Analysis of typical precision machined parts: General Shaft

I. Structural characteristics of general shaft

Shaft parts are rotating parts whose length is greater than their diameter. They are usually composed of external cylindrical surfaces, conical surfaces, threads, splines, keyways, transverse holes, grooves and other surfaces. General shaft parts are divided into four categories according to their structural characteristics: smooth shafts, stepped shafts, hollow shafts and special-shaped shafts (including crankshafts, half shafts, camshafts, eccentric shafts, cross shafts and spline shafts, etc.).

II. Dimensional tolerances of general shaft

The main surfaces of shaft parts are often divided into two categories: one is the outer journal that matches the inner ring of the bearing, that is, the support journal, which is used to determine the position of the shaft and support the shaft. The dimensional tolerance level is higher, usually It is IT5~IT7; the other type is the journal that cooperates with various transmission parts, that is, the matching journal, and its tolerance
The level is slightly lower, usually IT6~IT9.

III. Surface roughness of general shaft

The machined surface of the shaft has surface roughness requirements, which are generally determined based on the performance and economy of processing. The surface roughness of the supporting journal is usually Ra0.2~1.6um, and the matching journal of the transmission part is Ra0.4~3.2um.

IV. Analysis of processing technology of general shaft parts

For parts with higher precision requirements, roughing and finishing should be separated to ensure the quality of the parts. The processing of shaft parts can generally be divided into three stages: rough turning (rough turning of the outer circle, drilling of center holes, etc.), semi-finish turning (semi-finish turning of various outer circles, steps, and grinding of center holes and minor surfaces, etc.) , rough and fine grinding (rough and fine grinding of all outer circles). Each stage is roughly divided into heat treatment processes.

VI. Materials and blanks of general shaft

(1) Generally, 45 steel is commonly used as the material for shaft parts. For shafts with higher precision, 40Cr, GCr1565Mn, or ductile iron can be used; for high-speed, heavy-load shafts, 20CMnTi, 20Mn2B, 20C and other carburizing steels or 38CrMoAl can be used. Nitrided steel.
(2) For general shaft parts, round bars and forgings are commonly used as blanks; for large shafts or shafts with complex structures, parts are used. After the blank is heated and forged, the internal fiber structure of the metal can be evenly distributed along the surface to obtain higher tensile strength, bending strength and torsion strength.

VII. Heat treatment of general shaft

1) Before processing, forging blanks must be normalized or annealed to refine the internal grains of the steel, eliminate forging stress, reduce material hardness, and improve processability.
2) Quenching and tempering is generally arranged after rough turning and before semi-finishing turning to obtain good comprehensive mechanical properties. 3) Surface quenching is generally arranged before finishing, so that local deformation caused by quenching can be corrected. 4) Shafts with precision requirements, After partial quenching or rough grinding, low temperature aging treatment is required.