Self-piercing Riveting Research Articles

Strength and Failure of Self-Piercing Riveted Aluminum and Steel Sheet Joints: Multi-axial Experiments and Modeling

The mechanical failure of self-piercing rivet (SPR) joints connecting seven series aluminum and high strength steel sheets is investigated, both numerically and experimentally. The joint strength and failure mechanisms are characterized for a total of four distinct loading modes, including the lap-shear, cross-tension, inclined cross tension and coach peel. For the analysis of the underlying influential parameters in each loading case, joint designs with equal total sheet thickness and equal rivet head diameters are considered. The highest strength values are obtained in lap-shear loading for all joint types, while high rivet interlock joints are observed to pair with increased cross-tension strength values. Moreover, the loading mode in which the highest energy is absorbed directly relates to the joint type. Depending on the material combination to be joined, either the cross-tension or the coach-peel cases yielded the highest energy absorption. The experimental results indicate that high rivet hardness and bottom sheet strength values have a favorable impact on the coach-peel strength and the associated deformation response. For all failure modes, the lowest rivet hardness employed (H4) was proven sufficient to prevent rivet failure in the joint types employed, despite the substantial equivalent plastic strains developed in it. Furthermore, high interlocks were noted to primarily affect the lap shear failure mode, inducing significant bottom sheet damage upon fracture, with the failure response observed in all other loading cases to remain practically insensitive to the interlock magnitude.

Effect of shot peening on static and fatigue properties of self-piercing riveting joints

The joint strength of self-piercing riveting is a key factor for evaluating riveting quality. Shot peening is a useful process to strengthen sheet metal. To improve the performance of self-piercing riveting joints, the shot peening process and self-piercing riveting process are combined in this work. The shot peening of AA5052-H32 aluminum alloy sheets, static and fatigue experiments of the self-piercing riveting joints are executed, the effects of shot peening on the mechanical performance of the joints are performed. The results show that: The shot peening process can induce residual compressive stress in the surface layer of aluminum sheets, which can improve the performance of the joints; In the shot peening process, the largest residual stress is around −187.3 ± 5.1 MPa; The shot peening process can improve the static strength of the joints by about 9.5%, and has little effects on the tensile failure forms of the joints; The fatigue strength of the shot-peened self-piercing riveting joints is increased by about 9.2%. The main fatigue failure type is the damage of the lower sheets at the contact zones with the rivet leg. The contact surfaces for the shot-peened self-piercing riveting joints are suffered less from the fretting damage than that of non-shot peened joints. The static strength, fatigue strength are increased, and the fatigue crack growth rate is decreased for shot-peened joints. The shot peening process can be innovatively combined with the self-piercing riveting process to improve self-piercing riveting joint performance. This work provides new ideas to improve the self-piercing riveting quality.

Riv-Bonding of Aluminum Alloys with High-Strength Steels against the Favorable Joining Direction

In order to exploit the advantages offered by multi-material design, this work studies the feasibility of joining aluminum alloys with high-strength steels (HSS) against the favorable joining direction by using self-piercing riveting (SPR) combined with adhesive bonding, so-called riv-bonding. Therefore, riv-bonding of four joint configurations including different aluminum alloy sheets (AW-6014-PX, AW-6451-T4), HSS sheets (HC420LA, HC450X) and rivet types (C5.3×8.0-H4, U5.5×5.0-H6) was experimentally investigated. Moreover, riv-bonding of two joint configurations was exemplarily modeled using the Simufact Forming finite element (FE) software. The viscoelastic properties of the liquid adhesive layer between the sheets were substituted with “equivalent” elastoplastic properties to model the adhesive as solid with strain rate-dependent flow behavior. Good agreement of joint cross sections and force-displacement curves between experiments and simulations confirms that the presented numerical model of riv-bonding is suitable for predicting both the joinability of aluminum alloys with HSS and the final quality of hybrid joints.

Mechanical testing of adhesive, self-piercing rivet, and hybrid jointed aluminum under tension loading

Joining technologies play a crucial role in facilitating vehicle weight reduction, while maintaining structural performance and vehicle crashworthiness. Adhesive and self-piercing rivet (SPR) joining have individually been assessed in joining multi-material structures including aluminum alloys; however, limitations include fixturing requirements for adhesive joints and non-uniform load distribution within SPR joints. Hybrid (adhesive-SPR) joining has been proposed to potentially address these limitations. Yet, there is limited data regarding the strength, stiffness and energy absorption of hybrid joints under tension loading, and a lack of quantitative comparisons between adhesive, SPR and hybrid joints. In the present study, adhesive, SPR and hybrid joints were created in aluminum H-shaped tension specimens and the joint morphologies were quantified. Joint strength, stiffness and energy absorption were compared for two aluminum sheet metal alloys and three sheet thicknesses. Adhesive joints exhibited higher strength (up to 20.5%) and stiffness (up to 422%) than SPR joints, while SPR joints demonstrated higher energy absorption (up to 352%). Hybrid joints in 3 mm sheet exhibited reduced strength and stiffness relative to adhesive joints. Importantly, hybrid joints for 1 and 2 mm sheet thicknesses demonstrated strength and stiffness comparable to adhesive joints (<8% difference), and improved energy absorption compared to adhesive (up to 336%) and SPR joints (up to 53.5%), enhancing the performance of the individual methods. The study results could facilitate identifying suitable joining method, sheet thickness and alloy type according to structural applications (e.g. intrusion prevention versus energy-absorbing structures), and support future adoption and improvement of hybrid joints.

Investigation of the influence of the tumbling angle on a tumbling self-piercing riveting process

To achieve the climate objectives, various measures are taken to increase the efficiency of raw materials and energies used. A sector with a large proportion of the global consumption of resources is the mobility sector. To increase the efficiency in this field, large efforts are made to reduce the weight of moving masses. One approach is the use of multi-material systems, which utilises different materials and their specific properties depending on the local requirements. Multi-material systems consist often of materials which differ in strength and density, for example, high-strength steels, aluminium alloys or polymers. Additionally, such a system can utilise different geometries of the components to be joined, characterised for example by varying sheet thicknesses. A central challenge of producing these systems is the joining of the individual components. This requires robust joining processes capable of covering the entire spectrum of possible variants and is feasible for different physical properties of the materials. Since conventional joining processes are rather rigid and have difficulty reacting to changing process and disturbance variables, new joining processes are necessary. With the objective of being able to react versatile to varying parameters, a process combination consisting of a semi-tubular self-piercing riveting process and orbital forming process with adjustable tumbling kinematic is introduced. Due to the process combination of tumbling and self-piercing riveting, mutual influences of the two process components are analysed in regard to material flow and process forces. Further, the investigations show the influence of a varying tumbling angle on the joining process itself and how the characteristic properties undercut, rivet head end position and residual sheet thickness of the joint are affected. The material used for the joining partners is an aluminium alloy EN AW-6014 typical for multi-material systems in the automotive industry and the rivets are from type Rivset C produced by the Böllhoff company.

A framework for calibration of self-piercing riveting process simulation model

This paper presents a framework that integrates machine learning and global sensitivity analysis to calibrate process simulation model of self-piercing rivet (SPR). In the present framework, surrogate models are trained to represent the intrinsic numerical relationship between selected model parameters (e.g., material properties, interface frictions, and clamping force) and cross-section dimensions of SPR joint obtained from simulation. Under the assistance of surrogate models, a global sensitivity analysis is performed to identify critical parameters that have significant effects on SPR joining process. Then, new surrogate models are trained to present the sensitive parameters and the cross- section dimensions obtained from process simulation. The parameter calibration of the simulation model is described as a two-objective optimization problem to minimize errors of key cross-section dimensions between simulation and experiment. Combined the newly trained surrogate models with genetic algorithm, the model parameters are calibrated efficiently. A case study of simultaneous calibration of four SPR process simulation models is used to illustrate the proposed framework and examine the effectiveness of the proposed framework. A good consistency is achieved between calibrated models and experiments.

FEM을 이용한 셀프 피어싱 리벳 냉간압조 해석

Self-piercing rivets (SPR) are manufactured using multistage cold heading of a constant length of steel wire rods. This study attempted to design molds for tolerable loading to material and make the metal flow of the SPR lines parallel and without cusp. During this process, beyond the existing virtual experiment, which was limited to the plastic deformation of the SPR material, the analysis of the molds’ stress, elastic deformation, and wear were simultaneously performed. This study mainly aimed to mimic the multistage cold process of the heading machine for manufacturing SPR using DEFORM (commercial finite element method software) and minimize differences between with manufacturing sites. Furthermore, deviating from the existing mold development process (shape design with trial and error), the development efficiency was maximized by the reduction of both the mold development period and the mold cost. Finally, the hardness homogenization of the manufactured SPR with a tempering finished was verified.

Joining Technologies and Solutions for Aluminum-based Battery Case Manufacturing

Recently, considerable research has been conducted to identify suitable replacement for aluminum material used in producing lightweight car bodies, and accordingly, various welding processes have been investigated. However, no research has been conducted to optimize joining processes through experimental comparisons of the various welding and fastening processes for the aluminum battery cases used in hybrid electric vehicle. Therefore, this study conducted a joint quality comparison of nine joining processes for the aluminum overlap welding for 1.2 mm thick Al5052-H32 material. The tested joining processes were self-piercing rivet(SPR), arc welding, refill friction stir spot welding(FSSW), laser welding, spot welding, adhesive bonding, clinching, hybrid joining, and flow drill screw(FDS). The test results were used to assess manufacturing based on OEM production guidelines for field production application. Each joining process was evaluated in terms of investment cost, joint strength, endurance, productivity, and weldability under different weight factors. The SPR was the most competitive process among the nine joining processes, and arc welding, refill FSSW, and laser welding were considered alternative choices for the joining process for aluminum-based battery case manufacturing. By contrast, adhesive bonding, resistance spot welding, hybrid welding, clinching, and FDS were determined to be challenging processes for use as primary processes.

Determining the properties of multi-range semi-tubular self-piercing riveted joints

By applying a variety of strategies, including both the development of new drive concepts as well as the use of lightweight constructions, it is intended to meet the climate targets set by the Paris Agreement. Multi-material design is often used when applying lightweight constructions, especially in the mobility sector. Herby, various materials with different properties are combined to well adapt the structure to the application of force in order to reduce weight. For example, this can result in the combined use of (high-strength) steel and aluminium. However, the increasing number of materials used and the number of resulting joints has led to the development of a number of different joining processes. These can only be used to a limited extent for joining multi-material joints and are usually inflexible facing changing boundary conditions. Examples of further difficulties affecting the established processes are metallurgical incompatibilities, which particularly pose difficulties for the use of thermal joining processes. A frequently used mechanical joining process is self-piercing riveting. Due to its high load-bearing capacities, a wide range of application and high process robustness it is often used when joining of dissimilar material is required. However, in case of self-piercing riveting used, the increasing number of multi-material joints and material-thickness combinations leads to the need of a large number of rivet-die-combinations to adapt the joining process to the respective joining task. Since the joining system cannot react to these changes, a tool change or an adjustment of the system is necessary, which leads to a reduction in efficiency and extended process times. To increase flexibility and process efficiency, new, versatile joining technologies are needed that can be adapted to changing boundary conditions. One possibility for this is the use of multi-range capable semi-tubular self-piercing rivets, which are inserted into the joint by using a new joining system with extended punch-sided actuator technology. The increased actuator technology enables the rivet to be set by an inner punch and subsequently to form a rivet head by embossing with an outer punch. All punch movements can be controlled independently of each other, enabling adaptive adjustment of the process parameters. Depending on the rivet geometry used, rivet head formation by the outer punch can be performed both with and without head deformation. The rivet without head deformation consists of a tubular shape with ring grooves in the rivet head area. Using the outer punch, punch-sided material is formed into the ring grooves creating an interlock in the head area of the rivet. The rivet with head deformation is designed differently. It is modified to enable subsequent forming to the respective thickness of the joint by forming the protrusion of the rivet head onto the punch-sided joining part. In the study presented here, the joining process of the versatile self-piercing riveting is presented, analysed and the property profile of the joints is determined on the basis of various material-thickness combinations. Here, both the characteristic parameters of the joints and the joint load-bearing capacities are determined. Finally the property profiles are compared with conventionally manufactured joints in order to identify potential for improvement.

Effect of low-velocity impact on mechanical property and fatigue life of DP590/AA6061 self-piercing riveted joints

The low-velocity impact behaviors of DP590/AA6061 self-piercing riveting (SPR) joints are studied at the impact energies of 5 J, 10 J, 20 J, 30 J, and room temperature (25 °C). The lap shear and fatigue tests, and the cross-sectional microscopies of joints are used to assess the mechanical property evolutions of the joints after low-velocity impact. The results show that the absorbed impact energies of SPR joints reach the critical value at an impact energy of 30 J, the exceeded impact energy causes crack failures in the sheets and decreases the interlocking performance of the joints. The static property and the absorbed energy of the SPR joints are reduced by 16% and 36% when the joints are impacted at 30 J, respectively. The low-velocity impacts do not change the failure forms of the joints, but significantly reduce the mechanical interlocking properties of the joints. The fatigue lives of the SPR joints are reduced due to low-velocity impact, and the impacted joints are more sensitive to cyclic loadings.

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

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

Self-Pierce Riveting of Three Thin Sheets of Aluminum Alloy A5052 and 980 MPa Steel.

Self-pierce riveting of three thin sheets of 980 MPa steel and 5052 aluminum alloy was performed to investigate the effect of sheet configuration on the deforming behaviors of the sheets and the rivet and joint strength. When the lower sheet was aluminum alloy, the joining range was relatively wide, i.e., the interlock hooking the rivet leg tended to be large. In the sheet configuration in which the upper and lower sheets were A5052 and the middle sheet was 980 MPa steel, the rivet leg spread out moderately and the joint without defects was obtained. In the lower 980 MPa steel sheet, fracture tended to occur due to the low ductility of the lower sheet, and the joining range was narrow with the small interlock although the three sheets were joined by an appropriate die shape. In joint strength of joined three sheets, fracture occurred in the lower-strength aluminum alloy sheet if interlocks of about 300 μm and 150 μm could be formed in the lower aluminum alloy sheet and 980 MPa steel sheet, respectively.

Incorporation of a Simplified Mechanical Joint Model into Numerical Analysis

In the development of new joining technologies, incorporation of mechanical joints in computer analyses for the evaluation of structures can be carried out by a practical, simplified mechanical joint model. Here, two most frequently used joining technologies were analysed, a self-piercing rivet joint and a clinch joint. Physical tests of static load capacity of the joints were performed and numerical models for simulations were set-up. An optimization method was designed for estimating the material parameters of the mechanical joint for the needs of numerical analyses. For optimization purposes during the plan of experiments, a range of possible parameter values was investigated using a response surface method, results of simulations, results of physical tests and a genetic algorithm. The results of simulations using the optimal values of the material parameters are comparable to the experimental observations for the both joints.

Increasing flexibility of self-piercing riveting by reducing tool–geometry combinations using cluster analysis in the application of multi-material design

A frequently used mechanical joining process that enables the joining of dissimilar materials is self-piercing riveting. Nevertheless, the increasing number of materials as well as material–thickness combinations leads to the need for a large number of rivet–die combinations as the rigid tool systems are not able to react to changing boundary conditions. Therefore, tool changes or system conversions are needed, resulting in longer process times and inflexibility of the joining processes. In this investigation, the flexibility of the self-piercing riveting process by reducing the required tool–geometry combinations is examined. For this purpose, various joints consisting of similar as well as dissimilar materials with different material thickness are sampled and analysed. Subsequently, a cluster algorithm is used to reduce the number of rivet–die combinations required. Finally, the effect of the changed tool geometries on both the joint formation and the joint load-bearing capacity is investigated. The investigation showed that a reduction by 55% of the required rivet–die combinations was possible. In particular, the rivet length influences the joint formation and the joint load-bearing capacity. An exclusive change of the die (e.g. die depth or die diameter) did not show a significant influence on these parameters.

Process-adapted temperature application within a two-stage rivet forming process for high nitrogen steel

Mechanical joining technologies like self-piercing riveting are gaining importance with regard to environmental protection, as they enable multi-material design and lightweight construction. A new approach is the use of high nitrogen steel as rivet material, which allows to omit the usually necessary heat treatment and coating and thus leads to a shortening of the process chain. Due to the high strain hardening, however, high tool loads must be expected. Thus, appropriate forming strategies are needed. Within this contribution, the influence of applying different temperatures for each forming stage in a two-stage rivet forming process using the high nitrogen steel 1.3815 is investigated. The findings provide a basic understanding of the influence of the temperature management when forming high nitrogen steel. For this purpose, the rivets are not formed at the same temperature in each stage, but an elevated temperature is applied selectively. Different process routes are investigated. First, cups are manufactured in stage 1 at room temperature, followed by stage 2 at 200°C. Second, cups are formed in stage 1 at 200°C and used for stage 2 at room temperature. By comparing the findings with results when applying the same temperature in both stages, it is shown that the temperature during the first forming operation has an effect on the forming behaviour during the second forming stage. The required forming forces and the resulting rivet hardness can be influenced by process-adapted temperature application. Furthermore, the causes for the temperature impact on the residual cup thickness in stage 1 are evaluated by a cause and effect analysis, which provides a deeper process understanding. The thermal expansion of the tool and the billet as well as the improved forming behaviour at 200°C are identified as the main influencing causes on the achieved residual cup thickness.

Fatigue strength estimation of single self-piercing riveted joints of steel and aluminium plates under different loading modes

Self-piercing riveting (SPR) has recently been adopted to join automotive body components because this method can reduce manufacturing costs via product automation while also providing a simpler process. In this study, fatigue tests were conducted using cross-tension and coach-peel specimens with aluminium alloy (A5052) and cold-rolled steel (SPCC) plates to evaluate the fatigue strength of SPR joints. For the combination of a top steel plate and a bottom aluminium alloy plate, designated here as T.S-B.A, the applied load amplitudes corresponding to the fatigue limit in the cross-tension and the coach-peel specimens are approximately 13% and 15% of the monotonic strength, respectively. The fatigue strength of SPR joints of aluminium and steel plates under various types loading conditions can be adequately predicted by the equivalent stress intensity factor amplitude.

Fatigue characteristic in non- combustible magnesium alloy dissimilar materials joint with different combination of upper plate / lower plate materials

Using non-combustible magnesium alloys for structural materials contributes to weight reduction in transportation equipment. Therefore, appropriate joining method for non-combustible magnesium alloy with high reliability is necessary. Self-Piercing Rivet (SPR) joint has been widely applied to joining aluminum alloys and is suitable for joining of dissimilar metals. In this study, SPR joint was applied to a non-combustible magnesium alloy AX41, and fatigue strength properties of AX41 similar material joint and dissimilar materials joints with AA6061 and SPCC were evaluated. The dissimilar material joints exhibited higher fatigue strength compared to AX41 similar material joint. Depending on the combination of the upper and lower plate materials, cracks may occur during the joining process, and fatigue properties may be affected. Regardless of the plate materials combination, stiffness of a plate is considered to have a significant effect on fatigue strength of SPR joint because deformation of upper and lower plates has an effect on fatigue mechanism.

Effect of process parameters on joint performance in self-piercing riveted dissimilar automotive steel joints

This work targets establishing self-piercing riveting (SPR) technology for dissimilar automotive steels used popularly in structural as well as skin parts and evaluating the joint properties. Interlock distance and the remaining bottom sheet thickness (Tmin) are two important cross-sectional quality parameters influencing the performance of the riveted joints. Rivet penetration (i.e., head height) is an important process parameter that controls the interlock distance and thus the mechanical properties. Optimization of rivet (i.e., diameter, length & hardness) and die design (i.e., shape, dia & depth) is equally important to achieve the desired joint properties. In this study, dissimilar lap shear joints of an interstitial free (IF), 300 MPa and a low carbon high strength quality (HSQ), 440 MPa steels were prepared for different head heights, and the cross-sectional quality was examined to explore the joint properties (i.e., Interlock, Tmin). IF-IF combination exhibited a tensile-shear strength of 7.4 kN at an actual head height (AHH) of −0.3 mm, which was significantly higher than the tensile-shear strength of 5.8 kN achieved at an AHH of 0.0 mm for the same combination.

Evaluating the Joinability of Thin-Walled High Pressure Die Cast Aluminium for Automotive Structures Using Self-Piercing Rivets

Evaluating the Joinability of Thin-Walled High Pressure Die Cast Aluminium for Automotive Structures Using Self-Piercing Rivets

Multiple Nonlinear Regression Model of Process Parameters for Aluminum Alloy Self-piercing Riveting

Multiple Nonlinear Regression Model of Process Parameters for Aluminum Alloy Self-piercing Riveting