Friction Stir Blind Riveting Process Research Articles

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.

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.

Numerical Analysis of Magnesium to Aluminum Joints in Friction Stir Blind Riveting

Friction stir blind riveting (FSBR) is a new dissimilar material joining method that takes advantage of both friction stir welding and mechanical blind riveting. However, no research has been conducted to investigate the stirring effects on energy transformation, material flow and temperature evolution in FSBR, which are critical to help understand the FSBR process. This paper described a hybrid numerical model integrating both finite element method (FEM) and smooth particle hydrodynamics(SPH) approach to predict the stirring effects in FSBR lap joint of Mg/Al. In this SPH-FEM model, only rivet plunging process was simulated, and the following mandrel pulling process was not considered. The Johnson-Cook equation was used to describe the constitutive material properties. The model was validated by comparing thrust forces and torques from numerical prediction and experimental results. From the simulation, it was found that (1) the main input energy was consumed by the torque to generate interfacial friction heat and the heat generated from workpiece deformation was negligible; (2) the maximum welding temperature in Mg (~620°C) was higher than that in Al (~590°C), and both maximum temperatures are close to the melting points; and (3) the evolution of material flow illustrated the formation process of interlocking between Mg and Al.

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.

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.

Mechanical Property of Al Alloy Joints by Friction Stir Blind Riveting

Dissimilar lap-shear joints were fabricated by the friction stir blind riveting process using AA6111 (0.9mm) as the top-sheet and AA6022 (2.0mm) as the bottom-sheet in a 2-sheet stack-up. Tensile testing of the friction stir blind riveting joints exhibited a combined fracture mode of initial shear followed by tearing. The maximum tensile load of the friction stir blind riveting joints increases slightly with increasing feed rate and shows little dependence on the spindle speed. The microhardness of the material at different layers along with the rivet penetration are analyzed and discussed.

A New One-Sided Joining Process for Aluminum Alloys: Friction Stir Blind Riveting

Friction stir blind riveting is a new joining process for one-sided joining (compared with the two-sided access required for, for example, self-piercing riveting) of aluminum alloys, which eliminates the need to predrill a hole for rivet insertion. A blind rivet rotating at high speed is brought into contact with the workpieces, thereby generating frictional heat between the rivet and the workpiece, which softens the workpiece material and enables the rivet to be driven into the workpieces under reduced force. Once fully inserted, the blind rivet is upset using the internal mandrel (as in a conventional blind riveting process) to fasten the workpieces together. Our study showed that friction stir blind riveting process can be carried out over a wide range of operating parameters. The resulting joints show consistent strength under tensile load with minimal influence of changes in operating parameters. The robustness of the process against variations in operating conditions shows that the process can be carried out without high-end equipment and without requiring precise initial setup. It also suggests that the process is feasible for rapid joint fabrication in volume production. Further study revealed superior static and fatigue strength from the friction stir blind riveting process, when compared with conventional spot welding, which suggests potential for reduction in the number of joints required in a structure.