Masters of Manufacturing: M. Eugene Merchant

Manufacturing Engineering, Jul 2004 by Destefani, Jim

Merchant: When I joined "the Mill," the research department was headed by a man named Hans Ernst. He was very curious-minded-an explorer in the field of machining, you might say. He was studying chip formation in machining by cutting metal at low speeds, then observing the process directly through a microscope.

When I joined the group, Hans naturally chose a project in metalcutting for me to work on. He was interested in the friction between the chip and the tool. When a chip moves over the tool face, it will either stick and cause a built-up edge, or it will fracture, or it will go smoothly. He had already classified those three types of chip formation, and he surmised that chip formation must be very much influenced by the amount of friction between the chip and the tool.

He wanted me to study the fundamentals of the friction process in chip formation. Because material tended to weld to the tool face and form a built-up edge, Hans guessed that the friction between the chip and the tool face must be very high. But there was no way of knowing how much friction there was. So, my thesis was a study of friction between chemically clean metal surfaces, and I developed a theory that explains the nature of friction between such surfaces. This yielded the basic equations for the mechanics of friction for either boundary-lubricated surfaces or very clean, dry surfaces that are still used today.

That research led me to thinking about the mechanics of the whole chip formation process. If I could figure out the mechanics of friction, could I apply mechanics to the entire chip formation process? What was happening? What were the forces involved? The amount of friction? How could you calculate it in the cutting process?

I found that application of the science of mechanics to the chip-formation process resulted in equations that made it possible to calculate machining forces and other variables from first principles. That provided the first step in developing a scientific basis for engineering the metal cutting process.

Those equations kind of broke the ice and opened up the field of manufactoring to science, and demonstrated to everyone that you can apply science to what goes on in the factory. People began to look at their processes and ask questions: were the processes amenable to application of various kinds of science-mechanics, thermodynamics, and other branches?

ME: So you built off the qualitative understanding of the metalcutting process that Hans Ernst had developed, and took that to the quantitative realm?

Merchant: Exactly. He had an empirical understanding.

ME: Along those same lines, your history of machining research in the US describes an empirical phase and a theoretical phase. Where are we now?

Merchant: We are of course continuing to develop the science of manufacturing. But the impact of computer technology on that is a factor that cannot be overemphasized. It allows you to bring in science much more readily than the old "hammer and tongs" way did. So the real revolution began with the introduction of computer technology about 50 years ago.