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Ed. by Che-Chih Tsao, PME, NTHU P 1 機械製造 MANUFACTURING PROCESSES 講義參考資料 -- 清大學生本課程中參考用 Casting (1) Revision 4f
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Ed. by Che-Chih Tsao, PME, NTHU P 1
機械製造
MANUFACTURING PROCESSES
講義參考資料 -- 清大學生本課程中參考用
Casting (1)
Revision 4f
Ed. by Che-Chih Tsao, PME, NTHU P 2
Casting
Processes and Equipment Fundamentals
Design, Materials and Economics
Ed. by Che-Chih Tsao, PME, NTHU P 3
Casting鑄 造
molten metal -- pattern -- mold
鐵(銅…) 水 -- 模 -- 範
模型 -- 鑄模
永久式(取出式)模型 消失式鑄模
消失式模型 永久式鑄模
Ed. by Che-Chih Tsao, PME, NTHU P 4
Fig. II.3
Ed. by Che-Chih Tsao, PME, NTHU P 5
Copper chariot of Shara temple, Tell Agrab (in today's Iraq), ~2700BC, Height 7 cm
(The earliest known metal casting by lost-wax technique)
(Ref. Past Worlds -- Atlas of Archaeology, Pub. by Harper Collins, 1999)
Ed. by Che-Chih Tsao, PME, NTHU P 6
Bronze ding tripod, Erlitou culture, Henan, ~1600-1400BC, Height 20 cm
(Study says this was an actual cooking pot for daily use.)
(Said to be made by 3-piece ceramic mold, with clay cores, casted upside down)
Ed. by Che-Chih Tsao, PME, NTHU P 7
(L) Bronze helmet, Jiangxi, Late Shang, ~1200-1050BC, Height 18.7 cm (Said to be made by 2-
section mold); (R) Bronze vessel, Late Shang, ~1200-1100BC, Height 35 cm (Lost-wax?)
(Ref. The Golden Age of Chinese Archaeology, and Past Worlds -- Atlas of Archaeology, Pub. by Harper Collins)
Ed. by Che-Chih Tsao, PME, NTHU P 8
Bronze, Sanxindui culture, Sichuan, ~1300-1100BC, Height 262 cm
(Ref. The Golden Age of Chinese Archaeology)
Ed. by Che-Chih Tsao, PME, NTHU P 9
Fig. 11.1
(a) Gray-iron casting
(b) Transmission housing
(c) (d) Die cast magnesium
case
Ed. by Che-Chih Tsao, PME, NTHU P 10
▲New HTC One 發表會現場展示了半成品狀態的手機外殼。 (Die casting?)
Ed. by Che-Chih Tsao, PME, NTHU P 11
Fig. II.1 (a) A die-cast aluminum transmission box. (b) A tree of rings by investment casting.
Ed. by Che-Chih Tsao, PME, NTHU P 12
Fig. II.2 (Kalpakjian & Schmid) Cast Parts in a typical automobile
Ed. by Che-Chih Tsao, PME, NTHU P 13
(Left)
Rotor Hub Enercon E82 at Hannover Energy International Fair, Photo by WWEA http://www.wwindea.org/technology/ch01/en/1_2_1_2.html
(Right)
Hub, SG Iron
http://www.indiamart.com/premier-limited-delhi/wind-turbine-s-g-iron-casting-parts.html
Ed. by Che-Chih Tsao, PME, NTHU P 14
Processes and Equipment: Sand Casting (Permanent pattern, Expendable mold)
Fig. 11.3 Sand mold features
鑄口
冒口
暗冒口
澆槽
流道
澆口
分型面
上型箱
下型箱
模穴
砂心
型砂
砂箱
Ed. by Che-Chih Tsao, PME, NTHU P 15
(http://www.ejsong.com/mdme/memmods/MEM30007A/processing/processing.html)
Ed. by Che-Chih Tsao, PME, NTHU P 16
Green molding sand (sand + clay + water)
Ed. by Che-Chih Tsao, PME, NTHU P 17
Pattern making
Prepare cope 加砂打實
Prepare drag
流道 模板
鑄口(棒) 冒口(棒)
上型箱
下型箱
模型 Wood, plastic, metal, rapid prototyping
Molds:
Green-sand (濕砂模): sand +clay +water
Skin-dried (表面乾燥模):
dry in air or by torch
Cold-box: +binder
No-bake: +synthetic liquid resin
Ed. by Che-Chih Tsao, PME, NTHU P 18
Core making
Set core Assemble cope and drag
(Rearranged from Fig. 9.12 of R.A. Lindberg)
砂心 sand (+binder)
鑄口
冒口
Ed. by Che-Chih Tsao, PME, NTHU P 19
Fig. 11.4 Metal match-plate pattern
Fig. 11.6 Sand cores
Ed. by Che-Chih Tsao, PME, NTHU P 20
Fig. 11.5 Draft angle depends on actual pattern shape, size, materials and mold characteristics. But in general, external features use 10-20 mm/m (or 1-2%) internal features use 30-60 mm/m (or 3-6%) (Ref. 徐仁輝 機械製造學 CH2)
拔模斜度
Ed. by Che-Chih Tsao, PME, NTHU P 21
(L) WATER JACKET for 4 wheeler Cylinder Head (Sand Core Mold) (R) WATER JACKET for 2 wheeler Cylinder (Sand Core Mold) (http://www.syegd.com/en/product-info.php?cid=17
SANYANG INDUSTRY CO., LTD. Engineering Division)
Ed. by Che-Chih Tsao, PME, NTHU P 22
Application of Virtual Development Tools for the Sustainable Processing of Multiphase Materials, Demonstrated for the Production of Foundry Sand Cores
BMBF Framework Programme Research for Sustainable Development (FONA) (http://www.fona.de/de/5266)
Ed. by Che-Chih Tsao, PME, NTHU P 23
Sand cast cylinder head
(http://www.ejsong.com/mdme/memmods/MEM30007A/processing/processing.html)
Ed. by Che-Chih Tsao, PME, NTHU P 24
KS Chaplets, Brazil http://www.kschapelins.com.br/
Ed. by Che-Chih Tsao, PME, NTHU P 25
Sand-molding Machines -- Sand hammering (tamping) 震搗製模
-- Vertical flaskless molding
Fig. 11.7
-- Sandlingers 拋砂機
-- Impact molding: Compressed gas or explosion to compact sand -- Vacuum molding (V process): Plastic film + Vacuum
Ed. by Che-Chih Tsao, PME, NTHU P 26
-- Core shooting machine
(http://qzjdjx.en.made-in-china.com/offer/JMsnQDNFXiWz/Sell-Jd-361-Z-Furan-Resin-Sand-Core-Shooting-Machines.html)
Ed. by Che-Chih Tsao, PME, NTHU P 27
Videos on the Internet for reference: (1) http://www.youtube.com/watch?v=rgL2Jn5mk1A Al casting in a lab environment -- University of Memphis (2) http://www.machinetools.net.tw/casting/taiwan_sand_casting.htm Cast iron for machine parts -- Cheng Feng Company
Ed. by Che-Chih Tsao, PME, NTHU P 28
Processes and Equipment: (Permanent pattern, Expendable mold)
Shell Molding 殼模
Other than sand, molds can be made from Plaster 石膏模
Ceramics 瓷模
Ed. by Che-Chih Tsao, PME, NTHU P 29
Shell Casting殼模法
fine sand + thermosetting resin binder
metal (175-370 C)
+ parting agent (silicone)
5-10mm thick
Bake before
remove shell
Ed. by Che-Chih Tsao, PME, NTHU P 30
Ceramic molding (or Shaw process) 瓷模法
瓷漿
Ed. by Che-Chih Tsao, PME, NTHU P 31
Fundamentals Fluid Flow
Fig. 10. 8 (徐仁輝 機械製造學 CH2)
-- Bernoulli's theorem: -- Mass continuity:
g
p1 h1 + = +
v1 2
2g g
p2 h2 + +
v2 2
2g + f
A1 v1 = A2 v2
A1
A2 =
h2
h1 √
√ v = c 2gh
0< c < 1
√ v = c 2g(h-x)
Eliminating dross/slag
撇渣
Ed. by Che-Chih Tsao, PME, NTHU P 32
(From NTHU PME Prof. Hochen's course slide)
Ed. by Che-Chih Tsao, PME, NTHU P 33
-- Reynolds number (for duct)
v: flow velocity D: duct diameter (characteristic size)
: fluid density
: fluid viscosity Re < 2000 laminar flow Re between 2000 ~ 20000 mixed Re > 20000 turbulent flow turbulent flow is bad!
vD Re =
Ed. by Che-Chih Tsao, PME, NTHU P 34
Fig. 10.9 An example of fluidity index test method
Ed. by Che-Chih Tsao, PME, NTHU P 35
Heat Transfer Flow too fast causes air inclusion. Flow too slow causes premature chilling and solidification.
Ed. by Che-Chih Tsao, PME, NTHU P 36
Thermal conduction:
: heat flow per unit area per unit time (W/m2) K: thermal conductivity (W/(m K)) Thermal convection:
h: heat transfer coefficient Heat equation:
: internal energy of material
specific heat capacity, density, volume, A surface area
thermal diffusivity
+
Tm
Ta
T1
T2
x
Ed. by Che-Chih Tsao, PME, NTHU P 37
-- Solidification Time Flat mold wall: Solidified thickness L = Chvorinov's rule: Solidification time = C ( )
n n = 1.5 ~ 2
See Example 10.1
Fig. 10.11 Growth of solidified "skin" (shell)
Volume
Surface area
b t √
Ed. by Che-Chih Tsao, PME, NTHU P 38
-- Shrinkage Molten metal contraction while temperature decreases Phase change contraction Solid metal contraction while temperature decreases to ambient temperature
Tab. 10.1
Affect dimension Could cause microcracks and porosity
Major amount of shrinkage
Ed. by Che-Chih Tsao, PME, NTHU P 39
Tab. 12.1 Linear shrinkage
Ed. by Che-Chih Tsao, PME, NTHU P 40
Solidification -- Microstructures
(a) Pure metal (b) Alloy (c) Using nucleating agents
columnar grain
homogenous nucleation
Ed. by Che-Chih Tsao, PME, NTHU P 41
Pure metal
Ed. by Che-Chih Tsao, PME, NTHU P 42
Alloy
columnar dendrites
freezing range
Width of mushy zone depends on alloying elements: Ferrous casting -- narrow Al, Mg alloys -- wide
Ed. by Che-Chih Tsao, PME, NTHU P 43
-- Effect of cooling rate Slow (~100 K/s): Coarse dendrites Higher (~ 10000 K/s): Finer dendrites Fast (~10
6-10
8 K/s): Amorphous [Ref. Sec. 6.14]
Finer grains: higher strength and ductility less microporosity (interdendritic shrinkage voids) less cracks (hot tearing) G/R ratio, for kinetics of liquid-solid interface
Thermal gradient G = T / x ~ 100-1000 K/m typical Interface moving speed R ~ 0.001-0.0001 m/s (1-0.1 mm/s) typical
(a) Columnar dendritic (b) Equiaxed dendritic (c) Equiaxed non-dendritic G/R ~ 10
5-10
7 G/R ~ 10
10-10
12
Ed. by Che-Chih Tsao, PME, NTHU P 44
Defects
-- Hot tear: metal unable to shrink freely during cooling due to mold/core constraint
Solution: Exothermic (heat producing) compounds at critical sections
Ed. by Che-Chih Tsao, PME, NTHU P 45
-- Voids etc.
Solution: Mold design and/or pouring procedure
Ed. by Che-Chih Tsao, PME, NTHU P 46
-- Porosity due to shrinkage
Solutions: Plenty of molten metal
Using chills at regions of thicker sections
Steep temperature gradient (fast cooling) by molds of
better thermal conductivity (for alloys)
Hot isostatic pressing
Ed. by Che-Chih Tsao, PME, NTHU P 47
-- Porosity due to gases
Gases released when metal solidifies.
Solutions: Vent and mold design
Flushing or purging with an inert gas on the molten metal
Melting and pouring in vacuum
Deoxidization
Ed. by Che-Chih Tsao, PME, NTHU P 48
