Simulation of Abrasive Machining Using Molecular Dynamics

The development of ultra–precision processes which can achieve excellent surface finish and tolerance at nanometre level is now a critical requirement for many applications in medical, electronics and energy industry. Presently, it is very difficult to observe the diverse microscopic physical phenomena occurring in nanometric machining through experiments. The use of Molecular Dynamics (MD) simulation has proved to be an effective tool for the prediction and the analysis of these processes at the nanometre scale. The complexity and the cost of experimental investigation have made this approach even more suitable as simulation results sometimes point interesting directions for experimentation

COVID-19 and the Global Impact on Colorectal Practice and Surgery

Background: The novel severe acute respiratory syndrome coronavirus 2 virus that emerged in December 2019 causing coronavirus disease 2019 (COVID-19) has led to the sudden national reorganization of health care systems and changes in the delivery of health care globally. The purpose of our study was to use a survey to assess the global effects of COVID-19 on colorectal practice and surgery. Materials and Methods: A panel of International Society of University Colon and Rectal Surgeons (ISUCRS) selected 22 questions, which were included in the questionnaire. The questionnaire was distributed electronically to ISUCRS fellows and other surgeons included in the ISUCRS database and was advertised on social media sites. The questionnaire remained open from April 16 to 28, 2020. Results: A total of 287 surgeons completed the survey. Of the 287 respondents, 90% were colorectal specialists or general surgeons with an interest in colorectal disease. COVID-19 had affected the practice of 96% of the surgeons, and 52% were now using telemedicine. Also, 66% reported that elective colorectal cancer surgery could proceed but with perioperative precautions. Of the 287 respondents, 19.5% reported that the use of personal protective equipment was the most important perioperative precaution. However, personal protective equipment was only provided by 9.1% of hospitals. In addition, 64% of surgeons were offering minimally invasive surgery. However, 44% reported that enough information was not available regarding the safety of the loss of intra-abdominal carbon dioxide gas during the COVID-19 pandemic. Finally, 61% of the surgeons were prepared to defer elective colorectal cancer surgery, with 29% willing to defer for ≤ 8 weeks. Conclusion: The results from our survey have demonstrated that, globally, COVID-19 has affected the ability of colorectal surgeons to offer care to their patients. We have also discussed suggestions for various practical adaptation strategies for use during the recovery period. We have presented the results of a survey used to assess the global impact of coronavirus disease 2019 (COVID-19) on the delivery of colorectal surgery. Despite accessible guidance information, our results have demonstrated that COVID-19 has significantly affected the ability of colorectal surgeons to offer care to patients. We have also discussed practical adaptation strategies for use during the recovery phase

Cellular automata modelling of micro abrasive machining.

This paper presents the use of Cellular Automata (CA) for modelling micro abrasive machining. A one-dimensional CA was initially used to model the workpiece, as having different heights, to represent the roughness; and the forces from the abrasive grits were modelled to randomly erode the workpiece, as such smoothening out and polishing the surface. The modelling was then extended further to two dimensions. Results of the simulations have shown that the mean heights of the peaks, depicting the surface roughness of the workpiece and the mean standard deviation sharply decrease as time evolved. Good surface finish was always observed just after 20 pass steps. The work carried out has demonstrated that it is possible to model and simulate abrasive machining processes by implementing simple rules of cellular automata

The Effect of The Variation of Tool End Geometry on Material Removal Mechanisms in Nanomachining

The selection of effective and optimal machining parameters is a major challenge for the manufacturing industries. The tool-work interactions may be affected by many process parameters including depth of cut, cutting speed, feed rate, cutting tool geometry et cetera. Proper selection of these parameters is critical in material removal processes. The effect of different geometric end shapes on the phenomena of rubbing and ploughing in nanomachining was investigated by using the Molecular Dynamics (MD) simulations. The shapes used were flat, pointed, spherical and trapezoidal. The tools in increasing order of sharpness are the following, namely; the tool with the flat end (least sharp), the tool with the spherical end, the tool with the trapezoidal end and the tool with the pointed end (sharpest). The tools show the initiation of ploughing in that order. The tool with the flat end geometry shows a fast initiation of ploughing, because it has the largest surface area to engage more atoms. The total energy is lowest for the tool with the pointed end and highest for the tool with the flat end. All the tools clearly show the phenomena of rubbing and ploughing in the depth of cut range of 0.05 to 0.5 nm. The tool with the pointed end has the lowest average cutting force and the tool with the flat end has the highest average cutting force. It is important to note that in nanomachining the tool with sharpest end may not necessarily cause the greatest material removal! The different tool ends may be suitable for different semiconductor and metal machining applications

The Effect of Depth of Cut on the Molecular Dynamics (MD) Simulation of Multi-Pass Nanometric Machining

The effect of depth of cut on multi-pass nanometric machining of copper workpiece with diamond tool was studied using the Molecular Dynamics (MD) simulation. The copper-copper interactions were modelled by the EAM potential and the copper-diamond interactions were modelled by the Morse potential. The diamond tool was modelled as a deformable body and the Tersoff potential was applied for the carbon-carbon interactions. It was observed that the average tangential and normal components of the cutting forces increase with increase in depth of cut and they reduced in consecutive cutting passes for each depth of cut. Also, the ratio of the tangential to normal force components decreases as the depth of cut increases, but remains fairly constant after 1.5nm depth of cut. The ratio of the cutting force to area decreases with increase in the depth of cut and remains constant after 2.5nm depth of cut

On Minimum Depth of Cut in nanomachining

The concept of Minimum Depth of Cut (MDC) is that the depth of cut must be over a certain critical thickness before any chip is formed. It is actually a major limiting factor on achievable accuracy in nanomachining, because the generated surface roughness is primarily attributed to the ploughing process when the uncut chip thickness is less than the MDC. This paper presents an analysis of a cutting process where a sharp pointed diamond tool with an edge radius of an atom acts on a crystalline copper workpiece. From the molecular dynamics (MD) simulation results, the phenomena of rubbing, ploughing and cutting were observed. The formation of chip occurred from the depth of cut thickness of 30.0 Ǻ (3nm)

The effect of tool geometry on rubbing and ploughing phenomena in nano abrasive machining

The effects of cutting edge shapes on the phenomena of rubbing and ploughing in nano-abrasive machining were investigated. The shapes under investigation include flat, spherical and trapezoidal shapes. The tool with the flat end geometry shows a fast initiation of ploughing, because it has the largest surface area to engage more atoms. It doesn’t show rubbing phenomenon at the (initial) depth of cut of 0.5 Angstroms. The tool with the trapezoidal end has the lowest average cutting force and the tool with the flat end has the highest average cutting force

The Effect of Interatomic Potentials on Nanometric Abrasive Machining

One of the major tasks in a Molecular Dynamics (MD) simulation is the selection of adequate potential functions, and if the potentials don’t model the behaviour of the atoms correctly, the results produced from the simulation would be useless. Three popular potentials namely; Embedded- Atom Potential (EAM), Morse and the Lennand-Jones, were employed to model copper workpiece and diamond tool in nanometric abrasive machining. From the simulation results and further analysis, the EAM potential was found to be the most reliable because it best describes the metallic bonding of the copper atoms and it demonstrated the lowest cutting force variation. More pile of atoms is observed during the phenomenon of ploughing and the potential and total energies are more stable with the EAM

Acoustic Emission Detection Signals in the Experimental Validation of Nanometric Machining Simulations

The molecular dynamics simulations of nanomachining processes have provided insight into process parameters, material removal and tool wear mechanisms. Simulation results clearly show the material removal phenomena of rubbing, ploughing and cutting. However, many of the simulation results are not backed up by experimental validations, even though they match intuitive guess. There is an attempt in this study to validate some of these results. In the validations of these molecular dynamics simulation of nanometric machining, experiments were carried out on a Nanoform 250 diamond turning machine tool. The tool-workpiece contact was determined by running preliminary passes and using Acoustic Emission (AE) sensors for the nano touch. The analyses of the acquired AE sensor signals have indicated that they can be useful in the detection of the material removal mechanisms

Multi-Pass Nanometric Machining Simulation using the Molecular Dynamics (MD)’

The multi-pass nanometric machining of copper with diamond tool was carried out using the Molecular Dynamics (MD) simulation. The copper-copper interactions were modelled by the EAM potential and the copper-diamond interactions were modelled by the Morse potential. The diamond tool was modelled as a deformable body and the Tersoff potential was applied for the carboncarbon interactions. It was observed that the average tangential and the normal components of the cutting forces reduced in the consecutive cutting passes. Also, the lateral force components are affected by atomic vibrations and the cross sectional area during the cutting process