OUTLINE
• Melt Preparation and Transfer • Die Casting Technologies
MAGNESIUM IN METALLURGY
CASTING
Hot Chamber Cold Chamber
Henry Hu, Ph.D.
• Thixomolding
Professor Engineering Materials Program Department of Mechanical, Automotive & Materials Engineering University of Windsor
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Mg Alloy Phase Diagram
2
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Melting Furnace for Mg Alloys
Atomic % Aluminum
700
10
20
650
30
Typical Casting Temperature Range 630 - 650 oC
600
Temperature C
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α + liquid
500
Die Casting Alloys • AZ91D • AM60B •AM50A,
400
α+β 300
Alloy Composition 9.0% Al 200
0
10
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20
30
40
Weight % Al
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Crucible for Holding Liquid Mg
Charging Ingots Prior to Melting
Materials: • • •
Cr-Mo Nickel Free Steel (life: 24 months) Laminated Cr Steel outer Shell (heating) Mild Steel Inner (life: 6-12 months) All Mild Steel (life: 6 months)
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• • •
Clean Dry Storage: - Dry to remove MgCO3 •H2O MgO + CO2 + H2O -> MgCO3 •H2O
•
Preheated (> 150 oC)
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1
Prevention of Melt Burning /Oxidization
Temperature (C)
3000
Prevention of Melt Burning /Oxidization
2450
2500 2000
1107
1500
650
1000
660
500 0 Mg Melting Al Melting
Mg Boiling
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Al Boiling COM2006, Montreal
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Prevention of Melt Burning /Oxidization
• Salt Flux
0.2% SF6 + CO or 0.5% SO2 + Dry Air - No flux contamination - Lower % of metal loss - Non-toxic (SF6)
Problems: Flux comtamination, corrosion,
- Need crucible cover +
HCl fume, Cl2 pollution
gas mixing system
• Burning Inhibitors
- High concentration causes corrosion problems
- Small quantity needed if well
(if not used properly)
distributed over the melt
e.g., 50% MgCl, 30% KCl and 20% NaCl
Disadvantages:
- Create strong, thin metallic film
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Prevention of Melt Burning /Oxidization
• Protective Gases Advantages:
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Addition of 0.0005% (5 ppm) Be
- Not efficient at very high T - Green house effect - Health concerns (SO2)
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Hot Chamber Die Casting
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Hot Chamber Die Casting Cooling Lines
Coolant In
Vacuum Manifold Goose Neck
Mold
Piston
Molten Metal Bath
Coolant Out
Step 1. -Mold is closed.
Step 2. - Vacuum is applied to draw liquid metal up goose neck.
Step 3. - Piston injects metal into mold.
Piston Ejection Pins
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Step 4. - Part solidifies.
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Step 5. - Vacuum is released, mold opened and part ejected.
Step 6. - Feed gates are machined off part.
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2
Hot Chamber Die Casting
Hot Chamber Die Casting- Vacuum
The hot chamber process is used extensively for casting of smaller magnesium parts with shot weights up to 2-3 kilograms.
Vacuum is used to a limited extent in hot chamber magnesium die casting. The technical literature is limited as to the effect of vacuum assistance on the properties of magnesium die castings. Further investigations are needed to document the extent to which vacuum provides significant improvements of properties in magnesium die castings.
This process is not used for aluminium parts. Static metal pressures are usually less than in cold chamber machines,typically in the range of 20-30 MPa (29004400 psi). A typical wall thicknesses of castings is around 1.50 mm for the complex stiffener frame or could be less than 1 mm for simple gemetries such as notebook computer and cellular phone cases. Short Course_Mg
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Hot Chamber Die Casting- Applications notebook computes
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Cold Chamber Die Casting – Cell Layout
Telecommunication
Power Tool
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www.cwmdiecast.com, www.lunt.com
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Cold Chamber Die Casting – Melt Transfer
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Cold Chamber Die Casting
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Die Casting:
Cold Chamber Die Casting
Magnesium vs. Aluminum
Coolant In
Cooling Lines Piston Coolant Out
Disadvantages
• lower density for weight reduction (up to 50%)
• higher material cost (1.3 times in volume)
• faster shot speed (up to 50%)
Shot Chamber
Step 1. - Metal mold is closed and the injector shot-chamber is filled.
Advantages
Step 2. - New and re-mixed alloy is injected into the mold.
• longer die life (2-5 times)
• poorer high temperature Properties • lower elastic modulus • more difficulties in scrap recycling
• thinner wall casting (1 - 2 mm) Step 3. - Rapid solidification of part under high pressure.
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• lower machining cost (up to 40%)
Step 4. - Ejection of part & runner.
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Cold Chamber Die Casting- Machines
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Cold Chamber Die Casting – Die Design
In general, the cold chamber die casting process, can be used for magnesium and aluminium alloys. However, the lower heat content in magnesium compared to aluminium is important to the die casting process. To avoid solidification of the magnesium alloy during die filling, a shorter fill time is required for magnesium than for aluminium. For this reason, some magnesium die casters specify machine designs with maximum shot plunger speeds exceeding 10 m/s. Static casting pressures are commonly in the range of 30- 70 MPa (4400-10000 psi). The locking force of the machine holding the two die halves together exceeding 4000 tons are commercially available. Short Course_Mg
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Cold Chamber Die Casting – Die Design
The die is a complex device that has to fulfill a multitude of functions. It defines the general geometry of the part and has a strong influence on the dimensional variations from shot to shot. The use of fixed or moveable cores adds to the flexibility to cast complex, near net shapes. The geometry of the runner and gate system determines the die filling characteristics. The thermal conditions in the die determine the solidification of each part and thereby the microstructure and quality. Over a large number of shots, the heat transfer characteristics of the die determine the attainable cycle time. The die is fitted with a system to eject the part after solidification. Short Course_Mg COM2006, Montreal 22 www.hydro.com/magnesium/en/
Cold Chamber Die Casting – Die Materials • steel resistant to thermal shock (commonly, H13 steel or a steel with similar qualities) • H13 premium quality steel is commonly supplied to the die manufacturers in a soft annealed condition with spheroidized carbides to improve machinability. After machining, the die cavity parts are hardened and partially annealed to a hardness typically in the range of 46-48 HRC. • Only the die cavity and special parts of the die need to be made of H13 steel. This usage typically corresponds to 20-25 % of the die weight. The remaining parts of the die are made from mild steel and medium carbon steel. Frequently, standardized unit dies are used, especially for smaller castings with relatively simple geometries. Such unit dies consist of the main frame of the die, including the ejector system. • The die cavity inserts can be exchanged, and the same unit die can thus be used for a number of different castings. •Magnesium die casting alloys contain less heat per unit volume than aluminium alloys, and the solubility of iron in the molten metal is very low. This leads to a considerably longer lifetime for the dies used for magnesium, a factor of two or more being quite common.
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www.hydro.com/magnesium/en/
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Cold Chamber Die Casting – Part Design
Cold Chamber Die Casting- Process
• Section thickness - 1-4 mm due to excellent die filling characteristics - Uniform to avoid local hot spots causing solidification shrinkage - Gradual change in section thickness
• Easy die filling
PQ2 Diagram
- Round edges and cornersto facilitate smooth filling
• Rib for strengthening - Strength and stiffen parts instead of increasing section thickness
•Local overheating - Direct impact of molten metal at high speed causing local overheating of the die especially at small protrusions
• Draft Angle
- Normally 2-5 degrees - Possibly 1-3 degrees, or even zero draft due to low thermal contraction of Mg
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Cold Chamber Die Casting – Max Metal Pressure 1
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www.hydro.com/magnesium/en/
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Cold Chamber Die Casting – Max Metal Pressure 1
Metal Pressure, pm The pressure required to force molten metal through the die’s gate
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Cold Chamber Die Casting – Max Metal Pressure 1
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Cold Chamber Die Casting – Max Metal Pressure 1
1
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Cold Chamber Die Casting – Max. Fill Rate
Cold Chamber Die Casting – Max. Fill Rate
2
2
1
2
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Cold Chamber Die Casting – Theoretical Fill Rate 3
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Cold Chamber Die Casting – Fill Time
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Cold Chamber Die Casting – Theoretical Fill Rate 3
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3
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Cold Chamber Die Casting –
Metal Pressures for Max and Min Gate Velocities 4 ,5
1
3
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2
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Cold Chamber Die Casting –
Cold Chamber Die Casting –
Metal Pressures for Max and Min Gate Velocities 4 ,5
Metal Pressures for Max and Min Gate Velocities 4 ,5
• 40 - 85 m/s (1600 - 3390 in/sec) for typical
1
Mg die castings 5
(Al: 25 -40 m/s, 1000 - 1600 in/sec
4
Zn: 40 – 55 m/s, 1600 – 2160 in/sec )
• 100 m/s (4000 in/sec) for thin-wall castings • less than 30 m/s for casting with 4-5 mm
3 2
wall thickness Short Course_Mg
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NADCA
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Cold Chamber Die Casting – PQ2 Diagram
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Cold Chamber Die Casting – Gate Area
1
Ag =
(minimum)
cd
7
Q p (2 g )
ρ
5 6
Q: volume flow rate p: metal pressure cd : constant (0.5) g: gravity
4 3 2
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Cold Chamber Die Casting – Gating & Plunger
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Cold Chamber Die Casting – Gate Velocity
• 40 - 85 m/s for typical Mg casting (Al: 25-40 m/s; Zn: 40 – 55 m/s)
• 100 m/s for thin-wall castings • less than 30 m/s for casting with 4-5 mm wall thickness
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www.hydro.com/magnesium/en/
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NADCA
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Global Die Cast Mg Applications Company
Magnesium Instrument Panel
Applications
• Audi and GM • AM60 and AM50 Alloys • One - piece die casting vs. 12 steel stampings and plastic parts • 30 - 50% weight reduction • Reduced cost • More styling flexibility
instrumental panels, clutch housing & piston, transmission stators, glove box door, roof frame, seat frame, pedal bracket, steering column bracket, road wheels, transfer case, valve cover, electric motor housing
GM FORD Chrysler
IP bracket, sun roof panel, pedal bracket, steering column bracket & component, transfer case, valve cover, clutch housing, steering wheels air bag housing, steering column bracket, valve cover, steering wheel, instrumental panels, alternator bracket, front headlight retainer
Audi
instrumental panels, manual transmission housing
BMW
wheels, gearbox housing, valve cove seat structure, instrumental panels, steering wheel
Fiat Mercedes-Benz
seat frames, sun roof panel, steering column component intake manifold
Honda
Oil pan, cylinder head cover, wheels, valve cover
Toyota
steering wheels, valve cover, bracket
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GM “W” Car Instrument Panel
GM “G” Van Instrument Panel
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Magnesium Seat Structure
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Alfa Romeo Seat Frames
• Fiat and Mercedes • AM60 Alloy • Total part count reduction • 50% weight reduction • Reduced assembly operations • Dimensional accuracy
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Magnesium Oil Pan
Honda Engine Oil Pan
• Honda • ACM522 Alloy • 35% weight reduction • Gasoline - power hybrid car- Insight • Best fuel consumption – 35 km/liter
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GM 4 Wheel Drive Transfer Case
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Potential Die Cast Mg Applications • Transmission housing • Road wheels • Engine cradle • Body panels (door and hood) • Engine block • Radiator support • Knuckle • Bumper reinforcement beam • Oil pan • Oil/water pump housing • Pulley • Break disk rotor and caliper
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Why Thixomolding?
Thixomolding
• Net shape metal part production • Higher quality than diecast • Increased design flexibility • Reduced gas permeability • Lower energy and operating costs than diecasting
• Better environmental cleanliness • Better worker safety Short Course_Mg
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Thixomolding
Mg Alloy Phase Diagram Atomic % Aluminum
Normal Die Casting Temperatures > 700 C
700
10
20
650
Temperature C
30
Typical Thixomolding Temperature Range 560 - 590 C
600
α + liquid
500
400
α+β 300
Alloy Composition 9.0% Al 200
560- 590 oC
0
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http://www.jsw.co.jp/en/mg_f/mg_indexe.htm
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565 - 585°C 175 - 250°C 700 - 1000 bar 100 - 250 rpm 400 cm/s 150 - 250 cm/s
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Thixomolded product
• Lower melting
• Fewer blow holes • Less shrinkage • Fewer hot cracks • Smaller distortion • Higher dimensional
temperature than die - casting • Smooth melt flow
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http://www.jsw.co.jp/en/mg_f/mg_indexe.htm
Item
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Thixomolding
Thixomolding vs.
H13 steel High temperature tolerances More robust design Vacuum venting Hot oil heated (250 oC) Technical Thin wall Mold
Die Casting
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Cold-Chamber
Molding temp. °C
590~610
630~650
680~700
Injection speed m/s
1~4
1~4
1~8
Injection pressure kgf/cm2
500~1200
250~350
400~700
Material
Chip
Ingot
Ingot
Project area at same clamping force
Medium
Large
Medium
Max. machine size
1600t
900t
4500t
Blow hole
Few
Small
Many
Surface defect
Few
Small
Many
Shrinkage crack
Few
Small
A few
Fluidity
Excellent
Good
Good
Surface roughness
Excellent
Good
Good
Flash
Small
Few
Much
Shrinkage
Few
Small
Many
Mold shrinkage Dimension accuracy
3.8~4.5/1000 Excellent
5~5.5/1000 Good
7~8/1000 Poor
Warp
Few
Small
Much
Mechanical properties
Excellent
Good
Good
Corrosion resistance
Good
Good
Poor
Shot cycle
1(Standard)
0.8
0.9
Material cost
1(Standard)
0.85
0.9
Material yield
1(Standard)
1
1.2
Die's life
1(Standard)
0.9
0.8
Safe operation
Excellent
Good
Poor
Protection gas
Ar
SF6
SF6
Nothing
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Die-Casting Hot-Chamber
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accuracy
Mold Requirements
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40
30
Thixomolding process
Thixomolding
• • • • • •
20
Weight % Al
Thixomolding
Typical Processing Parameters • Barrel Temperature: • Mold Temperature: • Injection Pressure: • Screw Rotation: • Max. Linear Inj. Rate: • Typical Inj. Rates:
10
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60
10
Thixomolding
Tensile Properties
Tensile properties (AM50A) vs. process parameters
Thixomolding vs. Cold Chamber Die Casting Material
Process
Barrel Temperature (K)
Injection velocitiy (m/s)
Y.S. (MPa)
U.T.S. (MPa)
El. (%)
AZ91D
Thixomolding
878
1.4
180
299
10
160
240
3
Die casting
AM60B
Thixomolding
893
1.4
148
278
19
Die casting
963
2.9
115
239
12
130
225
8
(Die casting)*
AM50A
Thixom olding
898
1.4
140
269
20
Die casting
963
2.9
112
232
13
125
210
10
157
249
9
140
215
6
(Die casting)* AS41B
Thixom olding
903
1.7
(Die casting)* * Values from the literature
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http://www.jsw.co.jp/en/mg_f/mg_indexe.htm
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Thixomolding – Tensile Properties Liquid
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http://www.jsw.co.jp/en/mg_f/mg_indexe.htm
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Thixomolding – Applications Digital Camcorder
Liquid
VL • • •
PD1
Five components 0.8 to 1.0 mm thick by Nifco, Japan
Solid Dendrite
Solid Dendrite
Conventional Dendrite Formation in Cast Alloy
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Sony DCR- PC10 • Right side housing • 0.8 to 1.0 mm thick
Thixotropic Structure of Semi-solid Alloy Resulting From Stirring
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Thixomolding – Applications
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Thixomolding – Applications Notebook Computers
Mini-Disc Players
HP Sojourn • base and LCD cover • 1.0 mm thick
Panasonic SJ - MJ5/7 • 0.4 to 0.6 mm thick
Toshiba • Libretto: base and LCD cover- 0.7 mm • Portege
Sony MZ - E50 • 0.6 mm
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Thixomolding – Applications
Thixomolding – Applications
Digital Cameras
Digital Projectors
Fuji DS - 300 • •
Three components 1.0 mm thick
EPSON
Powerlite 7300
VL-EF1
Sony VPL - X600U CV11 Short Course_Mg
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Thixomolding – Applications Cellular Telephones
Technical Challenges for Magnesium Expansion
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Technical Challenges
Technical Challenges
Component Requirements
Manufacturing Issues
• Creep Resistant Alloys • Mechanical Properties • Interaction of Mechanical properties with the Vehicle Environment • Failure Analysis • Surface Protection • Corrosion & Erosion • Composites
• Elimination of SF6 for Mg Melt Protection • Recycling • New Casting Processes (Squeeze, Semi-solid, Vacuum) • Techniques for Melt Cleanliness Evaluation • Rapid Prototypes • Joining • Wrought Products • Heat Treatment
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