The manufacturing process benchmark of precision mechanical parts refers to the benchmark used in the process of parts. According to different purposes, the process reference can be divided into process flow reference, precise positioning reference, precise measurement reference and installation reference.
1. Process Flow Benchmark:
In the process diagram, it is used to define the benchmark used for the size, appearance and position of the surface to be processed in this step, which is called the process flow benchmark.
2. Precise Positioning Reference:
During processing, it is used to define the reference used for the appropriate part of the product workpiece on the CNC lathe or in the fixture, which is called the precise positioning reference.
3. Precise Measurement Datum:
The datum used to accurately measure the appearance, position and size error of the product workpiece during or after processing is called precise measurement datum.
4. Installation Datum:
The datum used to define the relative position of parts or components on the commodity during assembly, which is called installation datum. For example, the inner hole of the gear shaft is the installation datum of the transmission gear. In general, the design scheme reference shall be given on the part sample drawing, and the process reference shall be selected and determined by the process staff according to the whole process of the specific process.
When Analyzing Benchmark Issues, Pay Attention To The Following Two Points:
1) As a datum, a point, line or surface may not actually exist on the product workpiece (such as hole axis, axis line, etc.), but is embodied by some specific surfaces, which are called datum surfaces. For example, the axis of the inner hole is reflected by the inner hole surface, the inner hole axis is the datum, and the inner hole surface is the datum. Therefore, the problem of selecting a datum is to select an appropriate datum. In particular, sometimes, if you want to describe it conveniently, you can call datum and base plane datum.
2) As a datum, it can be a point or line with theout area or a very small surface, but it means that base plane of the this kind of the datum always has a certain area. For example, assemble a short shaft beside the lathe, the datum is the axis line, and it has no total area; The base surface is a sphere, and its total area is not large, but it does have a certain total area