ENGINEERING COURSEWORK

Engineering coursework

Engineering coursework

Introduction

The exterior appearance of an automobile is one of the most important factors a customer considers when choosing a vehicle. While exterior design is typically a customer's primary appearance consideration, customers also have very exacting standards regarding the appearance of the so-called Class "A" surfaces. Consequently, manufacturers work hard to ensure that the surfaces produced are the Class “A” surfaces intended. While there are many benefits to using adhesives in automotive body components, their use can cause distortions in a Class “A” surface. Distortion caused by adhesives is often referred to as bond-line read-through (BLRT). BLRT has no impact on the structural performance of automotive body panels, yet it diminishes the customer's perception of the quality of a vehicle (Fuchs 2010, 982-1011).

Because the most straightforward solution to eliminating visible BLRT is to increase the thickness of the outer panel - essentially adding weight for appearance - the Automotive Composites Consortium (ACC) undertook a multi-year project to develop a better understanding of the causes of this distortion. The goals of the project were to a) develop an understanding of the material and process factors that cause BLRT-induced distortions to be visible on the surface of a component, b) develop a validated finite element model that can predict the occurrence and severity of BLRT, and c) establish material and process guidelines for automotive companies and suppliers to follow to insure that original equipment manufacturers (OEMs) will be able to specify minimum thickness (i.e. weight) panels while ensuring that those components will meet customer expectations for surface appearance.

BLRT has been seen in automotive applications periodically ever since bonded assemblies were introduced in the industry. Other researchers have completed studies on particular aspects of the cause of this distortion. No experimentally based, systematic study, however, had been completed on this topic. One of the reasons for this may have been that all assessments of BLRT severity had to be done subjectively by a jury because an objective, numerical measurement for quantifying the visual severity these distortions did not exist. Consequently, the first task that had to be completed was to develop a measurement that would quantify the severity of these distortions in a way that correlated with visual assessment of the severity of these distortions (Wang 2011, 15-16).

The measurement developed as part of this project is described in detail elsewhere. Once a method to obtain objective, quantitative data was available, a series of experiments could be completed to establish the relationship between material and process factors and BLRT severity. The data from those experiments was also used to determine the material properties and finite element methodology necessary to correctly predict BLRT severity analytically. The material and process factors that were found to have the most significant influence on the severity of these distortions in the physical and analytical experiments have been summarized in the literature. This paper summarizes design and manufacturing guidelines developed to control those factors and eliminate visible distortions from production assemblies (Lazarz 2010, ...