Cylindrical Grooves Research Articles

Обоснование стойкости и прочности резцов при точении канавок в заготовках из конструкционной стали повышенной твердости

Machine-building parts can have cylindrical and end grooves, for the machining of which compound and assembled cutters with different geometrical parameters and design features are used. These parts are made of structural steels, including hardened steels, corrosion-resistant steels and alloys, and other tough materials. Improving the efficiency of hard-alloy grooving cutters is an important research and technological challenge. This article presents the results of research concerning the development of methods for calculating forces and temperatures in the cutting area, wear rates and tool life for turning grooves in workpieces of various structural steels, including steels with increased hardness. A test strength calculation of the cutting wedge is conducted and an analysis of the influence of the operating and geometric parameters of the tool on the safety factors on the front and rear surfaces of the tool is performed. Based on the results of the strength and durability analysis, the choice of the hard alloy grade and the limiting values of the cutting speed and the cut layer thickness are validated. The developed recommendations concerning geometrical parameters of the cutting wedge and strength characteristics of the tool material can serve as the basis for designing assembled groove cutters equipped with interchangeable multi-faceted plates.

Experimental study on influences of cylindrical grooves on thermal efficiency, exergy efficiency and entropy generation of CPU cooled by nanofluids

An experiment set for researching the flow and heat transfer characteristics of nanofluids flowing through CPU is established and validated. The influences of groove depths (1 mm, 2 mm, 3 mm) and arrangement modes (aligned and staggered arrangements) on thermo-hydraulic performances of CPU cooled by TiO2-water nanofluids are explored. In addition, the influences of nanoparticle mass fractions (0.0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%) and Reynolds numbers (472–1198) are studied. It is found that there is a most appropriate nanoparticle mass fraction (0.3%) and groove depth (2 mm) for the lowest CPU temperature. Heat transfer augmentation of CPU heat sink is more sensitive to staggered arrangement grooves and high Reynolds number. Nanofluids (0.3%) in CPU heat sink with staggered arrangement grooves (2 mm) show the best heat transfer performances. Lastly, thermal efficiency, exergy efficiency and entropy generation are applied to analyze the cooling performance of enhanced structure. Results show that the thermal efficiency decreases with mass fraction when Reynolds number is less than 791, but increases with the depth of groove. Exergy efficiency of the groove structure can be obviously strengthened under the same pumping power and mass flow rate. From entropy generation analysis, it is found that the aligned arrangement shows lower entropy generation performance than aligned arrangement.

Analysis of dynamic characteristics of two-component granular mixture segregation in thin shear cell

Particle separation is important in industrial production. The granular powder exhibits the property that is like both fluid property and solid property, which makes it difficult to establish a mathematical model to reveal the particle motion mechanism. The fluid property of the granular powder can be partly explained by the classical fluid theory, but the solid property cannot be covered. Theories combining the fluid and solid properties are also used to explain the particle separation phenomenon. However, they are not in consensus about the granular theory to explain the particle separation mechanism. Friction dissipation, which represents the particle pairwise damp interactions, greatly influences the particle separation process. In order to understand the particle separation mechanism and the effect of friction coefficient on the particle motion, a three-dimensional discrete element model is used to simulate the separation of three-dimensional spherical binary particles in a cylindrical groove （shear cell）in this paper. Initially, the large particle is placed at the bottom and the other small particles pile into the groove. The shear flow of the particles is established by rotating the bottom plate of the groove. The large particles gradually jump to the top of the groove under the shearing action. The effect of particle friction coefficient on the separation is studied. Focusing on the characteristics of kinematics and dynamics in the jumping process of large particle, the influence of the friction coefficient on the trajectory, velocity and acceleration of particle are quantitatively analyzed. The conclusions are obtained as follows. 1) The process of large particle jumping can be divided into three stages: relaxation stage (the large particle stays at the bottom of the groove), the take-off stage (the large particle rises up), and the equilibrium stage(the large particle moves to the top and stays there). 2) The relaxation time decreases with friction coefficient increasing. 3) The equilibrium height of particles increases with friction coefficient increasing. 4) The amplitude of the force pulsation of the large particle increases with friction coefficient increasing. For the behavior analysis of the ascending motion of the large particle, we propose a neighborhood analysis method and define a floating factor. The ratio of the number of small particles arranged in the upper to that in the lower adjacent space of the large particle is defined as the buoyancy factor. It is found that the buoyancy factor drops sharply at the jumping point of the large particle, forming the opportunity for the large particle jumping. It is revealed that the take-off of the large particle is the result of both the high-frequency characteristics of force fluctuation and the steep drop of buoyancy factor. The rising motion of the big particle is determined by the force and the surrounding space.

Diamond cutting of micro-structure array on brittle material assisted by multi-ion implantation

Micro-structures have numerous applications for improving the surface functionability in various fields, such as surface mechanics, optics, and biology. However, machining micro-structures on brittle materials is difficult owing to the serious fractures that occur on the machined surface. To solve this problem, a method using ion implantation to modify the workpiece surface layer has been developed over the last seven years, but how to fabricate the modified layer efficiently is still unsolved and becomes a critical issue which blocks the application of this method in production. A modified layer that is thick enough for the machining is always preferred. This is difficult for the single-implantation approach studied before, owing to the large consumption in cost and time. In this study, diamond cutting assisted by multi-implantation is proposed to fabricate micro-structure array on silicon, a typical hard and brittle material. The novel method in this study shows distinct flexibility in the design of process parameters, as well as obvious improvement in efficiency. The result of surface modification is evaluated from aspects of crystal lattice and nanomechanics. The influence of channel effect is also discussed. Furthermore, chips with shear bands are discovered and analyzed in the cutting of modified silicon, which is extraordinary in the machining of brittle materials. And the brittle–ductile transition depth is significantly enhanced. Therefore, not only is multi-implantation capable of preparing thick modified layer, it also realizes further modification on material properties which is fundamental for improving the machinability. Finally, a micro-pillar array formed by 270 orthogonal cylindrical grooves (17956 micro-pillar units) is achieved in ductile mode by fly-cutting. It indicates that multi-implantation is a promising method for the micro-machining of brittle materials.

Visible frequency plasmonic perfect absorber made of a thin metal layer containing cylindrical grooves

In this communication, a visible frequency plasmonic perfect absorber (PPA) made of a thin metal layer (gold and aluminum) with an array of cylindrical grooves is demonstrated and studied numerically using the finite difference time domain solver. A novel design concept is used to achieve perfect absorption at tunable wavelengths between 400 and 1000 nm. The PPA unit cell is made of a cylindrical groove of appropriate depth, and the size of the groove is typically set to half the array period. By simply changing the array period, the perfect absorption (100%) spectral position is set to a desired wavelength. The PPA is observed to be very effective for wide incident angles and polarization states of input radiation. The study reports an attractive alternative way of designing all-metal-based PPA that may have potentials for various plasmonic and photonic applications.

A NUMERICAL STUDY OF FORCED CONVECTIVE FLOW IN MICROCHANNELS HEAT SINKS WITH PERIODIC EXPANSION-CONSTRICTION CROSS SECTION

This paper aims to study numerically the laminar convective heat transfer of ionized water flow inside rectangular heat sinks with periodic expansion-constriction cross-section; each heat sink consists of parallel microchannels system with 4 mm wide and 0.1 mm deep in constant cross-section segment.  Two-dimensional laminar numerical simulations, based on Navier-Stoks equations and energy equation, are obtained under the same boundary conditions for different microchannels. In this study, the heat transfer and pressure drop inside microchannels with cross-section (cylindrical grooves and triangular cavities) are compared with that of simple smooth microchannel at Reynolds number ranging from 150-1500; an increase in pressure drop of 44% for all microchannels  is observed with Reynolds number increasing.  The obtained results indicate an enhancement in Nusselt number for all microchannels at all Reynolds number values with a maximum enhancement of 36%, these ameliorated thermal parameters attribute to enhance the heat transfer efficiency of proposed microchannels. Which improve the effect of periodic expansion-constriction cross-section on the heat transfer performance for microelectromechanical systems (MEMS) cooling phenomena.  

Discrete modular serpentine robotic tail: design, analysis and experimentation

SUMMARYThis paper presents the design, analysis and experimentation of a Discrete Modular Serpentine Tail (DMST). The mechanism is envisioned for use as a robotic tail integrated onto mobile legged robots to provide a means, separate from the legs, to aid stabilization and maneuvering for both static and dynamic applications. The DMST is a modular two-degree-of-freedom (DOF) articulated, under-actuated mechanism, inspired by continuum and serpentine robotic structures. It is constructed from rigid links with cylindrical contoured grooves that act as pulleys to route and maintain equal displacements in antagonistic cable pairs that are connected to a multi-diameter pulley. Spatial tail curvatures are produced by adding a roll-DOF to rotate the bending plane of the planar tail curvatures. Kinematic and dynamic models of the cable-driven mechanism are developed to analyze the impact of trajectory and design parameters on the loading profiles transferred through the tail base. Experiments using a prototype are performed to validate the forward kinematic and dynamic models, determine the mechanism's accuracy and repeatability, and measure the mechanism's ability to generate inertial loading.

The Influence of the Inner Topology of Cooling Units on the Performance of Automotive Exhaust-Based Thermoelectric Generators

Automotive exhaust-based thermoelectric generators are currently a hot topic in energy recovery. The waste heat of automotive exhaust gas can be converted into electricity by means of thermoelectric modules. Generally, inserting fins into the cooling unit contributes to enhancing the heat transfer for a higher power output. However, the introduction of fins will result in a pressure drop in the cooling system. In current research, in order to enhance the heat transfer and avoid a large pressure drop, a cooling unit with cylindrical grooves on the interior surface was proposed. To evaluate the performance of the cylindrical grooves, different inner topologies, including a smooth interior surface,a smooth interior surface with inserted fins and an interior surface with cylindrical grooves, were compared. The results revealed that compared with the smooth interior surface, the smooth interior surface with inserted fins and the interior surface with cylindrical grooves both enhanced the heat transfer, but the interior surface with cylindrical grooves obtained a lower pressure drop. To improve the performance of the cylindrical grooves, different groove-depth ratios were tried, and the results showed that a groove-depth ratio of 0.081 could provide the best overall performance.

Generalised technique for calculation of plane director profiles in bounded nematic liquid crystals

ABSTRACTWe propose an improved conformal mapping technique for analytical calculation of two-dimensional profiles of the nematic liquid crystal (NLC) director in a cell with a simply connected cross-sectional region. We consider the case of the strong anchoring and the piecewise constant director pretilt on the piecewise smooth curve which bounds the region. Obtained expressions for the director profile explicitly depend on the conformal mapping which maps the region onto the upper half plane of a complex plane. An advantage of our method in comparison with the standard conformal mapping technique is that it does not require the knowledge of the inverse mapping and the calculation of the integral in the Poisson formula. Proposed technique allows to take into account topological defects in the bulk of the NLC on the symmetry axis of the region. As an example of how the method can be used, we find an analytical expression for the director profile in a horizontal cylindrical groove partly filled with the NLC. We consider the case where a disclination line parallel to the axis of the groove occurs in the bulk of the NLC. The equilibrium position of the disclination line is found.

Enhancement of heat transfer in a square channel by roughened surfaces in rib-elements and turbulent flow manipulation

PurposeThe purpose of this paper is to augment heat transfer rates of traditional rib-elements with minimal pressure drop penalties.Design/methodology/approachThe novel geometries in the present research are conventional cylindrical ribs with rounded transitions to the adjacent flat surfaces and with modifications at their bases. All turbulent fluid flow and heat transfer results are presented using computation fluid dynamics with a validated v2f turbulence closure model. Turbulent flow characteristics and heat transfer performances in square channels with improved ribbed structures are numerically analyzed in this research work.FindingsBased on the results, it is found that rounded transition cylindrical ribs have a large advantage over the conventional ribs in both enhancing heat transfer and reducing pressure loss penalty. In addition, cylindrical ribs increase the flow impingement at the upstream of the ribs, which will effectively increase the high heat transfer areas. The design of rounded transition cylindrical ribs and grooves will be an effective way to improve heat transfer enhancement and overall thermal performance of internal channels within blade cooling.Originality/valueThe novel geometries in this research are conventional cylindrical ribs with rounded transitions to the adjacent flat surfaces and with modifications at their bases. The combination of cylindrical ribs and grooves to manipulate the turbulent flow.

The influence of inner topology of exhaust heat exchanger and thermoelectric module distribution on the performance of automotive thermoelectric generator

The waste heat of automotive exhaust gas would be directly transferred into electricity by thermoelectric modules (TEM) because of the temperature difference between heat exchanger and water tank. For the vehicle thermoelectric generator (TEG), the electrical power generation was deeply influenced by temperature difference, temperature uniformity and topological structure of TEG. In previous works, increasing the difference of temperature would significantly enhance the power generation of TEG and inserted fins were always applied to enhance heat transfer in heat exchanger. However the fins would result in a large unwanted back pressure which went against to the efficiency of the engine. In current studies, in order to enhance heat transfer rates and to avoid back pressure increase, a heat exchanger containing cylindrical grooves (the depth-to-width ratio is 0.25) on the interior surface of heat exchanger was proposed. The cylindrical grooves could increase the heat transfer area and enhance the turbulence intensity, meanwhile there was no additional inserts in the fluid to block the flow. The surface temperatures of water tank and heat exchanger with three internal structures, such as grooved surface, flat surface and inserted fins, were studied by numerical simulation at each row of thermoelectric modules. The results showed that comparing to other structures, heat exchanger with cylindrical grooves could improve the TEG efficiency at a low back pressure. The influence of the channel height on the TEG performance was investigated and the TEG with a channel height of 8mm showed the best overall performance. It was also found that a portion of heat exchanger uncovered with thermoelectric modules at the downstream section could make the upstream section hotter and make full use of each TEM.

Force Controlled Grinding of Ceramic Materials

Brittle materials like ceramics or glass can be machined by cutting with negative rake angles and by abrasive machining processes. Especially grinding allows for low surface roughness and high shape accuracy. Conventional path-controlled grinding processes may damage functional surfaces if brittle fracture occurs and may thus lead to lateral, radial and axial cracks. High grinding forces can be a reason for brittle fracture when grinding ceramic materials. A solution for this effect may be the application of force controlled grinding processes. In this paper adapted control algorithms were implemented for force controlled grinding and verified in grinding experiments. As an example, cylindrical grooves were ground with an injection moulded spherical grinding tool in alumina and zirconia ceramics. After grinding surface roughness, shape accuracy and process forces are analysed and discussed.

Characteristic Evaluation of a Shrouded Propeller Mechanism for a Magnetic Actuated Microrobot

Medical microrobots have been widely used in clinical applications, particularly the spiral type locomotion mechanism, which was recently considered one of the main self-propelling mechanisms for the next medical microrobot to perform tasks such as capsule endoscopy and drug delivery. However, limits in clinical applications still exist. The spiral action of the microrobot while being used for diagnosis may lead to pain or even damage to the intestinal wall due to the exposed mechanisms. Therefore, a new locomotive mechanism, named the shrouded propeller mechanism, was proposed to achieve a high level of medical safety as well as effective propulsive performance in our study. The shrouded propeller mechanism consists of a bare spiral propeller and a non-rotating nozzle. To obtain a high effective propulsive performance, two types of screw grooves with different shapes including the cylindrical screw groove and the rectangular screw groove with different parameters were analyzed using the shrouded model. Two types of magnetic actuated microrobots with different driving modes, the electromagnetic (three-pole rotor) actuated microrobot and the permanent magnet (O-ring type magnet) actuated microrobot were designed to evaluate the performance of the electromagnetic actuation system. Based on experimental results, the propulsive force of the proposed magnetic actuated microrobot with a shrouded propeller was larger than the magnetic actuated microrobot with a bare spiral propeller under the same parameters. Additionally, the shrouded propeller mechanism as an actuator can be used for other medical microrobots for flexible locomotion.

Smooth bridge between guided waves and spoof surface plasmon polaritons.

In this work, we build a smooth bridge between a coaxial waveguide and a plasmonic waveguide with subwavelength periodically cylindrical radial grooves, to realize high-efficiency mode conversion between conventional guided waves and spoof surface plasmon polaritons in broadband. This bridge consists of a flaring coaxial waveguide connected with a metal cylindrical wire corrugated with subwavelength gradient radial grooves. Experimental results of the transmission and reflection coefficients show excellent agreement with the numerical simulations. The proposed scheme can be extended readily to other bands and the bridge structure can find potential applications in the integration of conventional microwave or terahertz devices with plasmonic circuits.

Synthesis of bio-inspired multilayer polarizers and their application to anti-counterfeiting

Some insects, such as Papilio blumei and Suneve coronata, are known for exhibiting polarization effects on light such as color contrast or geometrical polarization rotation by reflection on their wing scales. The photonic structures found on these species that show these properties are multilayered spherical cavities or triangular grooves which polarize the light due to multiple inner reflections. These polarization effects, in addition to the intrinsic color-mixing properties of these photonic structures, are of interest in the anti-counterfeiting field due to their invisibility to the naked eye. In this paper, we report micro-fabrication techniques to produce bio-inspired cylindrical grooves (C-grooves) and triangular grooves (V-grooves) that demonstrate the same properties. Theoretical analyses were carried out by using multi-scale simulation (MS) as well as by finite-difference time-domain (FDTD) in order to compare the polarization capability of both structures. The V-grooves show greater polarization contrast than the C-grooves, but the spectrum is specular. The C-grooves exhibit lower polarization effects but have a dispersive spectrum. In both cases, the structures show additional optical properties, such as diffraction, macroscopic color contrast under a polarizer, and contrast inversion due to geometries which contribute to their uniqueness.

Modeling and analysis of the droplet-ultrasonic stage system for nano concentration

In this work, a droplet-ultrasonic stage, in which a micro droplet located at the center of the ultrasonic stage is used to concentrate nanoscale material, is modeled and analyzed by the finite element method. The computation method is verified by experimental results, and the acoustic streaming pattern inside the droplet is revealed, which can well explain the operating principle. Moreover, the effects of the vibration velocity, droplet size, ultrasonic stage topology and size, and droplet's sound attenuation coefficient on the acoustic streaming field are also investigated and clarified. The results show that the concentrating capability can be maximized without sacrificing the concentrating stability by properly increasing the droplet volume, and disposing a cylindrical groove in the center of the ultrasonic stage's substrate. Also, it is found that a thin substrate and thick piezoelectric ring are helpful to enhancing the concentrating capability without sacrificing the concentrating stability.

Micromixing enhancement in a novel passive mixer with symmetrical cylindrical grooves

AbstractA passive micromixer with symmetrical cylindrical grooves along the channel was designed, fabricated and characterized. Systematic numerical simulations of mixing with Re ranging from 1.0 to 500 predict the optimized parameters and the mixing enhancement. The optimized depth of the cylindrical grooves is 100 µm. The experimental results have also confirmed the improvement of the mixing effect. Considering pressure drop and mixing enhancement, Re values of 10 and 100 are suitable for mixing of liquids with diffusion coefficients of 10−9 and 6 × 10−11 m2/s, respectively. The percentage of mixing of this micromixer is 2.22‐fold better than that of common Y‐mixer with Re of 10 at the distance of 19 mm from the meeting point of two fluids with the diffusion coefficient of 10−9 m2/s; similarly, the percentage of mixing of the new design is 2.18 times better than that of common Y‐mixer with Re of 100 at the distance of 19 mm from the meeting point of two fluids with the diffusion coefficient of 6 × 10−11 m2/s. This easy fabricated micromixer can be utilized for biological reactions and analytical assays. © 2015 Curtin University of Technology and John Wiley & Sons, Ltd.

Turbulent flow and heat transfer enhancement in rectangular channels with novel cylindrical grooves

Abstract Turbulent flow characteristics and heat transfer performances in square channels with different cylindrical-shaped grooves are analyzed and compared numerically in this research. The novel groove geometries are conventional cylindrical grooves with rounded transitions to the adjacent flat surfaces and with modifications to their bases. The objective of this work is to determine optimal configuration for augmenting heat transfer rates with minimal pressure drop penalties. The paper documents also provide the flow details near the groove surface. All turbulent fluid flow and heat transfer results are obtained using computation fluid dynamics with a verified v 2 f turbulence closure model. Five rectangular channels with different cylindrical groove shapes are computed. Heat transfer enhancement and flow details are analyzed and compared with results for conventional cylindrical groove geometry and for conventional square ribs. This investigation shows that the conventional cylindrical grooves have similar overall heat transfer enhancement with conventional square ribs, but the pressure loss penalty is much decreased from square rib values. The rounded transition of the grooves has a large advantage over conventional cylindrical grooved surfaces in both enhancing heat transfer and reducing pressure loss penalty. For the rounded-transition grooves, recirculating flows inside the groove are reduced and reattachment develops more smoothly and the separating zone is reduced compared with the flow over the conventional cylindrical groove. The velocity magnitude in the near-wall region of grooved surface is much larger compared with that over a ribbed surface, which essentially causes the larger heat transfer enhancement for the groove surfaces. The design for the rounded transitions is shown to improve the overall thermal performance for channel internal cooling.

Ultrasonic vibration–assisted polishing of cylindrical groove arrays on silicon carbide

Thanks to its superior mechanical and physical properties, silicon carbide is a promising mold material in glass molding of micro-structured optical elements. However, the high micro-structured surface quality can be hardly generated by means of conventional abrasive polishing because of the high hardness of silicon carbide. In this article, the ultrasonic vibration was introduced to assist abrasive polishing with an aim to improve the cylindrical groove arrays’ surface quality and also to increase the polishing efficiency. First, the comparison experiments between abrasive polishing and ultrasonic vibration–assisted polishing were conducted, and then, the factors affecting ultrasonic vibration–assisted polishing performance were investigated. The experimental results indicate that through conventional abrasive polishing, the surface roughness of silicon carbide cylindrical groove arrays decreases to 25.5 nm from the precision ground surface roughness ( Ra) of 115.6 nm, while through ultrasonic vibration–assisted polishing, the surface roughness decreases to 8.6 nm with a factor of three times improvement. Furthermore, a 35-kHz vibration frequency corresponds to a smaller surface roughness than a 25-kHz vibration frequency under identical processing parameters. In the vibration amplitude range from 1.0 to 2.5 µm, the surface roughness accordingly decreases linearly, while in the range of 2.5–4.0 µm, ultrasonic vibration presents no assistance in improving the surface quality.

Influence of Forming Conditions on Loads in Split-forging

More complicated parts having gear teeth, cylindrical grooves, or long branches are manufactured in cold forging. Nowadays, more precise dimensions are required for these parts. Reduction in forming load is a key factor to obtain more precise parts in cold forging, because high load causes the elastically large deformation of tools and machines. Furthermore, this reduction in forming load contributes to longer tool life. In this paper, the loads of split-forging including split-backward extrusion and split-heading to produce the branched parts are estimated under different conditions such as punch sizes, punch geometries, and lubricants.