Riveting Process Research Articles

Fatigue and failure mechanism in carbon fiber reinforced plastics/aluminum alloy single lap joint produced by electromagnetic riveting technique

Electromagnetic riveting (EMR) process is suitable for composite joining due to small damage. In this paper, the EMR experiments were conducted to obtain the fatigue samples. Specimens with normalized driven head dimensions were tested to obtain the fatigue behaviors. The experimental results showed that the driven head dimensions had a remarkable effect on fatigue property. The fatigue life increased first and then decreased with the increasing of D/D0 (D and D0 are the diameters of rivet driven head and original shaft, respectively). The electromagnetic riveted specimens with D/D0 = 1.5 had the best fatigue properties. The fatigue failure analysis showed that the specimens had three typical fatigue failure modes: failure in the rivet, failure in the Al sheet and failure in the CFRP and Al sheets as influenced by driven head dimensions and stress levels.

Characteristics of 5052 aluminum alloy sheets joint using electromagnetic force

Recently, trends in lightweight materials and their fabrication process have been focused on reducing global warming and environmental pollution. Therefore, the demand for aluminum is increasing as representative lightweight material. In general, a fusion welding process, such as high-speed GTA (Gas tungsten arc) welding, is used to join aluminum sheet, or for mechanical joining which accomplished using a rivet process. However, it is difficult to ensure a high-quality joint, given that various defects are often reported. Therefore, in this study, we propose not only welding aluminum sheets using a MPW (Magnetic pulse welding) process, but also analyzing characteristics of these joints through experimental and numerical analyses. In order to achieve this objective, a proper coil type was selected after preliminary testing in which a MPW process was performed using 0.5 mm thick A5052 sheets. After the welding, the characteristics on joint were analyzed using a peel test and optical microscope. Although there was an overlapping zone, and the coil shape was quadrangular, a circular joint shape was achieved with no evidence of welding in the center of the joint. These tests confirmed that nonuniform distributions of electromagnetic forces cause the only overlapping zone, located on the adjacent edge of the coil.

Assembly sequence optimization for minimizing the riveting path and overall dimensional error

Due to the complexities of calculations based on different representations of constituent parts in an assembly, the combined improvement of efficiency and precision for the riveting has seldom been studied by the sequence planning or dimensional engineering. This article develops an assembly sequence optimization method that simultaneously minimizes the path length and overall dimensional error for the solid riveting. The sequence is denoted by the order of classifications for the nodes around the rivet holes in the finite element model for the assembly. Ant colony algorithm is applied on the optimization by integrating two calculations, that is, the length calculation of riveting path and the calculation of the dimensional error related to rivet upsetting directions and assembly sequence. Results for three assemblies are presented which show a good degree of optimization in performance for different scales of assemblies with different numbers of rivets that share the same solid riveting process.

Assembly deformation prediction of riveted panels by using equivalent mechanical model of riveting process

The assembly deformation of skin panels can be introduced by the riveting process. However, it is computationally costly and time consuming to conduct the numerical simulation of the riveting process for each rivet in skin panels. Here, an equivalent mechanical model of the riveting process is established to improve the computational efficiency of the deformation prediction for the riveted structure. The axial pressure beneath the rivet driven head is solved in the equivalent mechanical model. The assembly deformation of riveted panels is found to be influenced by the axial pressure significantly, challenging the traditional analogy of riveting to the radial expansion process. In addition, the dependence of the radial pressure upon the radial displacement of the rivet hole is established. The characteristic of non-uniform distribution of the radial pressure along the thickness direction is taken into consideration. The deformations of riveted structures are predicted considering various heights of the rivet driven head and different materials of the panel. The effectiveness of the proposed model is evaluated by comparing the deformation results of the numerical simulation and those of the experimental measurement. This investigation can help to predict the deformation of large riveted structures and improve the awareness of the effect of axial pressure on the assembly deformation.

Friction Self-Piercing Riveting (F-SPR) of Dissimilar Materials

Abstract Mixed use of high strength materials and lightweight materials is becoming one of the essential methods for vehicle body lightweighting. However, multi-material vehicle bodies need multi joining processes for assembling, which significantly increases the assembly cost compared with traditional steel bodies. In this paper, an improved friction self-piecing riveting (F-SPR) process was proposed, aiming at joining different multi-material stack-up using the same equipment with just changing rivet and dies. The effectiveness of this process was validated via joining three typical stack-ups, i.e., F-SPRing of aluminum alloy to low ductility magnesium alloy, single-sided F-SPRing of aluminum alloys and F-SPRing of aluminum alloy to high strength steel. The effects of process parameters on the plastic deformation of rivet and materials inside the joint and the ductility improvement of materials were investigated.

Numerical and experimental investigations of hot driven riveting process on old metal structures

The assessment of the structural resistance of historical metal structures involves a depth understanding of many factors, such as the properties of the constructions materials and the structural behaviour of the connection mode. Available information regarding the behaviour of historical riveted connections is quite limited and more information about the residual strain and stress state is still needed in order to allow the preservation of these existing structures. This paper deals with the assessment of stress and strain field which exist around the rivet hole due to the hot riveting process. Experimental specimens were manufactured with riveting technique used in aged metal bridges and different metallic materials for the joined plates were considered. Strain and thermal measurements were done during and after the overall riveting process. The results of the experimental investigation allowed the assessment of the residual strain state and the thermal response of the riveted joint. The experimental results were then used for validation of a 2D axisymmetric model. On the basis of the results obtained, the pre-stress state can be evaluated as well as the stress concentration areas where fatigue cracks may initiate. Thus, the provide findings constitute a supportive tool for further studies regarding the assessment and rehabilitation of historical riveted structures.

An Inexpensive, Portable Machine to Facilitate Testing and Characterization of the Friction Stir Blind Riveting Process

The expanding use of materials that are difficult to join with traditional techniques drives an urgent need, in a wide array of industries, to develop and characterize production capable joining processes. Friction stir blind riveting (FSBR) is such a process. However, full adoption of FSBR requires more complete characterization of the process. The relatively inexpensive, portable FSBR machine discussed here facilitates in situ X-ray imaging of the FSBR process, which will enhance the ability of researchers to understand and improve the FSBR process. Real-time, unobstructed, angular X-ray access drives the functional requirements and design considerations of the machine. The acute angular access provided by the machine necessitates tradeoffs in stiffness and Abbe errors. An error budget quantifies the effect of the various trade-offs on likely sensitive directions and relationships. Additionally, the machine motivates more test parameters important to machine designers (e.g., parallelism and runout) that have not yet been explored in the literature. Ultimately, a machine has been developed, which has a single rotational axis that translates parallel to the rotational axis, can be built for under $12,000, has a mass of less than 110 kg, measures 915 mm × 254 mm × 624 mm, has a rotational speed range of 400–8000 RPM, has a feed rate range of 0.1–200 mm/min, can be installed on most test benches, has total rivet runout of 0.1 mm, has plunge and rotational axis parallelism of less than 0.1 deg, and has a plunge axis repeatability of better than 2 μ m over a 10 mm range.

Laser beam welded structures for a regional aircraft: weight, cost and carbon footprint savings

Laser beam welded structures offer great opportunities for the lightweight design of fuselage structures in order to reduce structural weight for increased fuel efficiency. Our main objective is to validate and demonstrate that laser beam welding (LBW) technology provides the best opportunities in terms of weight reduction, production time and energy consumption for manufacturing aircraft components. To this end, a comparison in terms of energy, process time, cost and carbon footprint is assessed against the ‘conventional’ manufacturing process of riveting, to prove that LBW is actually an environmental friendly process. Manufacturing of a four-stringer stiffened flat subscale component was the case of the present work that was called in the Clean Sky Eco-Design Airframe (EDA) project as the B1 demonstrator (742mm×384mm). The LBW process has been broken down into several sub-processes and activities according to the Activity Based Costing (ABC) methodology and the weight reduction, production time and energy consumption results were compared against the respective of the riveting process. It was proved that for the specific subscale LBW component, it consumes half the energy and can be processed in less than half the time needed (in serial processing of the component) with riveting. Manufacturing of the component with the LBW process (door to door approach) is more environmentally friendly, since it produces 53% less CO2e emissions than the respective riveted process. This is a clear advantage to this manufacturing process in order to assure a sustainable life cycle of the final product.

Fatigue strength of self‐piercing riveted joints in lap‐shear specimens of aluminium and steel sheets

AbstractThe self‐piercing riveting (SPR) process is gaining popularity because of its many advantages. This study investigated the fatigue strength of SPR joints in tensile‐shear specimens with dissimilar Al‐5052 and steel sheets. A structural analysis of the specimen was conducted. For this specimen, the upper steel sheet withstood applied load in a monotonic test and played a major role in the low‐cycle region. In the high‐cycle region, however, the harder surface of the upper steel sheet reduced the fatigue strength by enhancing fretting crack initiation on the opposite softer aluminium surface. Therefore, the fatigue endurance of the specimen was reduced. The fatigue endurance of a SPR joint with the combination of steel and aluminium sheets was found to be governed by the strength of the lower sheet, which is more vulnerable to the applied loading. Thus, it is desirable to use a stronger metal sheet as the lower sheet with regard to the fatigue performance. Scanning acoustic microscopy was effectively used to reveal and prove the formation and growth of subsurface cracks in SPR joints. The structural stress can predict the fatigue lifetimes of the SPR joint specimens within a factor of three.

Sensitivity analysis of correlated inputs: Application to a riveting process model

Sensitivity analysis evaluates how the variations in the model output can be apportioned to variations in model inputs. After several decades of development, sensitivity analysis of independent inputs has been developed very well, with that of correlated inputs receiving increasing attention in recent years. This paper introduces a new sensitivity analysis technique for model with correlated inputs. The new method allows us to quantitatively distinguish the effects of the correlated and uncorrelated variations of the model inputs on the uncertainty in model output. This is achieved by performing covariance decomposition for the uncertainty contribution of the inputs after decoupling the correlated and uncorrelated parts of the component functions in the high dimension model representation (HDMR) of the output. The proposed method can be implemented conveniently with any existing HDMR technique developed for independent inputs without any change of the original algorithm. It can be applied to nonlinear and non-monotonic models with correlated inputs. An additive model, two non-additive models with analytical sensitivity indices, and a riveting process model are employed to test the proposed method.

Modeling of Friction Self-Piercing Riveting of Aluminum to Magnesium

In recent years, higher requirements on vehicle performance and emission have been posing great challenges to lightweighting of vehicle bodies. Mixed use of lightweight materials, e.g., aluminum alloys and magnesium alloys, is one of the essential methods for weight reduction. However, the joining of dissimilar materials brings about new challenges. Self-piercing riveting (SPR) is a feasible process to mechanically join dissimilar materials, however, when magnesium alloy sheet is put on the bottom layer, cracks occur inevitably due to the low ductility of the magnesium alloy. Friction self-piercing riveting (F-SPR) process is a newly proposed technology, which combines the SPR with friction stir spot welding (FSSW) and has been validated being capable of eliminating cracks and improving joint performance. However, in the F-SPR process, the generation of the transient friction heat and its effect on interaction between the rivet and the two sheets are still unclear. In this paper, a three-dimensional thermomechanical-coupled finite-element (FE) model of F-SPR process was developed using an ls-dyna code. Temperature-dependent material parameters were utilized to calculate the material yield and flow in the joint formation. Preset crack failure method was used to model the material failure of the top sheet. The calculated joint geometry exhibited a good agreement with the experimental measurement. Based on the validated model, the transient formation of F-SPR mechanical joint, stress distribution, and temperature evolution were further investigated.

Integrated Ball-Screw Based Upset Process for Index Head Rivets Used in Wing Panel Assembly

A new high speed forming process for fatigue rated index head rivets used in wing panel assembly using ball-screw based servo squeeze actuation has been developed. The new process is achieved using a combination of force and position control and is capable of forming to 40,000 lbs at rates of up to 200,000 lbs/second whilst holding the part location to within +/− 10 thousandths of an inch. Multi-axis riveting machines often have positioning axes that are also used for fastener upset. It is often the case that while a CNC is used for positioning control, another secondary controller is used to perform the fastener upset. In the new process, it has been possible to combine the control of the upset process with the machine CNC, thus eliminating any separate controllers. The fastener upset force profile is controlled throughout the forming of the rivet by using a closed loop force control system that has a load cell mounted directly behind the stringer side forming tool. Panel assembly where the components are not pre-tacked is referred to as a ‘one-up’ process. This process requires that aircraft parts be rigidly and precisely fixtured, and that the fastening processes do not result in excessive part motion. The recently developed riveting process uses a separate position control loop and a position sensor to hold the location of the panel during rivet squeeze to within +/− 0.010′′. CITATION: Haworth, P., Peterson, D., and Hayes, C., Integrated Ball-Screw Based Upset Process for Index Head Rivets Used in Wing Panel Assembly, SAE Int. J. Aerosp. 8(1):2015, doi:10.4271/2015-01-2491. 2015-01-2491 Published 09/15/2015 Copyright © 2015 SAE International doi:10.4271/2015-01-2491 saeaero.saejournals.org MECHANICAL UPSET ARRANGEMENT Figure 1. Vertical fastening machine overall arrangement. The newly developed rivet upset process uses a multi-axis servo driven arrangement for fastener forming. The same axes used in machine positioning also serve as the fastener forming axes. Figure 1 shows the overall vertical panel assembly machine arrangement(2). Figure 2 shows the upset axis arrangement. Figure 2. Mechanical upset arrangement. Upset is primarily achieved by motion on the stringer side of the machine. However, servo motors controlling the skin side clamping head, and the skin side upset axis also move during fastener forming in order to control aircraft part motion. Rivet Process Overview The new upset process consists of the following stages; 1. Insertion. Using a high speed skip move which ensures accurate positioning in countersink. A sensor on the front of the upset tool detects when the rivet has bottomed out in the countersink (Figure 3). 2. Servo/Servo move. To ensure that all of the forming load is imparted into the rivet (and not into the surrounding panel surface) the servo driven pressure foot is lifted off the surface of the wing. Simultaneously the servo driven upset tool drives forward to maintain contact with the head of the rivet and ensures no part motion during this step (Figure 4). 3. Rivet forming. Forming is broken down into 4 stages. This is done so that the ramp rate can be varied at each of the 4 forming stages (elastic, plastic stage 1, plastic stage 2, final plastic) (Figure 5). 4. Dwell. The target forming load is maintained for a period of time defined as the dwell. 5. Ramp down. Load is ramped down to a zero load level. Figure 3. Rivet insertion and seating in the countersink. Figure 4. During the Servo/Servo move, the head is pinned into the countersink by the squeeze axis. Figure 5. Upset occurs from the stringer side, as the skin side moves to maintain part position. Figure 6 shows the key characteristics of a traditional, previouslyestablished rivet upset profile. The basic process parameters are forming rate, target upset force, dwell and ramp down rate. Haworth et al / SAE Int. J. Aerosp. / Volume 8, Issue 1 (September 2015)

Effect of Rivet Hardness and Geometrical Features on Friction Self-Piercing Riveted Joint Quality

Conventional magnesium alloys, due to their low ductility, have a poor self-piercing rivetability. Cracks always occur when the magnesium sheet is placed at the bottom layer, which brings great challenge to the use of the magnesium alloys. In this paper, friction self-piercing riveting (F-SPR) process was adopted to join 1 mm thick aluminum alloy AA6061-T6 to 2.2 mm thick magnesium alloy AZ31B, and the effect of rivet hardness and key geometrical features on joint formation were studied systematically. The experimental results showed that using rivets with a hardness of 190 HV, the top aluminum sheet could be well pierced and a larger rivet shank flaring value would be formed between rivet shank and the bottom magnesium. The effect of the rivet's geometrical features, including ribs under shoulder and inclination angle under shoulder, were examined using two evaluation criteria, i.e., rivet shank flaring value and remaining thickness, and found that the rivet with no ribs and 10 deg inclination angle under shoulder is suitable for joining 1 mm AA6061-T6 to 2.2 mm AZ31B in F-SPR process.

Friction Stir Blind Riveting for Joining Dissimilar Cast Mg AM60 and Al Alloy Sheets

A new one-sided joining method, friction stirring blind riveting (FSBR) was successfully implemented to form lap-shear joints for dissimilar metals from pairs of 3.05 mm thick cast Mg AM60, rolled 1.5 mm thick Al AA6022, and extruded 3.15 mm thick Al AA6082 specimens. The concept of this process is riveting the two workpieces with reduced force under frictional heat and fastening the workpieces through blind riveting once the rivet is fully inserted. In this research, the process was experimentally analyzed and optimized for four joint combinations. It was demonstrated that switching the positions of Mg and Al alloy specimens has a significant effect on the process window and maximum tensile load of the joints. Three quality issues of the FSBR joints were observed and discussed. During tensile testing, the sheet closer to the rivet tail work-hardens due to tail forming process but has worse loading condition than the sheet closer to the rivet head. For AA6xxx sheets, precipitate hardening due to frictional heat is another strengthening mechanism in FSBR compared to the conventional riveting process, which leads to higher tensile loads in FSBR joints.

이종재료 Self-Piercing Rivets 접합부의 인장-전단 피로강도

Abstract : Self-piercing riveting (SPR) process is gaining popularity due to its many advantages. The SPR does not require a pre-drilled hole and has capability to join a wide range of similar or dissimilar materials and combinations of materials. This study investigated the fatigue strength of self-piercing rivet joint with aluminum alloy (Al-5052) and steel (SPCC) sheets. Static and fatigue tests on tensile-shear specimens were conducted. From the static strength aspect, the optimal punching force for the specimen with upper SPCC (U.S) sheet and lower aluminum alloy(L.A) sheets was 34 kN. During static test the specimens fractured in pull-out fracture mod e due to influence of plastic deformation of joining area. There was a relationship between applied load amplitude   and number of cycles ;     and     for U.S-L.A and U.A-L.S specimens, respectively. U.A-L.S fatigue specimens failed due to fretting crack initiation around the rivet neck between upper and lower sheets.

Effect of Geometric Parameters in the Upsetting and Extruding Riveting Process on the Quality of Riveted Joints

Upsetting and extruding riveting is a new joining method, which is mainly used to join castings. In order to investigate the effect of geometric dimensions of punch and upper sheet hole diameter on the quality of joints, models with different geometric parameters were simulated via ABAQUS. According to the simulation results, the riveting process could be divided into five stages. Besides, diameter difference on rivet tail and interference value on upper sheet hole wall were selected as indicators to evaluate quality of joints. And a group of parameters is obtained for a better quality of joints. Finally, the simulation results were validated through experiments.

Mechanics in frictional penetration with a blind rivet

The mechanics of frictional penetration driven by a blind rivet to sheet metals is analyzed for a friction stir blind riveting process. Analytic models are deduced to calculate the material removal rate, penetration force and torque during the frictional penetration process. Frictional penetration tests with modified rivets and an Al alloy sheet were carried out at various rotation speed–feed rate combinations, where the penetration force and torque were recorded with a data acquisition system. An analysis of the contact condition between the rivet tip and the work material based upon the assumption of pure sliding contact in the initial penetration to partial sticking contact beyond a critical penetration depth of the rivet is completed, and the results are discussed based on the comparison of the analytically calculated and experimentally measured torque–force ratios.

Modeling and simulation of percussive impact for robotic riveting system

Riveting is one of the major joining methods used in assembly, and the robotic riveting has been gradually introduced into aircraft industry. In this paper, a method is presented for modeling and simulation of percussive robotic riveting. In percussive riveting, vibration always exists. When an impact force is employed, a forced vibration will be induced. If it resonates with a robot natural frequency, the vibration will cause damage to the robot. The main content of this paper is divided into three parts. Firstly, a robot dynamic model is established to compute the driving torque for each joint. Secondly, vibration responses under impact are analyzed for the percussive riveting process. Thirdly, the effect of riveting on robot vibration is studied over the robot workspace. The purpose of this paper is to discuss the suitable regions for riveting where the robot vibration is very minimal. It is shown that based on the presented method an appropriate trajectory can be planned for robotic riveting.

Process modeling, joint-property characterization and construction of joint connectors for mechanical fastening by self-piercing riveting

Purpose – The purpose of this paper is to propose a computational approach in order to help establish the effect of various self-piercing rivet (SPR) process and material parameters on the quality and the mechanical performance of the resulting SPR joints. Design/methodology/approach – Toward that end, a sequence of three distinct computational analyses is developed. These analyses include: (a) finite-element modeling and simulations of the SPR process; (b) determination of the mechanical properties of the resulting SPR joints through the use of three-dimensional, continuum finite-element-based numerical simulations of various mechanical tests performed on the SPR joints; and (c) determination, parameterization and validation of the constitutive relations for the simplified SPR connectors, using the results obtained in (b) and the available experimental results. The availability of such connectors is mandatory in large-scale computational analyses of whole-vehicle crash or even in simulations of vehicle component manufacturing, e.g. car-body electro-coat paint-baking process. In such simulations, explicit three-dimensional representation of all SPR joints is associated with a prohibitive computational cost. Findings – It is found that the approach developed in the present work can be used, within an engineering optimization procedure, to adjust the SPR process and material parameters (design variables) in order to obtain a desired combination of the SPR-joint mechanical properties (objective function). Originality/value – To the authors’ knowledge, the present work is the first public-domain report of the comprehensive modeling and simulations including: self-piercing process; virtual mechanical testing of the SPR joints; and derivation of the constitutive relations for the SPR connector elements.

Analysis of the Local Phenomena during Riveting Process

The riveting still remains the most popular and basic method of joining metal parts in airframes. At the same time, the rivets are critical from the fatigue point of view. The paper presents the selected investigations of local phenomena during the riveting process. At the beginning, some results from the literature, concerned on the riveting process influence on fatigue of the three-row lap joint were shown. The analysis of these results leads to the conclusion that the increase in fatigue life caused by higher riveting force is so high that the more beneficial residual stress cannot be the only explanation, but the new phenomena in riveting process occurs and it is a reason of huge increase in fatigue life. The working hypothesis has been assumed that during the riveting process adhesive joint (called cold welding) were formed between the rivet shank and the sheets. Several microstructure tests were conducted in order to verify this hypothesis. The tests include riveting the specimens for various configurations and analyses of the microsection of selected specimens with the use of optical and scanning electron microscope. In the case of several specimens the punctual and linear welding between rivet shank and sheets were observed. The paper presents the investigation and selected results. The authors are going to continue presented researches.