Bo Hyun Kim is a professor at the School of Mechanical Engineering, Soongsil University in South Korea. He is researching ultra-precision micromachining technology using digital microscopy and 3D laser confocal microscopy. We chatted with Bo Hyun to learn more about his research and the microscopes used to achieve meaningful results.
Q: What is ultra-precision micromachining technology?
Bo Hyun: Ultra-precision micromachining technology is a manufacturing technique that produces micrometer-sized features or parts with nanometer-level accuracy and roughness. The need for ultra-precision micromachining technology is rapidly increasing in information technology, electronic parts, and micro-mechanical parts and molds. The field of application is also expanding.
In response to these technological demands, the Precision Engineering and Manufacturing Laboratory (PREMA) is conducting research on ultra-precision processing technology, such as micro milling, drilling, and grinding, as well as electric discharge machining (EDM) and electrochemical machining (ECM).
The typical research fields include:
- Ultra-precision processing of high-hardness materials (ceramics, cemented carbide, sapphire glass, etc.)
- Micro-electric discharge machining (micro-EDM)
- Micro-tool fabrication technology
- Hybrid processing technology (a combination of processing technologies such as cutting, grinding, EDM, ECM, and laser processing)
Q: Can you share some results from your research in this field and the instruments that you used to achieve these results?
Bo Hyun: For my research, observing and measuring the surface machined by various methods is very important.
Various machining parameters can affect precision machining. Therefore, we must continuously check images and measure the machined surface to make sure that the machining has been performed properly at each stage.
Let's take the surface of Pyrex glass machined in ductile mode as an example.
The first image below (Figure 1, left) shows micro grooves machined on a Pyrex glass surface using micro polycrystalline diamond (PCD) tools. Since the glass material is very brittle, it is hard to machine micro features on the glass without cracks. For example, the vertical groove in the image was machined with a cutting depth of 1 µm. Even the cutting depth of 1 µm left many cracks on the glass surface. However, when the cutting depth was reduced to 0.25 µm in the horizontal groove, the glass was machined without cracks, which is called ductile mode cutting.
To increase the durability of the PCD tool or to eliminate the cause of cracks that occur frequently during machining, it is important to check the roughness and surface changes while changing the experimental conditions.
In this case, a digital microscope and laser confocal microscope are effective tools for observing and measuring the processed surface. Using the DSX1000 digital microscope and LEXT™ OLS5100 3D laser confocal microscope from Evident to observe and measure the surfaces, we could improve the quality of the machining to create a crack-free surface in ductile mode.
Here are the results from the microscopes:
Figure 1. Micro grooves machined on a Pyrex glass surface with PCD micro tools. Left: microscope image, right: surface profile. The images were taken and measured using the OLS5100 3D laser confocal microscope.
Figure 2. Micro grooves machined on a Pyrex glass surface. The close-up image shows that when the depth of cut is 0.25 µm, Pyrex glass can be machined without cracks, which is called ductile mode cutting. The image and measurements were taken using the OLS5100 3D laser confocal microscope.
| Feed rate (µm/s) | Depth of cut (µm) | Total depth (µm) | |
|---|---|---|---|
| Brittle mode | 100 | 1 | 10 |
| Ductile mode | 20 | 0.25 | 14 |
| Grinding Conditions | |
|---|---|
| Tool used | PCD |
| Grain size (µm) | 10 |
| Tool diameter (µm) | 150 |
| Working capacitance (pF) | 500 |
| Workpiece material | Pyrex |
| Rotating speed (rpm) | 60,000 |
| Feed rate (µm/s) | 20–100 |
| Depth of cut (µm) | 0.25–1 |
| Total depth (µm) | 14 |
- After producing a brittle surface under (1) condition, process in ductile mode by crossing under (2) condition
- Create a crack-free ductile mode surface while machining deeper than the brittle cracks (step difference: 4 µm)
| Feed rate (FR): µm/s | Depth of cut (DOC): µm | Total depth: µm | Average surface roughness (Ra): µm | Maximum height (Rz): µm | |
|---|---|---|---|---|---|
| 1. Brittle | 100 | 1 | 10 | 0.437 | 2.589 |
| 2. Ductile | 20 | 0.25 | 14 | 0.015 | 0.141 |
Figure 3. Surface roughness comparison of a glass surface machined in brittle and ductile modes. Equipment used: OLS5100 3D laser scanning microscope.
By using a 3D digital microscope and laser confocal microscope, the quality of machining can be dramatically improved if the roughness analysis data and machining accuracy are compared and reflected in the decision of the machining parameters. This is important as higher-quality machining will lead to better product quality.
Professor Bo Hyun Kim uses a DSX1000 digital microscope to check the roughness and surface changes on machined surfaces
Q: What are your research plans moving forward?
Bo Hyun: In the future, the Precision Engineering and Manufacturing Laboratory will continue to conduct meaningful academic and practical research on ultra-precision processing in various fields.
Further Reading on Ultra-Precision Micromachining Technology
To learn more about ultra-precision micromachining technology, check out these papers authored by Bo Hyun Kim.
- Applied Sciences | Free Full-Text | Experimental Study on Micro-Grinding of Ceramics for Micro-Structuring (mdpi.com)
- Micromachines | Free Full-Text | Microfluidic Chip Fabrication of Fused Silica Using Microgrinding (mdpi.com)
About the Interviewee
 | Professor Bo Hyun Kim is a professor in the School of Mechanical Engineering at Soongsil University, South Korea, and is an expert in the field of ultra-precision processing of hard materials. He contributes to academia through advanced research and published papers on ultra-precision micro-processing technologies, such as electric discharge machining, electrochemical machining, and laser machining, as well as mechanical machining, such as cutting, milling, and grinding. |
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