Simulation and Experiments of Material-Oriented Ultra-Precision Machining

Nanotwinned (NT) Cu containing a high density of growth twin boundaries (TBs) is one emerging precious metal for its extraordinary properties of high strength, intermediate ductility, and high electric conductivity. In the present work, we elucidate the deformation mechanisms of nanotwinned Cu subjected to the diamond cutting-based nanometric cutting by means of molecular dynamics simulations, with an emphasis on examining the influence of intrinsic microstructural parameters and extrinsic machining parameter on the nanometric cutting processes. The underlying deformation mechanisms of the materials are further correlated with the evolution of machining forces and the formation of machined surface and chips. Our simulation results indicate that dislocation slip, dislocation–TBs interactions, and TBs-associated mechanisms work in parallel in the plastic deformation of the NT Cu. In particular, dislocation–TB interactions and TBs-associated mechanisms are strongly dependent on rake angle of cutting tool, TB inclination angle, TB spacing, and grain size, which leads to strong anisotropic cutting response of NT Cu that originates from the heterogeneous localized deformation.

High-entropy alloys (HEAs), which contain more than five principal elements with equal or near equal atomic percent, exhibit high wear resistant, high strength, and great plasticity. However, the plastic deformation mechanism and the machining-induced subsurface damage of HEAs at nanoscale are not yet fully understood, to limit their widely practical utility. Based on the experiment, AlCrFeCuNi HEA of atomic model is built through a melting and quick quenching method. In this work, we study the mechanical behaviors of AlCrFeCuNi HEA under uniaxial tensile loading and scratching processes by molecular dynamics (MD) simulations, in terms of the scratching force, atomic strain, atomic displacement, microstructural evolution, and dislocation density. The results show that the HEA obtained from MD simulations not only has high strength, but also exhibits good plasticity which is qualitatively consistent with the experiment. The dislocation gliding, dislocation pinning, and twinning subjected to the severe atomic lattice distortion and solid solution effects are still the main mechanism of plastic deformation in HEA. In addition, the larger tangential and normal forces and higher friction coefficient take place in HEA due to its outstanding strength and hardness, and high adhesion over the pure metal materials. Furthermore, the excellent comprehensive scratching properties of the bulk HEA are associated with the combined effects of multiple strengthening mechanisms, such as dislocation strengthening, deformation twinning strengthening as well as solute strengthening. This atomistic mechanism provides a fundamental understanding of plastic deformation and scratching behavior in HEA.

It is widely believed that the minimum depth of material removal of single crystalline workpieces is one single atomic layer in nanoscale mechanical machining. However, direct evidence for this is still lacking. In this work, the minimum depth of material removal of single crystalline copper in nanoscale mechanical machining is investigated through nanoscratching using molecular dynamics simulations. We demonstrate that the minimum depth of material removal of copper workpiece can achieve a single atomic layer under certain machining conditions in nanoscale machining process. It is found that the minimum depth of material removal is closely associated with the crystal orientation and scratching direction of copper workpiece. Our results also demonstrate that even when the depth of material removal is a single atomic layer of copper workpiece under certain machining conditions, the workpiece material is not removed in a layer-by-layer fashion, which rejects the hypothesis that single crystalline metal materials can be continuously and stably removed one layer of atoms after another in nanoscale mechanical machining. These understandings not only shed light on the material removal mechanism in nanoscale mechanical machining but also provide insights into the control and optimization of nanoscale machining process.

Optical materials, such as calcium fluoride single crystals, are widely used across various industries for their light transmission capabilities. These materials possess excellent mechanical, physical, and chemical resistant properties but also tend to be very brittle, which poses a challenge to the microcutting of complex freeform shapes with optical surface quality. Ultraprecision single-point diamond turning is commonly used in ductile-regime machining of hard and brittle materials, and polishing is employed as a secondary process to achieve optical quality surfaces, which can be time consuming. To improve the machining efficiency of high-strength materials, hot machining techniques have been developed to improve workpiece plasticity and surface integrity after machining. Surface quality and subsurface damage evaluation of the machined material along with finite element analysis allow a deeper understanding of the effectiveness in heat-assisted machining. In this chapter, an introduction to ultraprecision single-point diamond turning and the fundamentals of ductile-regime machining of hard and brittle materials will be discussed, followed by its application in fabrication of calcium fluoride single crystal lenses. Subsequently, the anisotropic characteristics of calcium fluoride single crystal will be investigated through experimentally validated crack formation models and surface generation morphology to gain detailed appreciation of the challenges faced during production of brittle single-crystal materials. To conclude the chapter, the effects of elevated temperatures on the material properties and machinability will be evaluated using experimental and numerical solutions.

Ultra-precision raster fly cutting (UPRFC) is a discontinuous fly cutting, whereby the diamond cutting tool flies with spindle rotation and cuts the machined surface discontinuously. Accompanying the motion of spindle with a raster tool path covering the whole machined surface, the diamond tool can cut and form complex surface structures. The cutting mechanism of UPRFC makes it widely utilized in manufacturing non-rotational symmetric structures like pyramid array, free-form surface, F-theta lens, tetrahedron array, micro-lens array etc. The form accuracy of fabricated products could be down to submicron level, and surface roughness down to non-metric level. UPRFC is potentially used to fabricate products in multiple industry fields such as aerospace, automobile, laser, communication, optics. Study of the cutting mechanism of UPRFC and the influences thereof on surface integrity is a key topic since it helps to improve the machined surface quality. The intermittent cutting mechanism of UPRFC is quite different from other ultra-precision machining processes, e.g., single-point diamond turning, micro-milling; correspondingly, it may cause different effects on surface finish. This chapter will talk about the cutting mechanism and surface formation of UPRFC in five parts. Part 1 gives an overview to UPRFC technology and the application thereof on fabrication of optical products. Part 2 delivers a comprehensive knowledge on the material removal mechanism of UPRFC both in theoretical and experimental aspects. Part 3 talks about material sliding during chip formation, and it caused surface microwaves in UPRFC process; in this part, the appearance and influence factors of microwaves will be presented. Finally, tool wear features and their influences on the quality of machined surface were investigated in Part 4, and a short conclusion is summarized in Part 5. This chapter will give reader a comprehensive understanding of the cutting mechanism and surface generation in UPRFC.

Based on investigations of the mechanism of precision surface formation in workpieces of anisotropic monocrystalline materials for optoelectronics, a generalized model of material removal in polishing with suspensions of polishing powders has been constructed. The removal rate in polishing sapphire planes of different crystallographic orientations has been found to grow in the series m < c < a < r with increasing volume, surface area, and most probable size of debris particles as well as with energy of dispersion of material from the face being polished. A study of the mechanism of formation of monocrystal planes of different crystallographic orientations has revealed that in polishing of sapphire the surface roughness parameters Ra, Rq, Rmax decrease in the series c > r > m > a with decreasing dielectric permittivity and thermal conductivity coefficient of the workpiece material, debris particle height, and Lifshitz constant. As a result, studies of regularities mechanical polishing optoelectronic components of crystalline materials found that polishing efficiency decreases with an increase of the binding energy and the transfer energy. It is shown that the polishing efficiency increases with increasing heat conduction coefficient of the material being processed, a processed surface road friction element by lapping and Lifshitz force. It is found that the ratio of the volume wear coefficient to the temperature conductivity coefficient of the material being processed depends on the specific heat and the transfer energy. The relative roughness of the treated surfaces of silicon carbide crystals, gallium nitride, aluminum nitride, and sapphire is characterized by the ratio: 0.68:0.67:0.63:1.00.

Textured surfaces with sophisticated micro/nanostructures can provide advanced and useful functions. To promote widespread use of these textured surfaces with mass production, manufacturing technology of structured surfaces for ultra-precision dies and molds made of hardened steel and tungsten carbide becomes essential. Nowadays, elliptical vibration cutting (EVC) is attracting more and more attention due to its excellent machining performances in precision machining of difficult-to-cut materials. The emphasis on this chapter is the practical applications of EVC in micro/nanomanufacture process. The development of the EVC technology is introduced firstly, and then, the advantageousness of EVC in the micro/nanomachining process is explored in detail. Moreover, a unique amplitude control sculpturing method, where the depth of cut is arbitrary changed by controlling the vibration amplitude, is introduced. As following, a criterion to indicate how to obtain ductile machining of tungsten carbide is clarified by applying EVC. The feasibility of highly accurate micro/nanomachining of tungsten carbide and hardened steel is experimentally verified with a machining accuracy of about ±1 nm in the depth-of-cut direction. A series of functional surfaces with textured grooves, dimple patterns, and sinusoidal grids were successfully fabricated on tungsten carbide, hardened steel, and single-crystal silicon, which could be applied to the molding, encoder, optoelectronics, and semiconductor industries. The EVC technology is expected to promote the development of micro/nanomachining process in the actual industrial applications.

Many attempts have been made to achieve optical surfaces on hard and brittle materials by means of ductile diamond grinding using fine-grained diamond wheels. However, the large wear rate of the fine-grained grinding wheel, which is caused by dressing and by the grinding process, limited the achievable form accuracy and the maximum material removal volume, especially in case of ductile grinding of large optical surfaces. For solving this problem, a novel-type diamond wheel must be applied which features much higher grinding ratios than that of fine-grained diamond wheels to guarantee the machined surface form accuracy in ultra-precision grinding of hard and brittle materials. In this chapter, the precision conditioning methods of coarse-grained diamond wheels for ultra-precision grinding will be presented first. Subsequently, the ultra-precision grinding of hard and brittle materials with coarse-grained grinding wheels will be investigated in order to reveal the performance of these novel diamond wheels. To conclude the chapter, micro-structured surface will be machined on the diamond grain surfaces of coarse-grained wheels for improving ground subsurface damage.

Many industries employ a great variety of ball bearings, pumps, and other mechanisms, whose performance, service life, and reliability essentially depend on the quality of manufacture of precision ceramic balls. This chapter describes the traditional methods of processing precision balls, their advantages, and disadvantages in relation to the precision processing of ceramic balls. Several modern methods of precision machining of ceramic balls with the controlled position of the balls’ rotation axis during processing are considered and present a promising method of processing balls in guide V-grooves with variable curvature, which allows you to control both the quality and performance of processing. A mathematical model of processing balls with the variable position of the balls’ rotation axis is suggested. The mathematical model takes into account the forces, pressures, and wears of the guide V-grooves and allows determining the performance of the tool and assessing the quality of the balls surface coating by traces of processing. Examples of tools with guide V-grooves with variable curvature are shown, and the results of the proposed method of precision processing of boron carbide balls are given.

This chapter describes the effect of ion plasma sprayed coating on performance of diamond precision dressing tools under diamond-abrasive machining conditions. The use of thick wear-resistant titanium nitride and carbide coating with a compensating interplayer of plastic metal (cobalt) is demonstrated to be a promising method for improving efficiency of dressing tools manufactured by electroplating and electroforming.

Nitrogen-vacancy (NV) color center is one kind of luminescent point defect in diamond. NV color center is a composite structure composed of substituted nitrogen atoms and adjacent carbon vacancies in diamond. It can be applied in many fields, such as super-resolution fluorescence imaging, high-sensitive detection, and quantum computing. In order to meet the requirements of NV color center’s applications, many efforts have been devoted to study the manufacturing methods of NV color center. Nowadays, femtosecond (fs) laser technology has been widely used in the field of micro/nanomachining and gradually applied to the manufacturing of diamond NV color centers. In this chapter, the mechanism and characteristics of fs laser micro/nanomachining, the basic properties, and the applications of diamond NV color centers were concisely summarized. Moreover, the ultrafast laser processing of NV color center, the fluorescence detection of NV color center, and the anti-bunching analysis method of single NV color center are introduced and discussed in detail.