机电技术专业英语徐起贺张庆良pataalessonEighteen课件教学.pptVIP

* 机电技术专业英语 Lesson Eighteen Text In this section，a short description of the process examples will be given. But assembly and joining processes are not described here. Cold Forming and Hot Forming By applying a stress that exceeds the original yield strength of metallic material，we have strain hardened or cold worked the metallic material，while simultaneously deforming it1. This is the basis for many manufacturing techniques, such as wire drawing. Figure 18.1 illustrates several manufacturing processes that make use of both coldworking and hotworking processes. Material Forming Processes Lesson Eighteen Fine Blanking Fine blanking is a technique used for production of blanks perfectly flat and with a cut edge which is comparable to a machined finish. This quick and easy process is worthy of serious thought when the number of parts justifies the cost of a blanking tool especially when consideration is given to the fact that operations such as shaving are eliminated. Powder Compaction Powder compaction can be characterized as：mass conserving, granular state of material, mechanical basic processflow and plastic deformation. In this context, only compaction of metal powders is mentioned, but generally compaction of molding sand, ceramic materials, and so on, also belong in this category. Lesson Eighteen EDM Electrical discharge machining (EDM) can be characterized as：mass reducing, solid state of work material, thermal primary basic processmelting and evaporation (Figure A.13). In EDM, material is removed by the erosive action of numerous small electrical discharges (sparks) between the work material and the tool (electrode), the latter having the inverse shape of the desired geometry. Each discharge occurs when the potential difference between the work material and the tool is large enough to cause a breakdown in the fluid medium, fed into the gap between the tool and work piece under pressure, producing a conductive spark