Analysis of "Flow Drilling Screw" joining technology for Body in White production

The thesis refers to the automotive sector and more specifically to car body manufacturing, taking the "Flow Drilling Screw" joining technology as object of analysis. Commonly known by the acronym FDS, it represents a real breakthrough in the creation of multi-material joints, and has had considerable prominance in recent years with the ever-increasing use of aluminum alloys in car design in accordance with the objective of reducing vehicles weight. FDS is born as an evolution of the Flow Drilling technology, in which a hard metal rod with a pointed end is used to obtain a through hole in the workpiece by means of plastic deformation of the material at high temperatures, exploiting the heat of friction that is created during the high speed rod rotation. The fundamental innovation of the FDS technology is to providing a single element that acts both as a drilling tool and as a fastener. This paper aims to provide a detailed analysis of the technology in all its aspects, but in particular it focuses on the control of the FDS process through the implementation of an experimental test campaign. In the first sections of the paper there is an introduction to the processes related to the Body in White manufacturing, to then move on to the classification and brief description of the joining technologies currently used in the automotive field for aluminum alloys. The FDS technology is dealt with initially from a theoretical point of view by a description of the operating principles, the presentation of the various stages of the process, the range of utilization, the machinery employed on the manufacturing line, the quality criteria that must be respected to ensure the conformity of the joint. The core of the thesis project is the realization of an experimental testing campaign. The test plan is developed divided into several phases, each of these intended at evaluating different aspects. The first objective is to study the influence that the parameters set on the machine have on the final joint, until the optimal set of parameters is identified. For the subsequent phases, we move from a purely “laboratory test condition” to a condition as close as possible to what it would have in plant inside a manufacturing line, thus trying to model a real assembly of BiW components. In this way external factors related to product design and process constraints are introduced and the relative response of the FDS operation is evaluated. The results of the tests have provided several interesting indications that can be exploited for the control of the FDS technology in the production line and in particular allow to identify the optimal working conditions in order to limit the appearance of gap between the metal sheets in the proximity of the joining point.