Description

DISCRETE EVENT SIMULATION 

Coursework Assignment Create the model and optimise the profit for the plant described in the following. You need to simulate ten days operation after an appropriate warm-up period

Description 

A manufacturing plant that produces gearboxes has to be designed and optimized. Each gearbox is composed 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 time distribution defined in the excel file supplied. The conveyor is of a belt type, and gears have a footprint of 80 by 80 by 100 mm, and can be spaced on the conveyor 100 mm apart. The maximum capacity of the 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) and unloads them to a bin (maximum capacity 50). Unloading takes 0.5 to 0.9 minutes and the machining cycle takes 2.3 minutes. Every 20th machined casting is not loaded to the bin, but to an inspection station. 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 the operator(s). Previous tests have shown that after 20 samples inspected there is a 78% chance that the critical dimensions (bores for bearings) are at the upper tolerance limit. When this occurs, the tools in the CNC workstation are replaced and the machine is cleaned. The operation time is triangularly distributed with a minimum of 2.5, maximum of 3.7, and mode of 3.2 minutes. The failed gearbox is scrapped.

The gearbox assembly process is manually performed by an operator. Bearings are assumed to be always 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 a buffer for testing.

A testbench runs the gearboxes for 10 minutes and can initially take up to five at a time. An operator loads and unloads them to the test points. Loading and unloading both take from 0.2 to 0.4 minutes for each gearbox. There is a 93% chance of passing the gearbox for shipping, while the failed gearboxes are sent directly to a disassembly station where an operator will remove the gears and put them back on the conveyor 5 m from its end. The gearbox castings and bearings are instead discarded. Disassembly takes a mean of 2.3 minutes, with a standard deviation of 0.4, but no less than 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 Budget The company has already purchased the CNC workstation for £72K. The CNC workstation needs to be repaid in three years. The plant operates on a eight-hour shift. Operators have 15 minute break in the morning and afternoon, and one hour for lunch.