Casting Technologies CASTING Hot Chamber Cold Chamber Henry Hu, Ph.D

OUTLINE

• Melt Preparation and Transfer MAGNESIUM IN METALLURGY • Die Casting Technologies CASTING Hot Chamber Cold Chamber Henry Hu, Ph.D.

Professor • Thixomolding Engineering Materials Program Department of Mechanical, Automotive & Materials Engineering University of Windsor

Short Course_Mg COM2006, Montreal 1 Short Course_Mg COM2006, Montreal 2

Mg Alloy Phase Diagram Melting Furnace for Mg Alloys

Atomic % Aluminum 700 1020 30 Die Casting Alloys 650 Typical Casting 600 Temperature Range 630 - 650 oC • AZ91D

C • AM60B

e 500 r α + liquid •AM50A,

r e 400

e T α + β 300 Alloy Composition 9.0% Al

200

010 20 30 40 Weight % Al Short Course_Mg COM2006, Montreal 3 Short Course_Mg COM2006, Montreal 4

Crucible for Holding Liquid Mg Charging Ingots Prior to Melting

Materials: • Clean • Cr-Mo Nickel Free Steel (life: 24 months) • Dry • Laminated Cr Steel outer Shell (heating) • Storage: Mild Steel Inner (life: 6-12 months) - Dry to remove MgCO •H O • All Mild Steel (life: 6 months) 3 2 MgO + CO2 + H2O -> MgCO3 •H2O

• Preheated (> 150 oC)

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1 Prevention of Melt Burning /Oxidization Prevention of Melt Burning /Oxidization

3000 2450 2500

2000

1500 1107

1000 650 660

Temperature (C) 500

0 Mg Melting Al Melting Mg Boiling Al Boiling

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Prevention of Melt Burning /Oxidization Prevention of Melt Burning /Oxidization • Protective Gases • Salt Flux 0.2% SF6 + CO or 0.5% SO2 + Dry Air e.g., 50% MgCl, 30% KCl and 20% NaCl Advantages: Disadvantages: Problems: Flux comtamination, corrosion, - No flux contamination - Need crucible cover + HCl fume, Cl2 pollution - Lower % of metal loss gas mixing system - Non-toxic (SF6) - High concentration causes • Burning Inhibitors corrosion problems - Create strong, thin metallic film Addition of 0.0005% (5 ppm) Be - Small quantity needed if well (if not used properly) distributed over the melt - Not efficient at very high T - Green house effect

- Health concerns (SO2)

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Hot Chamber Die Casting Hot Chamber Die Casting

Coolant In Cooling Vacuum Lines Manifold Goose Neck Mold Molten Piston Metal Bath

Coolant Out

Step 2. - Vacuum is applied to draw Step 1. -Mold is closed. Step 3. - Piston injects metal into mold. liquid metal up goose neck.

Piston Ejection Pins

Step 5. - Vacuum is released, mold Step 6. - Feed gates are opened and part ejected. machined off part. Step 4. - Part solidifies. Short Course_Mg COM2006, Montreal 11 Short Course_Mg COM2006, Montreal 12

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 Vacuum is used to a limited extent in hot chamber up to 2-3 kilograms. magnesium die casting. The technical literature is limited as to the effect of vacuum assistance on the This process is not used for aluminium parts. Static properties of magnesium die castings. Further metal pressures are usually less than in cold chamber investigations are needed to document the extent to machines,typically in the range of 20-30 MPa (2900- which vacuum provides significant improvements of 4400 psi). properties in magnesium die castings.

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.

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Hot Chamber Die Casting - Applications Cold Chamber Die Casting – Cell Layout

notebook computes Telecommunication

Power Tool

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Cold Chamber Die Casting – Melt Transfer Cold Chamber Die Casting

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3 Die Casting: Cold Chamber Die Casting Magnesium vs. Aluminum

Coolant In Advantages Disadvantages Cooling Lines Piston • lower density for • higher material cost (1.3 Coolant Out weight reduction times in volume) (up to 50%) • poorer high temperature Shot Chamber Properties Step 1. - Metal mold is closed and Step 2. - New and re-mixed alloy • faster shot speed is injected into the mold. the injector shot-chamber is filled. (up to 50%) • lower elastic modulus • longer die life • more difficulties in scrap (2-5 times) recycling • thinner wall casting (1 - 2 mm) • lower machining cost Step 3. - Rapid solidification Step 4. - Ejection of part & runner. of part under high pressure. (up to 40%) Short Course_Mg COM2006, Montreal 19 Short Course_Mg COM2006, Montreal 20

Cold Chamber Die Casting - Machines 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 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 maximum shot plunger speeds exceeding 10 m/s. the dimensional variations from shot to shot. The use of fixed or Static casting pressures are commonly in the range of moveable cores adds to the flexibility to cast complex, near net shapes. 30- 70 MPa (4400-10000 psi). The locking force of the The geometry of the runner and gate system determines the die filling characteristics. The thermal conditions in the die determine the machine holding the two die halves together solidification of each part and thereby the microstructure and quality. exceeding 4000 tons are commercially available. 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 21 Short Course_Mg COM2006, Montreal 22 www.hydro.com/magnesium/en/

Cold Chamber Die Casting – Die Design 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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4 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 2 - Round edges and cornersto facilitate smooth filling PQ Diagram • 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 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 Cold Chamber Die Casting – Max Metal Pressure 1

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5 Cold Chamber Die Casting – Max. Fill Rate 2 Cold Chamber Die Casting – Max. Fill Rate 2

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Cold Chamber Die Casting – Theoretical Fill Rate 3 Cold Chamber Die Casting – Fill Time 3

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Cold Chamber Die Casting – Cold Chamber Die Casting – Theoretical Fill Rate 3 Metal Pressures for Max and Min Gate Velocities 4 ,5

3 2

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6 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 Zn: 40 – 55 m/s, 1600 – 2160 in/sec ) 4

• 100 m/s (4000 in/sec) for thin-wall castings 3 • less than 30 m/s for casting with 4-5 mm 2 wall thickness

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Cold Chamber Die Casting – PQ2 Diagram Cold Chamber Die Casting – Gate Area

1 Q A = (minimum) g p (2 g) cd 7 ρ 5 6 Q: volume flow rate 4 p: metal pressure 3 cd : constant (0.5) 2 g: gravity

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Cold Chamber Die Casting – Gating & Plunger 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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7 Global Die Cast Mg Applications Magnesium Instrument Panel

Company Applications

GM instrumental panels, clutch housing & piston, transmission stators, • Audi and GM glove box door, roof frame, seat frame, pedal bracket, steering column bracket, road wheels, transfer case, valve cover, electric motor housing • AM60 and AM50 Alloys FORD IP bracket, sun roof panel, pedal bracket, steering column bracket & component, transfer case, valve cover, clutch housing, steering wheels • One-piece die casting vs. 12 steel Chrysler air bag housing, steering column bracket, valve cover, steering wheel, stampings and plastic parts instrumental panels, alternator bracket, front headlight retainer • 30-50% weight reduction Audi instrumental panels, manual transmission housing

wheels, gearbox housing, valve cove BMW • Reduced cost seat structure, instrumental panels, steering wheel Fiat

• More styling flexibility 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 “G” Van Instrument Panel GM “W” Car Instrument Panel

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Magnesium Seat Structure 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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8 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 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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Thixomolding Why 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

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9 Thixomolding Mg Alloy Phase Diagram Atomic % Aluminum Normal Die Casting Temperatures > 700 C 700 1020 30 650 Typical Thixomolding 600 Temperature Range 560 - 590 C

e 500

r α + liquid

r e 400

e T α + β 300 Alloy Composition 9.0% Al

200 560- 590 oC

010 20 30 40 Short Course_Mg COM2006, Montreal 55 Short Course_MgWeight % Al COM2006, Montreal 56 http://www.jsw.co.jp/en/mg_f/mg_indexe.htm

Typical Processing Parameters Thixomolding

Thixomolding process Thixomolded product • Barrel Temperature: 565-585°C • Mold Temperature: 175-250°C • Lower melting • Fewer blow holes • Injection Pressure: 700-1000 b a r temperature than • Less shrinkage • Screw Rotation: 100-250 rpm die-casting • Fewer hot cracks • Max. Linear Inj. Rate: 400 cm/s • Smooth melt flow • Smaller distortion • Higher dimensional 150-250 cm / s • Typical Inj. Rates: accuracy

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Item Thixomolding Die-Casting Hot-Chamber Cold-Chamber Thixomolding 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 Mold Requirements Thixomolding Project area at same clamping force Medium Large Medium Max. machine size 1600t 900t 4500t vs. Blow hole Few Small Many • H13 steel Surface defect Few Small Many Die Casting Shrinkage crack Few Small A few • High temperature tolerances Fluidity Excellent Good Good Surface roughness Excellent Good Good • More robust design Flash Small Few Much Shrinkage Few Small Many 3.8~4.5/1000 5~5.5/1000 7~8/1000 Mold shrinkage Dimension accuracy • Vacuum venting Excellent Good Poor o Warp Few Small Much • Hot oil heated (250 C) Mechanical properties Excellent Good Good Corrosion resistance Good Good Poor • Technical Thin wall Mold 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 Short Course_Mg COM2006, Montreal 59 Short Course_MgDross/Sludge Nothing COM2006,Much MontrealMuch 60

10 Thixomolding Tensile Properties Tensile properties (AM50A) vs. process parameters Thixomolding vs. Cold Chamber Die Casting Barrel Injection Y.S. U.T.S. El. Material Process Temperature velocitiy (MPa) (MPa) (%) (K) (m/s) AZ91D Thixomolding 878 1.4 180 299 10

Die casting 160 240 3

Thixomolding 893 1.4 148 278 19 AM60B Die casting 963 2.9 115 239 12 (Die casting)* 130 225 8

Thixom olding 898 1.4 140 269 20 AM50A Die casting 963 2.9 112 232 13 (Die casting)* 125 210 10 AS41B Thixom olding 903 1.7 157 249 9 (Die casting)* 140 215 6 * Values from the literature

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Thixomolding – Tensile Properties Thixomolding – Applications Digital Camcorder Liquid Liquid VL-PD1 • Five components • 0.8 to 1.0 mm thick • by Nifco, Japan

Solid Solid Dendrite Dendrite Conventional Dendrite Thixotropic Structure of Sony DCR-PC10 Formation in Cast Alloy Semi-solid Alloy Resulting From Stirring • Right side housing • 0.8 to 1.0 mm thick

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Thixomolding – Applications Thixomolding – Applications Mini-Disc Players Notebook Computers HP Sojourn Panasonic SJ- MJ5/7 • base and LCD cover • 0.4 to 0.6 mm thick • 1.0 mm thick

Toshiba Sony MZ-E50 • Libretto: base and • 0.6 mm LCD cover -0.7 mm • Portege

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11 Thixomolding – Applications Thixomolding – Applications Digital Cameras Digital Projectors Fuji DS-300 • Three components EPSON Powerlite 7300 • 1.0 mm thick

VL-EF1 Sony VPL-X600 U

CV11

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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 • Elimination of SF6 for Mg Melt Protection • Mechanical Properties • Recycling • Interaction of Mechanical properties • New Casting Processes with the Vehicle Environment (Squeeze, Semi-solid, Vacuum) • Failure Analysis • Techniques for Melt Cleanliness Evaluation • Surface Protection • Rapid Prototypes • Corrosion & Erosion • Joining • Composites • Wrought Products • Heat Treatment

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