Implementing Quality Forensics to Dramatically Improve Your Supply Chain

Many of us are familiar with the bell curve, that it models a plethora of phenomenon from the distribution of grades, to random dice rolls, or even the height & weight measurements of newborn babies.

                                                                  Fig. 1

Bell curves can also help you detect hidden defects and save 100's of thousands of dollars in the purchasing function. Consider the following hypothetical situation:

You have a supplier on the other side of the world shipping parts that are dimensioned too short costing you and your customers time and energy. You request them to fix the problem and after multiple attempts, they assure you there's nothing to worry about. How can you judge the reliability of that assertion? What hidden in their latest batch of parts? -A ton.

Here's how you investigate like a pro. First, you identify the characteristic range. If it's a dimension, perhaps the range is 1.0 - 1.100". In this case, you simply divide up the range into sixths, using the six sigma model of a curve as in figure 1. 

Next, you simply count the number of parts that are in the first and last segment compared with the 3rd and 4th segments. If the supplier is manufacturing conforming parts, then they will be within the tolerance range AND only 5% of them will fall within the outer segments, 27% will fall within the 2nd and 5th segment, and a whole 68% of them will fall within the middle two segments of the bell curve.

Here's where it gets fun. If the supplier is shipping parts that have a similar number of parts in the outer segments as the middle two, then you have forensic evidence the process is not producing good parts and you can be sure of the following:

1. Your supplier is inspecting for good quality and throwing away all the bad parts before you see them, rather than making them right the first time.
2. The cost of bad quality parts is already factored into the price, you are paying too much.
3. The supplier will likely start shipping bad products to you again when their current inspector changes jobs.
4. There are significant process improvements to be made that will save everybody time, energy and you have scientific proof of it!

Depending on the cost of the products being purchased, the opportunity for savings could be hundreds of thousands of dollars. As the supply chain represents the largest cost of just about any manufacturing business, you can bet this is one of the best places to drive out costs and improve bottom line performance of any organization!