# Industry 4.0 and Lean Six Sigma Integration: A Systematic Review of Barriers and Enablers
## 2 Theoretical Background
### Lean Six Sigma  
The origins of LSS date back to the early 2000s, when the principles of Lean (L) began to be integrated into Six Sigma (SS) [1]. While the emphasis of SS has been on variability minimisation and defect eradication, mainly in manufacturing [27], the primary focus of L has been on removing all Muda, or waste, from all places and processes inside the system [28]. Hence, both approaches can be considered complementary.  
Different LSS implementation frameworks have been proposed in the literature, but so far, there has been no agreement on this or a definition [8; 29]. However, there appears to be a consensus that, at a basic level, LSS implies adopting the problem-solving approach DMAIC (Define-Measure-Analyse-Improve-Control) and incorporating L and SS techniques in each phase of this approach [30; 31].  
Multiple tools and techniques are used as part of Lean and SS. According to the work in [23], the Lean techniques and tools with the highest synergistic connection with I4.0 technologies are value stream mapping (VSM), Lean office, visual management, just-in-time (JIT), heijunka, 5 Ss, jidoka, kanban, cellular manufacturing, single-minute exchange of die  
\begin{table}
\begin{tabular}{c p{142.3 pt} p{142.3 pt} p{142.3 pt}} \hline \hline
**Authors** & **Description** & **Year** & **Article Citations** \\ \hline
[5] & Industry 4.0, or the fourth stage of industrialisation, is a technological evolution in the manufacturing domain enabled by cyber-physical systems (CPSs) and the Internet of Things and Services. & 2013 & 3825 \\ \hline
[24] & “Industry 4.0 collectively refers to a wide range of current concepts, whose clear classification concerning a discipline as well as their precise distinction is not possible in individual cases. [...] Fundamental concepts are: Smart Factory, Cyber-physical systems, self-organization, new systems in distribution and procurement, adaptation to human needs, and corporate social responsibility”. & 2014 & 3806 \\ \hline
[20] & “The term Industry 4.0 refers to the fourth industrial revolution and is often understood as the application of the generic concept of cyber-physical systems (CPSs) to industrial production systems (cyber-physical production systems).” & 2015 & 139 \\ \hline
[19] & Industry 4.0 is based on the principles of interconnection (i.e., a collaboration between physical objects and humans), information transparency (i.e., availability of digital data of the physical world and their exploitation using analytics), decentralised decisions (enabled by CPSs), and technical assistance. & 2017 & 708 \\ \hline
[25] & “I4.0 is aimed at creating intelligent factories where manufacturing technologies are upgraded and transformed by Cyber-physical systems (CPSs), Internet of Things (IoT), and cloud computing”. & 2017 & 1728 \\ \hline
[26] & “Industry 4.0 represents the current trend of automation technologies in the manufacturing industry, and it mainly includes enabling technologies such as the cyber-physical systems (CPSs), Internet of Things (IoT) and cloud computing”. & 2018 & 1990 \\ \hline \hline \end{tabular}
\end{table}
Table 1: A summary of relevant works.  
(SMED), total productive maintenance (TPM), and poka-yoke. Furthermore, according to [27], SS involves the use of the DMAIC approach for achieving operational excellence and DMADV (Define-Measure-Analyse-Design-Verify) for achieving excellence in the design process of new products and services (an area known as Design For Six Sigma), as well as the use of statistical tools, such as statistical process control (SPC), regression, design of experiments (DOE), failure mode and effects analysis (FMEA), and management tools, such as SIPOC (Suppliers-Inputs-Process-Outputs-Customers), Critical to Quality (CTQ) trees, or the Voice of the Customer (VOC), to name a few.