Clearance Angle Research Articles

Optimization in Milling of Polymer Materials for High Quality Surfaces

High quality surfaces with transparency are required for manufacturing of plastic products. In cutting of polymer materials, surface quality is sometimes deteriorated by tarnish and/or unequal spaces of area on a surface. The cutting parameters should be determined through understanding of surface finish characteristics. This paper presents an optimization approach in milling of polycarbonate with polycrystal diamond tools in terms of the surface finish. Surfaces are finished with changing the feed rate and the clearance angle of the tool. The surface finishes, then, were observed to classify the deterioration type into welding, adhesion, and the unequal space of cutter marks with measurement of the surface profiles. The measured surface roughnesses are decomposed into the theoretical/geometrical term and the irregular term induced by the thermal and the dynamic effects. A map is presented to characterize the irregular term for the feed rates and the clearance angles. Because the surface roughnesses are measured at discrete sets of the cutting parameters in the actual cutting tests, the process design cannot be conducted to optimize the operation parameters. Therefore, a neural network is applied to associate the cutting parameters with the irregular term in the map. An approach is presented to determine the number of hidden nodes/units in the design of the neural network. Three prominent areas of welding, adhesion, and unequal spaces of the cutter marks, appear in the map of irregular roughness. The map of the surface roughness is made to optimize the cutting process. The applicable feed rates and clearance angles are determined for the tolerable surface roughnesses. The gradient information in the map is used to evaluate the stability/robustness of the surface quality for changing the parameters. The optimum parameters were determined to minimize the gradient information in the applicable feed rates and clearance angles.

Nanosecond-Fiber Laser Cutting and Finishing Process for Manufacturing Polycrystalline Diamond-Cutting Tool Blanks

This paper presents a nanosecond-fiber-laser-based method for manufacturing polycrystalline-diamond (PCD) tool blanks. The effects of variations in the process path and operating parameters on the cut-surface morphology and surface-quality of the processed PCD workpieces have been analyzed. The results obtained in this study reveal the reactive fusion cutting mechanism to yield a processing depth of 155.2 µm at 30-W average laser power, 200-ns pulse width, and 30-kHz pulse frequency. The successful cutting of a 1.2-mm-thick PCD workpiece via implementation of the horizontal-shifting and vertical layer–by-layer processing methods is reported. Compared to the wire-electrical-discharge machining (WEDM), the proposed approach yields superior cut-surface roughness (Ra = 0.378 µm). Moreover, the laser processing was performed on a single-axis curved stage, on which the workpiece placed at an inclination during laser cutting and finishing. Thus, a PCD insert with an orthogonally cut edge, flat and pit-free finishing surface, and excellent tool-surface roughness (Ra = 0.202 µm) was obtained, thereby verifying the feasibility of the proposed approach. Furthermore, it is evident that the nanosecond-fiber laser can be used to not only cut and finish PCD inserts but also produce PCD workpieces oriented at different rake and clearance angles.

Modeling and Optimizing the Effects of Insert Angles on Hard Turning Performance

To analyze hard turning performance characteristics, a new mathematical model was developed for the hard turning process, and cutting force (CF), another important response for cutting machining, was also studied in the present work. The analysis of the mathematical model and experimental results revealed that thrust force (Fy) was the largest, followed by tangential force (Fz) and feed force (Fx). The resultant CF was most influenced by inclination angle (IA) with 25.02%, followed by rake angle (RA) (14.26%) and cutting edge angle (CEA) (10.04%). Increasing CEA changed the position of cutting on the tool-nose radius and increased local negative RA and correspondingly local clearance angle (CA). Meanwhile, increasing negative RA and IA resulted in larger local negative RA and CA. Moreover, local RA and local CA were the main geometric factors affecting surface roughness (SR), tool wear (TW), and CF. Increasing local negative RA resulted in higher SR and CF. In contrast, increasing local CA resulted in lower SR, TW, and CF. Under specific conditions, the positive effects of the local CA overcame the negative effects of the local negative RA, leading to a simultaneous decrease in SR and TW. The proposed novel mathematical model can be further applied to calculate local CF, cutting temperature, and TW for each cutting-edge element, to analyze and optimize the hard turning process.

Study of temperature and stresses using finite element analysis in turning of C45 material

Parts machined by high cutting speeds can often exhibit high fatigue strength, increased micro-hardness in the surface layers and plastic deformations, due to the tool cutting edge radius associated with the induced stresses. The changing of rake and clearance angles has an important influence on the chip formation, cutting forces, residual stresses, temperatures in both the workpiece and the tool. International research on the influence of geometric parameters of the tool on the entire cutting process, are of particular importance to understand this process development. The approach of this study, considers the parametric realization of the cutting tool profile - a coated TiC turning chisel, which will be used in the finite element simulation of the orthogonal turning process. Deform 2D application, which is a powerful simulation engine was chosen and allows the correct simulation of the cutting process in real machining conditions. Deform 2D enables the automatically meshing and remeshing generation and also the optimization whenever needed and wherever is required a high accuracy, thereby reducing the overall difficulty of the problem and the computational requirements. Using Lagrangian discretization, the machining process was simulated and made possible to observe and present a series of conclusions and own points of view regarding the temperature distribution at the tool tip and in the workpiece, the effective stresses distribution and the cutting force variation under the rake and clearance angles influences.

Tool wear and spring back analysis in orthogonal machining unidirectional CFRP with respect to tool geometry and fibre orientation

Machining abrasive carbon fibre reinforced polymers (CFRP) is characterised by extensive mechanical wear. In consequence, the cutting edge micro-geometry and thus the tool/material contact situation are continuously changing, which affects process forces and machining quality. As a conclusion, a fundamental understanding of the tool wear behaviour and its influencing factors is crucial in order to improve performance and lifetime of cutting tools. This paper focuses on a fundamental tool wear analysis of uncoated tungsten carbide cutting inserts with different combinations of fibre cutting angles and tool geometries. For this purpose, orthogonal machining experiments with unidirectional CFRP material are conducted, where the wear progression of the micro-geometry is investigated by means of five wear parameters lα, lγ, γ*, α*, and bc. For detecting the actual contact zone of the cutting edge and to measure the elastic spring back of the material, the flank face is marked via short pulsed laser processing. Furthermore, the process forces and the wear rate are measured. It is shown that the material loss due to wear clearly varies along the tool’s contact region and is highly dependent on the clearance angle and the fibre cutting angle Φ, while the influence of the tested rake angles is mostly negligible. Especially in machining Φ=30° and Φ=60°, a strong elastic spring back is identified, which is more intense for smaller clearance angles. For all tested configurations, the material’s elastic spring back increases in intensity as wear progresses which, in combination with the decreasing clearance angle, is the main reason for high thrust forces.

Power-skiving tool design method for interference-free involute internal gear cutting

Power-skiving is one of the most effective methods for manufacturing high-accuracy gears, especially internal gears. However, the machining accuracy of the gear is fundamentally dependent on the design accuracy of the tool. Due to their particularity, the design of power-skiving tools is complex and computationally intensive, and requires particular attention to the problem of interference. Solving the interference problem involves two main considerations, namely avoiding interference between the clearance surface of the tool or the tool itself and the original designed gear surface and preventing a zero or negative clearance angle. Both interference situations are particularly prone to occur in internal gear cutting. Accordingly, the present study proposes a new power-skiving design and full-view angle analysis method for the design of high-accuracy and simple cylindrical power-skiving tools which avoid both interference scenarios. The results obtained for a typical illustrative example confirm that the proposed method provides an uncomplicated and robust approach for modeling the design features of power-skiving tools.

The research of tool wear criterion in micro cutting using the elastic recovery ratio of high-strength elastic alloy 3J33B

In this study, indentation experiments were conducted on high-strength elastic alloy 3J33B material with a Berkovich indenter to study the elastic recovery of material. The experimental data showed that the load and material properties influence elastic recovery ratio of material. The functional expressions of elastic recovery ratio and load were established by regression analysis of experimental data. Therefore, the depths of elastic recovery of 3J33B can be controlled by adjusting the indentation load. Alloy 3J33B has the property of high elastic energy, so it is easy to produce large elastic recovery in the machining. Based on the functional expressions of elastic recovery ratio and load, it can be obtained that the relationships among the elastic recovery ratio of the machined surface, the yield strength of the material, the clearance angle, the average sliding friction coefficient between the tool and the workpiece, the wear width of the flank face and the cutting width. Then, the critical values of tool wear at different clearance angles can be obtained when the yield strength of material, the average sliding friction coefficient between the tool and the workpiece and the cutting width are known. Then, a group of micro milling experiments were conducted on alloy 3J33B using several single-edge micro milling cutters. Finally, it can be obtained that the clearance angle of cutting tool should not be more than 34° in micro cutting in order to reduce the tool wear.

Shape Optimization of Labyrinth Seals to Improve Sealing Performance

To reduce gas leakage, shape optimization of a straight labyrinth seal was carried out. The six design parameters included seal clearance, fin width, fin height, fin pitch, fin backward, and forward expansion angle. The CFD (Computational Fluid Dynamics) model was solved to generate the training and testing samples for the surrogate model, which was established by the least square support vector machine. A kind of chaotic optimization algorithm was used to determine the optimal design parameters of the labyrinth seal. As seal clearance, fin width, fin height, fin pitch, fin backward and forward expansion angles are 0.2 mm, 0.1 mm, 7 mm, 9 mm, 0°, and 15°, the discharge coefficient can reach its minimum value in the design space. The chaotic optimization algorithm coupled with least square support vector machine is a promising scheme for labyrinth seal optimization.

Evaluation of normal forces at varying cutting angles of conical picks on sandstones

In mechanical excavation, the response of the tool forces on the cutterhead is important when the excavation begins in actual cutting conditions because the reliability and efficiency of the cutting machine are influenced directly by the pick performance. The magnitude of the cutting force is utilized to estimate the specific energy, which is calculated from experimental tests to predict the performance of a mechanical excavation machine. However, the magnitude of normal force is also the other key parameter that used to calculate the load of the work unit of excavation machine. Therefore, based on linear rock cutting experiments performed on the low and high strength sandstones, the variation of the normal force and the variation of ratio of normal force to cutting force have been investigated under different cutting angles. The influence of related cutting angles, which have some direct or indirect effects on the normal force, has been discussed in detail. In this context, the attack angles lower than 80°, preferably between 50 and 60°, the clearance angle lower than 10°, resulted in a decrease on the normal forces. Besides, the positive values of rake angles led to more efficient cutting. Furthermore, it was suggested to employ the conical picks having the tip angles lower than 80° in order to obtain optimum cutting conditions. The certain ranges of the relevant angles exhibited the same characteristic both on low and high strength sandstones. As a result, the empirical models, which were found to be statistically significant, were put forward. These results would be essential for the design of the pick and cutterhead.

Optimal transmission angle and dynamic balancing of slider-crank mechanism with joint clearance using Pareto Bi-objective Genetic Algorithm

Following errors in manufacturing process and hinge movement, clearance occurs in the joints of mechanisms. Together with noise, vibration and abrasion caused by impact forces between the mechanism’s joints, this phenomenon also results in dynamic imbalance and reduced transmission quality. In the present study, these effects are mitigated properly. Since slider-crank mechanisms are widely used in internal combustion engines, the associated kinematic and dynamic equations are presented in this study considering clearances in crank and sliding pins. Moreover, the Lagrangian equation minimization method is utilized to simulate clearance angles and their derivatives. Besides, bi-objective functions are defined regarding optimization, one as the sum of shaking forces and shaking moment and the other as the transmission angle of the slider-crank mechanism. Then, the optimization process is performed using multi-objective genetic algorithm. The length of the links and the position of their mass center were subsequently considered as the design variables. The optimization results were illustrated through the Pareto front. Comparing the outcomes of this study with the main mechanism as well as the findings of previous studies, wherein only the transmission angle had been optimized without considering the necessary dynamic balance, revealed the superiority of the obtained results.

How does wearing slippers affect the movement strategy while crossing over an obstacle?

BackgroundWearing slippers may increase the risk of tripping while crossing obstacles, regardless of age. This is because slippers are more likely to leave the feet and come into contact with obstacles. However, how wearing slippers affects the movement strategy while crossing over an obstacle has not been clarified. Research questionHow does wearing slippers affect the movement strategy while crossing over an obstacle? MethodsThirty healthy young adults crossed over an obstacle using a comfortable speed under two conditions: barefoot and wearing slippers. The moment when the leading or trailing limb was crossing the obstacle was defined as obstacle lead (OL) or obstacle trail (OT), respectively. The margin of stability (MoS) as a measure of stability was measured at OL and OT. Toe clearance and lower limb joint angles of the leading limb were measured at OL, and those of the trailing limb were measured at OT. ResultsWearing slippers increased toe clearance and flexed the hip and knee joints, regardless of the crossing event (OL, OT). However, the ankle joint angle did not change between footwear conditions at OL and was significantly dorsiflexed in the slippered condition at OT. In addition, the MoS did not change between footwear conditions at OL and increased significantly in the slippered condition at OT. SignificanceThe increase of the MoS at OT when wearing slippers is probably a conservative strategy to reduce the risk of falling forward when a trip occurs. More attention to avoiding tripping likely caused the ankle to dorsiflex and increased toe clearance. This conservative strategy and increased attention are most likely due to the slippers coming off easily. Since these strategies are probably safety measures to prevent tripping, slippers may not be appropriate footwear in terms of tripping risk.

Tai Chi practitioners have lower fall risks under dual-task conditions during stair descending.

Stairs are among the most hazardous locations, and stair descending contributes to a high risk of falls among the elderly under dual-task (DT) conditions. The purpose of this study was to determine whether the practitioners of Tai Chi (TC), one type of mind-body exercise, have lower fall risks under DT conditions during stair descending, compared with their no-exercise (NE) counterparts. Fifteen TC practitioners with at least 10 years of experience in TC and fifteen NE participants were recruited in this study. They were asked to descend a six-step staircase under single-task (ST) and DT conditions. An eight-camera motion analysis system and two force plates were used for data collection. Results showed group by DT interactions in walking velocity (p = 0.016) and center of mass–center of pressure inclination angle (COM–COP IA) in the anteroposterior directions (p = 0.026). Group effects observed with foot clearance (p = 0.031), trunk (p = 0.041) and head (p = 0.002) tilt angles, and COM–COP IA in the mediolateral (p = 0.006) directions. Significant DT effects only detected in foot clearance (p = 0.004). Although both groups of participants adopted a more cautious gait strategy under the dual-task condition, the TC practitioners were less influenced by the DT paradigm than their NE counterparts. Our observations indicated that TC practitioners have lower fall risks under DT conditions during stair descending.

Optimizing the Geometric Parameters of a Straight-Through Labyrinth Seal to Minimize the Leakage Flow Rate and the Discharge Coefficient

A straight-through labyrinth seal is one of the most popular non-contacting annular seals through which energy dissipation by turbulence viscosity interaction is achieved with a series of teeth and cavities. The geometric parameters of the straight-through labyrinth seal, such as clearance, tooth width, tooth height, cavity width, and tooth inclination angle, affect its performance. The space for installing a labyrinth seal in turbomachinery is limited, and so it is important to optimize its geometry for a fixed axial length in order to minimize the leakage flow rate and the discharge coefficient. The objective of the current study is to understand the effects of changing the geometric parameters of the seal on the leakage flow rate and the discharge coefficient, and to determine the optimized geometry for a fixed axial length. When the whole axial length is fixed, the most effective way to decrease the discharge coefficient is to reduce the cavity width by increasing the number of cavities. However, if the number of cavities is too high, the beneficial effect of more cavities can be reversed. The results of this study will help turbomachinery manufacturers to design a more efficient labyrinth seal. Numerical simulations of leakage flow for the straight-through labyrinth seal were carried out using Reynolds-Averaged Navier–Stokes (RANS) models, and the results for their discharge coefficients and pressure distributions were compared to previously published experimental data.

Development of a Forward-Reverse Rotating cBN Electroplated End Mill Type Tool for Cutting and Grinding CFRP

Currently, the demand for carbon fiber reinforced plastic (CFRP) has increased in various fields. However, there have been few studies investigating the machined surface quality, degradation in CFRP mechanical properties with machining temperature, or machining tool cost. In particular, the machining temperature is considered to affect the machined quality because the CFRP matrix is a resin. In this study, a cubic boron nitride (cBN) electroplated end mill was developed; this novel tool can switch between cutting and grinding without needing to change the tool. To observe the relationship between the amount of abrasive grain in contact with the CFRP and the occurrence of burrs, a grinding test was conducted with different clearance angles of the end mill and different abrasive grain sizes. The temperature during the grinding processes was measured, and the burrs were estimated after the grinding processes. From these results, the contact amount of the abrasive grit suitable for grinding was derived.

Reaming of carbon fibre reinforced plastics: Influence of tool geometry on process forces and tool wear

Due to the high abrasive wear and the tendency to workpiece damages, the manufacturing of high-quality bores in carbon fibre reinforced plastics (CFRP) is still one of the major goals in tool development. In this work, reaming tests are performed on CFRP in order to characterise the relationship between tool geometry, process forces and tool wear. After a preliminary investigation of a taper reamer, diverse carbide tools have been tested which exhibit different values of rake and clearance angle. The forces measurement took place using a rotating dynamometer, while the evaluation of the tool wear has been realised by microscopic images via structured light projection. Different forms of wear appear, while hardly any differences in the force curves can be detected when applying different angles of the cutting wedge.

Improvement of material databases for cutting force prediction in finishing conditions of A-356 aluminium alloy

Prediction of cutting forces in finishing conditions is becoming essential for the automotive industry, in order to achieve the desired surface integrity and keep controlled phenomena as chatter, especially in workpieces with small thickness walls manufactured by die casting. For predictions, orthogonal to oblique models are widely used, which require a material database as input data. Databases found in the literature have been proven to predict forces accurately in roughing conditions. However, several geometric parameters of the inserts are not taken into account, which could lead to inaccurate predictions in finishing conditions. In this paper, the effects of the cutting edge radius and clearance angle are analysed over the cutting and feed forces during orthogonal turning. A material database for A-356 aluminium alloy is developed following a methodology in accordance with previous research. Finishing face milling tests are carried out for validation, obtaining good agreement with modelled forces.

In-process monitoring and empirical modeling of the tool wear in turning of aluminum alloys using thermoelectric signals

Tool wear is an important criterion for economic machining. It does not only determine the tool life, but also affects the surface layer properties of metallic components and thus their performance. In addition to the machining parameters, there are numerous other influencing factors like batch variations, workpiece inhomogeneities, process vibrations, or the formation of built-up edges that can impact the wear progression. Consequently, it is difficult to predict the tool wear analytically. Therefore, the determination of the tool condition during machining is of great importance. The tool-workpiece thermocouple enables the in-process measurement of a thermoelectric voltage and current during machining generated by the Seebeck effect at the interface between two electrically conductive materials. Thus, the thermoelectric signals are sensitive for the changing contact interface between the tool and the specimen. To allow for an in-process characterization of the tool wear, finding an empirical relationship between the flank wear land width of cemented carbide indexable inserts and the thermoelectric signals in turning is aspired. To vary the flank wear land width in a reproducible manner, tools with a flank face chamfer resulting in a clearance angle of 0° and five different flank face land widths (80 µm – 280 µm) are used. These geometrical properties are measured with a 3D laser scanning microscope. Afterwards, cylindrical specimens of the aluminum alloy EN AW-2017 are machined by turning applying the modified tools and cutting speeds in the range of 300 m/min to 550 m/min. The depth of cut (0.4 mm) and the feed (0.04 mm) are kept constant. Besides the tool-workpiece thermocouple, the components of the resultant force are measured by a dynamometer. The geometrical properties of the machined surfaces are characterized using a stylus measurement instrument.The experimental investigations show an increase of the temperature and the components of the resultant forces with increasing flank wear land width, which impacts the geometrical properties of the surface. An empirical regression model derived from the in-process measurement results depicts the relationship between the thermoelectric signals, the force components, and the changing area of the tool which is in contact with the specimen. Consequently, the combined in-process measurement of the process forces and thermoelectric signals allows for an in-process determination of the tool wear progression and therefore enables the prevention of a strong impairment of the surface-layer properties by a timely tool change or a controlled adjustment of the machining parameters.

Tool lifetime when drilling Inconel 718 in dependence of the cooling channel design –Influence of the clearance angle, the channel diameter, number, and shape

When drilling Inconel 718, the drills are exposed to high mechanical and thermal loads. The cutting zone is located inside the workpiece, whichmakes it challenging to provide sufficient metalworking fluid to the cutting zone. To solve this, drills with internal cooling channels are commonly used. However, no standard on the design of those channels exists. In this work, the influence of different cooling channel designs and different second tool orthogonal clearance angles on tool life, process forces and bore quality have been investigated experimentally. The results reveal that tool lifetime can be influenced in particular by the size of the cooling channels.

Flank face interaction in high magnitude chatter investigation in time domain.

A case of high magnitude chatter vibrations of a flexible tubular part is considered via dynamical modelling in time domain, in a delayed differential equation (DDE) framework. A ploughing term is introduced into the tool-workpiece interaction law. This term is based on a penalty-type law depending on the instant effective clearance angle. This ploughing interaction produces a vibration limiting mechanism featuring realistic maximum magnitudes, as compared to experimental measurements. It is also shown that in spite of interrupted surface pattern, the cut remains continuous under chatter. Furthermore, this model restitutes re-stabilisation at the exit of a stability lobe, with several instabilities occurring during the operation.

Nonlinear dynamic characteristics and control of planar linear array deployable structures consisting of scissor-like elements with revolute clearance joint

This paper comprehensively deals with the parametric effects of the joint clearance and friction coefficient on the dynamics of planar deployable structures consisting of scissor-like elements (SLEs). The dynamic model for scissor deployable structure is based on a comprehensive consideration of the symmetry and array characteristics of this mechanism and on a Lagrange method, which represents the motion equations. A modified nonlinear contact-force model is employed to evaluate the intrajoint contact force, and the incorporation of the friction effect between the inter-connecting bodies is included in this study. The total impact forces produced in the real mechanical joint are embedded into the dynamics and the differential equations of motion are solved numerically based on a set of initial conditions. The clearance size, angle velocity, and friction coefficient are analyzed and discussed separately. Using Poincaré map, the regular and irregular responses of the deployable mulitibody systems are observed. Next, a control scheme is evaluated to maintain a more stable behavior and continuous contact between the clearance joints. The controlled results are compared with those without control, concluding that some undesired effects caused by the clearance joints can be prevented or reduced, resulting in continuous contact at the clearance joint.