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Sheffield Hallam UniversityFoundation Integrated Mechanical EngineeringJoe Jopling10/1/2018Manufacturing ProcessesAssignment 1Contents   Introduction                                                                                                                           Page 2Detailed assessment of a Glass Bulb (materials and processes.)                              page 2-3Detailed assessment of the Bulbs Filament (materials and processes.)                      page 3      Detailed assessment of the bayonet (materials and processes.)                          page 3-4-5 The glass bulb production process                                                                                 page 6-7The bulbs filament production process                                                                         page 8-9 The bulbs bayonet production process                                                                     page 10-11 Cost of manufacturing the bayonet                                                                           page 12-16  Conclusion page                                                                                                                            16   Photo from ‘’IntroductionUsed in everyday life a glass bulb is one of the most important and most used engineering inventions in the world. This means that there are constant evaluations on what are the best production methods and the best materials to use when creating a light bulb. This report will go into detail all ideas when considering the best way to create a light bulb that. It will show what is the best material and process for each part of a light bulb. And will concluded the best way to create and mass produce a light bulb that meets the given specification for the cheapest cost.  Detailed assessment of the glass bulb The glass bulb itself requires several key features to be used for its proper functions. the 2 key features in the glass bulb are being heat resistant (or have a high melting point) and transparent, as well as these 2 features one more thing that could be important in the glass bulb part of a light bulb is that it is light weight. Therefore, the specification states that the glass bulb thickness should be no more that 0.51-1.14mm thick. Finally, the glass bulb must be able to last the hole lifetime of the bulb so it must not melt or deteriorate.       Some of the different materials to be looked at include plastics; thermoplastics and thermosetting plastics, metals and glass. After reviewing all types of materials, you can rule out the   following;Metals, can be taken away since they are not transparent, and they also conduct heat well, meaning the bulb its self would get very hot. as well as this most metals are quite heavy meaning that they do not fit any of the 3 required groups. Thermosetting plastics, such as PVC can be transparent and also, they are light weight. They have 2 of the 3 features that we are looking for however they are easily melted by heat meaning that when the light gets hot the bulb may melt. This also makes this an impractical material.  Thermoplastics, are highly transparent and light weight, however they can start to melt at 140°c and a normal light bulb can achieve temperatures much higher than this meaning that the shape of the light bulb could be deformed when the bulb gets hot.Glass, finally glass is a transparent and light material the has a high melting point (1538°c) also glass can be easily shaped into the correct shape for the light bulb. Glass is not totally heat resistant however its high melting point means that It will not deform. There are 2 main process in the production of glass these include using the ribbon production and also another production that could be used is glass blowing however this process is a lot more expensive, requires more man power and as well as this the production time for each light bulb would be much slower as it would take 2 people to make one. And they would have to make them on at a time, as supposed to the 50000 bulbs an hour that the ribbon method is capable of.        This concludes that in my opinion the best way to create a glass bulb is with glass as it is light weight and can be thin enough to reach the specification also it is resistant to the heat the filament wand gases will give off as well as this it is transparent and easy to make lots of In short amount of time meaning that the demand for the bulbs is easy to reach.Detailed assessment of the bulbs filamentThe filament in the bulb also requires some key features including the need for it to be able to operate in a high temperature range (2000-3300K) and the dimensions need to be fairly specific such, the filament must have a length of approximately 580mm and a diameter of just 0.046mm this means that such a small material must be able to cope with such a large amount of heat without deforming, braking or melting.        There are many alternatives to look at when deciding what material to use for the filament of a bulb, these include many metals such as aluminium, copper, lead, gold and many more but when looking back at the specification we realise that not all of these materials can comfortably hand the high temperatures, and also be strong enough not to brake with such a small diameter. One metal that does fit all this specification however is tungsten which Is why this is the material to be use.       The first option available when manufacturing tungsten light filaments is to draw it. This is where it is mixed with a binder material and put through a die into a fine wire, after this the second part of the process involves pressing the ends of the filament. This is lead is a good conductor and it also will stop the filament coming apart.       Another process that could be used to create filaments could be machining it with a milling machine, However the size of the filament would cause problems for this method as it would be a very fiddly job for the worker.       In conclusion I am convinces that the best material to use when making a filament for the reasons described. I also believe that the best method of creating the filament in the light bulb would be to draw in and press lead onto the ends.    Detailed assessment of the bayonet      The final part that makes up the light bulb is the bayonet, this is the part that screws into the light bulb socket and conducts the electricity to the filament. There are plenty of properties for the bayonet as well. These include; having to contain conducting parts to allow electricity to travel between the wires and the filament, as well as this it needs to have an insulating material so that the wires do not short against each other. That fact that this is a structurally integral part to the bulb means that the chosen metal should be able cope with holding the whole bulb together. It must fit well into the 22mm diameter fitting. Finally, it must be able to with stand the high temperatures and have a perfect finish with no burrs.       Narrowing down the materials at first is easy as you can dis regard everything bar metals, plastics both thermoplastics and thermosetting plastics are not conductors meaning that they are not useful for the main bayonet. The only material that is can be used for this job, and the best metals to look at include copper, aluminium and steel. However a idea could be that the best material to use for the outside part (screw part) may be stainless steel as it can withstand high pressures and hold a strong shape meaning that It would meet the structural specifications of the light bulb. Other metals such as copper could be to flimsy and steel would also not be good as it is not as strong as stainless, and it is a lot more prone to corrosion.       After finding the right material for the bayonet the correct insulating material can be looked at. This part of the bayonet cannot be a metal as metal are conductors meaning that a short circuit could possibly be formed. This would mean that the bulb would not work, and it is also a safety and fire hazard. All plastics however as rule are suitable in the way that they do not conduct electricity however some are still more practical than others. For example, plastic such as Polycaprolactone ( a biodegradable polyester) has a melting temperature of 60°C meaning that at the temperatures the bayonet is likely to get will melt the insulating material thus causing the bulb to short circuit. Another important factor to look at is that the material must be easy to be machined into the part of the bayonet, so a softer plastic would be beneficial. leaving us with one plastic. The elastomer, rubber. Rubber has all the features described as it has a high melting (minimum 260°C) and it is easily manufacturable into the bayonet. Therefore, rubber is the best suited plastic for this job.         Finally, the last material to look for in the bayonet is the wire/electrical conducting part that is covered by the insulating rubber. This must be a good conductor. Therefore, copper is the best material to use for this part. This is since it has an exceptionally high current transporting rate meaning that it more efficient than any other the other metals we could look art such as aluminium, steel or stainless. Plastics were ruled out again for this material since they are not conductors of electricity.      There are several different ways that a bayonet can be produced. The first way that a bayonet can be produced is sheet forming. The problem however is that sheet forming has a high capital cost and a high tooling cost, another good manufacturing process is die casting. Die casting has both a cheaper capital cost and tooling cost. However, a point to be made against die casting is that it has a much lower production rate compare to sheet forming. Following the 2 previous methods, a third method that can be used is sand casting. On the other hand, sand casting has a very slow production rate being that it is not suitable for mass production. Therefor the best method after reviewing these 3 processes must be sheet casting as it is the easiest to use for mass production although the initial cost may be more expensive.       In conclusion a bayonet should be made of a stainless body, rubber insultation for the connecting wire to the bulb copper would be the best material. Along with this the best manufacturing process for this final part of the light bulb should be sheet forming as it is the easiest for mass production. The glass bulb production process       The process of making the glass bulbs has several steps throughout the production the first of which is being heated in a furnace the glass, In the form of a constant ribbon, is then transported to the production line to a series of air nozzles perfectly positioned so that the glass is blown through holes in the conveyor belt into certain positions inside a mould this is the way the castings are created. This also the most effective process as a ribbon machine working a high speed could create over 50,000 blubs an hour. Picture showing a glass ribbon machine   Picture from the corning museum of glass The filament production process      The filament in a light bulb is created by using the drawing method, where the tungsten used in the filament is first mixed with a binder material, it is then pulled through a die at the bottom of the container, this pulls it into a fine wire. After that it is wrapped around a mandrel to make it form into the shape that it needs to be. Next the filament goes through an annealing process (this is where it is heated to soften the filament). Finally, It is placed in acid to dissolve the mandrel.Picture showing the drawing process Picture taken from: The bayonet production processThe bayonet is produced by a method called sheet forming, this is where sheets of metal are formed into different shapes, in this instance a light bulb bayonet. For this process 2 arms bend the sheet around die. The two edges of the bayonet are the welded together and it is then pulled through a die to tap it.          Looking at cost of manufacture    When considering the difference in price with different methods another variable that needs to be added to the equation is the batch size. If you are going produce something in small batches there is a chance that there may be a cheaper method that a process you might use in a bigger batch size. To prove this, you need to do the calculations as follows; First you need to work out the capital cost. To do this you divide the capital cost outlay (c capital) by the load time and cost write off time (in hours). The equation looks like the following… C capital L x t The best way to do this is by using a excel spread sheet with the table on as you can see below. now as an example you can see the calculation on excel for the capital cost of sheet forming.  Here it is apparent that if looking back at the table I8 is C Capital, i6 is load factor and 87600 is 10 years in hours (the write off time). Once that you have found the capital cost you can then put the main equation in to show the price of making one item. And then by just changing the number in the batch size column you can look at the cost of manufacture for a variety of different batches. The calculation to work this out is…   This also is shown in the spread sheet…   Here it is shown that that I3 is the material cost, I7 is the tooling cost, I10 is the batch size, K13 is the capital cost (calculated earlier), I9 is production rate and finally I4 is overheads.      A good selection of batch sizes needs to be used to properly show the fall in price, as shown in the table below  9The table shows how the fall in price alters between the rise in batch size and how once you get to a certain point the process does not get much cheaper for the higher batch sizes, for example the difference between a batch size of 1 and batch size of 10 is nearly £20000 whereas the difference between a batch size of 50000 and 1000000 is just 2p.  After doing the calculations and making the tables for the 3 processes being looked at (sand casting, die casting and sheet forming) a table can be made to compare the data of all there. The data in a table is shown on the next page.     Looking at the table the prices falls for each process can be assessed against each other. As seen in the table sheet forming is the most expensive when there is just one being made in the batch. However, it is the cheapest when there is 1000000 being made.      Another way to display this data is in graphs, below are some graphs showing different areas of the table   This is the original graph with all the data inputted. When this graph is viewed the price drop is so great at the begging it means that there is not much data shown on the graph. So here are some important sections of the graph;     The first of the 2 graphs shows the price dropping to similar point on all 3, and the second one shows that the cross over points of all three, in interesting thing that these graphs how is that all 3 of the process cost around the same price when the batch size is 1000. Sheet forming however then continues to fall a steep gradient meaning that it becomes cheaper than sand casting at around 2000 and eventually at around 4500 it becomes cheaper than die casting also.  Conclusion      In conclusion, the evidence I have just review argues both for and against the earlier conclusion of sheet forming being the best method. Upon reflection we can see when one of each of the processes is the cheapest one to use and when each of the processes are uneconomical. If you require a batch size of 2000 or less the best method to use would in fact be sand casting, if you needed a batch size of between 2000 and 4500 then die casting would be the cheapest, however if you needed a batch size of more than 4500 sheet forming is the most economical. 


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