Date of Award

2010

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

First Advisor

Owusu-Ofori, Samuel

Abstract

The goal of this research is to develop a technique to accurately determine the characteristics of the pressure distribution during a rolling process. The determination of the accurate characteristics of a pressure distribution within the contact zone is essential to the accurate estimation of the energy and power requirements for the plastic deformation of the part. It has been determined by metal formers that the nature of the pressure distribution is very sensitive to the value of the coefficient of friction between the roller and the deformed part. It has also been determined that the physics of the deformation process points to a variable coefficient of friction between the roller and the part. However, current research and practices result in the use of a constant friction coefficient. This dissertation explores the development of a technique to determine a quantitative relationship between the variable friction coefficient and the process parameters. This work considers the friction coefficient as a function of the roll angle and seeks to determine a quantitative relationship between them. The pressure distribution is then developed using a varying friction coefficient model. In this study, current insufficient research models are modified using a technique in which the contact region is analyzed in a piecewise manner from the entry to the exit points and the instantaneous coefficient of friction extracted for each element. Consequently, the friction coefficient is determined as a function of the roll angle. The pressure distribution is then developed within the contact region using the instantaneous friction coefficient model. Results show that a “rule-of-thumb” method used by industry overestimates the pressure distribution. This results in the use of more power than needed for the operation. The current published methods, on the other hand, underestimate the pressure distribution. A cost-effective friction coefficient measuring technique has been developed and tested. An experiment was run on a laboratory rolling mill equipment using 1100 aluminum as the work material. The experimental results show that the friction coefficient varies within the contact region as expected. The results indicate that the power requirement developed from the proposed varying coefficient of friction model is 18% less than the power developed by using the industry method and about 8% less than the current published methods.

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