Wes Bucey said:
In essence, this "pull" system is merely a variation of JIT (just in time.) the slight difference is that the downstream customer has a variable requirement and thus the lead times he expects (wants) are very short.
I would like to add one thing to this...."pull" is more of a sub-component of JIT, not really what I would I call a variation. The two are pretty much synonymous it just depends on what “buzz” word the consulting world is pitching at the time. Toyota referred to it as JIT with a mechanism of achieving it being “pull”.
Wes Bucey said:
Ultimately, simply because of physical production times required, one or more links in the supply chain are forced to carry inventory of finished goods or work in process which requires only minor finishing prior to delivery (a new paint job to match color requirement, for example.)
Yes, but those levels of inventory should be looked at as additional opportunities for improvement. Other methods such as reduction in set-up times, improvement in quality yields, and a host of other things should be addressed as well in order to ensure the lowest levels of inventory. Just because things are working smoothly doesn’t mean they shouldn’t be fixed.
Another key component should be to maintain materials in its most flexible condition. Simply put, if material
“111” can be manufactured into parts:
“A”,
“B”, and
“C” with parts each receiving the following operations:
“A” – Steps 1, 2, 3, 4
“B” – Steps 1, 2, 4
“C” – Steps 1, 2, 5
It makes the most sense to maintain inventory of material “111” that has had Steps 1 and 2 performed versus maintaining an inventory level of “A”, “B”, and “C” separately. Of course this depends on individuals process, product and business.
Wes Bucey said:
This is NOT easy. Really top-notch analysts who do this kind of prediction earn well over $100,000 up to $250,000 per year. It requires intimate knowledge of ALL the links in the supply chain and their capabilities and capacities, which is constantly monitored.
Where do I find one of those jobs. 
I’m fighting this battle as I type this, driving a conversion from a traditional system to a “pull” method. I’m essentially combining five non-adjacent buildings with three different business units into two adjacent facilities. Since we are seasonal, we will be maintaining levels of finished goods throughout the year, along with restructuring where the WIP levels build-up and at what level.
Capacity should also be designed into the manufacturing process. For instance, I’m taking two lines (they both run the same product) of three people each (no extra space for additional people on the line) and creating one line capable of supporting seven stations/people and cutting the materials sitting at the line in half. It doesn’t matter whether I run the line with the seven people or only three if the need occurs. I'll also be looking at about a 25-30% reduction in non-value added labor content.
The key fight isn’t with the production associates (in this case union), but with supervisors and middle managers who feel your taking away their power and hence, destroying the little empire they have built-up over the years.
Wayne
