Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-1 CHAPTER 11 Metal-Casting Processes.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-3 Die-Casting Examples (a) (b) Figure 11.1 (a) The Polaroid PDC-2000 digital camera with a AZ91D die-cast, high purity magnesium case. (b) Two-piece Polaroid camera case made by the hot-chamber die casting process. Source: Courtesy of Polaroid Corporation and Chicago White Metal Casting, Inc.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-5 Casting Examples Figure 11.2 Typical gray- iron castings used in automobiles, including transmission valve body (left) and hub rotor with disk-brake cylinder (front). Source: Courtesy of Central Foundry Division of General Motors Corporation. Figure 11.3 A cast transmission housing.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-9 Patterns for Sand Casting Figure 11.6 A typical metal match-plate pattern used in sand casting. Figure 11.7 Taper on patterns for ease of removal from the sand mold.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-10 Examples of Sand Cores and Chaplets Figure 11.8 Examples of sand cores showing core prints and chaplets to support cores.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-11 Squeeze Heads Figure 11.9 Various designs of squeeze heads for mold making: (a) conventional flat head; (b) profile head; (c) equalizing squeeze pistons; and (d) flexible diaphragm. Source: © Institute of British Foundrymen. Used with permission.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-12 Vertical Flaskless Molding Figure 11.10 Vertical flaskless molding. (a) Sand is squeezed between two halves of the pattern. (b) Assembled molds pass along an assembly line for pouring.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-13 Sequence of Operations for Sand Casting Figure 11.11 Schematic illustration of the sequence of operations for sand casting. Source: Steel Founders' Society of America. (a) A mechanical drawing of the part is used to generate a design for the pattern. Considerations such as part shrinkage and draft must be built into the drawing. (b-c) Patterns have been mounted on plates equipped with pins for alignment. Note the presence of core prints designed to hold the core in place. (d-e) Core boxes produce core halves, which are pasted together. The cores will be used to produce the hollow area of the part shown in (a). (f) The cope half of the mold is assembled by securing the cope pattern plate to the flask with aligning pins, and attaching inserts to form the sprue and risers. (continued)

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-14 Figure 11.11 (g) The flask is rammed with sand and the plate and inserts are removed. (g) The drag half is produced in a similar manner, with the pattern inserted. A bottom board is placed below the drag and aligned with pins. (i) The pattern, flask, and bottom board are inverted, and the pattern is withdrawn, leaving the appropriate imprint. (j) The core is set in place within the drag cavity. (k) The mold is closed by placing the cope on top of the drag and buoyant forces in the liquid, which might lift the cope. (l) After the metal solidifies, the casting is removed from the mold. (m) The sprue and risers are cut off and recycled and the casting is cleaned, inspected, and heat treated (when necessary). Sequence of Operations for Sand Casting (cont.)

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-15 Surface Roughness for Various Metalworking Processes Figure 11.12 Surface roughness in casting and other metalworking processes. See also Figs. 22.14 and 26.4 for comparison with other manufacturing processes.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-16 Shell-Mold Casting Dump-Box Technique Figure 11.13 A common method of making shell molds. Called dump-box technique, the limitations are the formation of voids in the shell and peelback (when sections of the shell fall off as the pattern is raised). Source: ASM International.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-17 Shell-Mold Casting-1*  Produce many types of castings with close tolerances and good surface finishes at a low cost  Mounted pattern made of a ferrous metal or aluminum is heated to 175-370˚C  The pattern is coated with a parting agent such as silicone and clamped to a box or chamber containing a fine sand containing 2.5 to 4.0% thermosetting resin binder such as phenol-formaldehyde, which coats the sand particles  The box is either rotated upside down or the sand mixture is blown over the pattern allowing it to coat the pattern  The assembly is then placed in an oven for a short period of time to complete the curing of the resin.  The oven is mostly a metal box with gas-fired burners  The shell hardens around the pattern and is removed from the pattern using a built-in ejector pins.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-18 Shell-Mold Casting-2*  Two half-shells are made and bonded or clamped together in preparation for pouring.  Thickness of the shell can be accurately determined by controlling the contact time  The shells are light and thin, usually 5-10 mm  The decomposition of the shell-sand binder also produces high volume of gas  The cost of the resin binder is offset by the fact that only 5% as much sand is used compared to sand casting  Shell-casting maybe more economical than other casting processes  The high quality of the finished casting can significantly reduce secondary operations.  Complex shapes and high precision components can be produced

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-19 Composite Molds Figure 11.14 (a) Schematic illustration of a semipermanent composite mold. Source: Steel Castings Handbook, 5th ed. Steel Founders' Society of America, 1980. (b) A composite mold used in casting an aluminum-alloy torque converter. This part was previously cast in an all-plaster mold. Source: Metals Handbook, vol. 5, 8th ed.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-20 Composite Molds*  Composite molds are made of two or more different materials and are used in shell molding and other casting processes  They are used when casting complex shapes such as impellers for turbines  Molding materials commonly used are shells, plaster, sand with binder, metal, and graphite.  Composite molds may also include cores and chills to control the rate of solidification in critical areas of castings.  Composite molds increase the strength of the mold, improve the dimensional accuracy and surface finish of castings.  It can also reduce overall cost and processing time.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-21 Expendable Pattern Casting- Lost Foam Figure 11.15 Schematic illustration of the expendable pattern casting process, also known as lost foam or evaporative casting.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-22 Expendable Pattern Casting- Lost Foam (1)*  This process uses a polystyrene pattern which evaporates upon contact with molten metal to form a cavity for the casting.  This process is also known as evaporative-pattern or lost- pattern casting and under the trade name Full-Mold process.  It can be used for ferrous and nonferrous metals particularly for the automotive industry.  First raw expandable polystyrene (EPS) beads containing 5- 8% pentane are placed in a preheated die (usually aluminum).  The polystyrene expands and takes the shape of the die cavity  Additional heat is applied to fuse and bond the beads together. The die is then cooled and opened and the polystyrene pattern is removed,  Complex pattern can be made by bonding various individual pattern sections using hot-melt adhesive.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-23 Expendable Pattern Casting- Lost Foam (2)*  The pattern is then coated with a water-base refractory slurry, dried and place in a flask.  The flask is filled with loose fine sand which surrounds and supports the pattern.  The sand maybe dried and mixed with bonding agents to give it additional strength.  The sand is periodically compacted  Then, without removing the polystyrene pattern the molten metal is poured into the mold which vaporizes the pattern immediately.  Typical applications are cylinder heads, crankshafts, brake components and manifolds for automobile and machine bases.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-24 Expendable Pattern Casting- Lost Foam (3)* The evaporative-pattern process has a number of advantages over other casting methods:  It is relatively simple  Inexpensive flasks are sufficient for the process  Polystyrene is inexpensive and can be easily processed into very complex shapes with fine details  The casting requires minimum finishing and cleaning ops  The process is economical for long production runs  The process can be automated

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-25 Lost Wax Precision Casting Process*  The wax object or pattern is covered by a plaster investment. The mold is heated, melting the wax and hardening the mold. Then the casting is filled with metal.  After cooling, the plaster investment is broken away, leaving the casting.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-26 Plaster-Mold Casting (1)*  The mold is made of plaster of paris (gypsum or calcium sulfate), with the addition of talc and silica flour to improve strength and control the time required for the plaster to set.  These components are mixed with water and the resulting slurry is poured over the pattern.  After the plaster sets (within 15 min), the pattern is removed and the mold is dried at 120-260˚C to remove the moisture (for some plaster types, higher drying temperatures can be used).  The mold halves are then assembled to form the mold cavity and preheated to about 120˚C.  The molten metal is then poured into the mold  Patterns are made of aluminum alloys, thermosetting plastics, brass, or zinc alloys.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-27 Plaster-Mold Casting (2)*  Max temp that plaster can withstand is 1200˚C, hence plaster molds are used only for aluminum, magnesium, zinc, and some copper-base alloys.  The castings have fine details with good surface finish.  Plaster molds have lower thermal conductivity than others, the castings cool slowly and more uniform grain structure is obtained with less warpage.  Wall thickness of parts 1-2.5 mm.  This process is called precision castings because of the high dimensional accuracy and good surface finish obtained.  Lock components, gears, valves, fittings, tooling, and ornaments are made this way.  Typical weight range is 125-250 g and as high as 10Kg and low as 1g can be produced

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-28 Ceramic Molds Figure 11.16 Sequence of operations in making a ceramic mold. Source: Metals Handbook, vol. 5, 8th ed. Figure 11.17 A typical ceramic mold (Shaw process) for casting steel dies used in hot forging. Source: Metals Handbook, vol. 5, 8th ed.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-29 Ceramic-Mold Casting (1)*  This is similar to the plaster-mold process, with the exception that is uses refractory mold materials suitable for high-temperature applications.  This process is also called cope-and-drag investment castings.  The slurry is a mixture of fine-grained zircon (ZrSiO4), aluminum oxide and fused silica which are mixed with bonding agents and poured over the pattern which has been in a flask.  The pattern may be made of wood or metal. After setting, the molds are removed, dried, burned off to remove volatile matter, and baked. The molds are clamped firmly and used as all-ceramics molds.  The facings are then assembled into a complete mold, ready to be poured.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-30 Ceramic-Mold Casting(2)*  The high-temp resistance of the refractory molding materials allows these molds to be used in casting ferrous and other high-temperature alloys, stainless steels, and tool steels.  This process is called precision castings because of the high dimensional accuracy and good surface finish obtained.  Somewhat expensive  Typical parts made are impellers, cutters for machining,, dies for metalworking, and molds for making plastics or rubber components.  Parts weighing as much as 700Kg can be cast this way

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-31 Figure 11.18 Schematic illustration of investment casting, (lost-wax process). Castings by this method can be made with very fine detail and from a variety of metals. Source: Steel Founders' Society of America. Investment Casting

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-32 Investment Casting of a Rotor Figure 11.19 Investment casting of an integrally cast rotor for a gas turbine. (a) Wax pattern assembly. (b) Ceramic shell around wax pattern. (c) Wax is melted out and the mold is filled, under a vacuum, with molten superalloy. (d) The cast rotor, produced to net or near- net shape. Source: Howmet Corporation.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-33 Investment and Conventionally Cast Rotors Figure 11.20 Cross- section and microstructure of two rotors: (top) investment-cast; (bottom) conventionally cast. Source: Advanced Materials and Processes, October 1990, p. 25 ASM International

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-34 Investment Casting (1)*  This process is called precision castings because of the high dimensional accuracy and good surface finish obtained.  Very smooth, highly accurate castings.  Useful in casting unmachinable alloys and radioactive metals.  Can be used for ferrous and non-ferrous alloys.  Expensive process  Usually limited to small castings.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-35 Investment Casting (2)*  Advantages of this method:  Intricate forms with undercuts  A very smooth surface is obtained without a parting line.  Dimensional accuracy is good.  Certain unmachinable parts can be cast to preplanned shape (net or near-net shape machining)  It may be used to replace die casting where short runs are involved.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-36 Ceramic-Shell Process*  Similar to the lost wax process, involves the removal of a heat-disposable pattern from a refractory investment.  The pattern is made from wax or a low-melting-point plastic.  Cost of producing plastic pattern is less than that for wax.  The pattern cluster is repeatedly dipped into a ceramic slurry and dusted with refractory material. This process is called stuccoing. This is repeated until the shell is 3/16- 1/2” thick.  Pattern is melted out of the mold, which is dried and then fired at 980-1095 o C to remove all moisture and organic material.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-37 Gravity of Permanent-Mold Casting  Utilizes a permanent metal or graphite mold  Mold are coated to reduce chilling effect on the metal and facilitate the removal of the casting.  No pressure is used.  Used for ferrous and nonferrous castings, because of the lower pouring temperature.  Good tolerances maintained  High initial cost of equipment and the cost of mold maintenance is a disadvantage for this process.  Cast iron is being increasingly cast by the gravity method.  Often dies are lined with sand about 6 mm thich by utilizing a core blower. This leads to smaller amount of sand used compared to sand casting, the cleaning cost are lower, and the accuracy is better.  Used for Aluminum pistons, cooking utensils, etc….

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-38 Slush Casting*  Slush casting produces hollow casting in metal mold without the use of cores.  Molten metal is poured into the mold, which is turned over immediately, so that the metal remaining as liquid runs out.  A thin-walled casting results.  Wall thickness depends on the chilling effect from the mold and the time of the operation.  Used for ornamental objects, statutes, toys and other  Metals used are lead, zinc, and various low-melting alloys.  Parts cast this way are either painted or finished to represent bronze, silver, or other more expensive metals.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-39 Vacuum-Casting Process Figure 11.21 Schematic illustration of the vacuum-casting process. Note that the mold has a bottom gate. (a) Before and (b) after immersion of the mold into the molten metal. Source: From R. Blackburn, "Vacuum Casting Goes Commercial," Advanced Materials and Processes, February 1990, p. 18. ASM International.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-40 Vacuum-Casting* (1)  A mixture of fine sand and urethane is molded over metal dies and cured with amine vapor. The mold is then held with an arm and partially immersed into molten metal held in an induction furnace.  Metal maybe melted in air (CLA) or in vacuum (CLV) processes.  The vacuum reduces the air pressure inside the mold to about 2/3 of atmospheric pressure, thus drawing the molten metal into the mold cavities through a gate in the bottom of the mold. The molten metal in the furnace is at temperature usually 50 o C above the liquidus temperature; consequently it begins to solidify within a fraction of a second. After the mold is filled, it is withdrawn from the molten metal.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-41 Vacuum-Casting* (2)  Suitable for thin-walled, complex shape with uniform properties.  Carbon, low- and high-alloy steel, and stainless steel parts weighing as much as 70 Kg have been vacuum cast.  The process can be automated and production cost is similar to those of green-sand casting.  CLA parts are easily made at high volume and relatively low-cost.  CLV parts usually involve reactive metals such as aluminum, titanium, zirconium, and hafnium.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-42 Pressure Casting Figure 11.22 (a) The bottom-pressure casting process utilizes graphite molds for the production of steel railroad wheels. Source: The Griffin Wheel Division of Amsted Industries Incorporated. (b) Gravity-pouring method of casting a railroad wheel. Note that the pouring basin also serves as a riser. Railroad wheels can also be manufactured by forging.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-43 Pressure Casting*  It is also called pressure pouring or low-pressure casting.  The molten metal is forced upward by gas pressure into a graphite or metal mold.  The pressure is maintained until the metal has completely solidified in the mold.  It is used generally for high-quality-castings.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-44 Die Casting* (1)  Two methods are employed: 1) Hot chamber and 2) cold Chamber (which is determined by the location of the melting pot).  The process is rapid because the die and core are permanent.  Produces a smooth surface, which minimizes the secondary operations (plating or other finishing operations).  Wall thickness is more uniform than in sand casting, consequently, less metal is required.  Optimum production quantity ranges from 1000 to 200,000 pieces.  Max weight of brass die casting is about 5 lbs, but Aluminum castings can be more than 100 lbs.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-45 Die Casting* (2)  Permanent molds are constructed of metals capable of withstanding high temperatures.  High cost, therefore, recommended when many castings are produced.  Advantageous for small and medium size castings.  Molten metal is forced by pressure into a metal mold known as a die.  The casting conforms to the die cavity in shape and surface finish.  Usual pressure is from 1500 to 2000 psi (10.3 to 14 Mpa)  Most popular of the permanent-mold processes.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-46 Die Casting* (3)  Waste is low because the sprue, runners, and gates are remelted.  Tolerances range from +-.0025 to.025 mm  Undesirable chilling of the metal unless high temperatures are sustained before the cast is removed.  Die casting is commercially limited to non-ferrous alloys.  Dies are similar in construction for hot and cold chamber machines  They are made in two sections to allow casting removal, usually equipped with heavy dowel pins to maintain the halves in proper alignment.  Dowel Pins are defined as high precision pins that maintain accurate alignment between assembled components. (Example Cylinder heads)  The life of the mold depends on the metal cast and may range from 10,000 fillings for brass to several million if zinc is used.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-47 Hot- and Cold-Chamber Die-Casting Figure 11.23 (a) Schematic illustration of the hot-chamber die-casting process. (b) Schematic illustration of the cold-chamber die-casting process. Source: Courtesy of Foundry Management and Technology. (a)(b)

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-48 Cold-Chamber Die-Casting Machine (a) Figure 11.24 (a) Schematic illustration of a cold-chamber die-casting machine. These machines are large compared to the size of the casting because large forces are required to keep the two halves of the dies closed.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-49 Figure 11.24 (b) 800-ton hot-chamber die-casting machine, DAM 8005 (made in Germany in 1998). This is the largest hot-chamber machine in the world and costs about $1.25 million. (b) Hot-Chamber Die-Casting Machine

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-50 Die-Casting Die Cavities Figure 11.25 Various types of cavities in a die-casting die. Source: Courtesy of American Die Casting Institute. Figure 11.26 Examples of cast-in- place inserts in die casting. (a) Knurled bushings. (b) Grooved threaded rod.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-51 Hot-Chamber Die Casting*  Metal is forced into the mold, and pressure is maintained during the solidification either by a plunger or by compressed air.  Low melting alloys of zinc, tin, and lead are the materials cast in hot-chamber machines.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-52 Cold-Chamber Die Casting*  Die casting brass, aluminum, and magnesium requires high pressures and melting temperatures and necessitates a change in the melting procedure from hot-chamber die casting.  Heat the metal in an auxiliary furnace and ladles it to the plunger cavity next to the dies.  Ejector rod ejects the casting from the movable half of the dies.  Pressure range from 5600 to 22,000 psi (39 to 150 Mpa)

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-54 Centrifugal Casting Process Figure 11.27 Schematic illustration of the centrifugal casting process. Pipes, cylinder liners, and similarly shaped parts can be cast with this process.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-55 True Centrifugal Casting*  Centrifugal casting is the process of rotating a mold while the metal solidifies so as to utilize the centrifugal force to position the metal in the mold.  Greater detail on the surface of the casting is obtained.  Dense metal structure has superior physical properties. Impurities forced to the center and can be machined out.  Generally, used for symmetrical shape castings.  Cores and risers of feed heads are eliminated.  More economical than other casting methods.  Thinner sections can be cast compared to static casting.  If a metal can be melted, it can be cast centrifugally.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-56 Semicentrifugal Casting Figure 11.28 (a) Schematic illustration of the semicentrifugal casting process. Wheels with spokes can be cast by this process. (b) Schematic illustration of casting by centrifuging. The molds are placed at the periphery of the machine, and the molten metal is forced into the molds by centrifugal force.  Cast parts with rotational symmetry such as a wheel with spokes.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-57 Centrifuging Casting*  Mold cavities of any shape are placed at a certain distance from the axis of rotation.  The molten metal is poured from the center and is forced into the mold by centrifugal forces.  The properties of castings vary by distance from the axis of rotation.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-58 Squeeze-Casting Figure 11.29 Sequence of operations in the squeeze-casting process. This process combines the advantages of casting and forging.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-59 Squeeze-Casting*  Also called Liquid-Metal Forging.  Involves solidification of molten metal under high pressure.  The machinery includes a die, punch, and ejector pin.  The pressure applied by the punch keeps the entrapped gases in solution, and the contact under high pressure at the die-metal interface promotes rapid heat transfer, resulting in a fine microstructure with good mechanical properties.  The application of pressure overcomes feeding problems that can arise when casting are lower than those for hot or cold forging.  Parts can be made to near-net shape, with complex shapes and fine surface detail from both nonferrous and ferrous alloys.  Typical products made are automotive components and mortar bodies (a short-barreled cannon).

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-60 Single Crystal Casting of Turbine Blades (c) Figure 11.30 Methods of casting turbine blades: (a) directional solidification; (b) method to produce a single-crystal blade; and (c) a single-crystal blade with the constriction portion still attached. Source: (a) and (b) B. H. Kear, Scientific American, October 1986; (c) Advanced Materials and Processes, October 1990, p. 29, ASM International. Only single crystal can pass through

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-61 Single Crystal Casting Figure 11.31 Two methods of crystal growing: (a) crystal pulling (Czochralski process) and (b) the floating-zone method. Crystal growing is especially important in the semiconductor industry. Source: L. H. Van Vlack, Materials for Engineering. Addison-Wesley Publishing Co., Inc., 1982.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-62 Single Crystal Casting* With the advent of the semiconductor industry, single crystal growing has become a major activity in the manufacture of microelectronics devices. There are basically two methods of crystal growing.  Crystal pulling method  Floating zone method

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-63 Crystal Pulling Method*  A seed crystal is dipped into the molten metal and then pulled out slowly at a rate of 10  m/sec while being rotated at 1 rev/sec. The liquid metal begins to solidify on the seed, and the crystal structure of the seed is continued throughout. Dopants (alloying elements), may be added to the liquid metal to impart special electrical properties. 50-300 mm in diameter and over 1 m long ingots can be produced by this technique.  Then wafers are then cut from the rod, cleaned and polished for use in microelectronic device fabrication.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-64 Floating Zone Method*  Starting with a rod of polycrystalline silicone rest on a single crystal, and induction coil heats these two pieces while moving slowly upward. The single crystal grows upward while maintaining its orientation.  Then wafers are then cut from the rod, cleaned and polished for use in microelectronic device fabrication.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-65 Melt Spinning Figure 11.32 Schematic illustration of melt-spinning to produce thin strips of amorphous metal (metallic glasses). Rapid Solidification involves cooling the molten metal at rates as high as 10^6 K/s so that it does not have sufficient time to crystallize. This results in extension of solid solubility, grain refinement, and reduced micro segregation. Chill Block

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-66 Electric Furnaces Figure 5.2 Schematic illustration of types of electric furnaces: (a) direct arc, (b) indirect arc, and (c) induction.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-68 Types of Melting Furnaces  Electric Arc: high rate of melting (high production rate), much less pollution than other types.  Induction: useful in smaller foundries and produce smaller compositions-controlled melts.  Crucible: heated with various fuels.  Cupolas: refractory-lined vertical steel charged with alternating layers of metal, coke and flux.  Levitation Melting: magnetic suspension of the molten metal. Induction coil heats and stirs and confines the melt from a solid billet.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-69 Furnace Selection  Economic consideration  Composition and melting point of the alloy  Control of furnace atmosphere to avoid metal contamination  Capacity and the rate of melting required  Environmental consideration  Power supply  Ease of superheating of the metal  Type of charge material that can be used

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-70 Trends in Casting* (1)  Computer-Aided design and manufacturing of castings, molds, and dies and gating and runner systems are being implemented at a rapid rate. Use it also to calculate weight, volume and dimensions for proper mold design and economic production.  Automation of molding and casting processes to reduce cost, using computer controls, sensors and industrial robots.  Research is in progress on automated inspection of castings such as with machine vision and the use of fiber optics to inspect internal surfaces of castings that cannot be viewed directly.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-71 Trends in Casting* (2)  Environmental impact of foundry operation is an important aspect of casting metals.  Semisolid metal forming is an emerging technology with application for aluminum-alloy parts for military, aerospace and automotive uses.  Improvements in melting and remelting techniques and refining the molten metal.  Use simulation tools to predict the solidification patterns and use that during he casting design to ensure good quality casting and prevent casting defects.

Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-1 CHAPTER 11 Metal-Casting Processes.

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Kalpakjian Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 11-1 CHAPTER 11 Metal-Casting Processes.

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