【導讀】系別.專業(yè).班級.姓名.學號.指導教師.Withmoldponents,withhighefficiency,goodquality,lowcost,economy.theoutputofview,sincethe80's,theUnitedStates,Japanandother. themoldinto.

　　

【正文】 ime on the toolpost , but a burret lathe is capable of holding five or more tools on the revolving turret . The lathe bed must be very solid to prevent the machine from bending or twisting under stress. The headstock incorporates the driving and gear mechanism, and a spindle which holds the workpiece and causes it to rotate at a speed which depends largely on the diameter of the workpiece. A bar of large diameter should naturally rotate more slowly than a very thin bar , the cutting feedshaft from the headstock drives the toolpost along the saddle , either forwards or backwards , at a fixed and uniform speed. This enables rotation of the shaft, and therefore the forward or backward movement of the toolpost. The gear which the operator will select depends on the type of metal which he is cutting and the amount of metal he has to cut off. For a deep or roughing cut the forward movement of the tool should be less than for a finishing cut. Centres are not suitable for every job on the lathe . The operator can replace them by various types of chucks, which hold the work between jaws, or by a frontplate, depending on the shape of work and the particular cutting operation. He will use a chuck, for example, to hold a short piece of work , or work for drilling , boring or screwcutting .A transverse movement of the toolpost across the saddle enables the tool to cut across the face of the workpiece and give it a flat surface. For screwcutting , the operator engages the leadscrew, a long screwed shaft which runs along in front of the bed and which rotates with the spindle. The leadscrew drives the toolpost forward along the carriage at the correct speed, and this ensures that the threads on the screw are of exactly the right pitch. The operator can select different gear speeds , and this will alter the ratio of spindle and laedscrew speeds and therefore alter the pitch of the threads. A reversing lever on the headstock enables him to reverse the movement of the carriage and so bring the tool back to its original position. The purpose of any machine tool is to remove metal. Each machine tool removes metal in a different way. For example , in one type (the lathe )metal is removed by a single point tool as the work is rotated , whereas in another type(the milling machine) a cutter is rotated and metal is removed as the work is progressed beneath it . Which machine tool is to be used for a particular job depends to a large extent upon the type of machining required . There is , however, a certain amount of overlapping and some machine tools can be utilized for several different operations but it must not be assumed that the particular machine tool is restricted to the operation shown. The machine tools which will be found in the modern toolroom are as follow： ⑴ Lathes for turning ,boring and screwcutting, ect. The primary purpose of the lathe is to machine cylindrical forms. The contour is generated by rotating the work with respect to a singlepoint cutting tool. ⑵ Cylindrical grinding machines for the production of precision cylindrical surfaces. The cylindrical grinding machine is used for precision grinding cylindrical mould parts. Metal is removed by the action of abrasive grinding wheel which is brought into contact with a contrarotating workpiece. ⑶ Shaping and planning machines for the reduction of steel blocks and plates to the required thickness and for ‘ squaring up’ these plates .As the primary purpose of a shaping machine is to produce flat blocks. The workpiece is mounted on a table and a reciprocating singlepoint tool removes metal in a series of straight cuts. ⑷ Surface grinding machines for the production of precision flat surfaces . An excellent surface finish bined with accuracy can be achieved on hard or soft steel with the surface grinding machine. The workpiece is mounted on a table which is reciprocated beneath a rotating abrasive grinding wheel and metal is removed in a series of straight cuts. ⑸ Milling machines for the rapid removal of metal , for machining slots, recesses, boring holes, machining splines, etc. Milling is an operation in which metal is removed from a workpiece by a rotating milling cutter. The workpiece can be moved in three directions at right angles to each other with respect to the cutter. The three directions are longitudinal, transverse and vertical, respectively. ⑹ Tracercontrolled milling machines for the accurate reproduction of plex cavity and core principle of tracercontrolled milling machine is similar to that of the vertical milling machine in that an end mill cutter is used to remove metal in a series of cuts. With tracercontrolled milling, however , the required form is generated by causing a tracer, directly coupled to a cutting head , to follow a template or a model. In addition to the above list of major machine tools there is, of course, ancillary equipment without which no toolroom would be plete. This includes power saws , drilling machines, toolpost grinders, hardening and polishing facilities, ect. 四、 Electric discharge machining Electric discharge machining is the latest process being used extensively in the moldmaking field. It can be applied to soft and hard metals, and it exters no mechanical forces that might be detrimental to frail parts. The process is constantly being improved not only in terms of new machines being capable of producing better finishes and closer tolerances at rates of metal removal, but also in terms of toolmakers gaining better knowledge and greater confidence in handling the equipment and producing predictable results. The operation of EDM will be described in greater detail so that it can be applied to existing molds with a view toward improving their performance. A good understanding of EDM, as well as of the c