By Isabelle Robinson, M.Sc.Feb 6 2019.jpg)
Image Credits: Dmitry Kalinovsky/shutterstock.com
The laser drilling process involves the creation of varyingly sized holes in a wide range of materials, most notably diamonds. However, there is a multitude of applications of such a process, including the creation of ‘thru-holes’ for air-cooling ventilation systems, or surface indentations on material surfaces for aesthetic, coating or bonding purposes.
Benefits of Laser Drilling
The method of laser drilling is simple to explain. Much like a traditional drill, the process creates small rounded indentations in a material, but it uses a fiber laser beam instead of the conventional rotating drill bit. While expensive, laser drilling offers the user complete control of its precision and accuracy by way of customization. The beam intensity, duration, and even heat can be adjusted for purpose and serviceability.
Another benefit of laser drilling is that it is a non-contact method of machining, meaning that the beam cannot be worn down and the original material, except for the drilled hole, remains untouched, ensuring the quality of the product or component in question.
The process can create varying size, depth and shape of holes due to its ease of control and adjustability levels. It is, also, able to carve a wide amount of materials including stainless steel, nickel, rubber, a variety of plastics, semiconductors, material composites, and, of course, diamonds.
At a micro scale, the process itself involves the required material to be removed via evaporation. It also includes melt expulsion and solid heating. It should be noted that melt expulsion is known to not occur if the lasers have a pulse length of approximately a nanosecond. This becomes important in laser drilling applications in which liquid ejection is wanted due to mass removal of materials. Thermal analysis and analytical modeling allow improvements to the laser drilling process, including the relationship between hole quality and drilling speeds.
Temperature Profile and Thermal Stress Propagation Model for Laser Drilled Holes
Analyzing the laser drilling process is notoriously difficult. This is mostly due to phase changes and fluid flow due to surface evaporation. Early analysis by Kroner in 1996 found that the ‘proportion of material removed by melt expulsion increases as the intensity increases’. Though more modern theories suggest that the increase is related to a pressure gradient being created within the hole itself due to material evaporation.
In 1972, Un-Chul Paek et al released a paper that described a temperature profile and thermal stress propagation model for laser drilled holes. The model was based on holes drilled in a high-purity fired alumina ceramic substrate material. The model used a continuously moving heat source to collect data on the temperature profile of the holes and the tangential stress distribution was calculated. This was done in order to identify factors which could potentially fracture the material itself, with the ultimate goal of establishing the laser-drilling parameters.
The data from these experiments have been continuously built upon in order to create a collection of parameters for laser drilling different materials precisely and with intention. Research into laser drilling is ongoing in order to establish more efficient techniques with a wide variety of materials.
Sources and Further Reading
- SPI Lasers. (2019). How Laser Drilling Works. Retrieved from SPIlasers.com: https://www.spilasers.com/application-drilling/how-laser-drilling-works/
- Un-Chul Paek, F. G. (1972). Thermal Analysis of Laser Drilling Processes. IEEE Journal of Quantum Electronics Vol 8 Issue 2.
- Yilbas, B. S. (2013). Thermal Analysis of Laser Drilling Process. Laser Drilling, 5-50.
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