DREAMS Remanufacturing case study (20%)

CASE INFORMATION:

DREAMS Remanufacturing is an end-of life remanufacturing facility for scrap cars. Vehicles are bought in

on trucks and the scrap cars are dismantled, bodies and engines are pressed into blocks of steel ready to

be taken away to another facility owned by the company where the blocks are melted and rolled into

sheet steel.

Trucks arrive at the DREAMS company main gates at an observed rate of every 10 minutes; analysis has

shown that the arrival distribution of the trucks is exponential. On average 55% of trucks arrive

individually, 25% arrive 2 at a time and 20% arrive 3 at a time. Analysis has also shown that 65% of

arrivals are for unloading scrap cars and 35% for loading scrap blocks. Two loading bays are used to load

and unload trucks. Each bay can take only a single truck at any one time. Bay 1 is for unloading trucks

with vehicles on board, Bay 2 is for loading empty trucks with steel blocks. The bays are not

interchangeable. Loading and unloading each take an average of 25 minutes (distributed exponentially).

After a truck has been unloaded it joins the queue for loading.

Once a truck has been loaded with steel blocks it must go to a weigh station to ensure that the laden

weight of the trucks does not exceed the maximum permissible weight limit. At the weigh station the

laden weight is checked, and this takes exactly 12 minutes. This is done automatically and does not

require a staff team. The laden weight follows a uniform distribution, with a lower limit of 7 tons and an

upper limit of 12.5 tons. Each loaded truck should not exceed 10.5 tons total weight. If a truck is

overweight it must have excess weight removed. This takes exactly 12 minutes. Each truck must then be

reweighed. A truck that has been lightened weighs exactly 9.5 tons. There are two staff teams, each

with six members. They are needed for loading, unloading, and load lightening. Loading takes priority

over anything else. Lightening the load takes least priority.

All queues are on a FIFO basis unless otherwise stated. Assume no staff breaks. Assume no changes of

shift. It is a 24 hour operation and you should run it for 2 weeks. Tip: use Simple Unit Count From Zero

when setting the Clock.

REQUIREMENTS:

1. build a model of the system as it exists, save the solution in a file called DREAMS A1 Model,

2. Study the above DREAMS Case Study and be prepared to be asked about it in the test and/or

presentation. This will include specific implementation or general opinion questions such as

a. how to put into effect a priority in a queue

b. or general improvement questions for the DREAMS Model as queried bellow

3. Using the existing model as your starting point:

a. Try to improve throughput and resource use by changing the priorities of the work

centers. Analyze & understand this model and save your new model as DREAMS A2

Model

b. Try to improve throughput and resource use by changing the use of the loading and

unloading bays so that each bay can both load and unload. Analyze & understand this

model and save it in the CD as DREAMS A3 Model (note Loading and unloading each

take an average of 25 minutes exponentially; although on the same bay, but they must

take each 25 minutes separately). Did you manage to model it? Have you used only one

work center per bay or more?

Remember: One work center can only process one work item at a time

4. The above changes are about trying to obtain improvements to the process that are effectively

cost-free. Consider other possible improvements that may have a cost, such as improvements to

the capital equipment or technology. For example, could Weigh be done as part of another

activity? If yes, where might it be done? What would incur cost?

5. Try to improve throughput and resource use by changing the use of the loading and unloading

bays so that each bay can both load and unload. Save it as DREAMS A4 Model. Analyze,

interpret and justify your conclusions.

6. The above changes are about trying to obtain improvements to the process that are effectively

cost-free. Consider other possible improvements that may have a cost, such as improvements to

the capital equipment or technology. For example, could Weigh be done as part of another

activity? If yes, where might it be done? What would incur cost? Write an appropriate analysis

of this and justify your conclusions.

All the best and Good Luck.

Dr. Mossab Al Hunaity