The minimum aperture that can be achieved for micro-hole drilling is determined by the diameter of the drill that can be manufactured. According to several companies, the diameter of micro drills can now reach 10 to 20 μm.
When drilling a small diameter hole, the setting of the cutting parameters differs depending on the material of the drill. Carbide and coated carbide drills have high modulus of elasticity (Young's modulus) due to the matrix material. When the high-speed rotation is caused by centrifugal force, the front end of the drill blade has little vibration, so the standard cutting speed of the tool material can be used. High number of revolutions for drilling. The sintered diamond drill bit can be drilled to the highest cutting conditions. Because of its excellent adhesion resistance, it can achieve high precision and long life machining.
There are also many cases of drilling hundreds or even thousands of tiny holes in a product. In this case, factors such as aperture expansion, bending, and pitch accuracy requirements need to be considered. The guide hole or the center hole shown in Fig. 4 can be used to prevent the front end of the drill from vibrating. The correct amount of reverse feed ensures that the chips are discharged and the drilling failure is effectively prevented.
On the other hand, the machining center suitable for micro hole machining has the characteristics of low vibration at high speed and high precision and stable positioning, and has good dynamic characteristics.
In recent years, it has been necessary to use micro-drilled workpiece materials ranging from high-hardness steels, stainless steels, copper alloys, and titanium alloys to ceramics. The range of conditions involved is very wide, and the optimum cutting conditions are also changed.
Coolant is required for bit cutting. For example, when drilling stainless steel, it is necessary to supply a cutting fluid with high lubricating performance to the cutting edge; and materials such as ceramics produce powdery chips, and only water-soluble cutting fluid can be used to effectively discharge the chips. Therefore, the corresponding cutting fluid should be selected for different materials to be processed.
In order to drill the micro-diameter drill at the optimum cutting speed, the machining center spindle should have a high-speed rotation function, and the maximum spindle rotation speed of the high-speed machining center is about 30,000 to 50,000 rpm.
Controlling the shape of the micro-drill and the oscillating motion of the shank are effective for improving the hole machining accuracy and prolonging the tool life. Therefore, high-precision drill grinding is indispensable, that is, it must have a feed mechanism capable of achieving a feed rate of 1 μm. High-precision tool grinding machine for high-swing precision grinding wheel spindles, as well as high-level tool grinding technology and high-precision inspection systems.
　　 Drilling tool system for high speed, high precision drilling
The wider use of the drill chuck tool system is a collet chuck system with high rigidity and high runout accuracy compared to a three-jaw chuck called a drill chuck.
The plug-in collet chuck system has excellent performances such as wide range of grippable drills, good clamping rigidity and high clamping precision. In recent years, in order to improve the clamping speed and accuracy, the hot-fit type clamping system has received increasing attention, and it is very suitable for holding a micro-diameter drill bit with a rotational speed of tens of thousands of revolutions.
High-speed, high-precision finishing and tapping of holes
The finishing tool that uses the most holes is still a reamer, a file, etc., but it is also possible to use an end mill for precision milling in a spiral or circular path. Boring tools with adjustable cutting edge size can be made from coated carbide and CBN to improve cutting speed and tool life.
For threaded hole machining, high-speed, high-precision thread cutting is achieved thanks to the use of thread end mills and helical interpolation machining. End mills for M3 small and small diameter threading have been available, and research on smaller diameter tapped hole machining technology is also underway.
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