scholarly journals (ECS 233rd) Multiphysics Modeling of Surface Finishing Performance in Pulsed-Waveform Electrochemical Machining

2018 ◽  
Author(s):  
Brian Skinn ◽  
Tim Hall ◽  
Jennings E. Taylor
Keyword(s):  
Boundary Layer ◽  
Mass Transfer ◽  
Layer Thickness ◽  
Current Distribution ◽  
Surface Finish ◽  
Boundary Layer Thickness ◽  
Electrochemical Machining ◽  
Pulse Plating ◽  
Surface Finishing ◽  
Local Surface

Electrochemical machining (ECM) is a manufacturing technology that allows metal to be precisely removed by electrochemical oxidation and dissolution into an electrolyte solution. ECM is suited for machining parts fabricated from “difficult to cut” materials and/or parts with complicated and intricate geometries. In ECM, the workpiece is the anode and the tool is the cathode in an electrochemical cell; by relative movement of the shaped tool into the workpiece, the mirror image of the tool is “copied” or machined into the workpiece. One notable difficulty with ECM is an inability to predict a priori the tool and process parameters required in order to satisfy the final specifications of the fabricated part [[1]]. Accordingly, there is potential value in development of a physical phenomenon-based design platform to predict optimal ECM tool shape. Such a capability is anticipated to dramatically shorten the process/tooling development cycle.A further goal of ECM is to simultaneously achieve a target surface finish on the machined part. It is thus of interest to develop the capability also to predict the distribution of local surface finish resulting from ECM processing. Modeling of the changes in local surface finish intrinsically operates on a different length scale from that of bulk material removal (μm, versus mm or cm), and thus is most easily treated separately. The physicochemical phenomena involved in the evolution of surface finish during ECM processing are strongly coupled, and include the electric field itself (primary current distribution), surface polarization and electrochemical kinetics (secondary current distribution), and fluid flow and mass transfer (tertiary current distribution). Of particular interest is modeling of pulsed-waveform ECM, for which significant practical advantages have been demonstrated [[2],[3],[4]]. While an extensive body of literature exists analyzing pulsed electrodeposition [[5],[6],[7]], comparatively little work has been published to date on pulsed ECM [[8],[9]].This talk will discuss recent modeling work seeking to develop a solid foundation for a predictive understanding of the surface finishing aspects of ECM processes. The work described herein encompasses time-dependent modeling of one-dimensional concentration profiles under the application of pulsed current ECM waveforms, providing a foundation for future development of quantitative descriptions of the transient and steady-periodic behavior on structured substrates. Prior work (see, e.g., Ref. 3) has demonstrated the value in differential pulsed-ECM processing of surfaces with features of size comparable to or larger than the hydrodynamic boundary layer thickness (“macroprofiles”) versus surfaces with features much smaller than the boundary layer thickness (“microprofiles”). Methods are discussed for accurate estimation of a quantity termed the “transition time,” which is the value for the pulse on-time for which the metal concentration at the surface rises exactly to saturation at the end of the forward pulse. Extending the pulse duration beyond this value thus introduces mass transfer limitations to the electrochemistry occurring at the surface.References[1]. Rajurkar, K.P. et al. Annals of the CIRP 82(2), 1999.[2]. Taylor, E.J. et al. “Breaking the Chemical Paradigm in Electrochemical Engineering: Case Studies and Lessons Learned from Plating to Polishing,” in Advances in Electrochemical Science & Engineering: The Path from Discovery to Product, x, y Eds. In press.[3]. Taylor, E.J. and M. Inman. “Electrochemical Surface Finishing.” ECS Interface, Fall 2014: 57-61.[4]. Taylor, E.J. et al. U.S. Patent 9,006,147, 14 Apr 2015.[5]. Puippe, J.C. and F. Leaman, eds. “Theory and Practice of Pulse Plating.” Orlando, FL: AESF, 1986.[6]. Hansel, W.E.G. and S. Roy. “Pulse Plating.” Bad Saulgau, Germany: Leuze Verlag KG, 2012.[7]. Ibl, N. “Some Theoretical Aspects of Pulse Electrolysis.” Surface Technology 10: 81 (1980).[8]. Sautebin, R. et al. J Electrochem Soc 127(5): 1096, 1980.[9]. Sautebin, R. and D. Landolt. J Electrochem Soc 129(5): 946, 1982.

scholarly journals (ECS 236th) Multiphysics Modeling of the Tertiary Current Distribution in Pulse/Pulse-Reverse Electrochemical Processing of Microstructured Workpieces

2020 ◽  
Author(s):  
Brian Skinn ◽  
Alan C West
Keyword(s):  
Boundary Layer ◽  
Mass Transfer ◽  
Current Distribution ◽  
Surface Finishing ◽  
Workpiece Surface ◽  
Structured Surfaces ◽  
Electrochemical Processes ◽  
Pulse Reverse ◽  
Primary Current ◽  
Primary Current Distribution

The physical phenomena governing the current distribution on an electrode of arbitrary shape are typically categorized as falling into primary, secondary, and/or tertiary effects. Primary current distribution effects are defined by the geometry of the system and the electrical properties of the relevant materials, whereas secondary and tertiary effects incorporate additional position-dependent polarizations that respectively arise from electrochemical-kinetic and mass-transfer/concentration physics. In industrial electrochemical processes, the uniformity of the current distribution across a workpiece is of vital concern. In electrodeposition processes, for example, it is usually desirable for the deposited metal to be as uniformly distributed as possible, regardless of the form of the workpiece. Conversely, in electropolishing processes, it is critical to focus the current density onto the tops of asperities on the workpiece surface, in a highly non-uniform fashion, in order to minimize material removal irrelevant to the goal of decreased surface roughness. In general, the primary current distribution leads to the most non-uniform current distribution possible for a given geometry, from which the secondary and tertiary effects tend to have varying degrees of a “leveling” effect, leading to a comparative increase in processing uniformity.In electrodissolution processes, saturation of the dissolved metal at the workpiece surface is an important mechanism by which the tertiary current distribution effects influence practical electrochemical processes. This saturation phenomenon leads both to an increase in the local overpotential, via concentration polarization, and also has the potential to occlude locally a fraction of the workpiece exposed area due to the formation of insoluble precipitates. As noted, both of these effects tend to increase the uniformity of the resulting overall current distribution, and thus it is important to be able to predict, even if approximately, when a given process will be operating in this regime and to what extent the uniformity of the current distribution might be affected.This talk will summarize results from multiphysics simulations developed to represent this occluded-surface aspect of the tertiary current distribution, in addition to primary and secondary current distribution effects. These simulations incorporate pulse/pulse-reverse waveforms applied to workpieces with structured surfaces, in an attempt to approximate a surface finishing application of industrial relevance. In particular, focus was placed on simulating a “microprofile,” the scenario where surface structures have characteristic dimensions much smaller than the hydrodynamic boundary layer for mass transfer—this choice simplifies the modeling by obviating consideration of the macroscopic fluid dynamics of the system. The effect of pulse waveform parameters on the uniformity of the overall current distribution will be discussed, and simulation results will be shown illustrating the tendency of suitably-chosen waveform parameters to “collapse” toward the workpiece surface the subdomain of the boundary layer in which the local concentration of dissolved material oscillates significantly in response to the applied electric field.

Scrutinization of Chemical Reaction Effect on Flow and Mass Transfer of Prandtl Liquid over a Riga Plate in the Presence of Solutal Slip Effect

2018 ◽  
Vol 16 (8) ◽  
Author(s):  
B.J. Gireesha ◽  
K. Ganesh Kumar ◽  
B.C. Prasannakumar
Keyword(s):  
Boundary Layer ◽  
Mass Transfer ◽  
Differential Equations ◽  
Layer Thickness ◽  
Chemical Reaction ◽  
Boundary Layer Thickness ◽  
Skin Friction Coefficient ◽  
Linear Ordinary Differential Equations ◽  
Similarity Transformations ◽  
Riga Plate

AbstractIn the present paper focused on flow and mass transfer of Prandtl fluid over a Riga plate. The effects of chemical reaction and solutal slip are taken into the account. The governing partial differential equations are reduced into a set of coupled non linear ordinary differential equations using suitable similarity transformations. These equations are then solved using Runge-Kutta-Fehlberg-45 method. Behaviour of emerging parameters are presented graphically and discussed for velocity and concentration distribution. Numerical values of reduced skin friction coefficient and Sherwood number are shown in table and are discussed. From the plotted results it can be observed that the solutal boundary layer thickness decreases for larger values of chemical reaction parameter and Schmidt number. Also, momentum boundary layer thickness rise with stronger modified Hartman number.

A Note on the Effect of Surface Finish on the Thrust of a Supersonic Conical Nozzle

1958 ◽  
Vol 62 (575) ◽  
pp. 829-829
Author(s):  
P. N. Rowe
Keyword(s):  
Boundary Layer ◽  
Layer Thickness ◽  
Surface Finish ◽  
Boundary Layer Thickness ◽  
Conical Nozzle ◽  
Polishing Process ◽  
Interior Surface ◽  
Before And After ◽  
Usual Process ◽  
Effect Of Surface

The Propelling Nozzles tested are turned from brass and the interior surface finish shows a centre line average of about 15 micro inches when examined on a Taylor Hobson machine. This is fairly rough compared with the estimated boundary layer thickness and it was required to know whether this in fact affected the thrust. The thrust of a nozzle manufactured by the usual process was measured before and after a polishing process. An improvement of one half per cent was recorded.

A Mathematical Model of Condensation Heat and Mass Transfer to a Moving Droplet in its Own Vapor

1984 ◽  
Vol 106 (2) ◽  
pp. 417-424 ◽  
Author(s):  
J. N. Chung ◽  
Tae-Ho Chang
Keyword(s):  
Boundary Layer ◽  
Mathematical Model ◽  
Mass Transfer ◽  
Liquid Phase ◽  
Heat And Mass Transfer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Droplet Radius ◽  
Integral Approach ◽  
Boundary Layer Equations

A mathematical model appropriate for predicting condensation heat and mass transfer rates along the surface of a droplet moving in pure vapor is developed. A Karman-Pohlhansen type of integral approach was adopted for the solution of vapor-phase boundary layer equations. The diffusion-dominated internal core was solved using a finite difference numerical scheme. The rate-controlling mechanism of pure vapor condensing on a droplet was found in the thermal core region of the liquid phase where the streamlines correspond to the isotherms and diffusion is the primary transport mechanism. The total rate of heat transfer is found to be inversely proportional to the droplet radius. The condensation velocity at the vapor-liquid interface reduces the boundary layer thickness and moves the separation point toward the rear stagnation point. The internal motion also helps increase the transport rates by reducing both the boundary layer thickness and thermal resistance in the liquid phase. The results predicted by this model compare favorably with available experimental values.

EFFECTS OF BOUNDARY-LAYER THICKNESS ON UNSTEADY FLOW CHARACTERISTICS INSIDE OPEN CAVITIES AT SUBSONIC AND TRANSONIC SPEEDS

2012 ◽  
Vol 19 ◽  
pp. 206-213
Author(s):  
DANG-GUO YANG ◽  
JIAN-QIANG LI ◽  
ZHAO-LIN FAN ◽  
XIN-FU LUO
Keyword(s):  
Boundary Layer ◽  
Unsteady Flow ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Sound Pressure ◽  
Flow Characteristics ◽  
Open Cavity ◽  
Aerodynamic Noise ◽  
Sustained Oscillation ◽  
Cavity Depth

An experimental study was conducted in a 0.6m by 0.6m wind-tunnel to analyze effects of boundary-layer thickness on unsteady flow characteristics inside a rectangular open cavity at subsonic and transonic speeds. The sound pressure level (SPL) distributions at the centerline of the cavity floor and Sound pressure frequency spectrum (SPFS) characteristics on some measurement positions presented herein was obtained with cavity length-to-depth ratio (L/D) of 8 over Mach numbers (Ma) of 0.6 and 1.2 at a Reynolds numbers (Re) of 1.23 × 107 and 2.02 × 107 per meter under different boundary-layer thickness to cavity-depth ratios (δ/D). The experimental angle of attack, yawing and rolling angles were 0°. The results indicate that decrease in δ/D leads to severe flow separation and unsteady pressure fluctuation, which induces increase in SPL at same measurement points inside the cavity at Ma of 0.6. At Ma of 1.2, decrease in δ/D results in enhancing compressible waves. Generally, decrease in δ/D induces more flow self-sustained oscillation frequencies. It also makes severer aerodynamic noise inside the open cavity.

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