On the Mechanics of Chip Segmentation In Machining

1981 ◽  
Vol 103 (1) ◽  
pp. 33-51 ◽  
Author(s):  
R. Komanduri ◽  
R. H. Brown
Keyword(s):  
Free Surface ◽  
Shear Zone ◽  
High Speed ◽  
Void Formation ◽  
Cutting Process ◽  
Large Strains ◽  
Second Phase ◽  
Forward Movement ◽  
Stick Slip ◽  
Partial Fracture

The mechanics of chip segmentation, during machining of a cold rolled steel has been investigated from a phenomenological point of view using a high speed movie camera and an explosive quick stop device. The latter was used for obtaining chip root samples at various stages of segmentation for subsequent examination in the Optical and Scanning Electron Microscope (SEM). The chip segmentation process is found to arise as a result of instabilities in the cutting process and is further augmented by the dynamic response of part of the machine tool structure. This process involves a slow forward movement of the plastic boundary in the primary shear zone forming a ramp on the free surface of the chip followed by a rapid return of the plastic boundary back towards the tool forming a step on the chip segment as a result of partial fracture at the free surface. This process is characterized by large strains, low shear angles that oscillate cyclically and stick-slip friction on the rake face. The instability in the cutting process is proposed to be due to the negative stress—strain characteristics of certain materials at large strains, as Walker and Shaw [1] proposed, involving void formation around second phase particles, their propagation into microcracks in the primary shear zone and coalescence of these cracks leading to partial fracture. Evidence for this has been obtained in this investigation.

Trajectory Tracking and Rate of Penetration Control of Downhole Vertical Drilling System

2018 ◽  
Vol 140 (9) ◽  
Author(s):  
Masood Ghasemi ◽  
Xingyong Song
Keyword(s):  
Trajectory Tracking ◽  
High Speed ◽  
Control Design ◽  
Second Phase ◽  
Drilling Process ◽  
Stick Slip ◽  
Rock Interaction ◽  
Rate Of Penetration ◽  
Modeling Uncertainties ◽  
Drilling System

This paper investigates a nonlinear control design for trajectory tracking and rate of penetration (ROP) control of the vertical downhole drilling process. The drilling system dynamics are first built incorporating the coupled axial and torsional dynamics together with a velocity-independent drill bit–rock interaction model. Given the underactuated, nonlinear, and nonsmooth feature of the drilling dynamics, we propose a control design that can prevent significant downhole vibrations, enable accurate tracking, and achieve desired rate of penetration. It can also ensure robustness against modeling uncertainties and external disturbances. The controller is designed using a sequence of hyperplanes given in a cascade structure. The tracking control is achieved in two phases, where in the first phase the drilling system states converge to a high-speed drilling regime free of stick–slip behavior, and in the second phase, the error dynamics can asymptotically converge. Finally, we provide simulation results considering different case studies to evaluate the efficacy and the robustness of the proposed control approach.

Aerodynamic and aeroacoustic performance investigations on modified H-rotor Darrieus wind turbine

2021 ◽  
pp. 0309524X2110039
Author(s):  
Amgad Dessoky ◽  
Thorsten Lutz ◽  
Ewald Krämer
Keyword(s):  
Wind Turbine ◽  
High Speed ◽  
Cfd Simulation ◽  
Vertical Axis ◽  
3D Models ◽  
Power Coefficient ◽  
Design Parameters ◽  
Second Phase ◽  
Vertical Axis Wind Turbine ◽  
Guide Vanes

The present paper investigates the aerodynamic and aeroacoustic characteristics of the H-rotor Darrieus vertical axis wind turbine (VAWT) combined with very promising energy conversion and steering technology; a fixed guide-vanes. The main scope of the current work is to enhance the aerodynamic performance and assess the noise production accomplished with such enhancement. The studies are carried out in two phases; the first phase is a parametric 2D CFD simulation employing the unsteady Reynolds-averaged Navier-Stokes (URANS) approach to optimize the design parameters of the guide-vanes. The second phase is a 3D CFD simulation of the full turbine using a higher-order numerical scheme and a hybrid RANS/LES (DDES) method. The guide-vanes show a superior power augmentation, about 42% increase in the power coefficient at λ = 2.75, with a slightly noisy operation and completely change the signal directivity. A remarkable difference in power coefficient is observed between 2D and 3D models at the high-speed ratios stems from the 3D effect. As a result, a 3D simulation of the capped Darrieus turbine is carried out, and then a noise assessment of such configuration is assessed. The results show a 20% increase in power coefficient by using the cap, without significant change in the noise signal.

Influence of Free Surface Environment on the Shear Zone in Metal Cutting

1966 ◽  
Vol 181 (1) ◽  
pp. 687-705 ◽  
Author(s):  
P. L. Barlow
Keyword(s):  
Free Surface ◽  
Carbon Tetrachloride ◽  
Strain Hardening ◽  
Shear Zone ◽  
Chemical Reaction ◽  
Cutting Forces ◽  
Metal Cutting ◽  
The Body ◽  
Surface Barrier ◽  
Rehbinder Effect

It has previously been suggested that the reduction in cutting forces obtained by the presence of fluids such as CCl4 on the backface or free surface of the forming chip was due to diffusion of the fluid into the body of the chip in the region of the shear zone. In the present work, experiments with carbon tetrachloride tagged with carbon-14 and with carbon tetrachloride tagged with chlorine-36 were performed with the object of assessing the extent of diffusion of lubricants into the chip when present on the free surface only. The results obtained disprove former hypotheses and suggest that the reduced cutting force is due solely to chemical reaction at the surface of the chip. Confirmation of the sensitivity of the surface of the deforming shear zone to change in surface condition was obtained by removing metal from this region by an electropolishing technique during slow speed cutting. By varying the electropolishing conditions increased or decreased cutting forces could be obtained. It is proposed that the result both of chemical reaction at the surface and of surface removal is to reduce the strain-hardening rate of the metal undergoing shear by reducing the surface barrier to the flow of dislocations out of the metal. The association of the surface reaction of carbon tetrachloride with a change in the strain-hardening characteristics of the metal in the shear zone leads to a classification of the backface phenomenon as a Rehbinder effect and enables this effect to be more closely defined than was hitherto possible. Evidence is also presented which indicates that the backface effect does not contribute to the reduction in cutting forces during rakeface lubrication and is therefore unimportant in practice where flood lubrication of the cutting region invariably occurs.

Predicting the High Speed Cutting Process of Titanium Alloy by Finite Element Method

2011 ◽  
Author(s):  
Xiangqin Zhang ◽  
Xueping Zhang ◽  
A. K. Srivastava
Keyword(s):  
Finite Element ◽  
Cutting Forces ◽  
High Speed ◽  
Cutting Temperature ◽  
Chip Morphology ◽  
Cutting Process ◽  
Fe Model ◽  
Dry Cutting ◽  
Friction Coefficients ◽  
Machining Conditions

To predict the cutting forces and cutting temperatures accurately in high speed dry cutting Ti-6Al-4V alloy, a Finite Element (FE) model is established based on ABAQUS. The tool-chip-work friction coefficients are calculated analytically using the measured cutting forces and chip morphology parameter obtained by conducting the orthogonal (2-D) machining tests. It reveals that the friction coefficients between tool-work are 3∼7 times larger than that between tool-chip, and the friction coefficients of tool-chip-work vary with feed rates. The analysis provides a better reference for the tool-work-chip friction coefficients than that given by literature empirically regardless of machining conditions. The FE model is capable of effectively simulating the high speed dry cutting process of Ti-6Al-4V alloy based on the modified Johnson-Cook model and tool-work-chip friction coefficients obtained analytically. The FE model is further validated in terms of predicted forces and the chip morphology. The predicted cutting force, thrust force and resultant force by the FE model agree well with the experimentally measured forces. The errors in terms of the predicted average value of chip pitch and the distance between chip valley and chip peak are smaller. The FE model further predicts the cutting temperature and residual stresses during high speed dry cutting of Ti-6Al-4V alloy. The maximum tool temperatures exist along the round tool edge, and the residual stress profiles along the machined surface are hook-shaped regardless of machining conditions.

Experimental Investigation of Boundary Layer Instabilities on the Free Surface of Non-Turbulent Jet

2012 ◽  
Author(s):  
Matthieu A. Andre ◽  
Philippe M. Bardet
Keyword(s):  
Boundary Layer ◽  
Free Surface ◽  
High Speed ◽  
Particle Tracking Velocimetry ◽  
Capillary Waves ◽  
Wave Growth ◽  
Image Velocimetry ◽  
Planar Laser ◽  
Surface Visualization ◽  
The Waves

Shear instabilities induced by the relaxation of laminar boundary layer at the free surface of a high speed liquid jet are investigated experimentally. Physical insights into these instabilities and the resulting capillary wave growth are gained by performing non-intrusive measurements of flow structure in the direct vicinity of the surface. The experimental results are a combination of surface visualization, planar laser induced fluorescence (PLIF), particle image velocimetry (PIV), and particle tracking velocimetry (PTV). They suggest that 2D spanwise vortices in the shear layer play a major role in these instabilities by triggering 2D waves on the free surface as predicted by linear stability analysis. These vortices, however, are found to travel at a different speed than the capillary waves they initially created resulting in interference with the waves and wave growth. A new experimental facility was built; it consists of a 20.3 × 146.mm rectangular water wall jet with Reynolds number based on channel depth between 3.13 × 104 to 1.65 × 105 and 115. to 264. based on boundary layer momentum thickness.

Hybrid Induction Plasma Cutting Process - A New Technology for High Speed Metal Cutting

2014 ◽  
Author(s):  
Jerald E. Jones ◽  
Valerie L. Rhoades ◽  
Mark D. Mann ◽  
Todd Holverson
Keyword(s):  
Induction Heating ◽  
Plasma Torch ◽  
High Speed ◽  
Metal Cutting ◽  
New Technology ◽  
Cutting Process ◽  
Plasma Cutting ◽  
Air Plasma ◽  
Aircraft Carrier ◽  
Initial Development

A new cutting process, a hybrid system, uses induction heating to heat the metal ahead of the plasma cutting torch. The process has demonstrated the ability to plasma cut steel parts at speeds of up to 4X the speed of the plasma torch without the induction heating. Although the total heat input per unit time is greater, because of the increase in speed, the heat which is conducted into the cut pieces is less. This causes less potential metallurgical damage, less potential distortion, and reduced coating damage and reduced emissions during cutting, in comparison to the plasma cutting process without the induction heating. The initial development was primarily for use in cutting nuclear submarine and aircraft carrier hulls, for scrapping after decommissioning. The process has been demonstrated cutting steel plates and can be used in ship production as well. The primary motivation of the SBIR project was to reduce the heating of the cut pieces, in order to reduce the particulate matter (PM) emissions which occur when coated ship hull material is cut. An induction coil is positioned in front of the plasma cutting torch, to bring the material to an elevated temperature of at least 1600° F, before the plasma is applied to the metal surface. Induction heating testing has shown that the 35 kW induction system can maintain the 1600° F surface temperature at travel speeds of above 220 inches per minute on steel as thick as 3 inches. Once the steel is at that temperature an air plasma torch can cut the metal much faster than cutting cold steel.

scholarly journals Insights into Machining of a β Titanium Biomedical Alloy from Chip Microstructures

Metals ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 710 ◽  
Author(s):  
Damon Kent ◽  
Rizwan Rahman Rashid ◽  
Michael Bermingham ◽  
Hooyar Attar ◽  
Shoujin Sun ◽  
...  
Keyword(s):  
Shear Band ◽  
Shear Zone ◽  
Biomechanical Properties ◽  
Temperature Fields ◽  
Large Strains ◽  
Shear Direction ◽  
Grain Sizes ◽  
Β Phase ◽  
Secondary Shear Zone ◽  
Cutting Speeds

New metastable β titanium alloys are receiving increasing attention due to their excellent biomechanical properties and machinability is critical to their uptake. In this study, machining chip microstructure has been investigated to gain an understanding of strain and temperature fields during cutting. For higher cutting speeds, ≥60 m/min, the chips have segmented morphologies characterised by a serrated appearance. High levels of strain in the primary shear zone promote formation of expanded shear band regions between segments which exhibit intensive refinement of the β phase down to grain sizes below 100 nm. The presence of both α and β phases across the expanded shear band suggests that temperatures during cutting are in the range of 400–600 °C. For the secondary shear zone, very large strains at the cutting interface result in heavily refined and approximately equiaxed nanocrystalline β grains with sizes around 20–50 nm, while further from the interface the β grains become highly elongated in the shear direction. An absence of the α phase in the region immediately adjacent to the cutting interface indicates recrystallization during cutting and temperatures in excess of the 720 °C β transus temperature.

Using Image Analysis Techniques for Single Evaluation of the Chip Shrinkage Factor in Orthogonal Cutting Process

2012 ◽  
Vol 504-506 ◽  
pp. 1329-1334 ◽  
Author(s):  
Moises Batista ◽  
Madalina Calamaz ◽  
Franck Girot ◽  
Jorge Salguero ◽  
Mariano Marcos
Keyword(s):  
High Speed ◽  
Orthogonal Cutting ◽  
Rake Angle ◽  
Cutting Process ◽  
Shrinkage Factor ◽  
A Value ◽  
Chip Shrinkage ◽  
Chip Geometry ◽  
Image Analysis Techniques

The forces involved in a cutting process are related, for example, with the power consumption, with the final quality of the workpiece and with the chip geometry obtained, since these forces determine the compression experimented by the chip and therefore its final geometry. The orthogonal cutting process assisted with a High Speed Filmation (HSF) permit obtains a digital filmation of the process with high magnification. This filmation permits to obtain a measurement of the longitudinal changes produced in the chip. This deforms are related with the Shrinkage Factor, ζ. And in this case the Stabler hypothesis is enabled, by that using the shear angle and the rake angle is possible obtain a value of the Shrinkage Factor in a different conditions.

scholarly journals High-Velocity Shear and Soft Friction at the Nanometer Scale

2021 ◽  
Vol 7 ◽  
Author(s):  
Per-Anders Thorén ◽  
Riccardo Borgani ◽  
Daniel Forchheimer ◽  
David B. Haviland
Keyword(s):  
High Speed ◽  
Surface Deformation ◽  
Soft Materials ◽  
Lateral Force ◽  
Velocity Shear ◽  
Polymer Materials ◽  
Amplitude Dependence ◽  
Dynamic Force ◽  
Stick Slip ◽  
Soft Polymer

We study high-speed friction on soft polymer materials by measuring the amplitude dependence of cyclic lateral forces on the atomic force microscope (AFM) tip as it slides on the surface with fixed contact force. The resulting dynamic force quadrature curves separate the elastic and viscous contributions to the lateral force, revealing a transition from stick-slip to free-sliding motion as the velocity increases. We explain force quadratures and describe how they are measured, and we show results for a variety of soft materials. The results differ substantially from the measurements on hard materials, showing hysteresis in the force quadrature curves that we attribute to the finite relaxation time of viscoelastic surface deformation.

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