Researchers at Purdue University have discovered a type of metal deformation, known as sinuous flow. This type of deformation results in very fine folds similar to patterns created during the flow of highly viscous fluids such as honey and natural rock formations.
Soon after the discovery, the researchers found a solution to not only suppress the folding deformation, but also increase efficiency in machining. These findings open the door to manufacturing advances, according to an article by Emil Venere, with Purdue University News.
The team discovered sinuous flow using high-speed microphotography and analysis to study what happens while cutting ductile metals. Results showed that metal deformed into folds, rather than shearing uniformly, as was previously assumed.
The team’s findings showed that required cutting force during machining can be reduced by 50 percent simply by painting the metals with standard marking ink or layout dye. This solution could result in a significant reduction of energy consumption during the machining processes. The ink also improves surface quality, said Srinivasan Chandrasekar, professor of industrial engineering at Purdue.
Applying less force generates less heat and vibration, reducing tool wear and damage to the metal. This results in improved accuracy of the process while reducing costs, according to W. Dale Compton, the Lillian M. Gilbreth distinguished professor emeritus of industrial engineering at Purdue.
Researchers point out that the ink was not applied between the cutting tool and the metal, but painted on the free surface of the metal where it was not in contact with the tool.
“This may sound eerie, even ridiculous to people in the field, because the cutting is not happening on the painted surface, it is occurring at some depth below," said Koushik Viswanathan, a Purdue graduate student.
According to Venere’s article, Ho Yeung, a post-doctoral research associate at Purdue, inked only half of a sample in one set of experiments. When the cutting tool reached the inked portion, the amount of force dropped immediately by half.
Various other coatings, including nail polish, resins and commercial lubricants, were also tested, as Yeung first tried coating metal with a lubricant before adding the ink. Test results showed the suppression of the sinuous flow was less effective as lubricants prevented the ink from sticking to the metal surface.
"It seems that the ink used commercially to mark metal is very good at suppressing the sinuous flow, probably because it is designed to stick well to metals," Chandrasekar said.
This discovery implies the possibility that coatings with improved adhesion might better suppress sinuous flow and further reduce required cutting force in machining.
Chandrasekar noted that understanding sinuous flow and how to suppress and control it could have a range of manufacturing applications that involve metal deformation, such as in machining, stamping, forging and sheet-metal processes.
It may also be possible to design new materials for energy absorption, “by deliberately enhancing sinuous flow — for applications in armor, vehicles and structures,” wrote Venere.
Future research will include work to develop a model of sinuous flow to learn more about its physical mechanisms, its suppression and properties of coatings.
The study was funded by the National Science Foundation and conducted through Purdue’s Center for Materials Processing and Tribology. The findings were published in Proceedings of the National Academy of Sciences, July 27, 2015.