【文章內容簡介】 mmer, the ram is lifted with oil pressure against an air cushion. The pressed air slows down the upstroke of the ram and contributes to its acceleration during the down stroke .thus。 the electro hydraulic hammer also has a minor power hammer action. Press fing employs a slow squeezing action in deforming the plastic metal, as contrasted with the rapidimpact blows of a hammer. Hydraulic fing press is operated by large pistons driven by highpressure hydraulic or hydrometric system. The squeezing action is carried pletely to the center of the part being pressed, thoroughly working the entire section. These presses are the vertical type and may be either mechanically or hydraulically operated. The mechanical presses, which are faster operating and most monly used, range in capacity from 5000 to 10000 tons. In the fing press a grater proportion of the total work put into the machine is transmitted to the metal than in a drop hammer. The machine and foundation absorb much of the impact of the drop hammer .press reduction of the metal is faster, and the cost of operation is consequently lower. most press fing s are symmetrical in shape ,having surfaces, which are quite smooth, and provide a closer tolerance than is obtained by a drop hammer .however ,drop fing can fe many parts of irregular and plicated shapes more economically. Fing presses are often used for sizing operations on parts made by other fing processes. For small fings closed impression dies are used, and only one stroke of the ram is normally require to perform the fing operation .the maximum pressure is built up at the end of the stroke ,which forces the metal into shape .dies may be mounted as separate units, or all the cavities may be put into a single block. for small fings individuals die units are more convenient .large ingots are now almost always fed with hydraulic presses instead of with steam hammers, since the 畢 業(yè) 設 計 (論 文 )參 考 文 獻 譯 文 work done by a press goes deeper. Further, the press can take a cooler ingot and can work to closer dimensions. The fing should be done at about the same temperature as rolling。 the process improves the physical properties of the steel just as rolling does. In the final fing it is important not to have the steel too hot, for overheated steel will have poor mechanical properties when cooled. in heating for fing the temperature is usually judged by the eye, but where a large number of the same patterns will be made, the pieces to be fed are heated in furnaces in which the temperature is indicated by pyrometers, and often is automatically controlled. 3. welding Welding techniques have bee so versatile that it is difficult nowadays to define “welding”. Formerly welding was “the joining of metals by fusion”, that is, by melting, but this definition will no longer do. Welding was next defined as the “joining of metals by heat”, but this is not a proper definition either. Not only metals can be welded, so can many of the plastics. Furthermore several welding methods do not require heat. Every machinist is familiar with heatless welding method under some circumstances. Besides these, we can weld with sound and even with the famous laser. Faced with a diversity of welding methods that increase year by year, we must here adopt the following definition of welding: welding is the joining of metals and plastics by methods that do not employ fastening devices”. There is also no uniform method of naming welding processes. Some processes are named according to the heat source or shielding method, other certain specialized processes are named after the type of joint produced. Examples are spot and butt welding. But an overall classification can not take account of this because the same type of joint may be produced by a variety of processes. Spot welding may be done by electric resistance, arc, or electronbeam processes and butt welding by resistance, flash or any of a number of other methods. Many welding processes are named depending on the heat applied, equipment used, and type of metal to be joined and the strength of the joint. Soldering is the process of joining two metals by a third metal to be applied in the molten state. Solder consists of tin and lead, while bismuth and cadmium are often included to lower the melting point. One of the important operations in soldering is that of cleaning the