A piston is manufactured mostly using cast aluminium alloys. Rings are made using either cast iron or stainless steel. The manufacturing process depends on the intended application of the piston. The most common process is through casting. Typically, casting process involves pouring molten metal into a mould with a design of the desired shape of the product (McNish, 2018). The first step is known as the foundry and involves heating aluminium ingots until it melts, and then the molten metal is directed into a hydraulic mould. From there a ladle is used to scoop it up from the crucible and finally allowed to cool. The next step involves a vertical milling machine to dehorn the pistons and then they are placed in an oven for hardening (McNish, 2018). A lathe machine is used to remove rough edges and to smoothen to the required degree through a turning operation. The third stage involves creating grooves for fitting the rings, making bore diameter, and finishing both the skirt and the crown. The third stage is best accomplished using a CNC lathe machine. Finally, the pin bore and oil slots are made using a VMC machining. Cam grinding completes the process.
Reasons
Piston operates in high temperature and pressure conditions, and constant static and dynamic forces. For piston to work effectively, they must have high strength and heat resistance to counter inertia forces and gas pressure. Also, it should have lightweight to reduce inertia forces and rigid construction to prevent mechanical and thermal distortions. The casting process is the most preferred manufacturing process of pistons because aluminium which is lightweight can be used as raw materials, it is easy, and fast compared to other methods (McNish, 2018). Also, it is possible to use other materials or alloys to improve its properties. In comparison to forging, casting is low cost and thus best suited for mass production (Giesko, Smolik " Zbrowski, 2015). Besides, using this process, it is possible to achieve complex geometry as a strategy for weight reduction. However, the initial tooling cost is high and a possibility of compromising strength during cooling.
Task B
Machining Process
Mechanical Properties. The cylinder head made from machining has excellent heat dissipation, high strength and toughness, high tensile strength and ductility. High toughness and fatigue strength are impacted during the forging process due to the grain flow pattern during the process of forging. However, machining interrupts the continuous flow of grains and can result in reduced strength.
Fitness for Purpose. The machining process is suitable in the production of cylinder heads because it is fast especially with advanced machinery that can be automated. Also, operations can be computerized necessitating complex geometry to be possible.
Surface Finish. The surface finish depends on the size of feed and the cutting tool used. Small feeds produce a very fine surface finish. Also, the process usually produces burrs and sharp edges which require additional work to remove. Emir cloth and sandpapers are used to produce a finer fish.
Production Volumes. Machining involves many steps in production which can hinder the speed of production, especially when done manually. When machining uses CNC machines, the process can be automated making it suitable for mass production.
Health and Safety. Machines used in operation move very fast and can cause serious physical injuries. Also, the burrs and chips can be dangerous to nearby persons.
Powder Metallurgy
Mechanical Properties. The properties of connecting rod made from PM are superior due to the directionality of the sintering process. It also has a greater homogeneity regarding composition and a finer microstructure (Tan, 2012). Also, it has a less internal discontinuity in comparison with forging process due to ingot defects. However, the connecting rod has less strength and fracture toughness may be low.
Fitness for Purpose. PM result in high dimension accuracy as a result of less machining requirement and the process is highly controlled, leading to close to dimension parts. Also, it offers higher dynamic properties through self-lubricating properties, necessary in smooth running in the engine.
Surface Finish. The process of manufacturing connecting rod using PM uses the sintering process, and the surfaces produced have good finishing, which requires less work for perfection purposes and glowing. It results in fewer burrs formation, thus less machining work during the finishing operation.
Production Volumes. PM is highly suited for moderate and high mass production since it reduces the number of steps in production compared to the traditional method like forging. It is preferred when the number of parts is about 100,000 and above. Thus it more economical provided the high initial cost.
Health and Safety. PM uses fine powders that pose a health hazard to the workers and operator.
Injection Moulding
Mechanical Properties. The intake manifold produced using injection moulding is made from polyphthalamide and reinforced with resin. The mechanical properties exhibited by these parts are high stiffness, high strength, and excellent resistance to chemical action. Also, it is a good insulator, low moisture absorption, and a wide range of heat resistance.
Fitness for Purpose. Intake manifold made from injection moulding is lightweight since most of the material is reinforced plastic. Also, the walls are smooth, and no additional work is required for finishing. The injection moulding process allows mixing of materials thus it is possible to improve mechanical properties to the desired level and aesthetics. The process also is affordable, and faster.
Surface Finish. The product from injection moulding is smooth enough and does not require additional machining.
Production Volumes. Injection moulding is suited for continuous production, and the process can be semi or fully automated to increase the output.
Health and Safety. Melting of plastic and additives used in the injection moulding emits toxic fumes, which are detrimental to the operators and other nearby workers. Occupation asthma is a significant problem in the plastic industry. Also, it involves heating of the material at high temperature, which can be hazardous to immediate persons. The process also produces huge noises which can affect hearing capability.
Task C
Connecting rods are made mainly using conventional forging and then machined to desired size and surface finish. However, the powder metallurgy (PM) process is gaining popularity in many automobile industries. A connecting rod made through traditional drop forging, specifically using wrought iron is more superior in fatigue performance, having 37KN compared to 32KN when using PM (Singh, Ramakrishna, " Singh, 2017). Compacted powder in PM process results in reduced cross-sectional than when it is drop forged. Also, the tensile strength in connecting rods is higher by 19% in wrought forged than those manufactured using PM. The weight comparison also indicates conventional machined connecting rods are lighter by 25% compared to those made by PM (Wills, 2014). Comparatively, the initial cost of using the conventional method is lower to that of powder metallurgy that required advanced equipment and tooling. Traditional machining methods can make complex geometry shapes and high range in sizes, but this is limited in metallurgy technique. Also, powder metallurgy causes health-related complication to the workers due to the very fine-powder used in the process, which can be avoided in conventional machining processes.
One of the limitations of making connecting rods using conventional process resulting in the production of excess waste compared to when using powder metallurgy material utilisation is high, utilise approximately 97% of the raw material (Wills, 2014). The surface finishes when using conventional method requires further processes for proper finishing, but metal metallurgy results in the excellent surface finish because of fewer burrs. Conventional machining uses many operational steps thus limited number of items that can be produced. Powder forged, on the other hand, reduces the number of steps considerable, therefore support moderate to high mass production of parts (Wills, 2014). Also, conventional machining is limited on the material used, but metallurgy offers greater material flexibility such that the connecting rods mechanical properties can be improved through blending (Singh, Ramakrishna, " Singh, 2017). Weight fluctuations are also minimum in powder forged connecting rods than in conventional methods, thus easy replacement of parts.
References
Giesko, T., Smolik, J., " Zbrowski, A. (2015). Advances in Manufacturing Engineering. Zurich: Trans Tech Publishers.
McNish, T. (2018). Piston Manufacturing Process. Retrieved from https://itstillruns.com/piston-manufacturing-process-5502005.html
Nee, A. Y. (Ed.). (2015). Handbook of manufacturing engineering and technology. Springer Reference.
Singh, S., Ramakrishna, S., " Singh, R. (2017). Material issues in additive manufacturing: A review. Journal of Manufacturing Processes, 25, 185-200.
Tan, H. (2012). Mechanical properties of materials and information technology. Durnten-Zurich, Switzerland: Trans Tech Publications.
Wills, A. (2014). How Metallurgical Structure Affects the Machinability of Aluminum. Retrieved from https://www.productionmachining.com/articles/how-metallurgical-structure-affects-the-machinability-of-aluminum
