The Carbon Footprint of Aluminum and Magnesium Die Casting Compared to Injection Molded Components

Transcription

1 The of Aluminum and Magnesium Die Casting Compared to Injection Molded Components William A. Butler Extra-CarbonFootprint.indb /10/2008 3:00:36 PM

2 Although great care has been taken to provide accurate and current information, neither the author(s) nor the publisher, nor anyone else associated with this publication, shall be liable for any loss, damage or liability directly or indirectly caused or alleged to be caused by this book. The material contained herein is not intended to provide specific advice or recommendations for any specific situation. Any opinions expressed by the author(s) are not necessarily those of NADCA. Trademark notice: Product or corporate names may be trademarks or registered trademarks and are used only for identification and explanation without intent to infringe nor endorse the product or corporation by North American Die Casting Association, Wheeling, Illinois. All Rights Reserved. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming, and recording, or by any information storage and retrieval system, without permission in writing form the publisher. Extra-CarbonFootprint.indb 2 7/10/2008 3:00:36 PM

3 The of Aluminum and Magnesium Die Castings Compared to Injection Molded Components By: William A. Butler NADCA 2008 Table of Contents 1. Introduction Executive Summary Overview Life Cycle Assessment Goal and Scope Life Cycle Inventory Life Cycle Impact Assessment Life Cycle Assessment Interpretation Conclusions and Recommendations.. 25 References.. 27 Page i Extra-CarbonFootprint.indb 3 7/10/2008 3:00:36 PM

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5 1. Introduction This carbon footprint study was initiated by the North American Die Casting Association (NADCA) for the benefit of its member companies. NADCA is the sole trade and technical association of the die casting industry. NADCA membership consists of both corporate and individual members from more than 950 companies located in every geographic region of the U.S. These companies include custom die casters (who produce die castings for sale to others), captive die casters (who produce castings for their own use in manufacturing a product) and suppliers to the die casting industry. Die casting is a century-old process of injecting molten metal into a steel die under high pressure. The metal, usually aluminum, zinc, magnesium and sometimes copper, is held under pressure until it solidifies into a net-shape metal part. In modern applications, using computerized controls, die casters produce precision and high-strength products at a rapid production rate. No other metalcasting processes allow for a greater variety of shapes, intricacy of design or closer dimensional tolerance. Die casters contribute more than $7.3 billion to the nation s economy annually and provide more than 63,000 jobs directly and indirectly. The die casting industry is a microcosm of American business. About 58% of these companies have fewer than 100 employees, while the larger firms are world leaders. To meet the challenges posed by today s global marketplace, the North American die casting industry is leading the rest of the world with new technology, higher productivity, innovative applications and superior quality. The increased use of lighter weight metal components, such as aluminum die castings, has spurred growth in the automotive sector. Today, there is an average of 300 lb. of aluminum castings per vehicle, an amount projected to grow to each year. The die casting industry has long been built on recycling. The metal alloys used by the die casters are produced from recycled raw materials, created with far less energy than is required for virgin alloys. More than 95% of the aluminum die castings produced in North America are made of post-consumer recycled aluminum, helping to keep the aluminum content of municipal solid waste to less than 1%. In response to questions from NADCA member companies about the carbon footprint of automotive die castings compared to alternative materials and processes for automotive components, this study was authorized. Specifically, the study compares the cradle-to-grave carbon footprint of aluminum and magnesium die cast components with the carbon footprint of injection molded plastic components. The results of the study provide environmental impact information to the die casting industry, provide a baseline for further component carbon footprint evaluations in the future and identify opportunities for industry improvement in the environmental impact of die casting operations. Page 1 Extra-CarbonFootprint.indb 5 7/10/2008 3:00:37 PM

6 Introduction The report is divided into eight sections. Following this Introduction, an Executive Summary is provided with the general results of the study and an outline of the recommendations to the die casting industry. The third section provides a Carbon Footprint Overview to provide a basis for the study and explain the terms and concepts associated with carbon footprint studies as well as the limitations of these techniques. Chapter 4 provides information on the Goal and Scope of Life Cycle Assessment study. Chapters 5, 6 and 7 provide the detailed information determined by the study of aluminum and magnesium die castings compared to injection molded components, including a Life Cycle Inventory, a Life Cycle Impact Assessment and information on interpreting the results of the study. Chapter 8 provides a summary of the study, some general conclusions from the study and recommendations for the die casting industry. A list of References utilized to develop the study is included at the end of the report. Page 2 Extra-CarbonFootprint.indb 6 7/10/2008 3:00:37 PM

7 2. Executive Summary This study examined the carbon footprint, defined as equivalent carbon dioxide (CO 2 ) emissions, of an automotive cam cover produced by aluminum die casting, magnesium die casting and plastic injection molding. The study was done by utilizing the four phases of Life Cycle Assessment (LCA): goal & scope, life cycle inventory, impact assessment and interpretation. The procedures for LCA are a part of the ISO environmental standards being used throughout the world. Despite some criticisms concerning the measurement of carbon footprint and disagreement as to the causes and appropriate mitigations of global warming, the topic has come to the forefront of discussion throughout the world. NADCA commissioned this project in response to member interest in such an evaluation. The cam cover component selected as the subject of this study is for a four-cylinder engine. The part is produced from secondary 380 aluminum alloy by the die cast process, from primary AZ91D magnesium alloy by the die cast process and from nylon 66 GF35 (35% glass fiber reinforced) material by injection molding. The designed volume of the magnesium component is 10% more than the aluminum component, and the volume of the nylon component is 20% more than the aluminum component to meet strength requirements. The resulting mass of the finished components were 2.61 kg for the aluminum component, 1.89 kg for the magnesium component and 1.58 kg for the nylon component. Process flow diagrams were developed for each process, and the energy used and resulting carbon footprint, in terms of the kilograms of equivalent carbon dioxide emissions of each step of the process, were tabulated. This information is discussed in detail in Chapters 5 and 6 of this report. The study computed the carbon footprint for four phases of product life of the cam cover: material production, product manufacture, product use and product disposal. The results of the LCA indicate that most of the carbon footprint results from the use of the product in the vehicle over its life. More than 90% of the carbon footprint for the aluminum die casting was from Product Use, and 75% of the carbon footprint for the nylon component was produced in this phase. The magnesium die cast component had 33% of its carbon footprint generated in the Product Use phase because its total carbon footprint was much larger due to the use of SF 6 as a cover gas during material production and product manufacture. This practice is addressed in the conclusions and recommendations that follow. Several conclusions and recommendations were drawn from the study and are provided. Page 3 Extra-CarbonFootprint.indb 7 7/10/2008 3:00:38 PM

8 Executive Summary Conclusions The greatest contributor to carbon footprint identified in the study is the use of SF 6 as a cover gas during production of the magnesium die cast cam cover. Neglecting the contribution of Product Use to the total carbon footprint, aluminum die casting has the lowest carbon footprint because of its use of secondary aluminum alloys and its ability to be recycled. The production of the nylon material in the study contributed much more to the carbon footprint than material production for the aluminum component. If the use of SF 6 were discontinued, magnesium production, even for primary alloys, would also be favorable to the production of nylon. The Product Manufacture phase of component life was essentially equal for all three components, except for the use of SF 6 for the magnesium cam cover. Disposal of plastic is a growing problem. If resistance to landfilling scrap plastic grows, the recycling or incineration of scrap plastic will significantly increase the carbon footprint of these components. Corresponding to this, additional energy and cost will be required to meet more stringent environmental requirements. The use of secondary magnesium alloys for automotive components would significantly reduce the carbon footprint of these components. Recommendations 1. The use of SF 6 as a cover gas for magnesium should be eliminated. 2. The ability to recycle aluminum die castings and their resulting low carbon footprint should be marketed heavily by the industry. 3. Industry initiatives which reduce energy consumption and increase energy efficiency should be strongly encouraged, and their contribution to reducing the carbon footprint of the components should be stressed. 4. The die casting industry should initiate and support the development of material property data to encourage the use of secondary magnesium alloys. Currently, primary magnesium alloys are specified for many components due to a lack of confidence in the material properties of recycled alloy. 5. Additional carbon footprint studies should be considered by NADCA, utilizing software programs that are being developed. These programs will provide a more complete analysis of the contributions to the carbon footprint for components. They also provide the ability to ask what if questions and perform sensitivity analysis of alternatives. If NADCA were able to gain access to one or more of these computer tools, this study could be expanded and validated. Page 4 Extra-CarbonFootprint.indb 8 7/10/2008 3:00:38 PM

9 3. Overview A carbon footprint is a description of the impact human activities have on the environment in terms of the amount of greenhouse gases (GHG) produced during an activity 1. This impact is measured in units of carbon dioxide (CO 2 ). This measurement is meant to be useful for individuals and organizations to conceptualize their personal or organizational impact in contributing to global warming. The carbon footprint can be seen as the total amount of carbon dioxide (CO 2 ) and other GHG emitted over the full life cycle of a product or service. Normally, a carbon footprint is expressed as a CO 2 equivalent (usually in kilograms or tonnes) which accounts for the same global warming effects of different greenhouse gases. Carbon footprints are often calculated using a Life Cycle Assessment (LCA) method. Life Cycle Assessment (LCA), which is also known as life cycle analysis, ecobalance and cradle-to-grave analysis, is the investigation of the environmental impacts of a given product or service. It is a variant of input-output analysis, focusing on physical rather than monetary flows. The goal of LCA is to compare the full range of environmental damages assignable to products and services, and to be able to choose between alternatives. The term life cycle refers to the idea in which all phases in the life a product, from raw material production, manufacture, distribution, use and disposal, as well as all transportation between each step, are included in the analysis. The procedures for LCA are a part of the ISO environmental management standards being used throughout the world. Specifically, ISO 14040:2006 and 14044:2006 outline the LCA process. (ISO replaced earlier versions of ISO to ISO ) As the global automotive industry, a major user of die castings, incorporates ISO into its operations, environmental considerations are receiving increased emphasis and discussion. There are four phases to LCA: goal & scope, life cycle inventory, impact assessment and interpretation, which will be discussed in detail in subsequent sections of this report. Page 5 Extra-CarbonFootprint.indb 9 7/10/2008 3:00:39 PM

10 Overview The concept of a carbon footprint is not without criticism 1. This criticism is usually based on disagreement with one or more of the following assumptions underlying the calculation of a carbon footprint. 1. That carbon emissions are a significant cause of global warming. 2. That human activity is a significant cause of these emissions. 3. That it is possible to attribute all or most emissions to particular individuals. 4. That individual initiative is necessary because market forces or legislation will not be powerful and timely enough. 5. That other causes, such as methane emissions, are more important. 6. That human activity is not as significant a cause as natural processes such as vulcanism or solar radiation. 7. That many emissions cannot reasonably be attributed to any individual. (For example, should emissions from commuting be attributed to commuters or consumers of what they produce?) 8. That market forces or political action will correct human activity in sufficient time. 9. That population growth invalidates the calculations. 10. That one cannot limit everyone to equal emissions. (For example, those in urbanized societies may be unable to avoid some emissions, while lessdeveloped countries may not have the technology to mitigate others.) In spite of the criticisms described above, the topic of global warming and the measurement of the carbon footprints of both individuals and organizations have come to the forefront of discussion throughout the world. Therefore, NADCA has embarked upon this project to define the carbon footprint of die cast automotive components in both aluminum and magnesium compared to the carbon footprint of the same component produced by plastic injection molding. Page 6 Extra-CarbonFootprint.indb 10 7/10/2008 3:00:39 PM

11 4. Life Cycle Assessment Goal and Scope The goal of Life Cycle Assessment (LCA) is to compare the full range of environmental damages assignable to products and services and to be able to choose the least burdensome one2. The term life cycle refers to the idea that a fair assessment requires consideration of raw material production, manufacture, distribution, use and disposal, including all intervening transportation steps necessary or caused by the product. The sum of all those steps is the life cycle of the product. For the purposes of developing a carbon footprint, the assessment is made in terms of equivalent CO2 emissions. There are four phases to a LCA study. These are: Goal & Scope, Life Cycle Inventory, Life Cycle Impact Assessment and Interpretation. These four phases are presented in this and the next three chapters. The first phase of LCA specifies the goal and scope of the study in terms of a functional unit. For example, if a study were comparing glass versus plastic bottles, the functional unit might be 1 liter bottle container for refrigerated juices. Comparing 1 kilogram of plastic bottles with 1 kilogram of glass bottles would not be an appropriate functional unit. The purpose of this LCA study is to compare the cradle-to-grave carbon footprint of an aluminum, magnesium and injection molded component. The functional unit is an automotive cam cover used in a four-cylinder engine, similar to that shown in Figure 1. Figure 1 Typical Cam Cover Component Extra-CarbonFootprint.indb 11 Page 7 7/10/2008 3:00:40 PM

12 Life Cycle Assessment Goal and Scope A specific automotive design, already designed for both 380 alloy aluminum and nylon 66 GF35, was utilized to determine the appropriate part volume. The 380 alloy aluminum cover has a part volume of cubic meters and the nylon 66 GF35 (35% glass fiber reinforced) cover has a part volume of cubic meters, a 20% increase over the aluminum, presumably to provide structural rigidity. For the purposes of this study, the part volume for an AZ91D magnesium version of the cover is assumed to have 10% more volume than the aluminum part, or cubic meters, also to provide the required structural rigidity. The volume of this part is fairly large, but would be similar to the combined volume of the two-valve covers required for a typical V6 or V8 engine. The resulting mass of each component is shown in Table 1. Table 1 Volume and Mass of Functional Unit Aluminum (380 alloy) Magnesium (AZ91D) Nylon 66 GF35 Part Volume (cm 3 ) Density (gm/cm 3 ) Part Mass (kg) In its simplest form, the life cycle of a product has four stages: material production, product manufacture, product use and product disposal. The diagram in Figure 2 shows this generic product system for the functional unit described above. The four stages are shown in the dotted boxes. Material production involves creation or preparation of raw materials for the product and their transport to the manufacturing site. Product manufacture includes the production of the functional unit (in this case, the automotive cam cover), transportation of the part to the site of final product assembly, machining of the product and its assembly into the final product, and transportation of the final product to the customer. Product use includes the use of the product (in this case, the operation of the vehicle by the consumer), as well as transportation of the product at the end of its life to recovery facilities. Product disposal includes disassembly of the vehicle to recover useful materials, the recycling of those materials and transportation to a landfill for disposal, back to the material production site for recycling, or to another site for reuse of the material in some other way. The actual flow of the product from cradleto-grave is different for each material. These actual material flows for die cast aluminum and magnesium cam covers and for injection molded cam covers are presented in the next chapter on Life Cycle Inventory. Page 8 Extra-CarbonFootprint.indb 12 7/10/2008 3:00:40 PM

13 Life Cycle Assessment Goal and Scope Figure 2 Generic Product System for Automotive Engine Cover An important aspect of LCA studies is to provide a clear understanding of the assumptions made about the product and process at each stage of the life of the product. Changes in these assumptions may often drastically affect the results of the study. These assumptions also provide opportunities for identifying technological or management initiatives that can improve the carbon footprint of a particular alternative. The following assumptions were utilized for the purposes of this study. 1. Material Assumptions The aluminum die casting is produced from secondary 380 alloy, delivered to the production plant in the form of ingots. Both the smelter and the die casting operation have 5% melt loss from alloy melting. The magnesium die casting is produced from primary AZ91D alloy, delivered to the production plant in the form of ingots. The magnesium part volume is 10% more than the aluminum part for rigidity. There is 5% melt loss at the smelter. Both the smelter and the die caster utilize SF 6 as a cover gas. The nylon 66 GF35 injection molded part is produced from pellet material delivered to the plant in tote bins. The injection molded part volume is 20% more than the aluminum part to permit necessary rigidity. 2. Recycling of Plant Scrap and Machining Fines The aluminum die casting yield is 50%, and biscuits, runners and scrap castings are remelted on-site. There is 10% material removed during machining, which is returned to the secondary smelter for recycling. The magnesium die casting yield is 50%, and biscuits, runners and scrap castings are transported off-site to produce secondary alloy for other uses. There is 10% material removed during machining, which is also utilized to produce secondary alloy for other uses. The nylon injection molding yield is 50%, and sprue, runners and scrap components are transported off-site and ground for reuse in other products. There is 10% material removed during machining, which is also transported and ground for reuse in other products. Page 9 Extra-CarbonFootprint.indb 13 7/10/2008 3:00:42 PM

14 Life Cycle Assessment Goal and Scope 3. Product Use The useful life of the end product, an automobile, is considered to be 200,000 kilometers at a gasoline fuel usage of 8.5 kilometers per liter (20 MPG). 4. End-of-Life Recycling At the end of the life of the vehicle, the aluminum is recovered and recycled into new 380 alloy secondary ingots. Magnesium recovered at the end of product life is utilized to produce secondary alloy for other uses. Nylon 66 GF35 recovered from end-of-life recovery becomes part of the fluff from recovery operations and is disposed of in a landfill. Page 10 Extra-CarbonFootprint.indb 14 7/10/2008 3:00:42 PM

15 5. Life Cycle Inventory The second phase of LCA is building a model of the product system, including inputs and outputs for all processes that compose the product system. Since this study is interested in the carbon footprint of the product, the material and energy inputs and outputs are of primary interest. Once these are established, the carbon footprint can be estimated. Die Cast Aluminum The model of the process flow for a die cast aluminum cam cover is shown in Figure 3. It reflects the assumptions discussed previously and shows the various stages of material and product production and processing. Figure 3 Die Cast Aluminum Engine Cover Process Flow Chart Page 11 Extra-CarbonFootprint.indb 15 7/10/2008 3:00:46 PM

16 Life Cycle Inventory The flow chart describes the flow of raw material through the manufacturing process, followed by the use of the component in the vehicle and the end-of-life recovery of the component for recycling. Since the energy inputs to the process depend on the mass of the alloy, it is important that the amount of alloy involved in each process step be identified. These are indicated on the process flow chart. The aluminum component has a finished mass of 2.61 kg, as indicated in Table 1. This means that the die cast component has a mass of 2.90 kg, with 0.29 kg being removed during machining. The machining fines are transported to the secondary smelter. The die cast process has a 50% yield, which means that 5.80 kg of alloy must be provided to the die casting machine. The remelt of 2.90 kg is returned to the melting furnace in the die casting plant for remelting. This melting operation has a 5% melt loss, so 3.21 kg of ingots are needed from the secondary smelter in addition to the 2.90 kg of remelt alloy to produce the 5.80 kg of alloy for the die casting machine. The secondary smelting operation also has a 5% melt loss and requires 0.48 kg of secondary scrap in addition to the 2.61 kg of alloy from end-of-life recovery and the 0.29 kg of alloy returned from machining operations. Die casting and injection molding require the use of steel dies or molds. In order to account for the energy required for the production of these tools, and their contribution to the carbon footprint of each process, a loop is shown attached to the die casting operation. To determine the carbon footprint of the aluminum die cast cam cover, the energy inputs and outputs for each step of the process flow are assessed in the next section. Die Cast Magnesium A similar process flow chart is shown in Figure 4 for a die cast magnesium cam cover. Since the magnesium alloy specified for this component is primary AZ91D alloy, it cannot be truly recycled (meaning reused to produce the same component) but must be sent to a secondary smelter to produce alloy which is used in alloying aluminum, the desulphurization of steel and producing secondary magnesium alloys. Page 12 Extra-CarbonFootprint.indb 16 7/10/2008 3:00:46 PM

17 Life Cycle Inventory Figure 4 Die Cast Magnesium Engine Cover Process Flow Chart The mass of the finished magnesium cam cover is 1.89 kg, as shown on the process flow chart. To produce this finished part, the die casting must have a mass of 2.10 kg, and 4.2 kg of material must be supplied by the primary magnesium producer. The secondary smelter receives 2.10 kg from the die casting remelt, 0.21 kg from the machining operation and 1.89 kg at the end of the component life. Since molten magnesium is very reactive with oxygen in the atmosphere, a cover gas is used by both the primary alloy producer and the die casting plant. Typically, the cover gas used is sulfur hexafluoride (SF6). The die casting operation requires a steel die, and its production is included with a die production loop in the flow chart. In the next section, the energy required for each step and the resulting carbon footprint for the magnesium die cast component are calculated. Injection Molded Nylon 66 GF35 The process flow chart for the injection molded nylon 66 GF35 cam cover is shown in Figure 5. This nylon material has glass fibers added to increase impact strength and rigidity. While necessary to provide the needed component strength, the glass fibers will degrade when reused, so this material is typically not recycled, but reused for less demanding applications. Extra-CarbonFootprint.indb 17 Page 13 7/10/2008 3:00:50 PM

18 Life Cycle Inventory Figure 5 Injection Molded Plastic Engine Cover Process Flow Chart The mass of the finished nylon cam cover is 1.58 kg as shown on the process flow chart. To produce this finished part, the injection molded part must have a mass of 1.76 kg, and 3.52 kg of material is required from the material supplier since 50% of the material is required for sprues, runners and scrap components. This results in 1.94 kg of material being reused for other applications. (This is usually referred to as reuse rather than recycling.) At the end of the component s functional life, these components are mixed with other non-metallic materials and placed in a landfill. Plastic components are not normally recycled because the various plastic materials must be separated, and the cost to accomplish this is excessive. Injection molding also requires a steel die, and its production is included with a die production loop in the flow chart. The energy required for each step in the process flow, and the resulting carbon footprint for the injection molded component is calculated in the next chapter. Page 14 Extra-CarbonFootprint.indb 18 7/10/2008 3:00:55 PM

19 6. Life Cycle Impact Assessment The third phase of LCA, Life Cycle Impact Assessment, is aimed at evaluating the contribution of each step of the Life Cycle Inventory to the carbon footprint of the process. The process flow diagram is divided into the four phases of product life, as described in the Introduction and shown in Figure 6. The phases of the life of the product are material production, product manufacture, product use and product disposal. Figure 6 The material life cycle. Transport is involved between the stages3. Most products have a dominant phase of life, a phase which contributes the most toward the life cycle carbon footprint of the product. One example of this dominant life cycle phase would be a multiple-story parking garage. The majority of its carbon footprint comes from the material production phase, in which the concrete and steel needed for the structure are produced. Once the raw materials are produced, there is little additional contribution to the carbon footprint during construction of the garage, its use by the public over its life or the ultimate demolition of the structure. On the other hand, a family automobile has most of its carbon footprint occur during the use of the vehicle over its lifetime. In fact, more than 80% of the carbon emissions are the result of the use of the product. Extra-CarbonFootprint.indb 19 Page 15 7/10/2008 3:00:56 PM

20 Life Cycle Impact Assessment In order to determine the carbon footprint of each of the three components that are the subject of this study, aluminum and magnesium die cast cam covers and an injection molded nylon cam cover, the process flow diagrams for each component were placed into spreadsheets so that the energy used and the resulting carbon footprint could be determined. These spreadsheets and the resulting carbon footprint for each component are reviewed in the remainder of this section. It should be remembered, however, that the assumptions for the study that were described earlier have a great impact upon the results of the study. Conclusions and recommendations concerning the study are presented in the last section. Die Cast Aluminum The Aluminum Die Cast Cam Cover calculation is shown in Table 2. Each process step from the flow chart is listed in the left column and described more fully in the second column. The third column indicates where the mass of the component is changed due to melt loss during melting or holding of alloy, machining of the component or the loss of biscuits and runners or scrap parts in the die casting process. The finished component weight is entered above the Comments heading, and the remaining mass figures are calculated based upon the data in the Material Loss column. These mass amounts are important because the factors for energy used and carbon footprint relate to the mass of alloy involved. The next few columns relate to the energy used during each step of the flow chart. Using reference documents relating to each step, the energy used is calculated in both megajoules (MJ) and British thermal units (Btu) 3-7. In a similar manner, the references are used to estimate the equivalent carbon dioxide (CO 2 ) generated by each step of the process by multiplying the CO 2 factor by the mass of the alloy. Review of the spreadsheet shows that Material Production for the aluminum die cast cam cover results in MJ of energy use and generates 1.88 kg of CO 2 equivalent emissions. The Product Manufacture phase of the life cycle uses MJ of energy and generates 8.09 kg of CO 2 equivalent emissions. The Product Use phase, in which the vehicle is driven 200,000 km at 8.5 km/liter (20 MPG) consumes MJ of energy and generates kg of CO 2 equivalent emissions. This calculation assumes that the 2.61 kg component is responsible for its proportionate share of the entire vehicle, which is assumed to weigh 1,360 kg. The Product Disposal phase of the life cycle, consisting of recovering the aluminum and transporting it to the secondary smelter 100 miles away, consumes 1.37 MJ of energy and generates an additional 0.09 kg of CO 2 equivalent emissions. As was discussed earlier concerning automobiles, the product use phase of life is quite dominant in the carbon footprint of the aluminum die cast cam cover. More than 85% of the CO 2 equivalent emissions are generated throughout the usable life of the product. The Material Production phase is responsible for 1.4% of the carbon footprint; the Product Manufacture phase, where the actual die casting takes place, generates about 6% of the carbon footprint during the life of the product. Page 16 Extra-CarbonFootprint.indb 20 7/10/2008 3:00:57 PM

21 Life Cycle Impact Assessment Table 2 Aluminum Die Cast Cam Cover Component Weight (kg) = 2.61 Energy Used Carbon Emissions Energy Used Material Loss Mass Usage Factor Process Step Comments or Yield (%) (kg) (MJ/kg) (MJ) (Btu) Material Production: Secondary Alloy Production Transport CO 2 Factor (kgco 2 eq/kg) CO 2 Equivalent (kg) Production of secondary 380 alloy from recycled scrap , Transport alloy ingots to die casting plant (160 km or 100 miles) Total , Product Manufacture: Reverb melting furnace for ingots Melting Furnace and remelt of plant scrap , Holding Furnace Electric holding furnace at the die casting machine , Die Casting Steel and Die Making Loop Transport Machining & Vehicle Assembly Transport machining fines 1,000-ton cold chamber die casting cell including lubricator, extractor and trim (30 second cycle) , Die making, transport of die, steel recovery, transport of scrap steel, die steel production and transport of steel to die maker divided by average die life of 200,000 parts , Transport rough casting to machining and assembly plant (160 km or 100 miles) Part is machined and assembled into vehicle Transport machining fines to secondary smelter for recycling (160 km or 100 miles) Transport finished vehicle to retail outlet kg (3000 lbs) transported for 800 km (500 miles) Transport vehicle Total , Product Use: Use in Vehicle 200,000 km of use at an average of 8.50 km/liter (20 MPG) of gasoline ,480, Transport Transport component to vehicle disposal center at end of life (160 km or 100 miles) Total ,481, Product Disposal: End of Life Recovery Transport Material recovery operations prior to recycling or disposal , Transport recovered aluminum back to secondary smelter (160 km or 100 miles) Total Grand Total ,599, Page 17 Extra-CarbonFootprint.indb 21 7/10/2008 3:00:57 PM

22 Life Cycle Impact Assessment Die Cast Magnesium The Magnesium Die Cast Cam Cover calculation is shown in Table 3. Each process step from the flow chart is listed in the left column and described more fully in the second column. The third column indicates where the mass of the component is changed due to melt loss during melting or holding of the alloy, machining of the component or the loss of biscuits and runners or scrap parts in the die casting process. The finished component weight is entered above the Comments heading, and the remaining mass figures are calculated based upon the data in the Material Loss column. These mass amounts are important because the factors for energy used and carbon footprint relate to the mass of alloy involved. Similar to the aluminum die cast component spreadsheet, the next few columns relate to the energy used during each step of the flow chart. Using reference documents relating to each step, the energy used is calculated in both megajoules (MJ) and British thermal units (Btu) 3,6,7. In a similar manner, the references are used to estimate the equivalent carbon dioxide (CO 2 ) generated by each step of the process by multiplying the CO 2 factor by the mass of the alloy. Review of the spreadsheet shows that Material Production for the magnesium die cast cam cover results in MJ of energy use and generates kg of CO 2 equivalent emissions. This is significantly higher than the aluminum die cast cam cover because the magnesium component is produced using primary alloy, which requires much greater energy usage than the production of the secondary aluminum. In addition to the increased energy usage, both the primary magnesium producer and the die caster utilize sulfur hexafluoride (SF 6 ) as a cover gas to prevent oxidation of the molten magnesium alloy. This gas is one of the worst for global warming potential (GWP). It has a GWP factor of 22,800 over a period of 100 years, which means that it is much worse than an equivalent amount of CO 2. This results in a high amount of CO 2 equivalent emissions. The Product Manufacture phase of the life cycle uses MJ of energy and generates kg of CO 2 equivalent emissions. Again, the high level of emission is the result of the use of SF 6 as a cover gas. The energy required and emissions from the die making loop are less than for the aluminum die cast component because the die life for magnesium is 350,000 parts compared to only 200,000 parts for aluminum. The Product Use phase, in which the vehicle is driven 200,000 km at 8.5 km/liter (20 MPG), consumes MJ of energy and generates kg of CO 2 equivalent emissions. This is lower than for the aluminum component because the magnesium part weighs only 1.89 kg compared with the 2.61 kg aluminum part. This calculation assumes that the 1.89 kg magnesium component is responsible for its proportionate share of the entire vehicle, which is assumed to weigh 1360 kg. Page 18 Extra-CarbonFootprint.indb 22 7/10/2008 3:00:58 PM

23 Life Cycle Impact Assessment Table 3 Magnesium Die Cast Cam Cover Component Weight (kg) = 1.89 Energy Used Carbon Emissions Energy Used Material Loss Mass Usage Factor Process Step Comments or Yield (%) (kg) (MJ/kg) (MJ) (Btu) Material Production: Primary Alloy Production Transport CO 2 Factor (kgco 2 eq/kg) CO 2 Equivalent (kg) Production of primary AZ91D alloy from ore using hydroelectric power and SF 6 cover gas , Transport alloy ingots to die casting plant (160 km or 100 miles) Total , Product Manufacture: Melting/Holding Furnace Die Casting Preheat and melt ingots using electricity for preheating and natural gas for melting with SF 6 cover gas , ,000-ton cold chamber die casting cell including lubricator, extractor and trim (20-second cycle) , Steel and Die Making Loop Die making, transport of die, steel recovery, transport of scrap steel, die steel production and transport of steel to die maker divided by average die life of 350,000 parts , Transport Machining & Vehicle Assembly Transport machining fines Transport rough casting to machining and assembly plant (160 km or 100 miles) Part is machined and assembled into vehicle Transport machining fines to secondary smelter for recycling (160 km or 100 miles) Transport vehicle Transport finished vehicle to retail outlet kg (3000 lbs) transported for 800 km (500 miles) Total , Product Use: Use in Vehicle 200,000 km of use at an average of 8.50 km/liter (20 MPG) of gasoline ,072, Transport Transport component to vehicle disposal center at end of life (160 km or 100 miles) Total ,072, Product Disposal: End of Life Recovery Transport Material recovery operations prior to recycling or disposal Transport recovered magnesium to secondary smelter (160 km or 100 miles) Secondary Alloy Production Produce secondary alloy for other uses , Total Grand Total 1, ,729, Page 19 Extra-CarbonFootprint.indb 23 7/10/2008 3:00:58 PM

24 Life Cycle Impact Assessment The Product Disposal phase of the life cycle, consisting of recovering the magnesium and transporting it to the secondary smelter 100 miles away, consumes MJ of energy and generates and additional kg of CO 2 equivalent emissions. This is also higher than for the aluminum component because the magnesium must be shipped to the smelter and processed to produce secondary magnesium alloy suitable for alternate uses. Unlike the aluminum die cast cam cover carbon footprint, the product use phase of life is not as dominant in the carbon footprint of the magnesium die cast cam cover. Only 33% of the CO 2 equivalent emissions are generated by product use throughout the life of the product. The Material Production phase is also responsible for 32% of the carbon footprint, and the Product Manufacture phase, where the actual die casting takes place, generates another 32% of the carbon footprint generated during the life of the product, because of the need for primary magnesium alloy and the use of SF 6 as a cover gas. Injection Molded Nylon 66 GF35 The Injection Molded Cam Cover calculation is shown in Table 4. Similar to the other spreadsheets, each process step from the flow chart is listed in the left column and described more fully in the second column. The third column indicates where the mass of the component is changed due to machining of the component, or the generation of sprues and runners or scrap parts in the injection molding process. The finished component weight is entered above the Comments heading, and the remaining mass figures are calculated based upon the data in the Material Loss column. These mass amounts are important because the factors for energy used and carbon footprint relate to the mass of material involved. The next few columns relate to the energy used during each step of the process. Using reference documents relating to each step, the energy used is calculated in both megajoules (MJ) and British thermal units (Btu) 5,6,8. In a similar manner, the references are used to estimate the equivalent carbon dioxide (CO 2 ) generated by each step of the process by multiplying the CO 2 factor by the mass of the material. Looking at the spreadsheet, it can be seen that Material Production for the injection molded cam cover results in MJ of energy use and generates kg of CO 2 equivalent emissions. Since the nylon 66 GF35 material cannot be recycled, new material is required for each cycle of the injection molding machine. Also, nylon is produced from petroleum by a petrochemical process that requires high inputs of energy and water, and which produces harmful air emissions of hazardous air pollutants and volatile organic compounds (VOCs) that contribute to smog. The Product Manufacture phase of the life cycle uses MJ of energy and generates 5.66 kg of CO 2 equivalent emissions. Page 20 Extra-CarbonFootprint.indb 24 7/10/2008 3:00:59 PM

25 Life Cycle Impact Assessment Table 4 Plastic Injection Molded Cam Cover Component Weight (kg) = 1.58 Energy Used Carbon Emissions Energy Used Material Loss Mass Usage Factor Process Step Comments or Yield (%) (kg) (MJ/kg) (MJ) (Btu) Material Production: Polymer Production Transport Compounder Transport Product Manufacture: Injection Molding Steel and Mold Making Loop CO 2 Factor (kgco 2 eq/kg) CO 2 Equivalent (kg) Transform raw materials into bulk polymer , Transport bulk polymer to the compounder (160 km or 100 miles) Polymer mixed with additives to produce Nylon 66 GF , Transport nylon material in totes to the production facility (160 km or 100 miles) Total , Molding on 1,000-ton hydraulic screw injection molding machine , Mold making, transport of mold, steel recovery, transport of scrap steel, mold steel production and transport of steel to mold maker Transport Transport rough parts to machining and assembly plant (160 km or 100 miles) Transport sprue, runners and scrap Machining & Vehicle Assembly Transport machining fines Transport sprue, runners and scrap parts to recycler for other uses (160 km or 100 miles) Part is machined and assembled into vehicle Transport machining fines to recycler for other uses (160 km or 100 miles) Transport vehicle Transport finished vehicle to retail outlet Total , Product Use: Use in Vehicle Transport Product Disposal: 200,000 km of use at an average of 8.50 km/liter (20 MPG) of gasoline , Transport component to vehicle disposal center at end of life (160 km or 100 miles) Total , Recycle sprue, runners, scrap and machining fines Grind material for use in other products Transport recycled material End of Life Recovery Transport recycled material for other uses (160 km or 100 miles) Material recovery operations prior to recycling or disposal Transport Transport material recovered as "fluff" for disposal (160 km or 100 miles) Landfill Dispose of material in landfill Total , Grand Total 1, ,283, Page 21 Extra-CarbonFootprint.indb 25 7/10/2008 3:00:59 PM

26 Life Cycle Impact Assessment The Product Use phase, in which the vehicle is driven 200,000 km at 8.5 km/liter (20 MPG), consumes MJ of energy and generates kg of CO 2 equivalent emissions. This is lower than for both the aluminum and magnesium components because the nylon part weighs only 1.58 kg compared with the 2.61 kg aluminum part and the 1.89 kg magnesium part. This calculation assumes that the 1.58 kg nylon component is responsible for its proportionate share of the entire vehicle, which is assumed to weigh 1,360 kg. The Product Disposal phase of the life cycle consumes 1.55 MJ of energy and generates an additional 0.09 kg of CO 2 equivalent emissions. Plastic material is recovered when metals are recovered from scrap automobiles. This material is mixed with other nonmetallics and separation is not usually cost effective, so the non-metallics, including the plastics, are normally placed in a landfill. As was discussed earlier concerning automobiles, the product use phase of life is quite dominant in the carbon footprint of the injection molded cam cover. More than 75% of the CO 2 equivalent emissions are generated throughout the usable life of the product. The Material Production phase, during which the nylon is produced, is responsible for 19% of the carbon footprint. The Product Manufacture phase, where the actual injection molding takes place, generates only about 5% of the carbon footprint generated during the life of the product. Summary The carbon footprint for each product is summarized in Table 5. The total carbon footprint for the aluminum die cast cam cover, in terms of CO 2 equivalent, is kg. The magnesium die cast cam cover has a carbon footprint of kg of CO 2 equivalent. The injection molded nylon cam cover has a carbon footprint of kg of CO 2 equivalent. The injection molded component is somewhat favored in the analysis because of the carbon footprint allocated during the Product Use phase of the product s life. The magnesium component is adversely affected in both the Material Production phase and the Product Manufacturing phase because of the use of SF 6 as a cover gas. In the next chapter, some interpretation, conclusions and recommendations are provided based upon this study. Process and Material Table 5 Life Cycle Impact Assessment Summary Material Production (kg CO 2 Equivalent) Product Manufacture Product Use Product Disposal Total Die Cast Aluminum (2.61 kg) Die Cast Magnesium (1.81 kg) Nylon Injection Molded (1.58 kg) Process and Material Material Production Energy Required (MJ) Product Manufacture Product Use Product Disposal Total Die Cast Aluminum (2.61 kg) , , Die Cast Magnesium (1.81 kg) , , Nylon Injection Molded (1.58 kg) , Page 22 Extra-CarbonFootprint.indb 26 7/10/2008 3:01:00 PM

27 7. Life Cycle Assessment Interpretation The last phase of LCA is Interpretation. It is most important and involves an analysis of major contributions, sensitivity analysis and drawing conclusions from the analysis. It is this phase that answers the question, What can be learned from the LCA? Several issues that should be considered concerning the data derived from the study are presented below. Understanding these issues provides additional information which may affect the initiatives that should be taken as a result of the study. 1. The most obvious issue is the use of SF 6 as a cover gas in magnesium die casting. While necessary to minimize oxidation of the alloy, it adversely affects the carbon footprint of the entire process. Alternate gases include hydrofluorocarbon-134a (HFC-134a) or carbon dioxide (CO 2 ). HFC-134a has a global warming potential (GWP) of 1430, compared to SF 6 which has a GWP of 22,800. The GWP of CO 2 is 1. Even if more of either of these gases was required and lost to the atmosphere, the environmental impact would still be much less. If HFC-134a were substituted for SF 6 at the same usage, the total carbon footprint for the magnesium die cast cam cover would be reduced to kg of equivalent CO The allocation of carbon footprint during the use of the product based upon the mass of the component as a percentage of the total vehicle carbon footprint is questionable. It is common practice for such studies, but this allocation may not be appropriate when trying to analyze one component versus another. The number of passengers in the vehicle or even a bag of groceries in the vehicle affects the total mass of the vehicle more than the difference in mass provided by the alternatives of this study. It is probably better to examine the other three phases of life when studying alternative component processes. The carbon footprint of the product use phase is more appropriately used when comparing various alternatives of the final product design. 3. The disposal of the nylon component in a landfill at the end of its life has zero contribution to the carbon footprint of the component. Most plastic materials are very stable and do not degrade, but the social and political consequences of large volumes of plastic being placed in landfills are becoming a concern. There is currently a significant discussion in several parts of the world relative to plastic beverage containers. Alternate uses for recycled plastic are being developed, but the uses developed so far utilize a very small amount compared to the volume of material entering the scrap stream. An alternative to placing plastic in landfills is incineration or waste-to-energy projects. The incineration of plastics generates significant amounts of greenhouse gases and may even approach the CO 2 equivalent emissions caused by the original material production. If the environmental consequence of incineration is added to the results of this study, the carbon footprint of plastic injection molding material production, product manufacture and product disposal become higher than that for the die cast aluminum component. Page 23 Extra-CarbonFootprint.indb 27 7/10/2008 3:01:00 PM

28 Life Cycle Assessment Interpretation 4. The current study assumed the use of nylon 66 SF35 material. There are several other plastic materials that could be used for automotive components. Each of these materials would have different carbon footprints. Depending on the material used, the energy required and the resulting carbon footprint could vary widely. Reference material 8 indicates that the usage factor for product manufacture for other materials could range from less than half of that shown in the study for nylon material to as much as five times more. This variation indicates that the carbon footprint from injection molding of many plastic materials is likely to be equal to or greater than that shown for die cast aluminum components. 5. An opportunity for reduction of carbon footprint in both aluminum and magnesium die casting is in improving the efficiency of metal melting and holding systems. Reference data from the U.S. Department of Energy 4 indicates that die casting facilities operate at about 23% overall energy efficiency. Significant opportunities exist to improve the efficiency of metal melting and holding systems. The selection of melting and holding equipment, and the operating procedures employed, can significantly impact the energy used by the plant and the resulting carbon footprint. In addition, ongoing research sponsored by both NADCA and the U.S. Department of Energy should be monitored to ensure timely implementation by the die casting industry of these improved systems. 6. If the yield of the various manufacturing processes could be improved, another significant reduction in the carbon footprint would occur. If the yield was improved to 60% by more efficient runner design or decreased scrap, the carbon footprint for components produced by aluminum die casting is reduced by about 1 kg of equivalent CO 2, or over 10% of the product manufacture phase carbon footprint. Similar reductions could be expected for both magnesium die casting and for plastic injection molded components. Several computer programs are now available to examine the carbon footprint of alternative manufactured components. These programs will provide a more complete analysis of the contributions to the carbon footprint of components. They also provide the ability to ask what if questions and perform sensitivity analysis of alternatives. While this study was completed with the best information that could be found, it is still fairly simplistic. If NADCA were able to gain access to one or more of these computer tools, the study could be expanded and validated. However, it remains important to clearly understand the assumptions made by these programs. Page 24 Extra-CarbonFootprint.indb 28 7/10/2008 3:01:01 PM

29 8. Conclusions and Recommendations This study of the carbon footprint of automotive components produced by different materials and processes has provided interesting results. These results should be of interest to the die casting industry because carbon footprint, for the most part, correlates directly to energy use. Of course, energy use also correlates directly to manufacturing cost. The only exception to this found in the study is the enormous carbon footprint contribution in magnesium die casting that results from the use of SF 6 as a cover gas. While still contributing to the manufacturing cost, the gas does not have such a dramatic affect on cost as it does on the carbon footprint. With this exception, the following conclusions and recommendations to the die casting industry for reducing the carbon footprint of its products are also relevant toward cost reduction. Conclusions The following conclusions can be drawn from the results of the study and consideration of the issues presented in the Interpretation section. The greatest contributor to carbon footprint identified in the study is the use of SF 6 as a cover gas during the production of the magnesium die cast cam cover. Neglecting the contribution of Product Use to the total carbon footprint, aluminum die casting has the lowest carbon footprint because of its use of secondary aluminum alloys and its ability to be recycled. The production of the nylon material in the study contributed much more to the carbon footprint than material production for aluminum. If the use of SF 6 were discontinued, magnesium production, even for primary alloys, would also be favorable compared to the production of nylon. The Product Manufacture phase of component life was essentially equal for all three components, except for the use of SF 6 for the magnesium cam cover. Disposal of plastic is a growing problem. If resistance to landfilling scrap plastic grows, the recycling or incineration of scrap plastic will significantly increase the carbon footprint of these components. Corresponding to this, additional energy and cost will be required to meet more stringent environmental requirements. The use of secondary magnesium alloys for automotive components would significantly reduce the carbon footprint of these components. Page 25 Extra-CarbonFootprint.indb 29 7/10/2008 3:01:01 PM

30 Chapter Title Recommendations The following recommendations are provided for the die casting industry which will improve the carbon footprint of its products and help grow the market for die cast components. 1. The use of SF 6 as a cover gas for magnesium should be eliminated. 2. The ability to recycle aluminum die castings and their resulting low carbon footprint should be marketed heavily by the industry. 3. Industry initiatives which reduce energy consumption and increase energy efficiency should be strongly encouraged, and their contribution to reducing the carbon footprint of the components should be stressed. 4. The die casting industry should initiate and support the development of material property data to encourage the use of secondary magnesium alloys. Currently, primary magnesium alloys are specified for many components due to a lack of confidence in the material properties of recycled alloy. 5. Additional carbon footprint studies should be considered by NADCA utilizing software programs that are being developed. These programs will provide a more complete analysis of the contributions to the carbon footprint for components. They also provide the ability to ask what if questions and perform sensitivity analysis of alternatives. If NADCA were able to gain access to one or more of these computer tools, this study could be expanded and validated. Page 26 Extra-CarbonFootprint.indb 30 7/10/2008 3:01:01 PM

31 References 1., Wikipedia, the free encyclopedia, 2. Life Cycle Assessment, Wikipedia, the free encyclopedia, 3. The CES EduPack Eco Audit Tool A White Paper, M. Ashby, N. Ball, and C. Bream, Granta Design, Cambridge, UK, U.S. Energy Requirements for Aluminum Production: Historical Perspective, Theoretical Limits and New Opportunities, W. Choat, BCS Incorporated, and J. Green, Aluminum Consultant, February, Life Cycle Analysis of Conventional Manufacturing Techniques: Die Casting, S. Dalquist and T. Gutowski, MIT, Cambridge, MA, USA, December, Aluminum Helps Cut Emissions at the Point of Consumption, S. Weller, European Aluminum Association, Lifecycle Assessment of Magnesium Component Supply Chain, A. Tharumarajah and P. Koltun, CSIRO Manufacturing & Infrastructure Technology, Australia. 8. An Environmental Analysis of Injection Molding, A. Thiriez and T. Gutowski, MIT, Cambridge, MA, USA Page 27 Extra-CarbonFootprint.indb 31 7/10/2008 3:01:02 PM

32 Page 28 Extra-CarbonFootprint.indb 32 7/10/2008 3:01:02 PM

33 Notes Page 29 Extra-CarbonFootprint.indb 33 7/10/2008 3:01:02 PM

34 Notes Page 30 Extra-CarbonFootprint.indb 34 7/10/2008 3:01:02 PM

35 Extra-CarbonFootprint.indb 35 7/10/2008 3:01:03 PM

36 North American Die Casting Association 241 Holbrook Dr. Wheeling, IL tel: fax: Extra-CarbonFootprint.indb 36 7/10/2008 3:01:15 PM