机械制造技术基础课件-chapter4-section2(new).pptx

4.2 Grinding machines,Grinding is the most important of the abrasive processes ,and it is the most common of all metalworking operations. Grinding is traditionally used to finish parts whose geometries have already been created by other operations. In addition to these traditional uses, applications of grinding are expanding to include more high-speed , high-material-removal operations.,Compare to other machining, abrasive machining processes have three characteristics. 1. each cutting edge is very small , and many of these edges can cut simultaneously. 2.extremely hard abrasive grits can be produced, including diamonds, very hard materials such as hardened steel, glass, carbides, and ceramics . 3. In grinding, you have no control over the actual tool geometry (rake angles, cutting edge radius) or all the cutting parameters (depth of cut),4.2 Grinding machines,Cylindrical grinding operations can be divided into two basic types : external cylindrical grinding and internal cylindrical grinding .,(1) cylindrical center-type grinders (外圆磨床) Cylindrical center-type grinders are used for grinding straight and tapered round pieces, round parts with curved lengthwise profiles, fillets, shoulders , and faces .,The size of a cylindrical center-type grinding machine is usually designated by the diameter in millimeters and length in millimeters the largest workpiece the machine can nominally take between centers .,A universal cylindrical centre-type grinder 1, bed; 2, headstock; 3,auxiliary wheelhead 4, wheelhead; 5 foothead; saddle; 7, handwheel; 8, worktable Video (津上精密数控磨床加工_halfok.flv),Movements of an external cylindrical grinding machine,4.2 Grinding machines,(2) Internal cylindrical grinding,An internal cylindrical grinding operates somewhat like a boring operation . The workpiece is usually held in a chuck and rotated to provide surface speeds of 23 to 60 m/min . The wheel spindles is rotated at 3000 rpm or higher. The wheel is fed in either of two ways :traverse feed , which is more common, or plunge feed.,1, bed; 2, worktable; 3,headstock; 4, wheelhead; 5 saddle; Video (內圓磨床),4.2 Grinding machines,(3) Centerless grinding,Centerless grinding makes it possible to grind both external and internal cylindrical surfaces without requiring the workpiece to be mounted between center or in a chuck . The principle of centerless external grinding is illustrated in fig 3-63 that the grinding wheel and a regulating wheel are required.,Viedo (無心磨床),Centerless grinding machine,centerless grinding 1, grinding wheel; 2, work rest blode; 3,regulating wheel; 4, workpiece; (b) through-feed centerless grinding (c) in-feed centerless grinding,The typical setup in internal centerless grinding is shown in Fig .3-65 . In place of the rest blade , two support rolls are used to maintain the position of the work.,Grinding wheels,A grinding wheel consists of abrasive particles and bonding material . The bonding material holds the particles in place and establishes the shape and the structure of the wheel . A simple grinding wheel is shown schematically in fig 3-66.,