Sorting of Automotive Manufacturing Wrought Aluminum Scrap


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Sorting of Automotive Manufacturing Wrought Aluminum Scrap
A Major Qualifying Project Submitted to the Faculty of Worcester Polytechnic Institute in partial fulfillment of the requirements for the Degree in Bachelor of Science in
Mechanical Engineering
By
Shady J. Zummar Ghazaleh
Date: 04/26/2018 Sponsoring Organization: Metal Processing Institute
Approved by:
________________________________________ Professor Diran Apelian
Alcoa-Howmet Professor of Engineering, Advisor Founding Director of Metal Processing Institute

Abstract
An increase of 250% in wrought aluminum usage in automotive manufacturing is expected by 2020. Consequently, the generation of new aluminum sheet scrap will also increase. Producing secondary aluminum only emits 5% of the CO2 compared to primary aluminum – a significant 95% decrease. With the advent of opto-electronic sorting technologies, recovery and reuse of new aluminum scrap (generated during manufacturing) is at hand. A series of interviews with industrial experts and visits to automotive stamping plants were performed in order to identify: (i) the most common wrought aluminum alloys from which scrap is generated; (ii) the present scenario — how scrap is collected today; and (iii) the types of contamination that must be accounted for during and after sortation. Recommendations are made herein that will support the development of an optimized scrap management system including sorting criteria that will enable closed loop recycling.
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Table of Contents

Abstract

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Table of Contents

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Acknowledgements

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1 Introduction

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1.1 Problem

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1.2 Motives

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1.3 Need

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2 Background

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2.1 Aluminum in automobiles

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2.2 Recycling

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2.3 Alloy Sortation

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3 Approach

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4 Results / Discussion

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4.1 Alloys Identified

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4.2 Handling

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1.1.1 Transport

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1.1.2 Collection Streams

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4.3 Summary of Contaminants

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4.4 Sortation of mixed streams

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1.1.3 Compositional Tolerance

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1.1.4 Sorting for Alloy Identification

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1.1.5 Sorting for Charge Melts

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4.5 Further remarks

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5 Conclusions / Implications

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6 Recommendations for Future Work

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7 Works Cited

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Appendix A: Supplementary Background

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Aluminum Production

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Primary Production

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Wrought Alloy System

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Cast Alloy System

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Manufacturing Technologies

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Casting

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Extrusions

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Sheet Metal Stamping

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Joining

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Recycling

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Downcycling, Recycling and Upcycling

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Aluminum Recycling

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Appendix B: Python Scripts and Sorting Algorithms

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Appendix C: Sorting Algorithm Output

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Appendix D: Other Content

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Acknowledgements
Above all, I would like to thank Professor Diran Apelian and Dr. Sean Kelly for the unconditional support especially during times of personal hardship. Their guidance and mentorship were not only helpful but also necessary for the completion of this project. I would also like to thank the Metal Processing Institute at Worcester Polytechnic Institute for providing the necessary platform and resources and for immediately accepting me as part of their
community. I would like to show gratitude to the industry representatives in the focus group that offered
counsel and guidance through their industry experience. I also want to express my greatest appreciation to Ford and General Motors for allowing us to
visit their stamping and assembling facilities.
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Glossary
Alumina: Al2O3, also known as aluminum oxide, aloxide, aloxite and alundum.
Bauxite: Ore from which aluminum is refined. Consists mostly of hydrated alumina and a range of iron oxides.
Body-in-White (BIW): refers to the stage in automotive design or automobile manufacturing in which a car body's sheet metal components have been welded together — but before moving parts, the motor, chassis sub-assemblies, or trim have been added and before painting.
Charge: Process of filling a melting furnace with material.
Compositional Tolerance: The ability of a melt to accept scrap of a certain alloy or composition without it hindering (or without substantial required efforts to rebalance) its composition.
Dilution: Addition of the primary base material to reduce the concentration of alloying elements.
Downcycling: The reprocessing of a material into a new product of lesser quality or value.
Extrusion: A manufacturing process that consists of pushing a billet of material through a die orifice using a ram.
In-House Scrap: Material discarded during the manufacturing of semi-fabricated products (metal sheets, ingots, plates, etc.).
Laser Induced Breakdown Spectroscopy (LIBS): Consists of pointing a high-energy laser beam into a piece of metal, making it fluoresce. Optical emission spectroscopy is used to determine the metal’s composition.
New Scrap: Material that is discarded when something is produced such as the punching scrap generated when producing an aluminum can.
Old Scrap: The material recovered after a consumer has discarded a used product such as an aluminum can after a consumer has drunk its contents.
Primary Aluminum: Metal produced from ore in deposits extracted from the earth’s crust.
Secondary Aluminum: Metal that has been produced from recycling.
Sorting Criteria: The set of rules used to determine how mixed scrap is to be segregated.
Stamping: A process consisting of changing the shape of sheet metal into a desired form using a die and mechanical press.
Sweetening: The addition of primary alloying material to a melt in order to achieve a desired composition.
Upcycling: The processing of a material to create a product of higher quality or value.
Wrought alloys: Alloys that have been turned into consumer products by solid-state processing including rolling, extruding and forging.
X-Ray Fluorescence (XRF): Consists of shooting x-rays into a material, making it fluoresce. The spectral ratios are analyzed to determine the composition.
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1 Introduction
1.1 Problem
Automotive manufacturers are pressured by regulatory bodies to limit weight to reduce emissions and by competitors and consumers to provide more fuel-efficient vehicles. Aluminum has now joined steel in the family of major materials used in car manufacturing due to its low density and high strength. Aluminum allows for weight reduction without sacrificing much of the structural strength required to ensure competitive performance and safety functionality [1]. This expected increase in aluminum usage has surfaced the need to predict scrap generation and management practice by the original equipment manufacturers (OEMs) that support the automotive sector.
Aluminum sheet usage is expected to increase to 61 pounds per vehicle in 2020 from 23 pounds per vehicle in 2015, a 250% increase. The majority of this growth is a direct result of the aforementioned advances in light-weighting efforts to maximize the incorporation of aluminum in auto-closure components. Aluminum hoods will increase to 71% from 50% and doors to over 25% from 5%. Aluminum Body in White (BIW) components are also expected to increase from 26 pounds per vehicle from 14 pounds per vehicle. Extrapolating this increase and assuming production stays at current levels, a total usage of 1.06 million tons of aluminum sheet can be expected by 2020 [2]. Up to 2/3 of the sheet consumed in stamping processes can become scrap meaning that up to 700 thousand tons of scrap could be generated by 2020 [8].
Downcycling is the reprocessing of a material into a new product of lesser quality or value [3]. The use of wrought scrap (new and old) to produce cast alloys can be considered a type of aluminum downcycling as the purity of wrought alloys is perceived as higher than that of cast alloys. This is due to the tighter compositional requirements in wrought alloys compared to their cast counterparts. The mixing of aluminum scrap of different alloys results in the downcycling of the aluminum due to a lack of compositional understanding of the resulting mixed stream.
1.2 Motives
Secondary aluminum production offers great energetic and environmental advantages over primary production. Secondary production requires ~2.8 kWh of energy and produces ~0.6 kg of CO2 per kilogram of aluminum compared to primary production that requires ~45 kWh and emits ~12 kg of CO2 per kilogram, around 5% of energy and emissions [4]. This energetic advantage makes aluminum recycling extremely desirable for both ecological and economic reasons.
Technologies are now available to sort or separate mixed alloy scrap. Most importantly, the advent of Laser Induced Breakdown Spectroscopy (LIBS) allows for high-volume industrial level scrap sortation required to prevent the downcycling of the increased scrap volumes. This technology combined with an automated sorting system and sound sorting criteria can optimize the recycling process by creating different scrap streams of known composition.
1.3 Need
Without proper management, the wrought scrap produced from the increase of aluminum usage in the automotive industry could be downcycled. To prevent this from happening a better understanding of the current state of scrap generation is required; specifically:
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 Identification of scrap-generating alloys is required. These alloys determine the composition of the streams to be sorted and are a key factor when developing sorting criteria using compositional sorting technologies.
 Comprehension of the current handling processes is needed. This includes the nature of scrap generation, the regularity of scrap mixing of different alloys and the infrastructure associated with handling high scrap volumes.
 Determination of contaminants that pose issues when sorting and recycling is necessary. Their origins and the manner in which these can affect the aforementioned processes is to be understood.
 Development of sound sorting criteria compatible with compositional sorting systems is necessary. The criteria must be able to sort through the mixed streams to reduce the required scrap recycling processing and prevent downcycling.
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2 Background
2.1 Aluminum in automobiles
Initially, aluminum was only used in high-performance luxury vehicles. The world of motorsport influenced this shift in material consumption by proving the performance benefits of light weighting. The first full aluminum body car released to the public was the Audi A8 in 1994 followed by other European luxury brands like BMW, Mercedes-Benz, Porsche, Land Rover, Jaguar, etc. The most recent and important milestone for aluminum in the automotive industry is the newest iteration of the iconic Ford F-150 truck, the bestselling pick-up for the last 38 years. A total reduction of 315 kg in weight was achieved, putting it above all its competitors in different categories including fuel efficiency, safety, carrying capacity, handling and emission reduction. Other companies have boasted their innovative usage of aluminum to increase safety and reduce weight. Tesla’s Model 3 is an example; it features an aluminum body with strategic steel reinforcement and low weight distribution allowing it to absorb the energy from impacts and redirect it away from the passengers earning it the title of the safest SUV on the road. Another company that is embracing aluminum is Toyota that has unveiled plans to shift closure production to aluminum including those of the Camry, America’s best-selling car in the last 12 years [5].
The biggest driving factor in the increase of aluminum usage are the 2025 fuel economy goals of 50+ mpg. Many technologies are being explored but no technology can single-handedly reach these targets [6]. Light weighting is among the main approaches taken by the automotive manufacturers to increase fuel efficiency using lighter materials. Aluminum is a good replacement for steel in bodies and closures. Aluminum has around one third the density of steel but also one third the elastic modulus. This weight advantage and strength disadvantage results in the need to redesign the structures previously made from steel. For example, the inner geometry of a hood has to be redesigned into a more complicated folded geometric pattern to improve component stiffness [1]. Aluminum also offers other advantages such as corrosion resistance (advantageous over steel), superb energy abortion properties (twice as much energy as steel and folding predictability) [7], great formability and cost effectiveness.
The most common aluminum alloys are those of 2xxx, 5xxx, 6xxx and 7xxx series. 2xxx, especially 2008, 2010 and 2036, experience bake-strengthening adding final panel strength. 5xxx, especially 5182, 5454 and 5754, do not have any bake hardening properties but have high formability, ideal for exterior panels. 6xxx, especially 6022, 6111 and 6009, do experience bake hardening and have high strength and great formability, which makes them great for exteriors. 7xxx are mainly used for extrusions [8].
Ducker Worldwide confirmed the increase in aluminum usage in their Aluminum Content in North America Light Vehicles 2016 to 2028 report released in July of 2017. Ducker expects an increase to 466 from 397 pounds of aluminum per vehicle by 2020 since 2015. Aluminum content will range from 262 pounds in the A/B segment passenger cars to over 550 in average pick-up trucks, with the average at 362 pounds in cars and 532 pounds in light trucks. Most of the content growth in the next five years will be for closures, crash management, steering knuckles and structural vacuum die casting parts. Beyond 2020, the most likely scenario for weight reduction is that of 7% by 2028 and not the proposed 7% by 2025.
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Aluminum sheet usage is expected to increase to 61 pounds per vehicle in 2020 from 23 pounds per vehicle in 2015, a 250% increase. Almost all of this growth is focused on closures. Aluminum hoods will increase to 71% from 50% and doors to over 25% from 5%. Aluminum Body-in-White (BIW) components are also expected to increase from 26 pounds per vehicle from 14 pounds per vehicle. Extrapolating this increase and assuming production stays at current levels, a total usage of 1.06 million tons of aluminum sheet can be expected by 2020 [2].
2.2 Recycling
Primary metal production is referred to metal produced from ore in deposits extracted from the earth’s crust while secondary metal production refers to material that has been produced from recycling. Aluminum recycling is also referred to as secondary aluminum production [9]. It is important to note that secondary production offers great energetic and environmental advantages over primary production. Secondary production requires ~2.8 kWh of energy and produces ~0.6 kg of CO2 per kilogram of aluminum compared to primary production that requires ~45 kWh and emits ~12 kg of CO2 per kilogram, around 5% of energy and emissions [4]. The material used to produce secondary metal can usually be divided into two general categories: new scrap and old scrap. New scrap refers to material that is discarded when something is produced such as the punching scrap generated when producing an aluminum can. Old scrap is defined as the material recovered after a consumer has discarded a used product such as an aluminum can after a consumer has drunk its contents. It is important to note that the main distinguishing factor between new and old scrap is the consumer’s involvement. New scrap can be considered preconsumer scrap and old scrap can be considered post-consumer scrap. Another scrap category is that of material discarded during the manufacturing of semi-fabricated products (metal sheets, ingots, plates, etc.) this category is often known as the in-house recycling loop or premanufacturing scrap.
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Sorting of Automotive Manufacturing Wrought Aluminum Scrap