Mapping the terrain for the Lean Supply Chain 4.0

Purpose – This study aims to carry out a systematic literature review (SLR) on the integration of Lean, Industry 4.0 and the supply chain or the Lean Supply Chain (LSC) 4.0. The research analyses the current research on the LSC 4.0 concept in an increasingly digitalised world. The authors present the benefits, motivations, critical success factors and challenges of integrating the LSC with Industry 4.0 technologies within this emerging area of research. Design/methodology/approach – AnSLRiscarriedoutonhowLeancanbeintegratedwithSupplyChain4.0. Using the search strings of “ Lean Supply Chain 4.0, ” “ Lean Supply Chain Management 4.0 ” and “ Lean Supply Chain Digitalisation, ” a review of published literature was carried out via searches on academic databases. Findings – Industry 4.0 has a synergistic effect on the LSC and, depending on the technology and sector applied in, can complement and enhance the LSC. Similarly, the LSC is a precursor for digitalisation. There are considerable implications in the LSC 4.0 for green and sustainable processes. Practical implications – Organisations can use this study to understand what the LSC 4.0 means to industry, the benefits and motivating factors for implementation, the critical success factors (CSFs) to implementation and the challenges for implementation. Originality/value – ThisstudyaddstostateoftheartaroundtheLSC4.0andfuturedirectionsinthisnascent research area. This study will aid organisations in understanding how Lean, supply chain management and Industry 4.0 can be integrated.


Introduction
With the dawn of the first Industrial Revolution, production evolved from craft production into mass production and ultimately into Lean production and supply chains.Lean Management (LM) is an operational excellence methodology to eliminate any source of waste and non-value-add activity in a value stream (Womack and Jones, 1996).The concept of Supply Chain Management (SCM) was put forward in the mid-1980s, incorporating a definition based on inter-organisational operations management, system integration and information sharing (Cooper et al., 1997).The incorporation of Lean principles has evolved to what has become known as the Lean Supply Chain (LSC).LSC consists of stakeholder organisations and functions linked by flows of products, services and monies and information combined to improve profits and reduce waste by pulling what is required to meet the customer's needs (N uñez-Merino, 2020).
Thus, the LSC concept refers to the integration of LM principles in the supply chain to reduce costs and eliminate waste by utilising Lean to establish flow and pull processes to meet the needs of individual customers (Reyes et al., 2021).However, the application of Lean practices at the supply chain level is much more complex than LM application internally within the company as it requires more coordination and management of physical, information and financial flows between the various stockholders involved (Moyano-Fuentes et al., 2018).
The concept of LM and I4.0 integration has not been widely studied (Antony, 2021a;Antony et al., 2021bAntony et al., , 2022;;Tortorella et al., 2020;Rossini et al., 2022).However, the area as a research theme and integration into practice has been evolving in recent years (Antony, 2022) and indeed there has been a "synergistic" effect described between LM and I4.0 (Snee and Hoerl, 2018;Calabrese et al., 2021).In terms of the concept of Supply Chain 4.0 or SCM 4.0 -this concept has also not been widely studied (Rossini et al., 2022).Frazzon, 2019 found that the term has only started to increasingly appear in the literature (with more than 10 publications annually on the concept) since 2016.
Frazzon, 2019 defined SCM 4.0 as "the integration and synchronisation of the product's entire value chain across different companies, using smart technologies (IoT, IoS and others) to build an interconnected and transparent system with real-time communication that can manage flows and optimise itself, leading to an autonomous, adaptive, intelligent, agile, and dynamic network that focuses on customers' requirements".
However, as traditional manufacturing and supply chains are now transitioning into increased digitalisation with the implementation and evolution of Industry 4.0 (I4.0) technologies, the LSC has become digitally ready or digitally enabled (Calabrese et al., 2021).Thus, there is a new evolution of the LSC or LSC 4.0 digitalisation.
However, the integrated effect of Industry 4.0 technology and Lean manufacturing practice on the Supply Chain (SC) has not been empirically investigated.The authors of this paper recently carried out a study on the LSC 4.0 presented as part of the International Symposium on Logistics conference in July 2022 to establish the current research themes around The LSC 4.0 (McDermott, 2022).Whilst there have been limited studies on the literature related to the theme of the LSC 4.0 (Mahdavisharif et al., 2022) in this study the authors proposed to answer a broader set of thematic questions in relation the LSC 4.0.We ask question as to how Lean; the Supply Chain and Industry 4.0 can support each other to deliver the LSC 4.0.Thus, this paper aims to contribute to this research area by investigating the themes within the LSC 4.0.
The research questions in this study are: RQ1.What is the current research on the LSC integrated with I4.0?
RQ2.What are the motivations for integrating the LSC and I4.0?
RQ3.What are the benefits of integrating the LSC & I4.0?
RQ4.What are the critical success factors (CSFs) and challenges to integrating the LSC and I4.0?
The methodology is described in section 2 followed by the results in section 3. The discussion and conclusion are outlined in sections 4 and 5.

Methodology-systematic literature review
To aid understanding of the LSC 4.0, a systematic literature review (SLR) was utilised.
In addition, systematic research was carried out for articles published between 2012 and 2022 using the academic databases Web of Science and Scopus.The body of literature was synthesised using Tranfield et al.'s (2003) approach to systematic literature research.
A benefit of SLR is that large quantities of information can be reduced into digestible segments (Mulrow, 1994).The systematic approach also aids scientific voracity as the process is structured and, therefore, replicable (Yang et al., 2017).
A SLR was carried out in stages following Tranfield et al. (2003) identifying the literature that was relevant to the research questions (RQs), a structured process of review and one that can be followed by future researchers through a research process flow.Tranfield et al. (2003) promoted 3 stages in an effective SLR process.These were Stage 1-5, which we planning the review, carrying out the review and reporting and dissemination of the review.
Stage 1: Planning the review Once the RQs were decided upon and written, next a review protocol was decided upon.The research was only within the academic databases to publications that contain research, or models specific to the LSC 4.0 published between 2012 and 2022 (year to date) due to the nascency of the topic.Therefore, a search string was applied to search all the above databases: "Lean Supply Chain 4.0", "Lean Supply Chain Management 4.0" and "Lean Supply Chain Digitalisation".Table 1 provides a detailed listing of the inclusion/exclusion criteria agreed before the review was carried out.As the research objectives for this study were specifically related to the combination of "Lean", "supply chain" and "digitalisation (or 4.0)" this keyword combination was agreed to eliminate articles that concentrated on two rather than three of the theme words.
Stage 2: Carrying out the review Utilising the search keywords, academic databases were searched utilising the inclusion/exclusion criteria from Table 1 and extracted and exported utilising Excel.The first search resulted in a total of 3,252 articles (950 in Scopus, 2,302 in Web of Science) which were stored in the reference management software "Zotero" to aid the screening process.Once duplicates were removed in Zotero, the list resulted in 3,252 papers which were then further screened in two stages.
Within the 3,252 screened articles, a search was conducted of the titles, abstracts and keywords of the articles to identify their relevance to the RQ's.The main criteria reviewed at this stage were whether the articles specifically referred to the LSC 4.0.and Many articles referred to the LSC and SC 4.0 but not to the integration of the LSC and I4.0 and thus were disregarded at this stage.The four authors of this research reviewed and independently assessed whether the studies matched the criteria for inclusion based on the search criteria (Parameswaran et al., 2020).The agreement as to whether to include was reached by discussions and consensus amongst reviewers.This stage concluded with a total of 56 articles.
In this stage of the screening procedure, the 56 articles that remained were next thoroughly evaluated for their relation to the research themes (LSC 4.0 or LSCM 4.0).The second review stage concluded with 29 articles to be included in the main analysis.The articles that were selected from the second stage were then used in the results and discussion section of the paper.
A flowchart aided the illustration of the SLR steps (Figure 1).The analysis then was started using various themes in response to the research questions, for example the year of publication, authors, journals, research methods, the benefits of LSC & I4.0 integration, motivations for LSC & I4.0 integration, challenges of LSC & I4.0 integration, and finally, the CSFs for LSC & I4.0 integration.These themes arose from initial analysis of the literature.
Stage 3: Reporting and Dissemination of the SLR Finally as part of stage 3 of the SLR process which was reporting and dissemination the insights from these publications were summarised through the review of any patterns and themes therein.The summary of the thematic analysis is documented in section 3 of this paper.

Results
Based on the research we see a tripartite relationship between Lean, the supply chain and Industry 4.0 is represented in Figure 2.  2).However there were 15 conference articles highlighting that the area is evolving and increasing.

Source(s): Author's own work
Most of the final selection came from conference papers/proceedings (15) versus with just slightly fewer from peer-reviewed journals ( 14).There was one article each from 12 different journal titles and 2 articles from the International Journal of Lean Six Sigma.As demonstrated in Figure 3 the theme of LSC 4.0 is a current theme of researcher interest, first appearing as recently as 2016 in conference proceedings and then in 2019 in per reviewed journals with a very low steady stream of research since then.Three main conferences contributed to the research.These were the Proceedings of the International Conference on Industrial Engineering and Operations Management (IEOM) (3 papers), Annual International Conference on Management Science and Engineering Management (ICMSEM) (2 papers).As LSC 4.0 is a recent evolving area of research several authors who have written about the topic have commented on the sparse literature on the concept (Frazzon, 2019;Tay and Loh, 2022;Marodin, 2019).The LSC 4.0 as a concept is still very much in its infancy.
The final selection of articles were screened for themes related to the benefits of the LSC & I4.0 integration, the motivations for the LSC & I4.0 integration, the challenges of the LSC & I4.0 integration and the CSFs for the LSC & I4.0 integration.These articles were screened to ascertain their alignment with the RQ's and research themes and summarised in Table 3.All authors of the selected articles were supportive of the benefits of integrating the LSC and Industry 4.0.However, few articles discussed the CSF's and the challenge of integrating the LSC and Industry 4.0 as this is still an evolving research area lacking longitudinal studies.

Discussion
The SLR clearly shows that LSC and I4.0 support each other in a symbiotic and synergistical relationship.The SLR analysis supports this as the LSC and I4.0 are hand in hand in multiple publications suggest their synergy.
As I4.0 technologies enhance the LSC with the digitalisation of traditional LSC elements, Lean SC practices act as enablers for the introduction of I4.0 technologies in the supply chain system.This mutual relationship is perfectly aligned with the recent research about interdependences between lean systems and I4.0 (Buer et al., 2021;Antony, 2022;Rossini et al., 2022).The literature reviewed in the SLR had a common theme of the benefits for integrating the LSC and I4.0.The challenges to the integration and CSF's to integrating the LSC and I4.0 were also very evident in the literature.As outlined in the previous section, this area is understudied at the moment, and very few research papers are devoted specifically to the LSC 4.0 or LSCM 4.0 in the literature (Tay and Loh, 2022).Lean and supply chain practices are positively aligned with Industry 4.0 technologies, and the concurrent implementation results in performance improvements (Chiarini, 2020).I4.0 and Lean practices are complementary to I4.0 technologies (Snee and Hoerl, 2018), and there is a synergistic relationship between both to increase operational excellence and supply chain improvement (Calabrese et al., 2020).Whilst there are many benefits and motivations to the LSC 4.0, many unknowns exist.For instance, there is importance to understand the technology being implemented in terms of what it can due for the LSC and look at one process and the applicability of that technology at a time (Mahdavisharif et al., 2022).A common thread across the literature around digital transformation and LM methodology are that both seek to continuously improve SC operational visibility and process performance and that I4.0 can enable a stronger LSC (Tay and Loh, 2022).

IJLM
In summary this research is in consensus with other studies that demonstrate the literature linking Industry 4.0 with SCM strategies is still in its infancy.Similarly Antony (2021a), Antony et al. (2021bAntony et al. ( , 2022) ) and Raji et al. (2021) discussed the requirement for sector-specific studies to study the specificity of the Industry 4.0 technologies for the Lean practices adopted in different sectors to study if practices and their effects vary.Much of the LSC 4.0 research published to date is SLR related (McDermott, 2022;Rossini et al., 2022) and that is a gap in itself in the literature as there are very few case studies on the LSC 4.0 with the exception of some studies for example from Frontoni, 2020, Tortorella andFettermann (2018), Freitas, 2017 andWoschank andDallasega (2021).
RQ2: What are the motivations the LSC and I4.0 integration?
The studies reviewed to discuss the interactive, symbiotic and synergistic nature of Lean with SCM and complemented and enhanced by the technologies of I4.0 (Bag, 2020;Raji, 2021;Tay and Loh, 2022).According to (Tortorella and Fettermann, 2018;Tortorella et al., 2019), the adoption of Industry 4.0 technologies moderate the relationship between LSC practices and supply chain performance in organisations.Furthermore, Tortorella et al. (2019) emphasised that integrating product and service-related Industry 4.0 technologies into flow practices can lead to significant operational and supplier chain performance improvement.
There is a structured relationship amongst lean, agile, sustainable, resilient and flexible principles to enhance SC performance by the implementing of digitisation technologies (Marodin, 2019;Raji, 2021;Mahdavisharif et al., 2022).Mahdavisharif et al. (2022) proposed a conceptual model, or LSCP 4.0, which they piloted with a case study in a large footwear company and had associated supply chain operations improvements (Mahdavisharif et al., 2022).
Currently, Industry 4.0 is considered the essential improvement of business processes that could improve LM, high organisational support and effective supply chain practices (Tiep et al., 2020).Moreover, the synergistic effect between I4.0 and LSCM is high and impacts results positively (with benefits including agility, data sharing, increased synchronicity and  Bag, 2020 discussed how big data analytics is an operational excellence approach to enhance sustainable supply chain performance.Ciliberto et al. (2021) discussed the benefits of I4.0 to supply chain operations in providing real-time tracking and monitoring of all SC system functions including product identification, tracking, communication and control along the value stream.Thus, information systems for management of data and communication allow the development of integrated end-to-end SC digitally connected processes and leaner ones.The digital environment enables lean value add customer processes including the circular economy to accurately forecast customer demand and management of the entire supply chain from incoming logistics to production, outgoing logistics, marketing, sales and assistance (Ciliberto et al., 2021).
RQ4: What are the CSFs and challenges of integrating the LSC & I4.0?
Adapting Lean principles outside of manufacturing and into the LSC is not straightforward (Hines et al., 2004) because waste at the production floor level is more straightforward to identify and quantify than at the SCM level.Tortorella et al.'s (2019) research emphasised that integrating Industry 4.0 technologies for products and services into Lean flow principles can result in significant improvements, but only if integrated cautiously and in a structured manner.They also found that organisational size and the length of the duration of LM deployment were highly positively correlated but that the duration of LM deployment was highly negatively correlated with increasing technology.
As many organisations have struggled with implementing Lean in the SC due to a lack of understanding and poor implementation approachessimilarly, it is important to understand how Cloud Computing, Big Data, IoT and artificial intelligence (AI) affect the LSC results at both the operations level of flexibility, improving quality, achieving delivery and service levels as well as its impact on the financial results of revenue, profits and increased market share (Bag, 2020).Organisational support and leadership are important for the LSC 4.0 successas they positively moderated the nexus of SCORM and LM (Tiep et al., 2020).
Tay and Loh (2022) discussed the importance of having a conceptual framework based on a structured Define, Measure, Analyse, Improve and Control (DMAIC) problem-solving methodological approach to drive improvements in supply chains.Thus this conceptual framework as a CSF provides a systematic method for big data to be integrated into Lean initiatives to optimise greater supply chain performance.Doh et al. (2016) put forward that it is necessary to consider some key points in implementing I4.0 along the value chain, as the LSC 4.0 requires the integration of production, systems and management stakeholders.They further elaborated that effective communication between all users and processes is key to systems working together with the same type of language which is a key challenge.
Many Industry 4.0 studies have discussed the importance of choosing the right technology and investing in the right digitalisation solution in readiness for Industry 4.0 deployment (Antony et al., 2021b).However before implanting complex technology basic infrastructures must be in place.Doh et al. (2016) discussed examples from Brazil where there is a need for transport investment and Internet network infrastructure which is a challenge to the integration of the I4.0 and the LSC.
It is important to understand how different Lean tools interact and impact the SC operations when integrated with I4.0 technologies to not make the wrong investment decisions.For example, Lean tools, such as Kanban, Just in time (JIT) and Value Stream Mapping (VSM), can enhance SC operations management when integrated with I4.0.On the other hand, simulation can lead to more collaborative management between suppliers and manufacturers and aid risk management and risk contingency planning (Mahdavisharif IJLM et al., 2022).A close cooperation with suppliers, which is a lean characteristic, is also critical for Industry 4.0.as through improved communications via hardware and software enables development of high compatibility (Duarte and Cruz-Machado, 2017).Ciliberto et al. (2021) reiterated the theme of investments in digital infrastructures to enable the dissemination of digital services and technologies not only across Europe, but globally.Specifically the development of broadband plays a crucial role in the implementation of innovative and competitive digital systems to avoid the risk of increasing the digital divide.Concurrent application of different technologies within a SC situation can help determine which mix of technologies are the most profitable ones in which to invest in order to guarantee successful outcomes (Mahdavisharif et al., 2022).Tortorella et al. (2019) stressed also the importance of having the right balance between the adoption of Industry 4.0 technologies and Lean practices for improving operational performance within their companies between upstream and downstream with a focus on operational performance improvement achieved via novel technology adoption.Haddud and Khare (2020) discussed the CSF of top management involvement in determining the level of supply chain digitalisation and in promoting and justifying acceptance of digitalising and leaning supply chains projects prior to embarking on adoption journeys.

Conclusion
The research set out to establish the research related to the LSC 4.0 and whilst it is still a nascent area as specifically related to the Lean Supply chain and digitalisation theme or concept the area is gaining more researcher interest.This study also specifically ascertained the benefits and motivations for integrating the LSC 4.0 as well as the challenges and CSF's of doing so.With the dawn of the fourth industrial revolution and increased digitalisation both future and ongoing, the researchers find that the technologies of Industry 4.0 will enhance the LSC.
However, it is very important to reap the benefits from this increased digitalisation and wide availability of process-enhancing technologies to review and integrate these right technologies to enhance the LSC.A limitation of the study is the limited research in this area as it is an evolving area.Also, the researchers excluded from this SLR research papers that did not contain all of the three themes of Lean, the Supply Chain and Industry 4.0 -whereas a combination of 2 of the 3 themes may have offered further research insights related to the LSC and Industry 4.0 integration.The implications for practice and society are to demonstrate how the LSC 4.0 can benefit organisations and enable leaner, greener and more efficient digitised supply chains.From a social and societal implications point of view understanding how the LSC 4.0 can eliminate waste and impact on both economic, social and environmental bottom-lines aids environmental sustainability.
Future research opportunities could include more longitudinal studies on organisations aiming to integrate their LSC's with the technologies of Industry 4.0 to understand further and benchmark the learnings in relation to the integration of the LSC and I4.0.In addition, further mixed methods studies with SC professionals working on the LSC and organisational digitalisation programs would be an opportunity to leverage further learnings around this new evolving area of the LSC 4.0.
Figure 1.A summary of the SLR process flow followed by the researchers Author's own derivation Figure 2. The Lean Supply Chain 4.0 trilogy Figure 3. Publications by year related to the LSC & I4.0 area

Table 2 .
RQ1: What is the current research on the LSC integrated with I4.0?