Surface integrity in material removal processes: Recent advances

Molecular dynamics (MD) simulation has enhanced our understanding about ductile-regime machining of brittle materials such as silicon and germanium. In particular, MD simulation has helped understand the occurrence of brittle–ductile transition due to the high-pressure phase transformation (HPPT), which induces Herzfeld–Mott transition. In this paper, relevant MD simulation studies in conjunction with experimental studies are reviewed with a focus on (i) the importance of machining variables: undeformed chip thickness, feed rate, depth of cut, geometry of the cutting tool in influencing the state of the deviatoric stresses to cause HPPT in silicon, (ii) the influence of material properties: role of fracture toughness and hardness, crystal structure and anisotropy of the material, and (iii) phenomenological understanding of the wear of diamond cutting tools, which are all non-trivial for cost-effective manufacturing of silicon. The ongoing developmental work on potential energy functions is reviewed to identify opportunities for overcoming the current limitations of MD simulations. Potential research areas relating to how MD simulation might help improve existing manufacturing technologies are identified which may be of particular interest to early stage researchers.

/pdf/diamond-machining-of-silicon-a-review-of-advances-in-h5mvksdo94.pdf

Diamond machining of silicon: A review of advances in molecular dynamics simulation

Journal of the American Ceramic Society: Introduction

This book describes Raman microscopy and its applications to the analysis of materials. It contains ten chapters contributed by eighteen authors. The editors and authors are all eminent Raman microscopists and many of them have a link with the Raman group at Lille which led the field in the infancy of this technique. There are contributions from Professors Delhaye and Dhamelincourt, who were responsible (along with Dr Etz in the USA) for the discovery and public scientific awareness of the potential of the subject over 20 years ago. At that time, the marriage of one of the oldest pieces of scientific apparatus, the microscope, to one of the newest, the visible laser, was completely novel in concept. Early successes in the application of the new technique of Raman microscopy and, in particular, molecular Raman probing and imaging (microprobing) to solid-state samples were evident. Improvements and developments of the early systems were soon forthcoming, and now there are CCD- and FT-Raman microscopes operating in the visible and near-infrared regions of the electromagnetic spectrum, with improved detectors and imaging devices which have opened up novel areas of application in biological science, biomedical diagnostics and in art and historical materials conservation. The development of Raman microscopy is thoroughly covered and a useful introduction to the principles of Raman spectroscopy, Raman microanalysis and the design concepts of micro-Raman instrumentation is included. The text is well written for the newcomer and there are many examples of the applications of the technique to materials analysis, with balanced comments on the strengths and limitations of the techniques. For experienced Raman spectroscopists, the critical evaluation of optical coupling and component design requirements and their effect on the microanalytical performance behaviour of the instruments is especially valuable. This book will be useful to a broad range of practising analysts and spectroscopists, who will find the literature up-to-date and extremely useful. Each chapter presents its material in an easily assimilated way without too much emphasis being given to detailed, comprehensive coverage. This recommends the book to potential new practitioners, who may then best assess the evaluation of the technique for their own applications. For example, chapter 5 considers combined microprobe analytical techniques, e.g. Raman/LMMS and Raman/XRD/EM. On balance, this book does an excellent task in presenting Raman spectroscopy to a multi-faceted scientific audience. The many examples cited will interest workers in a wide range of fields, from solid-state physics (high- superconductors) to biological scientists (studies of single cells). This book is highly recommended for purchase and will quickly become a classic of its type.

Raman Microscopy: Developments and Applications

Prior to any practical application, brittle material components may need to be machined to a high degree of precision in order to avoid functional breakdown as well as to maintain exacting surface dimensional integrity and retain strength. This usually means grinding in the ductile region. Optimization of the grinding process can shorten manufacturing time and cost and prolong component lifetime. This article reviews the current state of the art of ductile grinding and outlines the underlying science behind pertinent machining events. Engineering aspects of the grinding process will be surveyed, with consideration of wheel requirements and of such variables as grit characteristics, strain rate and temperature. Attention will be given to the fundamental role of removal processes from individual and cumulative microcontacts, using nanoscratch mechanics as the underlying basis for analysis. The critical influence of diversity in material microstructures in determining local deformation mechanisms and subsequent material removal will be highlighted. Practical requirements for optimal ductile grinding will be indicated.

Science and art of ductile grinding of brittle solids

Experimental Work on Micro Laser-Assisted Diamond Turning of Silicon (111)

Micro-laser assisted machining is a novel micro/nano machining technique developed for ductile mode machining of ceramics and semiconductors. Ductile mode material removal is possible in a nominally brittle material due to the high-pressure phase transformation (HPPT) phenomenon during the machining process. This paper investigates the mechanism of machining by analyzing the HPPTs under different scratch conditions, with and without laser heating. Micro-Raman (μ-Raman) spectroscopy studies of the nano-scratched regions provided evidence for HPPT in single crystal Silicon (Si). Annealing of the high-pressure phases into a recrystallized diamond structure (Si-I) at higher laser powers and its effect on machining characteristics is also discussed. This has been the first time that HPPT is reported in the material removed region where the material's phase transformation and laser heating occur simultaneously and instantaneously (the annealing process occurs instantaneously and is not time dependent in this case).

Ductile mode material removal and high-pressure phase transformation in silicon during micro-laser assisted machining

The application of microlaser assisted machining of precision optical components made of optical grade single-crystal Si is reviewed. An optical raytracing model is developed and used for predicting the laser interaction with the workpiece. Optical characterization of the system is shown to be in good agreement with that predicted by the model. Using the information from the simulation and experimental validation, the laser-assisted diamond turning of single-crystal Si samples is shown to have exhibited little to no brittle fracture on the surface and the potential of extending the diamond tooling life by 150%.

https://www.spiedigitallibrary.org/journals/optical-engineering/volume-58/issue-9/092607/Microlaser-assisted-diamond-turning-of-precision-silicon-optics/10.1117/1.OE.58.9.092607.pdf

Microlaser assisted diamond turning of precision silicon optics

Machining of hard, crystalline ceramics is time-consuming, expensive and vital in many industries, but getting good results is challenging because of the surface damage it can cause. For sapphire machining damage can be especially detrimental because it can create significant stresses in the surface and sub-surface regions. Worst case, the stresses are relieved by crack propagation, fracture, and chipping at the surface. Conventional machining with a single point diamond-turning machine was compared to the same method with a laser simultaneously focused through a diamond stylus. The laser makes ductile machining more favorable and provides in situ annealing of damage. Micro-Raman spectroscopy was used to quantify residual stresses and optical microscopy was used to identify cracking. A reduction in the residual stresses was achieved when using the laser. This is seen most dramatically at higher laser powers, where fracture, cracking and chipping can be alleviated.

Mitigation of damage during surface finishing of sapphire using laser-assisted machining

Machining brittle materials, such as silicon, is expensive and often causes detrimental damage, but a relatively new technique, termed microlaser-assisted machining (micro-LAM), improves the effica...

Process parameter effects on residual stress and phase purity after microlaser-assisted machining of silicon

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