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Analysis of 9 Reasons for Instability of Workpiece Processed by CNC Machine Tool(1)

Analysis of 9 Reasons for Instability of Workpiece Processed by CNC Machine Tool(1)

2022-07-01 14:18:10

1. The workpiece has accurate dimensions and poor surface finish

 

Fault reason: the tooltip is damaged and not sharp; The machine tool resonates and is placed unsteadily; The machine tool has a creeping phenomenon; The processing technology is not good.

 

Solution: if the tool is not sharp after being worn or damaged, regrind the tool or select a better tool to set the tool again; If the machine tool resonates or is placed unsteadily, adjust the level, lay the foundation, and fix it stably; The reasons for the creeping of the machine are the fierce wear of the carriage guide rail and the wear or looseness of the lead screw and ball. The machine tool should be maintained carefully. After going to and from work, the iron wire should be cleaned and lubricated in time to reduce the conflict; Select the coolant suitable for workpiece processing, and try to choose a higher spindle speed when it can meet the processing requirements of other processes.

 

CNC MACHINING TOOL

 

2. The workpiece has large and small taper head

 

Cause of the problem: the level of the machine tool placement is not adjusted well, one high and one low, resulting in unstable placement; When turning a long shaft, the dedication data is relatively hard, and the cutting tool eats the knife deeply, forming the phenomenon of giving up the knife; The ejector pin of the tailstock is not concentric with the main shaft.

 

Solution: use the level to adjust the levelness of the machine tool, lay a thick foundation, fix the machine tool, and improve its patience; Select a reasonable process and appropriate cutting feed to prevent the tool from being forced to yield; Adjust the tailstock.

 

3. The phased light of the driver is normal, and the size of the processed workpiece is sometimes large and sometimes small

 

Fault cause: the carriage of the machine tool runs at high speed for a long time, resulting in the wear of the screw rod and bearing; The repeated positioning accuracy of the tool rest has errors in the long-time application; The carriage can accurately return to the processing starting point every time, but the dimension of the processed workpiece is still changed. This phenomenon is generally caused by the spindle. The high-speed rolling of the spindle makes the bearing wear severe, resulting in the change of processing scale. WeChat for metal processing, with good content, deserves attention.

 

Solution: use the dial indicator to lean against the bottom of the tool rest, and revise a fixed cycle program through the system together, check the repeated positioning accuracy of the carriage, adjust the screw clearance, and replace the bearing; Check the repeated positioning accuracy of the tool rest with a dial indicator, adjust the machine or replace the tool rest; Use a dial indicator to check whether the processed workpiece accurately returns to the starting point of the program. If it can, overhaul the spindle and replace the bearing.

 

4. The dimension of the workpiece differs from the actual dimension by a few millimeters, or a certain axis is greatly changed

 

Fault reason: the speed of fast positioning is too fast, and the drive and motor cannot respond; After a long time of conflict and loss, the mechanical carriage screw and bearing are too tight and stuck; The knife rest is too loose and cannot be locked after changing the knife; The corrected procedural fault, the head, and tail are not taken care of or the knife repair is not canceled; The electronic gear ratio or step angle of the system is set incorrectly.

 

Solution: if the fast positioning speed is too fast, properly adjust the speed of go, cutting acceleration and deceleration and time to make the driver and motor work normally under additional operating frequency; If the carriage and screw crane bearings are too tight and stuck after the machine tool is worn, it is necessary to readjust and correct them; If the tool holder is too loose after changing the tool, check whether the reversing time of the tool holder is satisfactory, whether the worm and worm inside the tool holder are worn, whether the gap is too large, whether the device is too loose, etc; If it is caused by the program, it is necessary to revise the program, improve it according to the requirements of the workpiece drawing, select a reasonable processing technology, and write the correct program according to the instructions of the manual; If the scale error is found to be too large, check whether the system parameters are set reasonably, especially whether the parameters such as electronic gear and step angle are damaged. If this phenomenon appears, it can be measured by playing a dial indicator.

 

5. The effect of the machining arc is not ideal, and the scale is not in place

 

Fault cause: resonance caused by overlapping vibration frequencies; Processing technology; The parameter setting is unreasonable, and the feed speed is too large, which makes the arc machining out of step; Looseness caused by large screw clearance or out of step caused by too tight screw; The timing belt is worn.

 

Solution: find out the resonance parts, change their frequency, and prevent resonance; Considering the processing technology of workpiece data, reasonably compile the program; For stepper motor, the processing speed f cannot be set too large; Whether the machine tool is firmly installed and placed stably, whether the carriage is too tight after wear, the gap increases or the tool holder is loose, etc; Replace the timing belt. WeChat for metal processing, with good content, deserves attention.

 

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