining (HTM) and laser-assisted machining (LAM) are presented. Emphasis was placed on turning and milling of aluminum-, nickel-base-, titanium-, and ferrous alloys. Experimental cutting speeds ranged from 0.0013 smm (0.004 sfpm) to 24,500 smm (80,000 sfpm). Chip formation in HSM is found to be associated with the formation of either a continuous, ribbon-like chip or a segmental (or shear-localized) chip. The former is favored by good thermal properties, low hardness, and fcc/bcc crystal structures, e.g., aluminum alloys and soft carbon steels, while the latter is favored by poor thermal properties, hcp structure, and high hardness, e.g., titanium alloys, nickel base superalloys, and hardened alloy steels. Mathematical models were developed to describe the primary features of chip formation in HSM. At ultra-high speed machining (UHSM) speeds, chip type does not change with speed nor does tool wear. However, at even moderately high speeds, tool wear is still the limiting factor when machining titanium alloys, superalloys, and special steels. Tool life and productivity can be increased significantly for special applications using two novel cutting tool concepts – ledge and rotary. With ledge inserts, titanium alloys can be machined (turning and face milling) five times faster than conventional, with long tool life (~ 30 min) and cost savings up to 78 percent. A stiffened rotary tool has yielded a tool life improvement of twenty times in turning Inconel 718 and about six times when machining titanium 6A1-4V. Significantly increased metal removal rates (up to 50 in.3/min on Inconel 718 and Ti 6A1-4V) have been achieved on a rigid, high-power precision lathe. Continuous wave CO2 LAM, though conceptually feasible, limits the opportunities to manufacture DOD components due to poor adsorption (~ 10 percent) together with high capital equipment and operating costs. Pulse LAM shows greater promise, especially if new laser source concepts such as face pump lasers are considered. Economic modeling has enabled assessment of HSM and LAM developments. Aluminum HSM has been demonstrated in a production environment and substantial payoffs are indicated in airframe applications.

Chemical interaction between diamond and pure iron has been investigated in simulated grinding experiments. Using Auger electron spectroscopy (AES) an extremely thin diffusion layer (≃ 200 A) was observed in the iron work material after grinding with a single crystal synthetic diamond. A correlation between short time grinding tests and long time diffusion tests was obtained and checked analytically using simple diffusion theory.

Summary This paper deals with the machining of ferrous materials in their hardened condition (hardness: 50 to 70 Rc). Work materials considered include high-speed tool steels, die steels, bearing steels, alloy steels, case-hardened steels, white cast iron, and alloy cast iron. Prerequisites for the successful machining of hardened ferrous alloys include: • Use of an extremely rigid, high-precision machine tool system with adequate power and proper sensors and control for monitoring the cutting process • Very hard(> HV 1800) and tough (KIC > 6 MP m1/2) tool material • Negative rake (≥−10°) tool geometry with a high wedge angle (> 90°), strong shape (e.g., round), and in some cases appropriate chamfer or radius, honed at the cutting edge • Tool holders with high stiffness • Appropriate cutting conditions Submicron-grain cemented carbide with a low binder content (≅3%) can be used to machine ferrous alloys of hardness up to ≈Rc 58, ceramic tools for up to ≈Rc63, and cubic boron nitride tools up to ≈Rc70. In many applications, the machining of ferrous materials in their hardened condition can replace grinding to give significant savings in cost and increase in productivity. Fewer machine tools and fewer processing operations are needed as a result. Machining steels in their hardened condition is thus both techologically and economically feasible.

Spherical metal particles in the size range of 1/3 to 60 μ found when grinding chips are examined in the scanning electron microscope and a mechanism for their formation based on surface energy is presented.

Under certain conditions, carbontetrachloride is found to be a negative boundary lubricant (gives a higher coefficient of friction than that of dry surfaces in air), while under other conditions, it lowers friction and gives a beneficial effect. Both of these situations are illustrated for heavily loaded sliding surfaces where the subsurface is undergoing gross plastic flow and an explanation is presented which appears to be consistent with all experimental facts. Carbontetrachloride is found to be more reactive chemically when the sliding surfaces are heavily strained or galled under high normal and shear stresses and containing microcracks, a situation that arises when cutting at low speed.

The salient features of a simple, wear-tolerant cemented carbide tool are described. Results are presented for high-speed machining (3 to 5 times the conventional speeds) of titanium alloys in turning and face milling. This tool, termed the ledge cutting tool, has a thin (0.015 to 0.050 in.) ledge which overhangs a small distance (0.015 to 0.060 in.) equal to the depth of cut desired. Such a design permits only a limited amount of flank wear (determined by the thickness of the ledge) but continues to perform for a long period of time as a result of wear-back of the ledge. Under optimum conditions, the wear-back occurs predominantly by microchipping. Because of geometric restrictions, the ledge tool is applicable only to straight cuts in turning, facing, and boring, and to face milling and some peripheral milling. Also, the maximum depth of cut is somewhat limited by the ledge configuration. In turning, cutting time on titanium alloys can be as long as ≈ 30 min. or more, and metal removal of ≈ 60 in.3 can be achieved on a single edge. Wear-back rates in face milling are about 2 to 3 times higher than in straight turning. The higher rates are attributed here to the interrupted nature of cutting in milling. Use of a grade of cemented carbide (e.g., C1 Grade) which is too tough or has too thick a ledge for a given application leads to excessive forces which can cause gross chipping of the ledge (rapid wear) and/or excessive deflection of the cutting tool with reduced depth of cut. Selection of a proper grade of carbide (e.g., Grades C2, C3, C4) for a given application results in uniform, low wear-back caused by microchipping. Because of the end cutting edge angle (though small, ≈ 1 deg) used, the ledge tool can generate a slight taper on very long parts; hence an N.C. tool offset may be necessary to compensate for wear-back. The ledge tool is found to give excellent finish (1 to 3 μm) in both turning and face milling. In general, conventional tooling with slight modifications can be used for ledge machining. The ledge tool can also be used for machining cast iron at very high speeds.

Scanning electron micrographs of different types of commercial abrasive grains used in grinding are discussed. Surface topography is found useful, along with other physical and chemical properties, in characterizing abrasive materials. The results of this study explain some of the differences in performance of several types of abrasive presently used in grinding practice.

Results of sliding experiments under high normal pressure using a sapphire ball on a modified Brinell hardness testing machine and different work materials are reported. A rational approach to the mechanism of metal build-up on Al2O3 abrasive developed recently has been extended in the present sliding tests to verify the hypothesis, and good agreement was found. The results of this study show a wide range of behaviour relative to the equilibrium level of friction and the time required to reach equilibrium when different materials are rubbed against the sapphire ball.

The mechanics of chip segmentation, during machining of a cold rolled steel has been investigated from a phenomenological point of view using a high speed movie camera and an explosive quick stop device. The latter was used for obtaining chip root samples at various stages of segmentation for subsequent examination in the Optical and Scanning Electron Microscope (SEM). The chip segmentation process is found to arise as a result of instabilities in the cutting process and is further augmented by the dynamic response of part of the machine tool structure. This process involves a slow forward movement of the plastic boundary in the primary shear zone forming a ramp on the free surface of the chip followed by a rapid return of the plastic boundary back towards the tool forming a step on the chip segment as a result of partial fracture at the free surface. This process is characterized by large strains, low shear angles that oscillate cyclically and stick-slip friction on the rake face. The instability in the cutting process is proposed to be due to the negative stress—strain characteristics of certain materials at large strains, as Walker and Shaw [1] proposed, involving void formation around second phase particles, their propagation into microcracks in the primary shear zone and coalescence of these cracks leading to partial fracture. Evidence for this has been obtained in this investigation.

Chemical interaction between the work material and the abrasive plays an important role in grinding. This will be more so in hot grinding. In this paper a novel experimental setup to study the wear and performance of various abrasives in hot grinding (up to ≈ 1000° C) is described. An oxy-acetylene torch under the work material is used as the heat soruce. Initial results on the performance of two commonly used abrasives, namely aluminum oxide and silicon carbide in simulated hot grinding of a cobalt base superalloy at 1000° C are presented using a scanning electron microscope. The results are compared with similar ones obtained at room temperature for the same combination of work material and abrasive. The results indicate that while silicon carbide wears more than aluminum oxide at room temperature, the reverse was found to be the case at high temperature. Also, the mode of wear and the nature of buildup were found to be different. In hot grinding, wear of aluminum oxide was found to involve the continuous release of micron sized crystallites while the formation of whiskers of silicon carbide was associated with the wear of silicon carbide. Buildup on aluminum oxide as metal was invariably found at room temperature while a uniform reaction product was present at high temperature.

Summary A new technique of dressing and conditioning a resin bonded superabrasive (diamond or cubic boron nitride) grinding wheel is presented. It comprises contacting the surface of the wheel with a wetting liquid (in this case a suitable lubricant), forming a film on the surface of the resin, and using the resulting wetted wheel surface to grind a hot pressed silicon carbide or silicon nitride ceramic alongside the workpiece of interest. The resulting thin ceramic chips (whose surfaces are extremely active as they are freshly generated) adhere to the wetted resin face forming a thin slurry layer. Such a layer if rejuvinated protects the resin bonding material from thermal and/or mechanical degradation or damage and the superabrasive from premature pullout, thus increasing the grinding wheel life.

The deformation in chips produced in machining a nickel-iron base superalloy (Inconel 718), at various speeds up to 213.5 m/min [700 surface feet per minute (SFPM)] has been investigated. In addition to slip, considerable twinning in the chips is observed at all speeds. Up to a cutting speed of about 30.5 m/min (100 SFPM), the chips formed are essentially continuous and ribbon-like, although deformation in the chip is inhomogeneous. At cutting speeds above 61 m/min (200 SFPM), shear-localized chips form. The longitudinal midsections of the chips show gross inhomogeneous deformation with shear localization between any two segments, and relatively low deformation within any individual segment. With an increase in speed the extent of contact between segments decreases rapidly, until a speed is reached where the individual segments become completely detached. The speed at which this occurs for other difficult-to-machine materials, such as AISI 4340, was found in an earlier study, to depend upon the metallurgical condition of the material and its hardness. Based on this study, the mechanism of chip formation when machining Inconel 718 is very similar to that reported earlier for machining both titanium alloys and hardened AISI 4340 steels at higher speeds. While the hcp crystal structure of titanium alloys in addition to titanium’s poor thermal properties (kρc) is believed to be partly responsible for the intense shear localization in that material, results with Inconel 718 (fcc) and AISI 4340 steel (bcc) indicate that the effect of structure on shear localization is not yet well understood.

Surface topography of several types of synthetic diamonds and cubic boron nitride (CBN), have been studied using a Scanning Electron Microscope (SEM). Information relative to the geometry of cutting edges and smoothness of crystal faces (of importance to friction on the rake face and bonding ability) is presented and discussed. Observations are also given concerning the role of morphology with respect to grain strength and recommended use.

A mechanism for the accelerated wear of bearing surfaces due to the cutting action of the spherical particles between bearing surfaces in sliding contact is proposed and verified experimentally.

With the increasing need to use titanium alloys for aerospace structural applications and because of the difficulties experienced in machining them (except at low speed), an investigation on the fundamental mechanism of chip formation when machining these alloys was undertaken. An attempt is made in this paper to clarify various aspects related to the mechanism of titanium chip formation based on a critical review of the literature and machining studies on a Ti-(6Al-4V) work material at various speeds with the aid of high speed photography and in situ machining experiments inside a scanning electron microscope.

This paper presents a methodology for determining the machine tool system requirements for high-speed machining (HSM)/high-throughput machining (HTM). Both technological and economic factors should be considered in the formulation of the model for determining machine tool system requirements. The HSM function model is given here in the form of ICAM-defined (IDEFo) charts with corresponding text. For machining most aluminum alloys, the maximum cutting speed is not limited by tool life, and the technology for high-speed machine tools (spindles, table drives, controls, chip management, and other features) exists today. Therefore, HSM of aluminum alloys can be implemented. Selection of a suitable HSM system involves detailed technological analysis and economic justification for a given part-family production configuration. The recent introduction of Si3N4 based tool materials has enabled significantly higher cutting speeds (up to 1524 mpm or 5000 sfpm) in the machining of gray cast iron. However, the machine tools using this type of tool material should be more rigid and capable of higher power, higher speed, and faster feed in order to increase productivity and reduce manufacturing costs. In the machining of the difficult-to-machine materials (e.g., superalloys), the cutting speed is still limited by tool wear. Nevertheless, a high-throughput machining (HTM) strategy is pertinent for this application.

Attritious wear of silicon carbide rubbing against a cobalt base superalloy at high speed was studied using a scanning electron microscope (SEM) and an Auger electron spectroscope (AES). The SEM study of the wear area on the silicon carbide grain showed it to be very smooth. The AES study of the groove-like marking generated by a silicon carbide grain showed a heavy concentration of carbon in areas where submicron wear debris was present. No indication of chemical reaction of the abrasive with the work material was evident. Instead, it appears that the surface atoms on the abrasive are removed preferentially, layer by layer, by oxidation under high temperature and a favorably directed shear stress.

An AISI 4340 Steel (325 BHN) was machined at various speeds up to 2500 m/min (8000 SFPM). Longitudinal midsections of the chips were examined metallurgically to delineate the differences in the chip formation characteristics at various speeds. Chips were found to be continuous at 30 to 60 m/min (100 to 200 SFPM) but discontinuous below this speed. Instabilities in the cutting process, leading to different types of cyclic chip formations, were observed at cutting speeds above 60 m/min (200 SFPM). Fully developed catastrophic shear bands separated by large areas (segments) of relatively less deformed material, similar to that when machining titanium alloys, were observed in the chips at cutting speeds above 275 m/min (800 SFPM). The intense shear bands between the segments appeared to have formed subsequent to the localized intense deformation of the segment in the primary shear zone. As the cutting speed increases, the extent of contact between the segments is found to decrease rapidly. At speeds of 1000 m/min (3200 SFPM) and above, due to rapid intense, localized shear between the segments, these segments were found to separate completely as isolated segments instead of being held intact as a long chip. The speed at which this decohesion occurs was found to depend upon the metallurgical state of the steel machined and its hardness. As in the case of machining titanium alloys, the deformation of the chip as it slides on the tool face, i.e., “secondary shear zone,” appeared to be negligible when machining this AISI 4340 steel at high speed. Based on the metallurgical study of the chip and the similarities of machining this material at high speed and that of titanium alloys at normal speed, a cyclic phenomenon in the primary shear zone is identified as the source of instability responsible for the large-scale heterogeneity and a mechanism of chip formation when machining AISI 4340 steel at high speed is proposed.