1、 Basic characteristics of thread
In the case of machinery, threaded connection is widely used, including external thread and internal thread. According to the profile shape of thread, it is mainly divided into four kinds: triangular thread, trapezoidal thread, sawtooth thread and rectangular thread. According to the number of threads, it is divided into single thread and multi thread. In various machines, the functions of threaded parts mainly include the following points: first, for fastening and connection; Second, it is used to transmit power and change the form of movement. Triangle thread is often used for connection and firmness; Trapezoidal thread and rectangular thread are often used to transmit power and change the form of motion. Their technical requirements and processing methods have a certain gap due to different uses.
2、 Machining method of plane thread
In addition to using ordinary machine tools for processing, in order to effectively reduce the processing difficulty of processing threads, improve work efficiency, and ensure the quality of thread processing, NC machine tools are often used for processing.
Three instructions G32, G92 and G76 are commonly used by CNC machine tools to process threads. Of which:
Instruction G32: it can process one-way thread. The task of single programming is heavy and the program is complex;
Instruction G92: simple thread cutting cycle can be realized, which is helpful for simplifying program editing, but the workpiece blank must be roughened in advance.
Instruction G76: it overcomes the shortcomings of instruction G92 and can process the workpiece from blank to finished thread at one time. It is of great help to simplify the program and save programming time.
G32 and G92 belong to straight cutting methods, and the two cutting edges are easy to wear, which is mainly caused by the large cutting force and difficult cutting arrangement caused by the simultaneous operation of both edges. When cutting threads with large pitch, due to the large cutting depth, the blade wears faster, resulting in the error of the pitch diameter of the thread; However, the tooth shape accuracy of its processing is high, so it is generally used for small pitch thread processing. Because its tool movement and cutting are completed by programming, the machining program is long, but it is more flexible.
G76 belongs to the oblique cutting method. Because it is processed with a single edge, the right edge is easy to be damaged and worn, making the machined thread surface not straight; In addition, once the knife tip angle changes, it will cause poor tooth shape accuracy. However, the advantage of this machining method is that the cutting depth is decreasing, the tool load is small, and chip removal is easy. Therefore, this processing method is applicable to the processing of large pitch threads.