What is a CNC milling machine?

2022-08-05

CNC milling machine is also called CNC (Computer Numerical Control) milling machine. In English, it means a milling machine controlled by digital signals with an electronic meter. [1]

CNC milling machine is a kind of automatic processing equipment developed on the basis of general milling machine, the processing process of both is basically the same, the structure is also somewhat similar. CNC milling machines are divided into two categories: those without tool magazines and those with tool magazines. Among them, the CNC milling machine with tool magazine is also called machining center.
The development of science and technology and the rise of the world's advanced manufacturing technology and continue to mature, the CNC machining technology has put forward higher requirements; ultra-high-speed cutting, ultra-precision machining and other technology applications, the CNC machine tool CNC system, servo performance, spindle drive, machine structure and other higher performance indicators; the rapid development of FMS and CIMS continues to mature, and will be on the reliability of CNC machine tools, communication function, artificial intelligence and adaptive control and other technologies to put forward higher requirements. With the development of microelectronics and computer technology, the performance of the CNC system is increasingly perfect, the field of application of CNC technology is expanding.
CNC milling machine is a processing function is very strong CNC machine tools, the rapid development of machining centers, flexible machining units, etc. are in the CNC milling machine, CNC boring machine on the basis of the production, both can not be separated from the milling method. As the most complex CNC milling process, the need to solve the most technical problems, therefore, people in the research and development of CNC systems and automatic programming language software, but also has been the focus of milling processing.

The emergence and development of CNC machine tools

With the rapid development of social production and science and technology, mechanical products are increasingly sophisticated and complex, and the demand for frequent changes, especially in the field of astronautics, shipbuilding, military and other mechanical parts required, high precision requirements, complex shapes, small batch. Processing of such products require frequent modification or adjustment of equipment, ordinary machine tools or a high degree of specialization of automated machine tools have been unable to adapt to these requirements. In order to solve the above problems, a new type of machine tools - CNC machine tools came into being. This new machine tool with strong adaptability, high processing accuracy, stable processing quality and production efficiency and other advantages. It is a comprehensive application of electronic computers, automatic control, servo drives, precision measurement and new mechanical structure and other aspects of technological achievements, is the future direction of the development of CNC machine tools.

CNC Milling Machine Machining

The shape of the machined surface of a milling machine is generally made up of straight lines, circular arcs or other curves. The operator of a general milling machine follows the requirements of the drawing. Constantly changing the relative position between the tool and the workpiece, and then with the selected milling tool speed, so that the tool can cut and process the workpiece, it can process a variety of different shapes of the workpiece.
CNC machine tool processing is to divide the coordinates of the tool and workpiece movement into the smallest amount of units, that is, the minimum amount of displacement. By the CNC system according to the requirements of the workpiece program, so that the coordinates move a number of minimum displacement, so as to achieve the relative movement of the tool and the workpiece, in order to complete the processing of parts.

Functional characteristics

In addition to the characteristics of ordinary milling machine processing, CNC milling processing also has the following characteristics.
1, strong adaptability and flexibility of parts processing, can process the contour shape is particularly complex or difficult to control the size of the parts, such as mold-type parts, shell-type parts, etc..
2, can process ordinary machine tools can not be processed or difficult to process parts, such as complex curve parts described by mathematical models and three-dimensional space surface parts.
3, can process a clamping positioning, the need for multi-process processing of parts.
4, high processing accuracy, stable and reliable processing quality, the pulse equivalent of the CNC device is generally 0.001mm, high-precision CNC system up to 0.1μm, in addition, CNC machining also avoids operator error.
5, a high degree of production automation, can reduce the operator's labor intensity. Facilitate the automation of production management.
6, high production efficiency, CNC milling machine generally does not need to use special fixtures and other special process equipment, in the replacement of the workpiece only need to call the machining program stored in the CNC device, clamping tools and adjust the tool data can be, thus greatly reducing the production cycle. Secondly, the CNC milling machine has the function of milling machine, boring machine, drilling machine, so that the process is highly concentrated, greatly improving the production efficiency. In addition, the spindle speed and feed speed of CNC milling machine are steplessly variable。

Basic structure

There are various forms of CNC milling machines, and although different types of CNC milling machines differ in composition, they have many similarities. The following XK5040A CNC vertical lifting table milling machine as an example to introduce its composition. D Ⅺ saw 040A type CNC vertical lifting table milling machine with Ⅳ four 3MA CNC system, using a full digital AC servo drive. The machine tool consists of six main parts. That is, the bed part, milling head part, table part, cross-feed part, lifting table part, cooling, lubrication part. The internal layout of the bed is reasonable, with good rigidity, the base is equipped with four adjusting bolts, easy to adjust the machine level, the cutting fluid reservoir is located inside the machine base.

System classification

①Cooling system. The cooling system of the machine tool is composed of cooling pump, outlet pipe, return pipe, switch and nozzle, etc. The cooling pump is installed in the inner cavity of the machine base, and the cooling pump will beat the cutting fluid from the reservoir in the base to the outlet pipe, and then sprayed by the nozzle to cool the cutting area.
② lubrication system and way. Lubrication system is composed of manual lubrication donor oil pump, oil distributor, throttle valve, oil pipe and so on. The machine tool adopts the cycle lubrication method, with manual lubricant pump, through the oil distributor to the spindle sleeve, longitudinal and transverse guide and three-way ball screw lubrication, in order to improve the service life of the machine tool.
From the digital control technology features, due to the use of CNC machine tools with servo motors, the application of digital technology to achieve the direct control of the machine tool execution of the sequence of work and movement displacement, the traditional machine tool gearbox structure was canceled or partially canceled, and thus the mechanical structure is greatly simplified. Digital control also requires the mechanical system has a high transmission stiffness and no transmission gap to ensure the implementation of control instructions and control quality. At the same time, due to the level of computer and control capabilities continue to improve, the same machine tool allows more functional components at the same time to perform the various auxiliary functions required has become possible, and thus the mechanical structure of CNC machine tools than traditional machine tools have a higher degree of integration of functional requirements.
From the requirements of the development of manufacturing technology, with the emergence of new materials and new processes, as well as market competition for low-cost requirements, metal cutting processing is moving toward higher and higher cutting speed and accuracy, higher and higher production efficiency and system more and more reliable direction of development. This requires the development of CNC machine tools based on the traditional machine tool precision, drive power is more too, mechanical mechanisms, static and thermal stiffness is better, more reliable work, can achieve a long time with continuous operation and as little downtime.

Milling head part

The milling head part consists of two parts: the stepped (or stepless) gearbox and the milling head. The spindle of the milling head is supported on the high precision bearings. The spindle is equipped with quick tool change nut and the front end taper is 1$0505 taper; the spindle adopts mechanical stepless speed change, which has wide adjustment range, smooth transmission and convenient operation. The brake mechanism can make the spindle brake quickly, which can save the auxiliary time. When braking, the spindle will be braked immediately by propping the stop ring through the brake handle. When starting the main motor, care should be taken to loosen the spindle brake handle. The milling head is also equipped with servo motor, internal gear pulley, ball screw and spindle sleeve, which form a vertical (z-direction) feed drive chain to make the spindle move in a vertical linear direction.
The table and bed saddle are supported on the wide horizontal guide rail of the lifting table, and the longitudinal feed of the table is driven by the servo motor installed at the right end of the table. The longitudinal feed of the table is driven by a servo motor mounted on the right end of the table. The left end of the table is equipped with a hand wheel and a dial for manual operation. The longitudinal and transverse guideway surfaces of the bed saddle are TuRcllE B veneer surfaces, thus improving the wear resistance, smoothness of movement and accuracy maintenance of the guideway and eliminating low-speed crawling phenomenon.

Foundation parts

CNC milling machine foundation parts usually refers to the bed, column, beam, table, base and other structural parts, its size is large (commonly known as large parts), well constitute the basic framework of the machine tool. Other parts are attached to the foundation pieces, some parts also need to move along the foundation pieces. As the base member plays a supporting and guiding role, and thus the base member of this requirement is good stiffness.

Variable-frequency Drive (VFD) is a power control device that applies variable frequency technology and microelectronics to control AC motors by changing the frequency of the motor's operating power supply. In the CNC machine tool, the frequency converter is mainly used to control the action of the spindle.

Spindle box

Including the spindle box and spindle drive system, used to clamp the tool and drive the tool rotation, spindle speed range and output torque have a direct impact on the machining.

Feed servo

It consists of feed motor and feed actuator, which realize the relative motion between tool and workpiece according to the programmed feed speed, including linear feed motion and rotary motion.