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Kui Liu

Bio: Kui Liu is an academic researcher from Agency for Science, Technology and Research. The author has contributed to research in topics: Machining & Chip formation. The author has an hindex of 26, co-authored 102 publications receiving 1993 citations. Previous affiliations of Kui Liu include Nanjing University of Aeronautics and Astronautics & National University of Singapore.


Papers
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Journal ArticleDOI
TL;DR: In this article, finite element analysis (FEA) of micromachining using the arbitrary Lagrangian-Eulerian (ALE) method showed that chip is formed through material extrusion under a critical a/r

118 citations

Journal ArticleDOI
TL;DR: A theoretical analysis for the mechanism of ductile chip formation in the cutting of brittle materials is presented in this article, which shows that large compressive stress can be generated in the chip formation zone with two conditions.
Abstract: A theoretical analysis for the mechanism of ductile chip formation in the cutting of brittle materials is presented in this paper. The coexisting crack propagation and dislocation in the chip formation zone in the cutting of ductile materials are examined based on an analysis of the geometry and forces in the cutting region, both on Taylor’s dislocation hardening theory and the strain gradient plasticity theory. It was found that the ductile chip formation was a result of large compressive stress and shear stress in the chip formation zone, which shields the growth of pre-existing flaws by suppressing the stress intensity factor K I . Additionally, ductile chip formation in the cutting of brittle materials can result from the enhancement of material yield strength in the chip formation zone. The large compressive stress can be generated in the chip formation zone with two conditions. The first condition is associated with a small, undeformed chip thickness, while the second is related to the undeformed chip thickness being smaller than the radius of the tool cutting edge. The analysis also shows that the thrust force F t is much larger than the cutting force F c . This indicates that large compressive stress is generated in the chip formation zone. This also confirms that the ductile chip formation is a result of large compressive stress in the chip formation zone, which shields the growth of pre-existing flaws in the material by suppressing the stress intensity factor K I . The enhancement of material yield strength can be provided by dislocation hardening and strain gradient at the mesoscale, such that the workpiece material can undertake the large cutting stresses in the chip formation zone without fracture. Experiments for ductile cutting of tungsten carbide are conducted. The results show that ductile chip formation can be achieved as the undeformed chip thickness is small enough, as well as the undeformed chip thickness is smaller than the tool cutting edge radius.

110 citations

Journal ArticleDOI
TL;DR: In this article, an experimental study on UEVC of hardened stainless steel (a typical Stavax, hardness 49 HRC) using the PCD tools was carried out to investigate the effects of three machining parameters: nominal depth of cut, feed rate, and nominal cutting speed on output performances.

106 citations

Journal ArticleDOI
10 Apr 2019
TL;DR: Feng et al. as discussed by the authors reviewed the development of atomic and close to atomic scale manufacturing (ACSM) based on atomic level operation modes in subtractive, transformative, and additive manufacturing processes.
Abstract: Human beings have witnessed unprecedented developments since the 1760s using precision tools and manufacturing methods that have led to ever increasing precision, from millimeter to micrometer, to single nanometer, and to atomic levels. Researchers led by Prof. Fengzhou Fang from Tianjin University/University College Dublin have recently reviewed the development Atomic and Close to atomic Scale Manufacturing (ACSM) based on atomic level operation modes in subtractive, transformative, and additive manufacturing processes. Fang has formally proposed three phases of manufacturing advances: • Manufacturing I: Craft based manufacturing by hand, as in the Stone, Bronze, and Iron Ages, in which manufacturing precision is at the millimeter scale. • Manufacturing II: Precision controllable manufacturing using machinery where the material removal, transformation, and addition scales are reduced from millimeters to micrometers and nanometers. • Manufacturing III: Manufacturing objectives and processes directly focused on atoms, spanning the macro through the micro to the nanoscale where manufacturing is based on removal, transformation, and addition at the atomic scale, namely, atomic and close to atomic scale manufacturing. In this review article, the authors systematically analysed literatures in area of subtractive manufacturing including ultra precision machining, high energy beam machining, atomic layer etching, atomic force microscope nanomachining, where atomic wide line was achieved by focused electron beam sculpture based on 2D materials, such as transition metal dichalcogenides. Sub nanometer finish can be achieved with ultra precision polishing and atomic layer etching, where defects free and single atomic layer removal are still not possible. Atomic scale additive manufacturing, featured with macromolecular assembly with feedstocks, such as DNAs, proteins and peptides, represents atomic precision manufacturing of biological machines. Atomic scale transformative manufacturing, such as using Scanning Tunnelling Microscopy, Atomic Force Microscopy and Scanning Transmission Microscopy, has demonstrated capability for operation of single atoms. They also summarized the metrology technologies for ACSM and current applications. Today, the famous Moore’s law is approaching its physical limit. Computer microprocessors, such as the recently announced A12 Bionic chip and Kirlin 980, use a 7 nm manufacturing process with 6.9 billion transistors in a centimeter square chip. Such limits have been pushed to a 5 nm node and even a 3 nm node, which represents a few tens of atoms. Human beings are already stepping into the atomic era. Meanwhile, human society is facing unprecedented global challenges from depleting natural resources, pollution, climate change, clean water, and poverty.What shall we do? Such challenges are directly linked to the physical characteristics of our current technology base for producing energy and material products. According to the authors, it is the time to start changing both products and means of production via ACSM, which includes all of the steps necessary to convert raw materials, components, or parts into products designed to meet users' specifications. They believe research should focus on extensive study of fundamental mechanisms of ACSM, development of new functional devices, exploration of ACSM of extensive materials and amplifying throughput for future production.

101 citations

Journal ArticleDOI
TL;DR: In this article, a theoretical and experimental study on the ductile cutting of tungsten carbide is presented, in which the critical undeformed chip thickness for ductile chip formation in the cutting process can be predicted from the workpiece material characteristics, tool geometry and cutting conditions.

99 citations


Cited by
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Journal ArticleDOI
TL;DR: A survey of the current efforts in mechanical micro-machining research and applications, especially for micromilling operations, can be found in this paper, where the authors suggest areas from macro-milling that should be examined and researched for application to the improvement of micro-mechanical cutting processes.
Abstract: The miniaturization of machine components is perceived by many as a requirement for the future technological development of a broad spectrum of products. Miniature components can provide smaller footprints, lower power consumption and higher heat transfer, since their surface-to-volume ratio is very high. To create these components, micro-meso-scale fabrication using miniaturized mechanical material removal processes has a unique advantage in creating 3D components using a variety of engineering materials. The motivation for micro-mechanical cutting stems from the translation of the knowledge obtained from the macro-machining domain to the micro-domain. However, there are challenges and limitations to micro-machining, and simple scaling cannot be used to model the phenomena of micro-machining operations. This paper surveys the current efforts in mechanical micro-machining research and applications, especially for micro-milling operations, and suggests areas from macro-machining that should be examined and researched for application to the improvement of micro-machining processes.

690 citations

Journal ArticleDOI
TL;DR: In this paper, the basic kinematic relationships for 1D and 2D VAM (circular/elliptical tool path) are described and the periodic separation between the tool rake face and uncut material, characteristic of VAM, is related to observed reductions in machining forces and chip thickness.
Abstract: Vibration-assisted machining (VAM) combines precision machining with small-amplitude tool vibration to improve the fabrication process. It has been applied to a number of processes from turning to drilling to grinding [9] , [36] . The emphasis on this literature review is the turning process where VAM has been applied to difficult applications such as diamond turning of ferrous and brittle materials, creating microstructures with complex geometries for products like molds and optical elements, or economically producing precision macro-scale components in hard alloys such as Inconel or titanium. This review paper presents the basic kinematic relationships for 1D (linear vibratory tool path) and 2D VAM (circular/elliptical tool path). Typical hardware systems used to achieve these vibratory motions are described. The periodic separation between the tool rake face and uncut material, characteristic of VAM, is related to observed reductions in machining forces and chip thickness, with distinct explanations offered for 1D and 2D modes. The reduced tool forces in turn are related to improvements in surface finish and extended tool life. Additional consideration is given to the intermittent cutting mechanism and how it reduces the effect of thermo-chemical mechanisms believed responsible for rapid wear of diamond tools when machining ferrous materials. The ability of VAM to machine brittle materials in the ductile regime at increased depth of cut is also described.

657 citations

Journal ArticleDOI
TL;DR: Indentation is a remarkably flexible mechanical test due to its relative experimental simplicity as discussed by the authors, and the ease of implementation has made indentation a ubiquitous research tool for a number of different systems across size scales (nano to macro) and scientific/engineering disciplines.

423 citations

Journal ArticleDOI
TL;DR: In this paper, the critical maximum undeformed equivalent chip thickness for ductile-brittle transition (DBhmax-e) of zirconia ceramics under different lubrication conditions was investigated.
Abstract: This study investigates the critical maximum undeformed equivalent chip thickness for ductile-brittle transition (DBhmax-e) of zirconia ceramics under different lubrication conditions. A DBhmax-e model is developed through geometry and kinematics analyses of ductile-mode grinding. Result shows that DBhmax-e decreases with increasing friction coefficient (μ). An experimental investigation is then conducted to validate the model and determine the effect of dry lubrication, minimum quantity lubrication (MQL), and nanoparticle jet minimum quantity lubrication (NJMQL) conditions on DBhmax-e. According to different formation mechanisms of debris, the grinding behavior of zirconia ceramics is categorized into elastic sliding friction, plastic removal, powder removal, and brittle removal. Grinding forces per unit undeformed chip thickness (Fn/h and Ft/h) are obtained. The lubrication condition affects the normal force and ultimately influences the resultant force on workpiece. In comparison with dry grinding (DBhmax-e = 0.8 μm), MQL and NJMQL grinding processes increase DBhmax-e by 0.99 and 1.79 μm respectively; this finding is similar to model result. The theoretical model is then assessed by different volume fractions of nanofluids under NJMQL condition with an average percentage error of less than 8.6%.

359 citations

Journal ArticleDOI
TL;DR: Molecular dynamics simulations have been used to understand the occurrence of brittle-ductile transition due to the high-pressure phase transformation (HPPT), which induces Herzfeld-Mott transition.
Abstract: 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.

291 citations