application of life cycle design to aluminum intake manifolds

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Application of Life Cycle Design to Aluminum Intake Manifolds

K. Kar and G. A. Keoleian University of Michigan

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Application of Life Cycle Design to Aluminum Intake Manifolds

K. Kar and G. A. Keoleian University of Michigan

ABSTRACT

Life cycle design (LCD) is a framework for designing product systems which are both economically and ecologically sustainable. Key elements of this framework are systems analysis, multicriteria analysis and multistakeholder participation. This paper illustrates the application of life cycle design for a comparative evaluation of a prototype sand-cast 2.0 1 aluminum manifold for the 1995 Ford Contour and a 2.0 1 equivalent of the 1.9 1 multi-tube brazed aluminum manifold for the 1995 Ford Escort.

A life cycle inventory analysis was performed for the intake manifolds by evaluating the energy and wastes in the raw material acquisition, material processing, manufacturing, use and retirement stages. The environmental data for the two manifolds were integrated with life cycle cost and performance data to enhance product design and decision making.

The stakeholders for this study consisted of different levels of suppliers (tier 1, tier 2, tier 3, etc.), Ford, users, dismantlers, shredders, non-ferrous processors, scrap metal dealers, waste managers, and regulators. The interaction of these diverse stakeholders and their individual needs defined the design requirements of the manifold system. These requirements were identified and evaluated by a cross- functional team from Ford including powertrain product, manufacturing and environmental engineering, materials research, energy analysis, environmental quality, casting operations, advanced vehicle technology and their vehicle recycling program.

The results of the analysis show that the life cycle energy, most air emissions and waterborne waste are lower for the multi-tube brazed manifold. Life cycle solid wastes are lower for the sand-cast manifold. Life cycle cost of the two manifolds are almost identical.

INTRODUCTION

This paper is one output of a collaborative research work between National Pollution Prevention Center (NPPC) and a cross functional core team within Ford

Motor Company including powertrain product, manufacturing and environmental engineering, materials research, energy analysis, environmental quality, casting operations, advanced vehicle technology and vehicle recycling program. The intake manifold was selected by Ford's core team in a pilot project to apply the life cycle design (LCD) framework and tools [ I ,2] in support of their emerging Design for Environment (DfE) program. Significant weight reduction in intake manifold design has been achieved by substitution of lightweight materials such as sand-cast aluminum for cast iron, extruded aluminum for sand-cast aluminum, and glass reinforced nylon for aluminum. Automotive material selection is a complex procedure because it requires tradeoffs between several interrelated criteria.

A number of studies in the past [3-71 have addressed material selection as a tradeoff between several interrelated and complex criteria such as materials and processing cost, weight, warranty cost, performance requirements, safety, recyclability and regulations. These studies have investigated only discrete aspects of the material selection process rather than performing a complete systems analysis of the material life cycle. Beginning in the early 1980s, several investigators evaluated life cycle energy tradeoffs by comparing material production and part fabricati~n energy with the contribution of a part to fuel consumption [8-131. A few investigators [ I 4-1 61 have performed life cycle analyses (LCA) of automotive parts to characterize the burdens including energy, waste, and emissions associated with each of stage of a product life cycle. The most widely recognized framework for LCA includes inventory analysis, impact assessment and improvement assessment [17]. The application of a systems approach to the integration of environmental considerations into the material selection process is currently constrained by the following weaknesses of LCA [18,1]:

Availability and accessibility of environmental data can be limiting; these data are often not as complete as performance and cost data Time requirements for performing an LCA may exceed development cycle time constraints Procedures for impact assessment are limited


Ability to communicate results in an efficient and accurate way to designers and managers is limited by methods for data aggregation and valuation; these individuals often lack expertise in interpreting environmental data.

Recognizing the limitations of LCA, life cycle design (LCD) was developed as a comprehensive framework to integrate environmental considerations into the product design process using a system based methodology. LCD emphasizes the application of practical tools which address both the specification of design requirements and the analysis of design alternatives. The specification of requirements can be aided by the use of design guidelines, checklists and requirement matrices. Analytical tools to evaluate design alternatives include LCA, streamlined LCA [19], life cycle costing, and such conventional tools as CAD, FMEA, and QFD.

Life cycle design (LCD) offers a framework for ecologically and economically sustainable product system design. Principles of life cycle design are [ I ,2]:

Systems analysis of the product life cycle addresses the integration of product, process and distribution components across each stage of the life cycle. A generalized life cycle system is shown in Figure 1. Multicriteria analysis includes the identification and evaluation of environmental, performance, cost, and legal requirements as indicated in Figure 2. A description and the qualitative application of the matrix tool is presented elsewhere [20]. Multistakeholder (suppliers, OEMs, users, end-of-life mangers, and regulators,) participation and cross- functional teamwork is essential throughout design different phases of design and planning.

The Ford Life Cycle Design Project focuses on the comparative assessment of three intake manifold designs for a 2.0 1 1995 Contour engine which were constructed of a glass reinforced nylon composite, sand- cast aluminum, and multi-tubed brazed aluminum materials. Existing and prototype manifolds were selected for this project based on the availability of data and relative comparability of engine size. Recently, Ford of Europe along with Stuttgart University in Germany have performed a life cycle inventory analysis of aluminum and composite manifold [14,15]. The project team used this study as an initial source for inventory data. The nylon manifold is currently used in the 1995 ContourIMystique. Aluminum manifold designs which can be manufactured by several different processes including sand casting, permanent mold casting, die casting and multi-tube brazing were considered as alternatives. A prototype sand-cast manifold was developed as an alternative design for the composite Contour manifold.

In this paper, analytical tools of the LCD framework are applied for a comparative evaluation of the 2.0 1 prototype sand cast Contour 1995 and a 2.0 1 equivalent of the 1.9 1 multi-tube brazed Escort 1995 aluminum intake manifold. Environmental and cost metrics are defined and evaluated for each life cycle stage. These metrics in addition to key performance metrics provide a data set to enhance design decision making.

M, E material and energy inputs for process and distribution

W waste (gaseous, liquid, solid) output from product, process and distribution

+ material flow of product component

Figure 1 : Product life cycle stages

Product . INPUTS

. INPUTS

Distribution . INPOTS

Figure 2: Multi-criteria matrix for developing requirements

LCD METHODOLOGY

The basic principles of LCD are defined and applied for the aluminum intake manifolds as illustrated below :

SYSTEMS ANALYSIS - The manifold system involves the product, process and distribution components of the intake manifold in different phases of its life cycle (raw material extraction, material processing, manufacturing, use and retirement stages). The characterization of the

2


product systems for the intake manifold involves evaluating the scope, product composition, boundaries and assumptions used in the study. Figures 3 and 4 illustrate the life cycle product system of the sand cast and multi-tube brazed aluminum intake manifolds.

Scooe and Product Comoosition - The scope of the study is to perform a comparative evaluation of the sand- cast and multi-tube brazed aluminum intake manifolds used for a 2.0 1 engine in the 1995 Ford Contour. The sand cast aluminum manifold was used as a prototype for the currently used composite manifold in the 1995 Ford Contour. The sand-cast manifold weighs 6.5 kg.

The multi-tube brazed manifold is currently used in the 1.9 1 Escort engine. The Escort manifold weighs 3.43 kg. An assumption is made to correct for engine size differences and its possible affect on manifold size. For uniform baseline comparison, the weight of the Escort 1.9 1 manifold (3.43 kg) is converted to a 2.0 1 equivalent by multiplying with the weight ratio of the two engines (1.05). The converted 2.0 1 multi-tube brazed manifold weighs 3.62 kg.

The sand-cast manifold consists of 100% secondary aluminum. The Escort aluminum manifold consists of bent extruded tubes and an extruded air collection chamber screwed to the motor block through a sand-cast flange. The sand cast flange section comprises 65% of the manifold weight; the extruded sections account for the remaining 35%. The sand cast flange section is assumed to be made of 100% secondary aluminum, whereas the extruded sections are assumed to be made of 70% primary and 30% secondary aluminum [21] which is a representative mix of the extruded parts. Thus, overall the multi-tube brazed manifold consists of 24.5% primary aluminum and 75.5% secondary aluminum.

Boundaries and Assumotions - The boundary for the comparative study of the manifold system encompasses raw material acquisition, material processing, manufacturing, use and retirement stages. Table 1 illustrates the boundaries and assumptions for this study.

MULTlCRlTERlA ANALYSIS - Environmental and cost metrics for different life cycle stages are evaluated using the methodology as described below:

Environmental Metrics (i) Raw Material Acauisition and Material Processina

Phase - The aluminum intake manifold studied involves both primary and secondary aluminum. Primary aluminum production is a two-step process that refines bauxite into alumina by the Bayer process and reduces alumina to aluminum metal by electrolytic reduction process commonly known as Hall-Heroult process [22]. Molten aluminum is then cleaned and cast into ingot. Thus, total energy for primary aluminum production Ep is obtained from:

Secondary aluminum production involves two general operations- scrap pretreatment and smelting1 refining. Pretreatment includes sorting, carbonizing and briquetting [23]. The smeltinglrefining operation include melting down, melting in salt bath furnace, dross processing, melt cleaning and casting (alloying). The energy for secondary aluminum is obtained as follows :

Es = Ecarbonizing + Ebriquetting + Edross processing + Emelling down + Esalt bath furnace

+ Esa~t slag processing + Ec~eaningksting (2)

Total waste for primary and secondary aluminum is obtained using similar equations.

Table 2 illustrates the energy and waste from primary and secondary aluminum processing. The source of data is indicated in the right hand side column. Table 2 shows representative data for energy and waste for primary and secondary aluminum processing obtained from several sources [14,21,24,25]. The average energy for primary aluminum production is 177.9 MJ/kg k 28.3 (99% confidence interval) and the average for secondary aluminum production is 17.9 MJ/kg + 10.0 (99% confidence interval). This variation results from different assumptions such as the inclusion of energy to transport scrap, shredding and decoating, type of furnace used and power source efficiency. Waste data from Eyerer, et al[l4] have been validated by Alcoa and uncertain or missing data have been replaced by Alcoa's estimates [21,24]. Primary aluminum processing has a considerably higher environmental burden in terms of energy use (9.9 times), solid waste (39 times), C02 (15 times) and water consumption (7 times) compared to secondary aluminum processing. Primary aluminum processing also leads to about 0.85 kg / mt of fluorocarbons consisting of 90% CF4 and 10% C2F6 due to anode effects from local deficiencies in alumina concentration in the electrolytic bath [24]. The CF4 and C2F6 concentrations can range from 0.03 to 1.0 kg/mt depending upon the type of electrolysis cells (prebake or Soderberg) used during alumina production [26,27].

The energy and waste for material production of sand cast aluminum manifold is obtained by multiplying the corresponding value per kg of secondary aluminum by the mass of sand cast aluminum manifold. Energy for multi-tube brazed manifold consisting of 24.5% primary and 75.5% secondary aluminum are obtained as:

where, Ep and Es are energy per kg of primary and secondary aluminum ingot and Mp and Ms are mass of primary and secondary aluminum processed for the multi-tube brazed manifold. The total waste was also calculated using a similar averaging procedure.

Ep = Ealumina production + Emelt flow electrolysis + Eme~t cleaning + Ecasting (1 )


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Table 1 : Boundaries, assumptions and data sources for the LCD of intake manifold

Life Cycle Sand Cast Aluminum Manifold Multif ube Brazed Aluminum Manifold Stage

Material production

Manufact- uring

Use

Retirement

100 % secondary aluminum is assumed for the manifold.

The mass of secondary aluminum ingot processed is 6.552 kg. 6.175 kg of the ingot is obtained from recycled manifold and the remaining 0.377 kg is obtained from other components.

The mass of in-house scrap used is 1.005 kg. The cost metrics include the secondary aluminum ingot cost.

The energy for the production of sand cast aluminum manifold is obtained from 1281 for 7.557 kg of molten aluminum. 95% recycling efficiency is assumed for in-house scrap. 25% scrap rate in the start up period of first two months and 5% for the next 5 years is assumed based on experience from the Ford project team. This results in 0.37 kg of scrap.

An average 10% scrap rate [29] is assumed for sand castinglmachining, which results in 0.687 kg of scrap.

The crucible furnaces for sand casting are assumed to be gas fired. The average efficiency factor for natural gas is 0.89 [30].

Process wastes for sand casting are filter dust, sand and salt slag. Mass of filter dust, salt slag and sand per kg of manifold is about 0.046 kg, 0.45 kg and 1.85 kg [I 41. Assuming all filter dust ends up as solid waste and 95% recycling for sand and salt slag, the mass of process solid waste generated is 1.045 kg.

Waste associated with energy consumed during manufacturing process is obtained from [30].

Manufacturing cost is obtained from two correlations - ratio of dealer cost to the manufacturing cost - differential cost of the composite and prototype aluminum manifolds.

100% secondary aluminum is used for the cast flange section of the manifold.

The mass of primary aluminum ingot processed is 1.076 kg and the mass of secondary aluminum ingot processed is 2.496 kg. All the secondary ingots are assumed to be obtained from recycled manifolds.

The mass of in-house scrap used is 0.61 5 kg and the mass of scrap from recycled manifolds is 0.081 kg.

The cost metrics include material costs for primary and secondary aluminum ingots and scrap. Linear addition rule is used to obtain cost of the materials comprised of ~rimarv and secondarv aluminum.

The energy for the production of the sand cast flange is obtained from [28] for 2.731 of molten aluminum. Production energy for the extruded part is obtained from [31,32] for 1.537 kg of billet consisting of 70% primary and 30% secondary aluminum [24]. The energy involves remelting the primary ingot and mixing it with scrap to produce a billet, reheating the billet and forcing the billet through the die opening. 95% recycling efficiency is assumed for in-house scrap. 25% scrap rate in the start up period of the first two months and 5% for the next 5 years is assumed based on experience from Ford project team. This results in 0.20 kg of scrap.

An average 10% scrap rate [29] is assumed for sand castinglmachining, which results in 0.248 kg of scrap. 15% scrap rate for extrusion process is assumed, which results in 0.2 kg of scrap.

Process solid waste for the sand cast flange is 0.4 kg. Process waste for extrusion is assumed to be zero.

Waste associated with energy consumed during manufacturing process is obtained from [30].

The average efficiency factor for natural gas is 0.89, and for electricity, average efficiency is 0.32 [30].

The manufacturing cost is obtained from the correlation using ratio of dealer cost to the manufacturing cost.

Fuel economy correlation for Contour 1995 is used to calculate the manifold weight (6.5 kg for sand cast manifold and 3.62 kg for multi-tube brazed manifold) contribution to the use phase energy consumption by assuming that decrease in weight is linearly proportional to fuel consumption reduction.

* Secondary weight effect or mass decomposition is not considered. Use phase emissions data are obtained from the Contour tail pipe emissions data tested and certified by EPA emission testing laboratory. The life of the manifold is assumed to be 150,000 miles.

The manifold contribution to vehicle emissions is obtained by assuming that emissions are proportional to vehicle mass; the allocation rule is accurate for C02 but for other gases the relationship is non-linear.

Precombustion emissions associated with fuel production are evaluated. Gasoline cost is obtained from [33].

During the dismantling stage it is assumed that no manifolds are recovered and sold for reuse. An overall 5% loss in aluminum recovery is assumed in the shredding and separation stage. The breakdown of this loss between shredding and separation is not known. The 5% loss is assumed to occur during shredding. For the sand cast manifold 6.175 kg (95% of the manifold weight) of separated aluminum is recycled back into the manifold. For the multi-tube brazed manifold 3.439 kg of the aluminum (95% of the manifold weight) is recycled. Of this 3.439 kg, 2.577 kg is separated and recycled back into the manifold, and the remaining 0.862 kg leaves the manifold system and is utilized by another product system.

Shredding energy for the vehicle is obtained from Texas Shredder (1 995). Transportation energy is obtained from Franklin data base [30]. Separation energy and processing cost are obtained from Huron Valley Steel (1995). Other retirement cost metrics are obtained from [34], National Solid Waste Management Association (NSWMA) (1 995) and American Metal Market (1995).


Table 2: Energy and waste from primary and secondary aluminum production

Metrics Primary Secondary Data Source Aluminum Aluminum

Energy (MJ / kg) 163.73 16.76 188.40 13.25

[I 41; German condition [21]; Alcoa Worldwide operations [37l; Swiss study [38]; European study [25]; US condition

Solid waste (kg / kg) Total alumina production electrolysis cleaningcasting energy smelting energy supply alumina production

2.42 0.062 2.1 (red mud = 2.0) 3.57 x 10-2 2 . 0 ~ 102 0.27

4.3 x 10-2 1.87 x 1 w2

3.0 (red mud) 2.9 (red mud)

[I 41; German condition [24]; estimate Europe [14]; German condition [I 41; German condition [I 41; German condition [14]; German condition [14]; German condition [24]; estimate Western Australia [141; German condition

Air emissions (kg / kg)

co2 13 CO 1.65 x 1r2 so2 9 . 1 9 ~ ' NO, 2.85 x 1 o - ~ particulates 1 . 9 6 ~ 1p2 ' HC 3.77 x lo-3 FC 8.5 x lo4 HCI H2 others 1 . 0 ~ 10"

[14] [24], [21]; reasonable average condition

[21]; Alcoa worldwide operations [I 41; Europe condition '[24], *'[I41 Europe condition *[24], **[I41 Europe condition *[24], **[14]; Europe condition [I 41; German condition 2241; Europe condition [I 41; German condition [I 41; German condition [I 41; German condition

Water use (m3 / kg) 11.44' 1.6" '[24]; estimate Western Australia **[14]; German condition

(ii) Manufacturina Phase - The manufacturing energy of the sand-cast aluminum manifold involves transportation, machining and sand casting in a foundry. The site energy for sand casting is obtained from site energy for gravity die casting, which is about 39.36 MJIkg [28]. The 6.5 kg sand cast manifold is associated with 0.687 kg castinglmachining loss and 0.37 kg scrap loss. Thus, 7.557 kg of aluminum has to be processed to manufacture a 6.5 kg sand cast manifold. Therefore, the total energy for manufacturing the sand cast manifold is 297.44 MJ. Sand casting energy consists of melting, holding and distribution of molten metal.

Manufacturing energy for the multi-tube brazed aluminum manifold involves sand casting the flange portion, extrusion and brazing. The extrusion process generates 15% scrap [29], which results in a scrap loss of 0.20 kg. In addition, a machining loss of 0.248 kg is estimated to be associated with the sand cast portion of the manifold. The mass of molten aluminum sand cast is 2.731 kg for the 2.483 kg flange section and the mass of billet extruded is 1.537 kg for the 1.337 kg of the extruded section. A further 0.2 kg is lost in production, resulting in a final multi-tube brazed manifold weight of 3.62 kg.

The energy for the sand cast flange, assuming a 39.36 MJIkg energy density [28], is 107.49 MJ. The average energy for extrusion is obtained from averaging extrusion data from three different plants in Europe [31] and the average data for extrusion in a US extrusion mill [32]. The extrusion data. include remelting primary aluminum ingot and mixing it with scrap to produce a billet, reheating the billet and forcing the billet through a die opening [29,31,32]. the average primary energy for extrusion is calculated to be 16.76 MJ I kg.

The four bent extruded tubes (5cm diameter and 3mm thickness) are brazed to an air collection chamber and a cast flange. There will be a total of eight brazed joints divided equally between the cast flange and the air collection chamber end. Typical brazing length for aluminum tubes is assumed to be 0.15 mm [29,35,36]. The commercial filler material for brazing aluminum contains 91% aluminum and 7% silica and has an average density of 2601 kg 1 m3. The total mass of filler material to be brazed is calculated to be about 1.6 grams. The specific heat of fusion for aluminum is 0.356 MJ I kg and the mean specific heat for the filler material is 0.92 KJ 1 kg-K. The temperature difference for the furnace and room temperature for furnace brazing applications is about 900 K. Therefore, the minimum


energy supplied for brazing is calculated from thermodynamics as 1.9 KJ.

Therefore, the manufacturing energy of sand cast part, extruded part and brazed joints are 104.81, 1.66 and 1.9 x 1 0-3 MJ per manifold respectively. The relative magnitude of the brazing energy indicates that uncertainty associated with the estimation of this value is not significant.

Most common furnaces in aluminum foundries are crucible type, which are either gas fired, electric arc or induction furnaces [28,29]. The exact mix of gas fired and electric powered (electric arc or induction) furnaces in a foundry is difficult to predict. However, the Ford core team reported that most furnaces for sand casting in Ford facility are gas fired. Using an efficiency factor of 0.89 for natural gas 1301, the primary energy required for manufacturing the sand cast manifold is calculated to be 334.21 MJ. The primary energy equivalent for manufacturing the sand cast flange is 120.77 MJ, assuming efficiency factor of 0.89 for natural gas. The primary energy equivalent for the brazing energy is 0.006 MJ, assuming an efficiency factor of 0.32 for electricity. Therefore, the total primary energy for the multi-tube brazed manifold is 146.54 MJ.

Process wastes for sand casting are obtained from [39,40] as quantities of chemicals released in the green sand process for sand casting in an iron foundry. It is assumed that bonding green sand in iron and aluminum foundries has the same property, therefore process emissions become a function of the mass of metal poured only. Process wastes for extrusion and brazing are neglected. The wastes and emissions associated with electricity and natural gas use are obtained from [301.

(iii) Use Phase - Use phase energy and waste are calculated for 150,000 miles (241,350 km) life of the intake manifolds.

Enerav - The procedure used for energy calculation is explained below:

The specifications for the Contour 1995 is indicated in Table 3.

Table 3: Weight and fuel economy of the Contour 1995

Parameter Metrics

Test weight 1471 kg or 3250 Ib

Fuel economy 7.46 1 1 100 km or 31.5 mpg

Weight to fuel economy 10% weight reduction = 4% fuel correlation consum~tion reduction

The contribution of the manifold to vehicle fuel consumption (Fg))is obtained using following correlation:

where, Fg) = fuel (liters) used over the life of intake

manifold (L)

MIM = mass of the intake manifold MV = test weight (mass) of vehicle = 1471 kg Af - = fuel consumption correlation with mass, for AM

the 1995 Contour the correlation was obtained from Ford's core team as 10% weight reduction is equivalent to 4% fuel consumption reduction, therefore Af - - - 0.4 AM

FEU) = fuel economy in litres / km, for the 1995 Contour the fuel economv is 7.46 1 / 100 km. Therefore FE = 0.0746

L = life of intake manifold = 241,350 km

Therefore, the lifetime fuel consumption of 6.5 kg sand- cast manifold = 31.82 1 = 8.40 gallons = 1337.39 MJ assuming that 1 I gasoline is equivalent to 42.03 MJ of energy comprising of 34.87 MJ of combustion energy and 7.16 MJ of precombustion energy [30].

Using similar procedure as above, the 3.62 kg multi- tube brazed manifold will result in 17.72 1 (4.68 gallons) life time fuel consumption, which is equivalent to 744.77 MJ of energy.

Waste - Both combustion and precombustion wastes are calculated. Combustion emissions - Air emissions evaluated from EPA test results are CO, HC and NO, The C02 data are evaluated as follows: Assume gasoline has a mean chemical formula of and a density of 0.74 kg / I 1 kg of gasoline is equivalent to 3.1 6 kg C02 emission The tail pipe emission from the Contour, 1995 is indicated in Table 4.

Table 4: Certified emission data for the Contour, 1995. Emission data include deterioration factors [41]

Description Contour, 1995

EPA test # Engine family name Vehicle ID # Air emissions (me$, kg / mile) co2 CO Cold CO HC Nonmethane HC NO, Eva~orative

The mass of air emissions over the life of intake manifold is obtained from mass of air emissions per vehicle miles traveled using EQ (5)

me = me, FE(gal) x (5) where, me = mass (kg) of air emissions over the life of

intake manifold (L) me$ = mass of air emissions per mile (kg / mile)

8


FEbaI) = fuel economy in miles per gallon F a = fuel (gallons) used over the life of intake

manifold (L)

Precombustion Waste - The precombustion waste (air emissions, waterborne waste and solid waste) per 1000 gallons of gasoline is obtained from the Franklin database [30]. The Franklin waste data is multiplied by gasoline used in gallons per manifold to obtain waste in kg per manifold.

The total use phase waste is obtained by adding the precombustion waste with the combustion waste. The use phase energy and waste are calculated by neglecting the secondary weight effect. This means that the intake manifold is replaced in the vehicle without altering any other parts.

(iv) Retirement Phase - Retirement of the manifold involves the following steps and model idealizations:

Transportation from the dismantler as part of the whole vehicle to the shredder (100 miles) Shredding Transportation from the shredder to the non-ferrous separators (200 miles) Separation of aluminum from automotive shredder residue (ASR) and other non-ferrous metals. Two separation processes are involved - light media for ASR and heavy media for aluminum Disposal of non-recovered aluminum (5%) to landfill (200 miles) For the sand cast manifold 6.175 kg of shredded aluminum is separated and recycled back into the manifold. For the multi-tube brazed manifold, 3.439 of shredded aluminum is recycled. 2.577 kg of the shredded aluminum is recycled back into the manifold and the remaining 0.862 kg leaves the system for another application. 2.496 kg of recycled aluminum is utilized as ingot for sand casting the flange section and 0.081 kg of recycled aluminum is used as scrap for extruding the tubes and the air collection chamber. This model was used to allocate recycling burdens.

The energy for different processes is given below: Shredding energy = 0.097 MJ 1 kg (42 BTU / lb). The shredding energy was obtained from Texas shredder (1 995). Separation energy for aluminum = 0.1 MJ / kg. The separation energy was obtained from Huron Valley Steel (1 995) Transportation energy = 2.05 MJ 1 ton-mile [30] Shredders and separators are run by electric motors. Transportation trucks are diesel operated. Total waste in the retirement stage from electricity and diesel fuel use is obtained from Franklin [30].

Cost Metrics (i) Material Production Phase - Processing costs for primary and secondary aluminum are not available. Therefore, this analysis uses only material cost. The material cost for the two manifolds is obtained by subtracting the value of scrap generated during

processing from the cost of materials processed as shown in EQ (6).

Crnat~ = Mp X Cp + Ms X Cs + Msci x Csci + Mscp x Cscp (6) where,

Mp = mass of primary aluminum ingot processed Ms = mass of secondary aluminum ingot processed MSci = mass of in-house scrap processed Mscp = mass of purchased scrap processed Cp = Ford's commodity price for primary aluminum ingot

=$2.12/ kg C, = Ford's commodity price for secondary aluminum

ingot = $1.89 / kg Csci = cost of in-house scrap = 0 C,,, = cost of purchased scrap = C, For the sand cast manifold, M, = 0, M, = 6.552 kg, Msci = 1.005 kg and Mscp = 0 Therefore, the total material cost (CmatI) for the sand cast manifold is $12.88. For the multi-tube brazed manifold, Mp = 1.076 kg, M, = 2.496 kg, Msci = 0.615 kg and Mscp = 0.081 kg. Therefore, the total material cost (CmatI) for the multi-tube brazed manifold is $7.1 5.

(ii) Manufacturina Phase - The manufacturing cost of the manifold is obtained by the following approximate correlations provided by Ford's manifold product division:

Because manufacturing costs are proprietary, indirect cost estimates are used. The manufacturing and material cost of the manifold is one sixth of the part cost of the dealer

Cdealer Crnanf + Cmat~ = - 6 (7)

The dealer part cost for the intake manifold of 1995 Ford Contour and Escort are $300.95 and $244.78 as of August, 1995. These costs were obtained from Ford dealers at Ann Arbor[42,43]. There is a price revision every three months. The manufacturing cost of the multi-tube brazed Escort manifold is obtained from EQ (7) as $33.65. The manufacturing cost of the sand-cast manifold is obtained from EQ (7) and differential cost correlation with respect to composite manifold as $26.28. The cost to Ford includes both material and manufacturing cost and is $38.66 for the sand-cast manifold and $40.80 for the multi-tube brazed manifold.

(iii) Use Phase - In the use phase it is assumed that both the manifolds will run without maintenance for 150,000 miles. Therefore, only cost to the user will be the cost of gasoline. The national average cost for gasoline is obtained from [33] as $1.17 / gallon. The life time fuel cost for the multi-tube brazed aluminum manifold is found to be $5.47 as opposed to $9.82 for the sand cast aluminum manifold.

(iv) Retirement Phase - Cost analysis for each stage of the retirement process was conducted :

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The value of a used 1991 Escort multi-tube brazed manifold was found to be $50.00 [44]. The 1991 Escort manifold, however, weighs more than the 1995 Escort manifold. Although some aluminum manifolds are recovered during the dismantling stage, no data are available to estimate the fraction sold for used parts. Therefore, this credit was not incorporated in the life cycle cost analysis. The aluminum intake manifold will be transported from the dismantler to the shredder. Transportation cost from dismantler to shredder, 100 miles [30]: flattened hulks $0.12 I ton-mile, un-flattened hulks $0.18 / ton-mile. Assuming a 50% split between flattened and unflattened hulks, total transportation cost is $0.15 / ton-mile. The total costs and credits to the shredder operator were obtained from APC retirement spreadsheet model [34] as $116.64 / hulk and $125.21 / hulk respectively. The cost of the shredder (Csh) includes hulk sale value (C,,), transportation cost (C,), disposal cost (Cd)and the processing cost (C,,) as shown in EQ (8).

Since the actual processing cost was not available, the processing cost was estimated from EQ (8) using

the following data. The APC model was based on a 1992 average automobile [34]. The average weight of a 1992 vehicle is 1425.22 kg [45]. The material composition of this automobile includes 953.41 kg of ferrous material, 136.82 kg of non ferrous metals, 254.54 kg of non metals and 80.45 kg of fluids [45]. Assuming the dismantler drains all the fluids and transport the reamaining materials to the shredder, the weight of the hulk sold to the shredder is 1344.77 kg. The APC study assumed a hulk sales value (Ch) to the shredder to be $30.00 and a transportation cost of $0.12 / ton-mile. The metal portion (ferrous and non-ferrous) of the hulk weighing 1090.23 kg will be transported from the shredder to the metal recyclers to an average distance of 200 miles and the non metal portion weighing 254.54 kg will be transported from the shredder to the landfill to an average distance of 100 miles 1341. Thus the total cost for transportation (CJ is calculated to be $32.14. The APC study assumed a disposal fee for non-hazardous waste to be $75.00 /ton. Since, the automotive shredder residue (ASR) in US is classified as non-hazardous, the total disposal cost (Cd) of 254.54 kg of non-metal ASR is calculated to be $21.00. The processing cost (Cpr) for the hulk is estimated from EQ (8) to be $33.50.

Table 5 : Itemized cost description for different ELV managers and processes for the intake manifolds

ELV managers Cost descriptors Sand cast manifold, Multi-tube brazed 6.5 kg manifold, 3.62 kg

Dismantler transportation cost (a)

Shredder transportation cost to metal recycler (95% by weight) (b)

transportation cost to landfill (5% by weight) (c) disposal cost (5% by weight) (d) processing cost (e)

Non-Fe processor 1 processing cost (f) metal recycler scrap value (g)

Total cost (a) + (b) + ( 4 + (d) + (e) + (f) Total value of Al innot (n)

The processing (separation) cost for aluminum is estimated by Huron Valley Steel to be $0.22 / kg [46]. The scrap value for aluminum is obtained from American Metal Market to be $0.96 / kg [47]. The retirement cost information for end of life vehicle (ELV) managers as described above are converted to cost per manifold as shown in Table 5. The disposal cost is calculated using national average tipping fee of $30.25 / ton [48]. The total retirement cost for the sand cast and multi-tube brazed manifold are $1.81 and $1 .OO respectively. The scrap value of the sand cast and multi-tube brazed manifolds are $5.93 and $3.30 respectively.

Performance Metrics (i) Manufacturina Phase - The multi-tube brazed Escort manifold is comprised of a cast aluminum flange, four bent aluminum tubes and an air collection chamber

joined together by brazing. The aluminum tubes and the collection chamber is manufactured by extrusion. After extrusion, aluminum tubes are bent into desired shape

. by a movable mandrel. The casting is placed into a die and pressurized hydraulic fluid turns out the four openings from inside [14]. The manufacturability of the multi-tube brazed manifold is far more complex than a simple sand-cast manifold. A typical cycle time for manufacturing the sand-cast manifold is 14 minutes. This includes 1 minute for core fabrication, 2 minutes for casting, 5 minutes for cooling, 0.5 minute for premachining pressure test, 0.5 minute for machining and 2 minutes for washing, assembly, testing and packaging. The tool life for a typical aluminum manifold is about 250,000 cycles. The die life is about 1 x lo5 to 2 x 1 O5 mold parts before reconditioning. The cycle time of multi-tube brazed manifold is expected to be higher than that of sand-cast manifold because of the cycle time requirements for extrusion and brazing.

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(ii) Use Phase - The smoother wall of the multi-tube brazed manifold is expected to lead to less friction loss compared to the rough wall, sand-cast manifold. This will theoretically translate into higher volumetric efficiency and higher power output at the same throttle opening. However Ford test engineers reported no significant difference in power between engine equipped with rough walled sand-cast manifold and a smooth walled composite manifold at part throttle. At full throttle a 2% increase in power for the composite manifold was obtained. Similar conclusion can be inferred about the smoother walled multi-tube brazed manifold.

Since the sand-cast manifold has not been used in actual vehicle production, the warranty data for this manifold is not available. For the multi-tube brazed Escort manifold, Ford has found 262 warranty claims out of 1,438,593 vehicles sold in last five years. This leads to 0.18 defects per 1000 vehicles. The warranty data includes manufacturing flaws, assembly errors, mis-bins (wrong parts serviced) and accident repairs.

RESULTS AND DISCUSSIONS

The life cycle environmental burden for the sand cast and the multi-tube brazed aluminum manifolds are presented in Figures 5 , 6, 7, 8 and 9. All data are expressed per one intake manifold (IM).

Figure 5 shows that the overall life cycle primary energy for the sand-cast manifold is about 1.59 times higher than that of the multi-tube brazed manifold. The material production energy of the multi-tube brazed manifold is about 2.01 times higher than the sand-cast manifold because of the high processing energy required for bauxite reduction into alumina and alumina smelting to molten aluminum.

Sand cast manifold

LlFE CYCLE STAGE The manufacturing energy of the multi-tube brazed manifold is estimated using surrogate data. IM denotes one intake manifold.

Figure 5: Life cycle energy of intake manifolds.

The manufacturing energy of the sand cast aluminum manifold is about 2.28 times higher than the manufacturing energy of the multi-tube brazed manifold

because of the higher processing energy required for sand casting compared to extrusion and brazing. In the use phase, the sand-cast manifold results in 1.79 times more energy consumption compared to the multi-tube brazed manifold because of its higher weight. The use phase represents the bulk of the total energy consumption for the sand cast (74%) and the multi-tube brazed (66%) manifolds. The higher weight of the sand- cast manifold is also responsible for 2.2 times higher processing energy compared to the multi-tube brazed manifold in the retirement phase. The retirement phase represents only a small fraction (0.4-0.5%)of the total energy consumption for the manifold system.

Figure 6 shows the life cycle solid waste generated from the multi-tube brazed manifold is about 1.66 times that of the sand-cast manifold. Material production of the of the primary and secondary aluminum mix for the multi- tube brazed manifold results in 76% of the life cycle solid waste.

Multi-tube brazed manifold

LlFE CYCLE STAGE Solid waste reported are the sum of process waste and waste due to energy generation.

Figure 6: Life cycle solid waste of intake manifolds.

As shown in Table 2, the red mud generated during alumina production accounts for 87% of the solid waste for the primary aluminum processing. The solid waste in the manufacturing stage comprised of process waste from sand casting, product waste and energy waste. The sand casting waste consists of fume dust and the 5% loss in recycling sand and salt slag. The product waste consists of 5% loss in recycling the scrap generated from the manifold. The process and product waste for the sand cast manifold are1.045 kg and 0.052 kg respectively. For the multi-tube brazed manifold, the process and product waste are 0.4 kg and 0.255 kg respectively. The solid waste during use phase primarily results from waste generated in the production of gasoline. The retirement solid waste includes the 5% loss in recycling the aluminum manifold at the end of life of the vehicle.

Figure 7 shows that life cycle C02, CO, HC and NO, emission for the sand-cast manifold are about 1.38, 1.70, 1.71 and 2.04 times higher than the multi-tube brazed manifold. The SO2 emission of the multi-tube brazed manifold is about 1.28 times higher than that of the sand-


cast manifold. It is apparent from Figure 7 that the majority of air emission results in the form of COP

Go2 GO +.$C +o+ AIR EMISSIONS

Both process and energy emissions are included. IM denotes one intake manifold.

Figure 7: Cumulative life cycle air emissions of intake manifolds.

Figure 8 illustrates that the majority of global warming potential (GWP) results from C02 emissions. Although fluorocarbons have a very high GWP relative to C02 (6300 for CF, and 12500 for C2F6: time horizon of 100 years [49, 50]), fluorocarbon emissions for primary aluminum processing for the multi-tube brazed manifold are only 0.91 gram. Therefore, fluorocarbon emissions result in only 6.33 kg of C02 equivalent, relative to 64.67 kg of C02 for the multi-tube brazed aluminum manifold. The COP equivalent GWP for the sand cast manifold is about 1.25 times higher than that of the multi-tube brazed manifold.

I &j Sand cast manifold 1007 I

Multi-tube brazed manifold 2 \

ol 75 0 0 .M

O 50 0) Y c .- B 25 Q

0

Go2 G+k G$6 <Ox@' GREENHOUSE GASES

Time horizon of 100 years

Figure 8: Life cycle greenhouse gas emissions for the two manifolds in C02 equivalents.

Figure 9 shows that the life cycle dissolved solids, suspended solids and oil for the sand cast manifold are about 2.10, 1.78 and 1.80 times that of the multi-tube brazed manifold. Conversely, the BOD, COD, acids and metal ions for the multi-tube brazed manifold are 1.45, 8.60, 3.07 and 2.30 times that of the sand-cast manifold.

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WATER EFFLUENTS Waste includes both process waste and energy waste. Solids include both dissolved and suspended solids in water. IM denotes one intake manifold.

Figure 9: ' Cumulative life cycle water effluents of intake manifolds.

Figure 10 shows that the life cycle costs of the multi- tube brazed manifold is 39 Q: lower than that of the sand cast manifold. The material cost of the sand-cast manifold is about $5.23 higher than that of the multi-tube brazed manifold. The material cost of the multi-tube brazed manifold is calculated using EQ (7). The higher material cost of the sand cast manifold is due to its higher weight compared to the multi-tube brazed manifold. The estimated manufacturing cost of the multi- tube brazed manifold is about $7.37 higher than the sand-cast manifold because of the manufacturing difficulty of the multi-tube brazed manifold.

Multi-tube brazed manifold

LIFE CYCLE STAGE The material cost is estimated using EQ 6. The manufacturing cost excludes the material cost and is estimated using EQ 7. The scrap value is obtained from dealer's Detoit based buying price.

Figure 10: Life cycle cost of intake manifolds.

The multi-tube brazed manifold requires sand casting, extrusion, careful assembly of manifold parts and brazing. The gasoline cost to the user of the sand-


cast manifold over a useful life of 150,000 miles is about $4.35 higher than that of the multi-tube brazed manifold because of its higher weight. In the retirement stage, the sand-cast manifold requires 81 G higher processing cost but has $2.63 higher scrap value of aluminum compared to the multi-tube brazed manifold. The manufacturing process accounts for majority of life cycle cost for the sand cast (59.24%) and multi-tube brazed (76.53%) manifolds.

The environmental, cost and performance metrics evaluated in this paper provide a set of data to support the selection between two alternative intake manifold designs. Additional information currently under investigation including design guidelines, corporate policies and targets, and regulatory drivers also will strongly influence the decision process. Although these factors were not evaluated here several insights into the decision process can be made.

Inherent in many decision processes are tradeoffs between criteria. The environmental, performance and cost metrics differ relative to each other in their respective measuring units, relative importance to internal and external stakeholders and in their integration into the design process. Furthermore, the different environmental loads (inputs and outputs) represent a heterogeneous set of impacts from depletion of primary energy sources to global warming. Life cycle impact assessment is an emerging tool for characterizing and evaluating inventory data [51-541. Techniques for impact assessment range from less is better approach to site specific risk assessment models that account for routes, duration and frequency of exposure to pollutant releases as well the size of the population at risk.

The original product design and material selection for alternative intake manifolds at Ford included several evaluation criteria such as weight, recyclability, prototype tooling cost, variable cost, production tooling cost, 120 K durability, first time quality capability, airflow1 performance, fastener compatibility, joint sealing, material dimensional stability, flammability resistance, high and low temperature performance, positive pressure capability, NVH structural and acoustical, prototype lead times, production lead times, appearance, established NAAO supply base, manufacturing flexibility, component integration and design flexibility. Decision making processes can range from intuitive approaches to the use of rational decision making techniques [55,56]. In either case, corporate policies, targets, and experience will help guide the decision maker. For rational decision making approaches criteria are weighted and scored.

CONCLUSIONS

This paper applied elements of the life cycle design framework to a comparative evaluation of a sand cast and multi-tube brazed aluminum manifold for a 2.0 1 engine.

The following conclusions can be derived for this study :

* Environmental, cost and performance metrics were evaluated for each life cycle stage and these metrics

can be integrated with existing metrics to enhance product design and decision making.

The life cycle design approach enables the OEM product development team to understand the interactions and relationships between environmental, cost and performance factors. This allows the decisionmakers to systematically integrate environmental considerations into the conventional design process.

The life cycle design study highlighted several key tradeoffs including energy, solid waste, air emission, water effluents, cost and performance.

Although the multi-tube brazed manifold consists of 24.5% primary aluminum which requires higher energy (about 10 times) for processing compared to secondary aluminum, the overall life cycle energy for the multi-tube brazed manifold is about 1.59 times lower than that of the sand-cast manifold. This results from energy savings in manufacturing and use phase based on a lower total mass of the part due to a weight reduction of 2.88 kg associated with the multi-tube brazed manifold.

The cumulative life cycle solid waste for the multi- tube brazed manifold is about 1.66 times that of the sand-cast manifold. Primary aluminum production results in 39 times more solid waste generation compared to secondary aluminum per kg of materials processed. The solid waste from manufacturing of the sand cast manifold is about 2.24 times higher than that of the multi-tube brazed manifold.

Other tradeoffs were demonstrated with air emissions. The life cycle C02 equivalent of global warming potential for a 100 years time horizon for the sand-cast manifold is about 1.25 times higher than that of the multi-tube brazed manifold. Although fluorocarbons have a relatively high global warming potential, they have relatively small contribution to the overall global warming.

The heterogeneous nature of environmental impacts, costs and performance across the life cycle raises fundamental questions regarding prioritization of these factors by a manufacturer. Life cycle cost metrics represent costs incurred by different stakeholders. With respect to costs borne by the manufacturer the estimated material and manufacturing costs were slightly higher for the brazed manifold $40.80 compared to $38.66. From the perspective of the consumer, the cost is higher for the sand-cast manifold by $4.35. From a societal perspective the market system indicates that the sand cast manifold costs 39 @ more than the multi- tube brazed manifold. The data presented in Figure 10 make these tradeoffs explicit. The actual cost to different stakeholders is difficult to evaluate because of difficulty in estimating and allocating hidden, less tangible and future costs born by each stakeholder and the society [I].

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Many challenges relating to methodology, data availability, current regulatory framework and time constraints in the product development cycle must be overcome before LCD tools can be effectively implemented by an OEM product development team. However, it is becoming apparent that the complexity of competing requirements of a new product design req'uires system based LCD tools to guide improvements and analyze tradeoffs.

The results of this study are currently being used by the NPPC-Ford LCD project team to develop recommendations regarding the use of life cycle inventory analysis, life cycle costing, and specific metrics throughout planning and product development processes.

ACKNOWLEDGMENTS

The authors wish to acknowledge the Ford's core team members for providing the resources and data for this research project. The Ford core team members participated in periodic meeting with the authors since the beginning of the life cycle design research project last year. The Ford core team members consist of Wayne Koppe, Gerald Czadzeck, Mitch Baghdoian, Fred Heiby, David Florkey and Cymel Clavon from Powertrain Operations (engine), Phil Lawrence from Environmental Quality Office, John Sullivan and Mia Costic from Scientific Research Laboratory, George Good from Casting Operations, Mike Johnson and Steve Church from Advanced Vehicle Technology, Susan Day from Environmental and Safety Engineering and Norm Adamowicz from Materials Engineering. We also thank Ken Martchek from Aluminum Company of America, Scott McGlothlin from Texas Shredder, Eric Ratting from Huron Valley Steel and Cliff Tyree from US EPA's National Vehicle Fuel Emissions Laboratory for providing valuable data for this project.

Funding for this research project was obtained from US Environmental and Protection Agency under cooperative agreement # CR822998-01-0. Ken Stone is the US EPA project officer for this research project. However, the contents of this paper do not necessarily reflect the views and policies of US EPA, nor does mention of the trade names or commercial products constitute endorsement or recommendation for use.

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