Riveting Process Research Articles

Influence of die geometry on self-piercing riveting of aluminum alloy AA6061-T6 to mild steel SPFC340 sheets

The self-piercing riveting (SPR) process was used to join 2.0-mm-thick aluminum alloy 6061-T6 and 1.2-mm-thick mild steel SPFC340 sheets. SPR joints produced with a conventional flat-bottom die and conical-section dies were investigated both experimentally and numerically. Lap shear tests were conducted under quasi-static conditions to evaluate the load-carrying capability of these SPR joints. The effect of variation in die geometry (such as variation in the die groove shape, cone height, and die radius) on the main mechanical response of the joints, namely the peak load and energy absorption, was discussed. The results showed that SPR joints produced with the conical-section dies exhibited a failure mode similar to those produced with a conventional die. All the joints failed by tearing of the top steel sheet. Cracks that occurred in the bottom aluminum alloy 6061-T6 sheet around the rivet leg were a result of tangential tensile stress. The cone height of a conical-section die is the most important parameter affecting the surface quality of Al/steel SPR joints. Conical-section dies with a moderate convex can ensure a good surface quality during the SPR process. In addition, SPR joints with single conical-section die allow higher tensile strength and energy absorption compared to those with double conical-section die.

Collaboration in a Hybrid Team of Human and Robot for Improving Working Conditions in an Aircraft Riveting Process

<div class="section abstract"><div class="htmlview paragraph">Aircraft production is facing various technical challenges, such as large product dimensions, complex joining processes, and organization of assembly tasks. Overcoming such challenges, as well as maintaining low tolerances and small batch sizes, is often difficult to achieve whilst retaining economic viability.</div><div class="htmlview paragraph">ZeMA believes that a semi-automated approach is the most effective way to optimize aircraft section assembly. This can be achieved with a semi-automated riveting process for solid rivets, using Human-Robot-Collaboration in combination with an intuitive Human-Machine-Interaction operating concept.</div><div class="htmlview paragraph">In the assembly of aircraft structures - in this scenario the aircraft aft section - the pressure bulk head is mounted to the section barrel. Two operators work collaboratively in uncomfortable, non-ergonomic positions, yet of course have to maintain exacting quality standards. In order to improve this process, a dynamic task sharing strategy between human and robot according to their respective skills, with due consideration given to ergonomic factors is proposed. The ideal solution involves placing a robot inside the section barrel. The robot’s workspace is expanded by mounting it on top of a lifting unit so that it can position the anvil properly. In the meantime, the human performs the more complex tasks of inserting the solid rivets and operating the riveting hammer from outside the section barrel.</div><div class="htmlview paragraph">In order to carry out the assembly tasks efficiently, the following components must be implemented: Human-Robot-Collaboration based on natural and intuitive interaction possibilities, and smart mixed reality devices for communication between human and robot in the hybrid team. By implementing a modular control system for configuration and operation of the assembly station with a variety of interaction possibilities, human and robot can perform the collaborative riveting process more efficiently than human operators alone. Additionally, due to the high forces and vibrations applied by the riveting hammer, a process-specific tool has been developed to prevent damage to the robot system. The implementation of natural and intuitive interaction within the Human-Robot-Collaboration achieves operator acceptance, improves ergonomics and therefore effectively optimizes aircraft production.</div><div class="htmlview paragraph">The results are part of the European Union’s Horizon 2020 research and innovation program, and present semi-automation as shown in the HRC riveting process.</div></div>

Influence of the deformation of riveting-side working head on riveting quality

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.

Joint Formation and Mechanical Performance of Friction Self-Piercing Riveted Aluminum Alloy AA7075-T6 Joints

AA7xxx series aluminum alloys have great potentials in mass saving of vehicle bodies due to pretty high specific strength. However, the use of these high strength materials poses significant challenges to the traditional self-piercing riveting (SPR) process. To address this issue, a novel process, friction self-piercing riveting (F-SPR), was applied to join aluminum alloy AA7075-T6 sheets. The effects of the spindle speed and rivet feed rate on F-SPR joint cross section geometry evolution, riveting force, and energy input were investigated systematically. It was found that the rivet shank deformation, especially the buckling of the shank tip before penetrating through the top sheet, has significant influence on geometry and lap shear failure mode of the final joint. A medium rivet feed rate combined with a high spindle speed was prone to produce a defect-free joint with sound mechanical interlocking. F-SPR joints with the failure mode of rivet shear fracture were observed to have superior lap shear peak load and energy absorption over the joints with mechanical interlock failure. The optimized F-SPR joint in this study exhibited 67.6% and 13.9% greater lap shear peak load compared with SPR and refill friction stir spot welding joints, respectively, of the same sheets. This research provides a valuable reference for further understanding the F-SPR process.

Single-sided joining of aluminum alloys using friction self-piercing riveting (F-SPR) process

Friction self-piercing riveting (F-SPR) process has shown advantages over traditional self-piercing riveting (SPR) process in joining magnesium alloys and aluminum alloys. Frictional heat produced by the rotation of the rivet plays important roles to the inhibition of cracking in riveting low ductility materials and the formation of solid-state bonding. However, the current F-SPR process needs a matching die to facilitate rivet deformation and formation of mechanical interlock between lower sheet and the rivet, which poses a big challenge in riveting large thin-walled structures, where a matching die is hard to apply. In this research, single-sided F-SPR process was proposed to join 2.2 mm-thick aluminum alloy AA6061-T6 to 3.0 mm-thick aluminum alloy AA6061-T6, and effects of process parameters, e.g., rotation speed and feed rate, on the morphology and mechanical properties of the joints were studied experimentally. It was found that higher rotation speed and lower feed rate which signified higher heat input could effectively reduce defects but lead to insufficient undercut. As such, a two-stage process was proposed to reduce frictional heat generation in lower sheet and thus increase the deformation resistance acted at the rivet tip. A preliminary study showed that the two-stage F-SPR process increased the tensile-shear and cross-tension strengths by around 25% and 81% respectively, compared to the one-stage process.

Challenges and Opportunities in Remote Laser Welding of Steel to Aluminium

In the last two decades, the automotive industry has been facing demands to reduce fuel consumption and to meet CO2 emissions through applications of lightweight materials. Therefore, aluminium alloys have replaced substantial amounts of steel; and they are receiving significant attention to achieve greenhouse emission targets. However, a critical factor in applications of advanced aluminium in automotive Body in White (BIW) designs depends on availability of cost effective and high performance joining processes. Currently, a Self-Pierce Riveting (SPR) process is extensively used for aluminium BIW sheet metal parts joining which is expensive, additionally increase the weight of the vehicle and cause inefficiency in manufacturing operations. As aluminium alloys are difficult to weld by conventional technologies such as electrical resistance spot welding, MIG arc welding etc., various joining technologies had proposed to weld aluminium alloys and dissimilar alloys over the years. Often, these technologies restrict design flexibility and are expensive for mass production. In this context, Remote Laser Welding (RLW) has gained popularity because of its distinct advantages such as design flexibility, production speed, material and cost savings. This paper provides a critical review of challenges and opportunities for application of RLW to dissimilar metal welding of steel to aluminium. Next steps of research and development are also highlighted.

Thermo‐mechanical modelling and finite element analysis of self‐piercing riveting processes

AbstractIn this contribution, a thermo‐mechanical finite element analysis of the self‐piercing riveting process of two steel sheets is carried out taking into account the conversion of plastic work into heat. Thereby, a user defined constitutive model recently proposed by BRÖCKER and MATZENMILLER is applied considering the highly temperature and rate dependent characteristics of metals. All constitutive parameters are identified with test data of the microalloyed steel HX340LAD typically used for car body structures. The numerical results of the self‐piercing riveting process are compared to the according test data for model validation by means of the final joint geometry and the setting force.

The Effect of Duration of the Rivet Process on the Strength of Single Lap Joining

Good airplane joining supports aircraft strength. The general joining process is using rivet as joining method. The parameter that affects the strength during the riveting process is the duration of the rivet head formation. The purpose was to determine the effect of the duration of rivet head formation on the quality of the joint. The research was carried out with the help of homemade tools, to ensure data consistency. The selected riveting duration is 3, 4, 5, 6 seconds. After connection, each connection was tested for strength through tensile testing and macro photo images from the joining. Results show that the 5-second duration provides the best connection with the tensile test results of 165 MPa. Based on the macro photo image, the 5 second rivet process produces the best connection because it produces the biggest rivet body so that it provides the greatest strength compared to the others.

Solid riveting process optimization for the reduction of key point distortions caused by locating

PurposeDeterminative locating and riveting distortions are highly coupled at assembly locale. Recent methods only take every tested or assumed locating errors at the mating surface into the process planning for the assemblies in a simple form. However, the growth of part number makes it nearly infeasible to take every locating error at every mating surface into the dimensional precision calculation. This paper aims to provide a solid riveting process planning for the reduction of practical locating-related distortions.Design/methodology/approachLarge-scale metrology firstly measures the determinative coordinates for the locating-deviated key points. Iterative finite element (FE) analyses then calculate the riveting-related key point distortions from every rivet upsetting directions (UDs) and assembly sequence. These key points on the actual assembly contour and relative FE nodes yield two virtual planes. Virtual plane manipulation adds the riveting distortions into the locating-deviated coordinates. Finally, optimal algorithm integrates the iterative FE analyses with virtual plane manipulation.FindingsCase studies validate that the virtual plane manipulation coincides with the test well, and the proposed method has good compensation of practical locating distortion.Research limitations/implicationsThe optimized rivet UDs may be set in a chaotic distribution, which may complicate the abundant riveting operations and the assembly appearance. Therefore, the use of automatic riveting systems can overcome the operational complexity, and the industrial design of rivet UD distribution will improve the assembly appearance.Practical implicationsThe optimized UDs and assembly sequence are for assembly workers or automatic riveting systems.Originality/valueThe proposed method is the first to reduce the determinative locating distortion by a novel and efficient solid riveting process planning in detail, and the solid riveting process designed is conservative and accurate for practice.

Development of a Human-Robot-Collaboration System using the Example of a Riveting Process in Aircraft Assembly

Assembly processes in aircraft production are particularly difficult to automate due to a variety of technical challenges including, small batch sizes, large product dimensions, small tolerances, and limited work space. Fully automated systems are expensive and require a large amount of servicing effort during their life time. The developed solution is therefore a semi-automated approach based on Human-Robot-Collaboration (HRC).

Self-Piercing Rivet (SPR) 공정의 유한요소해석 및 인장특성에 관한 연구

Self-Piercing Rivet (SPR) 공정의 유한요소해석 및 인장특성에 관한 연구

Durability of orbital riveted steel/aluminium joints in salt spray environment

In this work, aluminium alloy/steel joints were realised with an orbital riveting process. Two series of joints were made; i.e. in the first, the head of rivet touches with the aluminium sheet; in the second, it touches with the steel one. After their manufacturing, during tests were carried out by exposing the joints to a salt spray fog up to 10 weeks into a climatic chamber. Finally, mechanical tests were performed with the aim to know the effect of corrosion on performance and failure.

Effects of Process Parameters on Crack Inhibition and Mechanical Interlocking in Friction Self-Piercing Riveting of Aluminum Alloy and Magnesium Alloy

Friction self-piercing riveting (F-SPR) process has shown advantages over fusion welding, solid state welding, and traditional mechanical joining processes in joining dissimilar materials. Because of the thermo-mechanical nature of F-SPR process, formation of the joint is determined by both riveting force and softening degree of materials to be joined. However, it is still not clear that how exactly the riveting force and generated frictional heat jointly influence mechanical interlocking formation and crack inhibition during F-SPR process. To address these issues, F-SPR process was applied to join 2.2 mm-thick aluminum alloy AA6061-T6 to 2.0 mm-thick magnesium alloy AZ31B. The correlation of riveting force, torque responses, and energy input with joint quality was investigated systematically under a wide range of process parameter combinations. It was found that a relatively greater final peak force and higher energy input were favorable to produce sound joints. Based on that, a two-stage F-SPR method was proposed to better control the energy input and riveting force for improved joint quality. The joints produced by the two-stage method exhibited significantly improved lap-shear strength, i.e., 70% higher than traditional self-piercing riveting (SPR) joints and 30% higher than previous one-stage F-SPR joints. This research provides a valuable reference for further understanding the F-SPR joint formation mechanism and conducting process optimization.

Numerical simulation and experimental validation of self-piercing riveting (SPR) of 6xxx aluminium alloys for automotive applications

Two-dimensional axisymmetric models of the self-piercing riveting (SPR) process consisting of punch, blank holder, die, rivet, upper blank and lower blank were built using the finite element software package simufact.forming™. Three different joint configurations were modelled. An optical measurement system was used for capturing the actual geometries of both the die and the rivet which were then introduced into the simulation model. The stiffness of the riveting pliers was modelled as numerical spring. A combined model of Coulomb friction and shear friction was applied. Both friction coefficients were determined by inverse modelling. The deformation behaviour of the 6xxx aluminium alloy blanks to be joined was described with flow curves extrapolated from results of uniaxial tensile tests. In order to validate the results of the simulations self-piercing riveting experiments using 6xxx aluminium alloy blanks and coated steel rivets were conducted. Force-displacement curves of the punch were captured during the riveting process. Characteristic geometrical features of cross-sections of these joints including horizontal undercut of the rivet, bottom thickness of the lower blank and rivet head overlap were investigated using optical microscopy. The cross-sections of the self-piercing riveting joints obtained from simulations and experiments showed very good geometrical agreement, and just slight differences were observed between the force-displacement curves.

Damage mechanics modelling of material separation in self-pierce riveting (SPR) process

In numerical simulation of self-pierce riveting process (SRP) material separation criteria plays a critical role. In most of published works, material failure is simulated using numerical techniques, such as erosion criteria, that are calibrated on available experimental results. The lack of material based criteria strongly limits the use of numerical simulation as effective investigative tool for manufacturing process parameters assessment. In this work, damage mechanics is used to determine failure conditions in SRP considering dissimilar material sheets. In particular, the extended Bonora Damage Model (XBDM), which account for both void growth and void sheeting, was used. Damage model parameters for metal sheets have been determined independently and successively used in the simulation of SRP process. Results were compared with available experimental data.

Modeling and experimental validation of friction self-piercing riveted aluminum alloy to magnesium alloy

Friction self-piercing riveting (F-SPR) process has been proposed to achieve crack-free joining of low-ductility materials by combining SPR process with the concept of friction stir processing. The inhibition of cracking in an F-SPR joint is related to the in-process temperature as well as plastic deformation of materials, which are controlled by the process parameters, i.e., spindle speed and feed rate. However, the relationship between F-SPR process parameters and the temperature characteristics within the joint has not been established. In the current study, a coupled thermal-mechanical model based on solid mechanics was setup to study the F-SPR process of aluminum alloy and magnesium alloy. Temperature and strain rate-dependent material models and preset crack surface method were integrated in the model and geometry comparisons were conducted for model validation. Based on this model, the evolutions of temperature and plastic deformation in the rivet and the sheets of an F-SPR joint were obtained to reveal the formation mechanism of the joint. The temperature distribution and evolution of the sheet materials were correlated with F-SPR process parameters, and a critical spinning speed of 2000 rpm at a feed rate of 1.35 mm/s was determined capable of inhibiting cracking in the magnesium sheet.

Effect of Process Parameters on Joint Formation and Mechanical Performance in Friction Stir Blind Riveting of Aluminum Alloys

Aluminum alloys have been increasingly adopted in the fabrication of automotive body structures as an integral component of mass savings strategy. However, mixed use of dissimilar aluminum alloys, such as sheet metals, castings, and extrusions, poses significant challenges to the existing joining technologies, especially in regard to single-sided joint access. To address this issue, the current study applied the friction stir blind riveting (FSBR) process to join 1.2 mm-thick AA6022-T4 aluminum alloy to 3 mm-thick Aural-2 cast aluminum. A newly developed, robot mounted, servo-driven, FSBR equipment and the procedure using it to make FSBR joints were introduced systematically. The effect of rivet feed rate and spindle speed on joint formation and cross section geometry was investigated, and it was found that a high spindle speed and a low rivet feed rate, i.e., high heat input, are prone to produce good joints, and that low heat input can cause severe problems related to insufficient softening of the sheets. The rivet deformation, especially the notch location on the mandrel relative to the shank has significant influence on lap-shear strength and fracture mode of the final joints. A rivet pull-out fracture mode was observed at higher rivet feed rates and lower spindle speeds and exhibited significantly improved energy absorption capability, i.e., 62% higher compared to traditional blind riveted (BR) joints.

Thermal analysis and degradation of properties in carbon fiber/epoxy laminate riveting at high temperatures

A riveting process was developed to fasten carbon fiber/epoxy composite laminates. This process heats a thermoplastic composite rivet blank placed into the joint hole, above melt temperature, to form a rivet fastening the joined components. This process poses a threat to the integrity of the structure's epoxy matrix. To verify the state of matrix degradation, a pin-loaded mechanical test was applied on composite test pieces heat treated at various temperatures. The heat treatment was specifically designed to recreate the riveting process thermal cycle. A finite element model of the heat treatment was produced to obtain the time and temperature exposure of the test piece during the heat treatment. For use in the finite element model, emissivity was characterized through infrared image analysis, and thermal conductivity was characterized with an inverse method. The results show that a riveting process at nominal temperature of 350 °C will not affect the bearing properties of the composite laminates. However, the process at 450 °C does affect the bearing properties.

Cellular Automaton Simulation of Microstructure Evolution for Friction Stir Blind Riveting

Friction stir blind riveting (FSBR) process offers the ability to create highly efficient joints for lightweight metal alloys. During the process, a distinctive gradient microstructure can be generated for the work material near the rivet hole surface due to high-gradient plastic deformation and friction. In this work, discontinuous dynamic recrystallization (dDRX) is found to be the major recrystallization mechanism of aluminum alloy 6111 undergoing FSBR. A cellular automaton (CA) model is developed for the first time to simulate the evolution of microstructure of workpiece material during the dynamic FSBR process by incorporating main microstructure evolution mechanisms, including dislocation dynamics during severe plastic deformation, dynamic recovery, dDRX, and subsequent grain growth. Complex thermomechanical loading conditions during FSBR are obtained using a mesh-free Lagrangian particle-based smooth particle hydrodynamics (SPH) method, and are applied in the CA model to predict the microstructure evolution near the rivet hole. The simulation results in grain structure agree well with the experiments, which indicates that the important characteristics of microstructure evolution during the FSBR process are well captured by the CA model. This study presents a novel numerical approach to model and simulate microstructure evolution undergoing severe plastic deformation processes.

Experimental investigation of friction stir blind riveting process for similar and dissimilar alloy sheets

Friction stir blind riveting (FSBR) is a new joining method which eliminates the need to predrill a hole for rivet insertion. A new one-sided mechanical joining process, friction stir blind riveting (FSBR) was developed to form lap-shear joints for similar and dissimilar alloy sheets in different combinations. The similar and dissimilar joints are made from copper, Al 5052-H32, Al 6061-T6 metals. The process window was investigated of CNC machines using only three spindle speeds: 1110, 1750 and 2750 rpm. FSBR joints were observed and discussed during tensile testing. All the similar and dissimilar joints are well fabricated at 1750 rpm. Tensile testing results show that any material with copper combinations (copper used as a top plate) at 1750 rpm as riveting speed gives the appreciable ultimate tensile strength. Further study revealed micro structure of the joint interfaces, when compared with different combinations.