Prediction of Temperature Evolution During Self-Pierced Riveting of Sheets

Prediction of Temperature Evolution During Self-Pierced Riveting of Sheets

Deepak Mylavarapu (IIT Guwahati, India), Manas Das (IIT Guwahati, India) and Ganesh Narayanan R (IIT Guwahati, India)
DOI: 10.4018/978-1-5225-2440-3.ch018

Abstract

Weight reduction of automotive components by tailoring materials is the state of the art. This basically has resulted in the development of advanced joining methods like clinching, friction stir welding, self-pierced riveting etc. to assemble similar or dissimilar materials, with significant change in sheet properties. In the present work, the main aim is to predict the temperature evolution during Self-Pierced Riveting (SPR) of sheets by Finite Element (FE) analyses. Load evolution is also predicted. Generally temperature estimation during SPR is not attempted. The influence of a few selected SPR parameters has been studied on the temperature and load evolution through FE simulations. The relationship between these parameters and the temperature and the load evolution are revealed. Later a neural network model is developed to predict the temperature rise during SPR. The same has been validated at 20 intermediate levels and the predictions are accurate. Thus a hybrid FEM-ANN model for SPR has been developed to predict the SPR outputs efficiently.
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Introduction

The overall weight of an automobile has a great impact on fuel efficiency and vehicle emissions. According to Polmear (1995), fuel consumption can be reduced by 5.5% for every 10% reduction in weight. Moreover, for 1 kg weight reduction, 20 kg reduction in CO2 emission can be achieved for a vehicle running for 1,70,000 km. This results in an increased need of light weight vehicle structure having lightweight materials in automotive industries. Some of these light weight materials are difficult or impossible to weld with conventional spot welding technology. Hence, researchers have started developing new technologies suitable for joining lightweight materials such as friction stir welding (He et al., 2014), laser welding (He et al., 2012), mechanical clinching (Mucha, 2011), adhesive bonding (He, 2014), and different hybrid joining processes.

Self-Piercing Riveting (SPR) is a high speed mechanical fastening technique for joining similar and dissimilar sheet materials which does not require predrilling (He et al., 2015; Mori et al., 2014). Hence, its usage is increasing in automobile industry having light weight Al structure for most of the applications. In SPR process, a semi tubular rivet is pressed by a punch into two or more sheets of materials that are clamped between a die and a blank holder. The die shape causes the rivet to flare (plastic deformation) inside the bottom sheet to form a mechanical interlock. During SPR process, the upper and lower sheets are under severe plastic deformation and the upper sheet gets pierced.

The four different stages of SPR process with respect to load requirement (Figure 1) are discussed below.

  • 1.

    Clamping: Initially the sheets are clamped against the die with the help of a blank holder and it prevents wrinkling of the sheets.

  • 2.

    Piercing: A semi tubular rivet is pushed by a punch into the sheets. After some displacement the upper sheets gets pierced by the rivet tip.

  • 3.

    Flaring: The lower sheet undergoes deformation along with the upper sheet. Then the die is completely filled with the lower sheet. Due to the restriction by the die, the rivet flares in the lower sheet and mechanical interlock is formed.

  • 4.

    Compression: Finally to bring the rivet head upper surface along the sheet, it is compressed till it reaches the required tolerance.

Figure 1.

Load-displacement behaviour of SPR of two sheets

978-1-5225-2440-3.ch018.f01

When metals undergo plastic deformation, significant amount of heat is generated, especially in case of localised deformation. If the deformation process is rapid, heat generation can lead to large temperature rise, since there is little time to conduct heat away from the deformation zone due to adiabatic condition. To predict the rise in temperature, one should know the material mechanics and coupling between plastic deformation and heat evolution. Part of the mechanical energy spent in mechanical deformation is converted into heat and remaining part is stored in the material.

For elastoplastic solids, a number of specializing assumptions are often made, including infinitesimal deformation, additive decomposition of strain into elastic and plastic part, a relation between stress and elastic strain identical to that of isotropic linear thermo-elasticity and linear Fourier heat conduction law. Considering above assumptions, the first law of thermodynamics or energy balance equation reduces to the following form under uniaxial stress condition as shown in Eq. (1) (Rosakis et al., 2000).

978-1-5225-2440-3.ch018.m01
(1)

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