Design of Drilling and Riveting Multi-functional End Effector for CFRP and Aluminum Components in Robotic Aircraft Assembly

To fulfill the demands for higher quality,efficiency and flexibility in aviation industry,a multi-functional end effector is designed to automate the drilling and riveting processes in assembling carbon fiber reinforced polymer(CFRP)and aluminum components for a robotic aircraft assembly system.To meet the specific functional requirements for blind rivet installation on CFRP and aluminum materials,additional modules are incorporated on the end effector aside of the basic processing modules for drilling.And all of these processing modules allow for a onestep-drilling-countersinking process,hole inspection,automatic rivet feed,rivet geometry check,sealant application,rivet insertion and installation.Besides,to guarantee the better quality of the hole drilled and joints riveted,several online detection and adjustment measures are applied to this end effector,including the reference detection and perpendicular calibration,which could effectively ensure the positioning precision and perpendicular accuracy as demanded.Finally,the test result shows that this end effector is capable of producing each hole to a positioning precision within ±0.5 mm,aperpendicular accuracy within 0.3°,a diameter tolerance of H8,and a countersink depth tolerance of±0.01 mm.Moreover,it could drill and rivet up to three joints per minute,with acceptable shearing and tensile strength.

An Overview of Self-piercing Riveting Process with Focus on Joint Failures, Corrosion Issues and Optimisation Techniques

Self-piercing riveting(SPR)is a cold forming technique used to fasten together two or more sheets of materials with a rivet without the need to predrill a hole.The application of SPR in the automotive sector has become increasingly popular mainly due to the growing use of lightweight materials in transportation applications.However,SPR joining of these advanced light materials remains a challenge as these materials often lack a good combination of high strength and ductility to resist the large plastic deformation induced by the SPR process.In this paper,SPR joints of advanced materials and their corresponding failure mechanisms are discussed,aiming to provide the foundation for future improvement of SPR joint quality.This paper is divided into three major sections:1)joint failures focusing on joint defects originated from the SPR process and joint failure modes under different mechanical loading conditions,2)joint corrosion issues,and 3)joint optimisation via process parameters and advanced techniques.

Approach to Interference Riveting Process Control of Aircraft Automatic Drilling and Riveting

Interference fit riveting is an effective way to improve the fatigue life of aircraft.The accurate control of riveting interference of aircraft automatic drilling and riveting equipment is achieved by process parameters including upsetting force and upset head height.It is valuable for aircraft manufacturing engineering.An approach to interference riveting process control based on the analysis of interference riveting stress field is proposed.According to assembly structure,the upsetting force is calculated by the material property and interference fit level,and the upset head height is deduced by the upsetting force.The experimental result shows that the interference fit level can be controlled accurately by the upsetting force and upset head height,and then,the quality of aircraft automatic riveting can be improved.The proposed approach is verified by the good match between the predicted result and the experimental result.

Friction-based riveting technique for AZ31 magnesium alloy

A new friction-based riveting technique, Rotating Hammer Riveting(RHR), is demonstrated to fully form AZ31 Mg rivet heads in a mere 0.23 s. Heat and pressure generated through severe plastic deformation during the process was sufficient to form the Mg rivet head without the need for a pre-heating operation. Due to preliminary twinning and followed by dynamic recrystallization, AZ31 Mg grains in the rivet head were refined during RHR, which enhance the formability of Mg rivets by triggering grain boundary sliding and reducing plastic anisotropy of Mg. In addition, RHR joints showed a metallurgical bond between the rivet head and top AZ31 Mg sheet, which eliminates a significant pathway for corrosion.

Study of galvanic corrosion and mechanical joint properties of AZ31B and carbon-fiber–reinforced polymer joined by friction self-piercing riveting

A new testing methodology was developed to quantitively study galvanic corrosion of AZ31B and thermoset carbon-fiber–reinforced polymer spot-joined by a friction self-piercing riveting process.Pre-defined areas of AZ31B in the joint were exposed in 0.1 M NaCl solution over time.Massive galvanic corrosion of AZ31B was observed as exposure time increased.The measured volume loss was converted into corrosion current that was at least 48 times greater than the corrosion current of AZ31B without galvanic coupling.Ninety percent of the mechanical joint integrity was retained for corroded F-SPR joints to 200 h and then decreased because of the massive volume loss of AZ31B。

Friction self-piercing riveting(F-SPR)of aluminum alloy to magnesium alloy using a flat die

Friction self-piercing riveting(F-SPR)process based on a pip die has been invented to solve the cracking problems in riveting high-strength and low-ductility light metals,such as magnesium alloys,cast aluminum,and 7 series aluminum alloys.In this paper,in order to solve quality issues caused by the misalignment between rivet and pip-die in F-SPR,a flat-die based F-SPR process was proposed and employed to join 1.27 mm-thick AA6061-T6 to 3 mm-thick AZ31B.The results indicate that a 1.0 mm die distance is effective to avoid rivet upset and insufficient flaring.As the feed rate increases,the heat input in the whole process decreases,resulting in a larger riveting force,which in turn increases both the bottom thickness and interlock amount.Besides,solid-state bonding,including Al-Mg intermetallic compounds(IMCs),Al-Mg mechanical mixture,and Al-Fe atom interdiffusion was observed at the joint interfaces.The upper Al layer was softened,but the lower Mg layer was hardened,and both sheets exhibited a narrowed affected region with the increase of feed rate,while the rivet hardness shows no obvious change.Three fracture modes appeared accompanying the variations in lap-shear strength and energy absorption as the feed rate increased from 2 mm/s to 8 mm/s.Finally,the F-SPR process using a flat die was compared to those using a pip die and a flat bottom die to show the advantage of flat die on coping with the misalignment problem.

A Laser Line Scanner Based Hole Position Correction Mechanism for Automatic Drilling and Riveting in Aircraft Assembly

The low-stiffness of aircraft skins may results in the differences between aircraft actual parts and their theoretical models,which will consequently affect the accuracy of automatic drilling and riveting in aircraft assembly.In this paper,a novel approach of hole position correction using laser line scanner(LLS)is proposed to assign a single row of holes on the parts’surfaces.First,we adopt a space circle fitting method and the random sample consensus(RANSAC)to obtain the precise coordinates of center of the datum holes’coordinates.Second,LLS is calibrated by the laser tracker,and the relations between the LLS coordinate system and the tool coordinate system(TCS)can be calculated.Third,the kinematics model of the automatic riveting machine is established based on a two-point referencing strategy proposed in this paper.Thus,the positions of the holes to be drilled can be adjusted.Finally,the experimental results show that in TCS the measurement error of LLS is less than 0.1 mm,and the correction error of the hole position is less than 0.5 mm,which demonstrates the reliability of our method.

A Comparative Study of Friction Self-Piercing Riveting and Self-Piercing Riveting of Aluminum Alloy AA5182-O

In this paper,self-piercing riveting(SPR)and friction self-piercing riveting(F-SPR)processes were employed to join aluminum alloy AA5182-O sheets.Parallel studies were carried out to compare the two processes in terms of joint macrogeometry,tooling force,microhardness,quasi-static mechanical performance,and fatigue behavior.The results indicate that the F-SPR process formed both rivet–sheet interlocking and sheet–sheet solid-state bonding,whereas the SPR process only contained rivet–sheet interlocking.For the same rivet flaring,the F-SPR process required 63%less tooling force than the SPR process because of the softening effect of frictional heat and the lower rivet hardness of F-SPR.The decrease in the switch depth of the F-SPR resulted in more hardening of the aluminum alloy surrounding the rivet.The higher hardness of aluminum and formation of solid-state bonding enhanced the F-SPR joint stiffness under lap-shear loading,which contributed to the higher quasi-static lap-shear strength and longer fatigue life compared to those of the SPR joints.

Embedment Effect on Eliminating Damage of CFRP Pull-riveting Process by Simulation Study

The rivet joints have been widely applied in aerospace and vehicle fields.During the joining process of the carbon fiber reinforced plastic(CFRP)laminates,the pre-tightening force of pulling-rivet was the key factor to ensure the connection performance.To predict the impact of clamping loads on stress and failure of laminates,the value of stress and damage evolution of the wall of a hole under the pre-tightening force were simulated by the finite element method.The results of the simulation showed that excessive clamping force led to the damage and failure of CFRP in the hole edge.Connection performance together with progressive failure process and failure modes of CFRP laminates with various pre-tightening forces were investigated.A kind of metal embedded parts embedded in the laminates was designed to reduce the damage by the simulation study.Simulation results showed that embedment reduced the failure and damage efficiently.The embedment reduced about 64%of the maximum stress.

Progressive Failure Analysis of Composite/Aluminum Riveted Joints Subjected to Pull-Through Loading

Out-of-plane mechanical properties of the riveted joints restrict the performance of the wing box assembly of airplane.It is necessary to investigate the pull-through performance of the composite/metal riveted joints in order to guide the riveting design and ensure the safety of the wing box assembly.The progressive failure mechanism of composite/aluminum riveted joint subjected to pull-through loading was investigated by experiments and finite element method.A progressive damage model based on the Hashin-type criteria and zero-thickness cohesive zone method was developed by VUMAT subroutine,which was validated by both open-hole tensile test and three-point bending test.Predicted load-displacement response,failure modes and damage propagation were analysed and compared with the results of the pull-through tests.There are 4 obvious characteristic stages on the load-displacement curve of the pull-through test and that of the finite element model:first load take-up stage,damage stage,second load take-up stage and failure stage.Relative error of stiffness,first load peak and second load peak between finite element method and experiments were 8.1%,-3.3%and 10.6%,respectively.It was found that the specimen was mainly broken by rivet-penetration fracture and delamination of plies of the composite laminate.And the material within the scope of the rivet head is more dangerous with more serious tensile damages than other regions,especially for 90°plies.This study proposes a numerical method for damage prediction and reveals the progressive failure mechanism of the hybrid material riveted joints subjected to the pull-through loading.

铆接铝合金板铆钉失效缺陷检测方法研究

针对车身用铝合金板内部铆钉缺陷特征提取难度大、缺陷类型与程度识别准确率低的问题,提出一种基于高斯卷积深度信念网络与双向长短期记忆网络相结合的铆钉失效缺陷诊断模型与检测方法。首先,面向5种铆钉断裂缺陷设计试件并搭建自动检测系统,通过规划和调整探头姿态有效地降低提离效应对检测信号的影响。其次,设计双网络融合诊断模型提取和学习多维度缺陷特征信息,解决检测曲线中由时序变化特性和空间分布状态表征的缺陷信息提取难题。实验结果表明,与传统卷积网络及单一深度信念网络相比,优化后算法诊断模型的平均准确率为99.85%,相比提升了14.54%,且具有良好的通用性和鲁棒性,可实现铆钉内部缺陷的在线诊断。

基于改进DETR的机器人铆接缺陷检测方法研究

铆接作为铁道车辆结构件的主要连接方式,合格的铆接质量是车辆安全稳定运行的重要保证。针对现有铆接缺陷检测方法存在检测精度低、检测点位少、检测智能化水平不高等问题,提出一种基于改进DETR的机器人铆接缺陷检测方法。首先,搭建铆接缺陷检测系统,依次采集工件尺寸大、铆钉尺寸小工况下的铆接缺陷图像。其次,为了增强DETR模型在小目标中的图像特征提取能力和检测性能,以EfficientNet作为DETR中的主干特征提取网络,并将3-D权重注意力机制SimAM引入EfficientNet网络,从而有效保留图像特征层的镦头形态信息和铆点区域的空间信息。然后,在颈部网络中引入加权双向特征金字塔模块,以EfficientNet网络的输出作为特征融合模块的输入对各尺度特征信息进行聚合,增大不同铆接缺陷的类间差异。最后,利用Smooth L1和DIoU的线性组合改进原模型预测网络的回归损失函数,提高模型的检测精度和收敛速度。结果表明,改进模型表现出较高的检测性能,对于铆接缺陷的平均检测精度mAP为97.12%,检测速度FPS为25.4帧/s,与Faster RCNN、YOLOX等其他主流检测模型相比,在检测精度和检测速度方面均具有较大优势。研究结果能够满足实际工况中大型铆接件的小尺寸铆钉铆接缺陷实时在线检测的需求,为视觉检测技术在铆接工艺中的应用提供一定的参考价值。

轴向荷载作用下小规格拉铆钉和普通螺栓疲劳性能对比研究

拉铆钉因其良好的防松动、抗疲劳和防腐性能以及较强的环境适应性等特点而被广泛应用于航空航天、轨道交通、桥梁建筑等领域。为解决光伏支架中螺栓连接易发生疲劳的问题,现研究一种国产新型拉铆钉的轴向疲劳性能,用以代替普通螺栓连接进而提高光伏支架的疲劳寿命。对LMY8和LMY10小规格拉铆钉及同规格的普通螺栓进行了轴向荷载作用下的静力试验和疲劳试验,并利用ABAQUS软件进行了拉铆钉铆接过程的模拟,利用FE-Safe软件对拉铆钉疲劳寿命进行了模拟。研究结果表明:在同样条件下,铆钉的疲劳性能优于普通螺栓的疲劳性能;拉铆钉在轴向荷载作用下的疲劳断口位于套环和锁紧环槽啮合的第一圈螺纹处,此处应力集中是拉铆钉发生疲劳失效的主要原因;拉铆钉的疲劳寿命会随着最小荷载的增大而提高,随最大荷载的增大而降低;由疲劳云图可知,拉铆钉在承受轴向循环荷载作用时,铆钉头部下方R角过渡处也会产生较大的应力,此区域也是易发生疲劳失效的部位。

基于优化Hough变换的铆接高度差亚像素检测方法研究

针对飞机铆接高度差的检测问题,提出了一种优化的Hough变换铆接高度差亚像素检测方法。该方法首先通过空间域点运算的灰度变换法对采集的铆接孔图像进行增强处理,然后利用局部阈值分割法进行图像分割,采用Canny算法进行边缘粗提取,再利用优化的Hough变换进行亚像素级的边缘精细提取,提取出铆接孔和铆钉钉头的圆环区域,最后结合RANSAC算法进行圆拟合,利用开发算子get_current_region_z()分别提取内外圆环区域的高度平均值,再通过函数height_Z()将所得的高度平均值作差即可得到铆接表面的高度差。经试验证明,该检测方法亚像素精确定位能力强,检测结果准确率高、稳定性好,重复测量精度可达到±10μm。

改良铆钉缝合法在后腹腔镜下肾部分切除术中的应用

目的探讨改良铆钉缝合法在后腹腔镜下肾部分切除术中的临床效果。方法选取2019年3月至2022年3月因肾细胞癌于郑州人民医院泌尿外科接受后腹腔镜下肾部分切除术的患者,共81例,回顾其临床资料,根据缝合方法分为研究组(改良铆钉缝合,41例)和对照组(倒刺线连续缝合,40例),总结临床资料,比较两组患者的热缺血时间、术中出血量、术后引流量、术后尿漏发生率、术后肾周血肿发生率、术前术后血红蛋白下降情况。结果研究组热缺血时间短于对照组,术中出血量、术后引流量、术后尿漏及肾周血肿发生率均低于对照组(P<0.05)。术后研究组血红蛋白水平高于对照组,差异有统计学意义(P<0.05)。对照组中出现1例术后尿瘘和2例术后肾周血肿,经过治疗后好转,研究组未出现并发症。结论改良铆钉缝合法在后腹腔镜下肾部分切除术中效果确切,可缩短肾脏热缺血时间,减少术中出血量及术后并发症,值得在临床推广。

铆接夹层间隙对单搭接铆接头振动疲劳性能的影响研究

为了考虑装配间隙对单搭接结构振动疲劳性能的影响,利用ABAQUS软件建立了飞机发动机进气道局部结构金属铆接头的弹塑性有限元模型,采用Johnson-Cook失效模型模拟铆钉与被连接件的渐进失效行为,得到了不同装配间隙量的铆接头应力场分布与振动疲劳寿命。对单搭接铆接头进行振动疲劳试验,试验结果与仿真结果在疲劳寿命方面吻合较好,验证了数值模型的准确性。与无间隙模型相比,含间隙铆接试件各铆钉疲劳寿命降低了4.7%~18.0%,间隙的存在也导致了压铆过程中相邻铆钉间的挤压载荷传递,整体表现为铆钉与被连接板接触界面应力激增,导致有间隙铆接头残余应力场与无间隙铆接头残余应力场之间的差异,从而影响铆接头的振动疲劳性能。

螺栓连接和拉铆连接在剪切循环荷载作用下的松动行为研究

拉铆连接凭借其优秀的防松性能,被应用于越来越多的工程领域。为研究国产新型拉铆钉在剪切循环荷载作用下的松动性能,以应用最为广泛的螺栓连接为对照,分别对规格为8 mm的4.8级普通螺栓、4.8级防松螺栓以及小规格拉铆钉进行剪切循环荷载下的松动试验研究,分析了三类连接在剪切循环荷载作用下的松动过程,研究了荷载幅值和频率对螺栓连接和拉铆连接松动行为的影响。结合微观测试手段分析其损伤形貌,进一步研究剪切循环荷载下螺栓和拉铆钉的防松原理及微动损伤机制。研究表明:在同种工况下拉铆连接的防松性能优于螺栓连接的防松性能;当荷载幅值增大或荷载频率减小时,螺栓连接和拉铆连接的松动程度增大;相较于螺栓,拉铆钉独特的圆弧结构牙型和铆接成型后牙型配合面的过盈配合机制,使其防松性能有明显提升;螺栓与拉铆钉的磨损机制主要是磨粒磨损和疲劳磨损。

自攻螺钉与拉铆钉混合连接受剪承载性能试验

为改善自攻螺钉连接的构件在地震作用下易发生拉脱导致结构严重破坏的缺点,提升冷弯薄壁型钢组合墙体抗破坏能力,分析了组合墙体层间连接处的传力机理,针对自攻螺钉的破坏模式,提出拉铆钉与自攻螺钉混合连接。为研究混合连接的抗剪性能,共进行了48组连接接头抗剪性能试验,包含冷弯薄壁型钢结构常用的5种连接板厚度,不同搭接板厚比(变化范围1.0~2.0),包含纯自攻螺钉连接、纯拉铆钉连接及混合连接的连接方式。观察混合连接的破坏模式,自攻螺钉未发现拉脱破坏,其破坏模式主要表现为:板承压破坏与螺钉倾斜组合破坏、铆钉剪断破坏及板承压与铆钉部分剪断组合破坏3种;相较单一连接方式,混合连接荷载–位移曲线表现出更长的塑性阶段;当板厚比大于1.5且组合板厚小于3.0mm,混合连接的承载力及延性较单一连接增长明显;利用现有计算方法对混合连接的承载力进行累加计算,与试验结果对比,计算结果偏保守。研究发现:混合连接能较好地弥补拉铆钉和自攻螺钉受剪过程中的缺陷,有效改善自攻螺钉拉脱破坏,从而提升连接的承载力及延性;板厚和板厚比是影响混合连接破坏模式及承载力的重要因素,与单一连接相比,板厚比越大,承载力提升越大;排布方式对混合连接的力学性能及破坏机理影响有限;在本文试验工况下,结合混合连接的破坏模式,在现有计算方法的基础上,提出改善后的计算方法,其计算结果更合理。

基于结构光的铆钉凹凸量双目视觉检测方法

为了弥补飞机铆钉凹凸量的传统检测方式在精度、效率及稳定性方面的不足,提出了一种基于结构光的铆钉凹凸量双目视觉检测方法。首先通过工业投影仪将结构光投射到铆接表面,由双目相机采集投影图像。然后根据铆钉边缘特征提取出铆接区域,并采用改进的格雷码解相位方法计算铆接区域表面的相位信息。根据相位信息匹配特征点,利用视差原理计算出点云。最后通过点云数据处理,计算出铆钉的凹凸量。制作标准件并完成了凹凸量测量试验,测量误差在±20μm以内,重复测量标准差小于3μm,单个铆钉测量用时约2.2 s,能够满足现场测量精度和效率要求。

采用多元非线性回归模型的无头铆钉安装干涉量预测

为明晰被连接件材料性能对安装干涉量的影响规律,并进一步为新材料扩展应用提供可靠性预测,在铆接过程有限元仿真数据基础上,提出了一种采用多元非线性回归模型的无头铆钉安装干涉量预测方法。首先,根据实际铆接过程建立有限元仿真模型,通过铆接试验验证模型有效性。然后,采用有限元和正交试验法,研究了被连接件弹性模量、屈服强度、强化系数和应变强度指数及其交互作用对铆接干涉量水平的显著性,明确了各因素对安装干涉量的影响效果。最后,选用幂函数作为多元非线性回归的函数形式,剔除显著性较低因素项,建立了待测位置干涉量回归预测模型。结果表明,在一定铆接工艺条件下,屈服强度和应变强度指数及其交互作用是影响干涉量水平的主要因素。对比模拟值与回归模型预测值发现两者变化趋势一致,且误差不超过10%,表明干涉量多元回归预测模型具有有效性。