For economical numerical control transformation of ordinary lathes, when considering the overall design plan, the principle to be followed is: In the future of meeting the design requirements, the changes to the machine tools should be as small as possible to reduce costs.
First, the CNC transformation of the lathe
1. Working principle and composition of CNC machine tools
1) Working principle of CNC machine tools:
When machining parts on a CNC machine tool, the machining program for the part should be prepared first. This is the work instruction of the CNC machine tool. The processing program is input to the numerical control device, and then the numerical control device controls the change of the main movement of the machine, the start and stop, the direction, speed and displacement of the feed movement, and other options such as tool selection exchange, workpiece clamping release and cooling lubrication, etc. Close and other movements, so that the tool and the workpiece and other auxiliary equipment in strict accordance with the order of the processing procedures, trajectory and parameters of the work, in order to process the parts that meet the requirements.
2) The composition of CNC machine tools:
CNC machine tools are mainly composed of four parts: control medium, numerical control device, servo system, and machine tool body. Its block diagram is shown in the figure below:
2. Design Contents and Tasks The numerical control transformation design of ordinary lathes (C618) includes: determination and verification of the overall plan, design and calculation of the mechanical transformation section (including design and calculation of vertical and horizontal feed systems), and main movement automatic transmission principle And the transformation of the design of the machine tool transmission system diagram, the design of the machine speed control motor control circuit, electromagnetic clutch design and calculation. .
The design task is to carry out the numerical control transformation of the C618 horizontal lathe and realize the computer-controlled numerical control of the lathe. Utilize the microcomputer to carry on the digital control to the vertical and horizontal feed system of the lathe, and to achieve the minimum longitudinal movement unit of 0.01 / pulse, the horizontal minimum movement unit of 0.005 / pulse, the main movement to achieve automatic transmission, the tool holder should be transformed into automatic control Automatic indexing tool holder, to be able to automatically cut the thread.
3, the design and transformation of the numerical control part
1) The determination of the numerical control system's motion mode The numerical control system can be divided according to its motion trajectory: point control system, continuous control system. The point control system only requires controlling the position of the tool from one point to another point, but does not control the trajectory in principle. The continuous control system can perform strict uninterrupted control of the displacement in two or more coordinate directions. Because the C618 lathe needs to process complex contour parts, the microcomputer numerical control system adopts a continuous control system.
2) The design and reconstruction of servo feed system The servo feed system of CNC machine tools can be divided into open-loop servo system, semi-closed-loop servo system and closed-loop servo system according to presence or absence of position detection and feedback.
The advantage of the closed-loop control scheme is that it can achieve good machine accuracy and can compensate for various errors in the mechanical transmission system and eliminate the influence of gaps, disturbances, etc. on the machining accuracy. However, his structure is complex, technical difficulties, adjustment and maintenance are difficult, and the cost is high.
Since the semi-closed-loop control system has a wide speed range, strong overload capacity, and feedback control, the performance is much better than that of an open-loop control system driven by a stepping motor. However, the use of a semi-closed loop to control its tuning is more complicated than the open loop, and its design must also have its own characteristics, and the technical difficulty is greater.
There is no position controller and feedback circuit in the open loop control system, so the open loop system has poor accuracy, but its structure is simple and easy to adjust, so it is often used in applications where the accuracy is not high.
After the above comparison, because the target machining accuracy of the modified C618 lathe is not high, it is decided to adopt an open-loop control system.
3) The hardware circuit design of the numerical control system The numerical control system is composed of two parts: hardware and software. The hardware is the basis of the control system. The performance of the numerical control system directly affects the working performance of the overall numerical control system.
The design of numerical control devices usually has:
â— It can be all designed and manufactured by oneself â— It can be reconstructed by single board machine or STD module or industrial control machine â— Can use the ready-made numerical control device for a small number of adaptation changes In the economical NC transformation of ordinary machine tools, due to the first design cycle is longer It is not economical and quality is difficult to guarantee at the same time. The second type is even more uneconomical. So no course design will take the third clock solution.
4, the mechanical transformation part of the design
1) The transformation design of the main drive section The original machine's spindle motor is replaced by an inverter motor, and the stepless speed regulation is controlled by the inverter. Replace the original spindle of the machine tool with a manual transmission with an electromagnetic clutch control. After the transformation, the main movement and feed movement are separated, and the function of the spindle motor merely drives the rotation of the main shaft.
2) Renovation of the feed mechanism Remove the original machine's hanging wheel mechanism, feed box, carriage box, sliding screw, light bar, etc. Longitudinal and horizontal feeds are driven by a ball screw after the stepping motor is used as a drive element to decelerate through the first stage gear.
3) Renovation of other parts The tool holder part: remove the original manual tool holder and the small carriage, and install a four-station motor knife holder controlled by a microcomputer. The knife holder has high repeatability, good rigidity, long service life, and processability. Good advantages.
Second, feasibility demonstration
According to the "Automated Manufacturing System", the feasibility analysis enables the user to construct the technical and economical analysis report before the construction of the automated manufacturing system project, which is the basic basis for the approval and approval of the project by the higher authorities. Similarly, it is necessary to conduct reasonable and scientific feasibility demonstrations before the economical NC transformation of ordinary lathes.
According to the traditional method of argumentation, the feasibility demonstration of the economical CNC transformation of ordinary lathes should be carried out in the following aspects, namely, analysis of the status quo of production and operation of enterprises, analysis of existing problems, production and operation goals of enterprises, basic conditions of transformation, goals, and technical solutions. , investment estimates, benefit analysis, plans for implementation of the lathe after transformation, conclusions, etc.
Since this design is only used as a graduation design for undergraduate students, the designer here only makes a brief feasibility study of the estimated investment in the transformation.
This retrofit design is an economical CNC transformation of the ordinary lathe C618. In the retrofit design, the GSK980T CNC system manufactured by Guangzhou CNC Equipment Factory was used, together with two servo motors, two sets of ball screws and matching transmission parts and gear pairs, one frequency-variable-speed motor, and four Electromagnetic clutch and gear pair of main transmission part. In this way, the total cost of equipment renovation and old equipment will not exceed 150,000 yuan. Therefore, economical NC transformation of ordinary lathes is suitable for China's national conditions and is an effective choice for domestic enterprises to improve the automation capabilities and precision of lathes. It has a certain degree of typicality and practicality.