what’s the characteristics of the cobalt twist drill and how to regrind?
Cobalt twist drill, which is one of the HSS twist drills, due to high enough amount of cobalt in the material, also called as a cobalt twist drill, mainly for the processing of stainless steel and other hard processing material, at present the most widely is M35 high-speed steel raw materials in the market. The cobalt drill is mainly used in automatic lathe, with high wear-resisting, not easy to break, and better chip removal and so on. In the production, often bigger the point Angle, and spiral Angle, making it more suitable for stainless steel processing. So during use, what’s the characteristics of the cobalt twist drill and how to regrind?
The larger of the diameter of the twist drill bit is, the more serious its disadvantages are exposed, mainly including:
- The rake angle changes greatly, especially when near the center, it has become -30 degrees, which increases the cutting resistance and leads to poor cutting conditions.
- The chisel edge is too long with a large negative rake angle. In the cutting process, which is essentially extrusion and scraping, it will consume a large amount of machine tool power, generate a large amount of heat, increase the axial force and cause poor centering.
- There is no back corner on the edge and friction occurs with the hole wall, while the cutting speed is high, generating more heat and wearing fast.
- The cutting edge is long, the chips are wide and the cutting speed at each point is different, which is easy to form a coil with very wide curl, and it is unfavorable to chip removal and hinders the entry of coolant fluid. When drilling deeper holes, chip removal is more difficult.
Considering the above shortcomings of twist drills, they can be reground according to the different workpiece and cutting conditions. The main methods are as following:
- Regrind the chisel edge (decrease the length of the edge and increase the front angle)
- Regrind the rake faces (reduce the difference of rake angles at each point of the main cutting edge and enhance the strength of the main cutting edge, especially when reaming, the rake angle at the outer edge must be trimmed)
- Regrind the edges (when using drill bits with larger diameters or drilling holes with softer materials and higher drilling precision requirements)
- Double sharpening (double point angle is adopted, and the second point angle is 70-75 degrees to reduce bit wear and reduce the surface roughness of holes)
- Chip-dividing grooves (when the diameter of the drill bit is large, chip-dividing grooves should be opened on the rake face and back face. When sharpening, attention should be paid to stagger the positions of the left and right chip-dividing grooves)