Assembly Automation and Product Design - Essay Example

Case study for plug A13 1. Thesis statement Plug A 13common plug used is the most common plug used in united Kingdom. This plug is used in over fifty countries most of which have standards based on BS 1363.1 1. Introduction The plug A 13, also called a thirteen amperes plug has three rectangular pins forming an isosceles triangle. The plug has a fuse to protect appliances from damage due to overload. The three pins are categorised as earth, live and neutral. 2. Body 1 Performance and material selection The 13A plug is specially designed to ensure that all the functional requirements of the plug are okay. The functional requirements of the plug are the electrical functioning, the mechanical function, the aesthetic function and ergonomic function. The electrical function refers to the plugs ability to properly conduct current from the socket to the electrical device in a safe and proper manner. The mechanical function refers to the sockets ability to withstand all the forces required for safe installation of the plug into the socket. Mechanical function also includes the proper design of the plug so as to safely clip into the socket and be safely held and removed from the socket. Aesthetic function refers to the ability of the socket to have appealing features to the customer. Ergonomic function refers to the sockets ability to withstand fatigue due to continual use.2 The 13A pin is made of the following components. Conductors are the three pins; they are made of brass. Fuse element made of copper. Fuse clip made of copper, cable wires made of copper and fuse ends made of copper. The insulators are the plug body and base made of plastic. The cord clip made of nylon, Cable sheath made of PVC (polyvinylchloride) wire sheath and pin sheath made of PVC. Fuse body made of alumina. The pin has screws for firmly holding together all the parts. The cord grip screw is made of steel, the major plug screw is made of steel and the pin screw is made of steel or brass.3 In the process of material selection the engineer should consider the materials are the best conductors and those that are the best insulators. The engineer should consider the price and the ease of moulding and accessing the materials. Polymers can be shaped into the desired shape of the plug through moulding. This can be easily done for mass production. Wood can only be machined; this method is ineffective for mass production. Thermoplastics have various options for mass production such as welding, use of adhesives and moulding. Therefore, even though wood provides the cheapest source of raw materials, it is difficult to use it in mass production. The plug body should be strong and stiff so as to hold the pins safely. Through a material selection process an engineer is able to select the most suitable polymer to use. The strength of polymers is lower compared to that of other materials. However, with proper design, the polymers are able to be strong enough to support the pins. ABS and urea formaldehyde are the most commonly used polymers. Nylon is stronger than ABS and formaldehyde; however, it is very expensive. ABS is used for single piece plugs because thermoplastics can be easily joined after moulding. ABS is tough and best for plugs which might suffer repetitive impacts. Urea formaldehyde is tougher than ABS and is ideal for two piece construction. Urea formaldehyde should only be used for plugs where the appliance is unlikely to have impacts. When selecting the materials to use for the pin the engineer should consider the strength, the ability to conduct and the cost of materials used. There is a risk of overheating when a high resistance material is used- current is I2R. This might cause fire. The materials used in the pin must be firm because a lot of force is used when inserting and removing the pin from the socket. The plug must be affordable, therefore, low cost materials will be used. The most common materials that have low resistance are gold, aluminium, brass and copper. Gold is too expensive for use in a socket. Aluminium forms an oxide covering over it and therefore inappropriate for a socket. Between brass and copper, brass is the best option because it is stronger than copper. Higher strengths in copper can only be achieved through cold working which is expensive.4 Body II The engineer should consider the most appropriate method to use with brass is. There are various methods available for metal shaping such as sand casting, die casting, low wax casting, powder metal forming, forging, sheet forming, rolling, metal extrusion, milling, grinding, drilling, cutting, fasteners, solder/braze, welding and adhesive joining. The size and shape of the metal provide an appropriate indicator on the most appropriate method. The size and shape, the finish and quality of the final product will provide the engineer with the most appropriate method. Rolling is not suitable for the pin because of the pin’s size. The strength and quality of a material depend on how it is made. Casting would affect the quality of the brass. This is both the resistance and the strength. Joining is not suitable for the brass pin. Therefore fasteners, solder/braze, welding and adhesive joining are not appropriate. Other factors to consider are drilling to be done on the brass pin. 3. Body III Eco-Audit Machining is not an appropriate process for making pins. It is very expensive especially where there is bulk manufacturing of pins. When factoring the strength of the material and cost of manufacture forging or extrusion are the most appropriate process. Forging and extrusion provide near perfect pins. They however require going a further post-processing step to make holes and threads for the pin. The cost involved in further processing is not significant. When considering the method to select between forging or extrusion and engineer should consider the total cost. When calculating the cost for forging, the engineer should consider the start up cost, the hourly cost and the production rate. The sum of the start up cost and hourly cost share of the pin gives the total cost for the pin. To calculate the total cost for each brass pin the engineer should divide the hourly cost by the number of parts manufactured per hour. The start up cost should also be divided by the number of parts manufactured per hour. This would give each pin its share of the start up cost. The start up cost continuously decreases with the number of pins manufactured per hour. The cost to manufacture a pin per hour is the sum of share of the pin start up cost plus the share of the pin hourly cost. When calculating the cost for extrusion, the engineer should consider the start up cost, the hourly cost and the production rate. The sum of the start up cost and hourly cost share of the pin gives the total cost for the pin. To calculate the total cost for each brass pin the engineer should divide the hourly cost by the number of parts manufactured per hour. The start up cost should also be divided by the number of parts manufactured per hour. This would give each pin its share of the start up cost. The start up cost continuously decreases with the number of pins manufactured per hour. The cost to manufacture a pin per hour is the sum of share of the pin start up cost plus the share of the pin hourly cost. It has been found that either the forging or the extrusion method is best depending on the productivity level of the company. The engineer should select the best method depending on the volume of brass pins that he wants to produce. Other factors such as the cost of machinery, presence of machine operators and training costs will influence the operator on which method to select between forging and extrusion. 4. Conclusion There are still other factors that an engineer should consider when manufacturing the 13A plug. The quality of the plug such as strength, fire-resistance and materials used is governed by the UK Standards BS1363. 5 Bibliography  DWM Latimer. History of 13 amp plug and the ring circuit, 2007. 2 Geoffrey Boothroyd. Assembly Automation and Product Design, second edition, 2013. 3 Peacock David. The remarkable Evolution of BS 1363. 2013 4 Mullins, Malcolm. The Origin of BS 1363 Plug and Socket-Outlet Systems, 2006 5 ASTA Standards, 2014 Read More