How You can use Statistics in the Food Industry - Part 5

In this last part of the series I wanted to go through 2 items one being 6 Sigma and the other putting together an SPC program with the methods that I have blogged about.

6 Sigma

6 Sigma is a program that is taught for industry and the name comes from the following concept.  At +/- 6 sigma (6 standard deviations) from the mean (average) of a process you will have 3.4 off specification units per million units produced.  Yes, I am use to seeing +/- 3 Sigma as the standard so 6 Sigma seams rather extreme.  However - considering the thousands of parts in a car, having each part at +/- 3 Sigma there would be a lot of defective cars on the road (the off spec parts are cumulative).  I will stick my neck out and comment that in some cases, 6 sigma IS extreme.  Consider the roasting of whole bean coffee.  There is one raw material and only 3 steps.  Roasting, weighing, and bagging.  In such a simple system - +/- 3 sigma is probably OK

In either case - it is the upper and lower specification that determines how much variability can be tolerated in your process.

SPC Program

The following is an example of putting together a SPC program.  This type of program cannot be created overnight - it will take time, training, patience, and support from MANAGEMENT.  Here are the steps of my example (NOTE - this will need to be repeated at each process step that you are doing testing):

1. Brainstorming - figure out (as a group) what you want to accomplish and at which points of the process.  Fishbone diagram is a good technique at this point.
2. Initial run charts - Creation of a run chart and training in the usage of the chart.  This will get you data to analyse.
3. Plot your Histogram and run your Cp and Cpk study to see if you are in control of the process step and have a normal distribution curve.  If you are in control and have a normal distribution then proceed to step 5, if not go to step 4.
4. Not in Control? Run a gauge R&R to find where the variation is coming from.  With the R&R test results you may need to do a root cause analysis (Fishbone, 5 Whys) and correct for the variation.  This correction will likely require retraining of the staff.  Redo step 3.
5. Great, you are in Control! - Redo your run charts if necessary, taking advantage of the lessons that you have learnt to this point.
6. Monitor - Keep the run charts and histograms going.  This is also your verification step.
7. Out of spec product - you can get samples of out of spec product and do a root cause analysis on them.  For me, this gets linked with customer complaints and is a great place to do a Paredo chart.  Based on the root cause analysis you will need to put a "plan of action" together to correct the issue.
8. The second to last step is the creation of a checklist.  The checklist is used at a frequency that is determined by risk and you.  This is also called the Validation step.  The checklist can include such items as;
• Training record check
• Log check
• Are the calibrations being done
• Preventative maintenance cycles completed
• Observation of the people (are they following protocol)
• Check on the written procedures (are they current, legible, visible)
• View the process
• Review the Cp, Cpk, Histograms, and any corrective actions
9. The last step - return to step 2.

Again - this will need to be done at each testing point of your process - which is why I said that doing an SPC program will take a lot of time and patience.