Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Engineering Science

Program

Mechanical and Materials Engineering

Supervisor

Tutunea-Fatan, Ovidiu-Remus

Abstract

One of the most used processes in the automotive industry is the moulding of parts made of thermoplastics filled with glass fibres. This research focused on a specific material: long fibre thermoplastics (LFT). On the one hand, the performance gain, in terms of lightweight and the strength of final components, justifies its wide use. On the other hand, due to the intrinsic characteristics of part manufacturing, warpage is evident and can influence or even compromise subsequent stages of production.

This research has three main objectives: recreate in the most faithfully way, in AbaqusTM environment, the conditions that precede the welding of LFT parts manufactured by moulding; compare gap distances between the assembly fixture and each part, due to their warpage, with the distances provided in the simulation; and finally, allow the prediction of the force acting on the welder's head while the welding is performed.

Summary for Lay Audience

The automotive industry adopts many strategies to produce more efficient vehicles in terms of fuel consumption. Some strategies include hybrid technology (electrical and fossil fuel engines working in parallel), engine power-efficiency and lightweight, which is the attempt to reduce the total mass of the vehicle, impacting and reducing its fuel consumption. On the latter, it is possible to simplify some vehicle systems or, instead, change the material of some components, opting for less dense alternatives, for instance, plastics and composite materials.

The composite material is a promising avenue in terms of technological development. It allows the engineering of parts, combining properties of different materials trying to reach a more efficient use of them with either the same or better performance. However, such a technological option presents its inherent challenges, being the prominent ones the dimensional reliability and precision along its manufacturing process. Dimensional variability observable at each intermediate step involve, for instance, shrinkage, expansion and warpage.

Parallel to it, joining parts is a technique that allows the production of parts with more complex geometries when the material change is not a good option. In some cases, both (change of materials and joining techniques) opens new developmental avenues. One of the joining techniques applicable to composite materials and one of the most efficient is ultrasonic welding, where parts are bonded by heating produced by fiction and vibration.

This work tries to recreate the welding process of specific parts to measure the pressure (or force) imposed on each of them, producing data to estimate the force level during the process.

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