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1、Lesson 19 Non-conventional Machining,Spark machining,This is one of the more recent additions to mould making methods and, strictly speaking, it should come under the machine tool section.,However, as the principle of operation is different from that of all other basic machine tools it is preferable
2、 to discuss this technique separately.,Spark machining is a process in which steel, or other metals, can be machined by the application of an electrical discharge spark. The spark is localized and metal is progressively removed in small quantities over a period of time. ,First consider the spark ero
3、sion machine. The workpiece, which in our case is a mould insert blank, is mounted on a platen and submerged in a tank containing a dielectric fluid (normally paraffin).,The tank is mounted on the machine base. The tool, which has the required complementary form of the cavity (i.e. similar to a hob)
4、, is mounted in a chuck which is attached to a vertical rack.,A servomotor (not shown) actuates the rack via the pinion. Thus the tool can be moved in the vertical direction with respect to the workpiece.,Both the tool and the workpiece are connected to an electrical supply, and the tool becomes a n
5、egative electrode and the workpiece a positive electrode.,Hardened steel can be machined by this technique so that intricately shaped hardened cavities (which might be impracticable by conventional machine-tool methods because of possible distortion during hardening) can be formed.,Spark machining f
6、inds many applications in the repairing and modifications of hardened cavities and cores.,For instance, a small pocket can be machined into the mould plate and a suitable insert fitted, which saves the necessity of softening the mould plate which the possibility of distortion, etc.,The major limitat
7、ion of the process is that several tools are required to produce one cavity. If the cavity form is complex, the cost of machining these tools may make the use of this technique uneconomic.,Electro-deposition,Electro-deposition is an electrochemical process used to reproduce accurately a cavity or co
8、re form from a given pattern.,The pattern can be made in an easy worked material and is the reverse form to that required. That is, a male pattern is required for a cavity and a female pattern for a core.,Normally it is much easier to machine a male pattern than the reverse cavity form and it is for
9、 this reason that most applications for this technique are for intricate cavity work.,The main limitations of the process are in size and strength. The maximum size of electroformed insert which can be produced is limited to the size of vat available.,Moreover, while nickel-cobalt is relatively hard
10、 (4455 Rockwell C), the copper backing is less hard and this might allow a depression to form on the impression face due to a localised high force.,Notes, The spark is localized and metal is progressively removed in small quantities over a period of time. 电火花的放电位置是固定的，而被加工金属材料是在一定时间内以很小的去除率逐渐加工完成的。,
11、 Both the tool and the workpiece are connected to an electrical supply, and the tool becomes a negative electrode and the workpiece a positive electrode. 工件和电极均与电源相连接，当然，电极作为负极，工件作为正极。, Electro-deposition is an electrochemical process used to reproduce accurately a cavity or core form from a given pattern. 电解法精炼是一种通过精确复制所给出的样模来加工型腔和型芯的电化学方法。,
