1、Summary review,How to ensure or improve the quality of casting during casting process? The process, characteristics, applications of various casting processes.,Casting processes,The various processes are distinguished primarily by the mold material and pouring method.,Expendable-mold casting process
2、es,Multiple-use mold casting processes,permanent mold casting - gravity Low-pressure permanent mold casting - low pressure Vacuum permanent mold casting - vacuum die casting- high pressure Centrifugal casting- the inertial forces （惯性力） of rotation,Pouring method in multiple-use-mold casting processe
3、s,Problem in die casting,gas porosity Precaution: smooth metal flow (large gates, lower injection pressure) good venting proper application of pressure(lower injection pressure + higher pressure during solidifying) introducing oxygen into the mold,2.4 Powder Metallurgy ( P/M ),1 Introduction(1) What
4、 is powder metallurgy (definition)(2) characteristics and its application(3) history, development,(1) What is powder metallurgy?,It is a process by which fine powdered materials are blended, pressed into a desired shape (compacted), and then heated (sintered) in a controlled atmosphere to bond the c
5、ontacting surfaces of the particles and establish the desired properties.,http:/www.mpif.org/DesignCenter/videoclips.asp?linkid=68,(2) characteristics and its application,Advantages: suit for mass production of small, intricate parts of high precision, often eliminate the need for additional machini
6、ng or finishing little material waste can utilize unusual materials or mixtures can control the degrees of porosity or permeability,(2) characteristics and its application,Major areas of application: The P/M process has strong economical advantage. The desired properties and characteristics would be
7、 difficult to obtain by any other methods.,(3) history, development,a crude form in Egypt as early as 3000 B.C. mass manufacturing the mid- or late nineteenth century ( copper coins and medallions, platinum ingots, and tungsten wires) tungsten carbide cutting tool-tips and nonferrous bushings, self-
8、lubricating bearings and metallic filters by the 1920s a period of rapid technological developments after World War (automotive applications),(3) history, development,Full density products emerged in the 1960s High-performance superalloy component a highlight of 1970s Commercialization of rapidly-so
9、lidified and amorphous powder, and the development of P/M injection molding technology in the 1980s Recent years,2.4 Powder Metallurgy 粉末冶金,2 Basic processFour basic steps:powder manufacturemixing or blendingcompactingsintering,视频,2 Basic process,(1) powder powder manufacture 粉末制备melt atomization 熔体
10、雾化(Figure1.4-2), powder manufacture 粉末制备,melt atomization 熔体雾化 produce prealloyed powders other methods chemical reduction of crushed oxides or ores electrolytic deposition from solutions or fused salts pulverization or grinding of brittle(脆） materials thermal decomposition of hydrides or carbonyls
11、precipitation from solution condensation of metal vapors,(1) Powder, powder manufacture rapid solidified powder (microcrystalline and amorphous) rapid cooling: microcrystallinepropertiesamorphousproperties production methods: atomization of rapid coolingsplat quenching(喷溅淬火) of a metal stream onto a
12、 cooling surface,(1) Powder, powder manufacture rapid solidified powder powder testing and evaluationflow rateapparent density表观密度compressibility压缩性green strength湿态强度,2 Basic process,(2) powder mixing and blending粉末搅拌及混合,powders,+,lubricants or binders,Various sizes, different compositions,be remove
13、d finally,composite materials,2 Basic process,(3) compacting intention: get desired characteristics ?high density, uniformity, green strength for handing and transport,http:/www.mpif.org/DesignCenter/videoclips.asp?linkid=68,2 Basic process,(3) compacting ways: mechanical presses and rigid tools, or
14、 hydraulic and hybrid （复合）presses,typical compaction sequence for a mechanical press,http:/www.mpif.org/DesignCenter/videoclips.asp?linkid=68,(3) compacting, ways: mechanical presses and rigid tools, or hydraulic and hybrid （复合）presses be used widely, suit for small productsdynamic methods: an explosively induced shock wave provides the compaction pressuremetal forming processes: rolling, forging, extrusion, swaging （型锻）,Thank you!,
