Seminar: The Cutting of “Gummy” Metals

Abstract

It has long been known that highly strain hardening metals such as commercially pure aluminum, copper and iron; and nickel alloys and stainless steels, are quite difficult to cut, despite being relatively soft. This difficulty in cutting has earned them the moniker “gummy”. This seminar discusses the examination of the origins of this problem using high-speed, in situ imaging, complemented by force and surface characterization. It is shown that the fundamental cause of the problem is the tendency of these metals to deform via an unsteady, highly redundant mode of plastic deformation termed sinuous flow. Deformation in this flow mode is characterized by large-amplitude surface folding, significant thickening (straining) of material during chip formation, large forces and poor machined surface quality, e.g., rough surfaces, surface tears, large residual plastic strains. Sinuous flow is shown to be nucleated by plastic buckling of a thin surface layer ahead of the tool. The conclusion is that by highlighting a unique mechano-chemical effect, with common adhesive media (e.g., inks, glues), in large-strain deformation of metals, sinuous flow mode can be suppressed, and, thereby, greatly facilitate the cutting of gummy metals.

About the speaker

Srinivasan Chandrasekar is professor in the Schools of Industrial Engineering and Materials Engineering (courtesy) at Purdue University, where he also directs the Center for Materials Processing and Tribology. His research and teaching interests are in manufacturing, tribology and structural materials. His recent contributions all stem from the use of in situ high-speed imaging techniques to characterize material plastic flow and fracture phenomena at high spatial and temporal resolution. Besides enabling phenomenological discoveries pertaining to large-strain deformation and stability of plastic flow, the work has led to commercialization of modulation-assisted machining processes (R&D 100 award, 2010) and machining-based methods for materials manufacturing. He is a Fellow of the ASME and AAAS.

Hosted by Prof. Jami Shah.