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What is CNC technology and CNC machine tool?

CNC technology and CNC

 

Numerical control technology, referred to as Numerical Control (NC), is a method of controlling mechanical motion and machining processes using digital information. Since modern numerical control is controlled by a computer, it can also be called Computerized Numerical Control (CNC).

 

In order to control the digital movement of mechanical movements and processes, the corresponding hardware and software must be available. The hardware and software used to realize digital information control becomes a numerical control system (Numerical Control System), and the core of the numerical control system is a numerical control device (Numerical Controller).

 

A machine tool controlled by numerical control technology is called a CNC machine tool (NC machine tool). It is a typical mechatronic product that integrates advanced technologies such as computer technology, automatic control technology, precision measurement technology and machine tool design, and is the basis of modern manufacturing technology. Control machine tools are also the earliest and most extensive field of numerical control technology applications. Therefore, the level of CNC machine tools represents the performance, level and development direction of current CNC technology.

 

There are many kinds of CNC machine tools, such as drilling and milling boring machines, turning, grinding, electric machining, forging, laser processing and other special-purpose CNC machines. Any machine that uses CNC technology for control is called NC machine tools.

 

A CNC machine tool (with the exception of a CNC lathe with a rotary tool holder) with an automatic tool changer ATC (Automatic Tool Changer-ATC) is called a machining center (Machine Center-MC). Through the automatic exchange of tools, the workpiece can be processed in multiple steps and clamps, which realizes the combination of process concentration and process, which shortens the auxiliary machining time and improves the efficiency of the machine tool; reduces the number of workpiece installation and positioning, and improves the number of workpieces. Processing accuracy. The machining center is the largest and most widely used CNC machine tool in CNC machine tools.

 

On the basis of the machining center, the processing unit consisting of a multi-table (tray) automatic exchange device (Auto Pallet Changer-APC) and other related devices is called a Flexible Manufacturing Cell (FMC). FMC is not only the concentration of the existing process and the combination of the process, but also through the automatic exchange of the workbench (tray) and the more complete automatic monitoring and monitoring functions, it can carry out unmanned processing for a certain period of time, thereby further improving the processing of the equipment. effectiveness. FMC is the foundation of the Flexible Manufacturing System (FMS) and can be used as a stand-alone automated processing equipment, so it is growing faster.

 

On the basis of the FMC and the machining center, the manufacturing system is called the Flexible Manufacturing System (FMS) by adding logistics systems, industrial robots and related equipment, and centralized, unified control and management by the central control system. FMS can not only carry out long-term unmanned processing, but also realize the full processing and component assembly of multi-variety parts, realize the automation of the workshop manufacturing process, and it is a highly automated advanced manufacturing system.

 

With the development of science and technology, in order to adapt to the changing market demand, for modern manufacturing, it is not only necessary to develop the automation of the workshop manufacturing process, but also to realize the comprehensive from market forecasting, production decision-making, product design, product manufacturing to product sales. automation. A complete manufacturing system that combines these requirements is called a Computer Integrated Manufacturing System (CIMS). CIMS organically integrates a longer production and operation activity, and realizes intelligent production with higher efficiency and higher flexibility. It is the highest stage of development of today's automated manufacturing technology. In CIMS, not only the integration of production equipment, but also the technical integration and functional integration characterized by information. Computer is an integrated tool. Computer-aided automation unit technology is the foundation of integration. The exchange and sharing of information and data is the bridge of integration. The resulting product can be regarded as the material manifestation of information and data.

 

CNC system and its components

 

The basic components of the CNC system

 

The CNC system is the core of all CNC equipment. The main control object of the CNC system is the displacement of the coordinate axis (including moving speed, direction, position, etc.), and its control information mainly comes from CNC machining or motion control programs. Therefore, as the most basic components of the numerical control system should include: the program's input / output device, numerical control device, servo drive these three parts.

 

The input/output device input/output device functions to input and output data such as numerical control machining or motion control programs, machining and control data, machine parameters, coordinate axis positions, and detection switch status. The keyboard and display are the most basic input/output devices necessary for any CNC device. In addition, depending on the CNC system, it can also be equipped with optoelectronic readers, tape drives or floppy disk drives. As a peripheral device, a computer is one of the commonly used input/output devices.

The numerical control device numerical control device is the core of the numerical control system. It consists of input/output interface lines, controllers, operators, and memory. The function of the numerical control device is to compile, calculate and process the data input by the input device through internal logic circuits or control software, and output various information and instructions to control various parts of the machine tool to perform prescribed actions.

 

Among these control information and commands, the most basic are the feedrate, feed direction and feed displacement command of the coordinate axes. It is generated after the interpolation operation, and is supplied to the servo drive, which is amplified by the driver and finally controls the displacement of the coordinate axis. It directly determines the movement of the tool or axis.

 

In addition, depending on the system and equipment, such as: on the CNC machine, there may be spindle speed, steering and start and stop commands; tool selection and exchange instructions; cooling and lubrication device start and stop commands; Open and clamp commands; auxiliary instructions such as indexing of the workbench. In the numerical control system, they are provided to the external auxiliary control device through the interface in the form of signals. The auxiliary control device performs necessary compiling and logic operations on the above signals, and amplifies and drives the corresponding actuators to drive the mechanical parts of the machine tool and hydraulic pressure. Auxiliary devices such as pneumatics complete the actions specified in the instructions.

 

The servo drive servo drive is usually composed of a servo amplifier (also called a driver, a servo unit) and an actuator. On CNC machine tools, AC servo motors are currently used as actuators; linear motors have been used on advanced high-speed machine tools. In addition, DC servo motors are also used in CNC machine tools produced before the 1980s; for simple CNC machines, they are also useful as actuators. The form of the servo amplifier is determined by the actuator and it must be used with the drive motor.

The above is the most basic part of the CNC system. With the development of numerical control technology and the improvement of machine tool performance level, the functional requirements of the system are also increasingly enhanced. In order to meet the control requirements of different machine tools, the integrity and uniformity of the CNC system are guaranteed, and it is convenient for users to use. The system generally has an internal programmable controller as an auxiliary control for the machine. In addition, on the metal cutting machine, the spindle drive can also be a part of the CNC system; on the closed-loop CNC machine, the measuring and detecting device is also essential for the CNC system. For advanced numerical control systems, sometimes even computers are used as the human-machine interface and data management and input/output devices of the system, so that the numerical control system has stronger functions and better performance.

 

In short, the composition of the numerical control system is determined by the performance of the control system and the specific control requirements of the equipment. The configuration and composition are very different, except for the three basic components of the input/output device, numerical control device and servo drive of the machining program. In addition, there may be more control devices. The dotted line frame portion of Figure 1-1 represents a computer numerical control system.

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