DISCRETE EVENT SIMULATIONCoursework AssignmentCreate the model and optimise the profit for the plant described in the following. You need to simulateten days operation after an appropriate warm-up period.DescriptionA manufacturing plant that produces gearboxes has to be designed and optimized. Each gearbox iscomposed of the following components: two gears, two bearings, and one casting.Gears are manufactured in a separate plant and arrive via a 20 m conveyor belt, according to a timedistribution defined in the excel file supplied. The conveyor is of a belt type, and gears have a footprintof 80 by 80 by 100 mm, and can be spaced on the conveyor 100 mm apart. The maximum capacity ofthe conveyor is 180 parts, and the speed is 5 m/min.Castings are drawn from stock and loaded to a CNC workstation for additional machining and boring.An operator loads each casting to the workstation (loading operation takes 0.5 to 1 minutes) andunloads them to a bin (maximum capacity 50). Unloading takes 0.5 to 0.9 minutes and the machiningcycle takes 2.3 minutes. Every 20th machined casting is not loaded to the bin, but to an inspectionstation. The inspection operation cycle time is triangularly distributed with a minimum of 0.8 minutes,a maximum of 2.2 minute, and a mode of 1.1 minutes. The inspection is manually carried out by theoperator(s). Previous tests have shown that after 20 samples inspected there is a 78% chance thatthe critical dimensions (bores for bearings) are at the upper tolerance limit. When this occurs, thetools in the CNC workstation are replaced and the machine is cleaned. The operation time istriangularly distributed with a minimum of 2.5, maximum of 3.7, and mode of 3.2 minutes. The failedgearbox is scrapped.The gearbox assembly process is manually performed by an operator. Bearings are assumed to bealways available. The process takes a mean of 3 minutes with a standard deviation of 0.7 minutes,but no less than 2.2 minutes and no more than 5 minutes. Each assembled gearbox is put into abuffer for testing.A testbench runs the gearboxes for 10 minutes and can initially take up to five at a time. An operatorloads and unloads them to the test points. Loading and unloading both take from 0.2 to 0.4 minutesfor each gearbox. There is a 93% chance of passing the gearbox for shipping, while the failedgearboxes are sent directly to a disassembly station where an operator will remove the gears and putthem back on the conveyor 5 m from its end. The gearbox castings and bearings are insteaddiscarded. Disassembly takes a mean of 2.3 minutes, with a standard deviation of 0.4, but no lessthan 1.7 minutes and no more than 3.5 minutes.The plant is staffed by a number of operators (to be decided) who are trained in all activities.Costs and BudgetThe company has already purchased the CNC workstation for £72K. The CNC workstation needs tobe repaid in three years. The plant operates on a eight-hour shift. Operators have 15 minute break inthe morning and afternoon, and one hour for lunch.Additionally, you have a budget of £15K to set up the remainder of the plant. This expenditure mustbe repaid within one year.Costs
Assembly tations with appropriate tooling: Bins for machined gearboxes: Text bench space per gearbox: Fixed cost for hiring an operator (advertising, training, etc …): Operator hourly rate including on-costs: £1800£200£2200£1500£15.60
TaskOptimise the plant to achieve maximum profit within the allotted budget. You may need to optimisethe plant for the priorities of the machines first. The expected profit for each completed and workinggearbox is £80.Investigate what effect a breakdown of the CNC workstation and the conveyor belt for 90 minutes hason the daily production rate.Write a report describing your model and present results on a series of tests on the model. In yourconclusions, present an evaluation of the model in the light of all the assumptions made and whatlimitations they place on the model. The report must be in the form of a standard technical report orarticle and should include:AbstractIntroductionThis should include some explanation of stochastic modelling and methods and tools available tocarry out discrete-event simulation to form a literature review. For example, you might want to discusssoftware packages other than Witness and techniques such as Petri Net models.You should also introduce the problem by a description of the plant; the use of a block diagram mayhelp.MethodsDescribe your modelling technique and the structure of the Witness model. Justify your approaches tobuilding the model and include any relevant references. Describe the approach to optimisation anddescribe all equations or functions used.ResultsPresent the results of the optimisation(s) and experiments and the expected daily and hourlyproduction and profit from the plant.DiscussionDiscuss the model, its performance and implications on the real system. Discuss and evaluate thelimitations of the model.ConclusionsProvide some conclusions in a form that will advise the company management on the feasibility andexpected returns for the plant.The report will be submitted to UniHub as a PDF or WORD document, with a copy of your model andoptimisation / experimentation files. The report will be submitted to a Turnitin dropbox and the modeland other files to a separate dropbox. Assessment will be based on your research, the explanation ofthe model generation, description of the experimentation / optimisation, the presentation of resultsand conclusions. An element of assessment will be for a sensible and logical graphical presentation ofthe model in Witness.
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