Cutting Edge Effect Research Articles

Comparison of a quasi Newton method using Broyden’s update formula and an adjoint method for determining local magnetic material properties of electrical steel sheets

PurposePerforming accurate numerical simulations of electrical drives, the precise knowledge of the local magnetic material properties is of utmost importance. Due to the various manufacturing steps, e.g. heat treatment or cutting techniques, the magnetic material properties can strongly vary locally, and the assumption of homogenized global material parameters is no longer feasible. This paper aims to present the general methodology and two different solution strategies for determining the local magnetic material properties using reference and simulation data.Design/methodology/approachThe general methodology combines methods based on measurement, numerical simulation and solving an inverse problem. Therefore, a sensor-actuator system is used to characterize electrical steel sheets locally. Based on the measurement data and results from the finite element simulation, the inverse problem is solved with two different solution strategies. The first one is a quasi Newton method (QNM) using Broyden's update formula to approximate the Jacobian and the second is an adjoint method. For comparison of both methods regarding convergence and efficiency, an artificial example with a linear material model is considered.FindingsThe QNM and the adjoint method show similar convergence behavior for two different cutting-edge effects. Furthermore, considering a priori information improved the convergence rate. However, no impact on the stability and the remaining error is observed.Originality/valueThe presented methodology enables a fast and simple determination of the local magnetic material properties of electrical steel sheets without the need for a large number of samples or special preparation procedures.

Transient approach for iron loss separation of non-grain-oriented electrical steels considering the impact of cut edge effect

Transient approach for iron loss separation of non-grain-oriented electrical steels considering the impact of cut edge effect

Modelling and analysis of the specific cutting energy for ultra-precision diamond cutting of Ti6Al4V alloy

Ultra-precision diamond cutting (UPDC) is a promising method for fabricating precision parts of titanium alloys. Although energy consumption models have been proposed for conventional cutting methods with macro-cutting scale, few studies focus on the modelling of specific cutting energy for UPDC of titanium alloys with micro/nano-cutting scale. This study proposes an analytical specific cutting energy (SCE) model by fully considering two-phase material microstructures, spring back, size effect, cutting edge effect, temperature evolution and tool-chip frictional states. The theoretical and experimental results show that the significant cutting edge effect and large spring back amount jointly leads to the very high SCE at small undeformed chip thickness (UDCT). The minimum SCE is achieved at the transition UDCT where the cutting mechanism transforms from ploughing to shearing. Moreover, the severe resistance of dislocation movement induced by viscous drag effect results in the slightly increased SCE with increasing cutting speed. The heat accumulated at high cutting speeds can further increase the SCE through increasing the spring back amount of finished surface. The simulated SCE values are in good agreement the experimental results within an error of 6.3 %. By considering the round tool nose and tool wear rate, an energy-oriented machining parameters optimization method is proposed and validated to minimize the SCE in UPDC of titanium alloys.

Loss Parameter Identification After Cutting for Different Non-Oriented Electrical Steel Grades

The magnetic properties of nonoriented (NO) electrical steel sheet are sensitive to industrial cutting processes. Decreased operation point efficiency and an increase in local iron loss in the magnetic circuit of an electrical machine are the consequences. During the design of electrical machines, the cut-edge effect and its consequences can only be considered and assessed, if the effect is locally modeled. In fact, the cut-edge effect is often neglected as standardized magnetic characterization is performed, where the sheet material is measured on an Epstein frame or single sheet tester (SST) and gentle sample preparation is specified. In order to parameterize a local material model, a large number of samples and their detailed magnetic characterization at various magnetizing frequencies are necessary. In this article, the loss parameters of nine different industrial NO electrical steels are identified and analyzed in order to study the course of the parameters and possible interrelation with material properties. The sheet thickness, alloying content of silicon and aluminum, and grain sizes are considered as they are the dominant influences on the iron loss from the material side. The presented results help to increase the understanding of the cut-edge effect and its consequences on the iron loss modeling. Furthermore, they help to identify possibilities to decrease the measurement effort significantly.

Influence of stator segmentation on iron losses in PMSMs for traction applications

PurposeThis paper presents a comparative study of different stator-segmentation topologies of a permanent magnet synchronous machine (PMSM) used in traction drives and their effect on iron losses. Using stator segmentation allows one to achieve more significant copper fill factors, resulting in increased power densities and efficiencies. The segmentation of the stators creates additional air gaps and changes the soft magnetic material’s material properties due to the cut edge effect. The aim of this paper is to present an in-depth analysis of the influence of stator segmentation on iron losses. The main goal was to compare various segmentation methods under equal excitation conditions in terms of their influence on iron loss.Design/methodology/approachA transient finite element method analysis combined with an extended iron-loss model was used to evaluate discussed effects on the stator’s iron losses. The workflow to obtain a homogenized airgap length accounting for cut edge effects was established.FindingsThe paper concludes that the segmentation in most cases slightly decreases the iron losses in the stator because of the overall reduced magnetic flux density B due to the additional air gaps in the magnetic circuit. An increase of the individual components, as well as total power loss, was observed in the Pole Chain segmentation design. In general, segmentation did not change the total iron losses significantly. However, different segmentation methods resulted in the different distortion of the magnetic field and, consequently, in different iron loss compositions. The analysed segmentation methods exhibited different iron loss behaviour with respect to the operation points of the machine. The final finding is that analysed stator segmentations had a negligible influence on the total iron loss. Therefore, applying segmentation is an adequate measure to improve PMSMs as it enables, e.g. increase of the winding fill factor or simplifying the assembly processes, etc.Originality/valueThe influence of stator segmentation on iron losses was analysed. An in-depth evaluation was performed to determine how the discussed changes influence the individual iron loss components. A workflow was developed to achieve a computationally cheap homogenized model.

Investigating flank face friction during precision micro cutting of commercially pure titanium via plunging tests with diamond grooving tools

This study investigates flank face friction while micro machining commercially pure titanium (cp-Ti grade 2) work material considering size effects. It is important to understand friction phenomena at the tool flank and work material surface since they affect the surface integrity of the machined parts. A single crystal diamond grooving tool is used in machining experiments to reduce the influence of cutting edge radius. In addition, plunging type of cutting experiments were performed to investigate the influence of flank face contact on the machined surface. A friction model which is based on work and tool material properties is proposed to model the contribution of adhesion and deformation of the flank face coefficient of friction. The results show that for the cp-Ti and diamond tool pair, adhesion seems to be the dominant model of friction and also contributes to the size effect. The deformation friction becomes more dominant during the chip formation stage. When cutting edge effect is eliminated, the influences of flank and rake face friction on the size effect are shown.

Influence of edge cutting process on fatigue behaviour of spectrum loaded aluminum sheets

Car body and chassis components made of aluminum or steel sheets are produced with varying cutting processes in the different development stages. Whereas the series components are mainly manufactured by shear cutting, the prototype components are often produced with laser cutting. Each cutting process results in specific properties for the cut-edge like surface finish, hardness distribution and residual stresses in the near surface region. The fatigue crack in such components usually starts from a cut-edge, making the fatigue lifetime dependent on different cut-edge conditions. In literature the influence of the cut-edge conditions on the fatigue behaviour so far mainly focuses on constant amplitude loading. Therefore the influence of variable amplitude loading on the cut-edge effect is the objective of this paper. The results of stress-controlled fatigue tests with constant and variable amplitude loading, using a random Gaussian amplitude distribution, are compared for aluminum sheets with different cut-edge conditions. These results show an influence of the load-time-history on the cut-edge effect. The decrease of the fatigue strength under variable amplitude loading is significantly less than for constant amplitude loading. However since the Gassner-lines are shallower than the Woehler-lines the decrease of the fatigue life is higher under variable amplitude loading compared to constant amplitude loading.

Modeling of Scalar Dependencies of Soft Magnetic Material Magnetization for Electrical Machine Finite-Element Simulation

The magnetization behavior and thus the form of the magnetization curve of electrical steel strongly depend on the direction of the magnetic field, frequency of excitation, external mechanical stress, and cut edge effect. These factors influence the performance of electrical machines and need to be considered in advanced machine design processes or numerical modeling. Most of the aforementioned effects occur locally in the machine and, therefore, need to be described locally. It is crucial to characterize the material under realistic conditions for adequate identification and quantification of the influences. In this article, modeling and simulation of soft magnetic material are performed based on a detailed magnetic characterization, considering magnetization amplitude, angle with respect to the rolling direction of magnetization, mechanical stress, and cut edge effect. The dependent soft magnetic material characteristics are derived from the magnetic measurement data and concluded into interpolation surfaces. Subsequently, these surfaces are used to simulate a synchronous machine designed for a traction drive of an electric vehicle by finite-element simulation. One of the main challenges is the correct determination of the local material properties, depending on the operating point, which influences global quantities such as losses and torque. This article provides a methodology to consider different local influences on the magnetization behavior of electrical steel in a finite-element simulation, thus offering the potential for improving electromagnetic circuit design.

Experimental analysis of cutting edge effects on vibrations in end milling

The ability to minimize vibrations in milling by the selection of cutting edge geometry and appropriate cutting conditions is an important asset in the optimization of the cutting process. This paper presents a measurement method and a signal processing technique to characterize and quantify the magnitude of the vibrations in an end milling application. Developed methods are then used to investigate the effects of various cutting edge geometries on vibrations in end milling. The experiments are carried out with five cutting edge geometries that are frequently used in machining industry for a wide range of milling applications. The results show that a modest protection chamfer combined with a relatively high rake angle has, for the most of cutting conditions, a reducing effect on vibration magnitudes. Furthermore, dynamics of a highly positive versus a highly negative cutting geometry is explored in time domain and its dependency on cutting conditions is presented. The results give concrete indications about the most optimal cutting edge geometry and cutting conditions in terms of dynamic behavior of the tool.

Modelling of the combined microstructural and cutting edge effects in ultraprecision machining

The mechanics of ultraprecision machining (UPM) is known to be affected by materials microstructures and cutting tool geometries when cutting magnitudes are reduced to micron-scale. To model the combined effects, a flow stress model that correlates the grain size and chip thickness to the relative tool sharpness is first proposed. Subsequently a novel behavioural chip formation model is developed to distinguish the transitions in chip formation regimes due to the microstructural and cutting edge effects. This led to the discovery of a unique finishing regime where surface roughness is improved by 61.7%, 63.9% and 86.4% for Al-alloy, Mg-alloy and Cu-alloy respectively.

Prediction of Thrust Force and Torque in Drilling of Glass Fiber Reinforced Plastic Using Mechanistic Force Model Approach

High strength to weight ratio along with non-corrosive characteristics make glass fiber reinforced plastics (GFRPs) most promising material in aerospace, navel, automobile and construction sector. However its non-homogeneous and anisotropic nature leads to unfavorable hole quality when subjected to drilling. Among all the drilling induced defects delamination has received considerable attention. Delamination of the material at drill entry occurs above critical torque where as it occurs above critical thrust force at drill exit which adversely affect product quality and results into rejection. Paper presents, a mechanistic approach to develop cutting force models to predict thrust force and torque in GFRP drilling. The mechanistic approach exploits different set of fundamentals of the process including speed, feed rate and tool geometry. Tool point angle, diameter and primary cutting edge effects are mainly considered in this model to predict thrust forces and torque for cutting speed and feed rate combinations. Drilling experiments were conducted on unidirectional glass fiber with stacking sequence of (0/90) sheet with carbide drill to study the influence of various combinations of speed and feed on thrust force and torque. Proposed model is validated for the drill point angle, drill diameter and primary cutting edge of drill bit for GFRP drilling over a wide range of machining conditions.

Numerical Identification of Meso Length-Effect and Full-Field Edge-Effect of 3D Braided Composites

A study is conducted with the aim of developing two numerical models, meso-scale model and fiber embedded matrix model, for evaluating the length-effect and full-field edge-effect of 3D braided composites. Also, for the validation of fiber embedded matrix model, a series of digital image correlation measurements are conducted along the axial directions. The results show that the predicted mechanical behaviors of the tensile and compressive samples are essentially sensitive to the RVC number. Moreover, the proposed fiber embedded matrix method is capable of accurately predicting the cut-edge effect on the full-field mechanical behaviors of 3D braided composites when subjected to the axial tensile and compressive loading, validated by the comparison of the full-field displacement and strain fields.

Numerical investigation of cutting edge effect on fluid flow and heat transfer for in-phase trapezoidal air channels

This work is concerned with the numerical investigations of heat transfer and friction factor penalty inside trapezoidal in-phase corrugated-plate air channels. The influence of the flow rate represented by Reynolds number (100–1000), corrugation aspect ratio (0.2–0.5) and cutting edge ratio (0–0.6) on the flow characteristics and heat transfer was investigated. By cutting the sharp edged corners for trapezoidal channel, the large lateral vortex of the triangular channel was gradually damped resulting in lower recirculation area, lower recirculation velocities and lower velocity gradients damping the high peaks of the shear stress observed in the triangular case resulting in lower isothermal friction factor. However, the mixing effect produced by the lateral vortex decreased with its damping, which led to less uniform temperature profile resulting in lower sharper wall temperature gradients with thicker boundary layer thickness, so lower values of the Nusselt number were obtained. New correlations were developed based on the present results to evaluate Nusselt number and friction factor as a function of Reynolds number, corrugation aspect ratio, relative spacing ratio and cutting edge ratio for different corrugation shapes. The predicted results are consistent with the numerical and experimental data and lie within ±10% deviation.

End-milling of Inconel 718 Superalloy - An Analytical Modelling

In this work, a predictive machining theory, taking into account the thermo-visco-plastic response of the work material, is applied to the end milling process. In order to consider the particular conditions of end-milling operation, when the uncut chip thickness becomes in range of the cutting edge radius, the cutting edge effect has been also introduced. The proposed model appears as an interesting alternative to the mechanistic approach which requires many experimental tests to determine the milling cutting force coefficients. The predicted cutting forces are in good agreement with experimental data for dry machining of Inconel 718.

Investigation on the Bearing Abilities of Three-Dimensional Full Five-Directional Braided Composites with Cut-Edge

The longitudinal tensile experiments of cut-edge effect on the mechanical performance of three-dimensional full five-directional (3DF5D) braided composites were conducted. The specimens involved two different braiding angles and two different cutting ways. Fracture appearance of specimens without cut-edge and cutting along width direction presented flush, while explosive for specimen with cut-edge along thickness direction. The fracture of axis yarns mainly contributed to the damage of specimens. Cut-edge had little influence on the stiffness of 3DF5D braided composites and had approximately 20 % reduction in tensile strength compared with specimens without cut-edge. The periodic boundary conditions under cut-edge and uncut-edge situations were applied to the RVC to simulate the mesoscopic damage mechanism using finite element method. The stress–strain curves and damage evolution nephogram were obtained. The variation of cut-edge effect with the number of inner cells was predicted by superimposing inner cells method, the addition of inner cells could strengthen the performance of 3DF5D braided composites with cut-edge. These results will play an important role in evaluating the mechanical properties of braided materials after cutting.

Predictive modelling of cutting forces in end milling of titanium alloy Ti6Al4V

A cutting force model, based on a predictive model for orthogonal cutting, is developed for force predictions in end milling of titanium alloy Ti6Al4V. The model assumes a semi-stationary process for the serrated chip formation. The Johnson–Cook material model that couples strain hardening, strain rate sensitivity and thermal softening effects is applied to represent the material strength. A thermal model considering the tool thermal properties is integrated to account for the high temperature rise due to the low thermal conductivity of Ti6Al4V. To extend the predictive model to milling, the end mill is discretised into several axial slices, and an equivalent cutting edge is used to include the end cutting edge effect caused by the first axial slice. The model is assessed by comparing its prediction with the experimental results and a mechanistic model for verification. The results show that the proposed model outperforms the mechanistic model with higher accuracy in force prediction.

Prediction of the hobbing cutting forces from a thermomechanical modeling of orthogonal cutting operation

The common external cylindrical gears are manufactured by gear hobbing process. The particularity of this operation is due to the nature of the interaction between the tool cutting edge and the workpiece material which is more complex than in conventional machining operations such as turning, milling or drilling. This can affect significantly the thermomechanical process of the chip formation. The main goal of this paper is to propose a coupled approach to analyze accurately the cutting edge effect and to predict the evolution of cutting forces during the finishing hobbing process. This model is based on two parts: (i) during the hobbing operation, the evolution of the undeformed chip section generated by each hob's tooth is determined from the CAD geometrical simulations and (ii) the cutting forces are calculated from a mechanistic model. In this mechanistic approach, the specific force coefficients (cutting and edge effects) have been determined from a thermomechanical model, based on the ALE (Arbitrary Eulerian Lagrangian) approach, by considering the material characteristics such as strain rate sensitivity, strain hardening and thermal softening. It can be noted that the ALE approach allows to accurately take into account accurately the cutting edge effect and to analyze the triboligical conditions at the tool-chip interface (i.e. the contact nature: sliding, sticking or sticking-sliding contact). Indeed, this kind of information is of great importance to analyze the effect of cutting condition on the tool wear. The numerical and experimental results are compared for several cutting velocities in orthogonal process. The present approach leads to a three dimensional cutting force model for hobbing process and appears as an interesting alternative to the classical mechanistic approach which requires many experimental tests to determine the cutting force coefficients. Finally, the proposed model has been applied to analyze a finishing hobbing gear with very large sizes (several meters).

Bearing Abilities and Progressive Damage Analysis of Three Dimensional Four-Directional Braided Composites with Cut-Edge

Cut-edge is a kind of damage for the three-dimensional four-directional (3D4d) braided composites which is inevitable because of machining to meet requisite shape and working in the abominable environment. The longitudinal tensile experiment of the 3D4d braided composites with different braiding angles between cut-edge and the ones without cut-edge was conducted. Then representative volume cell (RVC) with interface zones was established to analyze the tensile properties through the fracture and damage mechanics. The periodic boundary conditions under the cut-edge and uncut-edge conditions were imposed to simulate the failure mechanism. Stress-strain distribution and the damage evolution nephogram in cut-edge condition were conducted. Numerical results were coincident with the experimental results. Finally the variation of cut-edge effect with the specimen thickness was simulated by superimposing inner cells. The consequence showed that thickness increase can effectively reduce cut-edge influence on longitudinal strength for 3D4d braided composites. Cut-edge simulation of braided composites has guiding significance on the actual engineering application.

Modelling the cutting forces in micro-end-milling using a hybrid approach

This paper presents the development of a cutting force model for the micro-end-milling processes under various cutting conditions using a hybrid approach. Firstly, a finite element (FE) model of orthogonal micro-cutting with a round cutting edge is developed for medium-carbon steel. A number of finite element analyses (FEA) are performed at different uncut chip thicknesses and velocities. Based on the FEA results, the cutting force coefficients are extracted through a nonlinear algorithm to establish a relationship with the uncut chip thickness and cutting speed. Then, the cutting force coefficients are integrated into a mechanistic cutting force model, which can predict cutting forces under different cutting conditions. In order to account for the cutting edge effect, an effective rake angle is employed for the determination of the cutting force. A comparison of the prediction and experimental measured cutting forces has shown that the developed method provides accurate results.

Comparison of thermo-mechanical characteristics of non-doped and 3mol% B-site Zr-doped Ba0.5Sr0.5Co0.8Fe0.2O3−δ

A dense membrane layer supported by a thick porous substrate is a favorable design for advanced oxygen separation units used in Oxy-fuel processes and membrane reactors. Based on the highest permeation rates verified so far, Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3− δ appears to be the most promising membrane and substrate material. This material, however, suffers from partial decomposition of cubic structure to hexagonal polymorphs at ∼825 °C, which is associated with a significant oxygen permeation drop. The partial substitution of the B-site with 3 mol% zirconium has been suggested as one of solutions for suppressing this transformation. The current study concentrated on the comparison of the thermo-mechanical characteristics of doped and non-doped Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3− δ . Although the later material showed higher elastic modulus and fracture strength in absolute values, overall their characteristics mostly agree. It was shown that shortening of the membrane tube from 1 m to half its length should not influence fracture strength significantly. Fractographic analysis ruled out the cutting edge effect in O-ring bending.