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Metal powder metallurgy product hole processing technology

Categories: ZCMIM NewsStars: 3StarsVisit: -Release time: 2018-09-05 15:27:00
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Hole processing technology is one of machining technology which widely use in metal powder metallurgy field. the holes of metal powder metallurgical products are typically formed directly from the mold. If the accuracy of the hole cannot be achieved directly from the mold, it will be post-processed after the powder metallurgy process: drilling or reaming.

1. Drilling process

Drilling is the first process of machining holes on solid materials. And the diameter of the hole is generally less than 80 mm. There are two ways to drill holes: one is the rotation of the drill bit; the other is the rotation of the workpiece. In the drilling method of bit rotation, when the bit is deflected due to asymmetric cutting edge and insufficient rigidity of the bit, the center line of the processed hole will be deviated or not straight, but the hole diameter is basically unchanged; On the contrary, in the drilling mode of workpiece rotation, the deviation of the drill bit will cause the hole diameter changes, and the hole center line is still straight.

The commonly used drilling tools include: twist drill, center drill, deep hole drill, etc. Among them, the most commonly used is twist drill.

Due to the structural limitations, the bending stiffness and torsion stiffness of the drill bit are both low, and the poor centrality and the precision of drilling machining is low, generally only reaching IT13 ~ IT11; the surface roughness is also large, Ra is generally 50. ~12.5μm; but the metal cutting rate of the drill hole is large, and the cutting efficiency is high. Drilling is mainly used for processing holes with low quality requirements, such as bolt holes, thread bottom holes, oil holes, etc. For holes with high machining accuracy and surface quality requirements should be achieved by bearizing, reaming, boring or grinding in subsequent processing.

Compared to other processes, the metal powder metallurgy process directly forms holes from the mold, which on the one hand reduces the chipping process and on the other hand ensure the consistency of quality.

2. Reaming process

The reaming is to further drill the hole that has been drilled, cast or forged by the reaming drill to enlarge the hole diameter and improve the processing quality of the hole. The reaming process can be used as pre-machining before finishing the hole or as a final processing of holes that are not required. The reaming drill is similar to a twist drill, but with a large number of teeth and no chisel edge.

Compared with drilling, reaming has the following characteristics: (1) the number of reaming drills is large (3~8 teeth), the guiding is good, the cutting is stable; (2) the reaming drill has no chisel edge and the cutting conditions are good; (3) The machining allowance is small, the chip pocket can be made shallower, the core can be be made thicker, and the strength and rigidity of the cutter body are better. The precision of the reaming process is generally IT11~IT10, and the surface roughness Ra is 12.5~6.3. Reaming is often used to process holes with smaller diameters. When drilling a hole with a larger diameter (D ≥ 30mm), it is often pre-drill with a small bit (0.5 to 0.7 times the diameter of the hole),and then drill the hole with the corresponding size of reaming, so as to improve the machining quality and production efficiency of the hole.

In addition to being able to process cylindrical holes, a variety of special shaped counterboring (also known as counterboring) can be used to process various countersink bore and counterface faces. The front end of the facer often has a guide column, which is guided by the processed hole.

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