1、Chapter 11 Metal-Casting Processes第11章 金屬鑄造工藝11.1 Introduction 簡介11.2 Sand Casting 砂型鑄造11.3 Shell-mold Casting 殼型鑄造11.4 Expendable-Pattern Casting (Lost Foam) 一次模鑄造（消失泡沫）11.5 Plaster-Mold Casting 石膏型鑄造11.6 Ceramic-Mold Casting 陶瓷型鑄造11.7 Investment Casting 熔模鑄造11.8 Vacuum Casting 真空鑄造11.9 Permanent-M

2、old Casting 永久型鑄造11.10 Slush Casting 凝殼鑄造11.11 Pressure Casting 壓力鑄造11.12 Die Casting 壓模鑄造11.13 Centrifugal Casting 離心鑄造11.14 Squeeze Casting and Semisolid-Metal Casting 積壓鑄造和半固態金屬成型11.15 Casting Techniques for Single-Crystal components 單晶零件的鑄造技術11.16 Rapid Solidification (Amorphous Alloys) 快速凝固（非晶和

3、金）11.17 Inspection of Castings 鑄件檢驗11.18 Melting Practice and Furnaces 熔化操作和熔爐11.19 Foundries and Foundry Automation 鑄造廠與鑄造自動化11.1 INTRODUCTIONThe first castings were made during the period 4000-3000 B.C., using stone and metal molds for casting copper. Various casting processes have been developed

4、over a long period of time, each with its own characteristics and application, to meet specific engineering and service requirements.Carburetor: 化油器, engine block: 氣缸體, plumbing fixture: 衛生潔具, gun barrel: 槍筒，炮筒, frying pan: 煎鍋, hydraulic turbine: 液力渦輪Two trends are currently having a major impact on

5、 the casting industry. The first is continuing mechanization and automation of the casting process; the second is the increasing demand for high-quality castings with close dimensional tolerances and no defectsdimensional tolerance: 容許尺寸公差TABLE 11.1 Summary of Casting processes, Their advantages and

6、 LimitationProcessAdvantagesLimitationsSandAlmost any metal cast; no limit to size, shape or weight; low cooling cost.Some finishing required; some what coarse finish; wide tolerances.Shell moldGood dimensional accuracy and surface finish; high production ratePart size limited; expensive patterns an

7、d equipment required.Expendable patternMost metals cast with no limit to size; complex shapes.Patterns have low strength and can be costly for low quantities.Plaster moldIntricate shapes, good dimensional accuracy and finish; low porosity.Limited to nonferrous metals; limited size and volume of prod

8、uction; mold making time relatively long.Ceramic moldIntricate shapes; close tolerance parts; good surface finish.Limited size.InvestmentIntricate shapes; excellent surface finish and accuracy; almost any metal cast.Part size limited; expensive patterns mold and labor.Permanent moldGood surface fini

9、sh and dimensional accuracy; low porosity; high production rateHigh mold cost; limited shape and intricacy; not suitable for high-melting point metals.DieExcellent dimensional accuracy and surface finish; high production rate.Die cost is high; part size limited; usually limited to nonferrous metals;

10、 long lead time.CentrifugalLarge cylindrical parts with good quality; high production rate.Equipment is expensive, part shape limitedIntricate: 復雜的, finish: 光潔度, intricacy: 復雜, nonferrous: 非鐵磁的， lead time: 交付周期Transmission valve body: 變速閥體, hub rotor: 轉子轂, disk-brake cylinder: 制動盤柱體, transmission ho

11、using: 變速箱體TABLE 11.2 General Characteristics of Casting ProcessesProcessTypical materials castWeight (kg)Typical surfacefinish (m, Ra)Porosity*Shape complexity*Dimensional accuracy*Section thickness (mm)MinMaxMinMaxSandAll0.05No limit5-2541-233No limitShell moldAll0.05100+1-342-322-Expendable patte

12、rnAll0.05No limit5-204122No limitPlaster moldNonferrous (Al, Mg, Zn, Cu)0.0550+1-233-421-InvestmentAll (high melting pt.)0.005100+1-3311175Permanent moldAll0.53002-32-33-41250DieNonferrous (Al, Mg, Zn, Cu)<0.05501-21-23-410.512Centrifugalall-5000+2-101-23-432100* Relative rating: 1 best, 5 worst.

13、This chapter is organized as 3 major categories based on different mold materials as follow:1. Expendable molds, made of sand, plaster, ceramic and similar materials, used just one time, shown in 11.2-11.8.2. Permanent mold, used many time, shown in 11.9-11.14;3. Composite mold, made by two differen

14、t materials in order to get desired properties.11.2 SAND CASTINGSand casting, the oldest casting process, consists of (a) placing a pattern having the shape of the desired casting in sand to make an imprint (印記), (b) incorporating a gating system, (c) filling the resulting cavity with molten metal,

15、(d) allowing the metal to cool until it solidifies, (e) breaking away the sand mold, and (f) removing the casting.Till now, the sand casting is still the most prevalent (普遍的，流行的) form of casting.Fig. 11.4 Schematic illustration of a sand mold, showing various features.Flask: 型盒, cheek: 中砂箱, Vent: 通氣

16、孔, parting line: 分型線, cope: 上砂箱， drag: 下砂箱, core sand: 型芯砂Fig. 11.5 Outline of production steps in a typical sand-casting operation11.2.1 SandsSilica sand (SiO2), two types: naturally banded (bank sand: 岸沙), synthetic (lake sand: 湖沙)Requirement: fine-grained sand results in lower mold permeability (

17、滲透率), good collapsibility (退讓性).Mulling: 混沙, clay (bentonite): 粘土 (皂土), as cohesive agent (粘性劑) to bond sand particles, giving sand strength; Zircon (ZrSiO4) (鋯英石), olivine (Mg2SiO4) (橄欖石), and iron silicate (Fe2SiO4) (硅酸鐵) sands are often used in steel foundries for their low thermal expansion; chr

18、omite (FeCr2O4) (亞鉻酸鐵，尖晶石) is used for it high heat-transfer characteristics.11.2.2 Types of Sand MoldsThree basic types of sand molds: green-sand (濕型砂), cold-box (冷芯盒), and no-bake (自硬的) molds.Green molding sand: mixture of sand, clay and water, moist or damp while metal poured, least expensive met

19、hod of making mold.Skin-dried method, dried in air of torches (吹焰器), used for large castings because of their high strength.Oven dried method: dried in oven before metal poured, stronger than green-sand molds and better dimensional accuracy and surface finish; drawbacks: distortion (變形), lower colla

20、psibility resulting in more susceptible to hot tearing, low production rate.Cold-boxed mold process, various organic (有機的) and inorganic (無機的) binders (粘結劑) are blended (混合) into the sand to bond the grains chemically for greater strength, more dimensional accuracy, but more expensive compared with

21、green-sand mold.No-bake mold process, mixed with synthetic liquid resin(樹脂), Harding by self, called cold-setting processes. The major component of sand mold is shown in fig. 11.4. 11.2.3 Patterns (模型)Patterns are used to mold the sand mixture into the shape of the casting. They may be made of wood,

22、 plastic, or metal. The selection of a pattern material depends on the size and shape of the casting, the dimensional accuracy, the quantity of castings required, and the molding process.Table 11.3 Characteristics of Pattern MaterialsCharacteristicRatingaWoodAluminumSteelPlasticCast ironMachinabilit

23、yEGFGGWear resistancePGEFEStrengthFGEGGWeightbEGPGPRepairabilityEPGFGResistance to corrosioncEEPEPSwellingcPEEEEaE, excellent, G, good, F, fair, P, poor.bAs a factor in operator fatigue.cBy water.Machinability: 可加工性， Wear resistance: 耐磨性, Repairability: 可修性, Resistance to corrosion: 耐蝕性, Swelling: 脹

24、大Parting agent: 脫模劑，分型劑, One-piece patterns (整體模), also called loose or solid patterns, are generally used for simpler shapes and low-quantity production, wood.Split patterns (分體模): Two-piece patterns made such that each part form a portion of the cavity, complicated shapes.Match-plate patterns (雙面模

25、板模), popular type of mounted pattern in which two-piece patterns are constructed by securing (定位) each half of one or more split patterns to the opposite sides of a single plate. Gating system is in the drag side, to produce smaller casting in large number.Rapid prototyping: 原型機制造Pattern design is a

26、 crucial aspect of the total casting operation. 11.2.4 Cores (型芯)Cores are placed in the mold cavity before casting to form the interior surface of the casting and are removed from the finished part. Strength, permeability, ability to withstand head, and collapsibility, made by sand aggregates (聚合體)

27、.The core is anchored by core point, or metal support (chaplets), and made in similar manner for mold made.Core point: 核點, chaplet: 撐子，型芯撐, majority: 大多數, core box: 砂芯盒，core blower: 吹砂機，型芯吹砂機11.2.5 Sand-Molding MachineMolding machine: 模塑創新獎，造型機, jolt: 震動, anvil: 鐵砧.Process: the flask, molding sand,

28、and pattern are first placed on a pattern plate mounted on an anvil, and then jolted upward by air pressure at rapid intervals. Jolting produces the highest compaction at the horizontal parting line (水平分型線), whereas in squeezing, compaction is highest at the squeezing head. Thus, more uniform compac

29、tion can be obtained by combining squeezing (擠壓) and jolting (震動).Conventional flat head: 常規平封頭, Profile head: 齒形封頭, Equalizing squeeze piston: 均衡壓實活塞, Flexible diaphragm: 柔軟膜片Vertical flakless molding (垂直無箱模): easy and very high production rate;Sandslinger: (投砂器), impeller: 葉輪，ram: 填塞Impact molding

30、 (沖壓制模): the sand is compacted by controlled explosion (爆炸) or instantaneous (瞬時的) release of compressed gases. This method produces molds with uniform strength and good permeability.Vacuum molding (真空模塑法) produces castings with high-quality detail and dimensional accuracy. It is especially well sui

31、ted for large, relatively flat casting.11.2.6 The Sand Casting OperationA complete sequence of operations in sand casting is shown in Fig. 11.11.Shake: 震動, sand blasting: 吹砂磨蝕, shot blasting: 噴丸清理, grit: 吹砂, sawing: 鋸斷， shearing：剪斷，abrasive wheel： 研磨輪11.3 SHELL-MOLD CASTINGShell-mold casting was fir

32、st developed in the 1940s and has grown significantly because it can produce many types of castings with close dimensional tolerances and good surface finish at low cost. In this process, (a) a mounted pattern (模板) made of a ferrous metal of aluminum is heated to 175-370OC, (b) coated with a parting

33、 agent (脫模劑，分型劑) such as silicone, and (c) clamped to a box or chamber, as shown in Fig. 11.13.Ejector pin: 起模桿，頂桿, clamp: 夾住，夾緊, permeability: 滲透性, 11.3.1 Composite MoldsComposite molds are made of two or more different materials and are used in shell molding and other casting processes. They are g

34、enerally employed in casting complex shapes such as impeller (葉片) for turbines. Molding materials commonly used are shells, plaster, and sand with binder, metal and graphite. Composite molds increase the strength of the mold, improve the dimensional accuracy and surface finish of castings, and may h

35、elp reduce overall cost and processing time.Rib: 肋條11.3.2 Sodium Silicate Process 水玻璃化工藝The mold material in the sodium silicate process is a mixture of sand and 1.5% to 6% sodium silicate (waterglass) as a binder. The mixture is packed around the pattern and hardened by blowing carbon dioxide gas t

36、hrough it. This process, also known as silicate-bonded sand or the carbon-dioxide process, was first used in the 1950s and has been developed further, for example, by using various other chemicals for binders.11.3.3 Rammed Graphite Molding 沖壓石墨制模In this process, rammed graphite is used to make molds

37、 for casting reactive metals such as titanium and zirconium. The mold are packed rather like sand molds, air dried, baked (烘烤) at 175oC, fired at 870oC, then stored under controlled humidity (濕度) and temperature. The casting procedures are similar to those of sand molds.11.4 EXPENDABLE-PATTERN CASTI

38、NG (LOST FOAM)The expendable-pattern casting process uses a polystyrene (聚苯乙烯) pattern, which evaporates upon contact with molten metal to form a cavity for the casting, evaporative-pattern or lost-pattern casting, trade name: Full-Mold process, for ferrous and nonferrous metals, especial for the au

39、tomotive industry.Pattern made sequence: expendable polystyrene beads (珠子) + 5-8%pentane (正戊烷) (a volatile hydrocarbon: 揮發性碳氫化合物) placed under preheated die usually made by aluminum, then expand and take the shape of the die cavity, fuse and bond the heads together, cooled and removed pattern.Comple

40、x patterns may also be made by bonding various individual pattern sections using hot-melt adhesive.Molding: water-based refractory slurry: 耐火水性漿料, Pouring molten metal immediately vaporizes the pattern (ablation: 消融) and fills the mold cavity, completely replacing the space previously occupied by th

41、e polystyrene pattern. The heat degrades (depolymerizes: 去聚合) the polystyrene and the degradation products are vented into the surrounding sands.Characteristics: laminar flow, Reynolds number: 400-3000, velocity of flow: 0.1-1m/s, increased velocity by forming patterns with cavity or hollow section.

42、 Cooling rate higher than sand casting leads to less fluidity and directional solidification of the metal.Advantages:a. Relatively simple, design flexibility;b. Inexpensive flaskc. Inexpensive polystyrene, easily pattern made with complex shape, various sizes and fine surface detail.d. Minimum finis

43、hing and cleaning operation requirede. Automate and economical for long production runs.Typical applications: cylinder heads: 氣缸體蓋, crankshaft: 曲軸, brake components: 制動元件, Recent developments include the use of polymethyl methacrylate (PMMA: 有機玻璃), and polyalkylene carbonate (聚烷碳酸鹽) as pattern mater

44、ials for ferrous castings.Polystyrene pattern surrounded by a ceramic shell (Replicast C-S process), which burned prior to pouring molten metal into the mold. Principal advantage: carbon pickup into the metal is entirely avoided.11.5. PLASTER-MOLD CASTING 石膏模鑄造In the plaster-mold casting process, th

45、e mold is made of plaster of pairs (gypsum, or calcium sulfate: 石膏, 硫酸鈣), with the addition of talc (滑石粉) and silica flour (石英粉)to improve strength and to control the time required for the plaster to set. These components are mixed with water, and the resulting slurry is poured over the pattern.Afte

46、r the plaster sets, usually within 15min, the pattern is removed and the mold is dried at 120oC to remove the moisture. Higher drying temperature may be used depending on the type of plaster. The mold halves are assembled to form the mold cavity and are preheated to about 120oC. The molten metal is

47、the poured into the mold.Low permeability, vacuum or under pressure casting used. Antioch process: the molds are dehydrated (脫水) in an autoclave (pressurized oven: 高壓爐) for 6-12 hours, then dehydrated in air for 14 hours. Another method of increasing permeability is to use foamed plaster containing

48、trapped air bubbles.Pattern materials: aluminum alloys, thermosetting plastic: 熱固性塑料, brass, of zinc alloys. Temperature withstanded< 1200oC. Application: aluminum, magnesium, zinc and some copper alloys.Fine details and good surface finish; more uniform grain structure with less warpage (折曲)obta

49、ined due to low cooling rate. Wall thickness of parts can be 1mm-2.5mm.Plaster-mold, ceramic-mold and investment casting process are know as precision casting (精密鑄造) because of the high dimensional accuracy and good surface finish obtained. Typical parts made are lock components, gears, valves, fitt

50、ings (配件), tooling (封面壓花件), and ornaments (飾物). Weight range: < 10kg, usually 125-250g, also 1g.11.6 CERAMIC-MOLD CASTING 陶瓷模鑄造The ceramic-mold casting process, also called cope-and-drag investment casting, is similar to the plaster-mold process, with exception that it uses refractory mold materi

51、als suitable for high-temperature applications. The slurry is a mixture of fine-grained zircon (ZrSiO4), aluminum alloys, and fused silica (硅石玻璃), which are mixed with bonding agents and poured over the pattern.Clamp: 夾緊, back: 支撐, fireclay: 耐火土, firebrick: 耐火磚, torch: 吹焰器Application: ferrous and ot

52、her high-temperature alloys, stainless steels, and tool steels.Good dimensional accuracy and surface finish over a wide range of sizes and intricate shapes, expensiveTypical parts: impellers: 葉輪，cutters (刀具) for machining operations, dies for metalworking (金屬加工), and molds for making plastic or rubb

53、er components. Parts weighting as much as 700kg have been cast by this process.11.7 INVESTMENT CASTINGThe investment casting process, also called the lost-wax process (熔模鑄造法), was first used during period 4000-3000 B.C. The pattern is made of wax (蠟) or a plastic by molding or prototyping techniques

54、. The sequences involved in investment casting are shown in Fig. 11.18. the pattern is made by injecting (噴射) molten wax or plastic into a metal die (金屬壓型) in the shape of the pattern. The pattern is then dipped into a slurry of refractory material such as very fine silica (石英) and binders (粘結劑), in

55、cluding water, ethyl silicate (硅酸乙酯), and acids. After this initial coating has dried, the pattern is coated repeatedly to increase its thickness. Vacuum or pressure casting.Eject: 拋出，射出, stucco coating: 鍍砂, autoclave: 高壓釜, inverted position: 倒轉層位, slurry investment: 泥漿圍模料，It is suitable for casting

56、 high-melting-point alloys with good surface finish and close dimensional tolerance. Gear, cam (凸輪), valve, and ratchet (單向齒輪).Ceramic-Shell Investment Casting: A variation of the investment-casting process is ceramic-shell casting. It uses the same type of wax or plastic pattern, which is dipped fi

57、rst in ethyl silicate gel (硅酸乙酯膠體) and subsequently into a fluidized bed (流化床)of fine-grained fused silica or zircon flour (粉末). The pattern is then dipped into coarser-grained silica to build up additional coatings and proper thickness so that the pattern can withstand the thermal shock of pouring. The process is economical and is used extensively for precision casting of steels and high-temperature alloys.Leach: 浸出, caustic: 腐蝕性的, integral: 整體的, rotor: 轉子11.8 VACUUM CASTINGA schematic illustration of the vacuum casting process, or counter gr