Cutting Metal inside an Electron Microscope

I made this little widget which is designed to cut metal but it's designed to do that inside of a vacuum chamber of a scanning electron microscope so that we can watch it happen in microscopic detail and I have to tell you this is some of the coolest footage I've seen in a long time [Music] right so let's back up and talk about what's going on here there are a lot of different ways to cut metal small milling machines fancy five axis cncs or even in drill press and hacksaw fundamentally the principle is very simple you take something that is harder than the metal add a sharp edge to it and then push it through the metal if everything goes well you just cut some metal congrats now of course it's a little more complicated than that but fundamentally that's the idea cutting tools were traditionally made of a hard metal called high speed steel it's an alloy that is harder than older carbon Steels and lets you cut faster hence the name high speed but high speed steel isn't generally used anymore because we have a better material called carbide this is actually a Tungsten Carbide powder mixed with Cobalt binder the powders are pressed together into a shape and then sintered it makes a very hard tool that can keep a sharp edge cutting tools come in all varieties although the common form is a cylinder with sharp fluted edges the sharp flutes cut the metal and the space behind the flute helps remove the material from the cut and eject it there are tons of variations of this you can have square edges or round edges single flute or many flutes super tiny or extra large weird shapes geometries that drill and even though carbide is the most common there are other materials too like polycrystalline diamond or even single monocrystalline diamond sometimes the carbide is pressed into little shapes called inserts that's what we're going to use today these are three different cutting inserts and you can see they all have slightly different shapes and Coatings and materials these little differences can have a big impact on how they actually cut the metal to help demonstrate this I'm going to cut some clay using an improvised cutting device it's just a piece of brass that I've bent into a specific shape and while all these folds look random they all serve a specific purpose The Cutting Edge is down here at the bottom so if I take this tool and I push it through the clay you can see that the clay starts to pile up at the base and then once enough has accumulated it starts to curl forward over top of itself that's what those creases and folds are for as the material gets pushed up the face of the cutting tool the little bumps increases kind of push the material out and forward which makes it start to curl back on itself this is a useful property because it helps get the material out of the way you want it to form tight little curls that are easy to break off and don't get kind of gummed up at The Cutting Edge if you have a tool that has a flat cutting surface like this one you can see that the material just sort of piles up on the face of the tool and doesn't really go anywhere it kind of gets stuck so there's little bumps and creases are almost as important as the actual Edge that's doing the cutting so there's a lot of finesse into the geometry of these cutting tools I've always wanted to see this in action under a microscope so that we could watch the carbide cut real metal and watch all these features interact with the metal in real time time and I wanted to see it under a scanning electron microscope because I don't know how cool that be so to do this we need to make a little fixture to cut the metal inside of my microscope this is what I came up with it uses an off-the-shelf linear stage which provides the cutting motion that mounts onto a base which also acts as a vise holding our material to be cut and on top of the device is the holder for the carbide cutter which also allows precise positioning so we can adjust the depth of cut vacuum Chambers are pretty picky about what goes into them most Plastics and a lot of other materials will off gas when you put them in a vacuum so we need to clean all of our components really well by first degreasing it in an ultrasonic bath of simple green followed by some solvent the stage came with this green generic random grease which I don't know what it is but it's almost certainly not vacuum compatible so we need to carefully make sure it's all been cleaned out and replace it with a vacuum safe grease I'm using Molly coat which is a high vacuum grease I mostly use it for greasing like o-ring seals stuff that comes on and off of a chamber to make sure there's a good seal but you can also use it for lubricate things moving back and forth reassembling this stage took far longer then I'm honestly willing to admit on camera so we're just going to fast forward through all of that process and start talking about how this actually works so first we Mount the material that's to be cut in this case it's just a small piece of aluminum then we position the cutter with the help of a microscope and finally we advance the cutter five ticks on the micrometer this moves the cutter forward about 50 microns because we're advancing this by hand with a little micrometer screw we need to take a relatively shallow cut in this case I was aiming for between 100 and 200 Micron or about 0.2 millimeters then we pop it into the scan electron microscope pump down the vacuum chamber position the image focus and finally take a photo then we pull it out and repeat the process moving forward another 50 microns I don't really know why but I didn't think this would take too long like I knew it would take a little while taking it in and out of the microscope but I assume to be like an hour or two and be done I was very wrong and this takes about five minutes from you know putting it in the chamber to pulling it back out of the chamber and repositioning and I took about 70 photos so you can do the math I was here for a little while but honestly I'm not even mad about it it was totally worth it I mean how cool is this [Music] [Music] [Music] thank you [Music] [Music] thank you [Music] so if you look closely and watch these stripes in the material you can see how the aluminum gets stacked on top of itself you'd think it'd be like peeling a vegetable right and the skin kind of comes off in one long continuous strip but it's actually a lot more like that clay demonstration as the cutter advances layers get sort of piled on top of each other the area where this is happening is called the primary Shear Zone and it lays in sort of a diagonal to The Cutting Edge there's also a secondary Shear Zone which is all the metal that gets pushed up against the Cutter's face these areas are of particular importance to researchers because they have altered material properties compared to kind of the bulk metal as the cutter is moving through the metal it's displacing and shearing atoms in the lattice of the metal in those two different zones and so you end up getting different Arrangements of the metal after it's been cut and the way that the sheer zones interact with the cutter can be pretty important and change how the cutter performs as the cup progresses you can see that the the back side where it's being cut gets cleaner and sharper and then eventually the whole chip starts to curl over itself which is basically those chip Breakers in action I have the cutting tool position basically perpendicular to the surface which is known as a neutral rake angle you can also have positive and negative angles which will affect how it cuts the metal if we go back to the clay you can see that a positive angle has a pretty dramatic effect it causes the clay to curl a whole bunch compared to before and in contrast to negative angle just sort of smooshes it into the clay itself and causes it to pile up at the base there's no right or wrong angle The Rake angle that's chosen is often dependent on the material different types of materials and their properties how hard or soft or gummy they are will dictate what sort of rake angle you should be using I really want to show the impact of the different angles and how it affects different materials aluminum stainless carbon steel but I just I couldn't do any more seven hour Imaging sessions I just didn't have it in me you can buy Chambers for my microscope that have an electrical pass-through connection So in theory I could rig up some sort of like stepper motor to move the cutter forward and automate the whole process for me but to be honest those chambers are sort of unreasonably expensive for what they are it's like several thousand dollars for basically an empty box and I just had a hard time justifying it for a project like this if someone from Thermo is watching this and wants to send me one you know I'm all here's shoot me a message but otherwise I think what I might do is make some sort of like mechanical Clockwork wind-up mechanism and use that to drive the cutter forward so the idea would be you would wind it up ahead of time put it inside the chamber and then start Imaging really quickly and it just will cut as long as that Clockwork spring is giving it energy that would take a pretty significant amount of CAD work on my side so I think I'm going to bump that to the Future it might surprise folks given the nature of my channel but my background in training is actually in biology although I've spent the better part of my career working in software specifically on distributed search and analytics algorithms that's why you often see software adjacent projects on this channel or some type of analysis of the data that's being collected in the mems video for example I wrote a python script to capture the tracking Point data and Export it so that we could analyze the plots and see some interesting Trends in the Raw data I learned all of this over the years through both work and just fun personal projects but if I were to do it again today I probably start with brilliant.org there are a lot of ways to learn math computer science statistics but I think brilliant is probably one of the best because it's interactive I think it's obvious from this Channel and the things I work on that I'm a very Hands-On learner I learn best when I'm doing or making something you're not sitting through a lecture on brilliant you're actively engaging with the material and learning through interaction with it which is something that really resonates with my learning style I'm something of a probability and stats nerd which is 100 from my biology background and it makes sense because probability is the science of quantifying uncertainties which naturally arise in biology as well as Material Science the world is just a chaotic place and having the skills to quantify and work with those probabilities really lets you start thinking about problems differently it gives you a way to reason about populations and distributions or determine if the effects you're seeing are really real or just random chance probability and statistics unfortunately has a bit of a bad reputation because frankly it's taught badly in most places usually you're staring at an Excel spreadsheet full of numbers being lectured at by someone who's bored like that's not a great way to learn probability and stats in contrast the less lessons at brilliant are visual and interactive and really let you play with the data to get a deeper understanding of what the lesson is trying to teach you to try out brilliant free for 30 days visit brilliant.org breaking taps or just click the link down below the first 200 folks that sign up will also get 20 off the annual premium subscription well I think that's all I got for you thanks for watching and I'll see you next time

Channel: Breaking Taps

Views: 1,583,034

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Length: 13min 12sec (792 seconds)

Published: Wed May 31 2023