https://escholarship.org/content/qt8rf718jm/qt8rf718jm.pdf?t=krnesf

Recent Advances in Mechanical Micromachining

The abrasion mechanism in solid-solid contact mode of the chemical mechanical polishing (CMP) process is investigated in detail. Based on assumptions of plastic contact over wafer-abrasive and pad-abrasive interfaces, the normal distribution of abrasive size and an assumed periodic roughness of pad surface, a novel model is developed for material removal in CMP. The basic model is MRR=/spl rho//sub w/NVol/sub removed/, where /spl rho//sub w/ is the density of wafer N the number of active abrasives, and Vol/sub removed/ the volume of material removed by a single abrasive. The model proposed integrates process parameters including pressure and velocity and other important input parameters including the wafer hardness, pad hardness, pad roughness, abrasive size, and abrasive geometry into the same formulation to predict the material removal rate (MRR). An interface between the chemical effect and mechanical effect has been constructed through a fitting parameter H/sub w/ a "dynamical" hardness value of the wafer surface, in the model. It reflects the influences of chemicals on the mechanical material removal. The fluid effect in the current model is attributed to the number of active abrasives. It is found that the nonlinear down pressure dependence of material removal rate is related to a probability density function of the abrasive size and the elastic deformation of the pad. Compared with experimental results, the model accurately predicts MRR. With further verification of the model, a better understanding of the fundamental mechanism involved in material removal in the CMP process, particularly different roles played by the consumables and their interactions, can be obtained.

Material removal mechanism in chemical mechanical polishing: theory and modeling

Advances in Modeling and Simulation of Grinding Processes

This paper provides a comprehensive review of the literature, mostly of the last 10-15 years, that is enhancing our understanding of the mechanics of the rapidly growing field of micromachining. The paper focuses on the mechanics of the process, discussing both experimental and modeling studies, and includes some work that, while not directly focused on micromachining, provides important insights to the field. Experimental work includes the size effect and minimum chip thickness effect, elastic-plastic deformation, and microstructure effects in micromachining. Modeling studies include molecular dynamics methods, finite element methods, mechanistic modeling work, and the emerging field of multiscale modeling. Some comments on future needs and directions are also offered.

/pdf/the-mechanics-of-machining-at-the-microscale-assessment-of-9kfioocc84.pdf

The Mechanics of Machining at the Microscale: Assessment of the Current State of the Science

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

Effect of tool geometry in nanometric cutting: a molecular dynamics simulation approach

Ultraprecision grinding, like ultraprecision machining, involves removal of material (or cut depths) of the order of a few nanometres or less. Consequently, the material removal by this process is denoted as nanometric cutting. In this paper, the results of the molecular dynamics (MD) simulation studies conducted over a wide range of negative-rake-angle tools to simulate grinding are presented. The variations in the cutting forces, specific energy (energy required for removal of unit volume of work material), nature of subsurface deformation and size effect with rake angle were investigated by comparing the MD simulation results with the experimental results published in the literature. An increase in the magnitudes of forces, the ratio of the thrust to the cutting force, the specific energy and the sub-surface deformation were observed with increase in the negative rake. The specific energy in nanometric cutting was found to be nearly an order of magnitude larger than in conventional cutting, st...

Some aspects of machining with negative-rake tools simulating grinding: A molecular dynamics simulation approach

Molecular Dynamics (MD) simulations of nanometric cutting on single crystal aluminum were conducted to investigate the nature of the chip formation process with crystal orientation. Extensive dislocation generation ahead of the tool in the workmaterial was found principally along, normal to, along and normal to, or at −45 ° or −60 ° to the cutting direction depending on the specific orientation and direction of cutting. These differences in the dislocation motion observed here for the first time lead to significant variations in the nature of plastic deformation ahead of the tool and consequent variation in the magnitude of the forces, force ratio, specific energy, and subsurface deformation.

Orientation Effects in Nanometric Cutting of Single Crystal Materials: An MD Simulation Approach

Molecular dynamics (MD) simulation of nanometric cutting (ultraprecision machining involving cutting depths of the order of a few angstroms) involves considerable computational time (a few days to several weeks) and significant memory usage even for a few thousand workpiece atoms using workstations with fast processors (e.g. Digital Alpha workstation with 333 MHz clock speed). Consequently, it becomes necessary to use one of the following alternatives: extremely high cutting speeds, (about 500 m s−1), simulations using a smaller number of atoms, two-dimensional modelling, or acceptance of long computational times (several weeks) to address such problems. In order to reduce the computational time and at the same time to reduce the memory requirements significantly, a new method called length-restricted molecular dynamics (LRMD) simulation is proposed. In this method, the length of the work material is maintained constant but its position shifts along the direction of cut, that is atoms from the ma...

L. M. Raff

Papers

Effect of tool geometry in nanometric cutting: a molecular dynamics simulation approach

Some aspects of machining with negative-rake tools simulating grinding: A molecular dynamics simulation approach

Orientation Effects in Nanometric Cutting of Single Crystal Materials: An MD Simulation Approach

A new method for molecular dynamics simulation of nanometric cutting