The Influence of Position Error in CNC Machine Tool Processing on Machining Accuracy

I. Machining principal error refers to the use of approximate blade profile or approximate transmission relationship. Errors caused by processing. Machining principal errors mostly appear in threads, gears, and complex curved surfaces Processing.

For example, the gear hob used for processing involute gears, in order to facilitate the manufacture of the hob, the use of The Archimedes basic worm or the normal straight profile basic worm replaces the involute basic worm, so that the tooth The involute tooth profile of the wheel has an error. Another example is when turning a modular worm, due to the pitch of the worm, etc. On the circumference of the worm wheel (ie mT), where m is the modulus and T is an irrational number, but The number of teeth of the matching gear of the lathe is limited. When choosing the matching gear, it can only be reduced to an approximation. Calculate the fractional value (r=31415), which will cause the tool to form movement (screw The inaccuracy of rotating motion) causes pitch error.

  In processing, approximate processing is generally used, and the theoretical error can meet the processing accuracy requirements.

Under the premise of demand (<=10%-15% dimensional tolerance), to improve productivity and economy.

 

II. The machining accuracy of CNC machine tools refers to the degree to which the actual geometric parameters (size, shape, and position) of the parts after machining conform to the ideal geometric parameters specified in the drawings. The higher the degree of this conformity, the higher the processing accuracy.  

High machining accuracy The machining accuracy of CNC machine tools can generally reach 0.050.1MM. CNC machine tools are controlled in the form of digital signals. Each time the CNC device outputs a pulse signal, the moving parts of the machine tool move a pulse equivalent (generally 0.001MM), and The average error of the backlash of the machine tool feed drive chain and the screw pitch can be compensated by the numerical control device. Therefore, the positioning accuracy of the numerical control machine tool is relatively high. However, the machining accuracy of each numerical control machine tool depends on the machine tool brand, machine tool type, and technology of the CNC machine operator. Factors such as those will cause differences in the machining accuracy of CNC machine tools.  

The machining accuracy of CNC machine tools is generally up to 0.050.1MM. CNC machine tools are controlled in the form of digital signals. Each time the CNC device outputs a pulse signal, the moving parts of the machine tool move a pulse equivalent (usually 0.001MM), and the machine tool feeds The backlash of the transmission chain and the average error of the screw pitch can be compensated by the numerical control device. Therefore, the positioning accuracy of the numerical control machine tool is relatively high.  

 

Numerical control machine tools will inevitably be affected by various factors in the processing process, which will cause certain deviations in their processing accuracy and bring some inconvenience to production and life. How to improve the machining accuracy of CNC machine tools is a matter of great concern to engineers. 

The influence of position error in CNC machine tool processing on machining accuracy 

Position error refers to the amount of change or deviation between the actual surface, axis, or symmetry plane of the processed part relative to its ideal position, such as perpendicularity, position, symmetry, etc. The position error in CNC machine tool processing usually refers to the dead zone error. The cause of the position error is mainly due to the gap and elastic deformation generated during the transmission of the machine tool parts during the processing of the machine tool, and the tool head of the machine tool needs to overcome the friction force during processing. Factors such as lead to position error. In the open-loop system, the position accuracy is greatly affected, while in the closed-loop follow-up system, it mainly depends on the accuracy of the displacement detection device and the speed amplification factor of the system, and the effect is generally small.


 

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