Clearance Angle Research Articles

Thoracolumbar Fractures, Posterior versus Anterior Management: A Case Series and Literature Review

Background Data: The management of unstable traumatic thoracolumbar fractures has shifted from more conservative treatment towards more operative treatment modalities. Different surgical options have been reported in the literature. Purpose: To review two surgical techniques, anterolateral and posterior approaches, in management of thoraco-lumbar fractures and present a brief literature review. Study Design: A retrospective case series with review of literature. Patients and Methods: Thirty patients managed in the period from October 2012 to November 2016 for thoraco-lumbar burst fractures. Two patients’ groups were identified, group 1 underwent anterolateral fixation and included 15 patients whereas group 2 underwent posterior fixation and included 15 patients. Follow up was done at 3 months, 6 months and one year postoperative using VAS for pain assessment and ASIA scale for neurological status evaluation. Radiological outcome involved the vertebral height restoration, spinal canal compromise and kyphus deformity correction. Operative time, operative blood loss and perioperative complications were all reported for both groups. Results: The most common spinal level affected in our study was L1 vertebra in 10 cases. Operative time and blood loss were found to be significantly less in the posterior approach. A significant improvement of VAS has been reported in both study groups with more improvement in the posterior group compared to the anterolateral one. 93.3% of anterior group patients within the showed either improved or fixed neurological status according to ASIA scale where in posterior group all patients showed either improved or fixed neurological status. The mean canal compromise percentage decreased in group 1 from 69.3% preoperatively to 15.62% postoperative whereas in group 2 it decreased from 66.2% preoperative to 18.8%. Kyphotic angle has been corrected in posterior group from 13.42° preoperative to 11° at 6 months and 12.5° at one year, where in anterolateral group has been corrected from 19.42° to 17.57° and 20.9° respectively with a statistically significant difference between both groups (P<0.01). Conclusion: Our data suggest that both anterior and posterior approach showed no difference in neurological outcome in patients with thoraco-lumbar fractures. However anterior approach was superior to the posterior one in spinal canal compromise clearance and kyphotic angle correction.

Chatter stability in ultra-precision fly cutting considering tool wear effect

In ultra-precision flying cutting (UPFC), a vibration is a unique dynamic response due to periodic intermittent excitation of cutting forces, which has a significant impact on surface generation. In UPFC, cutting forces act on the machine tool system intermittently and periodically, which may cause a self-excited vibration. This self-excited vibration will cause chatter, which maybe occurs during machining operations and even catastrophically degrades surface quality and limits productivity. This study has been motivated by the fact that chatter occurrence is generally in relation to the tool wear, which has seldom been investigated comprehensively in literature. In this paper, a chatter model for UPFC that can account for the effects of tool wear and process damping was presented. A number of experiments with different machining conditions were conducted to investigate the effect of the tool wear on the chatter stability. These experiments proved that the stability lobe is closely related to tool wear and with the tool wear increase, which increases the tendency for chatter in UPFC. Finally, it was found that increasing the tool clearance angle and reducing the spindle speed can improve the stability limit.

Aerodynamic Forces Acting on a Race Car for Various Ground Clearances and Rake Angles

Computational model was developed to investigate aerodynamic forces acting on a closed-wheel race car. A particular focus was on the effects of ground clearance and rake angle on aerodynamic drag and lift forces. Computations were performed for a steady viscous fluid flow using the realizable k-ε turbulence model and non-equilibrium wall functions. The computational results indicate a strong influence of ground clearance and rake angle on aerodynamic loading of a race car. The largest drag force coefficient was obtained for the largest ground clearance. The drag force coefficient for the squatting car is larger by 5% compared to the reference case, where the both front and rear ground clearances are 100 mm. For the nose-diving car, the drag force coefficient is equal to the reference case. Increasing the ground clearance caused a negligible increase in the lift force coefficient in comparison with the reference case. A decrease in the ground clearance yielded an increase in the lift force coefficient. The largest positive lift force coefficient was obtained for a squatting car, whereas the largest negative lift force coefficient was observed for a nose-diving car. While the favorable aerodynamic downforce acting on front wheels is larger for a nose-diving car, for rear wheels it is larger for a squatting car.

The Influence of Part Geometry on Changes of the Dynamic Geometric Parameters of Cutting Tools and Cutting Conditions when Contour Turning on CNC Lathes

Contour turning is a specific process of the machining on CNC lathes. In the finishing operation, to create the part profile, the turning tool must be moved in a trajectory of a complex flat curve (a toolpath) based on the part profile . The variation of feedrate vector on the toolpath according to the part profile in the machining process will results in changing dynamic geometric parameters of the cutting tool, which affects cutting conditions and machined part quality. This article presents the results of theoretical studies on the influence of part geometry on rake angle, clearance angle, approach angle and end cutting-edge angle of the turning tool. Based on the theoretical development, the authors also set up mathematical expressions that allow to define gouge-free cutting condition and the limit of feedtate for contour turning. An empirical model to define the influence of part geometry on the roughness of the part when countour turning on CNC lathe is also presented in this report.

Determining the Optimal Parameters of Chip Shrinkage Coefficient and Cutting Force in High-Speed Machining for Aluminum Alloy A6061

Nowadays, increasing the productivity and the quality of machining become major challenges of the metal cutting process. Due to the complexity of the chip formation process, in particular, at high cutting speeds, finite element model (FEM) has been frequently used as an alternative solution. Chip shrinkage coefficient and cutting force are the two basic parameters of the cutting process, which determines the productivity and quality of the workpiece. This study uses a Grey correlation relationship to analyze and select the common set of parameters for cutting force and chip shrinkage coefficient of the chip. Simulation of the A6061 aluminum alloy high-speed milling is done by Bao-Wierzbicki's (B-W) model. The optimal parameters are determined cutting depth 1 mm, clearance angle 6oand rake angle 10o. This parameter set adjusts the cut parameters so that the cutting process achieves the highest machining efficiency.

Clearance angle and evolution of depth of cut in actuated disc cutting

This paper investigates the effect of cutter clearance angle on variation of depth of cut and cutting process with an actuated disc cutting (ADC). ADC is a cyclic cutting method with two main characteristics: (i) a disk-shape cutter is used to attack the rock in an undercutting mechanism; and (ii) the cutter is dynamically actuated as it is moved across the rock. Hence, the cutting process of such system is periodic, each recurrence known as actuation cycle. The first ADC model, developed in 2016, represented an idealization of the technology with a flat disc cutter, where no clearance angle was considered. The evolution of the contact between the disc and the rock was, therefore, computed only on horizontal x-y plane, ignoring the effect of normal component of the force acting on cartridge. This article reports on a study that incorporates the cutter inclination angle in derivation of cutter/rock interface laws. It extends the proposed kinematic and geometry based model to take into account the variable depth of cut in estimating the forces associated with cutting in one actuation cycle. Experiments were conducted using Wobble to test the predictions of the improved model at various operating conditions. The model predictions are matched with the experimental results and effects of various factors are analysed.

A New Cutting Tool Design for Cryogenic Machining of Ti⁻6Al⁻4V Titanium Alloy.

Titanium alloys are extensively used in aerospace and medical industries. About 15% of modern civil aircrafts are made from titanium alloys. Ti–6Al–4V, the most used titanium alloy, is widely considered a difficult-to-machine material due to short tool life, poor surface integrity, and low productivity during machining. Cryogenic machining using liquid nitrogen (LN2) has shown promising advantages in increasing tool life and material removal rate whilst improving surface integrity. However, to date, there is no study on cutting tool geometry and its performance relationship in cryogenic machining. This paper presents the first investigation on various cutting tool geometries for cryogenic end milling of Ti–6Al–4V alloy. The investigations revealed that a 14° rake angle and a 10° primary clearance angle are the most suitable geometries for cryogenic machining. The effect of cutting speed on tool life was also studied. The analysis indicated that 110 m/min cutting speed yields the longest tool life of 91 min whilst allowing for up to 83% increased productivity when machining Ti–6Al–4V. Overall the research shows significant impact in machining performance of Ti–6Al–4V with much higher material removal rate.

Investigation of tool geometry in nanoscale cutting single-crystal copper by molecular dynamics simulation

Molecular dynamics has been employed in this paper to investigate the nanoscale cutting process of single-crystal copper with a diamond tool. The behavior of the workpiece during material removal by diamond cutting has been studied. The effects of tool geometry including rake angle, clearance angle, and edge radius are thoroughly investigated in terms of chips, dislocation movement, temperature distribution, cutting temperature, cutting force, and friction coefficient. The investigation showed that an appropriate positive rake angle ([Formula: see text]), a suitable clearance angle ([Formula: see text]), or a smaller edge radius tip resulted in a smaller cutting force and a better subsurface finish. It was found that a tool with a rake angle of [Formula: see text] generated more chips, had a higher cutting efficiency, and produced a lower temperature in the workpiece, but a smaller rake angle tip was more conducive to protecting the groove compared to a large rake angle tip. Compared with a tool with a small clearance angle, the tool with a larger clearance angle generated more chips and caused a lower temperature rise in the copper workpiece, and prolonged its lifetime. In addition, a larger clearance angle tip was more conducive to protecting the groove. A smaller edge radius tip reduces the cutting heat during the nanoscale cutting process, while the volume of chips decreases. These results indicated that it is possible to control and adjust the tool parameters according to the tool rake angle, clearance angle, and edge radius during the machining of single-crystal copper, and a set of tool parameters were obtained: [Formula: see text] rake angle, [Formula: see text] clearance angle, and 0 nm edge radius which could reduce surface damage and the required cutting force.

Influence of tool material and geometry on micro-textured surface in radial ultrasonic vibration-assisted turning

Surface texturing has been widely used to fabricate functional surface, which can improve the friction performance or achieve suitable wettability for different mechanical products. In order to fabricate micro-textured surface in an efficient and cost-effective way, a surface texturing method of radial ultrasonic vibration-assisted turning (RUVT) was proposed. The texturing generation mechanism of RUVT was firstly analyzed through a theoretical model. Then, the influence of tool geometry on micro-texture, including clearance angle and nose radius, was further characterized by a surface topography simulation. The simulated and experimental results show that the clearance angle and nose radius have important effect on the shape and width of micro-dimples of the textured surface, respectively. Compared with a cemented carbide tool, the diamond tool is more preferable to be used to generate well shaped and distributed micro-dimples, because of its sharp cutting edge and less wear during the texturing process. The experimental textured surfaces, fabricated under different clearance angles of 0°, 7° and 20°, also have shown different wetting properties through wettability tests. It is verified that the RUVT can be a cost-effective texturing way for fast generation of micro-dimpled surfaces by choosing appropriate tool parameters.

The coupling effect and damage analysis when drilling GFRP laminates using candlestick drills

During the research on high-quality hole drilling technology for glass fiber–reinforced polymer (GFRP), more and more researchers have discovered and focused on the coupling effect between the machining parameters on the damage at the hole exit. Most of them have verified and described this phenomenon by mathematical statistics, but there is no further analysis for its mechanism. In this paper, a set of orthogonal experiments were conducted to investigate the coupling effect between the clearance angles of outer cutting edges, the spindle speed, and the feed speed when drilling the GFRP materials with candlestick drills. Through the experimental results shown by the response surface, the influencing factors of the exit damage were divided into the pushing effect, cutting effect, and the physical properties of the material according to the special damage formation process. It was found that the reason for the coupling effect of the machining and tool parameters was that the change of these parameters would have different effect on the pushing, cutting, and physical properties of the materials at the same time. In addition, the optimal machining parameters for each candlestick drill were also given according to the experimental results.

Investigations on edge quality and its effect on tensile property and fracture patterns of QP980

Advanced High Strength Steel (AHSS) sheet metals have been widely used in automotive structures due to its safety performance and lightweight potentials, and some AHSS materials have been found more sensitive to edge crack during the stamping process. The tensile property of the sheared edge has great influence on flangability for AHSS. In the present work, the effects of the blanking clearance and shear angle on the quality of the sheared edge and subsequent tensile property for QP980 have been investigated experimentally by microscope and sheared-edge tension test based on digital image correlation (DIC) technology. In addition, the tensile properties of the specimens prepared by wire electrical discharging machining (Wire-EDM) and laser cutting were tested as well. The results show that promising and stable sheared edge quality, and tension with postponed fracture can be achieved if the clearance ratio is set as 7% or 11% for QP980. During blanking with 5° or 10° oblique edge, the ratios of burnish zone and burr zone decrease simultaneously, and the subsequent tensile performance increases significantly. The oblique edge blanking obtains smaller and smoother burr, and the sheared surface benefits from less void damage. In addition, based on the fracture surface morphology and the tracking of the fracture process with DIC technology, two typical fracture patterns (oblique crack and transverse oblique crack) in tension test are illustrated. Oblique crack occurring on the specimens with good edge quality shows obvious necking phenomenon and belongs to the typical ductile fracture. While transverse oblique crack exhibiting with high frequency on the sheared specimens is typical edge fracture and shows mixed characteristics of ductile fracture and brittle fracture.

Modeling and analysis of force prediction in milling process of unidirectional fiber reinforced polymer composites

The cutting force is one of the main factors that influence the processing quality of fiber-reinforced polymer composites (FRPs). However, since the material removal mechanics of composites are quite different from those of metals, the cutting mechanisms of metals cannot be directly used for orthogonal cutting of composites. This paper aims to develop a novel force prediction model without the need to run any experiments. The deformation of fiber and the support of surrounding matrix are analyzed based on the minimum potential energy principle and the dynamic equilibrium. A force prediction model of FRP cutting is obtained for fiber orientations ranging from 0 to 90° + γ. The relevant experiments conducted showed the validity of the proposed model. The influence of rake angle and clearance angle on cutting force is analyzed.

Analysis of surface texturing in radial ultrasonic vibration-assisted turning

Surface texturing has become a potential way to achieve good friction performance or suitable wettability for different mechanical product surfaces. For fabricating micro-textured surface efficiently and cost-effectively, a texturing method of radial ultrasonic vibration-assisted turning (RUVT) was proposed. The theoretical model of texturing generation was established, which can describe the arrangement and geometry of micro-textures. Based on the theoretical model, a surface topography simulation was further used to characterize the influence of processing parameters on micro-dimpled patterns. This experimental process was performed on a CNC lathe and copper 1100 was chosen as the workpiece material. The simulated and experimental results show that surfaces covered with evenly distributed micro-dimples can be fabricated, which basically confirms the validity of theoretical model. The processing parameters, including clearance angle, spindle speed, feed rate and vibration amplitude, play important influence on the arrangement and geometry of micro-dimples. It is demonstrated that the method of RUVT is an efficient and cost-effective way for fast generation of cylindrical micro-textured surface.

Проектирование геометрической формы инструмента для операций фрезоточения

The paper reports the method for tool geometrical parameter computation for outer surface machining in solids of rotation by milling. The advantage of this method of machining is shown. The formulae for the curvature radius computation in a tool tip of the tool used in milling are presented. The formulae for the computation of a front clearance angle and a back angle in an actual plane are shown.

Steady tool wear and its influence on tool geometry in ultra-precision fly cutting of CuZn30

In ultra-precision fly cutting (UPFC), steady tool wear progresses gradually when cutting ductile materials. The steady wear of diamond tools changes the tool geometry, and further affects the topography of the machined surface. In this study, a theoretical and experimental investigation was conducted on the forms of steady tool wear and their influence on the tool geometry in UPFC. The features of steady tool wear in UPFC were investigated, the displacement of the cutting edge under the effects of tool flank wear was modeled, and factors affecting the cutting edge roundness were investigated. The study results indicate the following: (1) the features of steady tool wear in UPFC include crater wear on the rake face, smooth and flat wear on the cutting edge, and flank wear on the tool clearance face. (2) A smooth wear-land on the cutting edge changes the top rake of the cutting tools, whereas flank wear on the tool clearance face affects the clearance angle and roundness of the cutting edge. (3) The maximum width of the tool material loss zone, the nose radius of the original fresh cutting edge, and the arc angle of the wear-land have a certain influence on the nose radius of the worn cutting edge. The results of this study will provide deep insight into steady tool wear and its influence on the tool geometry, which can potentially be used to predict or evaluate the finish of a machined surface under tool steady wear.

Effects of sawtooth side edges with different radial clearance angles on the cutting force in wood sawing

AbstractThis study focuses on the influence of the sawtooth side edges on the cutting force and analyzes the functions of the side edges in wood sawing by separating the total cutting force into the force from the main edge and the side edges. Birch (Betula spp.) is used as the material for conducting the experiment. The influence of the sawtooth side edges with different radial clearance angles on the cutting force was studied by comparing closed cutting with open cutting for different cutting thicknesses, cutting speeds, and directions using a single sawtooth. The cutting force from the side edges accounts for 4.6 % to 16.9 % of the total cutting force when the sawing kerf is 1.6 mm. As the radial clearance angle increases or the cutting thickness decreases, the cutting force from the side edges and the proportion of the force from the side edges decrease. The cutting force from the side edges increases with an increase in the cutting speed but the cutting speed does not have a clear influence on the cutting force from the side edges. For the same radial clearance angle, the cutting force from the side edges is the largest for the (0°–90°), followed by the (90°–0°) and the (90°–90°).

Effect of punching die angular clearance on punched hole quality of S275 mild steel sheet metal

Metal punching processes are widely used in mass production because of their simplicity, high levels of productivity, and low costs. The quality of the product made by punching greatly depends on various processing parameters such as the tool geometries, sheet material properties, punching conditions, punch and die material properties, and tooling wears. In this study, the effects of die clearance angles and die opening sizes were compared on the accuracy and quality of punched holes produced on 1.4-mm thick S275 mild steel metal sheet. A total of nine punching dies were made with die clearance angles of 0.25°, 0.50°, and 0.75° for each die opening sizes of o20.225 mm, o13.225 mm, and o12.225 mm. The burr formations and die weight losses were monitored for 10th, 50th, 100th, 500th, and 1000th strokes. The results show that the die weight loss, indicative of wear, increases as the number of strokes increase, with the most losses at the initial stages of the punching process (10th–50th strokes). The lowest weight loss was obtained for dies with 0.75° angular clearance, corresponding to the lowest wear occurrence. The low wear indicates that the shearing edge remains relatively sharp and thus able to produce good quality holes. Thus, for producing good quality holes and increasing tool life, it is recommended that an angular clearance of 0.75° is considered in the design of punching dies.

Investigation into Hand Scraping: A Microanalysis

Hand scraping is a manual surface finishing process that, despite its low productivity and high cost, is still applied in many industries because of its advantages concerning accuracy and tribology. In the presented microanalysis forces, movement patterns and tool orientation of individual hand scraping strokes were measured using a test stand, specifically designed for this purpose. It utilizes a camera, a three dimensional dynamometer, and an inertial measurement unit (IMU). The results show the basic characteristics of hand scraping. Typical courses of relevant quantities like cutting force, passive force, clearance, and directional angle are shown. In addition, the movement pattern of the tool during individual scraping strokes is analyzed. This research aims to contribute to a later implementation of automated scraping. The conducted research creates a base for future research regarding different scraping methods and achieved results.

Auto‐reclosing scheme with adaptive dead time control for extra‐high‐voltage transmission line

Discrimination between transient fault and permanent fault is contemporary problems for protection of transmission line. Auto-reclosure is one of the foremost solutions for the same. This study presents the development of auto-reclosure scheme using modified full-cycle discrete Fourier transform with adaptive dead time control. The discrimination between transient and permanent fault is done using differential voltage across the contacts of circuit breaker. Reclosing instance is identified by comparing absolute value of positive sequence voltage, phase difference and frequency difference with a respective preset threshold using synchronism check relay. The proposed scheme has been validated by simulating power system considering variation in fault location, fault clearance angle, fault resistance and load flow in PSCAD/EMTDC. The algorithm for the auto reclosing scheme is validated in MATLAB software. Real time emulation of the proposed algorithm is performed using AVR ATmega 328P controller on laboratory prototype. The test results of simulation and hardware emulation corroborate the efficacy of the proposed technique.

Model for the prediction of whirling vibrations in drilling processes through semi-discretization of the drill motion equation

In this work, a model for the prediction of drilling stability against low-frequency lateral vibrations, named as whirling in the literature, is proposed. These vibrations are lateral displacements of the tool that arise at frequencies near multiples of the rotation frequency of the drill. The appearance of whirling vibrations leads to the generation of lobe-shaped holes. In order to predict whirling vibrations, the motion equation of the drill is deduced taking into account the modal characteristics of the drill and the cutting and process damping forces that act on it. In this paper, forces that arise in two different regions of the drill are considered: (1) forces on the main cutting edges and (2) forces on the chisel edge. Different force models are presented for each region that include both the regenerative effect of the vibration on the cutting area and the process damping. An oblique cutting model and an orthogonal model are employed for the calculation of cutting forces acting on the main cutting edges and on the chisel edge, respectively. The cutting force model for the main cutting edges takes into account the cutting angle (inclination angle, rake angle, and chip flow angle) variation along the main cutting edges. For the chisel edge region, where the feed speed is no longer negligible with respect to the cutting speed, the dynamic cutting angles are employed for the force model development. Concerning the process damping force model, previous works in the literature consider a constant value of the clearance angle for the calculation of the process damping coefficient. However, in this work, the variation of the normal clearance angle along the main cutting edges is considered. It is shown that, depending on the clearance face grinding parameters employed, the clearance angle can double its value along the main cutting edges. Considering the force models and through the semi-discretization of the motion equation of the drill, the appearance of low-frequency lateral vibrations is predicted regarding the drill geometry and cutting conditions such as drill rotation speed and feed. In addition, given cutting conditions at which whirling vibrations are expected to occur, the model is able to predict the vibration frequencies that are excited. The drilling model and the stability predictions are experimentally validated by means of drilling tests with different drill diameters and cutting conditions. In comparing the experimentally obtained results and the predictions obtained by the model, it is concluded that the model can reasonably predict the appearance of whirling vibrations as a function of drill geometry and cutting conditions. Generated hole shape is also analyzed through the measurement of hole roundness and bottom surface geometry. It is observed that, when drilling in the presence of whirling vibrations, holes with lobed shape and polygonal bottom surface are generated. It is also noticed that both the number of lobes and the number of sides of the polygonal bottom surface are directly related to the vibration frequencies that arise.