Advanced Materials and Manufacture, Microstructures and Properties of Cast Iron - Case Study Example

Lecturer Advanced Materials and Manufacture Introduction Currently, connecting rods are applied in the internal combustion piston ofthe automotive engines. These modern connecting rods are very different in properties and characteristics, from the earlier connecting rod types utilized in steam locomotives and in steam engines. The quality of components of the connecting rods in the automobile machines is determined through intended vehicle usage. Connecting rods for racing cars are very different from connecting rods for passenger vehicles (White, 2002). Section A Connecting Rod Operation in the Engine Connecting rod is mostly applicable in the reciprocating piston engine. The connecting rod joins the piston and the crankshaft, also called the crank. The connecting rod and the crank together form a basic mechanism which changes the reciprocating effect into rotating motion. Connecting rods are also capable of performing the reverse action of changing the rotating motion into the reciprocating motion. The connecting rod is rigid and therefore, applies the push and pulls effect to rotate crankshaft using both halves of the revolution; for instance the piston pushing or pulling. Automotive engines utilize the connecting rods in the internal combustion engines. In modern cars, the internal combustion engines utilize connecting rods that are mostly made from steel. However, these connecting rods can also be produced using T6-2024 aluminum alloy, and T651-7075 aluminum alloy; because of the desired engineering quality of lightness and capability of high impact. These connecting rods are also produced using titanium and cast iron. Titanium ensures proper strength and lightness characteristics of the connecting rods. Cast iron is normally utilized in applications like motor scooters. The connecting roads are not fixed firmly or rigidly in both ends; this enables the angle connecting the piston and the rod to change when the connecting rod goes up or down; and when the connecting rod rotates along the crankshaft. Connecting rods of mostly racing engines are referred to as billet rods, this is because they are made from solid metal billet, and not cast metal or forged metal (White, 2002). Influence of Design and Operational Requirements on Properties of Connecting Rods Design requirements affect the material property requirements of connecting rods. This is because when designing high performance engine; a lot of emphasis is given to the rods, through eliminating stress risers. Stress risers elimination is achieved through techniques like; smoothening rod edges by grinding, magnafluxing in order to identify small and invisible cracks that can cause failure of the rod due to stress, shot peening that hinders crack initiation, and balancing the weight of connecting rod and piston components. Great care is required in usage of bolts of the connecting rod. The bolts must be used according to the exact identified value; the bolts should also be continuously replaced, instead of being continuously reused. In high performance engines design, it is ensured that caps of the connecting rods cannot be interchanged. When engine rebuilding is being undertaken, it should be ensured that there is no mixing of caps of the different connecting rods. The connecting rods and their respective bearing caps should be embossed using the relevant position number of the engine block (Ashby et al, 2002). Operational requirements affect the material properties of the connecting rods. Modern engines like the Chrysler 2.0 liter or Ford 4.6 liter engine utilize connecting rods produced from powder metallurgy, which ensures precise and effective control of the weight or size. The powder metallurgy also ensures less machining and reduced excess mass that is machined off in balancing. The cap is separated from rod through the fracturing process that ensures uneven mating surface. This creates perfect positioning of the cap and the rod, during reassembly. Material Selection Using CES Software The CES Software is a computer selector application which enables the automobile designers and engineers to find and apply the materials property data. The CES selector is important in the automobile industry because it enables the engineers and designers to; make better and informed decisions during the early stage design, material placement and redesign; ensure confidence in the material choices; communicate required recommendations; and minimize the time for problem solving or responding to material related queries. According to the CES selector Aluminum alloys are suitable materials for connecting rods due to; lightness quality, and capability of absorbing high impact. Titanium is also a suitable material for connecting rods if the desired characteristics are high strength and adequate lightness (Hinckley & Barkan, 1995). Section B Microstructures and Properties of Cast Iron The properties of engineering materials like cast iron are influenced by the detailed microstructure. The issues that determine the cast iron properties are chemical properties, size, volume fraction, morphology, and distribution of individual micro structural components. Spheroidal graphite (SG) is an example of cast iron that is deeply studied; and it illustrates the close correlation of microstructure and the engineering properties. Austempered ductile iron has a superior integration of strength, ductility, cost effectiveness, design flexibility, toughness, fatigue and wear resistance, and damping capacity in relation to any other material. Austempering entails full austenitization, enabling isothermal transformation, and finally air cooling. Austempering takes place in two phases. In the first stage the matrix austenite changes to ausferrite, which is composed of acicular ferrite mixed with stabilized austenite that has carbon. During the second stage, stabilized austenite reduces to carbide and ferrite, hence reducing the stabilized austenite phase proportion (Degarmo et al, 2003). The influence of retained austenite on mechanical characteristics of austempered ductile iron (ADI) is researched extensively. Studies illustrate that the fine dispersion and the high volume fraction of the retained austenite; ensures greater ductility and toughness, increased fracture toughness, and ensures flow stress of material. The matrix structure greatly influences the resonant vibration fracture (RVF) characteristics of the SG cast irons. The upper bainitic matrix show greater deflection amplitude with higher crack resistance than the ferritic cast irons. The resonant vibration fracture resistance increases due to increased nodularity of the identical matrix. Microstructures and Properties of steel Steel is currently one of the most reliable, used and important materials in the automotive manufacturing industry. In relation to chemical composition and the thermo mechanical processing trend, the mechanical properties of steel varies significantly, and covers different ranges of ductility, strength and toughness. Steel is also a comparatively cheaper material in the manufacture of automobile parts like the connecting rod. These qualities therefore explain why steel and iron comprises more than 80% weight of the alloys utilized in the automobile industry. Carbon steels are especially popular due to its compatibility which allows inducement, through rapid quenching, of a hard phase referred to as mantensite. The significant properties of steel for connecting rod purposes are; grip and longevity. The mechanical performance of the connecting rod can be realized through tracing the behavior of the steel rod through controlled conditions of stroke speed or normal force. The thermo chemical treatment of steel material during connecting rod production is divided into three parts. Firstly, the raw material is normalized through annealing and thereafter air cooling to get a ferritic structure, which has spheroidized carbide particles. Secondly, the obtained steel material is subjected to machining so as to get final connecting rod form. Thirdly, the thermal treatment is done to realize the hard martensitic stage. Producing the required hardness of the connecting rod entails rapid quenching (Smith & Hashemi, 2006). Microstructures and Properties of Titanium The interests of titanium or its alloys are due to the comparatively low density of titanium. Also, titanium has high yield strength (more so between the 200 and 450 degrees Celsius range); and high corrosion resistance. Therefore, titanium is applied favorably in the manufacture of automobiles due to corrosion resistance, and high strengths with great weight savings. Titanium undergoes allotropic phase transformations on reaching 882.5 degrees Celsius; hence changes structure from alpha phase (closely packed hexagonal crystal); to beta phase (cubic crystal structure). The transformation temperature is determined through interstitial and substitutional factors, depending on purity of metal. The intrinsic anisotropic properties of hexagonal crystal (alpha) have significant effect on the elastic or plastic deformation characteristics of titanium or its alloys. The elastic modulli decreases proportionally with increase in temperature until the transformation temperature is realized. Commercial titanium alloys are group based on three categories of; alpha, beta, and alpha+beta, depending on equilibrium constitution which differs according to the concentrations of the alloy elements. Commercial purity titanium has amounts of interstitial oxygen required to improve the yield stress and the alloys with the alpha stabilizers. Alloys in the beta phase can be kept at room temperature even in large quantities during air cooling. These metastable beta alloys can be changed to alpha+beta alloy mixture through isothermal aging (Hinckley & Barkan, 1995). Microstructures and Properties of ALSiC Aluminum alloys integrated with ceramic particulates have greater structural applications because of low density, high stiffness, and high specific strength. These superior properties have ensured that metal matrix composites are attractive for applicability in the weight sensitive and also stiffness critical parts in the automobile sector. Corrosion behavior is also significant in assessing application of composites in structural materials. Galvanic interactions of reinforcement and matrix can increase corrosion. The preferential corrosion in particle matrix interface can ensure rapid penetration through the large composite interfacial areas, and this result to increased corrosion. Corrosion reduces the load bearing capability resulting to structural failures; and this limits the application of aluminum alloys structures in corrosive environments, more so when there are lots of stresses. The ALSiC composites generally have higher densities in comparison to pure Al matrix. Increasing the volume of the SiC particulates in the aluminum composites also increases the composites’ density. Reinforcement increases the density of the aluminum matrix alloys. In addition, the increase in density of composites is a direct result of the increase particulate volume. ALSiC composites show greater corrosion levels at 50 and 75 degree Celsius than the pure matrix of aluminum (Duncan, 1991). Section C Manufacturing Route of Connecting Rods Forged steel rods are produced from carbon steel which has 33% carbon. The steel connecting rods used in 2.3 L engine applicable to small cars, usually weighs 455g. The forged steel rod is not supposed to be shot screened because compressive residual stress incurred on the surface due to shot blasting operation during cleaning process is enough to ensure enhanced fatigue resistance. Axial fatigue stress on forged steel is analyzed to understand the fatigue behavior of the connecting rod. Alignment of the steel connecting rod in relation to load strain is done before conducting the axial fatigue stress. To reduce misalignment, the ball joint pin is introduced at the test fixture bottom. Axial fatigue tests are conducted to analyze variability and scatter. The continuous casting process ensures the production of high quality and superior grey cast iron, for the manufacture of connecting rods. The continuous casting process entails usage of graphite die that is water cooled and mounted at the bottom of the casting crucible. Iron thereafter flows through the die and a skin is created that has the bar shape. The bar is again cast through the die in strokes; which are between 1 and 2 inches long. Pausing is done after each stroke to ensure the molten iron forms a rim. Most bars entails molten iron core which reheats at more than critical temperatures. When the bar extends from the die, the solidification process enables it to form a homogenized microstructure. The cast iron bar is then produced in many different shapes. The cats iron bar is the further shaped to produce the cast iron connecting rods utilized in the automobile sector (George et al, 2000). The process of titanium invention entails procedures of mixing titanium particles or titanium alloy particles, with non metallic materials, forming perform through mixture compressing, and lastly sintering of the preform at increased temperatures to produce various engine carts like the connecting rod. Titanium powder has particle size of around 1-100 microns, and more preferably 5-10 microns. The titanium particle surface is higher than 25m2/g, and more preferable 50-250m2/g. aspect ratio is approximately 5-300. Appropriate titanium alloys entail Ti-6Al-4V and Ti-6Al-6V-2Sn. The mixture has approximately 30 to 95 parts of titanium by weight or titanium alloy by weight; and approximately 20 to 40 parts of non metallic parts. Aluminum composites are produced using different routes; for instance the liquid metallurgy, two stages processing and solid state processing. Reinforcement distribution is key issue during analysis of microstructure which influences the mechanical properties. Appropriate mixing methods reduce the reinforcement agglomeration; and particle testing is minimized through quick pouring or chill casting technique. Secondary processing ensure proper reinforcement distribution; for example extrusion, rolling and forging. The strengthening of aluminum alloys through dispersion of ceramic particulates effectively increases structural applications and wear resistance potential. For example, the fly as composites of aluminum has many applications in the automobile industry, like manufacture of connecting rods. Manufacturing Process Effects on the Microstructure and Properties of Materials During manufacturing, the sample size of steel has influence on the properties of the material. The grain sizes with smaller diameters exhibit greater strength. Transverse and longitudinal hardness values are also higher in connecting rods with relatively smaller diameters. Large proportion of the pearlite has adverse effects on the ductility or toughness of the carbon steels. Increase in pearlite content leads to increased impact transition temperatures, and lower impact energy absorption. This is because pearlite in microstructure ensures sites for cracks nucleation. The percentage of carbon content highly influences the mechanical properties of steel. All the properties increase due to increase in carbon proportion; apart from impact strength that decreases with rise in carbon proportion. AlSiC composites are applied in the automobiles sector because of superior qualities like high electrical conductivity, high thermal conductivity, adequate wear resistance, proper corrosion resistance, high strength and stiffness, and less weight. The Al composites are produced through ceramic particles dispersion in the Al matrix; the majorly utilized ceramic particle is the SiC3-6. In liquid method preparation of Al composites, the particles are entered in the liquid Al through stirring and thereafter casting. But, the different thermal expansion coefficients of composite constituents, and weak wet-ability of molten SiC and A1 components, reduce the effectiveness of the liquid method in synthesizing the AlSiC composites (Duncan, 1991). The processing variables for electron beam melting (EBM) are divided into two major parts; inter build category, and intra build category. Inter build variations takes place over multiple builds, and intra build variations takes place in one build space and in one part. For EBM and related manufacturing methods, it is necessary to the effects of the variables on the properties or microstructure, so as to get connecting rods of acceptable quality, reproducibility, and repeatability. Relative temperatures reduce radially outwards the exterior of build space. As relative temperatures decreases, the cooling rates or time above the beta transus increases. For the Ti-6Al-4V microstructure, when cooling levels decreases alpha lath thickness increases. This ensures reduced ultimate tensile strength, micro hardness, and even yields stress. The metal matrix of cast iron is similar to the metal matrix of steel. The composition of metal matrix of cast iron depends on the carbon amounts which remain; and this is controlled by proper inoculation. Carbon integrates with iron to produce iron carbide which is a very brittle and hard component. As iron cools carbide develops in plates, which alternates with ferrite plates to form pearlite structure. Pearlite is less soft than the pure iron carbide. It also has high strength, wear resistant capabilities, adequate ductility, and can be easily machined. As amount of pearlite increases, the strength and hardness of the cast iron increases; but the machinability and the capabilities decreases (George et al, 2000). Section D Computer Integrated Manufacture (CIM) Computer Integrated Manufacture (CIM) involves the complete automation of a production or manufacturing facility, for example automobiles manufacturing plant. All manufacturing operations and functions are under the control of computers. The manufacturing process is initiated through the computer aided design, followed by computer aided manufacture, and finally automated distribution and storage. A single computer system that has integrated control ensures that, the automation process is effective and seamless. Stage one of the automated manufacturing involves computer aided design (CAD). The automobiles are designed entirely through the computer software. The complete design is tested on screen before making prototype. Improvements and alterations are made on model through CAD software. Stage two entails the prototype manufacture. Prototypes are made using computer components like 3D printers. Laser cutters or CNC routers can be used to make realistic models. Stage three entails the computer system determining the most effective and efficient manufacturing methods. Stage four entails the computer system requesting or ordering for adequate resources required in the manufacturing process. In the fifth stage the actual manufacturing begins, products are made using the Computer Aided Manufacture (CAM). Stage six ensures that quality control process is used in each and every stage of the manufacturing process. In stage seven, the products are assembled using robots. The robots are automated in the computer system. In stage eight the quality of the products is seriously ensured, before the storage of the completed products. Storage system is completely automated. The products are bar coded and stored in the computer system. During the ninth stage, the product is removed automatically from the store, for easier distribution to customers. In the last stage, the financial information system is updated automatically; bills are paid through computer system (Holweg, 2007). Advantages and Disadvantages of the CIM The automation process has several importances. Superior customer services are realized; because the automated system ensures effectiveness and efficiency in the distribution of quality products to customers. Employees experience increased job satisfaction; because repetitive or boring jobs are performed by robots, hence employees are motivated by other challenging tasks. High quality products are produced in the automation process; 6his is because quality control is a key component of each production level. However, automation has several negative effects. Automation is an expensive capital intensive venture; therefore, the bay back period on investments is longer. The automation process must also be continuously upgraded; the upgrading requires additional training of personnel for effectiveness and more financial resources. Unemployment rises in the country, because machines replace human labor. Flexible Manufacturing System (FMS) A flexible manufacturing system (FMS) entails manufacturing process that has some level of flexibility which allows the automated system to react during changes. Flexibility generally has two categories. Machine flexibility entails the first category. Machine flexibility involves the ability of the system to change the order of operations; and ability of the system to be changed so as to manufacture new products. The second category entails routine flexibility; which involves the ability of the system to utilize multiple machines in doing same operation. Routine flexibility also entails the capability of the production system to handle large scale production changes in capacity and volume (Holweg, 2007). Majority of the FMS have three major systems. The work machines are connected through material handling system to maximize on parts flow and central computers which controls movements of materials and effective machine flow. The main significance of the FMS is the high flexibility in the management of the production resources, for instance time and effort. The best use of the FMS lies in the manufacturing of small product sets, in a mass production facility. Advantages and Disadvantages of the FMS The FMS has several importances. FMS minimizes the manufacturing costs in the automobile sector; this is because of the increased efficiency in the production process. FMS also ensures increased machine efficiency, through the work machines which maximize effective machine flow. FMS also ensures improved product quality, because flexibility ensures that quality improvement procedures are utilized in any production phase. On the other hand, FSM has several shortcomings. Implementation of the system is expensive; this is because acquiring the computer controlled machines is expensive. The FMS requires skilled personnel for operation; training current employees to get required competencies, is a time consuming and expensive venture. FMS also requires a lot of substantial pre-planning; the pre-planning process is tedious because it involves a lot of technical know-how and financial resources. Poka Yoke and SMED Lean Methodologies Lean methodologies entails production practice that takes into consideration the financial expenditure of resources to the desired goal; rather than creating value for customers (Holweg, 2007). In this methodology, value is seen as what the customer is willing to pay for. Poka Yoke is a method in lean manufacturing process that ensures operators avoid mistakes (Nikkan, 1998). It aims at eliminating production defects and minimizing human errors in production process. Single – minute Exchange of Die (SMED) is another lean production method. It assists in the reduction of waste in the production process. SMED provides effective and efficient ways of converting production process from managing current product to manufacturing the next product (Shingo, 1995). Handling Increased Production Volume If the production volume greatly increases, then changes must be incorporated in the production system and procedures. In the design stage, the computer Aided Design should be reviewed to accommodate increased in production volume. The computer system will therefore utilize the design data to request for adequate resources needed in production process. Computer Aided manufacture system will finally control the production process. In the production stage, the increased production volume is monitored through enhanced quality control program. Storage and distribution systems and facilities are also enhanced to cater for increased production volume. Section E Commercial and Engineering Requirements effect on Materials Cast iron has been utilized in the automobile sector for many years. This is because it is a relatively inexpensive technology; due to economies of scale from mass production of interchangeable components that are simply bolted. Cast iron has effective engineering qualities which favor its usage. This is because the fatigue strength of cast iron is high; leading to increased hardness and tensile stress. Surface hardening of cast iron through induction heating increases the resistance of the iron to pitting or normal fatigue failures. Fatigue strength is enhanced through high surface stresses and hardness. Insulating steel products like connecting rods is a necessary cost, which ensures good investments. Insulation moderates temperatures in the engines and improve acoustics through damping sound. Insulation also leads to significant energy expense savings. Thermally applied metallic coatings are utilized in low carbon steel components so as to protect against wear or corrosion. But these coatings always have pores, cracks or oxides in microstructure, which influence protection performance. The spraying process determines the distribution or amounts of the defects, and various coating properties. The coating properties include hardness, adhesion and thickness to substrate. The final coating quality is greatly related to spray parameters like spray distance, fuel gas type, particles velocity and oxygen pressure (Duncan, 1991). Commercially pure titanium or titanium alloys has several characteristics. The titanium or titanium alloy are weldable, have medium strength, have adequate notch toughness, possess medium strength, non heat treatable and have adequate creep resistance at high temperatures. The great corrosion resistance of the titanium alloys is due to development of chemically stable, continuous protective, and highly adherent surface oxide film. Titanium metal is very reactive and possesses high affinity for oxygen; hence the surface oxide films are formed instantly when the surface of titanium alloy is exposed to moisture or air. Usually, the damaged oxide films regenerates instantly if air or moisture is present. The particle size of SiC has effect on the aluminum’s dimensional stability. The temperature impact on aluminum decreases in the presence of the micro silicon carbide, and nanosized silicon carbide. Also, the dimensional stability of nanocomposite is greater than conventional aluminum composites. The aluminum alloy with silicon is majorly applied in the automotive sector. The characteristics of the alloy are high corrosion resistance and excellent castability. The mechanical properties of the aluminium alloys are increased through heat treatment, especially the T6 heat treatment. Conclusion In certain forms of engines, the master connecting rods are applied instead of the simple type. The master rod has several ring pins which are used for bolting the smaller ends of slave rods. Radial engines usually have, in one of the cylinders, a master rod; and several slave rods in the other cylinders of the same bank. Other connecting rod types include; forked connecting rod and compound rod. Bibliography 1. White, L. (2002). Medieval Technology and Social Change, Oxford: Clarendon Press. 2. Ashby, M. et al. (2002). An introduction to microstructures, processing and design. London: Butterworth-Heinemann. 3. Degarmo, E. et al. (2003). Materials and Processes in Manufacturing. NY: Wiley. 4. Smith, F. & Hashemi, J. (2006). Foundations of Materials Science and Engineering. NJ: McGraw-Hill. 5. Duncan, B. (1991).The Economic History of Steelmaking, 1867–1939: A Study in Competition. Cambridge: Cambridge University Press. 6. George, L. eta al. (2000). Abrasion-Resistant Cast Iron Handbook, ASM International. 7. Shingo, S. (1995). A Revolution in Manufacturing: The SMED System. 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