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Materials used in automobile manufacturing and materials selected using Ashby chart

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https://www.eduzhai.net International Journal of Materials Engineering 2018, 8(3): 40-54 DOI: 10.5923/j.ijme.20180803.02 Materials Used in Automotive Manufacture and Material Selection Using Ashby Charts Mekonnen Asmare Fentahun1,*, Prof. Dr. Mahmut Ahsen Savaş2 1Department of Mechanical Engineering, Faculty of Engineering, Mizan -Tepi University, Ethiopia 2Department of Mechanical Engineering, Faculty of Engineering, Near East University, TRNC Abstract Need for higher fuel efficiency, weight minimization, environmental regulations and policies as well as customer demand forces the auto maker companies to focus on developing new materials and re designing of the existing one and selecting materials reasonably. All material industries plastics and polymer composites, as well as steel, aluminum, and magnesium, are operating to respond to the automotive industry changing needs. For decades, advanced plastics and polymer composites have helped the improvement of appearance, functionality, and safety of automobiles while reducing vehicle weight and delivering superior value to customers at the same time. Various materials are used to make cars. The main materials used for making cars, parts and components, along with future trends, are steel, aluminum, magnesium, copper, plastics and carbon fibers. The prime reason for using steel in the body structure is its inherent capability to absorb impact energy in a crash situation. The use of aluminum can potentially reduce the weight of the vehicle body. Recent developments have shown that up to 50% weight saving for the body in white can be achieved by the substitution of steel by aluminum. Magnesium is another light metal that is becoming increasingly common in automotive engineering. It is 33% lighter than aluminum and 75% lighter than steel/cast iron components Titanium has been mainly used in high temperatures zones, and high strength requirement areas, such as exhaust systems, suspension springs, valve springs, valves and connecting rods. Fiber reinforced composites offer a wide range of advantages to the automotive industry. It is because the composite structures are the high strength/low weight ratio. The use of lightweight plastics and composite materials in the automotive industry has been increasing in recent years due to legislative and consumer demands for lighter weight, fuel efficient vehicles. One of the methods to choose best materials for automotive applications is to use material selection charts, which provides the performance index of the materials to suit the requirement and conditions for specific application. Keywords Automotive manufacture, Ashby charts, Metals, Material performance index 1. Introduction The importance of materials selection in the product development process has been well recognized since past decades. To develop a systematic method for selecting the best material is not an easy task because the best material is determined by a number of factors that influence the selection process. There are two main reasons why materials selection is required: firstly, to design an existing product for better performance, lower cost, increasing reliability and reduced weight and secondly, to select a material for a new product. Materials selection is a main product design consideration because product’s overall performance is mainly affected and determined by materials selection process [1]. * Corresponding author: mekonenasmare@gmail.com (Mekonnen Asmare Fentahun) Published online at https://www.eduzhai.net Copyright © 2018 The Author(s). Published by Scientific & Academic Publishing This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/ The automotive composite materials, reinforced plastics and polymers are among widely preferred alternatives for light weighting of the automobile as they offer enhanced properties such as impact strength, easy mold–ability, improved aesthetics, and reduced weight as compared to conventional automotive components. The main advantages, which offer opportunities in the automotive industry, are their potential for maximum mass reduction of automobile and carbon emission reduction potential by light weighting of the vehicle. The factors restraining the market are high material costs and huge investments in material research activities by companies. The automotive industry is under increasing pressure to meet higher fuel efficiency, environmental and performance demands at competitive costs. All material industries plastics and polymer composites, as well as steel, aluminum, and magnesium, are operating to respond to the automotive industry changing needs. For decades, advanced plastics and polymer composites have helped the improvement of appearance, functionality, and safety of automobiles while reducing vehicle weight and delivering superior value to customers at the same time [2]. New regulations, shifts in International Journal of Materials Engineering 2018, 8(3): 40-54 41 consumer preferences, and recent technological innovations are encouraging automotive industry to continue increasing their use of advanced plastics and polymer composites to meet tomorrow’s challenges and opportunities [2]. Composite materials offer an opportunity to significantly reduce the weight of a vehicle while still meeting strength requirements. Today, engineered plastics are fast becoming the future for two industries, chemical and automotive as environmental concerns are increasingly affecting both. To preserve optimum fuel efficiency, automakers are using materials that are more lightweight plastics and polymer based components [2]. The automotive sector is under constant pressure to reduce carbon emissions and bring down fuel consumption by reducing the weight of vehicles, with an increase in safety requirements. The underlying reason for this is the need for lower weight, different types of materials, as well a stricter environmental legislation and related traffic regulations [2]. 2. Materials in the Automotive Industry an Overview Various materials are used to make cars. The main materials used for making cars, parts and components, along with future trends, are steel, aluminum, magnesium, copper, plastics and carbon fiber. The main factors for selecting the material, especially for the automobile body, are numerous and include thermal, chemical or mechanical resistance, easy manufacturing and durability [2]. Affordability is an important issue in vehicle manufacturing, which includes factoring in the costs associated with a car’s complete life–cycle, including manufacturing, operating and disposal costs. Composite materials may have big advantages over steel in automobile manufacturing in the future. Composites are considered to make lighter, safer and more fuel efficient vehicles. A composite is composed of high–performance fiber (such as carbon or glass) in a matrix material (epoxy polymer) that, when combined, provides enhanced properties compared with the individual [2]. Carbon fiber composites are equally good or better concerning stiffness and strength. They also do not rust or corrode like steel or aluminum, and they could significantly increase vehicle fuel economy by reducing vehicle weight. The issue with today’s composites is that they have been developed for aerospace applications where the cost is not so critical. Material costs of carbon fiber composites are at least 20 times higher than steel, and the automotive industry is unlikely to use them until the price of carbon fiber drops significantly. Therefore, if we want to choose material with these characteristics, steel is the first choice. There were many developments concerning iron and steel over the past couple of decades that made steel more lightweight, stronger, stiffer and improved other performance characteristics. Applications include not only vehicle bodies, but also engine, chassis, wheels and many other parts (doors, hoods, hatchbacks etc.). Iron and steel form the critical elements of the structure for the vast majority of vehicles, and are low cost materials [2]. The prime reason for using steel in the body structure is its inherent capability to absorb impact energy in a crash situation. Aluminum usage in automotive industry has grown within past years, due to its low density and high specific energy absorption performance and good specific strength. The use of aluminum can potentially reduce the weight of the vehicle body. Recent developments have shown that up to 50% weight saving for the body in white can be achieved by the substitution of steel by aluminum. Aluminum is used for body structures, chassis applications, closures and exterior attachments such as crossbeams, doors or bonnets. Magnesium is another light metal that is becoming increasingly common in automotive engineering. It is 33% lighter than aluminum and 75% lighter than steel/cast iron components [2]. Magnesium alloys have distinct advantages over aluminum that include better manufacturability longer die life and faster solidification. In addition magnesium components have higher machinability. Table 1. Summary of current automotive applications with mode of application, advantage and drawbacks Materials Mode Of Applications Advantages Current draw backs Steel BIW, chassis, power trains, bumpers and engine parts Strong and stiff, corrosion resistant, impact energy absorptivity properties, good formability and joining capability. Aluminum engine blocks, body panels, power train, pistons & cylinder heads, etc. Light weight, corrosion resistant, recyclable, energy efficient, safer. Very heavy compared to other auto materials Intolerance to heat Magnesium inner door structure, steering wheel core, steering column, car seat frame, transfer case, etc. lightest of all the engineering metals thus contribute fuel economy Low melting temperature (650°C), highly reactive metal and has inherently poor corrosion and wear resistance Copper Electromechanical applications, automatic transmissions and ABS braking systems Good electrical conductivity makes it suitable in electrical accessories and components in automobiles. Limitation to application in automotive parts Composites and Plastics Passenger cell, Roof compartment cover, trunk lid, Wheel rims, Cabin, floor, roof, pillars, hood, etc. High strength to weight ratio and good stiffness, good corrosion and chemical resistance. Very expensive, not recyclable, hard manufactory process and etc. (composites). 42 Mekonnen Asmare Fentahun et al.: Materials Used in Automotive Manufacture and Material Selection Using Ashby Charts Titanium has been mainly used in high temperatures zones, and high strength requirement areas, such as exhaust systems, suspension springs, valve springs, valves and connecting rods. Fiber reinforced composites offer a wide range of advantages to the automotive industry. It is because the composite structures are the high strength/low weight ratio. Carbon fiber–reinforced or fiber glass reinforced composites offer numerous new design possibilities for structural components in cars. These advanced materials are not only light in weight, but also stiff, strong and durable. The future lightweight materials will be used in the automobile industry. Now, carbon fiber is very expensive, but the automobile industry has been developing affordable carbon fiber, so the future cars will be lighter. Fiber reinforced composites are now being used to make structural and nonstructural components such as seat structures, bumpers, hoods, and fuel tanks [2]. 3. The Development of New Automotive Materials and Components The producers in the automotive industry are expressing more and more interest in the industrial applications of light, strong and thus energy efficient and cleaner solutions, such as composites. This requires innovations in materials, design, production, processing and process automation and, above all, cost effectiveness. The traditional production processes for cars are still focused mainly on the processing of metal chassis and other components. Although plastics are extensively used, the deployment of fiber reinforced composites for high volumes of cars is still in the pioneering phase [2]. To develop new automotive materials, components, and systems in the most effective way, the completely automotive supply chain needs to work together. The researches on composite materials, reinforced plastics and polymers have come up with improved material qualities that make them suitable for use in interior, exterior, and under bonnet components of automobiles. The automotive composite materials are used in various automotive components such as bumpers, seating, dashboards, internal and external trims. The careful selection of these automotive materials enables designers to improve durability meet load–bearing requirements, and achieve reduction in vehicle weight [2]. The Figure below provides the data on the tensile strength and density of filled plastics, polymer composites, metals, and alloys. As shown in fig.1, many plastics and polymer composites are significantly less dense than most metals and alloys while offering similar tensile strengths. These data illustrate the fundamental physical advantage that many plastics and polymer composites offer over metallic automotive materials: higher strength to weight ratios that can enable automakers to lightweight vehicles while maintaining safety and performance [4]. The use of lightweight plastics and composite materials in the automotive industry has been increasing in recent years due to legislative and consumer demands for lighter weight, fuel efficient vehicles. In some cases, plastics are replacing heavier ferrous materials whereas; in other cases, plastics and composites are being added for consumer comfort purposes. In addition to being lightweight, these materials are also durable and easily molded. Substituting heavier materials with plastics leads to an overall weight reduction. The percent of plastics by mass in an average vehicle has gone from 6% in 1970 up to 16% in 2010 and is expected to reach 18% in 2020 [2]. Figure 1. Tensile strength vs. density for automotive materials [4] International Journal of Materials Engineering 2018, 8(3): 40-54 43 Figure 2. Change in vehicle composition from 1970 to 2010 [2] Composite materials currently have high purchase price, but when viewed from a lifecycle perspective they make good economic sense. On top of low weight, composite materials provide strength and rigidity, while fatigue and ageing are not generally seen as problems. Composites also do not rust, and they do not degrade in the same way as metal structures. Another advantage with composite use in chassis structures is that it is possible to create larger integrated structures than with steel. This means fewer joints, which in turn further reduces weight. The researchers say that tomorrow’s vehicles will be made from a bigger mix of materials, with focus on both function and weight [2]. While the plastics and polymer composites industry has been working collaboratively with the automotive industry for many years, barriers remain that limit the use of plastics and polymer composites in vehicles. Plastics and polymer composites continue to deliver significant weight savings to automakers. In addition to their current role, as an excellent choice for light weighting, aesthetics, aerodynamic design and value in many interior and exterior applications, plastics and polymer composites particularly the fiber reinforced composites are also fast becoming a contender in structural applications like body–in–white and chassis components, due to their ability to drastically reduce overall vehicle weight while maintaining or improving safety and performance [2]. 4. Requirements of the Materials in Automotive The materials used in automotive industry need to fulfill several criteria before being approved. Some of the criteria are the results of regulation and legislation with the environmental and safety concerns and some are the requirements of the customers. In many occasions different factors are conflicting and therefore a successful design would only be possible through an optimized and balanced solution [3]. For the foreseeable future, ecological requirements emerging from the social and legal environment- the need to protect the natural environment and use resources sparingly - will almost certainly represent a major factor for change. The following table illustrates how these demands will affect the processes and the materials used in automobile construction [5]. The automotive industry is increasingly relying on a systematic approach to materials selection. The choice of materials for a vehicle is the first and most important factor for automotive design. There is a variety of materials that can be used in the automotive body and chassis, but the purpose of design is the main challenge here. For the automobile manufacturers, the most important criteria that a material should meet are [2]:  Light weight, this criterion is the most important one for an automotive company, in the context of the high emphasis on greenhouse gas reductions, reduction of emissions and improving fuel efficiency.  Economic effectiveness, having in view that one of the most important consumer driven factors in automotive industry is the cost, that determines whether any new material has an opportunity to be selected for a vehicle component;  Safety, which criterion have in view the ability to absorb impact energy through controlled failure modes and mechanisms and be survivable for the passengers; and  Recyclability of their products and life cycle considerations, having in view that the most important concerns in automotive industries are the protection of resources and the recycling possibilities, including strategies on research and development targeted on recycling techniques and the development of more easily recyclable materials and their incorporation into the vehicle and its constituent components. 44 Mekonnen Asmare Fentahun et al.: Materials Used in Automotive Manufacture and Material Selection Using Ashby Charts Table 2. Requirements on future materials in the automotive industry [5] The weight reduction in the automotive industry can be obtained in three ways:  Replacing materials of high specific weight with lower density materials without reducing rigidity and durability (for example replacement of steel with aluminum, magnesium, composites and foams.  Optimizing the design of load carrying elements and exterior attachments to reduce their weight without any loss in rigidity or functionality; and  Optimizing the production process. By continuing the development of composite materials technologies, the automobile industry is able to create cars increasing their performance and their appearance. The ability to leverage this kind of lightweight material gives a competitive advantage that will benefit the cars, as well as the production process, in the future [2]. However, the single main obstacle in application of lightweight materials is their high cost. Yet the weight reduction is still the most cost effective means to reduce fuel consumption. The cost includes three components [2]:  The actual  Cost of raw materials, manufacturing value added cost and  The cost to design and test the product. Aluminum and magnesium alloys are certainly more costly than the currently used steel and cast irons. Since the cost may be higher, decisions to select light metals must be justified based on the improved functionality. Meanwhile the high cost is one of the major obstacles in the use of composite materials. By 2030, the automotive industry and society will recognize plastics and polymer composites as preferred material solutions that meet, and in many cases set, automotive performance and sustainability requirements. Plastics and polymer composites provide the weight savings, strength, and versatility the automotive industry needs to meet new standards without sacrificing quality [4]. The automotive industry is constantly seeking to improve aesthetics and reduce the weight of vehicles while simultaneously increasing their strength and improving crash performance. However, balancing the feel and appearance of a material with its strength, stiffness, ability to withstand dimensional tolerances, and cost is a critical challenge [4]. For vehicle manufacturers and their suppliers, materials have never been more strategic. Materials choice influences cost, safety, risk, weight, market image, and vehicle emissions. Materials knowledge gives competitive advantage: it enables you to meet quality and emissions goals, it is a critical input for virtual product development processes, and it gives you the means to respond quickly to supply chain disruptions and new legislations [4]. Plastics and polymer composites, which already dominate vehicle interiors, exteriors, trim, and lighting, are gaining use in other vehicle systems as lightweight, value–producing materials that can meet increasingly challenging automotive requirements. These materials’ many advantages have enabled them to grow to become a significant part of the materials mix in the automotive industry over the past 40 years (figure 3). As the push to lightweight vehicles intensifies, projections indicate that plastics and polymer composites can and should play an even more substantial role in the automotive industry through 2025 and beyond (figure 3) [4]. The typical weight distribution in cars is Steel 71% (body panels), Cast iron 15% (engine parts, gear box, axle...), rubber (tires, hoses...) and others include Zink, Copper, Aluminum, polymers etc. [6]. International Journal of Materials Engineering 2018, 8(3): 40-54 45 Figure 3. Current and future tendencies in the automotive industry [2] 5. Current Materials in Use in Automotive The categories of current materials used in automotive industry such as metals, composites and others are discussed below Metals Steel Advanced iron and steel technologies have seen considerable development over the past decade and are frequently included into new designs and redesigns by all automakers. The steel industry and component suppliers are investing heavily in innovation. The result of the investment is numerous examples of successful, cost-effective use of stainless steel, new formulations of iron, high-strength steels, and an associated variety of new design, fabrication, and assembly techniques. Applications of steel in automotive industry include not only vehicle bodies, but also engine, chassis, wheels and many other parts. The usages commonly demonstrate weight reduction plus simultaneous improvements in strength, stiffness, and other structural performance characteristics. While body, chassis, engine and other powertrain components made of ferrous materials comprise the largest part of a vehicle by mass, lightweight steel and iron technologies compete with potential substitutes in all of these applications [3]. Mass reduction through advanced use of iron and steel is significant (ferrous materials), because they are the dominant material. Iron and steel form the critical elements of structure for the vast majority of vehicles, and are low-cost materials with an extensive experience base and familiarity to the industry (steel and cast iron contribute about 86% total weight of the automobile) [3]. The use of high-strength steels (HSS), many versions of which are referred to as high-strength, low-alloy (HSLA) steels in the past decades increases dramatically in the automotive sector. One of the applications of a high-strength, low-alloy (HSLA) steels is in Ultra-light Steel Auto Body (ULSAB) which demonstrated a 19% mass reduction in a body structure that had superior strength and structural performance (including crashworthiness) along with a reduced parts count and net manufacturing cost savings compared to a conventional steel body. [USAB, 1998] Comparable mass reductions and other benefits were achieved for doors, hoods, decklids, and hatchbacks. Improved steel materials and forming processes allow a significant optimization of vehicle body structures and components [3]. The prime reason for using steel in the body structure of an automotive is its inherent capability to absorb impact energy in a crash situation [Marsh, 2000]. This, in combination with the good formability and joining capability, makes these materials often a first choice for the designer of the body-in-white (BIW) structure. High-strength steel (HSS) is based on alloys that are categorized on the basis of yield strength. Standard HSS has a yield strength between 210 MPa and 550 MPa; ultra-high 46 Mekonnen Asmare Fentahun et al.: Materials Used in Automotive Manufacture and Material Selection Using Ashby Charts strength steel (UHSS) has a yield strength higher than 550 MPa. High-strength steels can cost as much as 50% more than traditional mild steels, but they allow use of lower thicknesses than milder steels for achieving needed part performance specifications. Recently Steel suppliers are developing steels with a range of properties that give engineers more flexibility in selecting an ideal grade of steel for any given application [3]. Stainless steel is a material of choice due to passivity and resistance to corrosion. Some of the stainless steel grades suggested for automotive are as follows: [Cunat, 2000]. 1. Duplex austenitic-ferritic stainless steel. The most commonly used duplex grade is 0.02% C – 22% Cr – 5.5% Ni – 3% Mo – 0.15% N alloy. 2. Austenitic stainless steel. These steels have chromium (18 to 30 per cent) and nickel (6 to 20 per cent) as the major alloying elements. The austenitic phase is stabilized by the presence of a sufficient amount of nickel. The principal characteristics are the ductile austenitic condition, rapid hardenability by cold working and excellent corrosion resistance. One of the most commonly used grade for structural applications is the 0.02% C – 17.5% Cr – 7% Ni – 0.15% N alloy. (1) In the solution annealed condition, (2) In the cold worked condition C 850 (850

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