Riveting Process Research Articles

Optimization of blind riveting process parameters of aluminum alloy based on finite element simulation

Optimization of blind riveting process parameters of aluminum alloy based on finite element simulation

Strengthening flat-die friction self-pierce riveting joints via manipulating stir zone geometry by tailored rivet structures

Achieving high-strength joints with flat surfaces is of significant importance for reducing wind resistance and enhancing aesthetic appeal. In this study, a novel flat-die friction self-piercing riveting (flat-die F-SPR) process is proposed. The rivet flaring without die guidance was achieved through the sophisticated design of rivet structures. Three types of rivets with different internal structures were designed to manipulate the material flow and microstructure evolution during the joining process. Based on the method of emergency stop, the load-stroke curves, evolutions of macroscopic morphology, and microstructure of the joints made with different rivets were investigated. A novel mechanism for solid-state bonding of joints was proposed to elucidate the generation and evolution of fine grain regions. The results indicate when downward pressure is applied to the material inside the rivet cavity, a central stirring zone appears. By using a rivet with an annular boss structure, the base material flows continuously into the stirring zone and piled up in the rivet cavity, forming a unique conical-shaped fine grain zone. Finally, a comprehensive assessment of the strength of different types of joints and the transition of the fracture modes were conducted based on different lower sheet thicknesses. The joints of Rivet_B and Rivet_C demonstrate 11.1 % and 6.9 % strength enhancement compared with the joint of Rivet_A, respectively. Two strategies for enhancing the strength of solid-state bonding are proposed, which offers insights for the optimizations of rivet structures.

Development of a coupled process - design numerical model for an automotive assembly

Abstract The product development process is a very challenging one, especially in the case of the automotive industry. The actual constructions require performance and quality while focusing on mechanical performance, lightweight and cost-effective. Thus, the virtual development stage is critical. Once the product is validated according to its geometrical definition and features, it is necessary to evaluate its mechanical performance. This process is usually performed using numerical simulation methods. In this paper, the numerical process performed for the validation of a safety part is discussed. As a specific feature, the assembly is finished using a riveting process. The manufacturing process’s influence on the assembly’s mechanical performance is further investigated. A discussion of the methods available for the design validation summarizes the finding of this specific work.

Investigation of the influence of the rivet geometry on joint formation for a versatile self-piercing riveting process

Investigation of the influence of the rivet geometry on joint formation for a versatile self-piercing riveting process

Study on the failure mechanism and mechanical properties of multi-layer hole-drilled self-piercing riveted three-layer steel/aluminum hybrid joints

To promote the application of the three-layer steel/aluminum hybrid sheet in the lightweight vehicle body, the multi-layer hole-drilled self-piercing riveting (MH-SPR) process is proposed. This paper aims to investigate the failure mechanism and mechanical properties of three-layer MH-SPR joints and explore the effects of overlap type and pre-drilled layer on forming quality, mechanical properties, failure modes, and fracture characteristics of the three-layer MH-SPR joint in detail. Three overlap types (e.g., type A, type B, and type C) and three pre-drilled layers (e.g., J0, J1, and J2) are designed for the experimental study and the shear experiments and full-field strain measurements are carried out. The results show that the pre-drilled layer can improve SPR joinability and reduce the peak force and energy consumption during the riveting process. Overlap types A and C can increase the peak force of the joint and type C can simultaneously enhance the peak force and energy absorption of the joint. The increase in the pre-drilled layer can increase the peak force and energy absorption of the joint. The overlap types and pre-drilled layers change the failure modes of the joints, which include five types of failure modes: middle sheet tearing, top sheet tearing, rivet fracture, interlock failure, and mixed failure. Full-field strain analysis shows that the overlap type improves the mechanical properties of the joints by altering the deformation mode of the steel sheet. This work provides a theoretical basis for expanding the industrial practice of the MH-SPR process and improving the joined quality of the three-layer joint.

Application of Friction Riveting technique for the assembly of electronic components on printed circuit boards (PCB)

This study focuses on the effects of reducing the diameter of rivets used in Friction Riveting due to the need for downscaling when joining assemblies on a smaller scale. The Friction Riveting process has shown promising feasibility for a variety of material combinations and applications in the transportation industry. Recent research has explored the potential application of this technique in electronics, specifically for the assembly of printed circuit boards (PCBs), using AA-2024-T351 rivets on thin glass-fiber-reinforced epoxy substrates (FR4). The joint formation of joints produced with PCBs was investigated in terms of process temperature evolution, microstructural changes, and mechanical properties. Joints were obtained at process temperatures ranging from 285 ºC to 368 ºC. The use of 4 mm rivets resulted in extensive delamination, weak joint mechanisms, and cracking, impaired by the different coefficients of thermal expansion of the materials involved. Reducing the rivet diameter to 3 mm significantly improved joint quality. A further reduction to 2.5 mm minimized delamination but led to insufficient anchorage and cracking. Joints produced with a 3 mm rivet diameter achieved the highest ultimate tensile force of 276 N. This study sets the foundation for applying the Friction Riveting process to practical PCB assemblies, demonstrating that optimizing the process parameters to the diameter-to-thickness ratio can balance sufficient rivet anchoring, minimize delamination, and reduce cracking.

Real-time modeling of the riveting process forces for aircraft panel structures

The riveting of large panels in aircraft manufacturing requires an automatic drilling and riveting machine capable of precise and stable operation. However, the significant nonlinearity and time-varying nature of riveting process forces severely impact the control capacity and operational accuracy of these machines. So, the objective is to provide technical assurance for the precise operation of the machine and ensure high-quality riveting of the panels. Therefore, a real-time modeling method for the automatic riveting process forces on aircraft panels is proposed, which focuses on the rivet die's downward compression displacement as the core variable and accounts for the non-uniform deformation of rivets. This method assumes a constant volume for the rivet rod. It combines power-law hardening and Coulomb's friction theories to establish three sub-models for different riveting stages: the elastic stage, the plastic deformation stage, and the driven head formation stage. Further, considering the continuity of rivet's deformation, rivet rod's cross-section stress, and the driven head dimensions changes with the driven head's downward compression displacement, a novel real-time continuous dynamic load model for the full compression riveting process of a single-rivet is developed. The results indicate that the model is effective, with a maximum deviation of 7.50 % between experimental and predicted values, demonstrating its accuracy and reliability. In conclusion, this research provides a real-time, continuous description of the riveting process force, enabling automatic machines to promptly detect defects and deformations in the riveting.

Multi-objective optimization of rivet and die for self-piercing riveting using finite element analysis

This study numerically investigated the effects of self-piercing riveting (SPR) process parameters on the quality of joints between steel and aluminum alloy sheets. First, the mechanical properties of each metal were experimentally evaluated, and a single-lap shear test was performed to validate a constructed finite element analysis model. This model was subsequently applied to optimize the die depth, die radius, and rivet length parameters of the SPR process using a multi-objective optimization method considering the shear strength, interlocking distance, and minimum thickness of the bottom sheet as objective functions. The results indicated that the maximum interlock distance was achieved with a longer die depth and larger die radius, and the largest minimum thickness of the bottom sheet was achieved with a shorter rivet length and larger die depth and radius. The die radius and depth were determined to be the most critical variables for all objective functions. The findings of this study can be applied to optimize the SPR of steel and aluminum alloy sheets.

Influence of local heat treatment of rivets on the joint formation of a versatile joining process

An efficient lightweight construction method is the combination of different materials in order to adapt the structure to the applied load. To join these multi-material structures mechanical joining technologies are applied. However, the rigid tooling systems cannot be adjusted to changing boundary conditions which is why new, versatile joining technologies are required. In the versatile self-piercing riveting (V-SPR) process presented in [1] different material combination are joined by using a multi-range capable rivet. The rivet head is formed onto the respective thickness of the joint by an outer punch. In order to punch thru the upper sheet a great rivet hardness is required whereas a lower hardness is required for the subsequent forming of the rivet head. To achieve a combination of these requirements, this study investigates a local heat treatment of the rivet. The aim is to determine the feasibility of such a heat treatment as well as to investigate the influence on the joint formation.

Development and mechanical evaluation of induction low Shear Friction Stir Spot rivets (ILSFSR) as crack arrest features in co-consolidated and welded thermoplastic laminates

The technique of Induction Low Shear Friction Stir Riveting (ILSFSR) stands as an alternative riveting process, which utilizes the melting and the resolidifying nature of thermoplastic resins to install metallic rivets into thermoplastic laminates without the need for pre-drilling. In this work, the aspects of the method’s implementation are presented, including its theoretical basis, the technical background, the apparatus, and the rivets’ installation procedure. Moreover, a mechanical evaluation of the resulting joints was held to determine their crack-arresting efficiency along carbon fiber reinforced co-consolidated low-melt PolyArylEtherKetone (LM-PAEK) laminates. A coupon scale testing campaign was employed, including mixed-mode Crack Lap Shear specimens containing the ILSFSR features, which were quasi-statically and fatigue-loaded. The interfacial crack growth results, which were compared to reference specimens, indicated the method's potential to provide significant damage retardation, resulting in an increase of 26% of quasi-static interfacial strength and complete confinement of fatigue crack growth, thus aiding in the damage tolerance design for critical engineering components.

Low-frequency vibration assisted self-pierce riveting (LV-SPR) of carbon fiber reinforced composite and aluminum alloy

Self-pierce riveting (SPR) has been widely applied to join carbon fiber-reinforced polymer (CFRP) composites and high-strength metallic plates in the automotive and aerospace fields. However, the CFRP is often damaged by rivet piercing owing to its brittleness as well as the relatively small interlocking that forms between the rivet leg and high-strength plate owing to the hard deformation characteristics. Therefore, in this study, a novel low-frequency vibration-assisted self-pierce riveting (LV-SPR) technology is proposed, which utilizes the vibration effect in softening the metal and reducing interfacial friction at room temperature. In riveting experiments involving CFRP and 5052 aluminum alloy utilizing 37Cr4 semi-hollow rivets, LV-SPR exhibited a significant reduction of 68.2% in the riveting force compared to the traditional SPR process. The decreased riveting pressure in LV-SPR effectively mitigated the CFRP damage by 36.2%, which was caused by a reduction in the interfacial friction force between the rivet and CFRP laminate. Moreover, owing to the improved deformation capacity of the rivet and alloy plate by the vibration softening effect, the lateral expansion of the rivet leg in the aluminum alloy was enlarged by 36.4% compared to that using the traditional self-piercing riveting (T-SPR) process. Microscopic characterization revealed that vibrations notably promoted grain refinement and enlarged the subgrain structures of the rivets and alloy plates. Finally, by superposing oscillations, the shear strength of the connection joint increased by 13.5% compared to the T-SPR joint. The proposed LV-SPR was validated as an effective technique to increase the connection strength of high-performance plates, which can efficiently improve the structural safety and promote the widespread application of CFRP/alloys in automobiles and aircrafts.

Rivet Structural Design and Process Optimization for the Double-Sided Countersunk Riveting of Composite Wedge Structures

Within the double-sided countersunk riveting process of aircraft wings with a composite wedge structure, riveting consistency is poor, and composite damage is severe, which seriously affects the performance and reliability of the aircraft structure. This paper used the principal stress method to establish a stress model of countersunk riveting, and, based on the analysis of the stress on the structure during the pressure-riveting process, a composite structure rivet was designed. A finite element simulation model of the double-sided countersunk riveting of composite wedge structures’ composite rivets was established. The influences of the structure and the matching parameters of composite rivets on both the plastic flow of pressure riveting and the compressive stress of the structure during the pressure-riveting process were analyzed. The structural parameters and riveting process of composite rivets were optimized. The results show that the composite rivet structure could significantly reduce the contact-compressive stress at the riveting joint by more than 20%, thereby reducing the damage caused by the riveting to the composite material. For 4 mm rivets, an aperture of 4.04~4.06 mm can achieve precise relative interference riveting at 0.6% to 1.0%. Employing a 2.6 mm rivet elongation can exactly fill the countersunk hole of the wedge.

Investigation on interference and damage behaviours of electromagnetic riveted double-sided countersunk 30CrMnSiA/CFRP joints

Carbon fibre reinforced polymer (CFRP) structures benefit from electromagnetic riveting (EMR). However, incorrect riveting parameters could result in damages in CFRP structures during the EMR process. Excessive interference size may introduce initial damages to the joints. As a result, in this paper, the damage behaviours and the interference characteristics of the 30CrMnSiA/CFRP double-sided countersunk electromagnetic riveted joints are investigated. The riveting damage experiment was conducted, with the regular pressing riveting (RPR) process as a comparison. Moreover, a progressive damage FE model considering multiple typical damage modes of CFRP was developed for EMR damage prediction. The results show that when the rivet-hole diameter increases by 5% (4.08mm to 4.28mm), the average interference size of the joint under EMR and RPR processes decreases by 41% and 53%, respectively. Double-sided countersunk riveted joint interference size along the rivet axial distribution is not uniform, the CFRP sheet side of the interference size is relatively small. The EMR achieves a tighter, more uniform interference fit, while causing more severe riveting damages to the CFRP structure. Initial riveting damage exhibits a variety of modes, with delamination damage showing most significant sensitivity to rivet hole clearance.

Extracting Technicians' Skills for Human-Machine Collaboration in Aircraft Assembly.

Research on the efficiency and quality issues faced in aircraft assembly was conducted in this article. A new method of human-machine collaborative riveting was proposed, which combined the flexibility of manual collaboration with the precise control of automatic riveting. The research works include: (1) a theoretical model of pneumatic hammer riveting was established to clarify the principle and parameters of riveting process. (2) A smart bucking bar was designed to support the data collection and extraction of manual collaborative riveting process. (3) An automatic riveting experimental platform was designed to test the automatic riveting process incorporating the extracted manual riveting process parameters, and further an optimization strategy was proposed for the automatic riveting process. (4) A human-machine collaborative riveting experimental platform was developed to conduct the verification work. Through the theoretical analysis, experimental research, system scheme design, and process parameters optimization, the application and verification of human-machine collaborative assembly technology have been achieved. This technology is expected to be comprehensively promoted in the field of aircraft manufacturing, and for breaking through the current difficulties of low production efficiency and poor assembly quality control.

Quality prediction using functional linear regression with in-situ image and functional sensor data

This article studies a general regression model for a scalar quality response with mixed types of process predictors including process images, functional sensing signals, and scalar process setup attributes. To represent a set of time-dependent process images, a third-order tensor is employed for preserving not only the spatial correlation of pixels within one image but also the temporal dependency among a sequence of images. Although there exist some papers dealing with either tensorial or functional regression, there is little research to thoroughly study a regression model consisting of both tensorial and functional predictors. For simplicity, the presented regression model is called functional linear regression with tensorial and functional predictor (FLR-TFP). The advantage of the presented FLR-TFP model, which is compared to the classical stack-up strategy, is that FLR-TFP can handle both tensorial and functional predictors without destroying the data correlation structure. To estimate an FLR-TFP model, this article presents a new alternating Elastic Net (AEN) estimation algorithm, in which the problem is reformed as three sub-problems by iteratively estimating each group of tensorial, functional, and scalar parameters. To execute the proposed AEN algorithm, a systematic approach is developed to effectively determine the initial running sequence among three sub-problems. The performance of the FLR-TFP model is evaluated using simulations and a real-world case study of friction stir blind riveting process.

Fatigue performance of electromagnetic self-pierce riveting-bonding hybrid joint under alternating load and corrosion coupling conditions

Electromagnetic self-pierce riveting (E-SPR) process was suitable for joining carbon fiber reinforced plastics (CFRP) and aluminum sheets. The E-SPR joints of dissimilar material still suffered from corrosion, and bonding could be an auxiliary process to improve corrosion resistance of joints. This paper investigated the fatigue characteristics of electromagnetic self-pierce riveting-bonding hybrid joints under alternating load and corrosion coupling conditions. Neutral salt spray (NSS) test, microscope observation, and fatigue test were conducted. Results showed that the adhesives not only improved the joint’s corrosion resistance, but also its mechanical properties. Specifically, the shear curves contained two peak loads, namely peak A and peak B. Corrosion was the greatest at 840 h, where peak A was 42.86% less than at 0 h, but peak B had little effect. Moreover, the addition of adhesives significantly impacted the fatigue characteristics of the joints after corrosion. The E-SPR-bonded joints still appeared good anti-fatigue characteristics within 168 h of corrosion. The fatigue failure modes were fractures in the CFRP sheets and the rivets remaining in the aluminum sheets. The influence mechanism of corrosion on fatigue was revealed. The water molecule and chloride ions penetrated the adhesives to cause hydrolysis, increased the plasticity of the adhesives and decreased the bond strength, which reduced the fatigue characteristics. The results provided theoretical guidance for E-SPR-bonded joints applied in engineering applications.

Double-flush riveting by punching and compression

This paper presents a new double-flush riveting process to fabricate flat lap joints that can be easily integrated in progressive or transfer multistage tool systems. The process is based on a punching-compression sequence and the design methodology combines experimentation and finite element modeling followed by destructive peel testing. Special emphasis is placed on the identification and selection of punch-to-die clearances to produce tapered cut surfaces that are appropriate for subsequent compression of the solid rivets into double-flush riveted lap joints. Results confirm that rivet materials with lower mechanical resistance than the sheet materials allow fabricating double-flush riveted lap joints with flat surfaces on both sides in which the mechanical interlocking in the undercut area is obtained by plastic deformation of the rivets instead of the sheets. The utilization of aluminum sheets and copper rivets allows extending the process scope of application from structural to energy distribution parts in which the electrical resistance of joints is a critical design parameter.

Experimental investigation and quantitative prediction in interference-fit size of CFRP riveted joints under a transversal ultrasonic vibration-assisted riveting

In this study, a transversal ultrasonic vibration-assisted riveting (TUVAR) process was developed to improve the uniformity of CFRP riveted lap joint interference-fit size, which provided a possibility for the quantization of riveted joint interference-fit sizes. The relationship between the process parameters of vibration amplitude, vibration duration, and roughness with interference-fit sizes by algorithms, through the minimum coefficient variance of interference-fit size (ICV-min) to confirm the riveting process parameters of the quantized average interference-fit sizes (IA). The experimental verification results showed that the mean absolute percentage error of measured IA and predicted IA is less than 10%. Furthermore, the tensile tests were carried out to investigate the effect of interference-fit size {1.4%, 1.6%, 1.8%, and 2.0%} on mechanical performances of CFRP riveted lap joints by TUVAR, and the tensile strength presents first-up then down with the interference-fit size increase, the maximum ultimate tensile strength is the riveted lap joint with the interference-fit size of 2.0%. Hence, the quantitative optimization method can well predict the riveting process parameters corresponding to the most uniform interference-fit size.

Influence of process parameters and heat treatment on self-piercing riveting of high-strength steel and die-casting aluminium

The application of steel/die-casting aluminum alloy is an inevitable trend in the development of automotive lightweight technology. The joining process of self-piercing riveting (SPR) is the key technology to guarantee the collision safety for the body. However, the crackings on joint button can be easily found owing to the low ductility of die-casting aluminum. This paper aims to investigate cracking mechanism and improve the SPR joinability by exploring methods of cracking inhibition. Parametric study is performed to explore the effects of heat treatment, process parameters on crack inhibition and forming quality of SPR with steel/die aluminum alloy. The results show that SPR joinability can be improved by larger elongation and lower yield strength by proper heat treatments, i.e., AlSi10MnMg-T6 and AlSi10MnMg-T7. Meanwhile, the depth and diameter of the die are the main factors affecting cracking generation and forming quality. Similar to the upsetting process, tangential tensile stress is generated on the bottom surface in the riveting process, it leads to cracking generation on the bottom surface. This paper further studies the effects of heat treatment and stack direction on joint quality and mechanical response of SPR joints. Tearing failure of the lower sheet is the main factor causing failure of steel-aluminium joint (steel is the top sheet). The heat treatment mainly affects the energy absorption value and has a relatively small effect on the peak force. The mechanical properties of the steel-aluminium joints are superior to those of aluminium-steel joints (aluminium is the top sheet).

Investigation of the flat clinch–rivet process with different blank holder structures

The increasing application of novel and high-performance metallic materials poses new challenges to the problem of joining sheets. Clinching technology has become the common means of green joining in the automotive industry. The application of conventional clinching to visible surfaces in automobiles is limited by the external protrusion of the clinched joint. It cannot be ignored the important role of the blank holder in controlling the material flow in the clinching process. In this study, the joint quality of Al5052 sheets for the flat clinch-rivet process was investigated by experimental methods. A flat bottom die and rivets were used to form joints under different blank holder structures. Geometric parameters, static strength, failure modes, and energy absorption were analyzed. The results indicate the flat clinch-riveted joints created by the conical stepped blank holder have the advantages of no indentation, high energy absorption, and high joint strength. The flat clinch-rivet process should preferably use a conical stepped blank holder.