Practical Operation Skills of CNC Lathes

Practical skills for basic operations

1.After the tool setting is completed, do not start the processing directly. First, adjust the feed ratio to the lowest and simulate the entire Z-direction movement with the handwheel to ensure that the tool does not hit the chuck or tailstock. Many novice machine collision accidents can be avoided in advance by this step. If it is the first time to run an unfamiliar program, prioritize the handwheel following mode. By controlling the program's running speed through the handwheel's rotational speed, you can clearly see each step of the tool path throughout the process. Only after confirming that the path is completely correct can you switch to the automatic mode.

2.When clamping short workpieces, the clamping length of the chuck should not exceed 10mm to prevent the workpiece from extending too far and swinging or shifting during rotation. When clamping large-diameter hollow workpieces, a wooden board can be tightly stuffed inside the workpiece, or a layer of grease can be pasted on the end face and covered with thin paper. By rotating at a low speed, the center can draw concentric circles on the paper. Fine-tune the three support feet of the center rest to align the centers of the circles with the tip of the center. In this way, the center of the workpiece and the center of the spindle can be quickly calibrated and aligned, effectively avoiding the problem of depresses and bulging on the machined end face.

3.When installing the cutting tool, the tip of the tool should be slightly higher than the center of the workpiece by 0.02 to 0.05mm. Do not install it too low; otherwise, it is easy for the tool to get stuck during turning, and there will still be residual protrusions from the turning end face to the center position. If during the trial cutting of the end face, it is found that there is still a small part that has not been turned, do not forcefully push the tool. Instead, place a thin copper sheet or a 0.01mm gasket under the tool holder and fine-adjust the height until the entire end face can be completely illuminated.

Special working condition targeted techniques

1.When turning slender shafts at high speed, calibrate the parallelism between the centerlines of the machine tool's spindle and tailstock and the large guide rail to within 0.02mm in advance. Select a bias tool with a main deflection Angle of 75°-90°, and control the secondary relief Angle at 4°-6°, not too large. The support claws of the tool rest should be ground in advance to ensure that the contact arc surface R is greater than or equal to the radius of the workpiece. When adjusting the support feet, they should just fit the workpiece tightly without applying excessive force. This way, workpieces with bambus-shaped or multi-faceted surfaces can be avoided from being processed. If the length-to-diameter ratio of the workpiece exceeds 40, the clamping force of the tailstock center should be fine-tuned at any time during processing to prevent the workpiece from being bent and deformed due to thermal expansion.

2.When turning viscous materials like stainless steel, do not blindly increase the rotational speed. Keep the cutting speed stable at 50-100m/min, and control the feed rate at 0.1-0.3mm/r. At the same time, ensure that the high-pressure coolant directly reaches the cutting area with a flow rate of no less than 10L/min. This can significantly reduce the built-up edge of the tool and prevent chipping. If drilling stainless steel, do not grind the drill bit into extra chip removal grooves. Keep the drill edge sharp, which can effectively prevent the drill bit from annealing and getting stuck during the drilling process.

3.When processing deep holes, a special tool holder with support sleeves at both ends is used. The tool holder is suspended in the support sleeves and slides, completely eliminating the shaking of the tool holder. This method increases the processing efficiency by more than five times compared to traditional methods and also ensures the coaxiality and surface roughness of the holes. If the ordinary twist drill is prone to out-of-tolerance runout during reaming, replacing it with a flat-bottomed drill and shortening the overhang length of the tool shank can stably control the reaming accuracy within 3 microns.

Efficiency and accuracy optimization techniques

1.The daily adjustment of parameters follows this rule: for every increase of 0.05mm/r in the feed rate, the spindle speed decreases synchronously by 50 to 80 revolutions. The slight decrease in speed offsets the tool wear caused by the increase in cutting force, which can not only ensure processing efficiency but also prevent the tool from wearing out too quickly. By observing the state of the iron filings in daily life, one can quickly determine whether the processing is normal: white iron filings indicate that the cutting temperature is below 200℃ and the state is normal. The appearance of blue-purple iron filings means that the cutting temperature has exceeded 300℃, and the rotational speed should be immediately reduced and the coolant flow rate increased.

2. If dimensional drift occurs during processing, do not directly add parameters. First, stop the machine and check the wear of the tool tip. Many times, it is not that the machine tool accuracy has deteriorated, but that the slight wear of the tool tip causes the workpiece to shift slightly in the chuck. After cleaning the accumulated chips at the tool tip or replacing it with a new tool, the size can return to the tolerance range. If the parts are to be processed in batches, it is advisable to ensure that the same tool is used for the entire shift of processing. For the precision processing of large parts, it is absolutely forbidden to change the tool during the process, which can minimize the tool connection error to the greatest extent.

3.When processing threads, the height of the external thread is calculated at 1.3 times the pitch, and that of the internal thread at 1.08 times the pitch. The rotational speed is set using the formula S=1200/ pitch ×0.8. The threads turned out have regular tooth shapes and are less likely to get tangled. If there is a slight ellipticity in the thread measurement after turning, do not directly modify the program. Check whether the workpiece clamping is loose. Use the same thread cutter to make two more fine feed passes, and the ellipticity error can be corrected.