曲面数控加工精度的研究

分析了影响曲面数控加工精度的因素,研究并提出了从数控程序设计、工艺系统和控制系统等方面提高曲面加工精度的方法。结果表明：数控加工工艺系统特性和数控系统误差是影响加工精度的重要因素,应尽量购置高精度的机床和数控系统,或采用工艺手段,或设置相应补偿参数,由系统自动补偿功能消除;程序设计的优劣也是影响加工精度的主要因素,应从刀具、加工方法、进退刀与走刀方式的选择和刀具路径规划的验证等方面采取措施,以保证曲面加工精度。     

螺旋桨叶面加工误差在线测量及补偿

为了解决在螺旋桨加工过程中由于刀具磨损、刀具和工件的变形等因素造成的叶面加工误差的问题,从逆向工程角度考虑了一种曲面重构的方法来补偿加工误差。根据多叶片螺旋桨的加工特点,采用在线测量成型叶面的加工误差值,并进行叶面点处理和叶面重构,对重构的叶面进行偏差分析,将满足拟合精度的叶面代替原叶面作为部件几何体进行加工,从而达到对原叶面加工误差的补偿效果。通过补偿前后曲面加工误差的对比实验,验证了曲面重构降低加工误差的有效性。该补偿方式对提高螺旋桨叶面加工精度具有重要意义。     

空间三维刀具误差补偿研究

目的研究空间三维状态下刀具误差补偿方法,提高多轴加工复杂自由曲面表面轮廓精度。方法首先对五轴加工中刀具与工件接触方式及刀具中心点、刀具接触点位置及矢量关系进行了分析,推导出空间刀具误差补偿数学模型,通过MATLAB初步对补偿算法进行了验证。基于双摆头式五轴机床运动学模型,结合刀具误差补偿模型,开发了带有刀具误差补偿功能的专用后置处理器。最后,通过开发的专用后置处理软件进行G代码转换,采用某叶片试件进行了仿真和实际切削实验,并对实验结果进行了分析。结果在复杂曲面加工中,通过合理的刀具误差补偿方法,可获得理论刀具尺寸下同样的表面质量及轮廓精度。刀具误差补偿值越小,补偿效果越明显,加工效果与理论结果越接近。叶片试件分别采用φ8、φ9、φ9.5及φ10刀具仿真加工,与理论φ10刀具加工的数据对比,三种尺寸刀具补偿加工后的残留误差差值分别约为0.08、0.06、0.04 mm,其中φ9.5的刀具误差补偿后的加工效果与理论结果最接近。结论采用刀具空间误差补偿方法,可获得与理论刀具一样的切削效果,有效提高零件的表面质量,不仅可以获得稳定的复杂零件轮廓精度,还可以减少辅助时间。误差补偿效果与实际补偿值的大小有关,补偿值越小,补偿效果越好。     

自由曲面数控三坐标投影加工误差及补偿对策

分析了自由曲面三坐标投影法数控加工的步长误差和行距误差。提出了自由曲面三坐标投影加工误差补偿对策。引入控制参数Δz,根据曲面加工精度要求设定限值Δzmax,当Δz>Δzmax时,进行插入刀位处理,以保证曲面加工精度。     

侧铣加工空间刀具半径补偿技术实现

通过对侧铣加工空间刀具半径补偿算法的研究,建立刀具和工件模型,并对其进行了求解和公式推导。对任意侧铣加工曲面进行偏置计算,生成带有刀具半径补偿的侧铣偏置曲面,从而解决了侧铣加工中曲面偏置位置的问题,实现了侧铣加工空间刀具半径补偿,该方法的应用为数控系统研究侧铣空间刀具半径补偿提供了参考。     

超精密铣削加工自由曲面光学元件误差补偿方法

为提高超精密金刚石铣削加工自由曲面光学元件的加工精度和消除光学系统设计误差,提出了一种适用于多轴金刚石铣削加工的误差补偿方法。通过建立自由曲面光学元件铣削加工过程中的刀具误差模型,用于校正刀尖半径误差、径向偏移误差以及刀具不平整度误差。标准球面测试结果显示其主要误差源产生的残余误差由194nm降低为40nm。在黄铜工件表面加工得到的自由曲面光学表面峰谷值误差和残余误差分别为336nm和49nm,证明了该误差修正方法的有效性。     

细长轴加工的单片机误差补偿系统设计

建立细长轴车削的数学模型,分析细长轴加工误差来源。设计一个误差补偿系统,利用单片机实时检测细长轴零件的变形,从而控制刀具的切削用量。试验结果表明:该系统可以有效提高零件的加工精度。     

刀具参数对非线性误差的影响规律及控制方法研究

针对复杂曲面五轴加工过程中,数控系统的插补原理会导致旋转轴在线性插补过程中偏离理想运动平面,继而引起非线性误差并严重影响曲面的加工精度问题,研究刀具参数对非线性误差的影响至关重要。根据五轴联动过程中刀具的运动规律建立了相应的运动方程,获得刀具参数对非线性误差影响的数学模型;应用MATLAB对3种类型刀具引起的非线性误差进行仿真分析,得到刀具参数对非线性误差的影响规律并提出有效控制非线性误差的措施;最后通过某叶轮的仿真加工验证刀具参数对非线性误差的影响规律。     

小深孔镗孔加工误差补偿方法研究

镗孔加工尺寸误差补偿是控制镗孔加工尺寸分散度、保证零件互换性的一种经济、有效的方法,而镗孔刀具微量补偿装置是实现误差补偿的关键技术之一.针对小深孔钻镗加工环境,设计一套高精度补偿的压电式微量补偿装置,该装置具有微米精度的在线镗削误差补偿功能.设计一种新型的抗振镗杆,有效减少了因加工过程中震动而带来的加工尺寸误差问题.该新型的刀具微量补偿方法能够满足大悬臂小深孔精密加工的要求.     

侧铣不可展直纹面模具原理性加工误差计算方法

分析了侧铣不可展直纹面模具的原理性加工误差的来源及特点，提出通过计算被加工表面各点到刀具旋转轴扫掠面的距离以确定误差分布，为刀位主动补偿和后续加工提供了依据。采用有限次离散和平面替代的方法求取点到曲面之间的距离，根据求解精度要求确定曲面最小离散次数，提高了计算效率，平面替代法将问题简化为可精确求解的点到平面的距离问题。实例通过与三坐标测量结果的对比验证了算法的可靠性。     

The prediction of dimensional error for sculptured surface productions using the ball-end milling process. Part 1: Chip geometry analysis and cutting force prediction

The study of machining errors caused by tool deflection in the balkend milling process involves four issues, namely the chip geometry, the cutting force, the tool deflection and the deflection sensitivity of the surface geometry. In this paper, chip geometry and cutting force are investigated. The study on chip geometry includes the undeformed radial chip thickness, the chip engagement surface and the relationship between feed boundary and feed angle. For cutting force prediction, a rigid force model and a flexible force model are developed. Instantaneous cutting forces of a machining experiment for two 2D sculptured surfaces produced by the ball-end milling process are simulated using these force models and are verified by force measurements. This information is used in Part 2 of this paper, together with a tool deflection model and the deflection sensitivity of the surface geometry, to predict the machining errors of the machined sculptured surfaces.     

The prediction of dimensional error for sculptured surface productions using the ball-end milling process. Part 2: Surface generation model and experimental verification

This paper presents a surface generation model for sculptured surface productions using the ball-end milling process. In this model, machining errors caused by tool deflections are studied. As shown in Part 1 of this paper, instantaneous horizontal cutting forces can be evaluated from the cutting geometries using mechanistic force models. In this paper, a tool deflection model is developed to calculate the corresponding horizontal tool deflection at the surface generation points on the cutter. The sensitivity of the machining errors to tool deflections, both in magnitude and direction, has been analyzed via the deflection sensitivity of the surface geometry. Machining errors are then determined from the tool deflection and the deflection sensitivity of the designed surface. The ability of this model in predicting dimensional errors for sculptured surfaces produced by the ball-end milling process has been verified by a machining experiment. In addition to providing a means to predict dimensional accuracy prior to actual cutting, this surface generation model can also be used as a tool for quality control and machining planning.     

PCD刀具加工有色金属的研究

本文主要研究PCD刀具加工有色金属时刃口及后刀面的刃磨质量对切削表面质量的影响。首先对PCD刀具切削有色金属模型进行了分析研究,然后分别采用金属结合剂金刚石砂轮、树脂结合剂金刚石砂轮和陶瓷结合剂金刚石砂轮刃磨出三把不同质量的PCD刀具进行了切削对比试验,并用扫描电镜对切削表面微观形貌进行了观察分析,发现加工有色金属时,PCD刀具后刀面与刃口刃磨质量对切削表面质量有着同等重要的影响作用。     

Dimensional errors in longitudinal turning based on the unified generalized mechanics of cutting approach.: Part I: Three-dimensional theory

During the machining of a part, a new surface is generated together with its dimensional deviations. These deviations are due to the presence of several phenomena (workpiece deflection under strong cutting forces, vibration of the machine tool, material spring-back, and so on) that occur during machining. Each elementary phenomenon results in an elementary machining error. Consequently, the accuracy of the manufactured workpiece depends on the precision of the manufacturing process, which it may be controlled or predicted.The first part of this work presents a new model to evaluate machining accuracy and part dimensional errors in bar turning. A model to simulate workpiece dimensional errors in longitudinal turning due to deflection of the tool, workpiece holder and workpiece is shown. The proposed model calculates the real cutting force according to the Unified Generalized Mechanics of Cutting approach proposed by Armarego, which allows one to take into account the three-dimensional nature (3D) of the cutting mechanism. Therefore, the model developed takes advantage of the real workpiece deflection, which does not lie in a plane parallel to the tool reference plane, and of the real 3D cutting force, which varies along the tool path due to change in the real depth of cut. In the first part of the work the general theory of the proposed approach is presented and discussed for 3D features. In the second part the proposed approach is applied to real cases that are mostly used in practice. Moreover, some experimental tests are carried out in order to validate the developed model: good agreement between numerical and experimental results is found.     

Refrigerated cooling air cutting of difficult-to-cut materials

One approach to enhance machining performance is to apply cutting fluids during cutting process. However, the use of cutting fluids in machining process has caused some problems such as high cost, pollution, and hazards to operator's health. All the problems related to the use of cutting fluids have urged researchers to search for some alternatives to minimize or even avoid the use of cutting fluids in machining operations. Cooling gas cutting is one of these alternatives. This paper investigates the effect of cooling air cutting on tool wear, surface finish and chip shape in finish turning of Inconel 718 nickel-base super alloy and high-speed milling of AISI D2 cold work tool steel. Comparative experiments were conducted under different cooling/lubrication conditions, i.e. dry cutting, minimal quantity lubrication (MQL), cooling air, and cooling air and minimal quantity lubrication (CAMQL). For this research, composite refrigeration method was adopted to develop a new cooling gas equipment which was used to lower the temperature of compressed gas. The significant experimental results were: (i) application of cooing air and CAMQL resulted in drastic reduction in tool wear and surface roughness, and significant improvement in chip shape in finish turning of Inconel 718, (ii) in the high-speed milling of AISI D2, cooling air cutting presented longer tool life and slightly higher surface roughness than dry cutting and MQL. Therefore, it appears that cooling air cutting can provide not only environment friendliness but also great improvement in machinability of difficult-to-cut materials.     

Cutting conditions for finish turning process aiming: the use of dry cutting

To avoid the use of cutting fluids in machining operations is one goal that has been searched for by many people in industrial companies, due to ecological and human health problems caused by the cutting fluid. However, cutting fluids still provide a longer tool life for many machining operations. This is the case of the turning operation of steel using coated carbide inserts. Therefore, the objective of this work is to find cutting conditions more suitable for dry cutting, i.e., conditions which make tool life in dry cutting, closer to that obtained with cutting with fluid, without damaging the workpiece surface roughness and without increasing cutting power consumed by the process. To reach these goals several finish turning experiments were carried out, varying cutting speed, feed and tool nose radius, with and without the use of cutting fluid. The main conclusion of this work was that to remove the fluid from a finish turning process, without harming tool life and cutting time and improving surface roughness and power consumed, it is necessary to increase feed and tool nose radius and decrease cutting speed.     

The effect of vibration cutting on minimum cutting thickness

In the ultra-precision diamond cutting process, the rake angle of the tool becomes negative because the edge radius of a tool is considerably larger compared to the sub-micrometer depth of the cut. The effects of plowing due to the large negative rake angle result in an unstable cutting process without continuous chip. For this reason, it is important to determine minimum cutting thickness in order to enable greater machining accuracy to be obtained by fine and stable machining. It was previously reported that the critical depth of cut with a continuous chip was determined by the tool sharpness and the friction coefficient between a workpiece and a tool [S.M. Son, et al., Effects of the friction coefficient on the minimum cutting thickness in micro cutting, International Journal of Machine Tools and Manufacture 45 (2005) 529–535]. For the same edge radius of a tool, the higher the friction coefficient of the tool–workpiece, the thinner the minimum cutting thickness becomes. Therefore, it is believed that increasing the friction coefficient by a physical method would be effective to achieve thinner stable cutting. In this study, the possibility of reducing the minimum cutting thickness was investigated through changing the friction coefficient of a tool–workpiece. The vibration cutting method is applied to increase the friction coefficient. Experimental results show that the cutting technology is efficient for increasing the friction coefficient and decreasing the minimum cutting thickness. The minimum cutting thickness was reduced by about 0.02–0.04 μm depending on materials and vibration conditions.     

Tool deflection and geometrical error compensation by tool path modification

Accuracy of CNC machined components is affected by a combination of error sources such as tool deflection, geometrical deviations of moving axis and thermal distortions of machine tool structures. Some of these errors can be decreased by controlling the machining process and environmental parameters. However other errors like tool deflection and geometrical errors that have a big portion of total error need more sophisticated solutions. Conventional error reduction methods are considered as low efficiency and human dependent methods. Most of recently developed solutions cannot fulfill workshop needs and are limited to research papers. In the present study, machining code modification strategy has been considered as an applicable and effective solution to enhance precise machined components. Appropriate tool deflection estimation model as well as geometrical error analyzing methods have been selected and complementary algorithms for compensation of these errors have been developed. Metal cutting process has been modeled in a 3D simulation environment and implemented in force/deflection calculations. A software has been developed to generate compensated tool path NC program by tracing the initial tool path and compensating deflection/geometry deviations. The new procedure developed in the present work has been validated by machining Spline contours. The results show that using the new method, accuracy of machined features can be improved by about 8-10 times in a single pass.     

A study of back cutting surface finish from tool errors and machine tool deviations during face milling

The surface finish of mechanical components produced by face milling is given by factors such as cutting conditions, workpiece material, cutting geometry, tool errors and machine tool deviations. The contribution of the different tool teeth to imperfections in the machined surface is strongly influenced by tool errors such as radial and axial runouts. The surface profile of milled parts is not only affected by chip removal due to front cutting, but also by back cutting, which must be taken into account when predicting surface roughness. In the present work, the influence of back cutting on the surface finish obtained by face milling operations is studied. Final part surface roughness is modelled from tool runouts and height deviations that affect the surface marks provoked by back cutting. Round insert cutting tools and surface positions defined by cutter axis trajectory are considered, and milling experiments are developed for a spindle speed of 750 rpm, depth of cut of 0.5 mm and feeds from 0.4 to 1.0 mm/rev. Experimental observations are compared with the theoretical predictions provided by the surface roughness model, and good agreement is found between both results. Surface imperfections caused by front and back cutting are analysed, and discrepancies between experiments and numerical predictions are explained by undeformed chip thickness variations along the tool tooth cutting edge, the tearing of the workpiece material, and fluctuations in the feedrate and height deviation during machine tool axis displacement.     

A study of the tool-chip interface contact problem under low cutting velocity with an elastic cutting tool

To understand the effects of elastic deformation of the tool and the crater phenomenon generated by the cutting force and high pressure during metal cutting processing on the cutting process, an iterative mathematical model for calculating the tool-chip contact is developed in this paper under the assumption of elastic cutting tools. In this model, the finite-element method is used to simulate the cutting of mild steel by a cutting tool of three different materials. The results obtained in the simulation are found to match experimental data reported by related studies. The simulation results also indicate that tools with a smaller stiffness produce greater elastic deformation. Further, decrease of the rake angle due to elastic deformation of the tool can result in greater difficulty in internal deformation of the material and an increase in cutting force. The micro-crater phenomenon on the tool face generated by high pressure at the tool-chip interface is the preliminary symptom of crater wear on the tool face. Therefore, under some machining conditions, such as in precision machining or in automation processing where tool compensation is required, the phenomenon of elastic deformation of the tool must be considered carefully to ensure product precision.