Other affiliations: Singapore Institute of Technology
Bio: K.S. Woon is an academic researcher from National University of Singapore. The author has contributed to research in topics: Drill & Deep hole drilling. The author has an hindex of 9, co-authored 17 publications receiving 330 citations. Previous affiliations of K.S. Woon include Singapore Institute of Technology.
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
TL;DR: In this paper, the effects of tool edge radius on the frictional contact and flow stagnation phenomenon, the stick-slide behavior and contact stress distributions, the evolutions of contact length, and the relationship between material deformation and total contact length were investigated.
Abstract: The contact phenomenon during micromachining is complicated due to the tool edge radius. This paper presents investigation of the effects of tool edge radius on the frictional contact and flow stagnation phenomenon, the stick–slide behavior and contact stress distributions, the evolutions of contact length, and the relationship between material deformation and total contact length. Through the arbitrary Lagrangian–Eulerian FE modeling approach, our findings revealed that the flow stagnation during material separations could be attributed to the counterbalance of shear contact components and it appeared to be insensitive to machining magnitude where a constant stagnation point angle of 58.5±0.5° was determined for a wide range of undeformed chip thicknesses. Three distinctive sticking and sliding regions associated with the flow stagnation phenomenon on the cutting tool were discovered following the identification of two stress criteria for sticking, τf=0 and/or τf=kf. In addition, the influence of tool edge radius on contact length and material deformation was determined and a theoretical model for the contact length of tool-based micromachining was proposed. It was also observed that tool–chip contact evolved in two successive stages through a series of intermittent sticking and sliding interactions as governed by the undeformed chip thickness and the transition of effective rake angle. An ultraprecision machining setup coupled with a high-speed and small field-of-view photography technique was proposed for experimental substantiation of the numerical results.
TL;DR: In this article, a mechanistic model uniting the underlying force, drill deflection, wall deformation and process kinematics is proposed and substantiated, as well as a model that unifies the underlying forces and drill's self-piloting capability.
TL;DR: The tool edge radius effect of micromachining is reflected by the characteristic changes in plastic deformation at varying combinations of tool edge radii, r, and undeformed chip thickness, a.
Abstract: Chip formation behavior of micromachining is governed by the tool edge radius effect as reflected by the characteristic changes in plastic deformation at varying combinations of tool edge radius, r, and undeformed chip thickness, a. At high a/r above unity, concentrated plastic deformation takes place at the primary and secondary deformation zones akin to conventional macromachining. Decreasing a/r below unity promotes localized deformation ahead of the tool edge radius, with the expansion in fraction of the primary deformation zone and the simultaneous shrinkage in fraction of the secondary deformation zone following the reductions in total tool–chip contact length. Further decrease of a/r below a critical threshold brings forth a total suppression of secondary deformation zone and resulted in an ultimate localization of plastic deformation ahead of the tool edge radius. This is perceived as a transition in chip formation mechanism from concentrated shearing to a thrust-oriented behavior.
TL;DR: In this paper, the authors show that material is removed by severe deviatoric stress within the boundary of elastic-plastic deformation during extrusion-like chip formation while this boundary is constantly redistributed to accommodate chip growth.
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.
TL;DR: A review of cutting edge preparation technologies and methods for cutting edge characterization can be found in this article, where the authors discuss the influence of cutting-edge geometry on chip formation, material flow, as well as mechanical and thermal loads on the tool.
TL;DR: In this paper, the authors compared the size effect behavior in micro-and macromilling by applying Analysis of Variance on the specific cutting force (kc) and relating it with the tool edge radius (re), workpiece roughness (Ra), cutting force and chip formation when cutting slots in AISI 1045 steel.
Abstract: This paper compares the size effect behaviour in micro- and macromilling by applying Analysis of Variance on the specific cutting force (kc) and relating it with the tool edge radius (re), workpiece roughness (Ra), cutting force and chip formation when cutting slots in AISI 1045 steel. Size effect is observed in micromilling through hyper-proportional increase of the specific cutting force for feeds per tooth (f) lower than endmill edge radius, reaching levels of grinding process (∼70 GPa) when f≅re/10. This particular milling condition does not produce chips. The minimum uncut chip thickness (hmin) varied between 22% and 36% of the endmill edge radius. This range was determined by proposing a curve (kc/Ra versus f/re) where specific cutting force becomes amplified (size effect) due to workpiece roughness association. In addition to the minimum uncut chip thickness, there is a cutting thickness between hmin and re that optimizes workpiece surface integrity and not only forms the chip completely. This thickness may be as important as hmin. Besides this, a relation between deformation mechanisms during chip formation and cutting force oscillations is proposed for micromilling and also related to tool tip radius (re). This cutting force behaviour enables the determination of certain characteristic chip thicknesses including hmin. Finally, it is concluded that minimum uncut chip thickness varies practically from 1/4 to 1/3 of tool cutting edge, regardless of workpiece material, tool geometry, mechanical machining process and technique used for measuring or estimating hmin, i.e. numerical, analytical or experimental.
TL;DR: In this paper, a slip-line field model was proposed to obtain the shear flow stress and hydrostatic pressure as functions of strain, strain-rate, and temperature in the primary shear zone.
TL;DR: In this paper, the authors give an overview of different methods, which are established to produce bore holes with demanding aspects related to diameter, length-to-diameter-ratio, bore hole quality, workpiece materials and complex internal contours.