铣削加工粗糙度的智能预测方法

提出了一种基于最小二乘支持向量机的铣削加工表面粗糙度智能预测方法.首先进行了铣削工艺参数对工件表面粗糙度影响的正交实验,再通过对主轴转速、进给速率和切削深度三因素,以及各因素之间交互三水平实验的数据分析,找出了铣削工艺参数对工件表面粗糙度影响的一些规律.利用最小二乘支持向量机算法建立了铣削预测模型,通过该模型能在有限实验基础上利用工艺参数方便地得到粗糙度预测值.实际预测表明,在相同情况下,该模型构造速度比反向传播神经网络建模预测方法高2个～3个数量级,预测精度高10倍左右.     

New mathematical method for the determination of cutter runout parameters in flat-end milling

The cutting force prediction is essential to optimize the process parameters of machining such as feed rate optimization, etc. Due to the significant influences of the runout effect on cutting force variation in milling process, it is necessary to incorporate the cutter runout parameters into the prediction model of cutting forces. However, the determination of cutter runout parameters is still a challenge task until now. In this paper, cutting process geometry models, such as uncut chip thickness and pitch angle, are established based on the true trajectory of the cutting edge considering the cutter runout effect. A new algorithm is then presented to compute the cutter runout parameters for flat-end mill utilizing the sampled data of cutting forces and derived process geometry parameters. Further, three-axis and five-axis milling experiments were conducted on a machining centre, and resulting cutting forces were sampled by a three-component dynamometer. After computing the corresponding cutter runout parameters, cutter forces are simulated embracing the cutter runout parameters obtained from the proposed algorithm. The predicted cutting forces show good agreements with the sampled data both in magnitude and shape, which validates the feasibility and effectivity of the proposed new algorithm of determining cutter runout parameters and the new way to accurately predict cutting forces. The proposed method for computing the cutter runout parameters provides the significant references for the cutting force prediction in the cutting process.     

Enhancement of a simplified model for maximum stress prediction

A simplified model for rapid estimation of maximum subsurface stress was previously reported by the authors. That model was found to predict the upper bound of the maximum von Mises stress in each layer below any surface with good accuracy. In this work, the model is enhanced by quantifying the difference between the predicted upper bound and the maximum stress for a specific rough surface. This is done by evaluating stress predictions for real rough surfaces, sinusoidal surfaces, ideal textured surfaces, and real rough surfaces with imposed computer generated texture. The difference between the predicted upper bound and the surface-specific maximum stress is found to be related to that surface’s roughness. The origin of this relationship is investigated in terms of apparent contact area. The enhanced simplified model provides an efficient means of estimating maximum stress in rough surface contact.     

平头螺旋刃立铣刀切削力预报模型的建立与数值仿真(一)——刀具几何参数对铣削力的影响

铣削力对刀具变形、工件变形、刀具寿命、加工表面质最均有重要影响,是计算切削功率,设计和使用机床、刀具、夹具和优化加工工艺不可缺少的依据,并直接影响切削热的产生.由于缺乏精确的切削力信息,在生产车间实际加工中通常采用较保守的加工条件,致使加上效率降低和生产成本提高.因此建立可靠的切削力预报模型,在实际加工之前预测出切削力...     

基于粗糙度形成机理的曲面高速铣精加工参数选用

为在曲面精加工中获得理想的表面粗糙度,通过分析表面粗糙度的形成机理,建立了粗糙度与走刀行距、进给率关系的数学模型;通过实验,建立了高速曲面铣削时粗糙度与加工倾角、主运动线速度关系的图谱,实现了在生产过程中按照加工目标的表面粗糙度确定相应的走刀行距、进给率、加工倾角、主运动线速度等加工参数.研究结果表明,该研究对提高加工...     

A numerical study of the effects of cutter runout on milling process geometry based on true tooth trajectory

Cutter runout is a common phenomenon affecting the cutting performances in milling operations. To date, most of the milling process models considering cutter runout were established based on the circular tooth path approximation, which brought errors into the runout estimation. In this paper, a new approach is presented for modelling the milling process geometry with cutter runout based on the true tooth trajectory of cutter in milling. The mathematical relationship between the trajectories generated by successive cutter teeth with runout is analysed. The milling process geometrical parameters, including the instantaneous undeformed chip thickness, the entry and exit angles of a cutting tooth, and the ideal peripheral machined workpiece surface roughness, are modelled according to the true tooth trajectories. Numerical method is used to solve the derived transcendental equations. A simulation study of the effects of cutter runout on milling process geometry is conducted using the models. It was found that the change of cutter radius for a tooth relative to its preceding one is the most important factor in evaluating the effects of cutter runout.     

A dynamic surface roughness model for face milling

This paper presents a newly developed mathematical model for surface roughness prediction in a face-milling operation. The model considers the static and the dynamic components of the cutting process. The former includes of cutting conditions as well as the edge profile and the amount of runout of each insert set into a cutter body. The latter introduces the dynamic characteristics of the milling process. It is verified that such a model predicts the maximum or the arithmetic mean surface roughness value through the cutting experiments. The model can evaluate the surface texture of the precision parts machined with face milling.     

Surface topography and roughness of high-speed milled AlMn1Cu

The aluminum alloy AlMn1Cu has been broadly applied for functional parts production because of its good properties. But few researches about the machining mechanism and the surface roughness were reported. The high-speed milling experiments are carried out in order to improve the machining quality and reveal the machining mechanism. The typical topography features of machined surface are observed by scan electron microscope(SEM). The results show that the milled surface topography is mainly characterized by the plastic shearing deformation surface and material piling zone. The material flows plastically along the end cutting edge of the flat-end milling tool and meanwhile is extruded by the end cutting edge, resulting in that materials partly adhere to the machined surface and form the material piling zone. As the depth of cut and the feed per tooth increase, the plastic flow of materials is strengthened and the machined surface becomes rougher. However, as the cutting speed increases, the plastic flow of materials is weakened and the milled surface becomes smoother. The cutting parameters (e.g. cutting speed, feed per tooth and depth of cut) influencing the surface roughness are analyzed. It can be concluded that the roughness of the machined surface formed by the end cutting edge is less than that by the cylindrical cutting edge when a cylindrical flat-end mill tool is used for milling. The proposed research provides the typical topography features of machined surface of the anti-rust aluminum alloy AlMn1Cu in high speed milling.     

Position-varying surface roughness prediction method considering compensated acceleration in milling of thin-walled workpiece

Machined surface roughness will affect parts’ service performance. Thus, predicting it in the machining is important to avoid rejects. Surface roughness will be affected by system position dependent vibration even under constant parameter with certain toolpath processing in the finishing. Aiming at surface roughness prediction in the machining process, this paper proposes a position-varying surface roughness prediction method based on compensated acceleration by using regression analysis. To reduce the stochastic error of measuring the machined surface profile height, the surface area is repeatedly measured three times, and Pauta criterion is adopted to eliminate abnormal points. The actual vibration state at any processing position is obtained through the single-point monitoring acceleration compensation model. Seven acceleration features are extracted, and valley, which has the highest R-square proving the effectiveness of the filtering features, is selected as the input of the prediction model by mutual information coefficients. Finally, by comparing the measured and predicted surface roughness curves, they have the same trends, with the average error of 16.28% and the minimum error of 0.16%. Moreover, the prediction curve matches and agrees well with the actual surface state, which verifies the accuracy and reliability of the model.     

高效铣削淬硬钢凸曲面的铣刀性能测试方法

本文设计和加工了多硬度拼接凸曲面淬硬钢试件,以替代大型淬硬钢凸模,给出了铣削多硬度拼接凸曲面淬硬钢模具的刀具性能测试实验方案;利用该测试方案,检测出铣刀振动、磨损及加工表面形貌特征,并通过进一步增大每齿进给量测试刀具的使用寿命和安全可靠性,得到铣刀优选方法。结果表明,该方法可有效揭示和评价淬硬钢表面曲率和硬度多变对铣刀切削性能的影响,满足高效、安全稳定切削汽车内板淬硬钢凸模的要求。     

微细精密铣削表面粗糙度DRSM研究

DRSM方法具有序贯性、可旋转性、模型的稳健性以及试验次数少等优点,近年来逐渐运用在微细精密车铣加工运用中,笔者着重对微细精密铣削表面粗糙度进行DRSM分析,得出了微细精密铣削条件下工艺参数对表面粗糙度的影响规律,并进行了表面粗糙度的预测,有较强的理论实践和现实意义。     

自由曲面数控加工用刀具

从刀具有效半径和切削速度的角度,分析比较了球头立铣刀在三坐标和平头立铣刀在五坐标自由曲面加工中的加工效率与切削性能,提出了球头立铣刀和平头立铣刀的优化刀具尺寸,并对叶片曲面的刀具轨迹进行了仿真模拟。     

Topology recovery technique for complex freeform surface model after local geometry repair

Intersections and discontinuities commonly arise in surface modeling and cause problems in downstream operations.Local geometry repair,such as cover holes or replace bad surfaces by adding new surface patches for dealing with inconsistencies among the confluent region,where multiple surfaces meet,is a common technique used in CAD model repair and reverse engineering.However,local geometry repair destroys the topology of original CAD model and increases the number of surface patches needed for freeform surface shape modeling.Consequently,a topology recovery technique dealing with complex freeform surface model after local geometry repair is proposed.Firstly,construct the curve network which determine the geometry and topology properties of recovery freeform surface model;secondly,apply freeform surface fitting method to create B-spline surface patches to recover the topology of trimmed ones.Corresponding to the two levels of enforcing boundary conditions on a B-spline surface,two solution schemes are presented respectively.In the first solution scheme,non-constrained B-spline surface fitting method is utilized to piecewise recover trimmed confluent surface patches and then employs global beautification technique to smoothly stitch the recovery surface patches.In the other solution scheme,constrained B-spline surface fitting technique based on discretization of boundary conditions is directly applied to recover topology of surface model after local geometry repair while achieving G 1 continuity simultaneously.The presented two different schemes are applied to the consistent surface model,which consists of five trimmed confluent surface patches and a local consistent surface patch,and a machine cover model,respectively.The application results show that our topology recovery technique meets shape-preserving and G 1 continuity requirements in reverse engineering.This research converts the problem of topology recovery for consistent surface model to the problem of constructing G 1 patches from a given curve network,and provides a new idea to model repairing study.     

球头立铣刀铣削加工表面粗糙度仿真技术研究

铣削加工表面粗糙度的形成与铣刀和工件振动、主轴偏心、刀具磨损、刀具变形等物理和几何因素有关。多年来中外学者针对各种影响因素建立了“相对单一”的数学模型。这些数学模型只考虑了一种或两种影响因素,还没有建立起描述物理和几何变化过程的综合数学模型,为此对这些相关因素进行了深入研究,建立了基于球头立铣刀的铣削加工表面粗糙度仿真的整体数学模型。从而为虚拟数控加工仿真提供技术支撑。     

变齿厚斜齿轮传动齿面接触数学模型的建立

变齿厚斜齿轮传动综合了斜齿轮和变位齿轮传动的优点,为保证平行轴变齿厚斜齿轮接触良好,传动可靠,应对设计的齿轮对进行齿面接触分析.根据设计的待加工齿轮参数,确定小、大齿轮的齿面方程,建立其接触的数学模型,进而对标准安装以及存在安装误差的齿面接触情况进行研究,为接触有限元分析及制造加工奠定理论基础.     

复杂形状工件的端铣切削力模型

以传统的端铣切削力模型为基础，提出了一种新的端铣加工中静态切削力的预报模型。该模型考虑了复杂的工件形状和不同的铣刀进给轨迹。给出了一种新的工件和铣刀接触算法。     

螺旋面数控加工刀具运动轨迹计算方法研究

在数控机床上加工螺旋面多采用平面啮合理论,但实际在工件表面的切削轨迹为空间曲线,针对平面编程方法存在不可消除的理论误差,对截面包络法数控加工螺旋面时刀触点和刀具运动轨迹进行研究,提出一种新的计算刀触点"最小有向距离算法"的理论并进行论证.     

球头铣刀高速铣削玻壳屏凸模表面粗糙度研究

通过用球头铣刀在屏凸模型面做切削试验,研究高速铣削时切削速度、进给量及其它因素对工件表面粗糙度的影响规律,获得了高速铣削屏凸模型面所需的优化切削参数,保证了表面加工精度,提高了加工效率。     

颗粒阻尼铣刀主要填充参数对切削性能影响的正交试验分析

采用正交试验方法,选取颗粒阻尼铣刀主要填充参数(颗粒填充率、颗粒密度、颗粒直径)作为试验因素,以加工后工件表面粗糙度作为铣刀切削性能影响因素的评价指标,设计L9(34)正交试验表得到9组方案。运用极差分析方法确定影响铣刀切削性能的主要因素和次要因素,找到试验因素对铣刀切削性能的影响规律,最终得出最优方案组合,并用方差分析方法对其进行验证。     

Improved analytical model for residual stress prediction in orthogonal cutting

The analytical model of residual stress in orthogonal cutting proposed by Jiann is an important tool for residual stress prediction in orthogonal cutting. In application of the model, a problem of low precision of the surface residual stress prediction is found. By theoretical analysis, several shortages of Jiann’s model are picked out, including: inappropriate boundary conditions, unreasonable calculation method of thermal stress, ignorance of stress constraint and cyclic loading algorithm. These shortages may directly lead to the low precision of the surface residual stress prediction. To eliminate these shortages and make the prediction more accurate, an improved model is proposed. In this model, a new contact boundary condition between tool and workpiece is used to make it in accord with the real cutting process; an improved calculation method of thermal stress is adopted; a stress constraint is added according to the volume-constancy of plastic deformation; and the accumulative effect of the stresses during cyclic loading is considered. At last, an experiment for measuring residual stress in cutting AISI 1045 steel is conducted. Also, Jiann’s model and the improved model are simulated under the same conditions with cutting experiment. The comparisons show that the surface residual stresses predicted by the improved model is closer to the experimental results than the results predicted by Jiann’s model.