New MIT Paper: Using Critical Path Drag to Optimize Manufacturing Throughput

Eureka! Through the wonders of Google, I have just discovered a new paper describing the practical application of the critical path drag metric to optimize a manufacturing process. The paper is by Blake Sedore and the paper was his thesis for his Master’s of Engineering degree in Manufacturing. It’s titled: “Assembly lead time reduction in a semiconductor capital equipment plant through constraint based scheduling.” You can find the abstract through the Massachusetts Institute of Technology website at the URL below. You can download the complete PDF file by clicking on the download link at the end of the abstract.

Manufacturing semiconductors

As far as I know, this is the first time that someone other than yours truly has analyzed a manufacturing process using this metric, and certainly the first time someone has written a paper about it. The paper is 83 pages long and, by my count, mentions drag about 37 times.

From the abstract:

“A preliminary build schedule was developed that prioritized critical path procedures. A trial of this build schedule achieved an assembly lead time of 39 hours, resulting in a 70% reduction from the current average of 5.5 days. This trial was also accomplished with 76% of the average labor hours for assembly. A production build schedule with a lead time of 43 hours was developed based on the trial results. This schedule allows for production rates of up to 5 machines per week to be achieved with the current shift structure of the company, without the incurrence of overtime. A critical path drag analysis identified critical procedures with the highest potential for lead time reduction. The highest drag of a critical path item was 260 minutes, accounting for 10% of the assembly lead time.”

In the paper, Mr. Sedore then goes on to describe how he analyzed the possible ways of reducing the drag and made recommendations based on considerations of greatest drag reduction, lowest cost of additional resources, and shortest disruption of the manufacturing process. This last item seems to me to be a new enhancement in the application of critical path drag analysis specific to the manufacturing industry, and I am very excited about it!

I contacted Mr. Sedore and asked him about his experience calculating drag “manually”, as the critical path software he was using (MS Project), like most, doesn’t perform the calculation. He said that it gave him some trouble until he laid it out in Gantt chart form, when the drags on the critical path became more obvious. He also agreed that it would be so much easier if only the software would compute it!

A Gantt chart is usable on a manufacturing project which is likely to consist of no more than a couple hundred steps. But for a project with over a thousand activities, I have found network logic diagrams (aka PERT charts) to be necessary (provided I am not using Spider Project which computes drag automatically). But it’s certainly high time that MSP, Primavera, MicroPlanner, Asta, Safron and all the others started including this functionality. (They will eventually – but when?)

Seeing drag analysis being used by engineers at the most prestigious engineering university in North America is extremely exciting to me! Yes, it should be used by all project and program managers – but it also should be standard usage for analyzing and optimizing circuit board design, software algorithm optimization, disaster emergency response: any procedure with integral steps. Maybe Mr. Sedore’s article will kickstart its usage in manufacturing.

I have invited Mr. Sedore to write a short guest blog for this website about his experiences in using drag analysis. I hope he will do so some time in the next few weeks.

Fraternally in project management,

Steve the Bajan

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