电子教案统一模板(数控)Unit2.ppt

Unit 2 NC/CNC Machining Equipment,2.1 Lesson 3 Types of CNC Machining Centers,Machining centers are the latest development in CNC technology. These systems come equipped with automatic tool changers with the capability of changing up to 90 or more tools.1 Many are also fitted with the movable rectangular worktables called pallets. The pallets are used to automatically load and unload work pieces. At a single setup machining centers can perform such operations as milling, drilling, tapping, boring, and so on. 2 Additionally, by utilizing indexing heads, some centers are capable of executing these tasks on many different faces of a part and at specified angles.,Turning centers with increased capacity tool changers are also making strong appearance in modern production shops.3 These CNC machines are capable of executing many different types of lathe cutting operations simultaneously on rotating part. In addition to machining centers and turning centers, CNC technology has also been applied to many other types of manufacturing equipment. Among these are wire electrical discharge machines (WEDM) and laser cutting machines.,WEDM machines utilize a very thin wire as an electrode. The wire is stretched between two rollers and cuts the part like a band-saw. Material is removed by the erosion caused by a spark that moves horizontally with the wire. CNC is used to control horizontal table movements. WEDM machines are very useful for producing mold inserts, extrusions and trim dies as well as form tools. 4,Laser cutting CNC machines utilize an intense beam of focused laser light to cut the part. Material under the laser beam undergoes a rapid rise in temperature and is vaporized. If the beam power is high enough, it will penetrate through the material. Because no mechanical cutting forces are involved, lasers cut parts with a minimum of distortion and have been very effective in machining slots and drilling holes.,2.2 Lesson 4 CNC Turning Center,CNC turning centers, while unlike chucking centers, are designed mainly for machining shaft-type work-pieces which are supported by a chuck and a heavy-duty tailstock center. On four-axis machines，two opposed turrets, each capable of holding different tools, are mounted on separate cross-slides, one above and one below the centerline of the work.1 Because the turrets balance the cutting forces applied to the work, extremely heavy cuts can be taken on a work-piece when it is supported by the tailstock. The dual turrets also lend themselves to other operations, such as:,1. Roughing and finishing cuts in one pass 2. Machining different diameters on a shaft simultaneously 3. Finish turning and threading simultaneously 4. Cutting two different sections of a shaft at the same time When the turning center is equipped with a steady-rest, operations such as facing and threading may be performed on the end of a shaft.,The most complex CNC machine tools are the turning center, shown in Figure 2-1(The typical turning center with a ten-station turret that accepts quick-change tools). The majority of NC/CNC machine tools are equipped with automatic tool changers, such as magazines on machining centers and turrets on turning centers.,2.3 Reading Materials 3 The Advantages of CNC Machines,CNC machines have many advantages over conventional machines, some of them are: 1. There is a possibility of performing multiple operations on the same machine in one setup. 2. Because of the possibility of simultaneous multi-axis tool movement, special profile tools are not necessary to cut unusual part shapes. 3. The scrap rate is significantly reduced because of the precision of the CNC machine and lesser operator impact.,4. It is easy to incorporate part design changes when CAD/CAM systems are used. 5. It is obvious to improve part quality and repeatability. 6. To reduce time to manufacture parts and increase production significantly. 7. Better control of tool motions under optimum cutting conditions. 8. Many different CNC programs can be stored in the MCU.,2.4 Reading Materials 4 The Disadvantages of CNC Machines,At the same time, CNC machines also have some disadvantages: 1. They are quite expensive. 2. They have to be programmed, set up, operated, and maintained by highly skilled personnel. Obviously, CNC machines have more advantages than disadvantages. The companies that adopt CNC technology increase their competitive edge. As always with new techn