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SSR - Enhancing the Die Casting Process

SSR Station 2-Platen SSR Die Casting Cell

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Advantages of SSR™ Advantages of SSR™

• INCREASE PRODUCTIVITY:

• REDUCE CYCLE TIMES

• EXTEND DIE LIFE

• REDUCE DIE LUBRICATION USAGE

• ELIMINATE IMPREGNATION

• REDUCE SCRAP

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SSR™ – The Process and How it Works: SSR™ – The Process and How it Works:

Based on the fundamental principle

that a fine grain structure is created at

or near the liquidus temperature, a

modified rheocasting approach was

developed at Massachusetts Institute

of Technology (M.I.T.) in 2000 that

uses a cooling/stirring rod to rapidly

extract heat from molten alloy and

initiate solidification.

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Aluminum Die Casting - Increasing Market Share

• Further growth of die casting (and to maintain existing market share compared with steel and polymers) requires improvement in quality, cost, and properties:– Quality: reduced scrap rates– Cost: improved cycle time, increased die life,

reduced metal waste– Properties: new alloys and capability to heat treat

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SSM Process

• SSM (ThixoCasting) has typically been applied to high performance alloys: 357/356

• SSR (Semi-Solid Rheocasting) can be used for both high performance alloys and also for increasing quality and reducing cost of traditional alloy castings:380/383/356/357

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Producing Die Castings Cheaper and Better with SSR

• Reduced Cycle Time (more parts, same overhead costs!)

• Extended Tool Life• Less Porosity (eliminate

impregnation)• Reduced core draft

angles (less machining)

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SSR 380 (AlSi8.5Cu3)• Most SSM processes transfer slurry at

~50% solid to the DCM and or maintain furnace temperature near the liquidus – Casting machine needs major changes to

use SSM - increased stroke and power on a horizontal machine or vertical injection

– 380 alloy is about 25% primary solid - existing SSM processes are not compatible with this

– Low-temperature pour slurry processes maintain temperature near the liquidus - non-ideal for 380

• SSR has the unique ability to create slurry of less than 20% solid and maintain higher temperatures in the holding furnace - all necessary for creating 380 slurry

Rod stirring and cooling the melt

Partial fill test

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Advantages of SSR Vs Other Systems

– Controlled heat removal and convection with the rod

• accommodates furnace temperature fluctuations for consistent slurry

• furnace temperature can be set above sludge formation temperature

– Heat removal is through the rod, and not through the outer surface of a container

• avoids dendritic skin.

– Low volume fraction solid

• operates with conventional die casting machines - no major changes to die casting machine

• minimizes cold flake formation unlike low-temperature pouring

– Uniform, fine microstructure without lengthy coarsening time - complete cycle time from liquid to casting is less than 30 seconds

• One vessel system - more process friendly

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SSRTM Station • Molten aluminum is brought to the station in a ladle

cup via a robot• Metal is stirred for a short duration, enough to

rapidly cool the metal through the liquidus temperature - PLC closed loop system based on furnace and rod temperature controls stir time

• Molten metal is delivered to the cold chamber for casting at a low fraction solid

• Rod is cleaned and air cooled before its next cycle - requires multiple rods because of air cooling limitations

• Machine footprint is approximately 1.2m x 1m - ideal for retrofitting to a die casting machine

• Designed to handle 5 kg of melt every 35 seconds with a superheat of 45 °C - other melt sizes can be handled with changes in cycle time and maximum superheat - have gone as large as 10 kg

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Ladling Robot

Furnace

SSRTM StationDie Casting Machine

1500-ton 2-Platen die casting cell

SSRTM Cell Layout

Easy to Retrofit!

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SSR 356 (AlSi7Mg) Alloy

Castings That Can Benefit from SSRTM

• Highly Engineered Die Castings– Typically made with 380 (AlSi9Cu3)– Castings with thick sections that have shrinkage

problems– Smaller core draft angles (less machining)– Castings that require high ductility for better energy

absorption characteristics– Pressure tight castings (avoid impregnation)– ABS pumps, master brake cylinders, fuel rails, rack

and pinion, differential carriers, transmission cases, etc.

• High Integrity Castings– Heat treatable and weldable– Currently made from 356 alloys (AlSi7Mg) by either

squeeze or permanent mold– Suspension and wheel castings (10%+ elongation)

SSR Produced Casting

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SSR 380• Cycle time improvement

– Demonstrated 10-25% through reduction in dwell and spray time

• Improved die life because of reduced thermal shock and fatigue

• Reduced shrinkage and other porosity– Demonstrated improved leak

performance• Ability to use reduced core draft

angles - avoid machining– Demonstrated reduced core draft

angles

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SSR 380 Alloy Microstructure (AlSi9Cu3)

SSR is unique in its ability to cast 380 - the combination of low fraction solid when transferring to the cold chamber and the ability to maintain a furnace holding temperature above 640 °C avoids sludge formation.

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SSR Casting Applications

•Shot weight of 6.5 kg (14.3 pounds)

•Cycle time reduction of 25%

•Eliminated need for impregnation - passed leak test of 5 bar (75 psi)

•Reduced core draft angle to 0.2° - reduces need for machining

Pump Filter Housing

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SSR Casting Applications

•Cycle time reduction of 20%

•Die lubrication reduction of 50%.

•Injection speed of 0.25 m/s.

•Reduced scrap rate by 50%

Steering Rack Casting SSR

Die Casting

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Benefits of SSRTM

• Dwell time reduction of 25-60% and reduced spray and cooling time - translates to 12-25% reduction in overall casting cycle time

• Potential die life increase of 50%+• Reduced lube usage of 50%• Observable reduction of porosity in thick

wall sections of die castings - elimination of impregnation

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Cost Justification of SSRA detailed cost model was developed to show the potential cost savings of using SSR. An example based on a case study casting is shown.

The cost model utilizes production data and variables such as castings produced per year, scrap rates, tooling and material costs, SSR Station operational and equipment costs, impregnation rates and costs, etc.

Cost Per CastingDie

CastingSSR

CastingMaterial € 4.90 € 4.90Overhead (labor, electricity, building, SSR Station cost) € 4.63 € 4.44Tooling € 1.03 € 0.69Impregnation € 0.70 € 0.07TOTAL COST € 11.26 € 10.10

Process ImprovementsCycle Time 15%Die Life 50%Impregnation Reduction 90%

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Why SSRTM?• SSM is a promising technology, but the costs are prohibitive• SSR is the first SSM process to offer an economical solution for

producing 380 die castings• SSR is unique among rheocasting processes

– Achieves the uniform, small grain, spheroidal microstructure necessary for semi-solid casting without sacrificing simplicity

– Larger process window - no need for special furnaces or die casting machine shot ends

– One vessel of alloy and no consumables– Flexible system for various die casting machine configurations

- easy and inexpensive to retrofit• SSR is a retrofittable rheocasting process that is simple and

efficient - without sacrificing ideal semi-solid microstructures - therefore, die casting can economically outperform permanent mold!