1. Analyzing the processed parts and choosing the characteristics of the blank turning process is that the workpiece rotates as the main motion and the turning tool moves as the feed motion. NC turning is suitable for processing complex axle parts and die cavity formed by complex curve rotation, and the more precise surface of parts is often achieved by rough, semi-finish and finish machining.
In the process design, the first step is to analyze the part drawings, which include the analysis of the geometric shape, size, tolerance requirements of shape and position, surface roughness requirements, blank, material and heat treatment requirements and number requirements of parts. These are the factors that must be considered in formulating a reasonable technological plan, and also directly affect the compilation of parts processing program and the results of processing.
When choosing the blank, we should consider that the type of the blank of the axle parts is related to the axle structure. Hot-rolled or cold-drawn round bars can be used for the stepped axles with little difference in optical axis or diameter; forgings are mostly used for the axles with large or important difference in diameter; and cast steel is also used for a few complex large axles.
2. The design of technological process includes the division of technological process, the selection of positioning datum, the selection of processing methods for parts surface and the arrangement of processing sequence.Several common methods of dividing NC machining processes are as follows:
(a) According to the number of installations, the process is divided, that is, each clamping as a process, this method processes parts with little content. This method is commonly used in special CNC machine tools and machining centers.
B) To divide the working procedure according to the processing position, that is, to divide the parts into several parts according to the structural characteristics of the parts, each part as a working procedure.
C) According to the cutting tool used, the method of tool centralization and sequencing is to divide the working procedure according to the cutting tool used, that is, to use the same cutting tool or the same kind of cutting tool to finish all the parts that need to be processed, in order to save time and improve efficiency.
D) According to roughing and finishing process, this method is more suitable for parts which are easily deformed or require high precision.
After reasonably dividing the processes, the processing sequence of each process should be arranged. The general principles are as follows:
(a) Processing of the previous process can not affect the positioning and clamping of the next process.
B) Processing the inner cavity first and then the outer shape.
C) The same positioning and clamping method or the same tool process, it is best to complete adjacent connections, so as to avoid errors caused by repeated positioning and reduce assistant time such as tool change.
The selection of positioning datum includes the selection of positioning mode and the selection of positioning surface of machined parts. Axis parts are usually positioned by one end of the cylindrical fixed, that is, using three-jaw chuck, four-jaw chuck to fix the surface of the workpiece, but this method has certain restrictions on the workpiece's overhang length. Over-extension of the workpiece will cause deformation in the cutting process. For the workpiece with too long cutting length, one clamp or two tips can be used to locate. Under the condition that clamping mode is allowed, the positioning surface should be chosen with high geometric accuracy.
3. Process design process design mainly includes selecting machine tools and process equipment, determining tool path, machining allowance, calculating process size and tolerance, determining cutting parameters and calculating man-hour quota, etc.
The difficulty in process design is to determine the cutter route and to select the cutting parameters reasonably. Cyclic cutting allowance, roughing and finishing are three processes in turning process. The method of cyclic cutting allowance should be determined according to the type of blank and the shape of workpiece, so as to reduce the number of cyclic tool-walking and improve the processing efficiency.
The following points should be grasped when determining the turning path:
(a) For axle parts, the principle of arranging tool path is radial feed of axial tool, and the end point of circular resection margin is near the starting point of rough machining, so as to reduce the number of tool-walking and avoid unnecessary empty tool-walking.
B) The principle of arranging tool path for disc parts is radial and axial feed.
C) The shape of casting and forging blank is similar to that of parts after processing. The tool path of circular removal margin moves according to the workpiece contour line, approaching the drawing size gradually. In essence, zero drift is adopted.