Saturday, February 04, 2006
Musings on "Just in Time" (JIT)
Just-In-Time (JIT): A "pull" system, driven by actual demand. The goal is to produce or provide one part just-in-time for the next operation. Reduces stock inventories, but leaves no room for schedule error. As much a managerial philosophy as it is an inventory system.One way of looking at it is to think of a weaving loom. Different threads enter one end and are woven into fabric. JIT is a way of eliminating the spools of thread feeding into the process. In a way, the thread is being created just before it enters the loom process. One problem with this: If there is an interruption of the supply of one thread, the whole process comes to a halt. Detroit automakers commonly use JIT to cut costs. However, because of the assembly line process, it is almost impossible to halt or continue production without any single part. If a shipment of bumpers for a particular model car is delayed because of a dock strike, the whole assembly line stops.
One thing I've recently observed: JIT is a common supply method for all sorts of things in American society, not just manufacturing. Because of the cost savings, it seems an attractive approach to any supply chain. Thus, to eliminate waste of perishables in the food supply, these items are rarely stored for more than 3 or 4 days before being stocked on market shelves.
The downside of using JIT is that all supply chains based on this method are extremely vulnerable to disruption. A gasoline shortage would mean the trucking industry would slow or halt. Some cities use JIT to supply the chemicals and minerals used to purify their water, keeping only a few weeks worth on hand at any one time.
Because JIT is a supply and distribution technique, anything which interrupts the flow of supplies brings a whole range of cascading logistical problems in its wake.
Our society has become quite dependent on the smooth and efficient flow of all kinds of material through our transport conduits. With such dependence also comes a restructuring of routes and hubs.
I have no conclusions. Just a suspicion that dependence on JIT will eventually bite us on the ass.