The detection of positioning accuracy of precision punching machines is very important because it indicates the accuracy that each moving component of the tested punching machine can achieve under the control of the CNC system. Therefore, by measuring the positioning accuracy value, the precision punching machine can determine the best workpiece processing accuracy that this punching machine can achieve in future automatic work. It must be emphasized here that the current inspection of positioning accuracy is based on rapid and positioning measurement. For some CNC punching machines with poor stiffness in the feed system, different positioning accuracy values will be obtained when using different feed rates for positioning.
In addition, the detection results of positioning accuracy are related to the ambient temperature and the operating status of the coordinate axis. Currently, most CNC punching machines use semi closed loop systems, and position detection components are mostly installed on the drive motor. There is no effective identification measure for the thermal elongation of the ball screw. Therefore, when measuring positioning accuracy, it is not surprising that an error of 0.01-0.02mm occurs within a 1m travel distance after several rapid round-trip operations. This is because after the screw moves rapidly several times, the surface temperature may increase by 0.5-1 ℃, resulting in thermal elongation of the screw. Some punching machines use pre stretching (pre tightening) to reduce the error caused by this thermal elongation.
The repeated positioning accuracy of each coordinate axis is the most basic accuracy indicator that reflects the stability of the motion accuracy of the axis. Punches with poor accuracy usually cannot guarantee production stability. Nowadays, due to the increasing number of functions in CNC systems, system errors such as pitch accumulation error and reverse clearance error in each coordinate motion accuracy can be systematically compensated. Only random errors cannot be compensated, and repeated positioning accuracy reflects the comprehensive random error of the feed drive mechanism. It cannot be corrected by CNC system compensation. When it is found to be out of tolerance, only fine adjustment and correction of the feed drive chain can be carried out. Therefore, when choosing a punch press, priority should be given to selecting a punch press with high precision in repeated positioning.
Precision punching machines need to be equipped with different stamping molds when used in different stamping situations. If used in stretching situations, stretching molds need to be used, and stretching molds have a special requirement. When using the punching machine for processing, there needs to be an edge pressing and product ejection action for the processed material. When the stretching process requires a large amount of stretching, a buffering device needs to be installed at the bottom of the punch die to complete the edge pressing and ejection actions, and this buffering device is called a die pad in the stamping industry.
At present, most of the mold pads used in stretching situations are hydraulic mold pads, but this type of mold pad has significant shortcomings, mainly manifested in three aspects:
1. Due to the use of hydraulic pressure, the manufacturing accuracy requirements for its various components are relatively high, resulting in higher costs;
2. The usage cost is relatively high. Due to the fact that existing stamping equipment generally uses pneumatic clutch brakes and only has an air source in the factory, using the existing mold pad requires an independent set of hydraulic pressure boosting equipment;
3. The requirements for oil pressure sealing are relatively high, with a high probability of oil leakage and a dirty working environment.
To fundamentally solve this deficiency, precision machinery has designed and produced a pneumatic cushion device for precision punching machine stretching production. It replaces hydraulic oil with an air source and does not require an independent source. It can share the air source with the punching machine and has the function of