Characterization of chip formation during machining 1045 steel

A deep understanding of the generation and characterization of chip formation can result for practical advices of chip type controlling in engineering applications. The chip formation is divided into the continuous chip and the serrated one in this study. The characterization of the continuous chip formation is expressed as the chip deformation and that of the serrated chip formation is expressed as the frequency of serration, the degree of segmentation, and the deformation of serrated chip. The chips of 1045 steel under different cutting speeds (100–3,600?m/min) are collected during machining. After inlay and polishing of the collected chips, the chip morphology is observed with VHX-600 ESO digital microscope. It is found that at the cutting speeds of 100–400?m/min, the chip type is continuous, at the cutting speeds of 600–2,200?m/min the chip type is serrated, and at the cutting speeds of 2,500–3,600?m/min the chip type is segmented. The quantitative relations between the characterization parameters of chip formation and the cutting speed are obtained. The chip deformation increases with the cutting speed, and the influence of the cutting speed on the shear strain rate is more sensitive than that on the shear strain during the continuous chip formation. All the characterization parameters including the shear strain rate, the frequency of serration, the degree of segmentation, and the shear strain increase with the cutting speed during the serrated chip formation. The sensitivity of influence of the cutting speed on these parameters is in the following: the shear strain rate, the degree of segmentation, the frequency of serration, and the shear strain.     

Analytical and experimental study on formation of concentrated shear band of saw tooth chip in high-speed machining

Saw tooth chip is a typical characteristic encountered in high-speed machining. It consists of nearly undeformed segments and highly sheared concentrated shear bands. However, no consensus on the formation of the concentrated shear band has been reached though several saw tooth chip formation models have been built. In this paper, the concentrated shear band formation procedure is analyzed based on a new proposed saw tooth chip formation model. Cutting experiments have been conducted to validate the proposed mode. It shows that the plastic side flow and elastic compression of the uncut chip are crucial for the concentrated shear band formation. The localized shear at the inner end (tool tip side) of the primary shear plane firstly takes place under the indentation of cutting tool. Then, the second localized shear is produced at the outer end (free surface side) of the primary shear plane due to stress concentration there, after which the whole concentrated shear band forms. The stress transition at the outer end of the primary shear plane makes the second localized shear easier evolve into cracks. Influences of material brittleness and cutting speed on initiation and propagation of the concentrated shear band are also analyzed.     

Direct examination of chip formation during metal machining by scanning electron microscopy

New insights into the mechanics and morphology of chip formation in metal cutting have been obtained by direct observation of an orthogonal cutting process in progress in a scanning electron microscope. A specimen stage specifically designed for this purpose is described. This stage permits dynamic viewing of all accessible areas of interest at magnifications up to ×5000 during cutting. Permanent records are obtained by videotaping each experiment. A brief summary of results is given, and extensions of the technique of dynamic scanner observation are suggested.     

Study on mechanism of chip formation during high-speed milling of alloy cast iron

By adopting an equivalent geometry model of chip, a finite element model was developed to study the mechanism of chip formation during high-speed milling of alloy cast iron. Several key technologies such as material constitutive model, friction model, chip separation criteria, chip damage criteria, heat dissipation, and transfer were implemented to improve the accuracy of finite element simulation. Saw-tooth chip of alloy cast iron was observed. The chip shape and cutting force agreed well with experimental results. The simulation results show that the maximum cutting temperature produced with appearance of saw-tooth chip crack, and it is located on the chip-tool contact surface. The saw-tooth chip is caused by double actions of thermoplastic instability and plastic instability. The chip saw-tooth degree decreases when increasing the rotating speed, while it increases when increasing the feed speed. This work provides a useful understanding for chip formation process and helps to optimize machining parameters and process of high-speed milling of alloy cast iron.     

Analytical modeling of adiabatic shear band spacing for serrated chip in high-speed machining

Theoretical prediction of adiabatic shear band spacing is beneficial to understand the mechanism of the serrated chip formation. The momentum equation, energy equation and compatibility equation in orthogonal cutting are established in this paper. Using perturbation analysis by regarding cutting speed and uncut chip thickness as basic disturbance, an analytical solution of adiabatic shear band spacing is developed. Adiabatic shear band spacing of serrated chip is related to the wave number of the perturbation when the growth rate reaches to maximum. It is found that adiabatic shear band spacing decreases with the increase of cutting speed but increases with uncut chip thickness. The experiment of orthogonal cutting Ti6Al4V under different cutting speeds (50 m/min-1800 m/min) and uncut chip thicknesses (0.02 mm-0.16 mm) verifies the validity of the theoretical prediction.     

基于单颗磨粒的高速外圆磨削成屑机理研究

高速磨削是解决磨削效率和磨削质量完美统一的一种可能途径,但对于高速外圆磨削机理的研究并不多见。基于切削仿真软件,构造了单颗磨粒高速外圆磨削仿真模型,对高速外圆磨削机理进行了仿真试验研究,研究结果表明:钛合金在单颗磨粒高速磨削作用下经历了滑擦→耕犁→成屑→滑擦4种状态变化;工件在磨屑形成之前,力与温度均呈上升趋势,随着工件温度的升高,磨削力出现拐点并急剧下降,成屑过程中磨削温度达到最高值时,磨削力降至最小值。     

New observations on the mechanism of chip formation when machining titanium alloys

Titanium and other aerospace structural superalloys are extremely difficult to machine except at low cutting speeds because of rapid tool wear. To increase productivity it is necessary to understand the mechanics of chip formation when machining these alloys. In this paper we report some new findings towards that goal.     

Study of cutting speed on surface roughness and chip formation when machining nickel-based alloy

Nickel-based alloy is difficult-to-machine because of its low thermal diffusive property and high strength at higher temperature. The machinability of nickel- based Hastelloy C-276 in turning operations has been carried out using different types of inserts under dry conditions on a computer numerical control (CNC) turning machine at different stages of cutting speed. The effects of cutting speed on surface roughness have been investigated. This study explores the types of wear caused by the effect of cutting speed on coated and uncoated carbide inserts. In addition, the effect of burr formation is investigated. The chip burr is found to have different shapes at lower speeds. Triangles and squares have been noticed for both coated and uncoated tips as well. The conclusion from this study is that the transition from thick continuous chip to wider discontinuous chip is caused by different types of inserts. The chip burr has a significant effect on tool damage starting in the line of depth-of-cut. For the coated insert tips, the burr disappears when the speed increases to above 150 m/min with the improvement of surface roughness; increasing the speed above the same limit for uncoated insert tips increases the chip burr size. The results of this study showed that the surface finish of nickel-based alloy is highly affected by the insert type with respect to cutting speed changes and its effect on chip burr formation and tool failure.     

Effect of cutting speed on surface integrity and chip morphology in high-speed machining of PM nickel-based superalloy FGH95

High-speed machining is being recognized as one of the key manufacturing technologies for getting higher productivity and better surface integrity. FGH95 powder metallurgy superalloy is a kind of nickel-based superalloy which is produced by near-net-shape technology. With increasing demands for high precision and high performance of FGH95 components in aerospace industry, it is essential to recognize that the machined surface integrity may determine machined part service performance and reliability. Then, little is known about the machined surface integrity of this superalloy. Thus, the surface integrity in high-speed machining of FGH95 is investigated in this paper. Experiments are conducted on a CNC milling center with coated carbide tools under dry cutting conditions. The surface integrity is evaluated in terms of surface roughness, microhardness, and white layer. The influence of cutting speed on chip morphology is also investigated. Experiment results show that surface integrity and chip morphology of FGH95 are very sensitive to the cutting speed. When cutting speeds are below 2,400?m/min, the values of surface roughness have little variation, while when cutting speeds are in the range of 2,800–3,600?m/min, the values of surface roughness are higher than that of other cutting speeds. Severe work hardening is observed resulting from high-speed machining of FGH95 superalloy. The higher the cutting speed, the higher the surface hardness. When cutting speeds are in the range of 2,800–3,600?m/min, the white layer thickness is slightly higher than that of other cutting speeds. In high-speed machining of FGH95, the chip is segmented and has a typical sawtooth shape. The degree of serrated chip increases with the cutting speed. When the cutting speeds exceed 2,400?m/min, serrated chips change into fragment chips.     

Material removal and chip formation mechanisms of UHC-steel during grinding

Laser shock forming (LSF) is a sheet plastic forming technology, which employs laser-induced shock waves to make sheet metal duplicate a desired shape of the mold. In this paper, a finite element analysis (FEA) model was developed to simulate dynamic forming process with the commercial finite element code ABAQUS/Explicit, and a series of dynamic deformation behaviors of the metal sheet shaped into conical cup at the end of different periods of time were displayed and discussed in detail. The springback of conical cup and the distribution of residual stress were analyzed with ABAQUS/Standard. All these investigations could provide insight into the physics process of the ultra-fast deformation. The LSF experiment was further conducted to verify the results predicted by FEA. The experiment results are well consistent with the numerical predicted data, which validates the FEA model. It indicates that FEA can be used to simulate the forming process and optimize its parameters.     

Effect of tool vibration on chip formation and cutting forces in the machining of fiber-reinforced polymer composites

This article investigates the chip formation mechanism and its influence on cutting forces during the elliptic vibration-assisted (EVA) cutting of fiber-reinforced polymer composites. To clarify the effect of the vibration, systematic finite element and experimental studies were performed on both the EVA and the traditional cutting of unidirectional fiber-reinforced polymers with various fiber orientations. The key factors that govern the cutting forces have been taken into account, such as the depth of cut, feed rate, tool vibration frequency and amplitude. The study found that fiber orientation significantly affects the chip formation and cutting forces. Fiber fracture can happen either above or below the trimming path, but that above the path dominates chip formation. When a fiber orientation is less than 90°, chipping is mainly through bending-induced fracture of fibers; when it is beyond 90°, however, chipping is mostly by crushing the fracture of fibers. Compared with a traditional cutting process, the EVA cutting can minimize the fiber orientation effect through localized fiber fracture. A dimensional analysis was then performed to provide a quantitative prediction of the cutting forces.     

A reliable method for predicting serrated chip formation in high-speed cutting: analysis and experimental verification

Serrated chip formation influences almost every aspect of a high-speed cutting (HSC) process. This paper aims to develop a reliable method to accurately predict such chip formation processes. To this end, a systematic finite element analysis was carried out and a series of HSC experiments were conducted on a heat treated AISI 1045 steel. It was found that the integrative use of the Johnson–Cook thermal-viscoplastic constitutive equation, Johnson–Cook damage criterion for chip separation, and the modified Zorev’s friction model can precisely predict the serrated chip formation in HSC without artificial assumptions. This advancement has removed the major barrier in the current machining investigations by numerical simulation. The present study also found that the tool rake angle has a significant effect on serrated chip formation. As the rake angle increases, the chip sawtooth degree and cutting forces decrease, but the chip segmentation frequency increases.     

高速切削中实例相似度及其应用的研究

为充分利用高速切削加工实践中积累的成功经验和数据,提出了运用基于实例推理方法的解决方式。研究了高速切削加工实例的表示方法及实例相似度的性质,将实例的局部相似度分为数值型、无关型、枚举型和依赖型4类,并给出了每种类型的局部相似度的计算方法及实例整体相似度复合算法的计算公式。应用结果表明,所提出的实例及其相似度计算方法是可行的。     

Development of web-based machining chip breaking prediction systems

The prediction of chip breaking in machining is an important task of automated manufacturing. A chip breaking predictive model has been developed to predict the chip breaking behaviour in steel turning with grooved tools. The model is based on the chip breaking limits theory. A web-based chip breaking prediction system has been developed and presented in this paper with industrial application examples. With the system, the chip breaking range in steel turning with grooved tools can be predicted under different cutting conditions. The experimental data for turning different steel material over a wide range of feed rates, cutting speeds and tool geometry showed agreements with the model prediction. The user-friendly system is accessible through the Internet for the purposes of cutting condition design and tool selection. Also, the system can easily be extended to contain new cutting tools and new workpiece materials with a small number of cutting tests.Nomenclature f Feed rate (mm/rev) - d Depth of cut (mm) - V Cutting speed (m/min) - f_cr The critical feed rate (mm/rev) - d_cr The critical depth of cut (mm) - r Insert Nose radius (mm) - W_n Insert chip breaking groove width (mm) - Cutting edge angle (deg) - ₀ Insert rake angle (deg) - ₀₁ Insert land rake angle (deg) - b₁ Insert/chip restricted contact length (mm) - _s Insert inclination angle (deg) - h Insert backwall height (mm) - WP Work piece - DB database     

Time modeling in high-speed machining of mold pocket

Numerical control milling (NCM) at high speed is the most used machining process in the manufacture of molds because it offers high productivity and workpiece surface quality. The aim of this work is to establish a methodology to evaluate the rough machining time, during high speed milling. In pocket machining, a 2.5D milling has been considered. The proposed approach considers the roughing cutting time as the ratio of the pocket volume by the removed material rate. The pocket is divided into volumes distributed according to the real radial depth. Since the radial depth varies during machining, the removed material rate is not constant. In this paper, an experimental study is carried out to validate models of machining time calculation. The obtained results show that the proposed method offers fast and easy calculation of the machining time of pocket roughing.     

Modal identification of spindle-tool unit in high-speed machining

The accurate knowledge of high-speed motorised spindle dynamic behaviour during machining is important in order to ensure the reliability of machine tools in service and the quality of machined parts. More specifically, the prediction of stable cutting regions, which is a critical requirement for high-speed milling operations, requires the accurate estimation of tool/holder/spindle set dynamic modal parameters. These estimations are generally obtained through Frequency Response Function (FRF) measurements of the non-rotating spindle. However, significant changes in modal parameters are expected to occur during operation, due to high-speed spindle rotation.The spindle's modal variations are highlighted through an integrated finite element model of the dynamic high-speed spindle-bearing system, taking into account rotor dynamics effects. The dependency of dynamic behaviour on speed range is then investigated and determined with accuracy. The objective of the proposed paper is to validate these numerical results through an experiment-based approach. Hence, an experimental setup is elaborated to measure rotating tool vibration during the machining operation in order to determine the spindle's modal frequency variation with respect to spindle speed in an industrial environment. The identification of natural frequencies of the spindle under rotating conditions is challenging, due to the low number of sensors and the presence of many harmonics in the measured signals. In order to overcome these issues and to extract the characteristics of the system, the spindle modes are determined through a 3-step procedure. First, spindle modes are highlighted using the Frequency Domain Decomposition (FDD) technique, with a new formulation at the considered rotating speed. These extracted modes are then analysed through the value of their respective damping ratios in order to separate the harmonics component from structural spindle natural frequencies. Finally, the stochastic properties of the modes are also investigated by considering the probability density of the retained modes. Results show a good correlation between numerical and experiment-based identified frequencies. The identified spindle-tool modal properties during machining allow the numerical model to be considered as representative of the real dynamic properties of the system.     

A universal slip-line model with non-unique solutions for machining with curled chip formation and a restricted contact tool

A universal slip-line model and the corresponding hodograph for two-dimensional machining which can account for chip curl and chip back-flow when machining with a restricted contact tool are presented in this paper. Six major slip-line models previously developed for machining are briefly reviewed. It is shown that all the six models are special cases of the universal slip-line model presented in this paper. Dewhurst and Collins's matrix technique for numerically solving slip-line problems is employed in the mathematical modeling of the universal slip-line field. A key equation is given to determine the shape of the initial slip-line. A non-unique solution for machining processes when using restricted contact tools is obtained. The influence of four major input parameters, i.e. (a) hydrostatic pressure (P_A) at a point on the intersection line of the shear plane and the work surface to be machined; (b) ratio of the frictional shear stress on the tool rake face to the material shear yield stress (τ/k); (c) ratio of the undeformed chip thickness to the length of the tool land (t₁/h); and (d) tool primary rake angle (γ₁), upon five major output parameters, i.e. (a) four slip-line field angles (θ, η₁, η₂, ψ); (b) non-dimensionalized cutting forces (F_c/kt₁w and F_t/kt₁w); (c) chip thickness (t₂); (d) chip up-curl radius (R_u); and (e) chip back-flow angle (η_b), is theoretically established. The issue of the “built-up-edge” produced under certain conditions in machining processes is also studied. It is hoped that the research work of this paper will help in the understanding of the nature and the basic characteristics of machining processes.