1. Benchmark
The mechanical parts of the Guangdong Machinery Processing Factory are composed of several surfaces. To study the relative relationship of the surface of the parts, a datum must be determined. The datum is the point, line, and surface on which the position of other points, lines, and surfaces are determined on the part. . According to the different functions of benchmarks, benchmarks can be divided into design benchmarks and process benchmarks.
1. Design basis
The reference used by Guangdong Machinery Processing Factory to determine the position of other points, lines and surfaces on the part drawing is called the design reference. As shown in Figure 32-2 [cc2], the design reference of each outer circle and inner hole is the axis line of the part, end face A is the design reference of end faces B and C, and the axis of the inner hole is the outer diameter Benchmark to jump.
2. Process benchmark
The datum used in the processing and assembly of the part is called the process datum. Process benchmarks are divided into assembly benchmarks, measurement benchmarks and positioning benchmarks according to different uses.
(1) Assembly datum The datum used to determine the position of the part in the component or product during assembly is called the assembly datum.
(2) Measurement datum The datum used to check the size and position of the machined surface is called the measurement datum. As for the part in Figure 32-2, the axis of the inner hole is the measurement datum for testing the radial runout of the outer circle; the surface A is the measurement datum for testing the length L and the size l.
(3) Positioning datum The datum used for positioning the workpiece during processing is called the positioning datum. The surface (or line, point) used as the positioning reference, in the first process, only the unprocessed blank surface can be selected. This positioning surface is called the rough reference. In the subsequent processes, the machined surface can be used as the positioning reference , This kind of positioning surface is called fine datum.
Five, the general principles of drafting the process route
The formulation of mechanical processing procedures in Guangdong mechanical processing plants can be roughly divided into two steps. The first is to draw up the process route of the parts processing, and then determine the process size of each process, the equipment and process equipment used, the cutting specifications, and the working hours quota. These two steps are interrelated and should be analyzed comprehensively.
The formulation of the process route is to formulate the overall layout of the process. The main task is to select the processing method of each surface, determine the processing sequence of each surface, and the number of processes in the entire process.
The general principles of drafting the process route are as follows.
1. Process the datum surface first
During the processing of the part, the surface as the positioning reference should be processed first, so as to provide a precise reference for the subsequent processing as soon as possible. This is called "benchmark first."
2. Divide the processing stages
Surfaces with high processing quality requirements are divided into processing stages, which can generally be divided into three stages: rough processing, semi-finishing and finishing. The main purpose is to ensure the processing quality; facilitate the rational use of equipment; facilitate the arrangement of the heat treatment process; and facilitate the discovery of blank defects.
3. Hole first, behind
[1] 　 For parts such as box body, bracket and connecting rod, the plane should be processed first and then the hole should be processed. In this way, the holes can be positioned on the plane to ensure the position accuracy of the plane and the holes, and it is convenient to process the holes on the plane.
4. The main surface finishing (such as grinding, honing, fine grinding, etc.) should be carried out at the final stage of the process route to prevent the finishing surface from being damaged due to the transfer and installation between the processes.
The above is the general situation of the process arrangement. Some specific situations can be handled according to the following principles.
(1) Guangdong Machinery Processing Factory In order to ensure the processing accuracy, it is best to perform rough and finish processing separately. Because of the large amount of cutting during rough machining, the workpiece is subjected to large cutting force, clamping force, heat generation, and the machined surface has a significant work hardening phenomenon, and there is a large internal stress inside the workpiece. If rough and rough machining Continuously, the precision of the parts after finishing will be quickly lost due to the redistribution of stress. For some parts that require high machining accuracy. After rough machining and before finishing, low temperature annealing or aging treatment procedures should also be arranged to eliminate internal stress.
(2) Choose equipment reasonably. Rough machining mainly cuts off most of the machining allowance and does not require high machining accuracy. Therefore, rough machining should be carried out on a machine with greater power and less precision, and the finishing process requires higher precision. Machine tool processing. Rough and fine machining are processed on different machine tools, which can not only give full play to the equipment capabilities, but also extend the service life of precision machine tools.
(3) Guangdong machinery processing plants often arrange heat treatment processes in the mechanical processing process. The location of the heat treatment process is arranged as follows: In order to improve the cutting performance of the metal, such as annealing, normalizing, quenching and tempering, etc., it is generally arranged before mechanical processing. In order to eliminate internal stress, such as aging treatment, quenching and tempering treatment, etc., it is generally arranged after rough machining and before finishing. In order to improve the mechanical properties of parts, such as carburizing, quenching, tempering, etc., it is generally arranged after machining. If there is a large deformation after heat treatment, the final processing procedure must be arranged.