chip formation

2 Articles

Getting A Close-Up View Of Chip Formation With An SEM

June 1, 2023 by 16 Comments

When all you’ve got is a hammer, everything looks like a nail. And when you’ve got a scanning electron microscope, everything must look like a sample that would be really, really interesting to see enlarged in all its 3D glory. And this is what [Zachary Tong] delivers with this up close and personal look at the chip formation process.

We’ve got to hand it to [Zach] with this one, because it seems like this was one of those projects that just fought back the whole time. Granted, the idea of cutting metal inside the vacuum chamber of an SEM seems like quite an undertaking right up front. To accomplish this, [Zach] needed to build a custom tool to advance a cutting edge into a piece of stock by tiny increments. His starting point was a simple off-the-shelf linear stage, which needed a lot of prep work before going into the SEM vacuum chamber. The stage’s micrometer advances a carbide insert into a small piece of aluminum 50 microns at a time, raising a tiny sliver of aluminum while it slowly plows a tiny groove into the workpiece.

Getting the multiple shots required to make a decent animation with this rig was no mean feat. [Zach]’s SEM sample chamber doesn’t have any electrical connections, so each of the 159 frames required a painstaking process of advancing the tool, pulling down a vacuum in the chamber, and taking a picture. With each frame taking at least five minutes, this was clearly a labor of love. The results are worth it, though; stitched together, the electron micrographs show the chip formation process in amazing detail. The aluminum oxide layer on the top of the workpiece is clearly visible, as are the different zones of cutting action. The grain of the metal is also clearly visible, and the “gumminess” of the chip is readily apparent too.

For as much work as this was, it seems like [Zach] had things a bit easier than [Ben Krasnow] did when he tried something similar with a much less capable SEM.

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Sharpies And Glue Sticks Fight The Gummy Metal Machining Blues

July 20, 2018 by 25 Comments

“Gummy” might not be an adjective that springs to mind when describing metals, but anyone who has had the flutes of a drill bit or end mill jammed with aluminum will tell you that certain metals do indeed behave in unhelpful ways. But a new research paper seeks to shed light on the gummy metal phenomenon, and may just have machinists stocking up on office supplies.

It’s a bit counterintuitive that harder metals like steel are often easier to cut than softer metals; especially aluminum but also copper, nickel alloys, and some stainless steel alloys. But it happens, and [Srinivasan Chandrasekar] and his colleagues at Purdue University wanted to find out why, and what can be done about it. So the first job was to get up close and personal with the interface between a cutting tool and metal stock, to observe the dynamics of cutting. In a fascinating bit of video, they saw that softer metals tend to fold in sinuous patterns rather than breaking on defined shear planes.

Source: American Physical Society.

Having previously noted that cutting through Dykem, a common machinist’s marking fluid, changes chip formation in soft metals, the researchers tested everything from Sharpies to adhesive tape and even correction fluid, and found that they all helped to reduce the gumming action to some degree. Under their microscope they can clearly see that chips form differently once the cutting edge hits the treated surface, tending to act more brittle and ejecting rather than folding. They also noted a marked decrease in cutting force for the treated metal, and much-improved surface finish to boot.

Will Sharpies and glue sticks enter the book of old machinist’s tricks like gauge-block wringing? Only time will tell. But for now, this is a pretty fascinating bit of research that you might be able to put to the test in your shop. Let us know what you find in the comments.

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