What are the standard processing procedures for precision mechanical parts?

(1) Process standards

The process reference refers to the reference adopted in the technological process of a part. According to their different uses, process references can be further classified into sequence reference, positioning reference, measurement reference and assembly reference.

1. Process reference
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In the process drawing, the reference used to determine the dimensions, shapes and positions of the machined surfaces after processing in this process is called the process reference.


2. Positioning reference

The reference used to determine the correct position of the workpiece on the machine tool or in the fixture during processing is called the positioning reference.

3. Measurement reference

The reference used to measure the shape, position and dimensional errors of a workpiece during or after processing is called a measuring reference.

4. Assembly reference

The reference used to determine the relative position of parts or components on the product during assembly is called the assembly reference. The inner hole of a gear serves as the assembly reference for that gear. Under normal circumstances, the design reference is given on the part drawing, while the process reference is selected and determined by the process personnel according to the specific process.

When analyzing the benchmark problem, pay attention to the following two points:

1) The points, lines and surfaces serving as references do not necessarily exist specifically on the workpiece (such as the centerline of a hole, the axis line, etc.), but are represented by certain specific surfaces, which are called base surfaces. For instance, the centerline of the inner hole is reflected through the surface of the inner hole. The centerline of the inner hole serves as the reference, while the surface of the inner hole acts as the base surface. Therefore, the issue of choosing a base is essentially the issue of choosing an appropriate base surface. In particular, sometimes for the sake of convenience in description, the reference and the basis surface can be collectively referred to as the reference.

2) As a reference, it can be a point or line without area or a very small surface, but the base surface representing such a reference always has a certain area. For instance, when installing a long shaft on a lathe, the reference is the axis centerline, which has no area. The base surface is a conical surface. It is very small in area but does have a certain area.
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