Threads are one of the common geometric features in mechanical engineering and are widely used. There are many thread processing techniques, such as thread rolling and twisting based on plastic deformation, turning, milling, tapping and threading, thread grinding, thread grinding, etc., based on cutting processing. Among them, thread turning is one of the commonly used processing methods for single part or small batch production. As a CNC lathe, thread turning is one of its basic functions. Today the editor will share with you common problems and solutions when turning threads on CNC lathes.
Knife
1. Main reason
(1) The cutting angle of the turning tool is too large, and the gap between the X-axis screw rod of the machine tool is large;
(2) The turning tool is installed too high or too low;
(3) The workpiece is not firmly clamped;
(4) The turning tool is too worn;
(5) The cutting quantity is too large.
2. Solutions
(1) Reduce the cutting angle of the turning tool, adjust the clearance of the X-axis screws of the machine tool, and use the automatic screw gap compensation function of the CNC lathe to compensate for the screw gap of the X axis of the machine tool.
(2) The turning tool is installed too high or too low: if it is too high, when the cutting tool reaches a certain depth, the flank surface of the turning tool will resist the workpiece, increasing friction and even bending the workpiece, causing the knife to stick; if it is too low, the chips will not be easily evacuated. The direction of the radial force of the turning tool is the center of the workpiece. Additionally, the space between the feed screw and the nut is. too large, resulting in continuous, automatic cutting depth, thereby lifting the workpiece and causing stabbing. At this time, the height of the turning tool should be adjusted in time so that the tool tip is at the same height as the workpiece axis (the tip of the tailstock can be used to adjust the tool). During rough turning and semi-finishing turning, the tool tip position is approximately 1% D higher than the center of the workpiece (D represents the diameter of the workpiece being machined) .
(3) The workpiece is not firmly clamped: the rigidity of the workpiece itself cannot withstand the cutting force during turning, resulting in excessive deflection, which changes the center height of the tool turning and the workpiece (the workpiece is raised), resulting in a sudden increase in cutting depth, stabbing occurs. At this time, the workpiece should be firmly clamped, and the tip of the tailstock can be used to increase the rigidity of the workpiece.
(4) Excessive wear of the turning tool: causing the cutting force to increase, the workpiece to bend, and the tool to jam. At this point the turning tool needs to be sharpened.
(5) The cutting amount (mainly the back cutting amount and cutting speed) is too large: choose a reasonable cutting amount according to the feed size of the workpiece and its rigidity.
Random deductions
1. Fault phenomenon
When the screw turns once, the part does not rotate one full rotation.
2. Main reasons
(1) The machine tool spindle encoder synchronous transmission belt is worn and the true spindle synchronous speed cannot be detected;
(2) The program compiled and entered into the host machine is incorrect; the X-axis or Y-axis screw rod is worn.
3. Solutions
(1) Wear of the spindle encoder synchronous belt
Because when a CNC lathe turns threads, the motion relationship between the spindle and the turning tool is controlled by instructions issued by the host information processing center of the machine tool. When turning threads, the spindle speed is constant. X or Y axis can be adjusted. depending on the thread size of the workpiece and the spindle. The rotational speed is used to adjust the movement speed, so the center must detect the true rotational speed of the spindle in order to issue correct instructions to control the correct movement of the X or Y axis.
If the system cannot detect the actual spindle speed, it will issue different instructions at X or Y during actual turning. Then, when the spindle turns once, the distance the tool travels does not constitute feed and the thread will be lost during turning. Second rotating tool. Random loops. In this case, it is enough to repair the machine tool and replace the spindle timing belt.
(2) Program entry is incorrect
In order to avoid random buckling when turning threads, it is necessary to ensure that the rotation path of the last tool coincides with the rotation path of the previous tool. On regular cars, we use the reverse turning method to avoid random buckling.
On CNC lathes we use programs to prevent random buckling. That is, when compiling machining programs, we use programs to control the wire cutter to retract after turning the previous cut, so that the starting point of the next cut coincides with the starting point. of the previous cut (equivalent to When turning threads on a general machine, the thread cutter returns to the spiral groove turned by the previous thread cutter), so that the resulting threads will not be randomly deformed.
Sometimes, due to incorrect pitch entry in the program (the pitch of the next program is inconsistent with that of the previous program), random buckling will also occur during filming.
(3) The X-axis or Y-axis screw is seriously worn: Repair the machine tool and replace the X-axis or Z-axis screw.
No incorrect thread
1. Main reason
The data transmitted to the machine tool system by the spindle encoder is inaccurate; the movement of the screw and spindle on the X or Y axis is too great; the compiled program and input are incorrect;
2. Solutions
(1) The spindle encoder transmits inaccurate data: repair the machine tool, replace the spindle encoder or synchronous transmission belt;
(2) The movement of the X-axis or Y-axis screw and spindle is too large: adjust the axial movement of the spindle and the deviation of the X-axis or Y-axis screw Y axis can be automatically compensated by the system deviation. remuneration function;
(3) Check the program and ensure that the instructions contained in the program comply with the requirements of the drawing.
Incorrect tooth shape
1. Main reason
The tip of the turning tool is not properly sharpened; the turning tool is incorrectly installed; the turning tool is worn.
2. Solutions
(1) Improper sharpening of the turning tool tip: Correctly sharpen and measure the angle of the turning tool tip. For thread turning that requires high profile angle accuracy, you can use a standard mechanical clamp thread cutter to turn the thread, or turn the thread. The knives are sharp. with a grinder.
(2) The turning tool is installed incorrectly: use a template to calibrate the tool when installing the tool, or use a dial indicator to align the threading tool holder to install the tool threading tool.
(3) Wear of turning tool: According to the actual conditions of turning processing, the cutting quantity should be reasonably selected, and the turning tool should be repaired and sharpened in time.
Failure Analysis of Large Thread Surface Roughness
1. Main reason
(1) A built-up edge occurs on the tip of the tool;
(2) The tool handle is not rigid enough and causes vibration during cutting;
(3) The radial rake angle of the turning tool is too large;
(4) When cutting threads at high speed, the cutting thickness is too small or the chips are discharged in an oblique direction and the rough surface of the flank is processed;
(5) The workpiece has poor rigidity and the cutting quantity is too large;
(6) The surface roughness of the turning tool is poor.
2. Solutions
(1) When cutting with high-speed steel turning tools, the cutting speed should be reduced and the cutting fluid should be selected correctly;
(2) Increase the cross section of the tool holder and reduce the extension length of the tool holder;
(3) Reduce the radial rake angle of the turning tool;
(4) When cutting threads in high-speed steel, the chip thickness of the last cut should generally be greater than 0.1mm, and the chips should be discharged along the vertical axis;
(5) Choose a reasonable cutting amount;
(6) The surface roughness of the tool cutting edge should be 2-3 degrees lower than the surface roughness value of the workpieces.
Common problems and solutions in thread processing
In short, there are various forms of defects that occur when turning threads. They are caused by equipment, tools, operators, etc. When troubleshooting, it is necessary to analyze the specific situation and find out the specific causes through various detection and diagnosis methods. . influencing factors and adopt effective solutions.
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