The 5 Most Common Causes of Reduced Machine Tool Accuracy and Their Solutions
For a machine tool, accuracy is the most important criterion for evaluating its quality. It can even be said that accuracy is the soul of a machine tool. However, in actual operation, machine tools can experience reduced accuracy due to various reasons, which can be quite frustrating. So today, we will discuss five situations that can cause reduced machine tool accuracy and their solutions.
Machining Situation 1
The machine tool can perform machining, and the workpiece dimensions are relatively accurate, but the surface finish of the workpiece is poor.
Summary of Causes
- l The cutting edge of the machine tool’s cutting tool is not sharp.
- l The machine tool generates resonance during operation.
- l The machine tool exhibits crawling phenomena.
- l The machining process has defects.
Solutions:
① If the cutting tool is worn or damaged and no longer sharp, simply regrind the tool or select a better tool for re-alignment.
② Machine tool resonance is primarily caused by unstable placement of the machine tool. Simply adjust the machine tool to a level position and secure it firmly to resolve the issue.
③ Machine tool crawling is often caused by severe wear on the saddle guideways, wear or loosening of the ball screws, or insufficient machine tool maintenance. It is recommended to clean the iron filings and promptly add lubricating oil to reduce friction. Additionally, it is recommended to increase the frequency of machine tool maintenance, with idle maintenance performed every 2–3 days. If the processing volume is large and the machine is operated continuously, it is best to clean the iron filings and add lubricating oil daily. Do not be too concerned about lubricating oil consumption, as the cost of lubricating oil is much lower compared to the output.
④ If there are defects in the processing technology, under the condition of meeting the processing requirements of other processes, it is recommended to use a higher spindle speed and select a more suitable coolant for the workpiece processing.
Machining Situation 2
The produced workpieces have inconsistent taper sizes
Summary of Causes
- l The machine tool is not placed on a level surface and is not securely fixed.
- l When turning long shafts, the workpiece material is relatively hard, and the tool cuts deeply, causing tool deflection.
- l The tailstock center is not aligned with the spindle.
Solutions:
① Use a level to adjust the machine tool’s levelness, lay a solid foundation, and securely fix the machine tool to enhance its rigidity;
② Select appropriate processes and cutting feed rates to avoid tool deflection due to excessive force;
③ Adjust the tailstock position to align the center pin with the spindle.
Machining Situation 3
The drive phase indicator is normal, but the dimensions of the machined workpieces vary.
Summary of Causes
- l The airport pallet has been operating at high speeds for an extended period, causing severe wear on the lead screw and bearings.
- l The tool holder has developed deviations after prolonged use.
- l Although the carriage can accurately return to the processing starting point each time, the dimensions of the processed workpiece still have deviations.
Solutions:
① Use a dial indicator to check the bottom of the tool holder, simultaneously edit a fixed cycle program through the system to verify the repeat positioning accuracy of the carriage, adjust the lead screw clearance, and replace the bearings;
② Use a dial indicator to check the repeat positioning accuracy of the tool holder, adjust the mechanical components, or replace the tool holder;
③ Use a dial indicator to check whether the machined workpiece accurately returns to the program starting point. If so, inspect the spindle and replace the bearings.
Machining Situation 4
The workpiece dimensions differ by several millimeters from the actual dimensions, or there are significant changes in a certain axis direction
Summary of Causes
- l The positioning speed is too fast, and the drive and motor cannot respond in time
- l After prolonged friction wear, the mechanical carriage lead screw and bearings become too tight and jam
- l The tool holder is loose and cannot be securely locked.
- l Programming errors, with no correspondence between the beginning and end, or tool compensation not canceled.
- l The system’s electronic gear ratio and step angle settings are incorrect.
Solutions:
① If the rapid positioning speed is too fast, adjust the G0 speed, cutting acceleration/deceleration, and time to ensure the drive and motor operate normally at their rated frequency;
② If the machine tool has worn out, causing the saddle, lead screw, and bearings to become too tight and jammed, simply readjust and repair them;
③ If the tool holder is too loose after tool change, check whether the tool holder’s reverse rotation time meets the specific tool requirements, and also check the wear and clearance of the worm gear inside the tool holder to confirm proper installation;
④ If the issue is caused by the program, the program must be modified according to the workpiece drawing requirements, selecting reasonable processing methods, and writing the correct program according to the instructions in the manual;
⑤ If significant dimensional deviations are found, check whether the system parameters are set reasonably, especially whether parameters such as the electronic gear and step angle have been damaged. This phenomenon can be measured using a dial indicator.
Machining Situation 5
Unsatisfactory arc processing results, dimensions not accurate
Summary of Causes
- l Overlap of vibration frequencies causing resonance
- l Unreasonable machining process
- l Unreasonable parameter settings, excessive feed rate causing arc machining to lose synchronization
- l Looseness due to large lead screw clearance or loss of synchronization due to overly tight lead screw
- l Wear of the synchronous belt
Solutions:
① Identify the components causing resonance and adjust their frequencies to avoid resonance;
② Improve the machining process for the workpiece material and compile the program reasonably;
③ For stepper motors, the processing speed should not be set too high;
④ The machine tool must be securely installed and placed on a level surface. Additionally, address issues such as excessive tightness of the saddle after wear, increased clearance, or loosening of the tool holder;
⑤ Replace the synchronous belt directly if it is worn.