In understanding the premise of precision shaft machining process, we should first have a deeper understanding and knowledge of its function, structural characteristics and technical requirements, and then analyze the process for different blank materials, then I will introduce the process of precision shaft machining of precision hardware machining to you!
First, the function, structural characteristics and technical requirements of precision hardware shaft parts
Precision hardware shaft is one of the typical parts frequently encountered in the machine. It is mainly used to support the transmission parts, transfer torque and bear the load. Shaft parts are rotating body parts, its length is greater than the diameter, generally by the concentric axis of the outer cylindrical surface, tapered surface, bore and thread and the corresponding end face composed of. According to the different structural shapes, shaft parts can be divided into light shaft, stepped shaft, hollow shaft and crankshaft, etc..
The shaft with length-diameter ratio less than 5 is called short shaft, more than 20 is called slender shaft, and most of the shafts are in between.
Precision hardware shafts are supported by bearings, and the shaft section that fits with the bearings is called journal. Journals are the assembly benchmark of the shaft, their accuracy and surface quality are generally required to be high, and their technical requirements are generally formulated according to the main function and working conditions of the shaft, which usually have the following items.
(A) Dimensional accuracy
In order to determine the position of the shaft, the journals that play a supporting role usually require high dimensional accuracy (IT5~IT7). The dimensional accuracy of the journals of assembled transmission parts is generally required to be lower (IT6~IT9).
(II) Geometric shape accuracy
The geometric shape accuracy of precision hardware shaft mainly refers to the roundness and cylindricity of journal, outer taper surface, Morse taper hole, etc. The tolerance should be generally limited to the dimensional tolerance range. For the inner and outer circular surfaces with high accuracy requirements, the allowable deviation should be marked on the drawing.
(C) Mutual position accuracy
The position accuracy requirement of precision hardware shaft is mainly determined by the position and function of the shaft in the machinery. Usually, the coaxiality requirement of the journal of the assembled transmission parts to the supporting journal should be ensured, otherwise it will affect the transmission accuracy of the transmission parts (gears, etc.) and generate noise. Ordinary accuracy of the shaft, the radial runout of the mating shaft section to the support journal is generally 0.01~0.03mm, and the high precision shaft (such as spindle) is usually 0.001~0.005mm.
(D) Surface roughness
The surface roughness of the shaft diameter that generally fits with the transmission parts is Ra2.5~0.63μm, and the surface roughness of the support shaft diameter that fits with the bearing is Ra0.63~0.16μm.
Second, the precision hardware shaft blanks and materials
(A) Precision hardware shaft blanks
Precision hardware shaft can be used in the form of bar, forging and other blanks according to the use requirements, production type, equipment conditions and structure. For shafts with a small difference in outer diameter, bar stock is generally used; for stepped shafts or important shafts with a large difference in outer diameter, forgings are often used to save materials and reduce the workload of machining, and also improve mechanical properties.
According to the different scale of production, there are two kinds of forging methods for blanks: free forging and die forging. Small and medium batch production more free forging, a large number of mass production using die forging.
(B) Material of precision hardware shaft
Precision hardware shaft should be used according to the different working conditions and use requirements of different materials and different heat treatment specifications (such as tempering, normalizing, quenching, etc.) to obtain a certain strength, toughness and wear resistance.
45 steel is a common material for shaft parts, it is cheap after tempering (or normalizing), can get better cutting properties, and can obtain higher strength and toughness and other comprehensive mechanical properties, quenched surface hardness up to 45 ~ 52HRC.
40Cr and other alloy structural steel is suitable for medium precision and high speed shaft parts, such steel after quenching and tempering, has a good overall mechanical properties.
Bearing steel GCr15 and spring steel 65Mn, after tempering and surface high-frequency quenching, the surface hardness can reach 50 ~ 58HRC, and has a high fatigue resistance and good wear resistance, can be manufactured with high precision shaft.
Precision machine tool spindle (such as grinding wheel shaft, coordinate boring machine spindle) can choose 38CrMoAIA nitride steel. This steel after tempering and surface nitriding, not only can obtain a very high surface hardness, and can maintain a softer core, so good impact resistance toughness. Compared with carburizing and quenching steel, it has the characteristics of little heat treatment deformation and higher hardness.