About Dalian high-speed CNC car and you share CNC lathe ordinary thread processing points

Four standard threads, metric, inch, modulus and diameter control, can be turned on the NC vertical lathe. No matter which thread is turned, the strict motion relationship between the lathe spindle and the tool must be maintained: that is, the tool should move a lead distance evenly every time the spindle rotates (i.e. the workpiece rotates). In the following, through the analysis of ordinary thread, we can strengthen the understanding of ordinary thread, so as to better process ordinary thread.

Four standard threads, metric, inch, modulus and diameter control, can be turned on the NC lathe. No matter which thread is turned, the strict motion relationship between the lathe spindle and the tool must be maintained: that is, for each rotation of the spindle (i.e. one rotation of the workpiece), the tool should move a lead distance evenly. In the following, through the analysis of ordinary thread, we can strengthen the understanding of ordinary thread, so as to better process ordinary thread.

1、 Installation and setting of common thread cutting tools

If the turning tool is installed too high or too low, when the cutting tool reaches a certain depth, the rear tool surface of the turning tool will support the workpiece, increase the friction, and even bend the workpiece, resulting in tool gnawing; If it is too low, the chip is not easy to be discharged. The direction of the radial force of the turning tool is the center of the workpiece. In addition, the clearance between the transverse lead screw and the nut is too large, resulting in the continuous automatic deepening of the cutting depth, so as to lift the workpiece and gnaw the knife. At this time, the height of the turning tool shall be adjusted in time to make the tool tip equal to the axis of the workpiece (the tool can be adjusted by using the center of the tailstock). During rough turning and semi fine turning, the position of the tool tip is about 1% d higher than the out center of the workpiece (d represents the diameter of the workpiece to be machined).

The workpiece is not clamped firmly, and the rigidity of the workpiece itself cannot bear the cutting force during turning, resulting in excessive deflection, which changes the center height between the turning tool and the workpiece (the workpiece is raised), resulting in a sudden increase in cutting depth and tool gnawing. At this time, the workpiece should be clamped firmly, and the tailstock center can be used to increase the rigidity of the workpiece.

The tool setting methods of ordinary thread include trial cutting method and automatic tool setting by tool setting instrument. You can directly use the tool to test cut and set the tool, or use G50 to set the workpiece zero point, and use the workpiece shift to set the workpiece zero point for tool setting. The tool setting requirements for thread processing are not very high, especially the tool setting in Z direction is not strictly limited, which can be determined according to the programming processing requirements.

2、 Dimensional analysis of common thread

The processing of ordinary thread by NC lathe requires a series of dimensions. The calculation and analysis of the dimensions required for ordinary thread processing mainly includes the following two aspects:

1. Diameter of workpiece before thread machining

Considering the expansion of thread processing profile, the diameter of workpiece before thread processing is D / d-0.1p, that is, the large diameter of thread is reduced by 0.1 pitch. Generally, it is 0.1 to 0.5 smaller than the large diameter of thread according to the small deformation capacity of material.

2. Thread machining feed

The thread feed position refers to the thread feed position Z.

Small diameter of thread: major diameter - 2 times of tooth height; Tooth height = 0.54p (P is pitch)

The feed rate of thread machining should be continuously reduced, and the specific feed rate should be selected according to the tool and working material.

3、 Common programming thread machining

In the current CNC lathe, there are generally three machining methods for thread cutting: G32 straight cutting method, G92 straight cutting method and G76 oblique cutting method. Due to different cutting methods and programming methods, the machining errors are also different. We should carefully analyze the operation and use, and strive to process parts with high precision.

1. G32 straight cutting method, because both edges work at the same time, the cutting force is large, and it is difficult to arrange cutting, so the two cutting edges are easy to wear during cutting. When cutting threads with large pitch, due to the large cutting depth and rapid blade wear, the pitch diameter error of the thread is caused; However, its tooth shape accuracy is high, so it is generally used for small pitch thread processing. Because the tool movement and cutting are completed by programming, the machining program is long; As the blade is easy to wear, frequent measurement should be done in processing.

2. G92 straight cutting method simplifies programming and improves efficiency compared with G32 instruction.

3. G76 oblique cutting method, because it is processed with one side edge, the processing edge is easy to be damaged and worn, so that the processed thread surface is not straight and the tool tip angle changes, resulting in poor tooth shape accuracy. However, because it works with a single edge, the tool load is small, chip removal is easy, and the cutting depth is decreasing. Therefore, this machining method is generally suitable for large pitch thread machining. Because this machining method is easy to remove chips and the working condition of blade machining is good, this machining method is more convenient when the requirement of thread accuracy is not high. When machining high-precision threads, it can be completed by two knives, i.e. rough turning with G76 machining method, and then finish turning with G32 machining method. However, it should be noted that the starting point of the tool should be accurate, otherwise it is easy to buckle randomly, resulting in the scrapping of parts.

4. After the thread processing is completed, the thread quality can be judged by observing the thread profile, and measures can be taken in time. When the thread top is not sharp, increasing the cutting amount of the knife will increase the large diameter of the thread, which depends on the plasticity of the material. When the top has been sharpened, increasing the cutting amount of the knife will reduce the large diameter in proportion. According to this feature, the cutting amount of the thread should be treated correctly to prevent scrapping.

4、 Detection of common thread

For general standard threads, thread ring gauge or plug gauge is used to measure. When measuring the external thread, if the thread "over end" ring gauge is just screwed in, but the "stop end" ring gauge is not screwed in, it means that the processed thread meets the requirements, otherwise it is unqualified. When measuring internal thread, use thread plug gauge to measure in the same way. In addition to the measurement of thread ring gauge or plug gauge, other measuring tools can also be used for measurement. The pitch diameter of thread is measured with thread micrometer, the pitch diameter of trapezoidal thread and the pitch diameter of worm are measured with tooth thickness vernier caliper, and the pitch diameter of thread is measured with measuring needle according to the three needle measurement method.