The method of selecting the drill bit of numerical control drilling machine

Straight shank fried dough twist drills are mostly used in single head drilling machines to drill simple printed boards or single panels. Nowadays, they are rarely seen in large circuit board manufacturers, and their drilling depth can reach 10 times the drill diameter. When the substrate stack is not high, the drill sleeve can be used to avoid drilling deviation. At present, most manufacturers use CNC drilling machines. CNC drilling machines use cemented carbide fixed shank drill bits, which are characterized by automatic replacement of drill bits. High positioning accuracy, no need to use drill sleeve. Large helix angle, fast chip removal, suitable for high-speed cutting. Within the full length of the chip removal groove, the drill bit diameter is an inverted cone, the friction between the drill bit and the hole wall is small, and the drilling quality is high. Common drill handle diameters are 3.00mm and 3.175mm.

2. Pay attention to the material of drill bit

The drill bits for PCB drilling are generally made of cemented carbide, because the epoxy glass cloth clad copper foil wears the cutting tools very fast. Cemented carbide is made of tungsten carbide powder as matrix and cobalt powder as binder by pressing and sintering. It usually contains 94% tungsten carbide and 6% cobalt. Because of its high hardness, wear resistance and strength, it is suitable for high-speed cutting. However, the toughness is poor and very brittle. In order to improve the performance of cemented carbide, some use chemical vapor deposition of a layer of 5 ~ 7 μ m hard titanium carbide (TIC) or titanium nitride (TIN) on the carbonized matrix to make it have higher hardness. Some use ion implantation technology to inject titanium, nitrogen and carbon into the substrate to a certain depth, which not only improves the hardness and strength, but also these implanted components can migrate inward when the bit is reground. Others use physical methods to generate a layer of diamond film on the top of the bit, which greatly improves the hardness and wear resistance of the bit. The hardness and strength of cemented carbide are related not only to the ratio of tungsten carbide and cobalt, but also to the particles of powder. The average grain size of tungsten carbide phase in ultra-fine cemented carbide bits is less than 1 micron. This kind of drill has not only high hardness, but also improved compressive and flexural strength. In order to save cost, many drill bits now adopt welded shank structure. The original drill bit is made of cemented carbide as a whole. Now the drill shank at the rear is made of stainless steel, which greatly reduces the cost. However, due to the use of different materials, its dynamic concentricity is less than that of the overall cemented carbide drill bit, especially in terms of small diameter.

3. Choose a good brand to ensure product quality

At present, there are many manufacturers of drill bits, including domestic and imported ones. There is a slight gap between domestic products and foreign products. Of course, the import price is also a little more expensive. There are also bits produced in Taiwan and Hong Kong, and some bits produced in Taiwan with American and European brands. In contrast, the quality of bits imported from Europe, America and Japan is stable. Although the price is slightly expensive, it is worth the money for technicians. In the actual use process, the probability of problems due to bit quality is very small, For example, if the product requirements are high, it is recommended to use imported drill bits. The hardness of European and American drill bits is high while that of Japan is relatively soft. European and American drill bits are rather inflexible. It is not easy to deviate but the probability of breaking is higher. The flexibility of Japanese drill bits is good, but it is easy to deviate, especially small drill bits. In the process of actual use, it can be selected according to needs.