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Daniel Schaeffler Daniel Schaeffler

Use Lean Six Sigma for Efficiency & Quality Improvement

October 27, 2023

The Six Sigma quality-system methodology developed by Motorola in the early 1980s uses statistical analysis to guide process improvements.

The Six Sigma quality-system methodology developed by Motorola in the early 1980s uses statistical analysis to guide process improvements. The term originates from a well-controlled process with a tolerance band within six standard deviations (±6σ) from the center line. A Six-Sigma-capable process will have Cp and Cpk (centered and non-centered stable process capabilities, respectively) measuring at least 2.0 and a maximum of 3.4 defects/million opportunities over the long term. This equates to 99.99966-percent defect-free operations.  

The statistical term sigma refers to the standard deviation of a process around its mean on a normal distribution. Although sigma represents variation, it says nothing about acceptability. An attribute with a small sigma outside of the acceptable range always is defective. Similarly, an attribute possessing a large sigma reflects a large range of likely values.  However, if it is not a key input variable to the process, then it may always be acceptable regardless of the variation. 

Lean Six SigmaThe Six Sigma-methodology focus on sigma comes from the recognition that variability in process-input parameters—such as tensile properties, binder tonnages, lubricant properties and gauging—affects stamped-part quality, including structural and dimensional integrity. These key output characteristics either must accommodate high sigma values in the key process inputs or accept an increase in the number of parts with out-of-tolerance features. Six Sigma focuses on reducing input-property variability to avoid the time, expense and quality problems associated with quality issues caused by this variability. 

Companies deploying the Six Sigma model aim to eliminate defects while driving toward six standard deviations between the mean and the nearest limit in any process. DMAIC (define, measure, analyze, improve and control) is a continuous-process-improvement methodology in widespread use, and provides a framework to achieve this goal. (Refer to the October 2023 issue of MetalForming for a DMAIC overview.)

Lean + Six Sigma = Lean Six Sigma

The Six Sigma methodology aims to help suppliers meet customer expectations by improving process output and quality through a reduction in defects and process variability. A related discipline, Lean Six Sigma, combines a lean mindset with the disciplines of Six Sigma.  Lean practitioners seek to remove any process action or step that requires resources to accomplish but does not add value. Such waste includes process steps related to defects, overproduction, excess inventory, unnecessary motion, excess processing, waiting and unnecessary transportation, as well as unused team-member creativity and experience.  

Lean Six Sigma combines aspects of Six Sigma, such as data analysis for improved quality and consistency, with those from the lean methodology, such as efficiency gains from using waste-eliminating tools. The goal: Improve process flow, maintain continuous improvement and achieve business goals.

Companies with a lean mindset strive to minimize inefficiency. This might result from something as simple as locating a toolbox closer to a press to reduce the walking distance of the repair crew. Or, efficiency might be gained from completing a more complex task such as changing the orientation of the part progression to get more hits per coil.

Either way, successful implementations often begin with a focus on lean—making the workplace as efficient and effective as possible—through a reduction in waste and by employing a technique called value-stream mapping to identify the truly important process steps. Remaining process problems may be addressed with a DMAIC approach aided by Six Sigma statistical tools. 

Where’s the Value?

Start the lean-Six Sigma journey by identifying the features and characteristics in your manufactured parts that your customers really care about. This represents the value they are paying for, with everything else being waste. Value-stream mapping traces in detail the steps involved in part production, including the flow of materials and information.

Knowing the attributes critical to quality and the features desired by the customer allows for the removal of non-value-added steps.

The kaizen philosophy, which focuses on continuous improvement, is based on PDCA (plan-do-check-act) cycles, also described in the October 2023 issue of MetalForming. PDCA cycles allow organizations to identify areas and processes having wasted resources. Avoiding unnecessary steps and eliminating delays results in a simpler, more efficient workflow—easier to maintain and control. In turn, the simpler process reduces opportunities for defects to occur. Reduced variation follows, leading to predictable performance, improved quality and lower costs. MF

Industry-Related Terms: Center, Model, Tolerance
View Glossary of Metalforming Terms


See also: Engineering Quality Solutions, Inc., 4M Partners, LLC

Technologies: Management, Quality Control


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