1 Significance of transformation of ordinary machine tools

Currently, the market competition is fierce and the demand is changeable. Ordinary machine tools are no longer suitable for the requirements of multi-variety and batch production. CNC machine tools combine advanced technologies such as CNC technology, PLC control, and detection technology to meet the requirements of batch, high-precision, complex shapes, and short production cycle parts. Only by changing the processing part program can different processing objects be met without making any adjustments to the machine tool. After many overhauls, the size of the parts of ordinary lathes has changed greatly. The main transmission parts have been replaced and adjusted many times, but there is still a high failure rate. Traditional repair solutions are difficult to meet the processing requirements, and the maintenance cost is high. Therefore, it is necessary to transform the CNC system. In the mechanical processing industry, CNC machine tools are used more and more widely. The development of CNC machine tools must be full-featured and high-performance, simple and practical, and have the basic functions of automatic processing, easy operation and maintenance.

2 Advantages after CNC transformation

(1) Improve processing accuracy and production efficiency. (2) Improve the quality and performance of machine tools to meet the processing requirements of complex surface parts. (3) Realize the automation of mechanical processing, and the efficiency can be increased by 2-6 times. (4) It can reduce the frequent handling time of parts between machine tools, reduce positioning errors, and realize the concentration of processes. (5) It can realize various self-checking functions such as automatic alarm, monitoring, compensation, etc., and can monitor the operating status of machine tools. (6) The use of CNC machine tools can not only reduce the labor intensity of workers, save labor, and greatly reduce tooling time, but also shorten the trial production cycle and testing cycle of new products, and respond quickly to market demand. 3 Main problems solved by CNC transformation (1) Find out the problems of ordinary machine tools and restore their functions. (2) Install digital display devices or CNC systems. (3) Restore mechanical accuracy. (4) In the transformation project, innovations should be made in processes and technologies to maximize CNC transformation.

4 Selection of various control systems

4.1 Selection of servo system

Servo systems are divided into three types: open-loop control system, closed-loop control system and semi-closed-loop control system. When renovating, you can choose according to the actual situation.

4.2 Selection of drive motor

For economical CNC transformation, the design uses stepper motors for servo control. Stepper motors are open-loop control elements that convert electrical pulse signals into linear displacement or angular displacement. Under normal operation, the speed and stop position of the motor are determined by the number and frequency of pulse signals, and the load change has no effect on it. When the motor receives a pulse signal, the motor turns a step angle. Because of this linear relationship, the stepper motor also has the characteristics of periodic error without cumulative error. In this way, it becomes very simple to use stepper motors to control speed, position, etc.

4.3 Selection of control system

According to a series of conditions such as different actual conditions, each person's usage habits, and renovation costs, the designer's choice of CNC system and PLC is also different. This requires the designer to achieve the maximum optimization under the existing conditions.

4.4 Selection of spindle motor

The spindle motor needs to be equipped with corresponding control elements, so that it can realize the functions of spindle forward, reverse, jog control and motor thermal protection. The command of the rotation direction needs to be written into the PLC program. The forward relay or reverse relay is controlled by the PLC output port to make the contactor operate, thereby completing the forward and reverse switching of the spindle. The spindle motor has high power and will generate a large current when starting, so three contactors are used in the design to complete the star-angle switching of the motor. In order to meet the requirements of thread processing, the encoder is installed on the spindle and the signal is fed back to the PCU unit. In thread processing, the operator must know the spindle speed and calculate the feed speed based on the spindle speed, so the encoder is installed on the spindle to detect the spindle speed to meet the processing requirements.