Sheet Panels Research Articles

Single-sided piercing riveting for adhesive bonding in vehicle body assembly

With increasing use of advanced high strength, lightweight materials and alternative vehicle architectures, materials joining issues have become increasingly important in automotive vehicle body assembly. Among the various joining methods, adhesive bonding is one of the important techniques for joining dissimilar materials in vehicle body assembly. During curing of the adhesive, it is necessary to fix and control the gap between the sheet panels to ensure the bonding strength and geometric quality. In this paper, a novel process, the single-sided piercing riveting (SSPR), is proposed for fixing and controlling the gap between the sheet panels during adhesive bonding of vehicle body assembly. The SSPR is a cold forming process for joining two or more sheet parts by driving a specifically designed U-shaped rivet using an impact force. The SSPR process is easy and convenient to implement without the need of a direct back support, and can meet the limited space requirement of vehicle body assembly. Joining experiments and performance tests were carried out to validate the effectiveness of the SSPR process. Performance comparison with other joining methods shows that mechanical properties of the lap-shear SSPR-bonded joints are superior to that of the SPR and SPR-bonded lap-shear joints.

Single-Side Resistance Spot Welding Process for Joining Pipes and Sheets

This paper describes a Single-Side resistance Spot Welding (SSSW) process which is expected to be a productive welding technology for the joining of stamped sheet panels to hollow parts for auto bodies. To obtain guidelines for making a sound weld with the SSSW process, the effects of welding parameters and the alignment of specimens on nugget growth are investigated experimentally. In addition, a numerical study is carried out to discuss the mechanism of nugget growth in the SSSW process.

Single-stroke mechanical joining of sheet panels to tubular profiles

This paper proposes an innovative mechanical joining process for fixing sheet panels against tubular profiles with a single ram stroke.The presentation includes independent determination of the mechanical properties of sheets and tubes, finite element modelling and experimentation under laboratory conditions. The aim is to identify the key parameters of the process, to diagnose possible sources of failure and to understand the routes for selecting the most appropriate joining conditions.Results and observations show that fixing sheet panels to tubular profiles by tube forming with a single ram stroke is a flexible and cost-effective mechanical joining process that can be easily industrialized in a small capacity press. Applications may span for a wide range of engineering applications where conventional technologies based on fasteners, glueing with structural adhesives, brazing and soldering or welding cannot be employed due to technical, aesthetical or economic constraints.

알루미늄 선박의 외판 가공을 위한 인장성형 시스템 연구

Recently, aluminum ships are constructed more than ever because of the environmental pollution generated by FRP (Fiber Reinforced Plastic) ships. In particular, FRP ships have been replaced by the Aluminum ships. The forming process of the curved aluminum plate has been performed only by labor works without systematic technique. Therefore, it is difficult to construct the aluminum ship that the design satisfies both required propulsion performance and hull design. Present study introduces a MPSF (Multi Point Stretching Forming) that is a flexible manufacturing technique to form large sheet panels of doubly curvature. The hull pieces are stretch-formed over the MPSD (multi-point stretching die) generated by the punch element matrix. In this study, MPSF is applied to deform the doubly curved surfaces of aluminum ship. The forming system including FEA (finite element analysis) of the processes for stretching the plate were carried out by static implicit analysis is suggested. Residual deformation of the surface is modeled by an elasto-plastic contact phenomena while the forming process is simulated by FEA. Finally, the proposed system is also validated, comparing the deformed shape by MPSF with that of object surfaces.

Application of axiomatic design theory to automotive body assembly in the sustainable manufacturing context

This paper presents an application of an axiomatic design theory-based analytical approach to autobody components assembly in the sustainable manufacturing context. The adjoining edges of autobody and closure steel sheet panels are machined via a computer-controlled laser cutting process. Following the hierarchies of the bill of materials designed in the CATIA V5 environment, the autobody components are assembled manually using the novel τ-stoss technology. The preliminary data obtained from the comparative analysis of the reported LS-DYNA crash simulation of 2 and 3 mm thick τ-stoss technology-based steel front rails shows that a high number of τ-stoss technology-based secondary beams present a preventive material failure at the integration joints. A series of experimental test drives of the τ-stoss technology assembled automobile validated the robustness of the design system and reliability of the τ-stoss technology.

Mechanical Property Characterization of Fiber-Reinforced Polymer Wood-Polypropylene Composite Panels Manufactured Using a Double Belt Pressing Technology

AbstractA novel manufacturing process for wood-polypropylene composite (WPC) panels reinforced with fiber-reinforced polymer (FRP) sheets was implemented using a double belt pressing technology. FRP sheets were placed on both sides of the WPC agglomerates during fabrication, which resulted in increased productivity and reduced thermal stresses compared with secondary bonding processes. Significant improvements in the mechanical properties of the FRP reinforced sheet panels were found during flexural and tensile tests on the coupon level. Even with addition of only one layer of FRP reinforcement on both sides of a WPC panel, the flexural modulus and strength increased by a factor of 2.6 and 3.8, respectively. Furthermore, the flexural and tensile properties of the WPC material considered in this study were found to be superior compared with the properties of an extruded WPC material. The changes in the flexural modulus of the FRP reinforced WPC panels with respect to the number of FRP layers were predicted...

Evaluation on Vibration Property of Magnesium Honeycomb Panels

The vibration and acoustic transmitting experiments and digital simulation were carried out on AZ31 magnesium sheet and magnesium honeycomb panels. The results show that the vibration characteristics and acoustic transmission loss (TL) of honeycomb panel are related to magnesium sheet and honeycomb core parameters. In full audible frequency spectra, TL of various honeycomb panels behaves in a similar manner, and the TL increases with the frequency at higher frequency. Damping enhancements of honeycomb panels contribute better vibration insulation. Vibration analysis shows that the dangerous positions are located in no-strutting areas.

Joining sheet panels to thin-walled tubular profiles by tube end forming

This paper is focused on novel utilizations of the fundamental modes of deformation of tube end forming for assembling sheet panels to thin-walled tubular profiles. The objective is to present an innovative and environmental friendly joining technology built upon the combination of compression beading with tube inversion that can successfully eliminate currently available technologies based on mechanical fixing with fasteners, welding and structural adhesive bonding. The technology works at room temperature, is capable of ensuring significant economic and time savings and offers potential for opening new markets for the assembly of lightweight frame structures. The presentation is supported by experimentation and numerical modelling based on independently determined mechanical properties of the materials with the purpose of characterizing and evaluating the process feasibility limits as a function of the major operative parameters. The feasibility of joining sheet panels to tubular profiles by means of the proposed technology is demonstrated by presenting industrial applications and by evaluating the performance of a safety auto part in an operation failure test.

A new method for 3D forming of extrusion-based sheets for light-weight hull applications

This paper presents a new, innovative forming method that has been developed for 3D bending of aluminum alloy sheets with integrated T-stiffeners. The main motivation for developing this technology is twofold: (a) reduce construction, operating and service (maintenance) costs while (b) lowering the environmental impact of aspects associated with use and recycling of working boats. Focus is placed on describing the overall system, demonstrating shape flexibility and dimensional capability of components. A prototype forming machine has been built for incremental bending of sheet panels into double curvature part configurations. Full scale forming trials were conducted using friction stir-welded aluminum alloy AA6082 panels with T-stiffeners. The panels were tested in both temper T4 (extruded and stabilized) and temper T6 (artificially aged) in order to determine differences in formability, springback and dimensional accuracy. An analytical method for springback compensation was established using conventional bending theory combined with the deformation theory of plasticity. A comparison between the analytical and experimental results shows that the former demonstrates good capability in predicting springback. The results, as represented by bending–springback diagrams, represent a suitable basis for establishing an automated steering model for forming of 3D geometry configurations based on CAD data received from product designers.

Influence of Welding Conditions on Nugget Formation in Single-Sided Resistance Spot Welding Process

This paper describes the single-sided resistance spot welding (SSSW) process which is expected to be a productive welding technology for joining stamped sheet panels to hollow parts for auto bodies. To obtain guidelines for making a good weld with SSSW process, the influence of welding parameters and set-up conditions of the specimen upon nugget growth were investigated experimentally. In addition, a numerical study was carried out to establish the mechanism of nugget growth in the SSSW process. Since deflection of parts during welding is one of the features of the SSSW process, this report focuses on the influence of electrode force and the stiffness of the specimen upon nugget formation. In addition, the effect of electrode geometry was examined.

Numerical simulation for the multi-point stretch forming process of sheet metal

Multi-point stretch forming (MPSF) is a flexible manufacturing technique to form large sheet panels of mild curvature. The traditional fixed shape-stretching die is replaced by a matrix of punch elements, and the sheet metal are stretch-formed over the multi-point stretching die (MPSD) generated by the punch element matrix. In this paper, extensive numerical simulations of the processes for stretching parabolic cylinder, toroidal saddle and sphere parts were carried out by dynamic explicit finite element analysis. The forming results using multi-point die were compared with those of using traditional die. The use of an elastic cushion to suppress dimpling of the part caused by the discrete punch elements was investigated along with a discussion of its influence on part shape accuracy. The effect of the size of punch element and the shape of MPSD on the shape accuracy of formed parts were analyzed. The results may provide useful guidance on determining MPSF parameters and optimizing MPSF manufacture processes.

Straight Hemming of Aluminum Sheet Panels Using the Electromagnetic Forming Technology: First Approach

Hemming is the last or one of the latest stage operations for the stamped parts. For this reason it has a critical importance on the performance and perceived quality of assembled vehicles. It is used to attach two sheet metal parts together or to improve appearance creating a smooth edge rather than a razor edge with burrs. However, designing the hemmed union is not always easy and is deeply influenced by the mechanical properties of the material of the bended part. Main problems for the automotive industry arise when bending aluminum alloys. Aluminum sheet is more difficult to hem due to its susceptibility to strain localization during the hemming process. This phenomenon produces cracking on the hemmed edge [1]. In order to avoid this problem and due to the limitations of conventional flanging and hemming technologies, the flange radii must be increased and a rope hem used (instead of the flat hem used with steels) when working with aluminum alloys. These changes on the design of the hem union give as a result a lower quality final product [2]. Dies and tools used for the hemming process are designed based on experience and on lengthy and costly die tryouts. Continuing with the development of new applications for the Electromagnetic Forming (EMF) technology, LABEIN-Tecnalia and Professor Glenn Daehn’s group from The Ohio State University carried out some first straight flat hemming experiments using the AA 6016 T4 aluminum alloy. The results obtained from these first trials are presented in this paper giving a first sight of the possibilities, advantages and disadvantages of using the Electromagnetic Forming technology for the hemming of aluminum sheet panels. Using a non-clouped FEM simulation method, the experimental results are compared to the ones obtained with the simulations. The future working line in developing this new application for the Electromagnetic Forming technology will be based on the results obtained by this study.

Robust pin layout design for sheet-panel locating

Sheet panels, represented as freeform surfaces in a CAD system, are widely used in manufacturing processes. Locating blocks and pins, collectively known as locators, are the most common fixtures for the joining and assembly of sheet panels. In this paper, a robust design approach is utilized to optimize the pin layout so that the sheet panel variations, expressed as translational and orientational variations at certain key product/process characteristic points (KPCs), are minimized. The advantage of this approach is that the locating variations at any given point on the panel can be obtained quantitatively, and hence, the optimal pin design can be selected from among an infinite set of feasible designs. Based on the analyses, some useful pin design guidelines will also be proposed.

Forming Defects Analysis of Auto-Panel Stamped Part with Experimental Strain Approach

This document explains and demonstrates an experimental method to determine principal plastic strains in industrially stamped sheet panels. The principal strains distribution after a given stamping process can be obtained using computer aided grid experimental method. In contrast with FLD (Forming Limit Diagram) obtained by the material testing, the measured results of strain distribution can be used to determine the sheet metal’s formability allowing to determine at which point the sheet metal cracks or uneven stretch occurs and other forming defects. The main principle and related theory of this approach are discussed. One automobile panel stamped part as a practical case was studied, the strain distribution of the part after a given stamping process was measured and calculated, a demonstration of how to deal with the results in comparison with FLD to determine and solve forming problems is analyzed.

Two Novel Techniques for Forming Regularly Spaced Deep Recesses on Aluminium Sheet Panels

Two Novel Techniques for Forming Regularly Spaced Deep Recesses on Aluminium Sheet Panels

In Process Control of Strain in a Stretch Forming Process

The process of stretch forming is used extensively in the aerospace industry to form large sheet panels of mild curvature. This has traditionally been a low precision process requiring considerable hand-working at assembly. However, recent demands for faster, less wasteful production have placed new demands on the accuracy and consistency (quality) of this process. In this paper the various modes of control for this process are examined, from both an analytical and experimental point of view. It is shown clearly that the process is least sensitive to material and machine property variations if controlled to a target level of strain in specific areas of the sheet. This method is compared with the conventional methods of controlling either the force applied to the sheet during stretching or the displacement of the stretch jaws. A series of both lab scale and full production experiments concur with the analytical findings, demonstrating reduced process variation if strain feedback is used. Lab experiments and analysis indicate that far greater reductions are possible if a more precise form of strain control is used. In production trials forming wing leading edges, a manually implemented strain control showed a shape variation reduction of 50 percent over normal factory practice using force control.

Bead pattern optimization

Plane sheet panels exhibit poor stiffness and NVH (noise, vibration, and harshness) performance due to their flexibility. A common and cost-effective approach in the automotive industry to improve the stiffness and NVH peformance of sheet panels is the addition of beads. However, no systematic methodology is available for determining the optimal pattern of beads in sheet metal. This research explores the feasibility of applying topology optimization methods to the bead design of sheet panels. The approach starts with adding beam elements to the shell element model of the sheet panel to simulate the stiffness improvement of the structure and then uses the topology optimization method to obtain the optimal layout of the beam elements. A cantilever plate is used to perform a preliminary study for bead pattern design and a simplified vehicle structure is used to demonstrate the applicability of the proposed method.

A comparative study of the methods used to evaluate the activity of Teredinidae molluscs

Different methodologies are usually employed to evaluate Teredinidae wood-boring activity. Many authors using panels made of solid wood, estimated density by counting Teredinidae punctures on the wood surface or using x-ray techniques. However this technique does not allow the identification of species. A second approach, employing a collecting device made of sheets of wood, can be more effective for quantitative and qualitative analyses. The present paper compares density, species composition and diversity when using both solid and sheet panels. In addition different methods of estimating density were analysed. The results show that the evaluation of Teredinidae activity can change according to the methodology employed.

The evaluation of large strains from industrial sheet metal stampings with a square grid

A method to determine surface strains in industrially stamped sheet panels has been studied. The method incorporates a quadrilateral grid imposed to the blank and automatic image analysis. The quadrilateral grid makes it possible to analyze complex strain histories with rotations of the deformation system. The grid size can easily be increased from a minimum value upward during the analysis of a panel, for example, from one area to the next. In areas of the panel where cracking occurs, a small size grid is required because of the sharp strain gradients close to the crack. In relatively flat areas of the panel with low levels of strain attention is usually focused on strain variations over larger distances than in failure regions, and larger grids are used. Such long range strain variations are of interest in analyzing buckling, springback, or shape fixation. An inner auto body component was stamped in a high strength rephosphorized sheet steel and analyzed in some detail. Complex strain histories were identified with rotations of the deformation system. The distribution of strains in different areas of the stamping was determined. The analysis gives both the magnitude of the strains and the direction of the largest strain. Such information can be used by a die engineer in tooling development and in selecting blank holder pressure. Cracking occurred at one location of the stamping. The corresponding strain path was complex. The failure could be predicted with the present strain analysis and the forming limit diagram.

The strength of structures and the applications of the fracture mechanics

After a short review of the papers by Odorico and Bathias presented to the AGARD Structures and Materials Panel Specialists' Meeting on Fracture Mechanics Design Methodology, 28–29 September 1976, London, the place of Fracture Mechanics in the Strength of Structures domain is considered as well as the still limited help afforded to the designer by the mass of published Fracture Mechanics data and the means of increasing the practical usefulness of these data by carrying out detailed investigations of actual cases of local failures occurring in static strength tests, full-scale fatigue tests and of damages in operations are discussed. It is proposed to discard the academic domain of cracks assumed to exist at the centres of thin sheet panels, far from the most probable damage origins, and to attempt to define classes of actual problems related to known or unknown stress concentrations in assemblies. These classes are so general that they justify detailed investigations which will supply tables of numerical data rapidly usable by the designer.