A method of using turning process excitation to determine dynamic cutting coefficients

Identification of the dynamic cutting force coefficients is an essential work in cutting process modeling. The excitation equipment employed to produce dynamic cutting process is usually sophisticated and may lead to potential error. An alternative method of turning process excitation is proposed to simplify the procedure of cutting dynamics measurement. A cantilever workpiece used in cylindrical turning process has been modeled with a double degree-of-freedom system that supports variable dynamic parameters. The structural dynamics of the equivalent system are analyzed with the theoretical derivation and the finite element simulations. The influence of structural dynamic variation on the chatter frequency is investigated, based on which the self-excited chatter is considered as a method of the turning process excitation. This method is applied in the cutting dynamics tests. The dynamic cutting force coefficients could be measured through a single chattering turning process. Stability analysis is conducted for verification of the measured dynamic cutting coefficients.     

工艺参数对单晶硅超精密加工切削力的影响

为了了解单晶硅超精密车削过程中不同切削参数及刀具前角对切削力的影响,利用单晶金刚石车刀对单晶硅进行单因素变量超精密车削试验。试验结果表明:进给量f和切削深度a_p对X、Y、Z方向的切削力F均有增大的趋势;而在切削速度v_c增加时,各方向的F逐渐减小;切削前角减小时,切削力反而增大。通过各因素对切削力F的变化幅值可以得到,对F影响较大的参数为a_p及f。选取最佳组合参数对单晶硅进行超精密切削试验,得到极为光滑的表面。     

CVD金刚石厚膜刀具切削参数对切削力及粗糙度影响的研究

为了探究CVD金刚石厚膜刀具切削参数(包括刀具后角、刀尖圆弧半径、切削速度、进给量和切削深度)对切削力和被加工表面粗糙度影响的初步规律,采用单因素方法进行了一系列CVD金刚石厚膜刀具车削仿真和试验研究。结果表明:AdvantEdge有限元仿真软件模拟切削力过程有一定的准确性;在试验参数范围内,随着刀具后角的增大,切削力和表面粗糙度都是先减小后增大,当后角为11°时,切削力和表面粗糙度值最小;随着刀尖圆弧半径的增大,切削力逐渐增大,而表面粗糙度则逐渐减小;随着切削速度的增大,切削力和表面粗糙度都是先增大后减小,当切削速度为90m/min时,切削力和表面粗糙度值最大;随着进给量的增大,切削力和表面粗糙度都显著增大;随着切削深度的增大,切削力和表面粗糙度都逐渐增大,但切削深度对表面粗糙度的影响较小。     

Development of a modular dynamometer for triaxial cutting force measurement in turning

Accurate and reliable measurement of cutting forces in turning is essential for tool geometry, tool trajectory and cutting parameters optimization, as well as for tool condition monitoring and machinabilty testing. In this work, an innovative dynamometer for triaxial cutting force measurement in turning, specifically designed to be applied at a milling-turning CNC machine tool endowed with an indexable head, is presented. The device is based on a piezoelectric force ring integrated into a commercial toolshank, and its modular design allows the easy change of the cutting insert without altering sensor preload. The prototype device was assembled and experimentally tested by means of static calibration and dynamic identification, which evidenced good static and dynamic characteristics. Eventually, the sensor was tested in operating conditions by machining a benchmark workpiece.     

A grey prediction fuzzy controller for constant cutting force in turning

Constant force control is gradually becoming an important technique in the modern manufacturing process. Especially, constant cutting force control is a useful approach in increasing the metal removal rate and the tool life for turning systems. However, turning systems generally have non-linear with uncertainty dynamic characteristics. Designing a model-based controller for constant cutting force control is difficult because an accurate mathematical model in the turning system is hard to establish. Hence, this study employed a model-free fuzzy controller to control the turning system in order to achieve constant cutting force control. Nevertheless, the design of the traditional fuzzy controller (TFC) presents difficulties in finding control rules and selecting an appropriate membership function. To solve this problem, a grey-theory algorithm was introduced into the TFC to predict the next output error of the system and the error change, rather than the current output error of the system and the current error change, as input variables of the TFC. This design of the grey prediction fuzzy controller (GPFC) cannot only simplify the TFC design, but also achieves the desired result in TFC implementation. To confirm the applicability of the proposed intelligent controllers, this work retrofitted an old lathe for a turning system to evaluate the feasibility of constant cutting force control. The GPFC has better control performance in constant cutting force control than does the TFC, as verified in experimental results.     

Reliable tool life measurements in turning — an application to cutting fluid efficiency evaluation

The paper proposes a method to obtain reliable measurements of tool life in turning, discussing some aspects related to experimental procedure and measurement accuracy. The method (i) allows an experimental determination of the extended Taylor's equation, with a limited set of experiments and (ii) provides a basis for the quantification of tool life measurement uncertainty. The procedure was applied to cutting fluid efficiency evaluation. Six cutting oils, five of which formulated from vegetable basestock, were evaluated in turning. Experiments were run in a range of cutting parameters, according to a 2^3–1 factorial design, machining AISI 316L stainless steel with coated carbide tools. Tool life measurements were associated to an estimation of their uncertainty, and it was found that by taking three repetitions the uncertainty calculated with a coverage factor of two was on average three times bigger than the experimental standard deviation.     

Chatter stability of a slender cutting tool in turning with tool wear effect

An analysis of the chatter behavior for a slender cutting tool in turning in the presence of wear flat on the tool flank is presented in this research. The mechanism of a self-excited vibration development process with tool wear effect is studied. The components contributing to the forcing function in the turning vibration dynamics are analyzed in the context of cutting force and contact force. A comparison of the chatter stability for a fresh cutting tool and a worn cutting tool is provided. Stability plots are presented to relate width of cut to cutting velocity in the determination of chatter stability. Machining experiments at various conditions were conducted to identify the characteristic parameters involved in the vibration system and to identify the analytical stability limits. The theoretical result of chatter stability agrees qualitatively with the experimental result concerning the development of chatter stability model with tool wear effect.     

Investigation on the influence of tool-tip vibration on surface roughness and its representative measurement in ultra-precision diamond turning

High frequency tool-tip vibration, in the cutting force direction, is an intrinsic feature of ultra-precision single point diamond turning (SPDT). This paper is dedicated to a study of the influence of the tool-tip vibration on surface roughness. The resulting periodic fluctuation of the surface profile is identified in a particular spatial frequency range by a tangential measurement method. The ISO standard provides merely a minimal, not an optimal requirement for surface measurement. Thus, in this paper, a more representative measurement method is proposed to better characterise the machined surface in SPDT. The conventional radial and aerial surface measurements yield a relatively biased result on surface roughness which cannot adequately reflect the detrimental effect of tool-tip vibration. Representative measurement takes account of the sample area ratios and is able to be used to objectively study the discrepancies in surface measurement. The proposed model for surface generation and representative measurement are applicable to the problems in surface generation in ultra-precision SPDT, such as the spiral turning marks and spatial errors in the radial profile measurement.     

Statistical analysis of surface roughness and cutting forces using response surface methodology in hard turning of AISI 52100 bearing steel with CBN tool

The present work concerns an experimental study of hard turning with CBN tool of AISI 52100 bearing steel, hardened at 64 HRC. The main objectives are firstly focused on delimiting the hard turning domain and investigating tool wear and forces behaviour evolution versus variations of workpiece hardness and cutting speed. Secondly, the relationship between cutting parameters (cutting speed, feed rate and depth of cut) and machining output variables (surface roughness, cutting forces) through the response surface methodology (RSM) are analysed and modeled. The combined effects of the cutting parameters on machining output variables are investigated while employing the analysis of variance (ANOVA). The quadratic model of RSM associated with response optimization technique and composite desirability was used to find optimum values of machining parameters with respect to objectives (surface roughness and cutting force values). Results show how much surface roughness is mainly influenced by feed rate and cutting speed. Also, it is underlined that the thrust force is the highest of cutting force components, and it is highly sensitive to workpiece hardness, negative rake angle and tool wear evolution. Finally, the depth of cut exhibits maximum influence on cutting forces as compared to the feed rate and cutting speed.     

基于Pro/Engineer的薄壁套加工变形仿真与验证实验

利用Pro/Engineer-Mechanica软件,针对薄壁套车削时受夹紧力和切削力影响的变形进行了有限元分析。通过对不同装夹方式和切削参数加工的模拟分析与对比,优化了工艺方案。切削试验结果表明:仿真模拟数据与实际测量数据具有较高的一致性。因此,这种分析方法可作为薄壁套类零件工艺方案制定的一种定量分析手段,改变了凭经验或通过试切调整确定工件装夹方式和切削参数的传统方法。     

Predictive machinability models for a selected hard material in turning operations

In this paper, empirical models for tool life, surface roughness and cutting force are developed for turning operations. Process parameters (cutting speed, feed rate, depth of cut and tool nose radius) are used as inputs to the developed machinability models. Two important data mining techniques are used; they are response surface methodology and neural networks. Data of 28 experiments when turning austenitic AISI 302 have been used to generate, compare and evaluate the proposed models of tool life, cutting force and surface roughness for the considered material.     

Investigation of the effect of rake angle and approaching angle on main cutting force and tool tip temperature

This paper deals with the comparison of measured and calculated results of cutting force components and temperature variation generated on the tool tip in turning for different cutting parameters and different tools having various tool geometries while machining AISI 1040 steel hardened at HRc 40. The geometric variables (approaching angle and rake angle) of the tool were changed using selected cutting parameters; thus, the cutting force components and temperature variations on tool face (in secondary shear zone) were determined. The selected cutting variables and the tools in different geometries were tested practically under workshop conditions. In this way, the essential information about the validity of selected values was obtained. During the tests, the depth of cut and cutting speed were kept constant and each test was conducted with a sharp uncoated tool insert. For making a comparison, the main cutting force/tangential force component for different cutting parameters and tool geometries were calculated by Kienzle approach and the temperature values were calculated based on orthogonal cutting mechanism. Finally, the effects of cutting parameters and tool geometry on cutting forces and tool tip temperature were analysed. The average deviation between measured and calculated force results were found as 0.37%. The cutting force signals and temperature values provided extensive data to analyse the orthogonal cutting process.     

Tool wear measurement in turning using force ratio

The aim of this work was to develop a reliable method to predict flank wear during the turning process. The present work developed a mathematical model for on-line monitoring of tool wear in a turning process. Force signals are highly sensitive carriers of information about the machining process and, hence, they are the best alternatives for monitoring tool wear. In the present work, determination of tool wear has been achieved by using force signals. The relationship between flank wear and the ratio of force components was established on the basis of data obtained from a series of experiments. Measurement of the ratio between the feed force and the cutting force components (F_f/F_c) has been found to provide a practical method for an in-process approach to the quantification of tool wear. A series of experiments was conducted to study the effects of tool wear as well as other cutting parameters on the cutting force signals, and to establish a relationship between the force signals, tool wear and other cutting parameters. The flank wear and the ratio of forces at different working conditions were collected experimentally to develop a mathematical model for predicting flank wear. The model was verified by comparing the experimental values with the predicted values. The relationship was then used for determination of tool flank wear.     

Predictive modeling of machining residual stresses considering tool edge effects

The surface integrity of machined components is defined by several characteristics, of which residual stress is extremely important. Residual stress is known to have an effect on critical mechanical properties such as fatigue life, corrosion cracking resistance, and dimensional tolerance of machined components. Among the factors that affect residual stress in machined parts are cutting parameters and tool geometry. This paper presents a method of modeling residual stress for hone-edge cutting tools in turning. The model utilizes analytical cutting force models in conjunction with an approximate algorithm for elastic–plastic rolling/sliding contact. Oxley’s cutting force model is coupled with a slip line model proposed by Waldorf to estimate the cutting forces, which are in turn used to estimate the stress distribution between the tool and the workpiece. A rolling/sliding contact model, which captures kinematic hardening, is used to predict the machining residual stresses. Additionally, a moving heat source model is applied to determine the temperature rise in the workpiece due to the cutting forces. The model predictions are compared with experimental data for the turning of AISI 52100. Force predictions compare well with experimental results. Similarly, the predicted residual stress distributions correlate well with the measured residual stresses in terms of magnitude of stresses and depth of penetration.     

车削加工过程建模与MATLAB仿真分析

建立了车削加工过程模型,考虑伺服机构、切削过程和测力仪等环节,并用Matlab对模型进行仿真,分析了阻尼系数、固有频率和切削力指数等参数变化对切削力的影响,研究结果对加工过程的计算机控制具有指导意义.     

A mechanistic model-based force-feedback scheme for voice-coil actuated radial contour turning

In this paper, a mechanistic model-based force feedback scheme is presented for improving the tracking performance of radial contour turning (also known as the non-circular turning process) with a voice-coil actuator. The current form of voice-coil actuation mechanism (with acceleration feedback) is briefly described and its limitations for high frequency disturbance rejection are identified. Stability issues for the proposed force feedback scheme are discussed via small gain theorem. Tracking performance improvements due to the force feedback scheme are investigated via simulations for different types of non-circular contours and cutting conditions. The effects of various process parameters on relative tracking improvements are also analyzed.     

A fast tool servo design for precision turning of shafts on conventional CNC lathes

A technique for precision turning of shafts on conventional CNC turning centers is presented. The shaft is semi-turned on a conventional CNC lathe. The precision finish turning operation is delivered by a piezoelectric based fast tool servo which is mounted on the same CNC lathe's turret. The precision tool tip motion is delivered by a proposed sliding mode controller which is robust to changes in the cutting process and hysteresis in the piezo actuator. Sliding mode controller is also quick to compensate the cutting force disturbances, and keeps the tool tip at the desired location within the displacement measurement sensor resolution (±0.1 μm). The fast tool servo system is packaged in a PC, and its effectiveness is demonstrated on a bearing location turning.     

A method for measuring cutting forces in boring operations

In boring operations, two methods of measuring cutting forces are possible: measurement of forces exerted on the tool, by means of a dynamometric boring bar, or measurement of forces exerted on the workpiece, by means of a dynamometric table.In the second method, it is difficult to read the three components of the cutting force (tangential, radial and axial force), because the tool is rotating with respect to the workpiece. A three-component dynamometer on which the workpiece is clamped gives the axial (feed) force directly. The other two outputs, instead, are projections on two fixed axes of a force that is the sum of the radial and tangential components, and that rotates at spindle speed.This paper describes a simple, reliable method for solving the problem of obtaining the single components of the rotating force. Tangential and radial forces are measured continuously by means of an electrical resolver and lowcost electronic equipment.     

A mechanistic force model for combined axial–radial contour turning

In this paper, a mechanistic force model for combined axial–radial contour turning is presented. Analytical expressions are derived for the computation of the mechanistic parameters as a function of the axial and radial contour variations. The force model is experimentally validated for axial and radial contour turning processes. The effects of the combined axial–radial contour variations and the tool geometry parameters on the cutting forces are analyzed via additional simulations for combined contour turning.     

花岗石锯切过程中的锯切力特征

本文通过测量和分析锯切花岗石过程中锯切力以及锯切功率，对锯片所受的单位宽度法向力Fn‘和切向力Ft‘以及单颗金刚石磨粒所平均承受的法向力和切向力进行了研究，实验过程中在保持金刚石节块表面状态基本不变的情况下，对锯切深度ap，进给速度vf和锯片圆周线速度Vs进行了较大范围的变化，另外还对锯片磨损过程中锯切力的变化进行了跟踪测量。