Common faults and solutions when machining threads on CNC lathes

Threads are continuous protrusions and grooves with the same cross-section and prescribed tooth profile formed along the spiral line on the surface of a cylinder or cone. Among various mechanical products, parts with threads are widely used. It is mainly used as connecting parts, fastening parts, transmission parts and measuring parts and so on. Thread machining on a CNC lathe is one of the more commonly used machining methods. Thread processing on CNC lathes is playing an increasingly important role in mechanical processing due to its advantages of high processing accuracy, good product uniformity, and wide processing range.
With the development of science and technology, CNC lathes are becoming more and more popular, and thread turning on CNC lathes is used more and more in machining. Numerical control lathes are playing an increasingly important role in machining with the advantages of high machining accuracy, good product identity, wide machining range, and convenient debugging. Common faults and solutions when turning threads on CNC lathes mainly include:
Knife
The rake angle of the turning tool is too large, and the X-axis screw gap of the machine tool is too large; the turning tool is installed too high or too low; the workpiece is not firmly clamped; the turning tool wears too much; the cutting amount is too large.
Solution
Reduce the rake angle of the turning tool, repair the machine tool to adjust the screw gap of the X axis, and use the automatic compensation function of the CNC lathe to compensate the screw gap of the machine tool X axis; the turning tool is installed too high or too low: too high , When the cutting tool reaches a certain depth, the flank face of the turning tool will resist the workpiece, increasing the friction, and even bending the workpiece, causing the phenomenon of cutting; if it is too low, the chips will not be easily discharged, and the direction of the turning tool’s radial force It is the center of the workpiece, and the gap between the traverse screw and the nut is too large, which causes the depth of the tool to be continuously and automatically deepened, thereby lifting the workpiece and causing the tool to pierce. At this time, the height of the turning tool should be adjusted in time to make the tip of the tool the same height as the axis of the workpiece. In rough turning and semi-finishing turning, the position of the tool tip is about 1% D higher than the center of the workpiece. Insufficient clamping of the workpiece: the rigidity of the workpiece itself cannot withstand the cutting force during turning, resulting in excessive deflection, which changes the center height of the turning tool and the workpiece, resulting in a sudden increase in the cutting depth, and the tool should be pierced. The clamping is firm, and the tailstock center can be used to increase the rigidity of the workpiece. Excessive wear of the turning tool: The cutting force increases, the workpiece is bent, and the tool is stuck. The turning tool should be reground at this time. Cutting amount is too large: Choose a reasonable cutting amount according to the lead size of the workpiece 5 and the rigidity of the workpiece.
Random deduction
Symptoms
When the lead screw rotates one revolution, the workpiece does not turn over an integer.
The main reason
The synchronous transmission belt of the spindle encoder of the machine tool is worn, and the synchronous real speed of the spindle cannot be detected; the program input to the host is incorrect; the X-axis or Y-axis screw is worn.
Solution
Spindle encoder synchronous belt wear: When the CNC lathe is turning the thread, the movement relationship between the spindle and the turning tool is controlled by the instruction issued by the information processing center of the machine tool host. When turning the thread, the spindle speed is constant, X or The Y-axis can adjust the moving speed according to the size of the workpiece lead and the spindle speed, so the center must detect the synchronous real speed of the spindle in order to issue the correct command to control the X or Y-axis to move correctly. If the system cannot detect the real speed of the spindle and will issue different commands to X or Y during actual turning, then the spindle rotates once, and the distance of the tool movement is not a lead, and the thread will be in the second tool turning. Random deduction. In this case, we only have to repair the machine tool and replace the main shaft timing belt.
The programmed input is incorrect: In order to prevent random buckling when turning threads, it is necessary to ensure that the turning trajectory of the next cut coincides with the turning trajectory of the previous one. In general turning, we use the reverse turning method to prevent random buckling. On CNC lathes, we use programs to prevent random buckling, that is, when compiling the processing program, we use the program to control the thread cutter to retract after the previous cut, so that the starting point of the next cut coincides with the starting point of the previous cut, so that the turning The thread will not be buckled indiscriminately. Sometimes, due to the incorrect lead input by the program, random buckles may occur during turning. The X-axis or Y-axis screw is severely worn: repair the machine tool and replace the X-axis or Z-axis screw.