圆锥刀侧铣非可展直纹面刀轴轨迹规划的特征线方法

针对圆锥刀侧铣加工非可展直纹面中复杂的刀轴轨迹规划问题,提出一种直观简便的刀轴轨迹生成方法。利用圆锥面的性质,给出法向映射曲线的定义即刀具轴线上诸点在设计曲面上的法向投影点的集合,将刀具包络面向设计曲面的逼近问题转化为每个刀位下法向映射曲线与特征线的最小二乘逼近问题,并给出刀具包络面尚未形成时单刀位下理想特征线的生成方法。用两点偏置法生成初始刀位,以此为基准,利用刚体运动学方法将刀轴位姿描述为3个回转与3个平移运动参数的函数,从而建立单刀位优化条件与6个运动参数的非显性的函数关系。采用拉丁超立方的试验设计方法求解,分析并优选计算过程中的影响因素,得到最优刀位,进而获得优化后的刀轴轨迹面。实例计算可知,刀轴优化后的包络误差显著降低,并且计算结果稳定。该方法可为非可展直纹面的圆锥刀侧铣加工提供一定的理论依据。     

Grey–Taguchi method to optimize the milling parameters of aluminum alloy

The grey–Taguchi method was adopted in this study to optimize the milling parameters of A6061P-T651 aluminum alloy with multiple performance characteristics. A grey relational grade obtained from the grey relational analysis is used as the performance characteristic in the Taguchi method. Then, the optimal milling parameters are determined using the parameter design proposed by the Taguchi method. Experimental results indicate that the optimal process parameters in milling A6061P-T651 aluminum alloy can be determined effectively; the flank wear is decreased from 0.177 mm to 0.067 mm and the surface roughness is decreased from 0.44 μm to 0.24 μm, leading to a multiple performance characteristics improvement in milling qualities through the grey–Taguchi method.     

Highly accurate 5-axis flank CNC machining with conical tools

A new method for 5-axis flank computer numerically controlled (CNC) machining is proposed. A set of tappered ball-end-mill tools (aka conical milling tools) is given as the input and the flank milling paths within user-defined tolerance are returned. Thespace of lines that admit tangential motion of an associated truncated cone along a general, doubly curved, free-form surface is explored. These lines serve as discrete positions of conical axes in 3D space. Spline surface fitting is used to generate a ruled surface that represents a single continuous sweep of a rigid conical milling tool. An optimization-based approach is then applied to globally minimize the error between the design surface and the conical envelope. The milling simulations are validated with physical experiments on two benchmark industrial datasets, reducing significantly the execution times while preserving or even reducing the milling error when compared to the state-of-the-art industrial software.     

Tool path planning for five-axis flank milling with developable surface approximation

This paper presents a novel approach that automatically generates an interference-free tool path for five-axis flank milling of a ruled surface. A boundary curve of the machined surface is subdivided into curve segments. Each segment works as a guide curve in the design method for developable Bézier surface that controls a developable patch for approximating the surface with available degrees of freedom. Geometric algorithms are proposed for calculating consecutive patches with G¹ continuity across the patch boundary. A tapered tool can move along the rulings of these patches without inducing local tool interference as a result of their developability. The machining deviation is controlled by the surface approximation error. A machining test is conducted with the generated CL data and the result verifies the feasibility of the proposed approach. This work successfully transforms avoidance of tool interference into a geometric modeling problem and provides a simple solution. It thus demonstrates a good potential for the developable surface theory of five-axis flank machining .     

铣削钛合金加工表面形貌特征参数的预测

钛合金在铣削过程中受迫振动明显,刀—工接触关系不断变化,加工表面形貌特征参数难以预测,已成为制约加工表面质量进一步提高的瓶颈。针对铣削振动与加工表面形貌的非线性随机变化特性进行了切削钛合金试验,采用高斯过程回归法构建铣削振动作用下的加工表面形貌高斯过程模型。分析刀齿误差和铣削振动对加工表面形貌特征参数的影响规律,为以加工表面质量分布一致性为前提的铣削钛合金工艺设计提供参考依据。     

An analytical approach to cutting force prediction in milling of carbon fiber reinforced polymer laminates

ABSTRACT

A prediction model of cutting force for milling multidirectional laminate of carbon fiber reinforced polymer (CFRP) composites was developed in this article by using an analytical approach. In the predictive model, an equivalent uniform chip thickness was used in the case of orthogonal plane cutting, and the average specific cutting energy was taken as an empirical function of equivalent chip thickness and fiber orientation angle. The parameters in the model were determined by the experimental data. Then, the analytical model of cutting force prediction was validated by the experimental data of multidirectional CFRP laminates, which shows the good reliability of the model established. Furthermore, the cutting force component of flank contact force was correlated with the surface roughness of workpiece and the flank wear of tool in milling UD-CFRP composites. It was found that surface quality as well as flank wear has a co-incident varying trend with the flank contact force, as confirmed by the observations of the machined surfaces and tool wear at different fiber orientations. So, it can be known that low flank contact force be required to reduce surface damage and flank wear.     

模具钢铣削中刀具磨损的试验研究

以面铣刀刀片磨损为研究对象,结合类神经网络系统建构高速数控铣削加工的预测模型。以加工参数为模型输入条件,刀腹磨耗为输出条件。采用多因素试验方法,选择切削速度、进给速度、切削深度三个试验参数,利用直交表式的试验计划法设计试验点。依照试验点铣削工件后再测量刀具加工后的刀腹磨耗量,进而求得倒传递网络所需的36组训练范例与11组验证数据。刀腹磨耗预测模式是利用类神经网络中的倒传递网络原理,以田口法求得倒传递网络参数的最优值。试验结果显示,刀腹磨耗随着切削速度、进给速度、切削深度增加而上升。铣削模具钢后,刀具磨耗预测值的平均误差为4.72%,最大误差为11.43%,最小误差为0.31%。整体而言,类神经网络对于铣削加工可进行有效预测。     

开式整体叶盘通道侧铣粗加工技术的研究

整体叶盘从锻造毛坯到最终零件加工成型,需要切除大量的多余材料。本文提出了一种开式整体叶盘通道区域五坐标粗加工刀具轨迹规划方法。该方法通过生成整体叶盘薄壁叶片的直纹包络面,以确定叶盘通道粗加工区域的边界轮廓;基于直纹面五轴侧铣加工刀具轨迹双点偏置生成方式,利用投影法规划开式整体叶盘通道区域粗铣加工的刀心点轨迹与刀轴矢量方向。加工实践表明,开式整体叶盘的粗加工效率提高30%以上,同时,显著优化了后续半精加工和精加工工序的环境。     

Geometry design model of a precise form-milling cutter based on the machining characteristics

This paper presents a new approach to design a form milling cutter for precisely obtaining the complex free-form surfaces. In this study, the intersection point of the rake surface, helix flute and clearance flank is appropriately defined due to its significant role in the design and grinding performance. The angle-solid-block analysis is developed to establish the new cutter geometry model. Hence, a new form-milling cutter satisfying the requirements of machining characteristics of workpiece can be designed. In addition, the cutter geometric model can be adopted to map out the measuring strategy with minimum measured points to attain the exact geometric feature of cutter.     

基于正向杜邦指标线的五坐标侧铣加工

为实现叶轮类零件的多坐标侧铣加工,通过引入正向杜邦指标线,利用鼓锥形刀对自由曲面的五坐标侧铣加工进行研究。针对具有严格凸切削刃的侧铣加工刀具,提出不发生局部干涉的充要条件是切触点处刀具曲面的正向杜邦指标线位于被加工曲面的正向杜邦指标线之内。给出利用鼓锥形刀侧铣加工自由曲面时实施干涉检查的判断准则以及消除干涉的修正方法,推导出具有严格凸切削刃的刀具在给定的残留高度下侧铣加工带宽的计算方法。在此基础上,利用等残留高度法实现鼓锥形刀侧铣加工自由曲面无干涉刀具轨迹的生成。算例表明,在相同残留高度下,鼓锥形刀侧铣较之球头刀加工效率提高37.44%,说明侧铣加工是提高切削效率和加工质量的一种有效途径。     

Barrel cutter design and toolpath planning for high-efficiency machining of freeform surface

Improvement of machining efficiency is always one of the most interesting problems in CNC machining. Traditionally, the ball-end cutter is widely used in sculptured surface machining for the highly flexible controllability. But the process efficiency is low especially for freeform surface machining, which generally needs multiple tool-paths. To improve the machining efficiency of multi-axis flank milling of freeform surface, a novel barrel cutter design method is proposed in this paper. There are two principle parameters determining the revolution surface of the barrel cutter: the radius of the generatrix curve and the maximum rotating radius. The main work in this paper is to calculate the two parameters for strip-width-maximization machining without local over-gouging. Firstly, the curvature properties are introduced by the geometry model of the barrel cutter. Then the contact condition between the barrel cutter and the freeform surface is analyzed, relationship between cutter parameters and surface curvature is derived. To avoid the over-gouging, based on the curvature constraint, the designed surface is fitted into the cutter surface by surface approximation theory, so that the cutter surface can approach to the designed surface as close as possible. After that, toolpath planning method for milling of freeform surface with the barrel cutter is presented. Finally, machining implementations are presented to verify the effectiveness of the proposed method.     

Optimization of surface roughness and flank wear using the Taguchi method in milling of Hadfield steel with PVD and CVD coated inserts

In this paper, the Taguchi method and regression analysis have been applied to evaluate the machinability of Hadfield steel with PVD TiAlN- and CVD TiCN/Al₂O₃-coated carbide inserts under dry milling conditions. Several experiments were conducted using the L₁₈ (2 × 3 × 3) full-factorial design with a mixed orthogonal array on a CNC vertical machining center. Analysis of variance (ANOVA) was used to determine the effects of the machining parameters on surface roughness and flank wear. The cutting tool, cutting speed and feed rate were selected as machining parameters. The analysis results revealed that the feed rate was the dominant factor affecting surface roughness and cutting speed was the dominant factor affecting flank wear. Linear and quadratic regression analyses were applied to predict the outcomes of the experiment. The predicted values and measured values were very close to each other. Confirmation test results showed that the Taguchi method was very successful in the optimization of machining parameters for minimum surface roughness and flank wear in the milling the Hadfield steel.     

Prediction of flank wear and engagements from force measurements in end milling operations

On-line knowledge of tool engagement and flank wear is critical for successful adaptive control of a machining operation. A method combining a mechanistic model and empirical relationships has been developed for helical end milling operations. Computation of cutting tool engagements and flank wear width occurs in real time as the cutting progresses using averaged force data. Response surface methodology has been used to investigate the effects of the process and operating variables on the process-dependent parameters; a second order relationship was obtained. The approach can also determine variation of wear land width along the length of the tool as axial engagement changes.     

Precision compensation method for tooth flank measurement error of hypoid gear

When measuring the tooth flank of hypoid gear, the measurement datum surface (the large end surface of the gear) does not always coincide with the design bases (the theoretical mounting distance), and this non-coincidence error would affect the tooth flank measurement results. Based on the measurement theory of the hypoid gear tooth flank, a precision matching method of the theoretical tooth surface and the measured tooth surface is designed, the objective function of the tooth flank matching method is established, and the search iterative method was used to calculate the compensation value of the measurement error of the tooth flank, when the two gear tooth surface is most accurately matched. As the mounting distance of the hypoid gear changes, two experiments are done to verify the proposed method. The experiment results show that, for different tooth flank of the measured gear, the measuring error of the tooth flank along Z-axis dropped significantly after compensated by this method, more than 80% of the error along Z-axis are compensated. It is obvious that this method could improve the measurement accuracy of the tooth flank form of hypoid gear.     

发动机叶轮侧铣数控加工方法及误差计算

为提高发动机叶轮的加工效率和加工质量,给出了一种新的利用球头铣刀侧刃线接触加工非可展直纹面整体叶轮的刀位轨迹计算方法。针对其中必定存在的理论误差问题,介绍了一种新的计算误差大小的数学方法。方法易于编程实现,计算结果准确。     

Adaptive Gregory Patch Approximation to Z-Map Data

A method is proposed for Gregory surface approximation to 3D array data points. Surface approximation is the process of constructing a compact representation to model an object surface based on a fairly large number of measured 3D data points. Based on an adaptive subdivision technique, the proposed method begins with a rough initialisation of the surface and progressively refines it in successive steps in the regions where the data is poorly approximated. The method has been implemented using piecewise bicubic Gregory patches with G 1 continuity. An advantage of this approach is that the refinement is essentially local, reducing the computational requirements that permit the processing of a large number of data points This method, combined with the inverse offsetting method, can be used to obtain an offset surface without self-interference. The offset surface can be used to generate gouging-free CL tool paths for machining compound surfaces on milling machines.     

齿轮盘铣刀后刀面多轴联动数控磨削仿真

设计直纹面组合刀头,对盘形齿轮铣刀后刀面的数控磨削加工进行仿真.首先根据后刀面设计的理论公式,提出参数化设计方法,给出了在不同前后角参数下后刀面磨削点坐标计算公式及UV网坐标.分析、计算出磨削过程中对应的旋转轴数据,并推导出砂轮半径补偿计算公式.然后,用曲率方法分析磨削时的局部干涉现象,推导出避免局部干涉的砂轮半径可选...     

A Novel Method of Efficient Machining Error Compensation Based on NURBS Surface Control Points Reconstruction

A novel method to improve the efficiency of error compensation in free-form surface machining based on the Non-Uniform Rational B-Splines (NURBS) surface control points reconstruction is proposed in this article. With the presented method, a relatively small number of inspection points are needed to be measured for error compensation. The machined surface is obtained by reconstructing the control points of the designed surface based on the on-machine measurement data. The machining error of the surface is obtained by calculating the difference between the machined surface and the designed one. Then a compensate surface is achieved using the mirror symmetry model and surface modification method to compensate the machining error. Experimental validation for the milling of a NURBS surface shows that the machining accuracy of the surface is improved by 62.57% through use of the proposed method.     

Envelope surface formed by cutting edge under runout error in five-axis flank milling

This paper investigates the analytical envelope surface model formed by specially designed cutting edge under cutter runout error, including axis offset error and tilt error, in five-axis flank milling. This model, which is independent of the machine tool type, is determined by the tangency condition in envelope theory. First, the cutter runout is defined by four parameters, namely offset distance, offset direction angle, locating angle, and tilt angle. Then, the cutting edge represented by cubic B-spline curve is used as the generator of cutter rotation surface to formulate the closed-form envelope surface model. In particular, the runout error and feedrate are both integrated into the model. In addition, we study special cases of the analytical model and the runout effect on envelope surface. Finally, computer example validates the feasibility of the proposed model with runout. We find that envelope surface formed by cutter edge is different from each other at the existence of runout, and envelope surface dedicated to final machined surface is generated by the composition of some segments of cutter edges. The results can be applied to tool path optimization in five-axis flank milling and NC simulation with cutter runout.     

Tool wear rate prediction in ultrasonic vibration-assisted milling

Abstract

In the current study, a predictive model on tool flank wear rate during ultrasonic vibration-assisted milling is proposed. One benefit of ultrasonic vibration is the frequent separation between tool and workpiece as the cutting time is reduced. In order to account for this effect, three types of tool–workpiece separation criteria are checked based on the tool center instantaneous position and velocity. Type I criterion examines the instantaneous velocity of tool center under feed movement and vibration. If the tool is moving away from workpiece, there is no contact. Type II criterion examines the position of tool center. If the tool center is far from the uncut workpiece surface, there is no contact even though the tool is getting closer. Type III criterion describes the smaller chip size due to the overlaps between current and previous tool paths as a result of vibration. If any criterion is satisfied, the tool flank wear rate is zero. Otherwise, the flank wear rate is predicted considering abrasion, adhesion and diffusion. The proposed predictive tool flank wear rate model is validated through comparison to experimental measurements on SKD 61 steel with uncoated carbide tool. The proposed predictive model is able to match the measured tool flank wear rate with high accuracy of 10.9% average percentage error. In addition, based on the sensitivity analysis, smaller axial depth of milling, larger feed per tooth or higher cutting speed will result in higher flank wear rate. And the effect of vibration parameters is less significant.