Introduction to CNC machine tools

First, the production of CNC machine tools

    CNC (Numerical Control Machine Tools) is a form of information with a digital code (program instructions) to control the tool according to the given procedures, velocity and trajectory of automatic processing machines, referred to as CNC machine tools.

    CNC machine tools in manufacturing technology and control technology developed on the basis of, the process is as follows:

    In 1948, the United States accepted the Air Force commissioned Parsons Corporation, developed a helicopter propeller blade profile test with a model of processing equipment. As the model shape complexity and diversity, high precision processing equipment is generally difficult to adapt, so make use of digital pulse control of the machine vision.

    In 1949, the company and the Massachusetts Institute of Technology (MIT) began to study, and in 1952 the first successful trial CMM CNC milling machine, numerical control device was used tube components.

    In 1959, the NC device using a transistor components and printed circuit board, appeared with automatic tool changer CNC machine tools, machining centers as (MC Machining Center), the numerical control device into the second generation. ,

    In 1965, the emergence of a third-generation integrated circuit digital devices, not only small size, power consumption, and improve the reliability of prices to decline further, to promote a variety of CNC machine tools and production development.

    The late 1960s, has emerged from the direct control of a computer more than a direct numerical control machine system (DNC), also known as group control system; a small computer-controlled CNC System (CNC), the numerical control device into the characteristics of small computer into the fourth generation.

    In 1974, the successful development of microprocessor and semiconductor memory using micro-computer numerical control device (referred to as MNC), which is the fifth generation of numerical control system.

    The early 1980s, with the computer software and hardware technology, the emergence of human-computer dialogue can be automatic programming of numerical control device; NC increasingly smaller devices can be installed on the machine; automation of CNC machine tools further improved, with automatic monitoring of tool breakage and automatic workpiece detection functions.

    The late 1990s, there have been PC + CNC intelligent CNC system, that system for the control of the PC hardware, PC software installed on the NC system, this way the system easy to maintain, easy to implement networked manufacturing.

Second, the characteristics of CNC machine tools

1, CNC machine tools with the difference between ordinary

    CNC machine tools for machining process is in strict accordance with the provisions of the processing parameters and action execution. It is a highly efficient automatic or semi-automatic machine tools, machine tools, compared with the ordinary, has the following distinctive features:

(1) for the processing of complex shaped parts

    CNC machine tools can be difficult to complete the general can not be completed or processing of complex parts, so in aerospace, shipbuilding, mold and other processing industry has been widely used.

    ◆ High-precision

    ◆ stable and reliable processing

    Achieve computer control, eliminate human error, machining consistency, quality and reliability.

    ◆ high flexibility

    Processing of the object changes, generally only need to change the NC program, reflecting the good adaptability, this will reduce production lead time. On the basis of the CNC machine tools can be composed of a flexible automated manufacturing systems higher-FMS.

    ◆ high productivity

    CNC machine tool itself, high precision, rigidity, choose the amount of benefit processing, production rate, generally for ordinary machine 3 to 5 times, for some complex parts, the production efficiency can be increased ten times or even several times.

    ◆ good working conditions

High degree of automation machine, the operator greatly reduce the labor intensity, the work environment better.

    ◆ help manage modern

The use of CNC machine tools are conducive to the production of computer control and management development for the realization of the production process automation to create the conditions.

2, the application of CNC machine tools

    As the above-mentioned characteristics of CNC machine tools for CNC machining of parts are:

  (1) a small but repeated batch production of parts;

  (2) the complex geometry of the parts;

3 precious parts machining;

4 need to test all the parts;

5 pieces of trial.

Third, CNC machine tools with numerical control system components

1, composed of CNC system

(1) control panel

  a. It is the operator and the numerical control device for information exchange tool.

  b. Composition: button station, status lights, key array (functions as a computer keyboard) and display.

  c. It is a unique CNC machine parts.

(2) control the media and the input and output devices

  a. Control medium to record parts of the media processing

  b. Enter the output device is CNC system to interact with external devices unit. Interaction information is usually the part program. About the preparation of a good record in the control media type CNC part program debugging system or a good part program stored or recorded by the output device in the corresponding control media.

  c. In addition to using modern CNC system input and output devices to exchange information, in general, have a way to exchange information with the communication capabilities. They are to achieve the CAD / CAM integration, FMS and CIMS basic techniques. The approach are:

  d. serial communication (RS-232 serial port, etc.),

  e. automatic control and regulate the private interface (DNC mode, MAP protocol, etc.)

  f. network technology (internet, LAN), etc.

(3) CNC device (CNC unit)

  a. composed of: computer systems, location control panel, PLC interface board, communication interface board, special function modules and the corresponding control software.

  b. role: according to the input part program for the appropriate treatment (such as trajectory processing, machine tool input and output processing, etc.), then output control commands to the appropriate implementation of the components (servo unit, drive and PLC, etc.), all of which work by the CNC control hardware and software within the coordination, rational organization, the orderly conduct of the whole system work. CNC CNC system is the core unit

(4) servo unit, drives and measuring devices

  a. servo drive unit and

  b. Spindle and spindle motor servo drive

  c. Feed feed servo drives and motors

 Measuring device

  a. position and speed measurement device. Feed servo system to achieve closed-loop control.

  b. role to ensure sensitive and accurate tracking of CNC control instructions:

  c. feed motion command: machining the parts forming movement (speed and position control).

  d. spindle motion commands, cutting processing of the parts movement (speed control)

(5) PLC, the machine I / O circuits and devices

  a. PLC (Programmable Logic Controller): used to complete and logical sequence of actions on I / O control, which consists of hardware and software components;

  b. machine I / O circuits and devices: to achieve I / O control of the implementation of the components (by the relays, solenoid valves, limit switches, contactors and other components of the logic circuit;

  c. Function:

    CNC to accept the M, S, T instruction, decode and convert them into corresponding control signals to control assistive devices to complete the switching action of the corresponding machine

   Accept the operation panel and the machine side of the I / O signals, sent to CNC devices, through their processing, the output commands to control the working status of the CNC and machine movements.

2, CNC machine parts:

   CNC machine tool main body, is to achieve the manufacturing process of the implementation of the components.

Components: the main moving parts, moving parts of the feed (table, extension units and the corresponding transmission), supporting parts (column, bed, etc.) and special equipment (automatic tool exchange system, automatic workpiece exchange system) and auxiliary devices ( such as chip devices, etc.).

Fourth, the classification of CNC machine tools

1, according to processing methods and technology use classification

(1) general CNC machine tools

    General CNC machining process generally refers to a process of automation on the digital control machine tools, such as CNC milling, CNC lathe, CNC drilling, CNC grinding and CNC machine tools and other gear. CNC machine tools in general the degree of automation is still not perfect, tool replacement with artificial parts needed to complete the setup.

(2) machining centers

    Machining center with tool magazine and automatic tool changer CNC machine tools, which CNC milling, CNC boring machine, CNC drilling machine functions together, the parts in one setup, you can conduct most of its processing surface milling, boring , drilling, expanding, so much hinges and tapping machining processes. As the processing center can effectively avoid positioning errors caused by multiple installations, so it applies to products change frequently, parts of complex shape, high precision, small volume production and short production cycle of the product.

2, according to the movement pattern classification

(1) point and control of CNC machine tools

    Shown in Figure 1, the control point is the control system controls only the tool index or table from one point to another point the exact location, then the fixed-point processing, and the path between points without control. The use of such controls are CNC drilling machine, CNC boring machine and CNC jig borer and so on.

2) point linear control of CNC machine tools

     Shown in Figure 2, point and line control is the index of linear control systems in addition to controlling the starting and ending track the exact location, but also between these two points to control the feed rate specified straight line cutting. The use of such controls are CNC milling machine, CNC lathe and CNC grinders.

Figure 3 Schematic outline of the control processing