模具设计与制造专业英语 黄义俊_ 电子教案统一模板(模具)Unit9.pptVIP

Unit 9 The Special-Purpose Machining Equipment 9.1 Lesson 21 Electro-discharge Machines Electrical discharge machining (EDM), or electro-discharge machining, or spark machining, as it is so-called, is based on the eroding effect of an electric spark on both the electrodes used to produce it. When applying the electro-discharge machining process, the material is eroded as a result of an electrical discharge between tool and work. As in the case of ECM, EDM is a copying process where there is no contact between tool and work. Contrary to ECM, there is some erosion of the tool in EDM, which must be allowed for in the tool design to ensure accuracy of machining. A further difference arises from the fact that in EDM there is no fixed tool feed, but the gap size must be maintained in accordance with the rate of metal removal and the conditions existing within the gap.[1] EDM is a form of metal removal in which pulsating direct current is applied to a shaped tool (electrode) and a workpiece, both of which are capable of conducting electricity. The two are held close to each other with a non-conducting fluid serving as an insulator between them．When a voltage high enough to break down the insulator is reached, a spark jumps the gap between the tool and workpiece. As a result, this spark removes a small portion of material. The main advantage is that electrical discharge machining processes with good surface finish and can machine metal of any hardness. 9.2 Lesson 22 Types of Electro-discharge Machines There are two basic types of electro-discharge machines described as below: ? Electro-discharge die-sinking machines—The construction principles of an EDM die-sinking machine are shown in Figure 9-1. Spark erosion takes place in a container filled with the dielectric, in which the workpiece is clamped. The controlled feed of the electrode is through an electro-hydraulic or electro-mechanical servo system. The el