1. SSR - Enhancing the Die Casting Process
SSR Station
2-Platen SSR Die Casting Cell

2. Advantages of SSR™ INCREASE PRODUCTIVITY: REDUCE CYCLE TIMES
EXTEND DIE LIFE
REDUCE DIE LUBRICATION USAGE
ELIMINATE IMPREGNATION
REDUCE SCRAP
SSR like other rheocasting processes (processes that create slurry from ordinary alloy within the die casting cell) allows for production of primary alloys such as 356 (AlSi7Mg) on a die casting machine.
However, a main benefit of SSR is that it also works with secondary, conventional die casting alloys such as 380 (AlSi8.5Cu3). We believe that based on the markets needs and the infrastructure of die casters, this is potentially an even larger market than the need for casting primary alloys on die casting machines.
The simplicity of SSR, which keeps the operational costs low, combined with its ability to work with secondary alloys allows for the reduction of cost of existing die castings!

3. 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.
The process is very straightforward. Prof. Merton Flemings and his research team realized that the critical step in creating a spheroidal, non-dendritic microstructure was during the initial phases of solidification. Rapid cooling combined with stirring produced a very fine microstructure that quickly coarsened into the necessary semi-solid structure. The other remarkable discovery was that stirring beyond the point that the metal cooled below liquidus had no further impact on the structure of the metal. Essentially, the only stirring necessary was that which cooled the metal below the liquidus (the onset of solidification).
The schematic depicts the process in three steps. 1) The metal is held in a molten state 2) The spinning rod is inserted into the melt just long enough to cool below the liquidus and 3) the rod is removed.
Initial experiments at MIT used a copper rod.

4. 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
Die casting is always competing with other materials and processes for market share.
Die casting needs to improve these three characteristics to increase market share.

5. 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
SSM in the past focused on improving properties to expand the die casting market - SSR not only does this, but it also reduces cost and improves quality of existing die castings!

6. 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)
Cycle time is reduced through shorter dwell times (solidification) and reduced spray of the die.
Reduced heat decreases thermal shock on the tool and improves die life.
Reduced porosity can in some instances eliminate impregnation
Lower temperatures and solidification outside the mold allows for use of reduced core draft angles

7. 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
High fraction solid SSM processes - the majority of SSM processes - requires a die casting machine with long stroke and a large injection force. Large injection force is required because of the more viscous material, but more importantly, the shape of the SSM material is that the length to diameter of the SSM material (2.5:1) is much smaller than the typical aspect ratio of a cold chamber (8:1). This means that for a given amount of metal, the plunger tip must be quite large. A die casting might use a 70 mm tip while the SSM material requires a 100 mm tip, reducing metal pressure.
When secondary alloys freeze slowly (for example in air or a sand mold), secondary phases that contain Fe form and enlarge that lower casting properties. SSM processes at 50% solid would form these coarse Fe phases. SSR transfers slurry to the cold chamber near 10% solid, before these phases begin to form.
Finally, many rheocasting processes other than SSR maintain the furnace temperature near the liquidus - this forms sludge in secondary alloys and makes these processes only suitable with primary alloys.
These unique features of SSR makes it ideal for use with secondary die casting alloys
Partial fill test

8. 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
Besides working with secondary alloy, SSR has unique capabilities compared with other systems: LISTED ON THE SLIDE.
Process friendly and controllable.
Heat removal at the source of stirring - other SSM systems cool from the outside walls - this forms dendritic skin on the walls because there is a lack of fluid flow.

9. 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
Straightforward to go through the process

10. SSRTM Cell Layout SSRTM Station Die Casting Machine Ladling Robot
Furnace
SSRTM Station
Die Casting Machine
1500-ton 2-Platen die casting cell
Easy to Retrofit!

11. 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
SSR 356 (AlSi7Mg) Alloy

12. 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
Some redundancy, but it gets the point across!

13. SSR 380 Alloy Microstructure (AlSi9Cu3)
SSR is unique in its ability to cast 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.
These micrographs show the roundness of the primary phase. It’s not as nice looking as micrographs for 356, but this is because the 380 alloy contains less primary phase and more eutectic liquid. No evidence of sludge in the micrographs.

14. 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
Oil pump filter housing.
Now in production at 60,000 parts per year

15. SSR Casting Applications
Steering Rack Casting
Cycle time reduction of 20%
Die lubrication reduction of 50%.
Injection speed of 0.25 m/s.
Reduced scrap rate by 50%
Die Casting
Steering rack casting.
Another steering rack for a different customer has reduced cycle time by 20% and lubrication usage by 50%.

16. 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
Summary of benefits seen with SSR.

17. Cost Justification of SSR
A 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.
An example of cost savings based on cycle time, die life, and impregnation elimination. When profit margins are typically less than 10% per casting, a 1 euro savings per part on an 11 euro part is very substantial.

18. 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!