Understanding Lean Six Sigma as a Waste Square

For decades, manufacturing has successfully applied Lean and Six Sigma methodologies to resolve process problems. Lean (Manufacturing) in the west derives from the Japanese Toyota Production System (TPS) (J. K. Liker, 2004; Womack & Jones, 2003) influenced post-war by W.E. Deming and developed during the 1950s; and Six Sigma (Breyfogle, 2003) was introduced during the 1980s by Motorola in the USA. These techniques are perfectly tested, function well to improve process efficiency and effectiveness, and fill a crucial role among current process-improvement methodologies. Lean and Six Sigma are thus widely applied, from industry to services, from healthcare to banking; however, those who have not learned and practised the approach sometimes struggle to find an ‘ umbrella ’ concept to properly understand what they are. This short paper attempts to provide such an explanation by proposing Lean Six Sigma as a complementary efficiency and effectiveness waste model (George, 2002).


Lean tools
What the west calls Lean tools were developed by Toyota initially to reduce working capital in their manufacturing. Aiming at one-piece flow and only line-side inventory (Ohno & Bodek, 1988) Toyota is largely able to successively assemble hundreds of versions of a car (colour, options, trim, motor, etc.) along a single production line in the sequence in which they are ordered.
Essentially, Lean removes 'Non-Value Added' process time (and space) by applying methodologies which ultimately result in smooth low-stress work. The techniques and jargon of Lean attack process lead time and foster flow in one way or another (Womack & Jones, 2003), and include: - Automated machine stopping in case of error, attracting immediate correction by the operator (jidoka) and audio-visual signals of production line stoppage (andon).  Cellular manufacturing to make flow visible.
 Identification and elimination of Non-value added time using VSM, which is Current-and Future-State Value-Stream Mapping, using time-data enriched process maps.  Kanban: small lot-size production using Pull where one-piece flow is not usable.
 Pull: Components consumed in a downstream process supplied by the upstream process only as and when 'called' by the downstream; the upstream stops producing when downstream demand is met.  Poka-yoke: error prevention which improves capability by making process mistakes impossible to commit, or at least immediately obvious.  SMED: machine set-up time reduction to tend towards one-piece flow.
 Takt time: the time to produce a single piece at an average demand level.

Six Sigma tools
The Lean end-to-end, process-long view represented in the Lean Value-Stream Map is totally different from the vertically focussed analysis used in Six Sigma of variation within individual process steps. In ensuring process-output precision and accuracy, Six Sigma tools improve (Wheeler, 2000): - Process Capability, which is the aptitude of each process step to precisely meet its output specifications, and;  Process Stability, which is the aptitude of the process not to vary (or shift or drift) over the longer term from its calibrated settings. 4 Six Sigma is thus a methodology to attain process effectiveness, that is, to produce by better meeting specifications and by better controlling process variation. Six Sigma meets quality, rather than process lead time objectives; it is about doing things well, rather than doing them quickly, which is the primary goal of Lean. To achieve this, Six Sigma adopts different tools (Breyfogle, 2003) using another jargon, including: - A team-based, process-problem solving approach using DMAIC 2 to focus on individual process steps, suppliers, customers, inputs, outputs and process parameters.  Cybernetic negative-feedback models to control process capability and stability, so better respecting customer specifications.  FMEA 3 to reduce process risk.
 Statistical methods to measure and to analyse process capability and stability using parametric and non-parametric statistical analyses.  The Experimental Method 4 to build process-regression models to optimise performance parameters and robustness. Michael George (2002), promotes the joint practice of Lean and Six Sigma in, Lean Six Sigma: Combining Six Sigma Quality with Lean Production Speed. In statements which illustrate the efficiency role of Lean and the effectiveness role of Six Sigma, this author writes:

Lean Six Sigma together
In the case of Lean, the key metric (used to measure and to improve process lead time) is Process Cycle Efficiency (PCE), which is the ratio of Value-Added time to total Process Lead Time (PLT). (George, 2002) Thus, Lean addresses process lead time to make processes efficient, however: Most of the methods and instruments associated with Six Sigma do not focus on time; they are concerned with identifying and eliminating defects. (George, 2002) Corresponding Author: Dr. Robert Gillespie of Blackhall, bob.gillespie@laremige.com Citation: Gillespie of Blackhall, R. (2022). Understanding Lean Six Sigma as a 'Waste Square'. Academia Letters, Article 5773. https://doi.org/10.20935/AL5773 5 Thus, Six Sigma addresses quality to make processes effective.
In this way, a combined Lean Six Sigma model can be seen to bring together: 1. A Lean efficiency vector through lead-time reduction supporting working capital reduction. 2. A Six Sigma effectiveness vector through quality impact, supporting direct cost reduction.
This is illustrated by a Process-Waste Square below (Fig. 1), which models the joint mechanism of Lean Six Sigma.

The Process-Waste square
To sum up, Lean tools generally attack wasted time and working capital, as a methodology of efficient process; and Six Sigma, generally attacks quality related direct cost as a methodology of effective process. In this model then (Fig. 1), Lean efficiency is about working quickly; Six Sigma effectiveness is about working well, where most work processes engage both speed and quality.
The function of Lean to eliminate wasted process lead time and of Six Sigma to eliminate process nonconformity are plausibly orthogonal and synergic to process performance, and the Process Waste Square (Fig.1) represents how Lean and Six Sigma appear to impact performance by working together across approximately orthogonal axes of waste. Thus, Lean and Six Sigma methodologies act independently but can be seen to act jointly on process waste: Six Sigma by reducing waste resulting from process variation and output nonconformities; and Lean by reducing wasted process time.

Fig 1. The Process-Waste Square
Ultimately, the Waste Square intuitively structures understanding of how these two methodologies interact.