Paul Sponsel
Thixomolding– Semi-Solid Injection Moulding
www.mmpmg.com
Paul Sponsel
Thixo-what?– Thixotropic flow characterics
“Thixotropy is a time-dependent shear thinning property. Certain gels or fluids that are thick, or viscous, under static conditions will flow (become thin, less viscous) over time when shaken, agitated, sheared or otherwise stressed (time dependent viscosity). They then take a fixed time to return to a more viscous state.” – Wikipedia
2
Examples?
Paul Sponsel
Thixo-what?– Thixotropic flow characterics
“Thixotropy is a time-dependent shear thinning property. Certain gels or fluids that are thick, or viscous, under static conditions will flow (become thin, less viscous) over time when shaken, agitated, sheared or otherwise stressed (time dependent viscosity). They then take a fixed time to return to a more viscous state.” – Wikipedia
3www.wikipedia.org
Paul Sponsel 4
1 Technical basics
2 Chemical and physical basics
3 Manufacturers
4 Applications
5 Summary and outlook
Agenda
www.nmfgmbh.de
Paul Sponsel
Semi-solid metal casting (SSM) – Processes
Semi-solid metalcasting
SIMAThixocasting Rheocasting Thixomolding
5www.wikipedia.org
Paul Sponsel
Semi-solid metal casting (SSM) – Processes
Semi-solid metalcasting
SIMAThixocasting Rheocasting Thixomolding
6www.wikipedia.org
Paul Sponsel
Thixomolding– Machine set-up
7
Mold Product
Slurry
Non-return
valve
Heater bands
Cylinder
Screw
Rotary drive
Accumulator
Automatic vacuum
conveying system
Feeder
Nozzle
Magnesium
chips
Inert gas
(Argon)
www.nmfgmbh.de
High speed
Injection system
Paul Sponsel
Thixomolding– Conditions and Process
• Basic material Magnesium granules (size ~0.5 – 5 mm)
• 3-zone-screw with feeding, compression and homogenization
• Granulat is molten by heater bands and sheared by screw
• Cylinder, screw and heater have to beheated up to operating temperature (560°C – 630°C)
• Injection speed up to 6 m/sHigh injection speed is necessary
due to low thermal capacity and conductivity of magnesium
• Cold slugs fall in separate cavity
8
Close tool Drive up injection
tool
Inject + press
Convey + cool
CoolDrive back injection
tool
Open tool
Remove work piece
Apply abherent
Thixospritzgießen von Magnesiumlegierungen - Gefüge und mechanische Eigenschaften; Scharrer, Martin [2008]
Paul Sponsel 9
1 Technical basics
2 Chemical and physical basics
3 Manufacturers
4 Applications
5 Summary and outlook
Agenda
Paul Sponsel
Magnesium– Grid structure and alloys
• Hexagonal structure underatmospheric pressure
• Stacking order is ABAB
• Most common alloy is Aluminum
• Eutectic at 436°C and 33% Aluminum
Improves castability through low melting point
• Technical alloys contain around 10% Aluminum bymass
Up to 12.7% by mass of Aluminum are solvable
Hardening process through heat treatment possible
Oxid layer improves corrosion protection
10
0 10 20 30 40 50
200
250
300
350
400
450
500
550
600
650
700
Aluminum % by mass
Tem
pera
ture
in °
C
Thixospritzgießen von Magnesiumlegierungen - Gefüge und mechanische Eigenschaften; Scharrer, Martin [2008]
Paul Sponsel
Magnesium– Aluminum, zinc, manganese alloys
• Zinc forms low melting eutectic at 51.3% by massand 342°C
• Maximal solubility 6.2% Zinc by mass
Improves castability through low melting point
Improves strength through solid solution hardening
Improves elongation
• Technical alloys contain up to 1% Zinc by mass
• Manganese improves corrosion behaviourIron impurities enter during alloying
Manganese binds them in Fe-Mn-Al compounds
• Technical alloys contain up to 0.4% Manganese
11
0 10 20 30 40 50 60
0
10
20
30
40
50
60
MgZnMg2Zn3
Aluminum % by mass
Thixospritzgießen von Magnesiumlegierungen - Gefüge und mechanische Eigenschaften; Scharrer, Martin [2008]
Paul Sponsel
Thixomolding– MicrostructureTwo-stage process:
1. Heating in the cylinder:
During heating in the cylinder the α-crystals
and melt exist in thermodynamic equilibrium,
the so called solidus-liquidus interval.
2. During and after injection:
The melt cools down at high cooling rates
which leaves the typical fine-grained casting
structure.
12Thixospritzgießen von Magnesiumlegierungen - Gefüge und mechanische Eigenschaften; Scharrer, Martin [2008]
Paul Sponsel
Rheology– Shear time, shear rate and temperature
13
Three parameters influence the viscosity of materials with thixotropic flow characteristics:
Shear time
Viscosity decreases with higher shear
time
Dendric structure is transformed to
equiaxed crystals
Shear rate
Viscosity decreases with higher share
rate
Local solid-phase accumulation in
the middle of the workpieces
Temperature
Viscosity decreases with higher
temperature
Lower solid-phase share in
the melt
Thixospritzgießen von Magnesiumlegierungen - Gefüge und mechanische Eigenschaften; Scharrer, Martin [2008]
Paul Sponsel
Thixomolding vs. die casting– Microstructure
14Thixospritzgießen von Magnesiumlegierungen - Gefüge und mechanische Eigenschaften; Scharrer, Martin [2008]
Paul Sponsel
Magnesium alloys– Short codes
“Magnesium alloys are referred to by short codes (defined in ASTM B275) which denote approximate chemical compositions by weight. For example, AS41 has 4% aluminum and 1% silicon; AZ81 is 7.5% aluminium and 0.7% zinc. If aluminium is present, a manganese component is almost always also present at about 0.2% by weight which serves improve grain structure; if aluminum and manganese are absent, zirconium is usually present at about 0.8% for this same purpose.” – Wikipedia
15
7.5% aluminum
A Z 8 1
0.7% zinc
Paul Sponsel
Thixomolding vs. die casting– Mechanical properties
16
Test.- temp.
(°C)
Thixomolding (NMF) Die Casting Reference
Rm
(MPa)
Rp02
(MPa)E (%)
Rm
(MPa)Rp02 (MPa) E (%)
AZ91D RT 260 170 8 260 160 6
150 175 130 19 160 100 18
AM60B RT 253 150 11 247 123 12
150 157 114 24 - - -
AZ70 RT 259 150 11 - - -
150 165 120 25 - - -
AJ52 RT 245 151 10 212 134 6
150 172 128 20 163 110 12
AJ62 RT 257 151 11 239 142 8
150 170 125 15 163 108 19
AS31 RT 251 145 13 216 130 8
150 155 113 26 - - -
AS41 RT 265 152 13 240 130 10
150 160 118 29 150 90 -
Advances in Magnesium Thixomolding®; Lohmüller et. Al. [2007]
Paul Sponsel
Thixomolding vs. die casting– PorosityOverall porosity can be measured with the Archimedes-principle (weighing each part in airand isopropyl alcohol).
17
6
4
2
0
8
poro
sity
in %
6
4
2
0
8
poro
sity
in %
AJ62ρ = 1,80 g/cm²
Pressure die casting
Thixomodling
AZ91ρ = 1,81 g/cm²
Pressure die casting
Thixomodling
Advances in Magnesium Thixomolding®; Lohmüller et. Al. [2007]
Paul Sponsel
Thixomolding vs. die casting– Energy consumption
A rough estimate for the needed energyfor heating up the alloy can be obtainedwith the following equation:
∆𝐸 = න
𝑅𝑇
𝑇𝑆
𝐶𝑃,𝑆𝑜𝑙𝑖𝑑𝑑𝑇 + ∆𝐻 + න
𝑇𝐿
𝑇𝑃
𝐶𝐿,𝑙𝑖𝑞𝑢𝑖𝑑𝑑𝑇
Depending on the solid phase contentThixomolding has a significant lowerenergy consumption compared to die casting.
18
-24% -17% -12% -4%
200
800
600
400
1000
0
580 590 600 650 680
AZ91
Thixomolding Die casting
Energ
y (
kJ/k
g)
Temperature (°C)
Advances in Magnesium Thixomolding®; Lohmüller et. Al. [2007]
Paul Sponsel
Thixomolding vs. die casting– Cover gas consumption
19
N2/
0,2% SF6
N2 /
0,25%
HCF-134a
N2 /
1,5% SO2
Cost
(%)
80
20
40
60
0
100
Thixo-
molding
24 Nl/h
Die casting
400 Nl/h
CO
2-E
quiv
ale
nt (t
/a)
ArgonN2/
0,2% SF6
N2 /
0,25%
HCF-134a
N2 /
1,5% SO2
Argon
Thixo-
molding
24 Nl/h
Die casting
400 Nl/h
800
200
400
600
0
1000
Toxic
, C
orr
osiv
e
1177 k
g S
O2/a
Advances in Magnesium Thixomolding®; Lohmüller et. Al. [2007]
Paul Sponsel 20
1 Technical basics
2 Chemical and physical basics
3 Manufacturers
4 Applications
5 Summary and outlook
Agenda
Paul Sponsel
Thixomolding manufacturers– Highly specialized machines
21
• Thixomolding machines are a relativlynew technology
• Only approximately 300 machines aresold worldwide
• Japan Steel Works Ltd. (Japan) and Husky Injection Molding Ltd. (Canada) are the only two manufacturers
• Machines are available with clampforces between 75t and 1600t
• In Europe there are only companies in Austria, Belgium, France and Germany who are dealing with thistechnology
300
250
200
150
100
50
0
Gesamt
Europa
Japan/Südostasien
Nordamerika
Num
ber
of
machin
es
Thixospritzgießen von Magnesiumlegierungen - Gefüge und mechanische Eigenschaften; Scharrer, Martin [2008]
Paul Sponsel 22
1 Technical basics
2 Chemical and physical basics
3 Manufacturers
4 Applications
5 Summary and outlook
Agenda
Paul Sponsel
Thixomolding– Applications in automobile industry
• Seat frames
• Steering wheels
• Road wheel
• Oil pumps
• Key lock housing
• Transmission parts
• Navigation system parts
23www.jsw.co.jp
Paul Sponsel
Thixomolding– Electronic equipment
• Cameras
• Notebooks
• Mobile phones
• Monitors
• Heat sinks
• LCD projectors
• Optical pickups
24Neue Entwicklungen beim Thixospritzgießen von Magnesiumlegierungen; Eibisch et. Al. [2005]
Paul Sponsel 25
1 Technical basics
2 Chemical and physical basics
3 Manufacturers
4 Applications
5 Summary and outlook
Agenda
Paul Sponsel
Thixomolding– Summary
26
Advantages Disadvantages
+ Low energy consumption
+ Only argon needed as inert gas (no global
warming potential and low price)
+ Low porosity of work pieces
+ High tensile strength (Rm)
+ High yield strength (Rp02)
+ High E-modulus
+ Narrow wall thicknesses achievable
+ Near net-shaped work pieces
+ High market growth potential (especially
automobile sector)
- Small temperature range to achieve solidus-
liquidus intervall
- New technology, not researched a lot yet
- Only a few manufacturers (support?)
Paul Sponsel
Thixomolding– New developments
Particle Reinforced Magnesium alloys (Power steering pump bracket)
• Intense mixing
• Short contact times
• Low processing temperatures
Hot Runner Systems• Pre heated molds
• Reduces shot weight up to 35%
Melt metallurgical production of Magnesium granules• Cost of Magnesium chips is crucial to Thixomolding
• Prototype equipment for melt metallurgical technique
27Advances in Magnesium Thixomolding®; Lohmüller et. Al. [2007]