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1、Chapter 12 Metal Casting: Design, Materials and Economics12章章 金属金属铸件：件： 设计、材料和、材料和经济性性制造工程与技术12MetalCastingContent12.1 Introduction 简介12.2 Design Considerations 设计考虑12.3 Casting Alloys 铸造合金12.4 The Economics of Casting 铸件经济性制造工程与技术12MetalCasting12.1 IntroductionIn the preceding two chapters, it was
2、noted that successful casting practice requires carefully control of al large number of variables. These variables pertain (属于) to the particular characteristics of the metals and alloys cast, the method of casting, the mold and die materials, the mold design and various process parameters. The flow
3、 of the molten metal in the mold cavities, the gating systems, the rate of cooling, and the gases evolved all influence the quality of a casting.从前两章中的介绍中，我们知道了只有对大量的变量进行仔细的控制才能获得成功的铸造生产。这些变量与金属和合金的铸造特性、铸造方法、铸型设计以及各种工艺参数相关。金属液在型腔中的流动、浇注系统、冷却率和卷入气体等都影响铸件质量。 制造工程与技术12MetalCastingThis chapter describes
4、 the general design considerations and guidelines for metal casting and presents suggestions for avoiding defects. It also describes the characteristics of the alloys that are commonly cast, together with their typical applications. The economics of casting operations are just as important as the te
5、chnical considerations that have already been described, so this chapter also outlines the basic economic factors relevant to casting operations.本章讨论金属铸件的一般设计考虑和指导方针，并给出如何避免铸件缺陷的建议。还结合器典型应用来讨论常用铸造合金的特性。铸造的经济性与已讨论过的技术性问题一样重要，因此本章也简略讨论与铸造有关的基本经济因素。 制造工程与技术12MetalCasting12.2 Design ConsiderationsThese
6、principles（原则） were established primarily through practical experience, but new analytical methods, process modeling, and computer-aided design and manufacturing techniques are now coming into wider use, improving productivity (生产力) and the quality of castings and resulting in significant cost savin
7、gs. 制造工程与技术12MetalCasting12.2.1 Design for expendable-mold casting (一次性模铸造的设计) 1. Corners, angles and section thickness. Sharp corners (方角), angles (倒角) and fillets (肩角) should be avoided (Fig. 12.1), because they act as stress raisers and may cause cracking and tearing of the metals (as well as of
8、the dies) during solidification. Fillet radii should be selected to reduce stress concentrations and to ensure proper liquid-metal flow during the pouring process. Fillet radii usually range from 3mm to 25mm, although smaller radii may be permissible (容许的) in small castings and in limited applicatio
9、ns. On the other hand, if the fillet radii are too large, the volume of the materials in those regions is also large and, consequently, the rate of cooling is lower. The most significant considerations are identified (标示) and addressed (强调).Fig. 12.1 Suggested design modifications to avoid defects i
10、n castings. Note that sharp corners are avoided to reduce stress concentrations.制造工程与技术12MetalCastingSection changes in castings should be smoothly blended into each other. Because the cooling rate in regions with large thickness is lower, they are called hot spots (热节), which can be developed to sh
11、rinkage cavities and porosity (缩孔和疏松). It is important to maintain (保持保持), as much as possible, uniform cross-sections and wall thicknesses throughout the casting to avoid shrinkage cavities. Fig. 12.2 Examples of designs showing the importance of maintaining uniform cross-sections in castings to av
12、oid hot spots and shrinkage cavities制造工程与技术12MetalCastingFig. 12.3 Examples of design modifications to avoid shrinkage cavities.Fig. 12.4 The use of metal padding (chills) to increase the rate of cooling in thick regions in a casting to avoid shrinkage cavities.制造工程与技术12MetalCasting2. Flat areas (平平
13、面面面面积). Large flat areas (plain surfaces) should be avoided, because they may warp (翘曲) during cooling because of temperature gradients or develop poor surface finish. Flat surfaces can be broken up with ribs (肋条) and serrations.3. Shrinkage. There should be allowances for shrinkage during solidific
14、ation. Stagger: 错 开 排 列 , intersection geometry: 横截面几何形状. Pattern dimensions should also provide for shrinkage of the metal during solidification and cooling. Patternmakers shrinkage allowances: 模型制作的收缩允许率, usually range from about 10mm/m to 20mm/m.4. Parting line. To be along a flat plane, rather t
15、han contoured, located at the corners or edges of castings. It is important for mold design and affects many factors.Fig. 12.5 Redesign of a casting by making the parting line straight to avoid defects制造工程与技术12MetalCasting5. Draft (减减面面率率). To enable removal of the pattern without damaging the mold.
16、 Ranging from 5mm/mm to 15mm/m, angles: 0.5o to 2o, for inside angles, 1o to 4o. 6. Dimensional tolerance (尺尺寸寸公公差差). As wide as possible, within the limits of good part performance, usually 0.8 to 6mm for small and large castings.7. Machining Allowance. Allowances usually range from about 2mm to 5m
17、m for small castings to more than 25mm for large castings.8. Residual stress (残残余余应力力). The different cooling rates with the body of a casting cause residual stress. Stress relieving may thus be necessary to avoid distortions in critical applications.制造工程与技术12MetalCasting12.2.3. Design for Permanent
18、-Mold Casting: 永久型模永久型模铸设计It is similar with expendable-mold casting, except draft angles reduce to 1/2 to 1/4o. galling: 咬住Fig. 12.7 Examples of undesirable and desirable design practices for die-cast parts. Note that section-thickness uniformity is maintained throughout the part.制造工程与技术12MetalCast
19、ing12.3 Casting Alloys: 铸造合金造合金Their properties and casting manufacturing characteristics are summarized in Fig. 12.8 and Tables 12.2 to 12.5.Piston: 活塞，clutch housing: 离合器壳，intake manifold: 进气管， pump：泵，gear blank：齿轮坯料， propeller：螺旋桨， heavy-duty： 重载的，block：缸体， drum：鼓，crankcase：曲轴箱，malleable iron: 韧性
20、铁，bearing：支座，railroad rolling stock: 铁路机车，blade: 叶片，die block：模具坯料，undercarriage：起落架，rock crusher jaw：碎石机卡抓， mill line：磨机衬里， shot blasting nozzle：喷丸清理喷口，brake shoe：制动块，pulverize：研磨机，radiator grill：散热器护栅，Table 12.3: sanitary ware: 卫生洁具，hardware: 五金器件，coupling：管接头，propeller hub： 螺旋桨毂制造工程与技术12MetalCast
21、ingFig. 12.8 Mechanical properties for various groups of cast alloys. Note that gray iron has very little ductility and toughness. Compared with most other cast alloys ,some of which undergo considerable elongation and reduction of area in tension. Note also that even within the same group, the prop
22、erties of cast alloys vary over wide range, particularly for cast steels.制造工程与技术12MetalCasting12.3.1. Nonferrous casting alloys: 非非铁磁性磁性铸造合金造合金1. Aluminum-based alloys (铝合金合金) have high electrical conductivity (电导率) and generally good atmospheric corrosion resistance. Nontoxic (非毒性) and good mach in
23、ability. Application: architectural and decorative use, automobile components. Fig. 12.8 Mechanical properties for various groups of cast alloys. Note that gray iron has very little ductility and toughness. Compared with most other cast alloys, some of which undergo considerable elongation and reduc
24、tion of area in tension. Note also that even within the same group, the properties of cast alloys vary over wide range, particularly for cast steels.Parts made of Al- and Mg-based alloys are known as light-metal casting. 制造工程与技术12MetalCasting2. Magnesium-based alloys with lowest density of all comme
25、rcial casting alloys, good corrosion resistance and moderate strength.3. Copper-based alloys, good electrical and thermal conductivity, corrosion resistance and nontoxicity, wear properties, suitable for bearing materials.4. Zinc-based alloys, good fluidity and sufficient strength for structural app
26、lications, common use in die casting.5. High-temperature alloys, Titanium alloys and superalloys, melting temperature up to 1650oC; special techniques are used to cast these alloys into jet- and rocket-engine components.制造工程与技术12MetalCasting12.3.3 Ferrous Casting Alloys 铁磁性磁性铸造合金造合金Cast irons, large
27、st amount of all metals cast, easily are cast into intricate shapes, good wear resistance, hardness, and good mechanability. Including gray cast iron (gray iron:灰铸铁), ductile (nodular or spheroidal: 粒状，球状的) iron （球磨铸铁）, white iron （白口铁）, malleable iron （ 可锻铸铁） , and compacted graphite iron (蠕墨铸铁).a.
28、 Gray cast iron , few shrinkage cavities and little porosity, termed ferric, pearlitic, and martensitic gray cast irons. Typical uses are in engine blocks, machine bases, electric-moter housings, pipes and wear surfaces for machines. Specified in many classes, as shown in Table 12.4: good damping (
29、阻尼，消声) and thermal conductivity but low ductility.Commonly cast ferrous alloys are as follows:制造工程与技术12MetalCastingb.Ductile (nodular) cast iron, typically used for machine parts, and crankshafts, specified by two-digit numbers, poor damping and thermal conductivity, high tensile strength and fatigu
30、e resistance.c.White cast iron used mainly in liners for machinery to process abrasive materials rolls for rolling mills, and railroad-car brakes because of its extreme hardness and wear resistance.d.Malleable iron. Used for railroad equipment and various types of hardware. Specified by a five-digit
31、 designation (命名).e.Compacted graphite iron. First produced commercially in 1976, with properties that fall between those of gray and ductile irons.制造工程与技术12MetalCasting2. Cast steels. The high temperatures involved present difficulties in the selection of mold materials, particularly in view of the
32、 high reactivity of steels with oxygen, in melting and pouring the metal. It possesses more uniform (isotropic) than those made by mechanical working possessing. Be welded, but affecting the microstructure and mechanical properties. Subsequent heat treatment needed to restore the mechanical properti
33、es. Cast Stainless Steels. Casting of stainless steels involves considerations similar to those for steels. They generally have long freezing ranges and high melting temperatures, developing several structures depending on their composition and processing parameters. Cast stainless steels are availa
34、ble in various compositions and can be heat treated and welded. High heat and corrosion resistance. Nickel-based casting alloys are used for severely corrosive environments and very high-temperature service.制造工程与技术12MetalCasting12.4 The Economics of Casting 铸造的造的经济性性The cost of a product includes the costs of materials, labor, tooling, and equipment. The sequence of casting cost is listed in Table 12.6.制造工程与技术12MetalCasting制造工程与技术12MetalCasting
