Christopher J. Evans

Modification of hydrogen‐passivated silicon by a scanning tunneling microscope operating in air

The chemical modification of hydrogen‐passivated n‐Si (111) surfaces by a scanning tunneling microscope (STM) operating in air is reported. The modified surface regions have been characterized by STM spectroscopy, scanning electron microscopy (SEM), time‐of‐flight secondary‐ion mass spectrometry (TOF SIMS), and chemical etch/Nomarski microscopy. Comparison of STM images with SEM, TOF SIMS, and optical information indicates that the STM contrast mechanism of these features arises entirely from electronic structure effects rather than from topographical differences between the modified and unmodified substrate. No surface modification was observed in a nitrogen ambient. Direct writing of features with 100 nm resolution was demonstrated. The permanence of these features was verified by SEM imaging after three months storage in air. The results suggest that field‐enhanced oxidation/diffusion occurs at the tip‐substrate interface in the presence of oxygen.

Self-calibration : Reversal, redundancy, error separation, and 'absolute testing'

Abstract Over the years many techniques have been developed for accurate measurement of part features without reference to an externally calibrated artefact. This paper presents a partial survey of such methods for dimensional metrology, their ranges of application, and their limits. Finally, the paper attempts to distil the common features of the various methods in the hope that this may provide the basis, or inspiration, for development of “new” methods.

“Structured”, “Textured” or “Engineered” Surfaces

Fine scale, periodic structures offer designers additional freedom to create novel functions or combinations of functions. This emerging field of “structured” surfaces is poorly defined. This paper attempts to define “structured” surfaces, and then to provide examples of such surfaces for a variety of applications. Manufacturing and metrology are also discussed

Chemical Aspects of Tool Wear in Single Point Diamond Turning

Abstract A hypothesis is proposed that ascribes chemical wear of diamond tools to the presence of unpaired d electrons in the sample being machined. This hypothesis is used to explain a range of results for metals, alloys, and other materials including “electroless” nickel. The hypothesis is further tested by experiments presented here on the machining of a range of high purity elements. The implications for diamond turnability of other materials are discussed.

Material Removal Mechanisms in Lapping and Polishing

Polishing processes are critical to high value production processes such as IC manufacturing. The fundamental material removal mechanisms, howeve, are poorly understood. Technological outputs (e.g., surface finish, sub-surface damage, part shape) and throughput of lapping and polishing processes are affected by a large number of variables. Individual processes are well controlled within individual enterprises, yet there appears to be little ability to predict process performance a priori. As a first step toward improving process modeling, this paper reviews the fundamental mechanisms of material removal in lapping and polishing processes and identifies key areas where further work is required.

White layers and thermal modeling of hard turned surfaces

Abstract White layers in hard turned surfaces are identified, characterized and measured as a function of tool flank wear and cutting speed. White layer depth progressively increases with flank wear. It also increases with speed, but approaches an asymptote. A thermal model based on Jaegers moving heat source problems (J.C. Jaeger, Moving source of heat and the temperature at sliding contacts, in: Proceedings of the Royal Society, NSW, vol. 56, pp. 203–224) is applied to simulate the temperature field in machined surfaces and to estimate white layer depth in terms of the penetration depth for a given critical temperature. The analysis shows good agreement with the trend in experimental results. White layer formation seems to be dominantly a thermal process involving phase transformation of the steel, possibly plastic strain activated; flank wear land rubbing may be a primary heat source for white layer formation. A strong material dependence of surface alteration is also observed.

Cryogenic Diamond Turning of Stainless Steel

Summary Tool wear is extremely rapid when ferrous materials are single point diamond turned. This paper reviews diamond tool wear mechanisms, showing that both fracture and chemical mechanisms may be important. The rate of all chemical reactions increases exponentially with temperature. Hence tool wear may be reduced significantly by machining at cryogenic temperatures. A cryogenic machining system comprising tool post and chuck with constrained liquid nitrogen flows has been built. Using this system a number of 35 mm diameter, 400 series stainless steel flats have been diamond turned. Surface finish is better than 25 nm Ra.

On chip morphology, tool wear and cutting mechanics in finish hard turning

Abstract Topography of surfaces produced in finish hard turning using cubic boron nitride (CBN) tools is affected by a large number of factors including tool wear and the mechanics of the chip formation process. This paper shows first that tool wear rates are affected by interactions between the work material and the binder phase of the CBN tool. For finish hard turning, low CBN content, ceramic binder tools give longer lives and better finish than high CBN content metallic binder tools. For low CBN tools, wear rate is directly related to the microstructure of the work material and to the CBN grain size. SEM studies suggest that chip morphology is independent of work material microstructure, but varies with tool wear. Orthogonal cutting tests show that, above a critical speed, segmented chips are formed by catastrophic localized shear and that chip segmentation spacing may be reflected in a modulation of the machined surface. Segment spacing is a function of depth of cut, rake angle, and surface speed, approaching a limiting value with speed. Specific cutting energies decrease with speed, also approaching an asymptote. A simple mechanical model gives reasonable predictions of segment spacing along the original surface, although a full thermo-plastic model will be required to account for other aspects of the chip formation process.

Test optics error removal

Wave-front or surface errors may be divided into rotationally symmetric and nonrotationally symmetric terms. It is shown that if either the test part or the reference surface in an interferometric test is rotated to N equally spaced positions about the optical axis and the resulting wave fronts are averaged, then errors in the rotated member with angular orders that are not integer multiples of the number of positions will be removed. Thus if the test piece is rotated to N equally spaced positions and the data rotated back to a common orientation in software, all nonrotationally symmetric errors of the interferometer except those of angular order kNθ are completely removed. It is also shown how this method may be applied in an absolute test, giving both rotationally symmetric and nonsymmetric components of the surface. A general proof is given that assumes only that the surface or wave-front information can be described by some arbitrary set of orthognal polynomials in a radial coordinate r and terms in sin θ and cos θ. A simulation, using Zernike polynomials, is also presented.

Experimental investigation on CBN turning of hardened AISI 52100 steel

Abstract This study investigated the performance and wear behavior of different cubic boron nitride (CBN) tools in finish turning of hardened AISI 52100 steel. Tool performance was evaluated based on the part surface finish and the tool flank wear. Wear conditions of CBN cutting tools were primarily characterized by scanning electron microscopy (SEM). Machining results showed that low CBN content tools (CBN-L) consistently perform better than high CBN content counterparts (CBN-H), despite the CBN-L has inferior mechanical properties. The flank wear rates were proportional to cutting speed and CBN-H showed accelerated thermal wear associated with high cutting temperatures. Reducing depth of cut would only improve surface finish to CBN-L, but not to CBN-H, despite similar wear rates. The transferred layer on the flank wear land may result in adhesion of the binder compound and significantly affect the tool wear process. The metallic binder in CBN-H has stronger affinity to the transferred layer and may result in plucking out of CBN particles and consequent severe abrasive wear.