The types of drill bits that can be used for CNC drilling and milling machines include twist drills, U drills, violent drills, and core drills.
Twist drills are mostly used in single-head drill presses to drill simpler single panels. Now they are rarely seen in large circuit board manufacturers, and their drilling depth can reach 10 times the diameter of the drill.
When the substrate stack is not high, the use of drill sleeves can avoid drilling deviation. The CNC drilling machine uses a cemented carbide fixed shank drill, which is characterized by the ability to automatically replace the drill. High positioning accuracy, no need to use drill sleeves. Large helix angle, fast chip removal speed, suitable for high-speed cutting. Within the full length of the chip flute, the diameter of the drill is an inverted cone, and the friction with the hole wall during drilling is small, and the drilling quality is high. Common drill shank diameters are 3.00mm and 3.175mm.
The drill bit for tube sheet drilling generally uses cemented carbide, because the epoxy glass cloth coated copper foil plate wears the tool very quickly. The so-called cemented carbide is made of tungsten carbide powder as a matrix and cobalt powder as a binder through pressure and sintering. It usually contains 94% tungsten carbide and 6% cobalt. Because of its high hardness, it is very wear-resistant, has a certain strength, and is suitable for high-speed cutting.
Poor toughness and very brittle. In order to improve the performance of cemented carbide, some use a layer of 5-7 microns of extra-hard titanium carbide (TIC) or titanium nitride (TIN) on the carbide substrate by chemical vapor deposition to make it have Higher hardness. Some use ion implantation technology to implant titanium, nitrogen, and carbon into the matrix to a certain depth, which not only improves the hardness and strength, but also these implanted components can migrate inward when the drill bit is reground. Some use physical methods to form a layer of diamond film on the top of the drill bit, which greatly improves the hardness and wear resistance of the drill bit. The hardness and strength of cemented carbide are not only related to the ratio of tungsten carbide and cobalt, but also to the particles of the powder.
For ultra-fine particles of cemented carbide drill bits, the average size of the tungsten carbide phase grains is below 1 micron. This kind of drill has not only high hardness but also improved compressive and flexural strength. In order to save costs, many drill bits now use welded shank structure. The original drill bit is made of hard alloy as a whole. Now the rear drill shank is made of stainless steel, which greatly reduces the cost. However, due to the use of different materials, the dynamic concentricity is not as good as the overall hard. Alloy drill bits, especially for small diameters.
Post time: Dec-13-2021