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.

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.

基于松辽盆地南部地震剖面中地质信息的砂岩型铀矿找矿预测方法研究

砂岩型铀矿勘查队伍在进行铀矿勘查的过程中收集了大量勘查区内地震剖面,部分地震剖面中隐藏的地质信息未得到充分发掘,文章从地质、物探相结合的研究视角,依托历年铀矿勘查工作经验对收集的地震剖面进行综合分析和二次开发利用,提高地震资料利用率,进一步发挥地震资料在砂岩型铀矿勘查过程中的指导作用。在地震剖面中识别构造、沉积等要素,将各类要素投影至平面图中进行叠合并筛选,进而确定铀成矿有利部位。该找矿预测方法综合反转与走滑构造预测成果、辫状河砂体预测成果、削截不整合预测成果、隆起构造预测成果、洼地预测成果,以岩性地化环境作为控制性指标,结合周围钻孔单孔、连孔信息,实现对铀成矿有利砂体的预测。文章提出松辽盆地南部坳陷期沉积地层处于右旋走滑构造背景下,走滑断裂的局部地区形成挤压应力场造成反转构造,进而形成了古隆起,这一过程同时伴生形成拉伸应力场,进而形成了深洼地,古隆起和深洼地之间过渡带形成一系列发育辫状河的山间河谷地形,应力场的转换形成一系列不整合界面和局部隆起构造,控制了铀矿化的具体位置,其能否最终形成富矿体取决于该具体位置是否处于氧化—还原的过渡带。文章预测了13片外围铀成矿潜力较大且可供下一步钻探工程查证的砂体,预测结果与部分外围铀矿体位置一致,在其中两片有利砂体附近勘查发现两处铀矿产地。文中基于地震剖面中地质信息的找矿预测方法对铀矿找矿具有一定指导和借鉴意义。

一种基于CATIA/CAA的轮胎型胶设计方法

介绍一种基于CATIA软件及CAA二次开发的型胶设计工具进行轮胎型胶部件设计的方法。利用型胶设计工具中的胶部件展平模块,精确求解出材料分布图中对应胶部件的展平体积线;再利用型胶设计模块,参考展平体积线的形状设计型胶部件形状。此方法使型胶部件尺寸和质量等与材料分布图要求相吻合,提高了设计质量和效率。

基于预埋件部位超前浇筑工艺的型钢混凝土基础结构施工

为加快型钢混凝土基础结构工期进度,保证施工质量和安全,解决型钢结构柱基础埋件标高低于筏板完成面标高的施工问题,通过对预埋件精准定位并固定,超前浇筑预埋件部位混凝土,同时调整传统分层浇筑的施工工艺,达到提前穿插吊装钢结构的效果。结果表明,超前浇筑预埋件施工方案是一种新型有效可行的施工方法,可提高混凝土和钢结构施工质量,减少后期维修隐患,同时通过提前工序穿插,能实现工期节约,为型钢结构柱预埋件低于筏板面工程施工提供了新的施工思路。

High-resolution Hyper-spectral Image Classification with Parts-based Feature and Morphology Profile in Urban Area

High-resolution hyper-spectral image (HHR) provides both detailed structural and spectral information for urban study. However, due to the inherent correlation between spectral bands and within-class variability in the data, the data processing of HHR is a challenging work. In this paper, based on spectral mixture analysis theory, a new stack of parts description features were extracted, and then incorporated with a stack of morphology based spatial features. Partially supervised constrained energy minimization (CEM) and unsupervised nonnegative matrix factorization (NMF) were used to extract the part-features. The joint features were then integrated by SVM classifier. The advantages of this method are the representation of physical composition of the urban area by the parts-features and the show of multi-scale structure information by morphology profiles. Experiments with an airborne hyper-spectral data flightline over the Washington DC Mall were performed, and the performance of the proposed algorithm was evaluated in comparison with well-known nonparametric weighted feature extraction (NWFE) and feature selection method. The results shown that the proposed features-joint scheme consistently outperforms the traditional methods, and so can provide an effective option for processing HHR data in urban area.

飞机复杂型材零件加工与质控研究

为了做好飞机复杂型材零件加工,并保障最终质量,本文将展开相关研究。研究首先介绍了飞机复杂型材零件的基本概念及加工、质控特点,其次对飞机复杂型材零件加工过程、质控要点进行了分析。通过研究,虽然飞机复杂型材零件加工、质控难度高,但只要按流程进行操作,并注意要点控制,就能给飞机复杂型材零件成品质量提供保障。

某散热板机械加工工艺研究

工艺优化就是将原有的工艺流程进行创新改进或重组,从而缩短加工制造周期、降低生产成本、提高运行效率的一种优于现行工艺的操作方法。就某一件产品而言,工艺流程具有不唯一性和不确定性。如何通过合理的工艺流程在保证精度的情况下尽最大可能提高产品的加工效率、降低成本、保持竞争优势是当前企业追求的共同目标。某车载系统散热板形状极不规则,在进入批量生产后材料利用率不高,加工周期长。通过分析散热板的外形结构,以缩短加工工序和加工时间为出发点,对该散热板批量生产机械加工工艺开展了分析研究,采用组合加工解决了异形件铣削装夹难的问题,利用零件的结构设计了工装吸盘,缩短了装夹时间,同时减少了加工工序,提高了散热板批生产的加工效率,有效降低了加工成本。

花键孔零件磨齿精度保证的工艺研究

以内孔为花键孔、非对称结构的异形齿轮件为研究对象,通过变形分析,设计热处理补偿套、花键心轴,优化了热后加工工艺,完成了异形内花键齿轮件磨齿试验加工,满足了产品图纸的设计要求。同时,探索了一种新的工艺加工方法,达到成本最优的目的。

典型非对称零件仿形精磨研究与应用

磨削加工因加工精度高、表面质量好,加工质量稳定并适合大批量生产,被广大制造企业长期使用。磨削采用零件或砂轮回转运动的形式使用砂轮的端面或者圆周面进行磨削工作。而非对称结构的零件由于自身的偏心作用,在旋转时产生振动或者离心,对磨削加工的精度和质量有很大的影响,也是一直以来制约磨削加工精度的重要因素。本文选取了典型的非对称产品,通过分析零件的结构特点,设计专用的装夹方案,并改造专用机床,结合经验进行加工用量的调整,最终加工出高质量的合格产品。

基于UG平台的塑料异型材挤出模标准件库的建立

针对塑料异型材挤出模中存在大量标准件这一特点,以UG软件为开发平台,利用VC++6 0面向对象的编程技术,在UG/OpenAPI开发平台上,创建参数化图库、设计用户界面、实现参数化尺寸驱动,总结了系统的主要功能和特点,建立了三维塑料异型材挤出模的标准件库。

测试条件的变化对草莓质地剖面分析结果的影响

研究草莓质地剖面分析(texture profile analysis,TPA)测试中不同的参数(测试速度、停顿时间、压缩距离)设置对测试结果的影响,同时比较草莓不同部位(中部、底部)的质地差异。研究发现:任何一个参数设置的改变都必然导致TPA测定结果中的部分参数测定值发生显著变化,其中压缩距离的改变导致的黏着性、回复性和凝聚性变化最为突出。同时,不同部位果肉的硬度、黏着性、弹性无显著差异,但中部果肉的咀嚼性、凝聚性和回复性数值要显著高于底部。

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。

深反射地震数据揭示的拉萨地体北部到羌塘地体南部地壳厚度的变化

由多个地体拼接而成的青藏高原,有着世界上最厚的地壳。在高原中部,从拉萨地体到羌塘地体,穿过班公湖—怒江缝合带(BNS)的地壳厚度变化长期存在争议。本文主要论述从拉萨地体北端横跨BNS到达羌塘地体的深地震反射剖面探测的结果。探测发现了清晰的Moho反射,揭示了拉萨地体—羌塘地体Moho深度和地壳厚度的变化。探测结果表明,在BNS下方Moho深度由南至北出现了6.2 km的急剧减小,并且与BNS向北28 km处的羌塘地体南部比较,地壳厚度变浅了12.5 km。否定了前人对BNS下方Moho存在20 km显著变化的认识。

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。