Problem and Process of Predicting Delivery Times in Jobs Shops - Sequencing and Scheduling Issues in Job Shops - Machine Shops

 

A LinkedIn Post from Prasad Velaga, Texas, USA,  who specilizes in scheduling and offers a software package for it at reasonable price.

A Simple Exercise to Quote A Rational Lead Time for A New Customer Order:

The attached document contains process times of 200 jobs on an 9-stage production line. Some jobs skip some operations on the line. The skipped operations are shown in grey color in the table. Suppose the jobs are to be released to shop floor in the order (J1, J2, J3, ..., J-200).

All work stations except W3 have only one machine and the eight machines are available 24x7. W3 is a vendor operation for which vendor quotes a fixed lead time of 5 calendar days for any job. Take an hour as the time unit.

There is an additional resource constraint in the system. A worker is needed for operations at W1 and W7 but only one worker is available in the shop at any time for this purpose.

If a customer gives a new order for a job with process times (0,12,0,5,14,5,7,0,0) at (W1,W2,....,W9), how many days will be needed to complete the job without affecting the existing jobs?

You may answer this question by considering any sequence of 200 jobs as you wish. I expect you to use at least Excel to answer the question. 

Please seek from me any clarifications and/or additional data that you need for answering the question.

In my honest opinion, this simple academic, numerical example is far simpler than production in real job shops. Many salespersons and managers in job shops face this kind of questions regularly. Many job shop people who contact me usually talk about the difficulty of predicting job completion times because they have to assure their customers of product delivery times. This is the reason why I posted the simple numerical exercise here.

My objective here is to highlight a common difficulty in managerial decision making in job shops.

Without predictive capability, factories may quote either longer lead times or shorter lead times but not necessarily the right ones. Quotation of longer lead times can reduce the chance of having orders from customers and quotation of shorter lead times can cause anxiety and firefighting on shop floor.

https://www.linkedin.com/posts/prasadvelaga_prediction-of-job-completion-times-on-a-production-activity-7171729649209688065-ju9B