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.

带锁髓内钉与锁定钢板内固定术治疗肱骨近端Neer二部分骨折患者的效果比较

目的:比较带锁髓内钉与锁定钢板内固定术治疗肱骨近端Neer二部分骨折患者的效果。方法:选取2021年2月至2022年2月该院收治的64例肱骨近端Neer二部分骨折患者进行前瞻性研究,按照随机数字表法将其分为观察组与对照组各32例。对照组采用锁定钢板内固定术治疗,观察组采用带锁髓内钉内固定术治疗,比较两组手术时间、术中出血量、住院时间、骨性愈合时间、ConstantMurley肩关节功能评分量表(CMS)评分、健康调查简表(SF-36)评分和并发症发生率。结果:观察组术中出血量少于对照组,住院时间和骨性愈合时间短于对照组,差异均有统计学意义(P<0.05);术后6个月,两组SF-36各维度评分高于术前,且观察组高于对照组,差异均有统计学意义(P<0.05);观察组并发症发生率为3.12%,明显低于对照组的25.00%,差异有统计学意义(P<0.05);两组手术时间和手术前后CMS评分比较,差异无统计学意义(P>0.05)。结论:带锁髓内钉内固定术治疗肱骨近端Neer二部分骨折患者可提高术后SF-36评分,缩短住院时间和骨性愈合时间,以及降低术中出血量和并发症发生率,效果优于锁定钢板内固定术治疗。

选择性激光熔化快速成形技术与装备

介绍了华中科技大学基于粉末材料选择性激光熔化(Selective laser melting,SLM)成形技术的一些最新研究成果,主要包括设备与软件,以及该技术的主要应用领域。由于SLM成形过程是一个复杂的物理化学冶金过程,金属粉末熔化快,熔池存在时间短,凝固成形时存在较大的温度梯度与热应力,液态金属表面张力大,因而容易产生翘曲变形、裂纹与球化现象三个国际性难题,针对这些难题,提出了相应的研究方案。

复杂线轮廓度误差坐标测量的数据处理方法

本文把平面上复杂轮廓的设计曲线统一地表示为参数矢函数描述 ,运用微分几何理论 ,导出被测工件上测点到设计曲线的距离函数 ,建立复杂线轮廓度误差坐标测量的数据处理模型。文章对算法进行了精度分析 ,并且设计加工了一个凸轮试件 ,通过坐标测量 ,用本文方法精确、快速地计算出凸轮的轮廓度误差。

复杂零件金属注射成形3D充模模拟

以实际生产的支持块为例,结合3D技术,模拟了注射成形喂料在复杂几何模腔中的流动情况。基于ANSYS提供的Z Buffer切片模型空间观测方式,预测了实际制品缺陷产生的部位并分析了缺陷形成机理。最后依据模拟结果,推荐在实际生产中采用INLET4位置浇口进行注射生产,实验表明制得的支持块无缺陷,产品通过了有关部门的验收,证明了充模流动3D模拟的可行性和准确性。

基于SL模型的复杂壳体快速铸造的研究

为解决复杂壳体快速铸造中SL模型代替金属、木模具的问题,分析数据处理过程对造型工艺的影响;针对不同精度需求,可采取多项措施;对模型的制作进行优化;结合新型变速器壳体的开发,实现了新品开发的快速铸造。研究表明:该方法制模周期短,模型稳定,尺寸精度明显高于木模;浇铸系统是保证铸件质量的关键;非强化光敏树脂模型适用于20件内、形状复杂壳体类新品的快速铸造;SLS法提供蜡型的成本较高,SL模型使铸件的成本大大降低;造型过程SL模型增强成为模具寿命的关键。

大型复杂型面铝合金翻边件电磁成形塑性流动行为研究

大型复杂型面铝合金翻边件电磁成形是一个电磁场和结构场耦合作用下的复杂塑性成形过程。由于大型复杂型面的影响,使得铝合金翻边件在电磁成形过程中的塑性流动行为与传统带凸模翻边成形不同。基于松散耦合法建立耦合电磁场和结构场的大型复杂型面铝合金翻边件电磁成形有限元模型,研究采用1层、2层和3层平板线圈电磁翻边下的板料塑性流动行为,并采用试验研究揭示了不同压边力控制下板料法兰部分塑性流动规律。结果表明,当采用3层平板线圈时,翻边件的复杂型面部分完全贴膜,法兰部分材料进入凹模腔的部分更多,促使板料发生更多的塑性流动;不同压边力控制下,法兰部分由塑性流动产生不同的工件形式,在压边力不足时,法兰部分产生明显的起皱现象;通过合理的压边力控制,可得到贴膜性良好的大型复杂型面铝合金翻边件。

应用数值模拟技术研究摩擦对板料拉深成形的影响

本文论述了摩擦对板料成形的特点和重要性 ,应用数值模拟技术研究摩擦对板料拉深成形的影响。结果表明 :模拟某复杂零件成形性能与摩擦系数关系密切 ;当摩擦系数为 μ3 时 ,冲压方向最大应力最小。研究结果表明采用数值模拟技术便于研究摩擦与板料冲压成形之间的相互关系。

胸部肿瘤手术病人围手术期动脉血气变化与心肺功能并发症发生的关系

目的:探讨动脉血气分析检测在胸部肿瘤病人围手术期的应用及其变化与心肺功能并发症发生的关系。方法:分别检测胸部肿瘤病人术前1周内,术后2h、8h以及第1、2、3d,第4d或第5d的动脉血气,对所检测数据进行统计学处理并与术后心肺并发症发生作相关性进行分析。结果:围手术期血气分析统计资料显示胸部肿瘤病人手术后第2天动脉血氧分压最低(P<0.01),二氧化碳分压最高,低氧血症造成手术后心肺并发症的发生率也高(P<0.05)。结论:围手术期血气分析的变化与手术后心肺功能并发症的发生有关,为减少手术后心肺功能并发症的发生和保证围手术期的安全,要注意保持呼吸道通常,并给予充分的氧疗以纠正低氧血症,必要时应用呼吸机辅助呼吸。

复杂线轮廓度误差评定方法

本文运用微分几何的活动坐标以及曲线上一点邻近结构理论 ,导出测量点到理想轮廓的统一形式的距离函数 ,建立平面上复杂线轮廓度误差最小条件评定的统一模型 ,并用有效集法精确、快速地进行处理。为三坐标测量机上高精度。