The machining of mechanical parts consists of several surfaces, and in order to study the relative relationship between the machined surfaces of the parts, a datum must be determined; the datum is the point, line and surface on the part that determines the position of other points, lines and surfaces. According to the different functions of the benchmark, the benchmark can be divided into two categories: design benchmark and process benchmark.
Types of parts machining.
Design benchmark: the benchmark used to determine the location of other points, lines and surfaces on the part drawing is called the design benchmark.
Process benchmark: the benchmark used in the process of parts processing and assembly is called the process benchmark. Process benchmark according to the different uses are divided into assembly benchmark, measurement benchmark and positioning benchmark.
(1) assembly benchmark: assembly used to determine the position of the part in the component or product benchmark is called the assembly benchmark.
(2) measurement benchmark: used to check the size and position of the processing surface benchmark called the measurement benchmark.
(3) positioning datum: the datum used to position the workpiece during processing, called the positioning datum. As a positioning reference surface (or line, point), in the first process can only choose the unprocessed rough surface, this positioning surface is called the rough benchmark. In each subsequent process can be used in the machined surface as a positioning reference, the positioning surface is called the fine reference.
The development of process procedures.
1, the reference first: that is, the first processing reference surface. In the process of parts processing, should be processed first appearance as a positioning reference, in order to provide accurate benchmarks for the subsequent processes as soon as possible.
2, divided into processing stages: the processing quality requirements of the surface into processing stages, generally can be divided into roughing, semi-finishing and finishing three stages. Mainly to ensure the quality of processing; conducive to the scientific application of equipment; easy to arrange the heat treatment process; and easy to find defects in the blank.
3, first face after the hole: for the box, bracket, connecting rod and other parts, should be processed first plane after processing holes. This can position the machined hole in the plane, to ensure the accuracy of the plane and hole position, and to bring convenience to the processing of the hole on the plane.
4, finishing process: the main appearance of the finishing process, such as grinding, honing, fine grinding, rolling processing, etc., should be placed at the end of the process route stage. The general principles of the development of precision parts processing process route.
