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General shaft parts processing technology analysis and positioning datum selection
1. Analysis of processing technology of general shaft parts For Precision parts, which require high accuracy, the rough and finish machining should be separated to ensure the quality of the parts. The processing of shaft parts can generally be divided into three stages: rough turning (outer circle of rough turning, drilling center hole, etc.), semi-finishing turning (outer circle, steps, and center hole of grinding center and time required for semi-finishing turning, etc.), Coarse and fine grinding (coarse and fine grinding of the outer circle). The division of each stage is roughly bounded by heat treatment. 2. Selection of positioning criteria for general shaft parts For the positioning base surface of general shaft parts, the two most commonly used are two central holes. Because the coaxiality of the outer surface and the thread surface of the shaft components and the perpendicularity of the end face to the axis are the main items of mutual position accuracy, and the design basis of these surfaces is generally the centerline of the shaft, and two central holes are used. Positioning can conform to the principle of benchmark coincidence; and because most processes use the central hole as the positioning base, multiple outer circles and end faces can be processed to the maximum extent, which also conforms to the principle of benchmark uniformity. However, in the following cases, the two central holes cannot be used as an outside standard: 1) When roughing the outer circle, in order to improve the rigidity of the workpiece, the outer surface of the shaft is used as the positioning base, or the outer circle and the center hole are used as the positioning base, that is, one clamp and one top. 2) When the shaft is a through-hole part, the center hole as the positioning base surface disappears due to the drilling of the through hole during processing. In order to use the center hole as the positioning base surface after the through-hole processing, the process uses three Ways: When the diameter of the central through hole is small, the central hole can be directly replaced by the orifice with a width not greater than 2mm and a 60 inner conical surface. When the shaft has a cylindrical hole, a tapered plug can be used with a taper of 1:500. When the taper of the shaft hole is small, the taper taper is the same as the taper of the positioning holes at both ends of the workpiece. If the shaft hole is a taper hole, when the taper of the shaft through hole is large, a mandrel with a tapered plug may be used, referred to as a tapered plug mandrel. When using a tapered plug or a tapered plug mandrel, it should be noted that it is generally not possible to replace or disassemble midway, until the finishing of the machining surface is finished, and it can not be disassembled when the center hole is not used.
