Optimal fixture design in peripheral milling of thin-walled workpiece

In order to optimize the positions of the locators in peripheral milling of a thin-walled workpiece, a finite element model along with an accurate cutting forces model is proposed in this paper. The finite element model takes into account the thickness variations of the workpiece in peripheral milling. The locators on the secondary locating surface directly influence the surface errors in peripheral milling of thin-walled workpiece, so this paper deals with the optimization of the positions of the locators on the secondary locating surface. A method including two steps is presented. In the first step, the initial positions of the locators are determined by adding the locators at the position with the maximum deformation. In the second step, a heuristic algorithm is proposed to optimize the positions of the locators. Finally, a simulation example is used to illustrate the method.     

一种卧式加工中心机床夹具的设计及应用

介绍在一台卧式加工中心B轴上加工四缸机体的自动液压夹具的设计.重点介绍上下料装置,过渡盘,输送定位与夹具定位的衔接等特殊设计.这副夹具已成功应用于生产实际.     

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。     

数控专用铣钻床压力夹具的创新设计

介绍用系统工程方法进行数控专用铣钻床压力夹具创新设计的过程，并对其机械系统进行方案分析和评价。     

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.     

A prediction of the machining defects in flank milling

In peripheral milling with great axial engagements, the tool deflections generate some geometrical defects on the machined surface. This article present a prediction method of these defects which is applicable on every ruled surface. The cutting forces are estimate with the cutting pressure notion. The parameters of the tool/workpiece material couple are identified by a test part. The prediction of the tool deflections requires controlling the tool immersion angle for each angular position of the tool. The deflections can be significant. An original procedure which is based on an engagement cards avoids an iterative calculation of the radial engagement. The experimental checking of the method of prediction is presented in a test.     

弱刚度工件夹紧顺序与夹具布局的同步优化

针对弱刚度工件在定位、夹紧过程中易变形的问题,建立了夹紧顺序与接触力及节点位移增量之间关系的数学模型,给出了各夹紧步骤中工件夹具系统的静力平衡方程;在此基础上,根据最小余能原理及库仑摩擦定律,构建了装夹方案优化模型,提出了基于遗传算法的夹具布局与夹紧顺序同步优化方法。算例结果表明,该方法有效降低了由于装夹所引起的工件变形。提高了加工精度。     

Simultaneous optimization of fixture and joint positions for non-rigid sheet metal assembly

This paper presents an optimization methodology for non-rigid sheet metal assembly variation by considering part variation, fixture variation, fixture layout, and joint positions, as well as the assembly spring back. The proposed algorithm integrates the finite element analysis (FEA) with a powerful global optimization algorithm, called the mode-pursuing sampling (MPS) method to simultaneously search for the optimal fixture and joint positions in order to minimize the assembly variation. An example application study is presented to demonstrate the optimization procedure and its effectiveness.     

以偏心轮为定位和夹紧元件的柔性夹具

设计了一种以偏心轮为定位和夹紧元件的柔性夹具.该夹具利用三个偏心轮作定位元件,一个偏心轮作夹紧元件.这种定位方式允许长方体形工件的尺寸在较大范围内发生变化,能较好的适应多品种、小批量生产方式对夹具的要求.     

装配加工法在保证夹具制造精度中的应用

装配加工法在夹具制造工艺方面上明显有别于装配调整法,其基本原理是,将夹具作为一个整体对待,对有位置精度要求的导向结构或定位结构,安排在夹具组装后进行加工,以最大限度地减少各元件之间的累积误差,提高夹具制造精度。以典型实例为例,论述了装配加工法在夹具制造中的应用过程,并总结了应用这种工艺方法制造的夹具在图样设计的主要特点。大量的实际应用表明,装配加工法是保证夹具制造精度的最简便有效的工艺方法。     

Three-dimensional process stability prediction of thin-walled workpiece in milling operation

High-speed machining of thin-walled workpiece is widely used in aerospace industry. To optimize the machining parameters in milling operations, the related process stability is required to be predicted. Compared to the existing two-dimensional (2D) milling stability model, a more completed three-dimensional (3D) regenerative process stability prediction model of thin-walled workpiece is presented based on the newly developed dynamic model. The efficiency and accuracy of the regenerative milling stability can be improved in the presented 3D model. The analysis procedure of the stability of flexible dynamic milling is developed in details. The 3D stability lobes are calculated according to the full discretization method and direct integration scheme. To verify the accuracy of presented 3D stability model, the thin-walled workpiece milling sound pressure signal and surface quality are determined in experiments.     

Development of a computer numerical control (CNC) modular fixture — Machine design of a standard multifinger module

This paper presents the first phase of our ongoing development of a computer numerical control (CNC) modular fixture involving the machine design of a standard multifinger module. The aim is to develop a modular fixture which consists of only one type of standard multifinger CNC module which can provide locating, supporting and clamping functions. The module consists of four fingers with eight degrees of freedom to conform to any arbitrary workpiece surfaces. The eight motions of the four fingers are controlled by one motor through the use of two transmission and clutch systems. Different fixture layouts or reconfigurations can be made by different combinations of a multiplicity of such modules for major product family changes; while adjustments to finger positions of individual modules can be made by direct computer numerical control for minor product changes within a product family. The machine design and operation of the module are presented in the paper. A prototype was built and tested and satisfactory performance was achieved. Finally, two examples are provided to illustrate the flexibility and use of the standard multifinger module.     

Determination of the feasible setup parameters of a workpiece to maximize the utilization of a five-axis milling machine

Frontiers of Mechanical Engineering - The machining industry must maximize the machine tool utilization for its efficient and effective usage. Determining a feasible workpiece location is one of...     

夹具CAD系统中夹紧机构及夹紧库的设计

对夹具机构中各夹紧机构建立CAD模型.采用面向对象的设计技术完成了典型夹具库及其界面的设计,并使得库的结构清晰且具有开放性.将所有典型夹紧对象采用面向对象的数据库管理起来,可实现对典型夹具库的实例化管理.     

Stability improvement and vibration suppression of the thin-walled workpiece in milling process via magnetorheological fluid flexible fixture

In aerospace industry, thin-walled workpiece milling is a critical task. Also, the machining vibration is a major issue for the accuracy of the final part. In this study, a new dynamic analytical model is proposed to determine the effect of damping factor on the dynamic response of thin-walled workpiece in machining. A complex structure workpiece is equivalent to a thin plate. The fixture constrains and the damping factor are crucial elements of this thin plate. Therefore, the magnetorheological fluid flexible fixture is designed to suppress the machining vibration in machining process. Then, the general dynamic cutting force model and the damping force model are proposed for the key dynamic equation for the prediction of dynamic response to evaluate the stability of the milling process with and without the damping control. Finally, the feasibility and effectiveness of the proposed model is validated by machining tests. The predicted values match on the experiment results.     

Modeling and compensation technology for the comprehensive errors of fixture system

Error modelling and compensating technology is an effective method to improve the processing precision.The position and orientation deviation of workpiece is caused by the fixing and manufacturing erro...     

数控铣床与加工中心夹具设计

提出针对数控铣床、加工中心所用夹具的设计方法.合理的夹具设计能充分发挥数控机床的潜力,提高加工效率.提供加工中心夹具设计实例.     

多齿圆周铣削残留面积高度研究

提出了一种非简化的多齿圆周铣削几何运动模型,该模型考虑进给速度对刀齿运动轨迹的影响,发现在多齿圆周铣削中存在残留面积的现象,并推导出计算残留面积高度的公式,公式表明多齿圆周铣削的残留面积高度与刀具齿数、每齿进给量和刀具半径有关;然后以残留面积高度公式为基础,利用Visual C++(MFC)为平台开发出计算和辅助分析残留面积高度的系统;最后采用Matlab仿真软件验证非简化模型的合理性和在多齿圆周铣削中存在残留面积.     

基于CATIA平台的夹具快速设计与制造系统的构建

重点研究CATIA在专用夹具设计及制造过程中的应用问题。夹具设计涉及到数值计算 ,图形绘制等一些算法问题。CATIA在解决这类问题时显示出其优越性。关键是研究如何在CATIA环境下建立专用夹具设计、制造快速响应系统的总体结构 ,特别是在如何建立专用夹具元件库及夹具可行性分析等方面作了一些研究。对有关夹具相似性比较的推理方法也作了一些探讨。     

The application of the simulated annealing method and heuristic algorithms in the selection of fixture elements

This paper deals with the selection of suitable fixture element combinations and fixture allocation for a workpiece to allow for the different positions of the fixturing points, which are already given based on related theories. The advanced modelling extension (AME) of AutoCAD R12 was used as the 3D graphic interface. The function suitable for the AME environment was also controlled to obtain detailed data of the workpiece.First of all, the concept of group technology (GT) was used to categorise and encode the modular fixture elements with similar functions for cutting purposes. Next, the AME was combined with API (application programming interface) and Autolisp to establish the graphic illustration system for fixture elements. Then different heuristic algorithms for fixture element selection were developed to correspond to different requirements in fixture functions. The required fixture elements were then selected with the help of the simulated annealing calculation method to derive a suitable and economical number of fixture element combinations. The height of the fixture element combination derived may not match the height of the fixture point originally located. The workpiece shape also affects the allocated position of the fixture elements. Therefore, a number of heuristic algorithms were developed in this study to process all the factors involved and to obtain a desirable selection for fixture elements.