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8/9/2019 Al Components Information

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28 ENGINEERED CASTING SOLUTIONS SPRING 2002

R

In an effort to increase automobileefficiencies by reducing vehicle weight,

automotive engineers are using castingdesign and process advantages toconvert designs to aluminum.

Alfred T. Spada

educed weight and cost. This is a magical phrase to designengineers as long as it is followed by and still achieves the

required mechanical and physical properties.The trend toward lightweight aluminum components contin-

ues to grow each day. Whether it is the corporate average fueleconomy (CAF) standards in the automotive industry or just anOEMs drive to improve product performance by increasing effi-ciency through weight reduction, manufacturers are searching outopportunities to replace stampings, weldments, fabrications andcastings with cast aluminum components.

At the forefront of this trend is the automotive industry. Pushedby the CAF standards, automobile manufacturers are achievingweight reductions in every system of the vehiclefrom the en-gine and powertrain to the suspension. The target for the U.S.automotive industry and its Big ThreeGeneral Motors, Fordand DaimlerChrysleris an efficiency level of 80 miles/gal formidsize vehicles, according to the Design and Product Optimiza-tion for Cast Light Metals study from the U.S. Dept. of Energy andthe American Foundry Society. To achieve this goal, mass in thechassis, body and interior subsystems of automobiles must be re-duced by 50% without a detrimental effect to vehicle safety, com-fort, ride, performance or, most importantly, cost.

According to Stratecasts, Inc., Ft. Myers, Florida, aluminumcasting shipments for automobiles and light trucks are expected

to increase from 1.07million tons in 2001 to 1.65 mil-lion tons in 2011, an increase of 4.4% per year. This translates toan increase from 185 lb of aluminum castings per automobileand light truck in 2001 to 270 lb/car by 2011. The forecast statesthat close to half of these aluminum castings will be produced as

die castings (67% are diecast now), with the remaining compo-nents produced via the permanent mold, lost foam and sand cast-ing processes. Tables 1 and 2 highlight the forecast for aluminumcasting use in automobiles and light trucks.

While some of this conversion to cast aluminum is occurringin lower stress areas of the automobile, such as the transmission,the focus for the future is the highly-stressed, safety-critical ap-plications such as the brake and suspension systems.

Within the last decade, automotive engineers and casting sup-pliers have begun partnerships to develop aluminum castings withthe necessary properties and consistency to succeed in safety-criti-cal applications. This success has been due to design engineersincreased understanding of how to design castings for these ap-plications as well as suppliers improved manufacturing processesand technology to ensure quality at high production levels.

Opening Aluminums DoorThe conversion to aluminum in automobiles is driven by

Daimler-C h r y s l e r s Prowler is a show-

case for aluminum, in-cluding the cast brakerotors that provide a50% weight reduction.

Cast Component: Steering column upper bearing assembly forMitsubishi cast by Intermet Corp.

Casting Process: Diecasting.Converted From: Steel weldment.

Previously a steel weldment, this aluminum component was con-verted to an aluminum diecasting at a cost and weight savings.

A steel tube is cast-in to improve strength. The diecasting pro-cess also provides a near-net-shape that was previously

unachievable.For more information, circle 052 on last page.

Cast Component: Brake rotor for the Chrysler Prowlerautomobile cast by Eck Industries, Inc.

Casting Process: Semi-permanent mold casting.Converted From: Traditional design in iron.

The brake rotor was converted to a 359/SiC/20p aluminummetal matrix composite (MMC) alloy casting at a 50% weightreduction and without a loss in performance.

In terms of mechanical properties, the aluminum MMC brakerotors modulus and its wear rate in application are the same

as cast iron.For more information, circle 051 on last page.


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SPRING 2002 ENGINEERED CASTING SOLUTIONS 29

the goal of increased fuel and engine and drive trainefficiency due to reduced weight, improved aerodynam-ics and reduced cost (as a lighter overall vehicle tendsto have a lower total cost).

The success of conversions to aluminum for automo-biles first began with intake manifolds in the late 1970sand early 1980s, said Thomas Prucha, Intermet Corp.s di-rector of process research and development and chairmanof the American Foundry Society research board. Cast ineither 319 or 356 alloy, aluminum intakes delivered the

necessary strength at the same wall thickness as their ironpredecessors. Before 1980, almost all intake manifolds weregray iron. By the mid-1980s, nearly all gas engine intakemanifolds were cast aluminum. Today, only 40% of all au-tomobile intake manifolds are cast aluminum as plastichas begun to take away market share.

According to Prucha, the trend in safety-critical appli-cation conversions to aluminum began with the road wheelin the mid-1980s. Pushed by aesthetics, cast aluminum roadwheels (356 alloy) were replacing fabricated steel rims. Thealuminum is able to withstand the stress because the com-ponent is dynamically loaded, said Prucha. Today, 63% ofall automobile and light truck wheels are cast aluminum.

Another strong push to aluminum at that time and stillcontinuing today is occurring with engine cylinder headsand blocks. By redesigning the heads and blocks for alu-minum (with iron cylinder liners for blocks and powdermetal valve seats and valve stem guides for the heads) andincorporating numerous cast-in features such as oil pas-sages and return lines, automotive OEMs and their cast-ing suppliers have made these foundation components forengines cost-effective for total automobile cost.

Although aluminum is a more expensive material, the50% weight reduction we are able to achieve in blocks andheads coupled with the numerous cast-in features makes thetotal system cost a push when compared to their iron prede-cessors, said Stephen Pruss, manager-engineering group atGeneral Motors Warren Powertrain Engineering Center.

Today, 40% of blocks and 90% of heads are cast alumi-num. It is forecast that in 2006 60% of blocks and 96% ofheads will be aluminum.

But the conversion trend that has todays automotive en-gineers and aluminum foundries most intrigued is in safety-critical applications such as steering knuckles, crossmembersand brake rotors. According to Paul Bujalski, supervisor-castmetals engineering & prototyping, chassis & powertrainmaterials engineering, DaimlerChrysler Corp., This is thearea of opportunity for automotive manufacturers.

Strength, Stiffness & PackagingThe ability of design engineers to replace iron and steel

components with aluminum is based on three materialpropertiesstrength (ultimate tensile and yield, as well aselongation), stiffness (modulus of elasticity) and fatiguelifeand one application propertypackaging.

When considering the conversion of a component toaluminum for an automobile or some other end product,Prucha identified four primary areas of concerns. Designengineers should:

1.Determine what the goal is in the redesign. Is it to reduceweight? Is it to reduce noise/vibration? Is it to reduce cost? Afunction of this goal is to establish an economic analysis forthe component. This analysis must include factors that af-

fect casting costincluding alloy, tolerances, surface finish,testing and inspection, machining and heat treatment.

Cast Component: Inline 6 cylinder block and head for General MotorsVortec 4200 sport utility engine cast by GMPowertrains Saginaw Metal Casting Operation.

Casting Process: Lost foam.Converted From: Iron in the early to mid 1990s.

Engine was designed with lost foam cast block and head in mind to

achieve top-in-class performance for horsepower, fuel efficiency, peaktorque and mass efficiency.

Lost foam allowed the designers to cast various features into the cylin-der block and head, including:

integrated crankcase ventilation system oil/air separator (eliminat-ing an additional bolt-on);

oil galleries (significantly reducing machining effort and cost); intricate water jacket design (eliminating oil cooler costs and the

potential for leaks), allowing maximum cooling efficiency; intricate convoluted oil drain-backs that provide structural stiffness

to lower noise and vibration as well as provide large, functional oildrain returns to the oil sump;

coolant passages (which traditionally require drilling or external

plumbing) cast directly into the block, resulting in less machiningand fewer opportunities for assembly error.

For more information, circle 053 on last page.

Cast Component: Fuel rail housing for four-cylinder, 2.0 and 2.2-L pas-senger car models cast by Madison-Kipp Corp.

Casting Process: Semi-solid casting.Converted From: Traditionally designed as fabricated steel tube.

An engine configuration required a fuel rail housing capable of withstand-ing high levels of impact without failure. The customer decided that tra-ditional fabricated brazed steel tube and plastic designs would not meetthe stringent impact requirements and opted for a cast component.

The customer, first-tier supplier, and casting and machining componentsupplier worked together to develop an aluminum casting that met the7000-lb crash test load and elongation requirements while keeping over-all mass and costs to a minimum.

Increased dimensional accuracy of critical features (especially injectorpositioning) produced close tolerance machining for special featuresand resulted in leak-free performance without impregnation (this was

aided by semi-solid castings inherent low porosity characteristic).For more information, circle 054 on last page.


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30 ENGINEERED CASTING SOLUTIONS SPRING 2002

Cast Component: Differential carrier for DaimlerChryslers Jeep GrandCherokee cast by Hayes Lemmerz International, Inc.

Casting Process: Tilt-pour permanent mold casting.Converted From: Iron.

Cast in A356 aluminum, the component achieves minimum mechani-cal properties of 228 MPa tensile strength, 179 MPa yield strength and4% elongation.

The conversion to aluminum resulted in a 40% weight reduction witha machined component weight of 7.3 kg.


2.Determine the various tensile, compression and torsionload factors (via finite element analysis) that are and will af-fect the component in service with the current design and theredesign. For example, all chassis components are analyzedfor maximum stress through the evaluation of more than 20standard suspension and powertrain load cases.

3.Determine what the packaging restrictions (size, weight,etc.) and operating environment are for the component. Theywill dictate design criteria. Packaging constraints will pro-vide the designer with necessary spatial parameters to honorin the initial design as well as down the road during designiterations. Operating environment helps determine the cast-ing material and processing requirements. For example, fa-tigue life can be influenced if the cast component is locatednear the ground line and subject to stone or chip contact,salt and/or silt. These can cause stress concentration sitesaffecting casting performance.

4.Evaluate component machining and assembly issues.It is critical to incorporate those considerations into theoverall design to ensure that the total cost of manufac-turing is factored into a conversion.

Once these points are outlined, redesigning to alumi-num can begin.

If an iron or steel component design were translated

directly to aluminum, the design would achieve a 67%weight reduction (aluminum has 33% the density of steel,but a higher strength-to-weight ratio). However, a straightmaterial substitution isnt possible because of aluminumsreduced strength, stiffness and resistance to stress.

The modulus of elasticity for steel, ductile iron, grayiron and aluminum are 30 x 106 lb

f/sq in., 24 x 106 lb

f/sq

in., 13 x 106 lbf/sq in. and 10 x 106 lb

f/sq in., respectively. To

overcome this material disadvantage, the goal in redesign-ing to aluminum is to optimize casting geometry so stressis reduced in the critical areas and distributed broadlythrough less critical areas to more uniformly apply itthroughout the cast component.

Stress is a function of loads applied and geometry of struc-turegeometry alone controls the amount of stress for agiven system of forces on a structure and material choicecontrols how much stress is allowable. Castings have an in-herent advantage over fabricated weldments because theycan apply stress more uniformly throughout the structure(and not have stress concentration factors at weld joints, forexample). This reduces the stress concentrated at any onepoint throughout the part and minimizes the chance to ex-tend beyond the allowable stress (modulus) and fatigue lifeexerted on any one particular area of the component.

The key is to design the component with both stiff-ness and geometry in mind to achieve the required prop-

erties, said Bujalski.To further offset the allowable stress in any one section

of an aluminum cast component, section sizes also can be

Table 1. Forecast of Automobiles and Light Trucks Using CastAluminum for the Listed Component

Component 2002 2006

Engine Block 40% 60%

Cylinder Head 90% 96%

Intake Manifold 40% 28%

Transmission Case 95% 94%

Wheels 63% 75%

Pistons 95% 94%

Brake, Suspension 15% 25%

Stratecasts, Inc., Ft. Myers, Florida

Cast Component: A brake pedal for theC7 Corvette cast by EckIndustries, Inc.

Casting Process: Low-pressure perma-nent mold casting.Converted From: Steel fabrication.

Converted from a steel fabrication, thisstructural, safety-critical B356 aluminum cast-ing achieves 0.5 in. deflection before fracture,ASTM E-155 Frame 2 requirements for shrink-age in critical areas, and exceptional appearanceand feature definition, which is mandatory be-cause the pedal face is visible.

To solve structural and mechanical property concerns, modified alloychemistries and heat treatment cycles were used with permanent moldcasting to achieve the mechanical properties of 35 ksi tensile strength,

25 ksi yield strength and 7% elongation.For more information, circle 057 on last page.

Cast Component: Rear subframe for Volvo cast by Alcoas ScandanavianCenter.

Casting Process: VRC/PRC.Converted From: Steel stamping.

Cast in A356 aluminum this component achieves property minimums of138 MPa tensile strength, 75 MPa yield strength and 12% elongation.

The design as a casting resulted in close to a 40% weight savings with amachined component weight of 17.2 kg.



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SPRING 2002 ENGINEERED CASTING SOLUTIONS 31

For More Information

Design and Product Optimization for Cast Light Met-als, a study performed under the U.S. Automotive Materi-als Partnership, a unit of the U.S. Council for AutomotiveResearch, available from the American Foundry Society,Des Planes, IL (2001).

Design Considerations for Automotive Castings, Pro-

ceedings # SP-1684 from the 2002 Society of AutomotiveEngineers World Congress, Dearborn, Michigan.

increased in the redesign. The key to these design alter-ations is the packaging restraints for the overall system.

The section sizes must be controlled, said Bujalski.In some cases, that can reach double the thickness of theprevious design.

This is when the casting designer, foundry engineersand overall product engineers must communicate the re-strictions on the design and manufacturing to ensure the

final component design is satisfactory.According to Prucha, Once all the issues have been re-

solved and a design is finalized, the typical expected weightreduction from a conversion to aluminum can reach 40%.

Manufacturing TechnologyThe ability for design engineers to redesign iron and

steel to aluminum goes beyond design principles. Thisability also is based in manufacturing growth by thefoundry industry.

By improving its technology and processes, the alu-minum foundry industry now can provide the repeatablequality that was limited 15 years ago, said Bujalski.

Bujalski cited vacuum and pressure casting processes(including permanent mold and semi-solid/squeeze cast-ing) and automated inspection and non-destructive test-ing techniques as critical to certifying high-productioncomponent quality.

According to Prucha, We also are able to better con-trol the metals microstructure through a variety of meansfor increased mechanical properties.

The key for the automotive OEMs, however, is consis-tent quality. Internal soundness of components and therelated defect issues such as microporosity are less of aconcern today, said Bujalski. Foundries have automatedinspection and other process control techniques that as-

sure us of component quality.As for the future, both automotive design engineers and

foundries see the continued drive toward aluminum in boththe powertrain and chassis systems of automobiles.

For a free copy of this article circle No. 341 on the Reader Action Card.

Table 2. Forecast of Cast Aluminum Use By Component in 2008

Component % Using CastAluminum By 2008

Rocker Arm Cover 25

Rocker Arm 30

Master Cylinder 60

Disc Brake Calipers 8

Disc Brake Rotors 8

Water Pump and Oil Pump Housings 50

Steering Knuckle 10

Suspension Control Arms 10

Differential Carrier Cover 10

Accelerator Pedal 10

Wheel Brake Cylinder Body 30

Stratecasts Inc., Ft. Myers, Florida

Cast Component: Crossmember used on the rear suspension for thePontiac Aztek and Buick Rendezvous sport utilityvehicles cast by Hayes Lemmerz International, Inc.

Casting Process: Permanent mold casting.Converted From: Stamped steel/welded assemblies.

Traditionally manufactured as stamped steel/welded assemblies, this

new 49-lb, A356 aluminum component design improved total productfunctionality by providing mounts for various other suspension/brake-related components that were not available in the previous design.

New casting design provided better tolerance controls, reducedweight, integrated features, improved ride and handling, and re-duced NVH/noise.


Cast Component: Steering knuckle cast by Intermet Corp.Casting Process: Pressure counter pressure casting (PCPC).

Converted From: Iron component.

Traditionally cast in iron, this 6.5-lb, 12 x 6 x 5.5-in. A356 aluminumsteering knuckle was designed by the foundry for its unique, self-devel-oped PCPC process. This process is similar to low-pressure permanentmold casting, but uses countering pressures in the furnace and castingchamber to control mold filling and maximize feeding in shrinkage-prone regions of the casting along with sequenced cooling of the moldto ensure directional solidification.

The casting process offers increased structural integrity due to porosityreduction, controlled solidification and higher strength and ductilitythan other metal die casting processes.

The benefits derived from this process made aluminum an attractivechoice for this safety-critical component.

The aluminum casting provides approximately 40% weight savings over

the traditional iron version.For more information, circle 059 on last page.

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