Service Requirements for an Automotive Crankshaft - Term Paper Example

Materials and Manufacturing Selection Analysis Materials and Manufacturing Selection Analysis Automotive Crankshaft Section 1: Functions and Service Requirements of an Automotive Crankshaft Functions of an automotive crankshaft The crankshaft is the part of a car engine that converts the up and down movements of the pistons into horizontal rotation. The shaft is a single piece that is made of cast iron or forged steel. Oil passages are cast or drilled into the crankshaft to distribute lubricant to the main end rod journals. The crankshaft is a link between the piston and the drive wheels that is located in the bottom end of the engine. It holds the huge forces produced by the explosions in the combustion chamber. The snout which is the front end of the crankshaft turns the turning gear to drive the camshaft. This turns the drive pulley that runs a belt that is connected to the flywheel that allows the starter motor to rotate the crankshaft. The resulting forces caused by the ignition of the spark plugs force the pistons to move downward with a huge force. The crankshaft changes this up and down motion of the pistons into a rotating motion. This is made possible when the connecting rods attached to the pistons connect to the crankshaft so that they go up and down their angle changes (Crankshaft Forming, 2005). Service Requirements for an Automotive Crankshaft An automotive crankshaft goes through a large number of load cycles during its service life in a car engine, fatigue performance and durability is a key consideration in its manufacture. It is important to manufacture a less expensive crankshaft with the least weight possible and the right fatigue strength. This will result in a lighter and smaller engine with better fuel efficiency and higher power output. The crankshaft must have enormous strength and made of material that are hard. The crankshaft will be made of medium-carbon steel alloys and alloying elements combinations. Specific service requirements must be in the mixture used and include surface and core hardness, nitridability, hardenability, ultimate tensile strength, temper-embrittlement resistance, corrosion resistance, impact resistance, yield strength, ductility and endurance limit. Titanium, aluminum, vanadium, cobalt, silicon, nickel, molybdenum, chromium and manganese are the alloying elements capable of producing these properties. The carbon content in these elements determines the hardness and the ultimate strength, and is used in making the crankshaft (Fatemi & Williams, 2007). Crankshaft Section 2: Material Requirements and Selection Material Requirements The crankshaft is made of steel alloys whose combination of properties will ensure ultra strength and hardness of the crankshaft. Iron and a little percentage of carbon, about 0.45%, are found in the medium-carbon steel alloys. This is combined with other alloying elements that produce a mixture that produce a specific alloy that is suitable to the manufacture of the crankshaft. The mixture needs to have enormous tensile strength, hardenability, corrosion resistance, impact resistance, ductility and an endurance limit or what is called fatigue strength. The alloying elements that can produce this type of mixture are titanium, aluminum, vanadium, cobalt, silicon, nickel, molybdenum, chromium and manganese. Specific properties will be added by each to the required material. The main determinant of the hardness and ultimate strength is the carbon content, which helps in heat treating the alloy (Fatemi & Williams, 2007). High strength steels are refined to remove undesirable impurities such as sulfur, phosphorous to increase the tolerance of the material. Other steels that are ultra-high-strength are known as “maraging” steels can be refined to remove as much carbon as possible in order to develop fatigue properties and extreme strengths. A high performance crankshaft will require a nickel-chrome-molly alloy which is used due to its good ductility, fatigue and high strength properties and good impact resistance. A nominal 40 points mainly of carbon is contained in it, and is often described as the standard for ultra strength alloys (Fatemi & Williams, 2007). A crankshaft is made of cast iron or forged steel. The difference between iron and steel is in the percentage of carbon contained. Those containing less than 2% carbon are known as steels and those with more than 2% are known as pig iron. The iron is processed further to reduce the carbon content to obtain steel. The properties of iron are that it is ductile, malleable, has a very high tensile strength and is very workable. This means it can easily be used to come up with a desired shape and thickness. It is one of the three naturally occurring elements. CES Material Selection The material selection for the manufacture of the automotive crankshaft will be done using the CES selector using a CES software. The selector is used to achieve reduction in costs of the components, enhances product performance and ensures high quality designs of the automotive crankshaft. Section 3: Manufacturing Route Selection Manufacturing Route Selection Carbon steel alloys that are medium are required for the manufacture of the crankshaft. Primary manufacturing processes fall into four categories. This include, machining, casting, forging and joining. The factors considered in choosing the manufacturing route are;- Quality. The crankshaft must meet certain specifications. The flexibility of the process required to produce the crankshaft in terms of shape, the materials and the finish. Costs of capital equipment and labor. The manufacturing route that will be used for the crankshaft is the forging process. Shaping or forming of bulk metal in between dies of the crankshaft is part of the forging process. There are normally two types of dies; open die for general or large numbers and a closed die that is for small and specific orders. A billet of a suitable size is heated using the appropriate temperature which is then pressed or pounded to come up with the desired shape of the crankshaft. The dies have the concave opposite shape form of the desired crankshaft. Crankshafts for motorsports vehicles are manufactured from a billet. These are fully machined from the billet of the selected medium steel alloys. This process provides the flexibility of the design required and allows for alterations to achieve the optimal service requirements (Kinaan, 2002). CES Process Selection Exercise This requires the results from the use of the CES software. Section 4: Manufacturing Route Manufacturing Route The manufacturing route that will be used for the crankshaft is the forging process. As earlier explained, shaping or forming of bulk metal in between dies of the crankshaft is part of the forging process. A billet crank is one of the strongest crankshafts manufactured. The manufacture process starts with a big heavy chunk of steel that goes through the manufacturing process. The billet crank will require more work than a forged crank due to the strength attained in the finished product. This is composed of iron and carbon, about 0.45%. This is in combination with other alloying metals such as manganese, chromium and nickel. The high strength steel is refined in order to remove any impurities such as sulfur, calcium and phosphorous that may reduce the strength of the metal. Highest quality steels are also used and these require a certain level of purity. The vacuum processing methods used are VIM (Vacuum Induction Melting) and VAR (Vacuum Arc Remelting). A billet of a suitable size is heated using the appropriate temperature which is then pressed or pounded into the most desired shape. The dies have the concave opposite shape form of the desired crankshaft. The main crankshafts are usually in most cases, fully machined from the billet of the selected medium steel alloys. This process provides the flexibility of the design required and allows for alterations to achieve the optimal service requirements. Manufacturing Process and Material Microstructure Crankshafts are manufactured using the forging process. The crankshafts are forged from a steel bas through roll forging or casting in ductile steel. The forging process is preferred due to the light weight and the capability of achieving more compact dimensions and better inherent dampening. Crankshafts that are cast are used for low output whereas forged crankshafts are normally used for more expensive outputs. The casting process is also used to manufacture crankshafts, however the forged method is preferred due to the poor mechanical and fatigue strength of a cast crankshaft. The solution to this the cast crankshaft has to be machined to get the desired accuracy, tolerance and finishing. High strength, ductility and fatigue strength are critical properties required from the crankshaft material and manufacturing process. The process selected has to ensure that these standards are achieved. Forged steel has significantly higher strength than ductile cast iron. The forged steel also has more ductility than the ductile cast iron. It is therefore the forging method is better then the casting method for the manufacture of the automotive crankshaft. References Crankshaft Forming, 2005. Metal Forming Virtual Simulation Lab. New York: John Wiley. Fatemi, A., & Williams, J., 2007. Fatigue Performance Evaluation of Forged Steel versus Ductile Cast Iron Crankshaft: A Comparative Study. New York: FIERF and American Iron and Steel Institute. Fatemi, A., & Williams, J., 2007. Fatigue Performance of Forged Steel and Ductile Cast Iron Crankshafts. SAE Technical Paper 2007-01-1001, SAE World Congress. Fatemi, A., & Williams, J., 2007. Dynamic Load and Stress Analysis of a Crankshaft. SAE Technical Paper 2007-01-0258, SAE World Congress. Kinaan, R., 2002. Inside the making of a SCAT crankshaft. NMRA. Read More