4 4 6 . 3 0 5 A M A N U F A C T U R I N G P R O C E S S E S

Chapter 5. Metal-Casting Processes and Equipment; Heat Treatment

Sung-Hoon Ahn

School of Mechanical and Aerospace Engineering Seoul National University 2 Casting

ƒ Casting is a manufacturing process by which a molten material such as metal or plastic is introduced into a mold made of sand or metal, allowed to solidify within the mold, and then ejected or broken out to make a fabricated part.

ƒ Advantages ƒ Making parts of complex shape in a single piece. ƒ Producing large number of identical castings within specified tolerances. ƒ Good bearing qualities and jointless product.

ƒ Disadvantages ƒ Limitations of mechanical properties because of the polycrystalline grain structure. ƒ Poor dimensional accuracy due to shrinkage of metal during solidification. ƒ If the number of parts cast is relatively small, the cost per casting increases rapidly.

ƒ Fundamental aspects in casting operations ƒ Solidification of the metal from its molten state. ƒ Flow of the molten metal into the mold cavity. ƒ Heat transfer during solidification and cooling of the metal in the mold. ƒ Mold material and its influence on the casting process. 3 Solidification of Metals

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 4 Solid solution

ƒ Solute(용질) ƒ Solvent(용매)

ƒ When the particular crystal structure of the solvent is maintained during alloying, the alloy is called solid solution. ƒ Substitutional solid solution(치환 고용체) ƒ Interstitial solid solution( 침입 고용체)

ƒ 5.2.2 Intermetallic compound(금속간 화합물) ƒ Complex structures in which solute atoms are present among solvent atoms in certain specific proportions.

ƒ 5.2.3 Two-phase system(이상계) ƒ Phase: a homogeneous portion of a system that has uniform physical and chemical characteristics

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 5 Phase diagg(ram (평형상태도)

Graphically illustrates the relationships among temperature, composition, and the phase present in a particular alloy system.

Lever Rule S C − C = O L S + L CS − CL L C − C = S O S + L CS − CL

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 6 Eutectic system, Pb-Sn

Ref. William D. Callister, Jr, "Fundamentals of Materials Science and Engineering", 2nd ed. Wiley 7 Iron-carbon system (1)

ƒ Pure iron(순철) : 0.008% C ƒ Steels(강) : 2. 11% C ƒ Cast irons(주철) : ~6.67% C ƒ α-ferrite(페라이트): BCC, soft and ductile ƒ δ-ferrite: BCC, stable only at very high temperatures ƒ Austenite(오스테나이트) : FCC, ductile

ƒ Cementite(세멘타이트): Fe3C, C 6.67%, iron carbide(탄화철), brittle

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 8 Iron-carbon system (2)

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 9 Amount of phases in carbon steel

Casting 1040 steel 10kg, calculate α phase and γ phase at (a) 900°C, (b) 728°C and (c) 726°C

(()a) Austenite:100% g

⎛ Cγ − Co ⎞ ⎛ 0.77 − 0.40 ⎞ (b) α(%) = ⎜ ⎟100 = 100 = 50%, that is 5kg, ⎜ ⎟ ⎜ ⎟ ⎝ Cγ − Cα ⎠ ⎝ 0.77 − 0.022 ⎠ ⎛ C − C ⎞ ⎛ 0.40 − 0.022 ⎞ γ (%) = ⎜ o α ⎟100 = ⎜ ⎟100 = 50%, that is 5kg, ⎜ γ ⎟ ⎝ C − Cα ⎠ ⎝ 0.77 − 0.022 ⎠

⎛ 6.67 − 0.40 ⎞ (c) α = ⎜ ⎟100 = 94%, that is 9.4kg ⎝ 6.67 − 0.022 ⎠ 10 Cast irons

ƒ Fe, C 2.11~4.5%, Si ~3.5%

ƒ According to solidification morphology :

Gray cast iron(회주철) ƒ Flake graphite(편상흑연) ƒ Gray fracture surface(회색파단면) ƒ Damping(진동감쇠) Ductile(nodular) iron(구상흑연주철) ƒ Ductile White cast iron(백주철) ƒ Large amount of Fe3C ƒ Brittle ƒ White fracture surface(흰색 파단면) Malleable cast iron(가단주철) ƒ Obtained by annealing white cast iron Compact graphite iron(컴팩트 흑연주 철)

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 11 Cast irons

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 12 Cast structures

ƒ Pure metal vs. alloys

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 13 Dendrites (수지상정)

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 14 Dendrites

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 15 Fluid flow

v = c 2gh p v2 h+ + = constttant ρg 2g p v 2 p v 2 h + 1 + 1 = h + 2 + 2 + f 1 ρg 2g 2 ρg 2g

Q = A1v1 = A2v2 A h 1 = 2 A2 h1 vDρ Re= η

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 16 Solidification time & shrinkage

ƒ Chvonrinov’s rule Solidification time = C(volume/surface area)2

ƒ Shrinkage occurs at ƒ Molten metal ƒ Phase change ƒ Solid metal

ƒ Cast iron expands ƒ Graphite has high volume/mass ƒ Net expansion during precipitation

ƒ Simil arl y Bi -SllSn alloys expand Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 17 Defects/DFM

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 18 Casting alloys

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 19 Applications

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 20 Properties

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 21 Casting processes

ƒ Expendable mold, permanent pattern ƒ Sand casting ƒ Shell-mold casting ƒ Plaster mold casting ƒ Ceramic mold casting ƒ Vacuum casting

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 22 Casting processes (2)

ƒ Expendable mold, expendable pattern ƒ EtiEvaporative-pattern cas ting (los t f oam) ƒ Investment casting (lost wax)

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 23 Investment casting

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 24 Casting processes (3)

ƒ Permanent mold ƒ In permanent-mold casting, a mold are ƒ Slush casting made from materials such as steel, bronze, refractory metal alloys, or ƒ Pressure casting graphite. Because metal molds are better ƒ Die casting heat conductors than expendable molds, ƒ Centrifugal casting the so lidify ing cas ting is su bjec te d to a ƒ Squeeze casting higher rate of cooling, which turn affects ƒ Semisolid metal forming the microstructure and grain size within ƒ Casting for single crystal the casting . ƒ Rapid solidification ƒ Cooling methods : water, air-cooled fin ƒ Used for aluminum, magnesium, and copper alloys due to their lower melting points ƒ Pros : ggg,ood surface finishing, close dimensional tolerances, and uniform and good mechanical properties ƒ Cons : not economical for small production runs, not good for intricate shapes 25 Pressure casting/centrifugal casting

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 26 Die casting

ƒ Hot-chamber process ƒ Cold-chamber process

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 27 Squeeze casting/single crystal

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 28 Casting for single crystal

Crystal-pulling method floating-zone (Czochralski process) method

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 29 Heat treatment-ferrous alloys

ƒ Pearlite ƒ Spheroidite ƒ Bainite ƒ Martensite ƒ Quenching(담금질) ƒ BdBody Cen tere d Tetragonal(BCT) ƒ Retained austenite ƒ Tempered martensite

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 30 Ferrous alloys

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 31 Nonferrous alloys/stainless steel (1)

Precipitation hardening Age hardening(시효경화) (석출경화)Al), Al-CllCu alloy Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 32 Nonferrous alloys/stainless steel (2)

ƒ Solution treatment ƒ Precipitation hardening ƒ Aging ƒ Maraging(martensite + aging) 33 Case hardening

ƒ Surface hardening ƒ CbiiCarburizing (침탄법) ƒ Carbonitriding (침탄질화법) ƒ Cyaniding (청화법) ƒ Nitriding (질화법) ƒ Boronizing (붕화법) ƒ Flame hardening (화염경화법) ƒ Induction hardening (유도경화법) 34 Annealingg( (풀림))g(/ tempering (뜨임)

ƒ Normalizing(불림)

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 35 Design consideration (1)

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 36 Design consideration (2)

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 37 Economics of casting

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 38 Case study

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley