FROM A DIFFERENT PERSPECTIVE

And do you have the answer to Problem 6, Pete? asked Professor Grasso. Yes sir, | have the answer according to the textbook, but Im not sure I get it, replied Pete. You dont understand how to get the solution?

Oh, I understand the numbers, but I dont know what theyre good for. Where I work, nobody ever sequences anything. You dont have time to calculate things like slack and critical ratio. You do whats next in line or on top of the stack, unless you see a red tag on something that needs to be rushed through. Or maybe you run whats most like what youve just finished working on so the machine doesnt have to be changed. Or you run what can get done the fastest because when you produce more you get paid more.

Pete, it sounds to me like you are using sequencing rulesFCFS, highest priority, minimum setup, and SPT.

Pete hesitated. Maybe youre right, but theres still something that bothers me. If youre going to go to all the trouble to rearrange a stack of jobs, youd want more information than what were working with.

What do you mean?

J mean, theres no use rushing a job at one station to let it sit and wait at the next. Its like those maniacs who break their neck to pass you on the road, but they never get anywhere. A few minutes later youre right behind them at a stoplight.

I see.

You need some way of looking at the entire job, where its going next, what resources its going to use, if it has to be assembled with something else, things like that.

You've got a point, Pete. Why dont you give us a real example we can work with? You talk, I'll write it on the board.

Pete talked for about 10 more minutes, and when he was finished, Professor Grasso had the following diagram on the board:

Okay, class, lets take this home and work on it. A, B, C, and D are products that comprise a customers order. They must all be completed before the order can be shipped. The circles represent operations that must be performed to make each product. Weve labeled them Al for the first operation of product A, A2 for the second operation, and so on. The numbers inside the circles are the machines that are used to perform each operation. We have only three machines 1, 2, and 3. Your job is to decide the sequence in which the products should be processed on each machine. There is.no setup time between processes, no inventory on hand, and nothing on order. Assume the customer has ordered 100 units of each product. We ll use a process batch of 100 units and a transfer batch of one. Make a Gantt chart for each machine to show us how quickly you can ship the customers order. Earliest shipment gets 5 extra points on the final exam.