Optimization of Fixture Number in Large Thin-Walled Parts Assembly Based on IPSO

There are lots of researches on fixture layout optimization for large thin-walled parts.Current researches focus on the positioning problem,i.e.,optimizing the positions of a constant number of fixtures.However,how to determine the number of fixtures is ignored.In most cases,the number of fixtures located on large thin-walled parts is determined based on engineering experience,which leads to huge fixture number and extra waste.Therefore,this paper constructs an optimization model to minimize the number of fixtures.The constraints are set in the optimization model to ensure that the part deformation is within the surface profile tolerance.In addition,the assembly gap between two parts is also controlled.To conduct the optimization,this paper develops an improved particle swarm optimization(IPSO)algorithm by integrating the shrinkage factor and adaptive inertia weight.In the algorithm,particles are encoded according to the fixture position.Each dimension of the particle is assigned to a sub-region by constraining the optional position range of each fixture to improve the optimization efficiency.Finally,a case study on ship curved panel assembly is provided to prove that our method can optimize the number of fixtures while meeting the assembly quality requirements.This research proposes a method to optimize the number of fixtures,which can reduce the number of fixtures and achieve deformation control at the same time.

Development of Fixture Layout Optimization for Thin-Walled Parts:A Review

An increasing number of researchers have researched fixture layout optimization for thin-walled part assembly during the past decades.However,few papers systematically review these researches.By analyzing existing literature,this paper summarizes the process of fixture layout optimization and the methods applied.The process of optimization is made up of optimization objective setting,assembly variation/deformation modeling,and fixture layout optimization.This paper makes a review of the fixture layout for thin-walled parts according to these three steps.First,two different kinds of optimization objectives are introduced.Researchers usually consider in-plane variations or out-of-plane deformations when designing objectives.Then,modeling methods for assembly variation and deformation are divided into two categories:Mechanism-based and data-based methods.Several common methods are discussed respectively.After that,optimization algorithms are reviewed systematically.There are two kinds of optimization algorithms:Traditional nonlinear programming and heuristic algorithms.Finally,discussions on the current situation are provided.The research direction of fixture layout optimization in the future is discussed from three aspects:Objective setting,improving modeling accuracy and optimization algorithms.Also,a new research point for fixture layout optimization is discussed.This paper systematically reviews the research on fixture layout optimization for thin-walled parts,and provides a reference for future research in this field.

A model of deformation of thin-wall surface parts during milling machining process

A three-dimensional finite element model was established for the milling of thin-walled parts. The physical model of the milling of the part was established using the AdvantEdge FEM software as the platform. The aluminum alloy impeller was designated as the object to be processed and the boundary conditions which met the actual machining were set. Through the solution, the physical quantities such as the three-way cutting force, the tool temperature, and the tool stress were obtained, and the calculation of the elastic deformation of the thin-walled blade of the free-form surface at the contact points between the tool and the workpiece was realized. The elastic deformation law of the thin-walled blade was then predicted. The results show that the maximum deviation between the predicted value and the actual measured machining value of the elastic deformation was 26.055 μm; the minimum deviation was 2.011 μm, with the average deviation being 10.154 μm. This shows that the prediction is in close agreement with the actual result.

Numerical simulation analysis for deformation deviation and experimental verification for an antenna thin-wall parts considering riveting assembly with finite element method

In the process of thin-wall parts assembly for an antenna,the parts assembly deformation deviation is occurring due to the riveting assembly.In view of the riveting assembly deformation problems,it can be analyzed through transient and static simulation.In this work,the theoretical deformation model for riveting assembly is established with round head rivet.The simulation analysis for riveting deformation is carried out with the riveting assembly piece including four rivets,which comparing with the measuring points experiment results of riveting test piece through dealing with the experimental data using the point coordinate transform method and the space line fitting method.Simultaneously,the deformation deviation of the overall thin-wall parts assembly structure is analyzed through finite element simulation;and its results are verified by the measuring experiment for riveting assembly with the deformation deviation of some key points on the thin-wall parts.Through the comparison analysis,it is shown that the simulation results agree well with the experimental results,which proves the correctness and effectiveness of the theoretical analysis,simulation results and the given experiment data processing method.Through the study on the riveting assembly for thin-wall parts,it will provide a theoretical foundation for improving thin-wall parts assembly quality of large antenna in future.

Welding thermal characteristics analysis with numerical simulation for thin-wall parts assembly under different conditions

In order to analyze the welding thermal characteristics problem,the multiscale finite element(FE)model of T-shape thin-wall assembly structure for different thicknesses and the heat source model are established to emphatically study their welding temperature distributions under different conditions.Simultaneously,different welding technology parameters and welding directions are taken into account,and the fillet weld for different welding parameters is employed on the thin-wall parts.Through comparison analysis,the results show that different welding directions,welding thicknesses and welding heat source parameters have a certain impact on the temperature distribution.Meanwhile,for the thin-wall assembly structure of the same thickness,when the heat source is moving,the greater the moving speed,the smaller the heating area,and the highest temperature will decrease.Therefore,the welding temperature field distribution can be altered by adjusting welding parameters,heat source parameters,welding thickness and welding direction,which is conducive to reducing welding deformation and choosing an appropriate and optimal welding thickness of thin-wall parts and relative welding process parameters,thus improving thin-wall welding structure assembly precision in the actual large-size welding structure assembly process in future.

Optimization of material removal strategy in milling of thin-walled parts

The optimal material removal strategy can improve a geometric accuracy and surface quality of thin-walled parts such as turbine blades and blisks in high-speed ball end milling.The dominant conception in the material removal represents the persistence of the workpiece cutting stiffness in operation to advance the machining accuracy and machining efficiency.On the basis of theoretical models of cutting stiffness and deformation,finite element method (FEM) is applied to calculate the virtual displacements of the thin-walled part under given virtual loads at the nodes of the discrete surface.With the reference of deformation distribution of the thin-walled part,the milling material removal strategy is optimized to make the best of bracing ability of still uncut material.This material removal method is summarized as the lower stiffness region removed firstly and the higher stiffness region removed next.Analytical and experimental results show the availability,which has been verified by the blade machining test in this work,for thin-walled parts to reduce cutting deformation and meliorate machining quality.

Initial residual stress experiment and simulation of thin-walled parts for layer removal method

Thin-walled parts have low stiffness characteristic. Initial residual stress of thin-walled blanks is an important influence factor on machining stability. The present work is to verify the feasibility of an initial residual stress measurement of layer removal method. According to initial residual stress experiment for casting ZL205 A aluminum alloy tapered thin-walled blank by a common method,namely hole-drilling method,three finite element models with initial residual stress are established to simulate the layer removal method in ABAQUS and ANSYS software. By analyzing the results of simulation and experiments,the cutting residual stress inlayer removal process has a significant effect on measurement results. Reducing cutting residual stress is helpful to improve accuracy of layer removal method.

Mapping relationship analysis of welding assembly properties for thin-walled parts with finite element and machine learning algorithm

The finite element(FE)-based simulation of welding characteristics was carried out to explore the relationship among welding assembly properties for the parallel T-shaped thin-walled parts of an antenna structure.The effects of welding direction,clamping,fixture release time,fixed constraints,and welding sequences on these properties were analyzed,and the mapping relationship among welding characteristics was thoroughly examined.Different machine learning algorithms,including the generalized regression neural network(GRNN),wavelet neural network(WNN),and fuzzy neural network(FNN),are used to predict the multiple welding properties of thin-walled parts to mirror their variation trend and verify the correctness of the mapping relationship.Compared with those from GRNN and WNN,the maximum mean relative errors for the predicted values of deformation,temperature,and residual stress with FNN were less than 4.8%,1.4%,and 4.4%,respectively.These results indicate that FNN generated the best predicted welding characteristics.Analysis under various welding conditions also shows a mapping relationship among welding deformation,temperature,and residual stress over a period of time.This finding further provides a paramount basis for the control of welding assembly errors of an antenna structure in the future.

Deformation Analysis and Fixture Design of Thin-walled Cylinder in Drilling Process Based on TRIZ Theory

Thin-walled cylindrical workpiece is easy to deform during machining and clamping processes due to the insufficient rigidi.Moreover,it’s also difficult to ensure the perpendicularity of flange holes during drilling process.In this paper,the element birth and death technique is used to obtain the axial deformation of the hole through finite element simulation.The measured value of the perpendicularity of the hole was compared with the simulated value to verify then the rationality of the simulation model.To reduce the perpendicularity error of the hole in the drilling process,the theory of inventive principle solution(TRIZ)was used to analyze the drilling process of thin-walled cylinder,and the corresponding fixture was developed to adjust the supporting surface height adaptively.Three different fixture supporting layout schemes were used for numerical simulation of drilling process,and the maximum,average and standard deviation of the axial deformation of the flange holes and their maximum hole perpendicularity errors were comparatively analyzed,and the optimal arrangement was optimized.The results show that the proposed deformation control strategy can effectively improve the drilling deformation of thin-walled cylindrical workpiece,thereby significantly improving the machining quality of the parts.

Relative Varying Dynamics Based Whole Cutting Process Optimization for Thin‑walled Parts

Thin-walled parts are typically difficult-to-cut components due to the complex dynamics in cutting process.The dynamics is variant for part during machining,but invariant for machine tool.The variation of the relative dynamics results in the difference of cutting stage division and cutting parameter selection.This paper develops a novel method for whole cutting process optimization based on the relative varying dynamic characteristic of machining system.A new strategy to distinguish cutting stages depending on the dominated dynamics during machining process is proposed,and a thickness-dependent model to predict the dynamics of part is developed.Optimal cutting parameters change with stages,which can be divided by the critical thickness of part.Based on the dynamics comparison between machine tool and thickness-varying part,the critical thicknesses are predicted by an iterative algorithm.The proposed method is validated by the machining of three benchmarks.Good agreements have been obtained between prediction and experimental results in terms of stages identification,meanwhile,the optimized parameters perform well during the whole cutting process.

Elliptical vibration cutting of large-size thin-walled curved surface parts of pure iron by using diamond tool with active cutting edge shift

Large-size thin-walled curved surface parts of pure iron are crucial in aerospace,national defense,energy and precision physical experiments.However,the high machining accuracy and surface quality are difficult to achieve due to the serious tool wear and deformation when machining the parts with conventional cutting tools.In this paper,an elliptical vibration cutting(EVC)with active cutting edge shift(ACES)based on a long arbor vibration device is proposed for ultraprecision machining the pure iron parts by using diamond tool.Compared with cutting at a fixed cutting edge,the influence of ACES on the EVC was analyzed.Experiments in EVC of pure iron with ACES were conducted.The evolutions of the surface roughness,surface topography,and chip morphology with tool wear in EVC with ACES are revealed.The reasonable parameters of ultraprecision machining the pure iron parts by EVC with ACES were determined.It shows that the ACES has a slight influence on the machined surface roughness and surface topography.The diamond tool life can be significantly prolonged in EVC of pure iron with ACES than that with a fixed cutting edge,so that high profile accuracy and surface quality could be obtained even at higher nominal cutting speed.A typical thin-walled curved surface pure iron part with diameter φ240 mm,height 122 mm,and wall thickness 2 mm was fabricated by the presented method,and its profile error and surface roughness achieved PV 2.2μm and Ra less than 50 nm,respectively.

带环形凸台薄盘形件旋压成形规律研究

目的探明带环形凸台薄盘形件旋压成形工艺的可行性,揭示成形过程的特点、成形缺陷的类型和产生机制,以及工艺参数对成形极限的影响规律。方法基于ABAQUS\Explicit有限元模型,分析成形过程中的材料流动、应力分布、缺陷的产生机制和工艺参数对成形极限的影响规律。结果旋压成形过程分为内槽填充、轴向隆起和径向扩展3个阶段,应力场沿径向和周向呈梯度分布,坯料在径向扩展阶段由于受压失稳产生了凸台凹坑缺陷。成形极限随凸台增厚比、盘缘宽厚比和型槽倾角的增大而增大,随旋轮进给比f的增大,成形极限先增大后减小。结论总结了增厚旋压工艺的成形特征、缺陷演化机制以及工艺参数对成形极限的影响规律,为带环形凸台薄盘形件旋压成形工艺的设计和优化提供指导。

环形丁腈橡胶件静刚度的有限元模拟

对矩形丁腈橡胶件进行静态拉伸试验,通过对试验得到的应力、应变数据进行拟合,得到了Mooney-Rivlin超弹性本构模型参数,利用此本构模型对环形丁腈橡胶件进行静压缩有限元模拟,进行了试验验证,并分析了环形丁腈橡胶件的壁厚、外径以及温度对其静刚度的影响。结果表明:通过有限元方法模拟得到矩形丁腈橡胶件静态拉伸大变形阶段的力-位移曲线与试验结果相吻合,相对误差小于5%,表明Mooney-Rivlin超弹性本构模型可准确描述丁腈橡胶的超弹性特性;环形丁腈橡胶件静刚度的有限元模拟结果与压缩试验结果的相对误差为13.1%,证明了该有限元方法的准确性;随着壁厚或外径的增加,环形丁腈橡胶件的静刚度减小;随着温度的升高,静刚度减小,但减小速率逐渐降低。

薄壁环形零件滚压成形研究

选择对称带槽薄壁环形零件,采用紫铜板料,通过有限元模拟及成形试验分析了薄壁环形零件滚压成形的力学特征、主要成形缺陷及成形极限,给出了试件变形区的应力应变分布、试件宽度与槽部高度的变化及滚压成形缺陷的试验结果.研究结果表明:采用滚压成形方法加工薄壁环形零件是可行的,滚压成形是局部变形,变形区壁厚变薄;当厚宽比t/b≤0.044时试件与模具接触的槽底部金属起皱,t/b≥0.058时开裂;可以通过增大板料厚度和滚压系数mG提高槽部成形极限.

环状零件的淬火变形规律及其在生产中的应用

研究了不同含碳量环状零件的淬火变形规律。结果表明:随含碳量的增加,环状零件的变形率呈先升高后降低的抛物线形状,50钢淬火时变形率达到最大值;当淬火介质的冷却速度较快时,其变形率增大,低合金碳钢的变形率较小;运用该规律可以在机械加工过程中对涨大的变形量进行补偿,从而使淬火之后的零件尺寸符合技术要求。

环形薄型零件加工工艺

为提高环形薄型零件的精加工质量,根据车床加工系统的刚度、装夹受力以及加工误差复映与被加工件之间的关系,提出1种针对外形为环形薄型零件的精加工工艺方案.该方案将装夹的定位点设定在环形薄型零件的轴向上,不使工件因装夹产生径向变形;并通过特制工艺装备使被加工件避开径向外力负载,将外径与环壁厚之比高达40以上的环形薄型零件加工到要求尺寸,同时保证工件的同轴度和表面粗糙度.检验按该特殊工装方案加工后的一批工件,合格率达95%.

一种大尺寸环形薄壁零件激光刻型新方法

在航空装备轻量化要求下,对于机匣类大尺寸环形薄壁零件,提出了一种激光刻型的新方法来减重。利用五轴直角坐标实验装置,配合CO_2激光器在三维筒形薄壁零件上做刻型加工,并开发出图形精密分割和在线拼接软件,解决了大尺寸复杂薄壁构建表面刻型存在的易变现、精度低以及刻型减重比低的技术难题。结果表明:所提出的激光刻型新方法能够较好的满足大型环形薄壁零件精确、高效刻型的要求,对提升我国航空发动机和飞机性能具有重要的意义。

陀螺仪环盖加工工艺分析及专用夹具的设计

针对陀螺仪环盖薄壁难加工问题,利用现有加工设备,设计专用夹具、制定合适的加工工艺,避免了力、热、振动变形对环盖加工造成的影响,保证了产品合格率,极大提高了经济效益,减少了对高性能机床的依赖,且在同类工件加工中具有一定的推广价值。

矩形断面环形件弯曲成形过程中断面变形的研究

本文采用三维弹塑性有限元方法对矩形断面环形件冷态弯曲成形过程的断面变形问题进行分析研究,通过对成型过程的计算机仿真,分析了在—定宽度和高度工况下弯曲成型后断面形状的变化,对确定矩形断面环形件生产过程中坯料的断面尺寸具有指导作用。

新型从动锥齿轮坯闭式精锻模设计

介绍了一种实用的从动锥齿轮新型锻模结构。锻模采用浮动模芯和浮动凹模结构,锻件在一个封闭环形模腔中成形,无飞边,毛坯重量减少5.5%,显著降低了生产成本。