What are the benchmark processes of precision mechanical parts processing?

u200b What are the benchmark processes for processing precision mechanical parts? (1) Process benchmarks Process benchmarks refer to the benchmarks used in the process of parts. According to different purposes, the process reference can be sub-process reference, positioning reference, measurement reference and assembly reference. 1. Process reference In the process diagram, the reference used to determine the size, shape, and position of the processed surface of this process is called process reference.u200b 2. Positioning datum The datum used to determine the correct position of the workpiece on the machine tool or in the fixture during processing is called the positioning datum. 3. Measurement datum The datum used to measure the shape, position and dimensional error of the workpiece during or after processing is called the measurement datum. 4. Assembly datum The datum used to determine the relative position of the parts or components on the product during assembly is called the assembly datum. For example, the inner hole of the gear is the assembly reference of the gear. Under normal circumstances, the design basis is given on the part drawing, and the process reference is determined by the craftsperson according to the specific process. When analyzing the benchmark problem, pay attention to the following two points: 1) The point, line, and surface used as the benchmark do not necessarily exist on the workpiece (such as the center line of the hole, the axis line, etc.), but are reflected by some specific surfaces. These surfaces are called base surfaces. For example, the centerline of the inner hole is embodied by the surface of the inner hole, the centerline of the inner hole is the reference, and the surface of the inner hole is the base surface. Therefore, the question of choosing a benchmark is the question of choosing an appropriate base. In particular, sometimes for the convenience of description, the datum and the base surface can be collectively referred to as the datum. 2) As a datum, it can be points and lines with no area or a very small surface, but the base surface representing this datum always has a certain area. For example, if a long shaft is installed on a lathe, the reference is the axis line, which has no area; the base surface is a tapered surface, which has a small area but does have a certain area.