It did not happen quickly but advocates of Six Sigma and lean methodologies have worked together to achieve a partnership of both approaches.
While lean manufacturing focuses on waste reduction, Six Sigma stresses process variation improvement. They have common outcomes like defect reduction and overall quality improvement.
If they are treated as standalone initiatives they compete for valuable resources which often leads to inefficiencies. When waste is eliminated from all aspects of manufacturing and delivering products to the customer, the manufacturer can achieve better margins and maximized profit.
With that said, however, many organizations, consultants and some quality professionals usually focus on either defect reduction or lean manufacturing. This leads to inefficiencies and failure to maximize improvement.
When the emphasis is on quality alone, there is a narrower definition of waste because the focus is on scrap, repair or rework. Most of the time, the outcome will be reducing these non-quality costs as the organization becomes more centered on point improvement.
Point improvement isn’t necessarily bad but it narrows the organization’s paradigm of thought patterns. They tend to work on specific elements of the process or product to create an improvement in a characteristic, feature or activity. Six Sigma activities are good examples of this narrow effort on specific elements.
Over the recent decades quality has evolved from inspection to quality management and improvement. However, the basic concepts have not changed much since Walter Shewhart’s creation of statistical process control and the work of Drs. W. Edwards Deming and Joseph M. Juran.
The purpose of quality has always been to concentrate on the process and identify sources of variation, control or eradicate them, and provide the customer, as much as is possible, product they are willing to purchase.
This is easier said than done. The amount of effort required to uncover sources of variation in a process or activity can be very involved and time consuming. Because of this effort, the underlying ideas of statistical process control can get muddy, lost or even ignored. The result can be reduced to product acceptance instead of variation improvement. Maybe a fine line but certainly not the same focus.
Meanwhile, lean activities are motivated by the elimination of waste (including variation) in a process. This effort has intense scrutiny on cycle (takt) time and total movement of the activity, product or process. It is not rare that blitz kaizens, a lean activity, performed with a narrow focus can ignore product conformance thereby generating more, not less, non-quality costs.
When properly focused, the lean activities can expose, reduce, or eliminate many situations that can create non-conformances. It makes sense that the fewer steps, touches, or product movements can reduce or eliminate variation which, in turn, limits potential areas for problems to occur.
Organizations, when establishing work cells or work stations, must not overlook the potential to introduce variation as it can have a significant impact on the total lean activity. Without this realization, the lean benefit from lower cycle time can be offset by costs due to excess variation.
As an example, a company asked me to review a process which had recently went through a lean initiative but results were not what management expected. This organization had held a kaizen blitz to create a manufacturing cell for a family of small parts.
Cycle times were lowered through improved machine layouts, combining operations, implementation of 5S and a significant improvement in work flow. End of the line inspection stations were centralized. A traditional inspection using hand gages and small location fixtures determined whether the product was acceptable. Where product was deemed unacceptable the product was sorted. Considering the overall costs, the results were not substantially improved.
The effort would have had much better results if the organization had integrated the determination of acceptance at each step in the process and applied process and quality control methods to drive out variation. The process was not optimized to eliminate waste. Nonconforming product (waste) was not discovered until the inspection or acceptance activity was performed by the independent inspection function. Steps were taken to rectify this oversight but significant costs were incurred to make the required changes.
Organizations, consultants and quality professionals need to realize Six Sigma and lean activities are complementary. The two should be used as partners and not as discrete activities. It is important to remember that the speed at which a lean event is implemented can compromise the ability to perform a thorough analysis of its impact on process and product quality. Without an effective partnership, doing anything faster might just mean making a lot more poor-quality product, which gives your competitors the advantage.