Today Zhejiang Weigao Bolt Factorywill explain the basic knowledge of hole processing for you.
Compared with the outer surface processing, the hole processing conditions are much worse, and the hole processing is more difficult than the outer circle processing. This is because:
1) The size of the tool used for hole processing is limited by the size of the hole to be processed, and the rigidity is poor, which is prone to bending deformation and vibration;
2) When machining holes with fixed-size tools, the size of the hole is often directly dependent on the corresponding size of the tool, and the manufacturing error and wear of the tool will directly affect the machining accuracy of the hole;
3) When machining holes, the cutting area is inside the workpiece, so the chip removal and heat dissipation conditions are poor, and the machining accuracy and surface quality are not easy to control.
- Drilling and reaming
Drilling is the first process for machining holes in solid materials, and the diameter of the hole is generally less than 80mm. There are two ways to drill holes: one is drill rotation; the other is workpiece rotation. The errors caused by the above two drilling methods are not the same. In the drilling method with the drill bit rotating, when the drill bit is deflected due to the asymmetry of the cutting edge and insufficient rigidity of the drill bit, the center line of the processed hole will be deviated or It is not straight, but the hole diameter is basically the same; while in the drilling method where the workpiece rotates, the opposite is true. The deviation of the drill bit will cause the hole diameter to change, and the hole center line is still straight.
Commonly used drilling tools include twist drills, center drills, deep hole drills, etc. The most commonly used one is twist drills with a diameter of 0.1-80mm.
Due to structural constraints, the bending rigidity and torsional rigidity of the drill bit are low, and the centering is not good, the drilling accuracy is low, generally only IT13 ~ IT11; the surface roughness is also large, Ra is generally 50 ~12.5m; but the metal removal rate of drilling is large, and the cutting efficiency is high. Drilling is mainly used to process holes with low quality requirements, such as bolt holes, threaded bottom holes, and oil holes. For holes that require high machining accuracy and surface quality, they should be achieved by reaming, reaming, boring or grinding in the subsequent processing.
Reaming is to use a reaming drill to further process a hole that has been drilled, cast or forged to enlarge the aperture and improve the processing quality of the hole. The reaming process can be used as pre-processing before finishing the hole or as Final machining of less demanding holes. Reamers are similar to twist drills, but with more teeth and no chisel.
Compared with drilling, reaming has the following characteristics: (1) The reaming drill has a large number of teeth (3-8 teeth), good guidance, and the cutting is relatively stable; (2) The reaming drill has no chisel edge and good cutting conditions; (3) The machining allowance is small, the chip pocket can be made shallower, the drill core can be made thicker, and the strength and rigidity of the cutter body are better. The reaming accuracy is generally IT11~IT10, and the surface roughness Ra is 12.5~6.3m. Reaming is often used to machine holes with a diameter less than . When drilling a hole with a larger diameter (D 30mm), a small drill bit (diameter 0.5~0.7 times of the hole diameter) is often used to pre-drill the hole, and then use the corresponding size reaming drill to ream the hole, which can improve the hole Processing quality and production efficiency.
China Nut's reaming can not only process cylindrical holes, but also use various special-shaped reaming drills (also known as countersink drills) to process various countersunk seat holes and countersinking end faces. The front end of the countersink often has a guide post, which is guided by a machined hole.