LIFE CYCLE ANALYSIS OF CONVENTIONAL MANUFACTURING TECHNIQUES: DIE CASTING

This summary is based on the working paper "LIFE CYCLE ANALYSIS OF CONVENTIONAL MANUFACTURING TECHNIQUES: DIE CASTING" from the Massachusetts Institute of Technology.

1. Overview:

• Title: LIFE CYCLE ANALYSIS OF CONVENTIONAL MANUFACTURING TECHNIQUES: DIE CASTING
• Author: Stephanie Dalquist, Timothy Gutowski
• Year of publication: 2004 (12 December)
• Journal/academic society of publication: Massachusetts Institute of Technology (Working Draft LMP-MIT-TGG-03-12-09-2004)
• Keywords: die casting, life cycle analysis, environmental impact, aluminum high-pressure die casting, energy analysis, metal preparation, die preparation, secondary aluminum, material byproducts, VOC emissions.

2. Abstract:

A system-level environmental analysis of die casting based on aggregate national data and representative machine characteristics could be applied to design and manufacturing decisions where environmental impact is accounted for. By examining the life cycle of a process, it is possible to consider the environmental impact of the metal forming process as well as the impact of associated processes such as metal preparation and die preparation. The emphasis on aluminum high-pressure die casting reflects the current state of the industry and its environmental footprint. An energy analysis exposes the clear and significant environmental benefits of the use of secondary aluminum. Analysis of material byproducts gives less straightforward solutions, where improvement on one field comes at the cost of another.

3. Introduction:

Die casting is a manufacturing process used to produce a part in near-net shape with high dimensional accuracy and a good surface finish in a short cycle time. Molten metal, most commonly aluminum, is forced into the cavity of a reusable steel mold (the die) under high pressure. The metal is driven through the feed system while air escapes through vents. There must be enough metal to overflow the cavity, such that a complete part will be cast. Once full, the pressure on the mold is increased during solidification. The die halves are separated and the part released.
Auxiliary functions of the manufacturing process that must be included in the life cycle analysis include mold (die) preparation, metal preparation, and finishing (Figure 1). Die preparation involves the machining of the die and its preparation for each casting. Though a die can be reused for many castings, between castings it must be relubricated to facilitate release. Meanwhile, the charge metal is melted and any oxidized metal is removed to scrap. Once the part is released after casting, some machining and cleaning has to be done to, at least, remove the traces of the feed system and any flashing. A variety of other treatments can be done to meet specifications.
As part of a life cycle inventory of the manufacturing process, the energy and material flows through the foundry must be accounted (Figure 2). Die casting uses significant quantities of energy, as well as materials like oil-based lubricants and cooling water.

4. Summary of the study:

Background of the research topic:

Die casting is a widely used manufacturing process for producing near-net shape metal parts, particularly with aluminum, offering high dimensional accuracy and good surface finish. The process, including essential auxiliary functions like die preparation, metal preparation, and finishing, has a notable environmental footprint due to its consumption of energy and materials. This study focuses on aluminum high-pressure die casting, reflecting its industrial prevalence and associated environmental concerns.

Status of previous research:

The paper indicates that a comprehensive, system-level environmental analysis of die casting, utilizing aggregate national data and representative machine characteristics, is valuable for integrating environmental considerations into design and manufacturing decisions. While specific data points and analyses existed for parts of the process, this study aims to provide a more holistic life cycle perspective.

Purpose of the study:

The primary purpose of this study is to conduct a system-level environmental analysis of the die casting process. By examining the entire life cycle, the research aims to quantify the environmental impact of the core metal forming process and its associated activities, such as metal and die preparation. A key objective is to perform an energy analysis, highlighting the environmental benefits of using secondary aluminum. Additionally, the study analyzes material byproducts to understand complex trade-offs where improvements in one area might negatively affect another.

Core study:

The core of the study is a life cycle analysis centered on aluminum high-pressure die casting. It investigates the environmental impacts, focusing on energy consumption and material byproducts, across the principal stages of the process:

• Die manufacturing and preparation (including lubrication)
• Metal preparation (including melting, use of scrap vs. virgin material, dross formation)
• The casting operation itself (energy use of machines, cooling)
• Finishing processes
• Recycling and waste generation
  The study also examines prevailing industry trends and their potential environmental consequences.

5. Research Methodology

Research Design:

The study employs a life cycle analysis (LCA) framework to conduct a system-level environmental assessment of the die casting process. The objective is to develop a life cycle inventory for the manufacturing process, accounting for energy and material flows.

Data Collection and Analysis Methods:

The analysis is based on "aggregate national data and representative machine characteristics." Data were compiled from various sources, including the US Environmental Protection Agency (EPA), US Census Bureau, Energy Information Administration (EIA), industry-specific reports (e.g., Roberts, 2003a; Bergerson, 2001), and academic literature (e.g., Chapman, 1983). The methodology involves quantifying energy inputs, material consumption (as illustrated in Figure 2), emissions (such as VOCs, HAPs, and greenhouse gases), and byproducts at different stages of the die casting life cycle. This includes an "energy analysis" and an "analysis of material byproducts."

Research Topics and Scope:

The research primarily focuses on "aluminum high-pressure die casting." The scope covers activities within an aluminum foundry performing high-pressure die casting, including die making and finishing, even if these are outsourced. The life cycle stages examined range from raw material considerations (virgin vs. secondary aluminum) through "die preparation," "metal preparation," "casting," "finishing," and "QA/shipping" (as outlined in Figure 1), and also addresses "recycling and waste" management and "industry trends."

6. Key Results:

Key Results:

• The major functions within a die casting foundry (die preparation, metal preparation, casting, finishing) consume approximately 7.9 MJ of energy per kilogram of final product. When accounting for energy losses during generation and distribution, this total energy consumption rises to 14.9 MJ/kg (Table 3).
• Key atmospheric emissions per kilogram of cast final product are estimated to be 850-997 grams of CO2, 3.35 grams of SOx, and 1.8 grams of NOx (Table 3).
• The use of secondary aluminum (scrap) offers significant environmental advantages. The energy required for preparing secondary aluminum for manufacturing is 16 MJ/kg, substantially lower than the 270 MJ/kg needed for virgin aluminum (Chapman, 1983, as cited on p.4).
• Oil-based lubricants used in die preparation and the casting process are identified as major sources of Volatile Organic Compound (VOC) emissions (Figure 3). While water-based lubricants can reduce VOC emissions, they may be associated with increased Hazardous Air Pollutant (HAP) emissions, presenting an environmental trade-off.
• Metal melting is a highly energy-intensive part of metal preparation, with gas-fired reverberatory furnaces being common. An average melting furnace operates at approximately 40% efficiency (p.3).
• The casting machine (typically cold-chamber for aluminum alloys) and its auxiliary systems, such as cooling water circulation, contribute significantly to overall energy consumption. A representative casting machine uses around 2.5 MJ/kg of metal cast, with the cooling system adding another 0.65 MJ/kg (p.4).
• Analysis of material byproducts often reveals complex situations where "improvement on one field comes at the cost of another" (Abstract), exemplified by the trade-offs between different types of lubricants.
• Industry trends suggest a consolidation towards larger foundries, which could improve environmental reporting and encourage investment in newer, more efficient technologies. However, the increase in offshore production poses a challenge, as it may shift environmental burdens to regions with potentially less stringent environmental standards (p.5).

Figure Name List:

• Figure 1. Major functions within the die casting process.
• Figure 2. Profile of major flows at a die casting foundry.
• Figure 3. Top TRI air releases for aluminum die casting SIC show high contribution of VOCs. The top air releases are metal compounds, cleaning fluids (ethylenes) or lubricants (glycol ethers). Source: US EPA, 1998.
• Figure 4. Metal distribution of US die casting in 2003. The total amount of die cast metal was 2.03 million tons. Source: Schifo and Radia, 2004.
• Figure 5. A typical cold-chamber die casting machine and its major elements. Adapted from Heine, 1967.
• Figure 6. A typical hot-chamber die casting machine and its major elements. Adapted from Heine, 1967.
• Figure 7. Output and Employment in the Manufacturing Sector. Source: US Congressional Budget Office, 2004.
• Figure 8. The number of small foundries has been decreasing at a greater rate than the number of large foundries, which have become a greater proportion of the US die casting industry.

7. Conclusion:

Within the foundry, the different major functions of the die casting process consume about 8 MJ of energy per kilogram (Table 3), and also release another kilogram of greenhouse gases from the foundry.
Given the current and rising demand for die cast parts, the environmental burden of the process must be understood in order to make sensible manufacturing choices for the future. The absolute numbers portray the current state of the industry, but are more valuable when considering the process in comparison with other manufacturing options. Analyzing the findings for one component can lead to improvements in the process and in design decision making with respect to environmental factors.

8. References:

• Bergerson, J. 2001. Greenhouse Gas Emissions Inventory of Toronto Area Aluminum Billet Casting/Extrusion Facility. University of Toronto: Toronto, Ontario, Canada.
• Boothroyd, G., Dewhurst, P., and Knight, W. 1994. Product Design for Manufacturing and Assembly. Marcel Dekker: New York, New York.
• Broadbent, K. “Furnace Efficiency: A User’s Guide.” 1991 Joint Conference of the Australian Die Casting Association and the Australasian Institute of Metal Finishing, 21-25 October 1991, Sydney, NSW.
• Chapman, P.F. and Roberts, F. 1983. Metal Resources and Energy. Butterworth and Co., Ltd: Thetford, Norfolk, England.
• Dahmus, J. and Gutowski, T., “An Environmental Analysis of Machining," Proceedings of the 2004 ASME IMECE, November 13-19, 2004, Anaheim, CA.
• Dalquist, S. and Gutowski, T. "Life Cycle Analysis of Conventional Manufacturing Techniques: Sand Casting," Proceedings of the 2004 ASME IMECE, November 13-19, 2004, Anaheim, CA.
• EIA (Energy Information Administration). 2000. The Changing Structure of the Electric Power Industry 2000: An Update. Chapter 3. eia.doe.gov/cneaf/electricity/chg_stru_update/update2000.pdf
• EIA (Energy Information Administration). 1998 Manufacturing Energy Consumption Survey. 2001. www.eia.doe.gov/emeu/mecs/contents.html
• EIA (Energy Information Administration). "Electricity InfoCard 2002,” EIA Home, EIA Brochures. 2002. www.eia.doe.gov/neic/brochure/elecinfocard.html
• Heine, R.W., Loper, C.R., Jr., and Rosenthal, P.C. 1967. Principles of Metal Casting. McGraw-Hill Book Company: New York, New York.
• OIT (Office of Industrial Technologies) Profiles and Partnerships. Aluminum Industry Profile. 2000. www.oit.doe.gov/aluminum/pdfs/aluminum.pdf
• Roberts, M.J. 2003a. A Modified Life Cycle Inventory of Aluminum Die Casting. Deakin University: Geelong, Victoria, Australia.
• Roberts, M., Hu, E. and Nahavandi, S. 2003. “A Life Cycle Inventory of Aluminium Die Casting." MACRO REVIEW Special Issue for The Review of Japan Macro-Engineers Society. Proceedings of the Asia-Pacific Conference on Sustainable Energy and Environmental Technologies, pp. 256-260, Japan Macro-Engineers Society, Japan.
• SCE (Society of Chemical Engineers). Summary of Manuals for Estimating Quantities of Released and Transferred Chemical Substances. March 2001. www.prtr.nite.go.jp/english/pdf/summary1.pdf.
• Schifo, J.F. and Radia, J.T. Theoretical/Best Practice Energy Use in Metalcasting Operations. Prepared under contract to the Advanced Technology Institute for the US DOE Industrial Technologies Program. May 2004. www.eere.energy.gov/industry/ metalcasting/pdfs/doebestpractice_052804.pdf
• Upton, B. 1982. Pressure Diecasting Part 1: Metals – Machines – Furnaces. Pergamon Press: Oxford, England.
• US Census Bureau. Statistics of U.S. Businesses: Aluminum die-casting foundries. 16 December 2003. www.census.gov/epcd/susb/1998/us/US331521.HTM .
• US Congressional Budget Office. Economic and Budget Issue Brief: What Accounts for the Decline in Manufacturing Employment? http://www.cbo.gov/showdoc.cfm?index=5078&sequence=0 18 February 2004.
• US DOE (Department of Energy). Energy and Environmental Profile of the U.S. Metalcasting Industry. September 1999. www.resourcesaver.com/file/sectorstar/program_269.pdf
• US EPA (Environmental Protection Agency). 1996. Pollution Prevention Practices for the Die Casting Industry. North American Die Casting Association: Rosemont, Illinois.
• US EPA (Environmental Protection Agency). EPA Office of Compliance Sector Notebook Project: Profile of the Metal Casting Industry. US EPA Office of Compliance. 1998. www.epa.gov/compliance/resources/publications/assistance/sectors/notebooks/casting.html
• US EPA (Environmental Protection Agency). Economic Impact Analysis of the Final Integrated Iron and Steel NESHAP. US EPA Office of Air Quality Planning and Standards. September 2002. www.epa.gov/ttn/ecas/regdata/IPs/Iintegrated%20Iron%20and%20Steel_IP.pdf
• US GPO (Government Printing Office). 2003. Code of Federal Regulations. 40 C.F.R. 51.100 (s).

9. Copyright:

• This material is a paper by "Stephanie Dalquist, Timothy Gutowski". Based on "LIFE CYCLE ANALYSIS OF CONVENTIONAL MANUFACTURING TECHNIQUES: DIE CASTING".
• Source of the paper: Not applicable (Working Draft LMP-MIT-TGG-03-12-09-2004, Massachusetts Institute of Technology. No DOI provided in the document).

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