How to solve the problem of precision deviation in CNC punching machines

As an indispensable key equipment in modern manufacturing,the machining accuracy of CNC punching machines directly affects the quality and production cost of products.

Whether it is positioning errors caused by mechanical wear or position deviations caused by control system response delays,they will lead to a decrease in product quality and an increase in scrap rates,thereby causing economic losses to the enterprise.

1.Common types of precision deviation in CNC punching machines

Positioning accuracy deviation is one of the most common accuracy problems in CNC punching machines.It mainly manifests as the inability of the workbench to accurately reach the predetermined position during movement,resulting in offset of the stamping point.
This deviation is often caused by various factors,including nonlinear displacement errors caused by screw drive,reverse clearance errors,and positioning errors caused by non perpendicular guide rails.
The deviation of bottom dead center accuracy directly affects the quality of stamped parts.In the high-speed stamping process,due to vibration and clearance,the actual bottom dead center of the slider will deviate from the theoretical bottom dead center,resulting in inconsistent stamping depth.

Dynamic contour accuracy deviation refers to the deviation between the actual machining trajectory and the theoretical trajectory caused by the mismatch of dynamic characteristics between axes when processing complex contours.

2.Mechanical component factors and solutions

Mechanical wear and tear is a chronic disease that leads to a decrease in the accuracy of CNC punching machines.After long-term use,the wear of key components such as guide rails,screws,and bearings can lead to increased clearance,directly affecting positioning accuracy.
Regular maintenance and inspection are crucial to address this issue.Lubricate the guide rail and screw every 500 hours,and replace the bearing grease once a year.
Reverse clearance error is another common mechanical problem.It is mainly caused by the gap between the screw nut pairs,and when the worktable moves in reverse,it will produce significant positioning errors.
The use of software compensation method can effectively reduce this error.By measuring the gap value in advance,pulse compensation is performed through the system during the worktable commutation to eliminate the impact of gap on accuracy.
Geometric errors include guide rail non perpendicularity,parallelism errors,etc.These errors can cause deviations in the motion trajectory of the entire workbench.

Regularly detecting the geometric accuracy of the machine tool using a laser interferometer and adjusting it in a timely manner is the foundation for ensuring the accuracy of CNC punching machines.

3.Control system factors and optimization strategies

Improper setting of servo parameters is the main cause of dynamic accuracy deviation.Unreasonable gain parameters can cause motor response lag or overshoot,affecting positioning accuracy.
By adjusting the control parameters of the position loop,speed loop,and current loop,the positioning performance of the servo axis can be significantly improved.
The PID control algorithm plays an important role in the control system of CNC punching machines.The control strategy based on PID algorithm can achieve precise control of the speed loop,and cooperate with PLC for outer loop position control,effectively improving the position control accuracy of the entire system.

Intelligent control strategies such as Taguchi method can help find the optimal combination of servo parameters.This method analyzes the impact of various parameters on the accuracy of dynamic contours through systematic experimental design,in order to determine the optimal parameter combination.

4.Thermal deformation factors and countermeasures

Hot deformation is a"hidden killer"that affects the accuracy of CNC punching machines.The heat generated during motor operation and cutting process can cause distortion of the bed,and a temperature difference of only 5℃can result in a deviation of 0.01mm.
During winter or when starting a cold machine,direct processing without preheating can cause precision fluctuations of over 30%.
To address the issue of thermal deformation,an intelligent preheating program is an effective solution.After starting up,let the machine run idle for 15 minutes until it reaches thermal equilibrium before processing,which can significantly reduce errors caused by thermal deformation.

Installing a circulating oil cooling system is an effective means of controlling temperature rise.A good cooling system can control the spindle temperature rise to≤2℃,greatly reducing the impact of thermal deformation.

5.Testing methods and precision maintenance

Regular precision testing is the foundation for maintaining the accuracy of CNC punching machines.The use of a laser interferometer can detect the pitch error of the screw and accurately compensate to 0.001mm.
Ball bar gauge is an effective tool for evaluating the dynamic contour accuracy of machine tools.It can measure the coordination between true roundness,vertical error,and servo gain,providing a basis for precision optimization.
Establishing a preventive maintenance plan is far more economical than repairing after a malfunction.According to the usage of the machine tool,a reasonable maintenance cycle table should be developed:heavy cutting machine tools should shorten the maintenance cycle by 30%,and three shift production lines need to increase monthly full inspections.
Precision maintenance is a systematic project that requires comprehensive consideration from multiple perspectives,including mechanical,control,thermal management,and maintenance.Regular inspection of screw wear,optimization of servo parameters,control of temperature rise,and implementation of error compensation are necessary to ensure long-term stable operation of CNC punching machines.
As a mechanical engineer once said,"A million dollar CNC punch press can extend its lifespan by 5-10 years even though its maintenance cost is less than 1%of the equipment price.