1. Deep hole machining is in the closed or semi closed state, so the cutting condition of the tool can not be observed directly.
2. Cutting heat is not easy to spread. In general, 80% of the cutting heat is taken away by chips in the cutting process, while only 40% in deep hole drilling. The cutting tool accounts for a large proportion of the cutting heat. It is easy to diffuse late and overheat, and the cutting edge temperature can reach 600 degrees. Therefore, forced and effective cooling method must be adopted.
3. Chips are not easy to discharge. Because of the depth of the hole and the long path of the chip, it is easy to block, which causes the bit to break. Therefore, the length and shape of chips should be controlled, and compulsory chip removal should be carried out.
4. The rigidity of the process system is poor. Due to the limitation of the hole size, the length diameter ratio of the hole is large, the drill pipe is thin and long, the rigidity is poor, it is easy to produce vibration, and the drilling hole is easy to deviate, so it is very important to support and guide.
In order to correctly guide the bit into the drill, the method of machining the guide hole on the workpiece or using the guide sleeve is usually adopted, the former is used for single piece processing, and the latter is used for batch production. The drilling error of deep hole is caused by the gap between the bit and guide sleeve (guide hole), and increases with the increase of axial force. The influence of the clearance between guide sleeve and bit on the drilling error. At the beginning of drilling, the radial force presses the bit guide block to the hole wall of the guide sleeve. Due to the gap between the two, the center of the bit deviates from the rotation center of the workpiece. At this time, the drilled hole diameter is smaller than the diameter of the bit. When the guide block begins to enter the machined hole, under the action of the hole wall with a slightly smaller diameter, the outer edge is squeezed outward, so that the center of the drill bit is shifted in the opposite direction to the rotation center of the workpiece, so that the hole diameter is expanded, and the friction between the guide block and the hole wall is squeezed, so that the drilling torque is increased rapidly.
