Machining accuracy refers to the degree of agreement between the actual value and the theoretical value of the geometric parameters (size, shape, and mutual position of the surface) of the part after machining. The higher the degree of compliance, the higher the machining accuracy. The difference between the actual value and the ideal value is called the processing error. Machining errors are divided into two categories: systematic errors and random errors.
In order to improve the machining accuracy of the machining center, the manufacturer has also developed and applied various compensation functions while increasing the resolution of the CNC system, improving the accuracy of position detection, and adopting feedforward control and nonlinear control in the position servo system. Compensate the servo system. Such as gear clearance compensation, lead screw pitch error compensation, space error compensation, knife county compensation and other technologies, thermal compensation technology, etc. to ensure product quality.
There are many supply factors affecting machining accuracy, which can be broadly divided into geometric and processing errors. Geometric errors include positioning accuracy, roll, yaw, sway, linearity, and verticality. Processing errors include errors caused by tool, fixture, NC program and temperature changes. It should be noted that measurement error is also one of the factors that must be considered.
Modern machining centers have a basic function called “linear compensation”. The concept of “linear compensation” is similar to the pitch error compensation of old NC machine tools. The purpose is to optimize the positioning accuracy of the machine tool coordinates. In the “linear compensation” of the machine tool, the error between the coordinate command position and the actual position is adjusted according to the measurement result determined in advance to correct the positioning accuracy. These measurements are measured with a laser or other high-precision instrument during commissioning of the reprocessing center and stored in the machine data sheet.
In general, the temperature characteristics of machining centers are closely related to the main materials of machining centers—the speciality of steel and cast iron. The linear expansion coefficient of the lead screw, cast iron + steel structure, and scale system is similar to that of cast iron or steel. However, the situation is different when wet cutting and machining non-steel or cast iron parts. At this time, the method of “linear compensation” should be used to linearly compensate the thermal expansion of the workpiece. In this way, the machining accuracy of the machine tool will be greatly improved.