The basic of nc machine tools

The basic composition of

The basic component of nc machine tool include machining program carrier, numerical control device, servo drive device, machine tool main body and other auxiliary equipment. The following basic working principle of each component is to outline.

Process carrier

Nc machine tool is working, don't need workers to operate machine tool directly, should control CNC machine, must prepare the processing procedure. Parts processing program, including the relative motion of the cutting tool and workpiece in machine tool trajectory, the process parameters (feeding spindle speed, etc.) and the supplementary motor, etc. Parts processing procedures in certain format and code, and stored in a program on the carrier, such as punched tape, cassette, floppy disk, etc., through the input device nc machine tool, the program information into the CNC unit.

Numerical control device

Nc device is the core of the nc machine tools. Modern Numerical Control device adopts CNC (Computer Numerical Control), the CNC device using multiple microprocessors commonly, in the form of a programmed Software CNC functions, therefore is also called the Software CNC Software (NC). CNC system is a kind of position control system, it is the ideal trajectory based on the input data interpolation, and output to perform part of the spare part I needed to work out. Therefore, the numerical control device is mainly composed of input, process and output of three basic parts. And all the work by the computer system program to carry on the reasonable organization, coordination of the whole system to work.

1) input device: the nc instruction input to the numerical control device, according to different application carrier, the corresponding different input device. Mainly include the keyboard, disk input, CAD/CAM system of direct communication way to connect the input and the superior computer DNC (direct numerical control) input, now there are still many systems still have tape input form of photoelectric reading machine.

(1) the paper tape input mode. Available tape photoelectric reader read in part program, direct control of machine tool movement, can also be tape content into memory, stored in the memory for parts program controlled machine tool movement.

(2) the MDI manual data input mode. The operator can use on the operation panel of keyboard input processing program of instruction, it is suitable for short program.

Under state control device editor (EDIT), use software input processing programs, and in the control unit of the memory, the input method of a reusable program. The general manual programming adopt this method.

In the session programming function of CNC device, can according to the prompts on the display, choose a different menu, choose and employ persons machine dialogue method, input about the size of the Numbers, can automatically generate the processing procedure.

(3) using DNC CNC directly input mode. Keep the parts program in upper computer, CNC system processing while receiving the follow-up procedures section from the computer. DNC way to design using CAD/CAM software is more complex artifacts and directly generate program parts.

2) information processing: input device to process information to the CNC unit, compiled into a computer can identify the information, the information processing parts in accordance with the provisions of the control program after storage and processing, step by step in position and speed through the output unit instruction to the servo system and the main motor control part. CNC system input data include parts of the contour information (the starting point and end point, line, arc, etc.), processing speed, and other ancillary processing information (such as tool change, variable speed, cooling fluid switch, etc.), the purpose of data processing is completed the preparing work before interpolation arithmetic. Data processing program also includes cutter radius compensation, speed calculation and processing of auxiliary functions.

3) output device: output device and servo mechanism. Output unit accept arithmetic unit output pulse by order of the controller, and send it to the coordinates of the servo control system, through the power amplifier, servo driving system, so as to control machine tools according to the specified requirements.

Servo and measurement feedback system

Is an important part of nc machine tool servo system, used to implement nc machine tool feed servo control and spindle servo control. Servo system is used to accept instructions from the nc device information, after power amplification, plastic processing, converted to perform component of machine tool of linear displacement or angular displacement movement. Because is the last link of CNC machine tool servo system, its performance will directly affect the precision and speed of the nc machine tools and other technical indicators, as a result, the numerical control machine tool servo drive device, requires performance of rapid response, accurate and sensitive tracking digital command signal from the numerical control device, and can be faithfully execute instructions from the nc devices, improve the system's dynamic following the characteristic and the static tracking precision.

Servo system including drive device and the executive body of two parts. Drive the spindle drive unit and feed drive unit and the spindle servo motor, feed servo motor. Stepper motor, dc servo motors and ac servo motor is a common drive.

Measuring element to nc machine tools of each coordinate axis measure out the actual displacement value and the feedback system is input into the CNC machine tool equipment, numerical control device to feedback the actual displacement value comparing with instruction value, and reach the set value to servo system output displacement instructions as needed.

Machine main body

Host machine is the main part of the nc machine tools. It includes the lathe bed, base, column, beam, slide, table, spindle box, feed mechanism, rest, and automatic tool change device, such as mechanical parts. It is on the nc machine tool automatically complete all kinds of cutting processing of mechanical parts. Compared with the conventional machine tools, CNC machine tool main body has the following structure:

1) using high stiffness, high shock resistance and small thermal deformation of machine tool the new structure. Usually use improve the static stiffness of the structure system, increasing the damping, adjusting structure quality and the natural frequency method to improve the rigidity and vibration resistance of host machine tool, the machine body can adapt to the needs of the CNC machine tools for automatically machining. To improve the machine layout structure, reduce fever, temperature control and the compensation measures such as adopting thermal displacement, can reduce the influence of thermal deformation of machine tool host.

2) widely used in high performance of the spindle servo drive and feed servo drive device, shortening of nc machine tool transmission chain, simplifies the structure of machine tool mechanical transmission system.

3) high transmission efficiency, high precision, no clearance of transmission and the moving parts, such as ball screw nut pair, plastic slide guide, linear rolling guide, hydrostatic guideway, etc.

Nc machine tools assist device

Assist device is necessary to give full play to the function of nc machine tools supporting device, commonly used auxiliary devices include: pneumatic, hydraulic equipment, chip removal device, cooling and lubricating device, rotary table and CNC dividing head, protection, lighting and other auxiliary equipment. Five-axis linkage machining center