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1、Chapter 6 Machining center,6.1 Introduction 6.2 Automatic tool changer 6.3 JCS018A machining center 6.4 Horizontal machining center,6.1 Introduction of machining center,6.1.1 Highlights Simultaneous control of at least three axes. Modern machining centers are able to perform 3D complex contouring ma
2、chining with control of more than three axes; Automatic tool changer (ATC) which is a symbol of machining center significantly improves machining efficiency. It provides possibility of continuous machining of multi-procedure; NC indexing rotary worktable can realize precise angular motion, e.g. 5. T
3、he rotary table with horizontal spindle provides optimum perpendicular surface machining, most of which can be performed with one clamping. Moreover, as a cantilever, short spindle improves machining rigidity;,(4) Intelligent NC system provides software functions to simplify programming, e.g. tool c
4、ompensation, machining circulation can instruction repeating. Some systems can even perform automatic programming; (5) Concentrated machining procedures significantly save time of workpiece clamping, measuring, transferring, storing, and machining tool adjusting. Therefore, machining center is 34 ti
5、mes efficient than conventional maching tools. (6) Continuous automatic machining eliminates manual errors, thus suitable for those workpieces that have complex contour, high accuracy requirement and frequent variety.,6.1.2 Types of machining centers 1. By machining tasks,2. By mechanical layouts 1)
6、 Vertical machining center (VMC) VMC indicates those machining centers with vertical spindle axis. They have relative simple structure, less area occupation and low price. Stationary column Rectangular worktable without rotation Liner axes of X, Y, and Z With NC rotary plate, helix machining is capa
7、ble.,A Five-axis VMC,JCS 018A vertical milling/boring center,2) Horizontal machining center (HMC) HMC indicates those machining centers with horizontal spindle axis. They are usually equipped with indexing rotary worktable. Control of 35 axes, usually X, Y, Z-direction moving and worktable rotation.
8、 It is suitable for machining boxes since it can perform machining of all sides (except top and bottom) with one clamping. Complex construction, large area occupation, heavy, expensive.,Stationary column (spindle box moves in Y direction and worktable in X-Z plane) Stationary worktable (spindle box
9、and column move in X, Y, Z directions),Fig7-3,Gantry machining center,3) Gantry machining center （龙门式加工中心） Similar to gantry milling machines; Usually vertical spindle; Rigid frame work and good thermal symmetry; Suitable for machining precise and complex large parts.,Fig7-4,4) Universal machining c
10、enter Have the functions of VMC and HMC; All except clamping surfaces of a workpiece can be machined with only one clamping; Surface machining is realized by worktable rotation or spindle standing/lying (page 194) ; Very complex constructions and high cost restrict its application.,3. By tool changi
11、ng mechanism 1) Equipped with tool magazine and manipulator Most machining centers (e.g. JCS 018A) adopt this mechanism.,2) Equipped with tool magazine but without manipulator Magazine or part of magazine is arranged where the spindle box can reach; Tool changing is performed by association of magaz
12、ine and spindle box; Most small size machining centers (e.g. XH754 HMC) are in this type.,3) Turret magazine Most small size drilling centers (e.g. ZH5120) adopt turret magazines for its simple construction.,ZH5120 drilling center,4. By NC system functions Axes controllability, e.g. two-axis control
13、, five-axis control Servo mechanism, e.g. open loop, closed loop, semi-closed loop,Fig7-7,6.1.3 Future development of machining center (1) High speed Japanese developed machining centers with maximum spindle rpm of 100,000 and maximum feedrate of 80m/min;,FZ08S machining center (Chiron, Germany) rea
14、ches 0.5s of tool changing period. Worktable moving speed reaches 40m/min during exchange, with repositioning accuracy of 3m.,A high speed machining center with motion acceleration of 2.5g (conventionally 0.10.3g), spindle speed of 60,000 rpm and feedrate of 60m/min has been developed in Germany;,(2
15、) Further increasing accuracy Swiss DIXI 1280TCA machining center reaches coordinate positioning accuracy of 0.003mm/500mm in moving and 3of rotation. (3) Improved intelligence Self-diagnosis realized by thermal sensors, acoustic sensors, electric sensors for safety. E.g. German WERNER TC series HMC
16、 can monitor spindle power, cutting load, tool length and tool damage (by sonar inspection) ; NC device controls peripheral equipments, e.g. robots and measuring instruments.,6.2.1 Rotary turret Turret contains spindle heads, each of which is pre-installed with a tool, e.g. drill, reamer, milling tool etc. Only the spindle head that locates working position connects transmission.,NC milling-boring machine with automatic tool changer,rotary turret head,6.2 Automatic tool changer,Cons
