CNC machining center is a kind of high-precision, high-efficiency automatic metal processing equipment, equipped with multi position turret or power turret, which can process linear cylinder, oblique cylinder, arc and various thread, groove, worm and other complex workpieces. It has various compensation functions of linear interpolation and arc interpolation, and has played a good economic effect in the mass production of complex parts. However, any problem in the control system, drive system and the electrical and mechanical system of the controlled object will lead to the error problem. In the following guide, we briefly introduces the causes and solutions of the error in the CNC machining.
① In high-speed machining, there may be speed up and down error and servo system lag error in CNC system.
② Due to the inertia of the control system, drive system and the electrical and mechanical system of the controlled object, dynamic errors such as impact, vibration, over travel and out of step will appear when the acceleration is large.
③ In the three-axis CNC end milling, the machining error is composed of two factors: linear approximation error and normal vector rotation error;
④ The machining error is related to the normal curvature of the machined surface, the tool radius and the interpolation length, and is proportional to the square of the interpolation length.
⑤ Programming, tool selection and human factors may also lead to abnormal machining accuracy.
⑥ The rotation error of normal vector is caused by the rotation of normal vector of machined surface along the direction of interpolation line, and it is proportional to the size of tool radius.
⑦ The accuracy error caused by the influence of tool material and cutting oil performance.
① The automatic speed up and down of the numerical control system is automatically realized by the software function of the numerical control system. The basic requirement is that the selected speed up and down law should ensure the trajectory accuracy and position accuracy, and ensure the rapidity, stability and stability of the speed up and down process. At the same time, the control algorithm should be as simple as possible and easy to be realized by computer.
② For convex surface, the normal vector rotation error can be compensated by modifying the tool center position, while for concave surface, no compensation is needed; When the system has no automatic compensation function, it adopts the method of reducing the tool radius to reduce the error.
③ The linear approximation error is determined by the interpolation chord length, which is related to the interpolation cycle and the tool feed rate of the numerical control system. The linear approximation error can be controlled by selecting the numerical control system with smaller interpolation cycle or reducing the feed rate.
④ The residual height error of cutting line is the main factor affecting the surface roughness of workpiece in curved surface machining. The error can be controlled by selecting reasonable cutting line width parameters.
⑤ The tool material and cutting oil of CNC center can directly affect the wear degree of the tool, and the tool with fast wear will produce large error to the workpiece. It is helpful to improve the accuracy of workpiece to select the corresponding tool and cutting oil for different processes.
The above is the reason of errors in CNC machining center, only by analyzing the mechanism of error can we take targeted measures to effectively improve the quality of the workpiece.