What are the problems and solutions in CNC machining?

What are the problems and solutions in CNC machining?

During the process of thread turning, due to the wear and collapse of thread cutting tools, it is often necessary to reinstall and adjust the tools. The quality of tool installation and adjustment directly affects the accuracy of thread turning. Especially for thread repair and turning, secondary clamping and tool adjustment are required, which limits the efficiency of CNC machining threads. When the precision of the thread is required to be high, such as precision machining on both sides of the trapezoidal thread, rough machining is required first, and then the precision turning tool is replaced for precision machining. If the problem of tool installation and setting during the machining process cannot be solved well, CNC thread turning will not be well applied.

There is a big difference between CNC turning threads and ordinary lathe turning threads. Ordinary lathe uses gear mechanical transmission and screw linkage for turning, that is, the tool holder moves one screw every time the spindle rotates. During the entire thread machining process, this transmission chain cannot be disconnected, otherwise it will be improperly fastened.

CNC turning is the process of sending pulse signals to the CNC system through an encoder installed on the spindle. The CNC system controls the operation, issues instructions to control the servo motor, and controls the movement of the tool through ball screws to achieve thread turning. In order to ensure that there is no disorderly bending during thread turning with multiple cutting tools, the initial machining position of the thread is controlled by detecting pulse signals. At the beginning of program processing, the spindle rotates and the tool waits for the spindle encoder to send a synchronization signal before executing the turning motion.

Tool alignment issues in thread turning:

1) Cutting and clamping tools

When clamping the threaded tool, the height of the front end of the threaded tool will not be equal to the rotation center of the workpiece. This is usually common in welding tools. Due to rough manufacturing and inaccurate tool holder dimensions, it is necessary to adjust the center height with a gasket, which will affect the actual geometric angle of the tool after turning. When installing the cutting tool, the angle of the tool tip is biased, which can easily cause errors in the thread contour angle and tooth profile distortion. If the thread cutting tool extends too long, it will generate vibration during the machining process, which will affect the surface roughness of the thread.

2) Coarse and fine turning tool settings

In the process of CNC machining high-precision threads and trapezoidal threads, two threading tools need to be used to separate rough turning and precision turning. The large deviation of the two cutting tools (especially in the Z direction) will increase the pitch diameter of the thread and cause scratching.

3) Repair workpiece tool settings

Due to the secondary clamping of the workpiece, the repaired spiral and encoder's first rotation signal have changed, resulting in disordered buckling during the repair and reprocessing process.

Solution to the problem:

1) After grinding with a sharp tool, the sharp tool should be aligned with the workpiece axis and kept on the workpiece axis. If a CNC machine tool is used to clamp the tool, due to the high manufacturing accuracy of the tool holder, the tool holder can usually be close to the side of the tool holder.

2) The tool alignment for rough machining and precision machining of thread cutting tools uses a set point as a reference point, and conventional methods can be used for tool alignment. In the actual tool alignment process, as long as the tool compensation is slightly adjusted, the trial cutting method is adopted.

3) In thread machining, if the tool is worn or broken, it is necessary to adjust the tool after regrinding. If the workpiece is not removed for maintenance, simply overlap the installation position of the threaded tool with the position before disassembly, which is equivalent to machining the same turning tool.

Precision machining