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.

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.

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.

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.

偏心不锈钢壳体零件的加工工艺改进及夹具设计

航空零部件属于典型的多品种小批量生产模式,近年来随着航空业的高速发展,新研项目成倍增加,航空零部件的高效加工已成为企业交付生产任务的重要保障。面对材料难加工、零件精度要求高且结构偏心的回转体,设计了专用车削夹具调节零件回转中心,同时设计车削加工端面的挖槽刀具提高刀具刚性,进一步应用ECRS(取消、合并、重排、简化)方法对零件加工工艺流程进行优化,并进行了应用验证,满足产品图纸尺寸要求,最终实现零件加工效率和加工质量的有效提升,缩短了零件的生产周期。

数控车床偏心零件加工方法与工艺优化技术分析

相对于一般的零件加工,偏心零件比较特殊,加工工艺也更为复杂,借助数控车床进行零件加工,目前已经成为偏心零件加工中一种常用的方法。对数控车床偏心零件加工方法和工艺优化技术进行分析,旨在为当前偏心零件的数控加工提供一些思路和参考。

偏心圆截面轴类零件的楔横轧成形数值模拟

提出了一种偏心轴类零件楔横轧成形新工艺,给出了楔横轧成形偏心轴类零件轧辊的辊型曲面。利用三维弹塑性有限元软件LS-DYNA对一种典型偏心轴类零件楔横轧成形进行了数值模拟,分析了其成形过程、应力应变场分布及工艺特点。模拟结果表明,从起楔开始就将坯料轧制成偏心圆截面的偏心轴类零件的楔横轧工艺是完全可行的,而且具有轧制力小、变形容易控制等优点。

汽车刹车蹄片轴的偏心精密成形

分析了利用楔横轧工艺成形偏心件的过程 ,给出了偏心件的特殊成形方法 ,并以CA1 41汽车刹车蹄片轴为例进行了试验 ,取得了满意的结果 。

带偏心轮压边装置的冲压模

为了批量生产小型封头类拉深件,设计了一种新型偏心轮压边装置。介绍了带偏心轮压边装置的冲压模结构和工作原理。利用冲压模具上的偏心轮压边装置对深拉延件进行压边,冲压设备为单动冲床;拉深时,通过楔杆驱动偏心轮压边,得到不随压机行程变化的压边力。经在Φ350 mm和Φ273 mm两种标准封头的模具上试验证明,具有压边可靠、工效高、制造工艺简单等优点。

偏心轴类零件楔横轧轧制力分析

利用有限元手段对偏心轴类零件楔横轧轧制成形中的轧制区轧制力进行了系统全面地研究,在此基础上分析了偏心轴类零件楔横轧非轧制区接触力的产生原因及其对偏心轴类零件楔横轧轧制成形带来的影响.研究结果对认清偏心轴类零件楔横轧轧制成形机理、旋转条件、偏心极限都具有十分重要的意义.

Y型偏心支撑钢框架受力性能有限元分析

对5个具有不同耗能梁段长度的Y型偏心支撑钢框架的滞回性能与耗能梁段的耗能性能进行了非线性有限元分析。研究表明:Y型偏心支撑钢框架具有良好的耗能性能和延性,耗能梁段能够充分发挥耗能和变形的作用;耗能梁段的长度对Y型偏心支撑钢框架的强度、刚度、延性和耗能性能均产生明显的影响,耗能梁段越短,其塑性变形越大,Y型偏心支撑钢框架的承载力越高,耗能梁段过长钢框架的抗震性能越差。

带偏心轮压边装置的冲压模

利用冲压模具上的偏心轮压边装置对深拉延件进行压边。冲压设备为单动冲床。拉深时,通过楔杆驱动偏心轮压边,从而得到不随压机行程变化的压边力。介绍了带偏心轮压边装置的冲压模的结构和工件原理。

双偏心孔工件的专用夹具设计

对双偏心孔零件在数控车床上的加工装夹进行了分析,阐述了双偏心孔工件专用夹具的相互定位与夹紧方式,以及专用夹具的制作工艺要求。为了平衡离心力,设置了平衡块,并详细分析和计算了平衡块的参数尺寸与质心坐标。经检验,达到了良好的效果。该夹具造价低、加工效率高及加工精度好,为企业带来了良好的经济效益。