Because deep hole drilling is carried out under closed or semi-closed conditions, it is not possible to directly observe the drilling condition of CNC inserts. Therefore, the effective and reasonable design of CNC tools is very important for the normal operation of drilling. Usually, the design principle of deep hole drill should have the following three standards:
1. Standard for specification and model of cutter teeth
The key of the cutter teeth specifications and models is to adopt the condition of the drilling load borne by each cutter teeth in the whole process of drilling. The drilling load is related to the total width of the cutter teeth. The total width of the cutter teeth should be distributed according to the drilling condition of each cutter teeth and the diameter of the bit. Three criteria should be considered for the distribution of the total width of the cutter teeth:
A. Guarantee the eccentricity e= (0.1-0.2) d0 of the drill point. The e value is related to the material being processed and the diameter of the drill bit. Its size determines the size and direction of the radial resultant force of the drill bit. Reasonable eccentricity makes the appropriate radial force press to the machined hole wall, which plays the role of stabilizing drilling, strengthening guidance and improving the surface quality of the hole. At the same time, the zero cutting of drill point is avoided, and the bad cutting conditions at the core are improved.
B, A + C + e + F > d0 / 2 + (1 ~ 2) mm, that is, there must be a certain amount of overlap between the cutter teeth;
C, A + C-e-F > (1-3) mm, which can make the cutting radial force always press the guide block, the guide block pushes forward close to the wall of the machined hole, making full use of the guiding role of the guide block to ensure the drilling straightness.
2. Standard for Raw Materials of Cutter Tooth
Raw materials of cutter teeth should be selected according to the load on each tooth and drilling conditions. The center teeth are subjected to large axial force, severe extrusion friction and poor drilling standards. Therefore, the YG or YW cemented carbide cutters with high flexural strength and impact resistance should be considered, while the YT type aluminium alloy with fast cutting speed, good application hardness and high wear resistance should be adopted for the outer and intermediate teeth, and the guide block should be durable. YT raw materials with high grinding performance. For the processing of alloy steel, all the cutter teeth materials should choose this kind of comprehensive raw materials, and YT798 should be selected at this stage.
3. Standard for Angle of NC Blade
The angle of CNC tool for deep hole machining depends on the raw material. Reasonable NC blade angle is very helpful to ensure the stability of the whole process of drill pin, chip breaking and improve tool durability. The front and rear angles of NC blades are the most critical angles. Usually the front angles of each drilling edge are 0=00, the hard-to-process raw materials are 0=1~30, the materials with good technological properties are 0=3~60, the brittle and cold-hard materials can be negative; the rear angles of the outer edge are usually 8~120, and the inner edge should be larger, taking alpha 0=12~150.