Castings drive fuel efficiency: lightweight castings continue to play an important role in reducing weight and increasing fuel efficiency of vehicles.

Seemingly now more than ever, fuel economy is playing an important role in consumers' choices for new automobiles. With gas prices spiraling out of control across the world and no relief in sight, the U.S. government and many consumers are looking to the automotive industry to find ways to improve fuel economy in new vehicles. To do this, the automotive industry is in turn looking to the metalcasting industry for assistance.

In 2001, lightweight cast components in passenger cars and light trucks saved more than 2.2 billion gallons of gasoline and reduced carbon dioxide (C[O.sub.2]) emissions by 20 million tons in the U.S. Aluminum, magnesium and other lightweight castings are facilitating the automotive industry's efforts to meet Corporate Average Fuel Economy (CAFE) Standards, which require manufacturers to comply with fuel economy mandates for passenger cars and light-duty truck fleets sold in the U.S. Congress set the standard at 27.5 miles per gallon (mpg) for automobiles and 20.7 mpg for light-duty trucks for model years produced after 1985.

This article will develop estimates of the fuel efficiency improvements and the reduction in gasoline costs and C[O.sub.2] emissions due to the use of lightweight aluminum and magnesium castings.

It will show that the replacement of heavier components (including stamped steel fabrications and even plastics) with lightweight aluminum and magnesium castings has been instrumental to the automotive industry's ability to improve vehicle fuel consumption.

Castings in Automobiles

Table 1 provides data on the breakdown of material components in a typical family vehicle for model years 1978, 1990 and 2002. The table demonstrates the dramatic (260%) increase in lightweight castings over a 24-year period.

Automotive castings have become a growth market for the U.S. metalcasting industry. The use of lightweight aluminum castings has increased from 92.3 lbs. in model year 1978 to 240 lbs. in model year 2002 and is projected to grow at a rate of 2.1% from 2004 2013. During that same time, use of magnesium is expected to increase at a rate of 13%/yr.

Figure 1 illustrates how lightweight castings are enabling manufacturers to meet new car CAFE Standards. The yellow line represents the new car CAFE Standard for each model year. The blue area represents mpg for each model year without aluminum and magnesium castings. The purple area represents improvements from lightweight components in mpg for each model year. The chart indicates that without lightweight castings, in most years, manufacturers would have met CAFE standards by only a small margin--if at all.

[FIGURE 1 OMITTED]

Methodology

The methodology used for estimating the contribution of lightweight castings to automotive energy savings is based on fleet and material composition data provided by Ward's Motor Vehicles Facts & Figures 2002 and 2003 as well as published information on the impact of weight reduction on fuel efficiency. First, the weight of aluminum and magnesium castings used in the typical automobile was identified. Next, the vehicle's weight with castings made of a heavier, ferrous material was estimated. By considering the weight differential, the estimated fuel efficiency improvement from the use of lightweight castings was determined. By establishing the estimated fuel efficiency improvement, the estimated fuel savings per model year was calculated. Subsequent fuel cost savings and reductions in C[O.sub.2] emissions were estimated based on these fuel savings. Cumulative fuel savings for all registered vehicles in 2001 attributed to lightweight castings was estimated by proportioning the fuel savings of the individual model year to the mix of all registered vehicles on the road in 2001. The information below provides the major assumptions and the steps used to calculate fuel and emission reductions.

* a 10% reduction in vehicle weight improves fuel efficiency by 7%. (Note: The literature values typically range from 6-8% efficiency for a 10% reduction in weight.);

* if a casting had not been made of aluminum or magnesium, it would have been cast using a ferrous alloy;

* 1 lb. of aluminum replaces 2 lbs. of ferrous metal. (Note: Aluminum is one third the density of ferrous material. However, in order to provide comparable strength and safety, aluminum castings many times have to be designed thicker. According to the literature, every pound of aluminum used in an automobile replaces an estimated 2-2.5 lbs. of ferrous components.);

* 1 lb. of magnesium replaces 3 lbs. of ferrous components. (Note: magnesium is 78% lighter than iron and steel.);

* 19.15 kg carbon equivalent (Ce) gases are generated for each 1 million Btu of regular unleaded gasoline used.

Calculating the Reductions

In order to perform the above steps to calculate fuel and emission reduction, a six-step program was carried out.

Step 1: Determine the weight of aluminum and magnesium castings forgiven years--Table 1 shows the average material make-up of automobiles. Aluminum castings represent approximately 82% of the aluminum content for these model years.

Step 2: Estimate weight of model years without select lightweight castings--Once the material make-up and weight of materials used in the typical family vehicle was determined, an estimate was developed to determine the weight of the automobile if aluminum and magnesium castings had been fabricated using a heavier ferrous alloy.

Table 2 illustrates the total automobile weight with aluminum and magnesium castings fabricated using iron or steel. Figure 2 illustrates the overall weight savings attributed to aluminum and magnesium castings from 1978-2002. After model year 1990, the average family vehicle began to increase in weight, reaching 3,357.5 lbs. in 2002. If aluminum and magnesium components had been fabricated using heavier alloys in 2002, the average family vehicle would have weighed 3,616.5 lbs.

Step 3: Calculate the percent improvement in fuel efficiency that occurred due to select lightweight castings--Having calculated the estimated weight of the typical family vehicle without select lightweight castings, the percent improvement in fuel efficiency could be calculated.

Table 3 shows the percent of weight reduction that occurred through use of aluminum and magnesium castings for select years. The table also illustrates the contribution these castings had on energy efficiency improvement. Casting-related fuel efficiency savings have increased from 1.8% in 1978 to 5% in 2002. Figure 3 illustrates the subsequent fuel efficiency improvement.

Step 4: Estimate fuel savings per model year based on total cars sold for a given model year fleet--Table 4 illustrates this calculation for select model years. Tables 2-4 show the calculations for all known years. For all interim years, a linear rate of change was assumed to estimate the portion of castings and the average weight of family vehicles.

Step 5: Calculate the fuel savings in 2001 attributed to the total 1988-2002 model years registered in 2001--To calculate the fuel savings attributed to the total number of 1988-2002 model years registered in 2001, the fuel efficiency improvement for each model year was multiplied by the percent of models registered in calendar year 2001. This value provides a weighted average of each model year's fuel efficiency improvement in 2001.

These weighted averages were then added to obtain the total average fuel efficiency improvement for calendar year 2001 due to the use of aluminum and magnesium castings. Table 5 provides the calculations values from 1988-2001.

In 2001, passenger cars consumed 73.6 billion gallons of gasoline. To calculate the estimated fuel savings, the amount of known gasoline consumed by passenger cars in 2001 was increased by the total weighted average and then subtracted from the total gasoline consumed.

Total savings in 2001 were estimated to be 2.2 billion gallons of gasoline. This translates into $3.2 billion in cost savings for the U.S. economy based on the average price of regular gasoline of $1.46. This estimate is conservative because it did not consider approximately 17% of the cars registered in 2001 of model years prior to 1988. Model year registration data for these prior years was not readily available and efficiency of 0% was assumed for these vehicles.

Step 6: Calculate the Emissions Reduction--The U.S. Dept. of Energy states that 19.15 kg Ce gases are generated for each 1 million Btu of regular unleaded gasoline used. Based on this assumption, fuel savings related to lightweight castings reduced C[O.sub.2] emissions by an estimated 20 million metric tons in model years 1988-2002 that were registered in 2001. Table 6 illustrates aluminum and magnesium castings' contribution to reduction in weight and C[O.sub.2] emissions by individual model years.

Castings Provide the Solution

Lightweight castings are a practical means to achieving the CAFE mandate without sacrificing vehicle size, safety and performance. Since the establishment of CAFE Standards in 1975, lightweight castings have made a significant, positive impact on America's fuel economy.

Data presented in this article clearly indicate the growing contribution of lightweight castings to the fuel economy beginning in 1978 to 2002. Even as typical family vehicles continued to grow in size and mass with the boom in SUVs, minivans and light trucks, manufacturers have been able to consistently maintain fuel economy by augmenting engine improvements and aerodynamics with lightweight aluminimum and magnesium castings.

Metalcasters must continue to develop new technologies that can produce increasingly thinner-walled, higher-strength and more fatigue-resistant lightweight castings in order to provide the transportation sector with cast components that contribute to fuel use reduction. Innovations in casting technologies can expand the auto motive markets for metalcasters and help the U.S. metalcasting industry stay competitive in global transportation markets.

Aluminum

Cast Component:    Inline 4 engine block and cylinder head for
                   General Motors' Vortec light truck engine.
Material:          A356 aluminum with T6 heat treatment.
Casting Process:   Lost foam.

* This cylinder block and head are the third in the Vortex engine series to be designed specifically for lost foam casting, which allowed designers to cast-in various features not possible with other processes. The aluminum block weighs in at 74.5 lbs., which is 15 lbs. lighter than a comparable iron design. The head weighs 37.5 lbs

Cast Component:    No. 2 crossmember for Ford.
Material:          A356 aluminum with T6 heat treatment.
Casting Process:   Vacuum riserless permanent mold casting.

* Prior to the 2003 model year. the crossmember used in the Crown Victoria. Town Car and Grand Marquis was produced as a steel stamping. Product designers decided they could achieve reduced weight with increased functionality by converting the design to an aluminum casting. The result was a one-piece component that weighs 51.6 lbs. as-cast and 45.8 lbs. after machining.

Magnesium

Cast Component:    Cam covers tot automotive light-duty track
                   applications.
Material:          Magnesium.
Casting Process:   Diecasting.

* Using a magnesium die casting offered a significant weight and noise-damping advantage over traditional-stamped steel construction. The covers reduce component weight by 75% when compared to their traditional steel construction.

Cast Component:    Front end support assembly for Ford F150 truck.
Material:          AM50 magnesium
Casting Process:   High-pressure diecasting.

The auto industry's first magnesium structural exterior body component, this one-prate casting was converted from 21 previously assembled components. This conversion provided a 22-lb, weight reduction. The cast component also has twice the life of the previous assembled component during structural durability vehicle tests and it meets or exceeds all crash standards.

Table 1. Material Content of a Typical Family Vehicle

Material                               1978              1985
                                   lbs.      %       lbs.      %

Regular Steel, Sheet Strip,       1,915     53.6   1,481.5   46.5
Bar and Rod
High and Medium Strength Steel      133      3.7     217.5    6.8
Stainless Steel                      26      0.7     29       0.9
Other Steels                         55      1.5      54.5    1.7
Iron                                512     14.3     468     14.7
Plastics and Plastic Composites     180      5       211.5    6.6
Aluminum Wrought                     20.2    0.7      24.8    0.7
Aluminum Castings                    92.3    2.8     113.2    3.5
Copper and Brass                     37      1        44      1.4
Powder Metal Parts                   15.5    0.4      19      0.6
Zinc Die Castings                    31      0.9      18      0.6
Magnesium Castings                    1      0         2.5    0.1
Fluids and Lubricants               198      5.5     184      5.8
Rubber                              146.5    4.1     136      4.3
Glass                                86.5    2.4      85      2.7
Other Materials                     120.5    3.4      99      3.1
Total                             3,569.5    100   3,187.5    100

Material                               1990            2001
                                   lbs.     %       lbs.     %

Regular Steel, Sheet Strip,       1,405     44.7   1,349.5   40.8
Bar and Rod
High and Medium Strength Steel      238      7.6     351.5   10.6
Stainless Steel                      34      1.1      54.5    1.6
Other Steels                         39.5    1.3      25.5    0.8
Iron                                454     14.5     345     10.4
Plastics and Plastic Composites     229      7.3     253      7.6
Aluminum Wrought                     31.7    1        45      1.4
Aluminum Castings                   126.8    3.9     210      6.4
Copper and Brass                     48.5    1.5      46      1.4
Powder Metal Parts                   24      08       37.5    1.1
Zinc Die Castings                    18.5    0.6      11      0.3
Magnesium Castings                    3      0.1      8.5     0.3
Fluids and Lubricants               182      5.8     196      5.9
Rubber                              136.5    4.3     146      4.4
Glass                                86.5    2.8      98.5    3
Other Materials                      83.5    2.7     131      4
Total                             3,140.5    100   3,309      100

Material                               2002
                                   lbs.     %

Regular Steel, Sheet Strip,       1,351.5   40.3
Bar and Rod
High and Medium Strength Steel      379     11.3
Stainless Steel                      56.5    1.7
Other Steels                         26.5    0.8
Iron                                328      9.8
Plastics and Plastic Composites     255      7.6
Aluminum Wrought                     39.5    1.1
Aluminum Castings                   240      7.1
Copper and Brass                     50      1.5
Powder Metal Parts                   40.5    1.2
Zinc Die Castings                     8.5    0.3
Magnesium Castings                    9.5    0.3
Fluids and Lubricants               198      5.9
Rubber                              149      4.4
Glass                                98.5    2.9
Other Materials                      127.5    3.8
Total                             3,357.5    100

Table 2. Estimated Weight of Model Years Without Select Lightweight
Castings

                                     1978      1985      1990    2001

Total Aluminum Castings Weight        92.3     113.2     126.8   210.0
   per Car (lbs.)
Total Magnesium Castings Weight        1         2.5       3       8.5
  per Car (lbs)
Select Lightweight Castings           93.3     115.7     129.8   218.5
  per Car (lbs.)
Total Actual Model Year Weight     3,569.5   3,187.5   3,140.5   3,309
  per Car (Ibs.)
Total Auto Weight without Select   3,663.8   3,305.7   3,3273.3  3,536
  Lightweight Castings per Car
  (est.) (Ibs.)

                                     2002

Total Aluminum Castings Weight        240
   per Car (lbs.)
Total Magnesium Castings Weight        9.5
  per Car (lbs)
Select Lightweight Castings          249.5
  per Car (lbs.)
Total Actual Model Year Weight     3,357.5
  per Car (Ibs.)
Total Auto Weight without Select   3,615.5
  Lightweight Castings per Car
  (est.) (Ibs.)

Table 20 percent Improvement in Fuel Efficiency to select Lightweight
Castings
                            1978   1985   1990   2001   2002

Percent Weight Reduction    2.6%   3.6%   4.1%   6.4%   7.2%
Nominal Energy Efficiency   1.8%   2.5%   2.8%   4.5%     5%
Improvement

Table 4. Fuel Savings per Model Year
                                           1978      1985        2001

Vehicles Sold per Model Year (1) (2)      15,423     15,724     17,472

Avg. Fuel Consumption per
passenger Car (gal per year) (7)             719        584        573

Gallons Consumed in Year              11,089,137  9,812,816  8,049,074

Gallons Consumed by Model without     11,292,400  9,418,273  8,280,940
Select Lightweight Castings

Gallons Saved Due to Lightweight         203,263    253,457    231,866
Castigns per Model Year

                                          2002

Vehicles Sold per Model Year (1) (2)      17,139

Avg. Fuel Consumption per
passenger Car (gal per year) (7)             587

Gallons Consumed in Year              10,060,593

Gallons Consumed by Model without     10,590,098
Select Lightweight Castings

Gallons Saved Due to Lightweight         529,505
Castigns per Model Year

Table 5. Weighted Average of Fuel Efficiency Improvement in the
2001 Registered Fleet

                    Prior to
Model Year            1998      1988     1989    1990     1991     1992

Nominal Energy
Efficiency
Improvement (%)           0      2.7      2.8     2.8        3      3.1

# of Models
Years Registered
in 2001 (000)        36,000    9,301   10,087   9,731   10,031   10,202

% of registration
of model years
in 2001                16.6      4.3      4.7     4.5      4.6      4.7

Fuel Efficiency
X Percent
Registered (%)            0    0.116     0.13   0.126    0.139    0.146

Model Year            1993     1994     1995     1996     1997     1998

Nominal Energy
Efficiency
Improvement (%)        3.2      3.4      3.5      3.6      3.8        4

# of Models
Years Registered
in 2001 (000)       11,568   12,513   14,129   12,459   13,969   13,953

% of registration
of model years
in 2001                5.3      5.8      6.5      5.7      6.4      6.4

Fuel Efficiency
X Percent
Registered (%)       0.171    0.196    0.228    0.207    0.245    0.258

Model Year            1999     2000     2001    2002

Nominal Energy
Efficiency
Improvement (%)        4.1      4.3      4.5       5

# of Models
Years Registered
in 2001 (000)       15,615   16,840   12,147     249

% of registration
of model years
in 2001                7.2      7.8      5.6     0.1

Fuel Efficiency
X Percent
Registered (%)       0.295    0.334    0.252   0.006

Weighted Average of Fuel Efficiency Improvement in 20012.85%

Total Gasoline Consumed in 2001 by Passenger Cars (gals)73.6 billion

Total Gasoline Saved in 2001 (gals)2.2 billion

Table 6. Emissions Reduction Due to Select Lightweight Castings For
Select Years

Year            1978       1982         1986       1990        1994

C[O.sub.2]
Reduction
(tons)       1,949,336   1,323,729   2,465,289   2,223,646   3,017,092

Year            1998       2001        2002

C[O.sub.2]
Reduction
(tons)       3,834,551   4,524,123   5,078,062

This article was adapted from a presentation at the 2004 Metalcasting Congress.

For More Information

"In Search of Lightweight Components: Automotive's Cast Aluminum Conversion," A. T. Spada, Engineered Casting Solutions, Spring 2002.

"Overcoming the Technological Barriers to a Magnesium-Intensive Engine," B. Powell, 2004 AFS Transactions, Paper No. 04-190,

"Lightweight Castings: Improving the Fuel Efficiency of America," R. Naranjo, E. HuangFu and M. Gwyn, 2004 Metalcasting Congress.

About the Authors

Robert D. Naranjo is an analyst for BCS Inc., Columiba, Md., Ehr-Ping HuangFu is a technology manager for the U.S. Dept. of Energy, Washington, D.C., and Mike Gwyn is the director of metals technology at the Advanced Technology Institute, Charleston, S.C.