Chapter 4 NC lathe,4.1 Introduction 4.2 Transmission of NC lathe 4.3 Turning center 4.4 Automatic tool changer,4.1 Introduction,4.1.1 Capabilities (page157) Turning revolution surfaces of shafts, bushes, plates, e.g. inner or outer cylindrical surfaces, conical surfaces, threads, other high accuracy contours, etc. Equipped with turning tools, drills, reamers, boring tools Machining accuracy reaches IT5IT6 Roughness Ra1.6m.,Economy NC lathe,(1) Economy NC lathe Modification based on conventional lathe Open loop servo control by single board microcomputer Simple construction and economy,Lack of automatic tool tip radius compensation and constant linear velocity functions.,4.1.2 Capabilities and types (page157),Full-functional NC lathe,(2) Full-function NC lathe. Known as NC lathe or standard NC lathe; Equipped with standard control system with high resolution（高分辨率）CRT, graphics simulation, tool compensation function and communication or network ports;,Closed or semi-closed loop servo control; Multi-axis controllability; High rigidity, high accuracy and high efficiency.,(3) Turning center Generally similar to full-functional NC lathe; Equipped with tool magazine, ATC, indexing device, milling power unit and robot arms; Different machining process such as turning, milling, drilling, reaming screw tapping, etc. can be performed with one clamping; Costly,Robot control cabinet,FMC lathe,(4) FMC lathe Actually a flexible manufacturing cell consists of NC lathe, robot, etc. Capable to perform automatic transfer, clamping for workpiece and automatic machining preparations.,4.1.3 Structure and features of NC lathe 1. Structure of NC lathe (1) Headstock Locates on the left of bed; Supports spindle and accommodates transmissions,(2) Turret tool post Locates on slide to hold tools for different machining purpose; Tools can be automatically selected as required,(3) Slides Longitudinal slide (Z-direction, locates on ways) Cross slide (X-direction, locates on longitudinal slide) Slides motion realize feeding in Z- and X-direction.,(4) Tailstock Locates on ways and can perform longitudinal adjusting; The center on tailstock is an assistant support for workpiece during machining; Can carry tools e.g. drill, reamer for machining,(5) Bed Locates on base; Carries main components of the lathe and ensures their accurate relative positions during machining,(6) Base. Supports bed and other components (e.g. shield, chip remover); Connected to electric control cabinet,(7) Shield Locates on base; Protects operator; Keeps clean,(8)Hydraulic transmission Drives assistant motions, e.g. spindle rpm shift, tailstock moving, automatic clamping (9) Lubricating system Provides lubrication and cooling for mechanical components (10) Cutting fluid supply Circulates cutting fluid for machining (11) Electric control system Consists of NC system (including NC device, servo system and PLC) Performs automatic control for the lathe.,2. Characteristics of modern NC lathe (1) High accuracy. Due to improved performance of control systems and optimized mechanical construction (2) High efficiency. Due to innovative tool materials and optimized mechanical components (e.g. rigidity, spindle rpm, rated power). It is 23 times efficient than conventional horizontal lathes. With the increasing complexity of the workpiece, its efficiency becomes obvious (3) High flexibility. More than 70 of all kinds of workpiece (in small batch production) can be automatically machined,(4) High reliability. Operating between failures reaches up to 30,000 hours; (5) Versatility. Both rough and finish machining can be performed. All or most machining processes can be completed with one clamping; (6) Modularized design. A lathe consists of functional modules that can be replaced as required to perform different machining tasks.,1 Headstock 8 Feeding mechanism 12 Fast moving mechanism 14 Tool post 19 Clamping mechanism 22 Tailstock 27 bed,4.1.4 Layout of NC lathes 1. Factors that determine layouts,Relationship between workpiece dimensions and lathe layout,Double column vertical lathe,2. Layouts of headstock and tailstock Similar to that of conventional lathe.,Layouts of NC horizontal lathe Horizontal bed - horizontal carriage Inclined bed - inclined carriage Horizontal bed inclined carriage Vertical bed vertical carriage,3. Layouts of bed and carriage The layouts of bed and ways affects characteristics of the lathe.,(1) Horizontal bed horizontal carriage Good manufacturability of bed and plane of guideways; Horizontal tool post has better motion accuracy thus applied on large NC lathes or small precise NC lathes; Less space under bed affects chip removing Horizontal carriage requires the lathe large in width.,(2) Inclined bed- inclined carriage The inclination of bed can be in 30, 45, 60, 75and 90, where 90bed inclination is know as vertical bed vertical carriage; Medium and small size NC lathes usually have 60inclination bed.,Small inclination