1. Mechanical Drilling Method
This is currently the most widely used method. It employs diamond core drills that rotate and penetrate ceramic materials until the desired depth is achieved. This method is particularly suitable for creating circular holes with diameters exceeding several millimeters.
As described by Suzuki Hiromu (1980), the material removal rate when drilling Si3N4 ceramics using diamond core drills can reach 1600 mm³/min. The advantages of this method include ease of operation and simplicity of equipment. However, due to the high hardness of ceramics, diamond drill bits wear out quickly during drilling. Additionally, the brittleness of ceramics often leads to edge chipping at the entrance and exit of holes, thereby affecting the quality of hole processing.
2. Ultrasonic Drilling Method
For ceramics with low tensile strength, ultrasonic machining is a suitable and effective method. Ultrasonic machining involves applying ultrasonic vibrations to the machining tool or the workpiece, where abrasive slurry particles continuously impact and grind the processed surface at high speeds and accelerations. Therefore, machining efficiency depends on factors such as ultrasonic power output, type of abrasives, and machining speed.
The advantage of this method is that it can create holes with special contours without the need for tool rotation. However, drawbacks include the complexity of tool replacement and subtle influences on machining quality due to variations in tool quality or the transmission of forces generated during machining.
In Japan, 20 kHz ultrasonic waves are commonly used for micro-hole machining in ceramics. Although effective, the process is slow due to the small size of abrasive particles. Subsequently, Japanese researchers have equipped diamond core drills with 40 kHz ultrasonic vibration on spindle shafts to enhance micro-hole machining quality, circumventing the limitations of 20 kHz ultrasonic machining. The spindle rotates at a speed of v = 30,000 r/min with a feed rate of a = 0.55 mm/r.
In 1996, Tianjin University developed a ceramic micro-hole ultrasonic grinding machine equipped with a piezoelectric ceramic transducer, conducting systematic studies on various advanced ceramic micro-hole machining. Compared to conventional ultrasonic machining, efficiency can be improved by 5 to 10 times. Another ultrasonic machining method combines diamond core drilling with ultrasonic vibration for deep hole machining, significantly enhancing inner surface quality and hole roundness.
3. Laser Drilling Method
Laser drilling is an effective method for machining small holes in superhard materials like ceramics. Typically using pulsed laser systems, laser beams are focused on ceramic workpieces through optical systems, utilizing high energy density (106~109 W/cm²) laser pulses to melt, vaporize, and remove material, thus achieving micro-hole machining.
Laser drilling offers advantages such as non-contact operation, simplicity, high speed, high efficiency, and easy mechanization and precision control via computer. By optimizing laser processing parameters, high-quality micro-holes can be achieved. Currently, CO2 lasers can precisely drill holes in Al2O3 ceramics, significantly reducing machining costs. Holes drilled using TLF750 CO2 lasers from UK-based Frumpt company have diameters of (0.762±0.013) mm with positional tolerances <0.0635 mm.
In Japan, Yasuo Anno and colleagues used Nd-YAG solid-state lasers to drill holes in ruby and Al2O3 ceramics, achieving hole diameters of 0.05-0.2 mm and a thickness of 0.33 mm with 2050 pulses, demonstrating very high machining efficiency (25 seconds per process).
Using a pulsed Nd-YAG laser machining system, Zhang Yinjiang et al. (2001) drilled holes in 0.65 mm thick Al2O3 ceramic substrates, achieving hole diameters <0.1 mm on 2 mm and 5 mm thick Al2O3 substrates with cone angles less than 1:20 and depth-to-diameter ratios >25:1. They also drilled micro-holes of 1015 μm on 0.6 mm thick substrates.
Research on laser drilling of silicon nitride ceramics indicates that undamaged holes with diameters of 0.5 mm can be drilled on 6.6 mm thick Si3N4 ceramic workpieces, achieving good circularity with depth-to-diameter ratios of approximately 12 and maximum depth-to-diameter ratios up to 18.5.
Additionally, Tianjin Laser Institute collaborated with Tianjin University on CNC machining platforms using YAG pulsed laser systems for systematic experiments on small hole machining in various ceramic materials. The research found that Si3N4 ceramics with good thermal conductivity exhibited excellent laser machining quality, whereas ZrO2 ceramics with low thermal conductivity required specific measures to prevent workpiece fractures due to concentrated thermal stress.
