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Automatic riveting systems play a crucial role in the field of aircraft manufacturing. In the riveting process, the machine tool bears a large axial squeezing force, and the resulting deformation will inevitably affect the riveting quality. In this paper, a dual-machine riveting system is developed first, the kinematic chain model and the lower-numbered body of the system structure are constructed sequentially. Then, considering the interaction and coupling effect of the two machines in the actual riveting process, the relative stiffnesses of the dual machine in the resisting state are identified by loading tests. Based on the stiffness data at a combination of postures within the workspace, a Kriging prediction model is established to describe the relationship between stiffness and postures. According to the prediction results, the influence of rotational and translational axes on the spatial stiffness distribution of the riveting system is revealed. Finally, the online deformation compensation is realized by modifying the displacement of the feed axis on both sides. A riveting experiment is carried out, and the results demonstrate that the riveting quality is significantly improved after compensation.

Riveting is an important interference-fit joining technology, which has been widely applied in aircraft assembly and many manufacturing fields. The rivet head flushness is an import industrial standard for the quality evaluation of a riveted joint. It would influence the aerodynamic performance of aircraft if not carefully controlled. In this paper, a finite element model (FEM) of automatic countersunk riveting is established and the formation of rivet head flushness is studied by the simulation results. Then, based on the coordinated motion of the riveting bar and the anvil tool, several compensation strategies are proposed to reduce the rivet head flushness and ensure the riveting quality, in which the riveting bar and anvil tool feed with the same speed (RASS) strategy is considered as the most efficient one. Finally, riveting experiments are conducted on a dual-machine-based automatic drilling and riveting system. The experimental results indicate that the simulation result is accurate, and the RASS compensation strategy is applicable and effective. This paper studies the formation mechanism and compensation method of the rivet head flushness for the countersunk rivet and provides scientific guidance for the riveting process optimization in engineering applications.

Automated fiber placement machine is the key equipment for low-cost and automated manufacturing of high-performance carbon composite materials. In order to meet the required position accuracy of fiber placement, this paper focuses on the kinematic modeling and parameter identification of the automated fiber placement machine. A kinematic model taking account of geometric deviations is established firstly. Since joint interfaces are the main origin of gravity deformation in a machine tool, an elastic beam deformation model is introduced to represent the joint interface, and then the former kinematic model is modified by analytical expressions of the gravity deformation for each joint interface. Based on the measurement data and the Levenberg-Marquardt optimization method, the parameter identification of the kinematic model is realized, and main issues such as measurement data selection, objective function definition are discussed. Finally, a kinematic calibration experiment is performed, and the experimental results verify the feasibility and validity of the modeling method. The position errors in Z direction of the automated fiber placement machine are effectively reduced by over 80%, which suggests that the proposed method reduces the effect of the gravity deformation and improves the accuracy of the automated fiber placement machine.

Riveting is widely used in aircraft manufacturing. The strap butt joint is often used in the aircraft’s main bearing area such as the aircraft docking area. The connection quality affects the reliability and safety of the aircraft directly. To study the effect of the rivet position on the connection quality of the strap butt joints, this paper analyzed the distribution of stress around the rivet hole at different positions by the finite element method, and then further analyzed the influence of the different rivet layouts on the connection quality of the strap butt joints by experiments. The static load tensile failure test of the joints was carried out, and the obtained tensile strength and failure mode of the strap butt joints showed that the main static tensile failure form of the single strap butt joint is that the whole rivets is sheared and the connecting sheets are separated. By changing the layout of different rivets, the connection strength can be maximized by reducing the outer row spacing (ORSD) of rivets. The results can be used for reference in the design of the riveting structure of aircraft panels.

Force-induced deformation of machine tools has a great influence on the workpiece dimension and surface quality. For the dual-machine-based riveting system, the great squeezing force during riveting process not only causes structural deformation of the machine tools but also leads to inaccurate positioning of the riveting bar and dimension deviation of riveted joints. Moreover, the force-induced deformation usually changes with the varying poses of the machine tools, which makes it more difficult to predict precisely. In this paper, an efficient prediction and compensation method of force-induced deformation is developed based on finite element modeling (FEM) and artificial neural network. Firstly, a series of finite element models at selected poses are established to obtain the deformation data. Then, a force-induced deformation prediction model is established through radial basis function neural network with adaptive genetic algorithm optimization (AGA-RBF). Furthermore, a basic strategy is proposed to compensate for the predicted error through the motion commands modification. Finally, a contrast experiment is carried out to verify the feasibility and efficiency of the proposed method.

Automatic drilling and riveting system has been widely used in aircraft manufacture field to satisfy the increasing demands of assembly quality. During the automatic riveting process, the riveting-side working head is the key component to perform the action of pressing rivet and its deformation has a great impact on riveting quality. In this paper, firstly, a theoretical model is established to investigate the factors influencing the deformation of riveting-side working head according to its structure and working situation. Then, the FE models with different squeezing displacements and riveting angles are established to analyze the effort of deformation of the riveting-side working head on driven head dimension, interference, and deformation of riveted hole on panels. Lastly, experiments are performed to verify the simulation results. The results show that the deformation of the riveting-side working head has a significant impact on the final riveting quality, and it can be compensated by increasing the riveting displacement.

Many previous studies have mainly focused on the effects of riveting parameters on single-row riveted lap joints. Little attention has been paid to multi-row riveted lap joints. The outer rows of a normal multi-row riveted lap joint usually bear a larger part of the tensile load. However, none of the studies relate the phenomenon to the squeezing displacement combination of a multi-row riveted lap joint. To improve the performance of a three-row riveted lap joint, this paper aims to reveal the internal relation between tensile load distribution, structural deformation and squeezing displacement combination. Theoretical discussion, numerical simulation and an experimental test have been conducted. Four different squeezing displacement combinations have been studied. The result indicates that an appropriate squeezing displacement combination can effectively make tensile load distribution more homogeneous. Each rivet can take approximately 33% tensile load. Structural deformation magnitude can be reduced as well. Compared with the worst situation, at the region most sensitive to tensile load, the max strain value can reduce about 53.22–79.76%. A suitable squeeze displacement combination is a simple approach for the performance enhancement of a three-row riveted lap joint. It can be practically applied in aircraft manufacturing without any additional equipment or skill learning.

Riveting is the most commonly used connection method in aircraft assembly, and its quality has a crucial effect on the fatigue performance of aircraft. Many factors affect the riveting quality, among which the influence of the riveting angle and direction is not clear. In this paper, a three-dimensional finite element model of single-rivet lap joints is established and verified by the driven head geometry and the riveting force data obtained from the riveting experiments. Then, by adjusting the angle and direction of the punch in the finite element model, the riveting process is simulated at the angles of 0°, 1°, 2°, and 3° and the directions of 0° and 180° to investigate the deformation of the lap joints, the stress distribution around the hole, and the stress distribution of the rivet. Finally, the fatigue tests of the single-rivet lap joints are performed and the influence of the riveting angle and direction on the connection quality and fatigue performance of the riveting joints is analyzed.

The slug rivet installation process is complex. A lot of parameters are included during the riveting deformation process. The workload and time cost of a traditional simulation study is very high since a traditional numerical model should be modified manually time by time when riveting parameters change. The data processing after simulation is another complex work. To improve the situation, this paper presents a parameterized modeling method. The modeling process and data processing algorithm can be developed using Python script. The parameterized model can automatically and continuously re-build without any manual intervention according to the riveting parameter auto-update condition. The post-processing analysis can be automatically conducted and saved as well. Then this paper conducts continuous analysis to illustrate the impact of riveting parameters on riveting quality. The parameterized model keeps running 41 times until the riveting parameter is out of range. The parameterized modeling method is a useful method for a simulation study. The study will pave the way for further investigations.

The automated installation of hi-lok nuts by the robot is an effective way to replace tedious manual labor. For this purpose, an appropriate end-effector needs to be designed to carry out the feeding, alignment and fastening tasks. According to the installation process of hi-lok nuts, a motor driven fastening tool is designed with two parts: the front nut runner and rear driving shaft. The fastening task is modeled based on the force balances in the nut screwing action, which present the nut runner can rotate the nut as well as feed it axially. Then, a feeding-alignment (FA) device is designed to engage the nut feeding for fastening tool. The alignment action is modeled through the force balance about hi-lok nut involved with the nut gripper and nut runner. Finally, a tool end-effector has been built and integrated with an industrial robot. The successful implementation of automated installation of hi-lok nut demonstrates the effectiveness of the proposed installation method and the validation of the designed robotic end-effector.

Interference-fit riveting is one of the most widely used mechanical joining ways in aircraft assembly. The fatigue performance of riveted joints has a significant impact on the service life and reliability of aircraft. In this paper, the fatigue performance of the riveted lap joints with various rivet diameters and pitches are studied based on stress distribution analysis under tensile load. First, a theoretical model of the riveted lap joint under tensile load is developed by using the spring-mass model. The rivet-load stress, bypass stress, and interference stress around the riveted hole are analyzed. Then, the finite element (FE) model of riveted lap joints are established. The influence of rivet diameter and pitch on stress distribution around the riveted hole are discussed. Finally, the fatigue tests are conducted with riveted lap joint specimens to verify the theoretical model and FE results, and a good agreement is observed. Based on the simulation and experimental results, a good combination of structural parameters of the riveted lap joint is found which can optimize the stress distribution around the riveted hole and improve the fatigue life of the riveted lap joint.

Interlayer burrs formation during drilling of stacked plates is a common problem in the field of aircraft assembly. Burrs elimination requires extra deburring operations which is time-consuming and costly. An effective way to inhibit interlayer burrs is to reduce the interlayer gap by preloading clamping force. In this paper, based on the theory of plates and shells, a mathematical model of interlayer gap with bidirectional clamping forces was established. The relationship between the upper and lower clamping forces was investigated when the interlayer gap reaches zero. The optimization of the bidirectional clamping forces was performed to reduce the degree and non-uniformity of the deflections of the stacked plates. Then, the finite element simulation was conducted to verify the mathematical model. Finally, drilling experiments were carried out on 2024-T3 aluminum alloy stacked plates based on the dual-machine-based automatic drilling and riveting system. The experimental results show that the optimized bidirectional clamping forces can significantly reduce the burr heights. The work in this paper enables us to understand the effect of bidirectional clamping forces on the interlayer gap and paves the way for the practical application.

Slug rivet interference-fit riveting is one of the advanced connection technologies. Many researches have been conducted to study the quality of slug rivet assembly. However, some previous theoretical studies have only focused on the riveted lap joints without countersunk hole structure. To make a more comprehensive understanding of the riveting quality, this paper first proposes an effective method to study the riveted assembly with countersunk hole structure. An effective and accurate theoretical model is built to reflect the mapping relationship between squeezing force and driven head dimension. Since the driven head dimension is the riveting quality control criterion, and the squeezing force is the most important riveting parameter. Simulations and experiments are conducted to verify the validity of the theoretical analysis. Comparison results prove the theoretical model’s ability to analyze the rivet deformation. Theoretical analysis can provide an effective compact analysis. The study will pave the way for further investigations.

Purpose The purpose of this paper is to design, analyze and optimize a new type of inner-side working head for automatic horizontal dual-machine cooperative drilling and riveting system. The inner-side working head is the key component of automatic drilling and riveting system, and it is a challenge to design an inner-side working head which must be stiffness and stable with a compact structure to realize its functions. Design/methodology/approach According to the assembly structure features of large aircraft panels and riveting process requirements, a new type of inner-side working head is designed for pressure riveting. The force condition of the inner-side working head during the riveting process is analyzed and the deformation model is established. Design optimization is performed based on genetic algorithm and finite element analysis. The optimized inner-side working head is tested with automatic horizontal dual-machine cooperative drilling and riveting system. Findings The deformation model provides the precision compensation basis for control system. Application test results show that the automatic drilling and riveting system can realize assembly of large aircraft panel with high efficiency and quality through the inner-side working head. Research limitations/implications The inner-side working head has been used in aircraft panel assembly. Practical implications The inner-side working head has been used in aircraft panel assembly. Originality/value This paper presents the design, analysis and optimization of a new type of inner-side working head which can realize automatic riveting for aircraft panel. The research will promote the automation of aircraft panel assembly.

Slug rivet interference-fit riveting is one of the advanced connection technologies, which has been widely applied in aerospace manufacture. In the fields of residual stress analysis, structural deformation analysis, load transfer mechanism analysis, and the assessment of the effects of process parameters on riveting quality, study accuracy needs increasingly accurate and comprehensive models. Since the simulation of riveting process is a particularly time-consuming case. The aim of this paper is to develop some appropriate FE models for the special applications with a compromise between model size, calculation time, and simulation precision. Different types of FE models have been established based on force-controlled approach and displacement-controlled approach. The comparison between different FE models is satisfactory in terms of riveting process and riveting quality control criterion. The study significantly deepens the comprehension of the slug rivet installation process. Subsequent research can select an appropriate model according to its special target. The study will pave the way for further investigations.

I n a dual-machine system, the positioning accuracy of coordinated machine tools is one of the most important performances. Considering the quasi-static errors of the developed system, the paper presents an effective error prediction and compensation method for coordinated five-axis machine tools under variable temperature. Firstly, for error prediction at a constant temperature, the workspace of coordinated machines is divided into the subspaces of translation and rotation axes, and an error prediction algorithm is presented with the known errors at sampled points. When the temperature changes, the thermal errors of the coordinated machines are analyzed by the simulation and error measurement, and an interpolation method is proposed to quickly determine the sampled data at any temperature. For error compensation, a recursive algorithm is proposed to compensate the absolute and relative pose error of dual machines. Validation experiments have been conducted to verify the proposed method on the developed system. The results have shown that, compared with previous method, the method presented in this paper is more accurate and time-efficient for error prediction and compensation under variable temperature conditions.

Automatic oval hole machining is a great challenge in monolithic wing assembly of aircraft. In this paper, a new six-axis machine tool for oval hole drilling in aircraft wing assembly is developed, and an efficient kinematic modeling and inverse kinematics method for six-axis machine tools is proposed. After a brief structure analysis, necessary coordinate systems are established to build the generalized kinematic model of the six-axis machine tool. Then, with the concept of separation and combination, an inverse kinematics strategy for six-axis machine tools is proposed to improve the accuracy, efficiency, and stability of the algorithm. All motion axes are separated into three groups and their joint coordinates are solved successively based on the joints separation strategy (JSS) for solution. Finally, the inverse kinematic solution of the six-axis machine tool is composed of the prismatic joints with analytical solutions, revolute joints with analytical solutions, and revolute joints with numerical solutions. To verify the validity of the proposed method, numerical and machining experiments have been performed on the developed six-axis machine tool. In the simulation, two error vectors for joint coordinates and the pose of tool tip are presented to evaluate the accuracy of the inverse kinematics algorithm. The simulation results show the great success of the proposed method. Moreover, the position and orientation errors of the drilled oval holes are within 0.093 mm and 0.408°, which is accurate enough to meet the requirement for automatic oval hole machining in aircraft assembly.

Some controllable process parameters in the riveting process such as the gap between sheets, have an important impact on the quality of a riveted butt joint. In this paper, the finite element model of a riveted single-strap butt joint is established with the help of ABAQUS analysis software, and the riveting process is simulated under five kinds of gaps between sheets. From the perspectives of rivet upsetting size, rivet interference, radial deformation of sheet, and analysis of residual stress around the hole of sheet, the influence of the gap between sheets on the connection quality of the riveted butt joint is summarized. The results show that the left and right sheets will contact each other and there is extrusion stress between the sheets when the gap is zero. When the applied tensile load continues to increase, due to the influence of the secondary bending, the strap sheet responsible for the connection produces warping deformation, and there will be no further contact between the sheets. When the gap between sheets increases from 0 to 2 mm, the maximum deformation of strap sheets increases from 0.876 to 0.927 mm, which proves that the gap between sheets have no significant effect on the deformation of the strap sheet.

This paper investigates the effect of Z-pin insertion angles (60°, 75° and 90°) on low-velocity impact mechanical response and damage mechanism for cross-ply and quasi-isotropic layups. The laminates were impacted with 25 J, 40 J and 60 J to obtain different mechanical response and damage status (permanent dent, delamination and backside damage). Experimental results demonstrate that the impact resistance is reduced with the decreasing Z-pin insertion angles, which is accompanied by more severe backside cracking, larger impact dent and delamination area. This phenomenon is more significant in cross-ply laminates compared with quasi-isotropic layups. Additionally, 60° pinned cross-ply laminates show asymmetry delamination because the damage modes of Z-pins on both sides of the impact center are different, which results in the different delamination resistance of the two sides. These findings can give some guidance for choosing Z-pin insertion angles when Z-pinning in different layups.

Purpose This paper aims to propose a united kinematic calibration method for a dual-machine system in automatic drilling and riveting. The method takes both absolute and relative pose accuracy into account, which will largely influence the machining accuracy of the dual-machine system and assembly quality. Design/methodology/approach A comprehensive kinematic model of the dual-machine system is established by the superposition of sub-models with pose constraints, which involves base frame parameters, kinematic parameters and tool frame parameters. Based on the kinematic model and the actual pose error data measured by a laser tracker, the parameters of coordinated machines are identified by the Levenberg–Marquardt method as a multi-objective nonlinear optimization problem. The identified parameters of the coordinated machines will be used in the control system. Findings A new calibration method for the dual-machine system is developed, including a comprehensive kinematic model and an efficient parameter identification method. The experiment results show that with the proposed method, the pose accuracy of the dual-machine system was remarkably improved, especially the relative position and orientation errors. Practical implications This method has been used in an aircraft assembly project. The calibrated dual-machine system shows a good performance on system coordination and machining accuracy. Originality/value This paper proposes a new method with high accuracy and efficiency for the dual-machine system calibration. The research can be extended to multi-machine and multi-robot fields to improve the system precision.

The paper introduces a new automatic drilling and riveting system for aircraft assembly which is composed of two five-axis machine tools in coordination. As a dual-machine system, relative position and orientation accuracy of coordinated machines is the decisive factor for high fastening quality. Considering all static/quasi-static error sources deteriorating relative positioning accuracy, an effective error compensation method which consists of a new error prediction model and an error compensation strategy is proposed for coordinated five-axis machines. Based on the decomposition concept, the coordinated workspace of dual machines is described as the superposition of the coordinated workspace of prismatic joints (CWP) and the coordinated workspace of revolute joints (CWR). They are separated to study the influence on the objective error, and a combined interpolation algorithm based on the shape functions is proposed for error prediction, which can avoid the curse of dimensionality essentially and be efficient to predict the relative position and orientation errors at any desired pose in the coordinated workspace of dual machines. For the error compensation of dual-machine system, a basic strategy is proposed which is to take the position and orientation of the driving machine as the reference and compensate the predicted error for the driven machine through the motion commands modification. To verify the feasibility of proposed method, experiments have been performed on the developed dual-machine system with different error compensation methods. The results show that the proposed method is more efficient which needs less time for sampled data measurement and calculation, and the relative positioning accuracy of the compensated dual-machine system is improved to 0.072 mm and 0.017° which meet the requirements for automatic drilling and riveting in aircraft assembly.

The paper introduces a new automatic drilling and riveting system for aircraft panel assembly which is composed of two five-axis machines in coordination. Kinematic modeling and base frame calibration are fundamental problems for the dual-machine system to improve its positioning accuracy. In this paper, a comprehensive kinematic model for the dual-machine system is established based on the modularization concept, and a new base frame calibration method is proposed which consists of the direct calibration based on laser tracker and calibration error compensation based on a specially designed instrument. In the kinematic modeling stage, the kinematic model of the dual-machine system is divided into three parts and three corresponding sub-models are established. With the pose constraints of coordinated machines, a comprehensive kinematic model of the dual-machine system is built. In the base frame calibration stage, the base frames of dual machines are firstly established by laser tracker. Due to many error sources in the calibration process, the relative pose errors of dual machines exist with the relationship between the base frames of coordinated machines. Then, the calibration error is measured by a specially designed instrument and used to modify the primary base frame calibration results. To verify the validity of the proposed method, experiments have been performed and the results have shown great improvement in base frame calibration accuracy. With the advantage of easy operation and high accuracy, this method can be extended to other multi-machine and multi-robot systems.

In order to develop equipment adapted to the aircraft pulse final assembly line, a vision-based aircraft transport platform system is developed. This article explores a guiding method between assembly stations which is low-cost and easy to change routes by using two-dimensional code and two complementary metal oxide semiconductor (CMOS) cameras. The two cameras installed on the front and back of the platform read the two-dimensional code containing station information to guide the platform. In the process of guiding, the theoretical position and posture of the platform at each assembly station are known, but there is a difference between the actual and theoretical values due to motion errors. To reduce the influence of the deviation on the navigation route, a localization method is proposed based on the two-dimensional images captured by the cameras. Canny edge detection is applied to the processed image to obtain the position of the two-dimensional code in the image, which can measure the angle/distance deviation of the platform. Then, the computer can locate the platform precisely by the information in the two-dimensional code and the deviation measured by the image. To verify the feasibility of the proposed method, experiments have been performed on the developed platform system. The results show that the distance and angle errors of the platform are within &plusmn, 10 mm and &plusmn, 0.15&deg, respectively.

Aluminum profile surface defects can greatly affect the performance, safety, and reliability of products. Traditional human-based visual inspection has low accuracy and is time consuming, and machine vision-based methods depend on hand-crafted features that need to be carefully designed and lack robustness. To recognize the multiple types of defects with various size on aluminum profiles, a multiscale defect-detection network based on deep learning is proposed. Then, the network is trained and evaluated using aluminum profile surface defects images. Results show 84.6%, 48.5%, 96.9%, 97.9%, 96.9%, 42.5%, 47.2%, 100%, 100%, and 43.3% average precision (AP) for the 10 defect categories, respectively, with a mean AP of 75.8%, which illustrate the effectiveness of the network in aluminum profile surface defects detection. In addition, saliency maps also show the feasibility of the proposed network.

A large aircraft fuselage panel is commonly composed of a variety of thin-walled components. Most of these components are large, thin and compliant, and they are also prone to some flexible deformation during assembly and remain deformed after assembly. Besides, many different fabrication and assembly manners are adopted in order to guarantee the complicated assembly relationships between each component. The above characteristics often cause large aircraft fuselage panels to exhibit low stiffness and weak strength, thereby inducing deformation during assembly. Since the posture of a large aircraft fuselage panel is commonly evaluated by matching the theoretical and actual positions of the measurement points placed on it, and its assembly deformation is also represented by the position errors of the measurement points, a reasonable measurement point placement is significant for the large aircraft fuselage panel in digital assembly. This article presents a method based on the D-optimality method and the adaptive simulated annealing genetic algorithm to optimize the placement of the measurement points which can cover more deformation information of the panel for effective assembly error diagnosis. By taking the principle of the D-optimality method, an optimal set of measurement points is selected from a larger candidate set through adaptive simulated annealing genetic algorithm. As illustrated by an example, the final measurement point configuration is more effective to maximize the determinant of the corresponding Fisher Information Matrix and minimize the estimation error of the assembly deformation than those obtained by other methods.

In aircraft manufacturing, riveting is one of the most important connection ways to fasten the sheet metal parts. The riveted single strap butt joints are mainly used in the load-bearing components of the aircraft such as the fuselage and wing panels. The connection quality and fatigue performance of the riveted joints directly affect the reliability and safety of the aircraft. In this paper, under the assumption of constant temperature, the fatigue strengthening mechanism of interference-fit riveting is introduced based on elastic-plastic mechanics and fracture mechanics. On this basis, the finite element (FE) models of the riveted single strap butt joints with various strap thickness and rivet sizes/arrangements are established. The residual stresses distribution around the riveted hole is analyzed. Furthermore, the fatigue tests of the riveted single strap butt joints with cyclic loading are carried out. The experimental results verified the correctness and effectiveness of the simulation model. Finally, the conclusion is drawn that increasing rivet size and strap thickness within the allowable weight range can improve the fatigue performance of the riveted single strap butt joints. The knowledge could be used to guide the structural design and optimization of the riveted butt joints against fatigue.

Slug rivet interference-fit riveting is one of the advanced connection technologies which has been widely applied in aerospace manufacture. This article presents an appropriate numerical model simulating the slug rivet upset process with countersunk hole structure. Many previous studies have focused on the riveted lap joints without countersunk hole structure and ignored its related process parameters. The main difference is that the hole expansion would be inhomogeneous through the thickness direction due to the impact of countersunk hole. To improve the riveting quality and reduce the inhomogeneity scale of the interference distribution, the effects of two procedure parameters have been assessed. The analysis results significantly improve knowledge about the slug rivet installation process as well as the effects of the corresponding process parameters. The study will pave the way for further investigations.

Purpose – The purpose of this paper is to propose a new model for optimizing pre-joining processes quickly and accurately, guiding workers to standardized operations. For the automatic riveting in panel assemblies, the traditional approach of determination of pre-joining processes entirely rests on the experience of workers, which leads to the improper number, location and sequence of pre-joining, the low quality stability and the high repair rate in most cases. Design/methodology/approach – The clearances computation with the complete finite element model for every process combination is time-consuming. Therefore a fast pre-joining processes optimization model (FPPOM) is proposed. This model treats both the measured initial clearances and the stiffness matrices of key points of panels as an input; considers the permissive clearances as an evaluation criterion; regards the optimal number, location and sequence as an objective; and takes the neighborhood-search-based adaptive genetic algorithm as a solution. Findings – A comparison between the FPPOM and complete finite element model with clearances (CFEMC) was made in practice. Further, the results indicate that running the FPPOM is time-saving by >90 per cent compared with the CFEMC. Practical implications – This paper provides practical insights into realizing the pre-joining processes optimization quickly. Originality/value – This paper is the first to propose the FPPOM, which could simplify the processes, reduce the degrees of freedom of nodes and conduct the manufacturers to standardized manipulations.

A large fuselage panel is always connected to a full-scale shape-preserving bracket to enhance its stiffness in digital assembly processes and reduce assembly deformation induced by factors such as gravity. However, the full-scale shape-preserving bracket’s characteristics, such as large size and weight, usually result in a complex installation process and high maintenance costs. A method for optimizing a multi load-transmitting device based discrete support layout is presented in this paper. By constructing finite element model including the fuselage panel and LTDs, the panel’s strain energy under different support layout parameters is obtained according to the principle of mixed uniform design. Using the method of partial least squares regression, the mathematical relationship between the strain energy and the support layout parameters is established, which is then used to obtain the optimum multi LTD based support layout. Furthermore, by comparing the panel deformation under the optimum multi LTD based support with that under the full-scale shape-preserving bracket-based support, we conclude that the optimum multi LTD based support can not only suppress panel deformation effectively, but also keep the panel’s stiffness comparable to that under the full-scale shape-preserving bracket-based support.

The interference fit can improve the fatigue performance of mechanical joints and is widely used in aircraft assembly. In this paper, specimens of lap plates and several interference fit sizes were designed, and then the interference fit hi-lock bolt insertion was carried out in an experimental test. Using the commercial finite element software ABAQUS, a two-dimensional axisymmetric finite element model was established to simulate the bolt insertion process. The finite element model was validated by comparison of experimental results and finite element prediction for insertion force and protuberance height. After the interference fitted bolt insertion, the changing characteristics of the non-uniform hole expansion and protuberance were presented with increases in interference fit size. Under low level of interference fit, the tensile hoop stress was produced mainly on the hole wall, and changed into compressive hoop stress when interference fit size is larger. The maximum tensile hoop stress point on faying surfaces went away from the hole wall with interference fit size increasing.

Purpose – The deformation of a large fuselage panel is unavoidable due to its weak-stiffness and low-rigidity. Sometimes, the assembly accuracy of the panel is out of tolerance. The purpose of this paper is to propose a method to predict and correct the assembly deformation of a large fuselage panel during digital assembly by using a finite element (FE) analysis and partial least squares regression (PLSR) method. Design/methodology/approach – A FE model is proposed to optimize the layout of load-transmitting devices to reduce panel deformation after the process of hoisting and supporting. Furthermore, another FE model is established to investigate the deformation behavior of the panel. By orthogonal simulations, the position error data of measurement points representing the precision of the panel are obtained. Then, a mathematical model of the relationship between the position errors of measurement points on the panel and the displacements of numerical control positioners is developed based on the PLSR method. Findings – The case study shows that the model has a high level of computing accuracy and that the proposed method is an efficient way to correct the panel deformation in digital assembly. Originality/value – The results of this study will enhance the understanding of the deformation behavior of a panel in aircraft digital assembly and help to improve the assembly precision systematically and efficiently.

To predict the distortion of aerospace monolithic components, a model is established to simulate the numerical control (NC) milling process using 3D finite element method (FEM). In this model, the cutting layer is simplified firstly. Then, the models of cutting force and cutting temperature are established to gain the cutting loads, which are applied to the mesh model of the part. Finally, a prototype of machining simulation environment is developed to simulate the milling process of a spar. Key factors influencing the distortion, such as initial residual stress, cutting loads, fixture layout, cutting sequence, and tool path are considered all together. The total distortion of the spar is predicted and an experiment is conducted to validate the numerical results. It is found that the maximum discrepancy between the simulation results and experiment values is 19.0%

A physics-based material processing simulation is approached to reveal the distortion law of aerospace monolithic components due to milling. To improve the efficiency of numerical calculation, a simplified cutting layer model is presented. The cutting force and temperature model are established to gain cutting loads. The cutting loads are applied to the mesh model of the part. The milling process of spar is simulated. Key factors influencing distortion such as initial residual stress, cutting loads, cutting sequence and tool path are considered. The total distortions of the spar are estimated. Machining experiment is carried out, and the distortion tendency of the machined part agrees well with the simulation. The results show the validity of the presented approach.