Manufacturing Engineering and Technology-4ed Kalpakjian.docx

工程材料读书笔记学校东北大学班级xx姓名xx学号xx日期xx老师xxPart 41.The physical and chemical properties of materials can have various important effects on manufacturing and on the service life of components. These properties and char-acteristics should be considered during material selection because they affect design, service requirements, and compatibility with other materials, including tools, dies, and workpieces. 2.Thermal conductivity and expansion are major factors in the development of thermal stresses and of thermal fatigue and shock, effects which are important in tool and die life in manufacturing operations. Low-expansion alloys (such as Invar) have unique applications. 3.Electrical and chemical properties are important in many advanced machining process-es such as electrical-discharge, chemical, and electrochemical machining. Chemical reactions, including oxidation and corrosion, are important considerations in material selection, design, and manufacturing, as well as on the service life of com- ponents. Passivation and stress-corrosion cracking are two important phenomena. Some physical properties are utilized in manufacturing processes and their control, such as the magnetostriction effect (for ultrasonic machining of metals and nonmetallic materials) and the piezoelectric effect (for force transducers and various other sensors). Commercially pure metals generally do not have sufficient strength for many engi- neering appkations; they must be alloyed with various elements which change their structures and properties. Important concepts in alloying are the solubility of alloy- ing elements in a host metal and the phases present at various ranges of temperature and composition. 4.Alloys come basically in two forms: solid solutions, and intermetallic compounds. Solid solutions may be substitutional or interstitial. There are certain conditions per- taining to the crystal structure and atomic radii that have to be met in order to devel- op these structures. 5.Phase diagrams show the relationships among the temperature, the composition, and the phases present in a particular alloy system. As temperature is decreased at vari- ous rates, correspondingly various transformations take place in microstructures that have widely varying characteristics and properties. Among the binary systems, the most important is the iron-carbon system, which includes a wide range of steels and cast irons. Important components in this system are ferrite, austenite, and cementite. The basic types of cast irons are the following: gray iron, ductile (nodular) iron, white iron, malleable iron, compacted-graphite iron. - 6.The mechanisms for hardening and strengthening metal alloys involve thermal treat- ments: heating the alloy, and subsequently quenching it at varying rates. As a result, important phase transformations take place, producing structures such as pearlite (fine or coarse), spheroidite, bainite, and martensite. Heat treating of nonferrous alloys and of stainless steels involves solution treatment and precipitation hardening. The control of the furnace atmosphere, the quenchants used, the characteristics of the equipment, and the shape of the parts to be heat treated are important considerations. Hardenability is the capability of an alloy to be hardened by heat treatment. The end- quench hardenability test (Jominy) is a method commonly used to determine hard- enability bands for alloys. 7.Case hardening is an important process for improving the wear and fatigue resistance of parts. Several methods are available, among then carburizing, nitriding, induction hardening, and laser hardening. 8.Annealing includes several alternative processes (normalizing, process annealing, stress-relieving, tempering, austempering, and martempering), each having the pur- pose of enhancing the ductility and toughness of heat-treated parts. Part 101.Casting is a solidification process in which molten metal is poured into a mold and allowed to cool. The metal may low through a variety of passages (including pour- ing basins, sprues, runners, risers, and gating systems) before reaching the final mold cavity. Bernoullis thcorcm, the continuity law, and the Reynolds number are the an- alytical tools used in designing, with the goals of an appropriate flow rate and the elimination of defects associated with fluid flow. 2.Solidification of pure metals takes place at a constant temperature; solidification of al- loys occurs over a range of temperatures, depending on composition. Phase diagrams are important tools for identifying the solidification point or points for technologi- cally important materials. 3.Composition and cooling rates of the melt affect the size and shape of grains and den- drites in the solidifying alloy. In turn, the size and structure of grains and dendrites in- fluence properties of the solidified casting. Solidification time is a function of the volume of a casting and its surface area (Chvorinovs rule). 4.The grain structure of castings can be controlled by various means to obtain the de- sired properties. Because metals contract during solidification and cooling, cavities can form in the casting. Porosity caused by gases evolved during solidification can be a significant problem, particularly because of its adverse effect on the mechanical prop- erties of the castings. Various defects can develop in castings from lack of control of material and process variables. 5.Although most metals shrink during solidification, gray cast iron and some aluminum alloys actually expand. Dimensional changes and cracking (hot tearing) are difficul- ties which can arise during solidification and cooling. Seven basic categories of cast- ing defects have been identified. 6.Melting practices have a direct effect on the quality of castings, as do foundry oper- ations such as pattern and mold making, pouring of the melt, removal of cast parts from molds, cleaning, heat treatment, and inspection. Part 111.Casting processes are generally classified as expendable-mold or permanent-mold casting. The most common expendable-mold processes are sand, shell-mold, plaster- mold, ceramic-mold, and investment casting. Common permanent-mold processes include slush casting, pressure casting, die casting, and centrifugal casting. Expend- able-mold casting usually involves lower mold and equipment costs, but produces less dimensional accuracy. 2.The molds used in permanent-mold casting are made of metal or graphite, and are used repeatedly to produce a large number of parts. Because metals are good heat conductors but do not allow gases to escape, permanent molds have fundamentally dif- ferent effects on casting than sand or other aggregate mold materials. In permanent-mold casting, die and equipment costs are relatively high, but the processes are economical for large production runs. Scrap loss is low and dimensional accuracy is relatively high, with good surface details. 3.Other casting processes include squeeze casting (combination of casting and forg- ing), semisolid metal forming, rapid solidification for the production of amorphous al- loys (metallic glasses), and casting of single-crystal components such as turbine blades for the hot stages of jet engines. 4.Melting processes are also important in casting operations. They include proper melt- ing of the metals; preparation for alloying; removal of slag and dross; and pouring the molten metal into the molds. Inspection of castings for any internal or external defects is also important. 5.Castings may subsequently be subjected to further processing, such as heat treatment and various machining operations, to produce final desired shapes and surface characteristics. Part 131.Continuous casting and rolling of both ferrous and nonferrous metals are being im- plemented at a rapid rate. 2.Spray forming of near-net-shape flat products is beginning to compete with direct strip casting. Also, the Osprey process of spray casting of tuhks, sheet, and billets is beginning to reach production status. 3.Further developments are taking place in minimills, in order to roll specialized prod- ucts efficiently and economically. 4.Computer controls are being implemented in all aspects of the rolling and of the sub- sequent processing of plates, sheets, and shapes. Rolling operations are being conducted with better control of material properties and microstructure, and they are, increasingly, producing smoother surfaces. 5.Ring rolling continues to displace machining operations in the production of bearing races. 6.There is an increasing trend toward pursuing environmentally-friendly lubricants. Tighter control of residual lubricants (mill oil) is being investigated, in order to im- prove its reliability for further processing.Part 141.The die design, the reduction in cross-sectional area per pass, and the selection of die materials and lubricants are all important parameters in obtaining drawn products of high quality and of good surface finish. Both external defects and internal defects (chevron cracking) can develop both in extrusion and in drawing; their minimization depends principally on the die angle, the reduction per pass, and the quality of the workpiece material. 2.Forging denotes a family of metalworking processes in which deformation of the workpiece is carried out by compressive forces applied through a set of dies. Forging is capable of producing a wide variety of structural parts with favorable characteris- tics such as strength, toughness, dimensional accuracy, and reliability in service. 3.The forging process can be carried out at room, warm, or high temperatures (above the recrystallization temperature). Workpiece material behavior during deformation, friction, heat transfer, and material-flow characteristics in the die cavity are important considerations, as are the proper selection of die materials, lubricants, workpiece and die temperatures, speeds, and equipment. 4.Various defects can develop if the process is not controlled properly, especially in workpiece quality, billet or preform shape, and die geometry. Computer-aided design and manufacturing techniques are now being used extensively in die design and man- ufacturing, in preform design, in predicting material flow, and in preparing for the possibility of internal and external defects during forging. 5.A variety of forging machines are available, each with its own characteristics and ca- pabilities. Forging operations have been highly automated, using industrial robots and computer controls. 6.In swaging, a solid rod or a tube is reduced in diameter by the reciprocating radial movement of a set of two or four dies. Swaging is suitable for producing short or long lengths of bar or tubing with various internal or external profiles. 7.Because die failure has a major economic impact, die design, die material selection, and die manufacturing methods are of major importance. A variety of die materials and manufacturing methods are available, including advanced material-removal process- es (especially electrical-discharge machining) and subsequent treatment and surface finishing operations. Part 151.Extrusion is the process of forcing a billet through a die, to reduce its cross-section or to produce a wide range of solid or hollow cross-sections. The process is general- ly carried out at elevated temperatures, to reduce forces and to