| Blog | https://engineerstephanie.blogspot.com/ |
Oh, hi everyone.
If you haven't noticed, I've been mostly avoiding social media. Too many negative things that I can't handle. I gotta take it a little bit at a time. Perhaps I can set up some filters sometime.
In the meantime, here's my cat.
Despite numerous experimental and theoretical studies reported in the literature, surface micro-texturing to control friction and wear in lubricated tribo-contacts is still in the trial-and-error phase. The tribological behaviour and advantageous micro-texture geometries and arrangements largely depend on the contact type and the operating conditions. Industrial scale implementation is hampered by the complexity of numerical approaches. This substantiates the urgent need to numerically design and optimize micro-textures for specific conditions. Since these aspects have not been covered by other review articles yet, we aim at summarizing the existing state-of-the art regarding optimization strategies for micro-textures applied in hydrodynamically and elastohydrodynamically lubricated contacts. Our analysis demonstrates the great potential of optimization strategies to further tailor micro-textures with the overall aim to reduce friction and wear, thus contributing toward an improved energy efficiency and sustainability.
If you're following along, here is a rather important paper looking at different densities, diameters, and depths of the dimple textured surfaces.
https://onlinelibrary.wiley.com/doi/10.1002/ls.168
Of note, the ratios all change depending on the hardness of the materials and the speed of movement.
Along the same line is this paper, which takes a more analytical approach through simulation.
https://journals.sagepub.com/doi/abs/10.1177/1350650114531939
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Eventually I'll post about other things than mechanical engineering, Metrology, and Tribology. But right now that just happens to be my interest. ADHD is a fickle thing.
But I find that reading research papers is fun. Even if I don't understand all the math, I can understand the concepts and their application. I only wish that I have enough money to apply them and run tests for myself. The world could do with more independent researchers - unbound by a corporate or institutional duty.
So lately I've been learning about making flat surfaces, and more importantly, making flat bearing surfaces for things like milling machines and lathes.
And about that, I found some articles that cover research of surfaces texturing to decrease surface friction.
If you know anything about old tool restoration, you've undoubtedly run into surface scraping as the ideal method to bring the ways to flatness and parallelism.
It's been thought as the pinnacle of a bearing surface... But it's not.🧵
One more paper comparing dimpled surfaces to scraped surfaces.
https://link.springer.com/article/10.1007/s00170-020-05350-6
And this article covers the laser etching process parameters.
https://www.mdpi.com/2075-4442/11/11/456
The economic and environmental cost of friction in machinery and transport is significantly remarkable, the machine tool being one of the most affected. In this sector, the movements are fully affected by the friction originated in the displacements between the guideways and the slides, which results in terms of precision, energy consumption and component deterioration. In this line, texturing has proved to be a useful tool to lessen friction. Nowadays, flaking is the technique in use for the texturing of machine tool guideways, a manual and costly process in which the final finish of the workpiece is not controllable. Other techniques like laser texturing constitute an effective and precise procedure which is at the same time expensive, requires fine tuning of process parameters and is not applicable in large workpieces. Therefore, the main challenge is to develop an industry-implemented technique capable of producing textures in a repetitive and economically viable way. In this work, a method that allows generating a wide range of controlled textures by grinding with wheels textured with an assisted dressing device is presented. With this technique it is possible to create textures in large workpieces, such as machine tool guideways and to do it in a repetitive way and in the same machine in which the guide has been ground previously, which involves a reduction in time and costs. The technique has been validated by means of tribological tests in which textures generated with this technique have obtained lower friction coefficients than flaking.
On dimple density, the 40% trends downwards, while the 30% trends upwards. Possibly the 35% would be perfect.
So we have our final parameters: 35% density, 100μm diameter, 36μm depth that will likely be reduced after grinding.
Who's ready to put their milling machine or lathe to the test? 🧵
This is important because it tells us about the process required.
First, grinding the surface to flatness and roughness below 1μm (ideally below 0.1).
Then laser etching.
Then a finishing process that would remove the mounds (maybe a very light grinding pass?)
Also note the graph trends, which are ignored in the paper. The deepest dimples have a very flat trend after initial wear in. The shallower ones trend upwards. We want the texturing to last decades, so flat is good. 🧵
This paper is full of data on the size and density.
It's interesting to note that deeper dimples reduce the friction, until 20μm, after which the friction increases. However there might be an explanation. The surfaces are unfinished after laser etching. The etching process leaves behind a donut mound around the dimple. You can see in the graphs the increased friction at the beginning of the test cycle, before levelling out. The deeper dimples would leave behind bigger mounds. 🧵
They even tell you the exact laser they use, which is a DPSS Q-CW Nd: YAG.
And they explain the process of what the dimples achieve: they create a rolling vortex, much like a ball bearing!
They claim the reduction in critical hydrodynamic velocity is 37%. And it also increases the lubricant film thickness.
But there are still a lot of variables to explore, like dimple size, depth, and coverage.
In comes https://iopscience.iop.org/article/10.1088/2053-1591/ab9ced
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