To address the deficits identified in Sect. 2 and to incorporate the requirements from Fig. 1, a chronologically structured I4.0 process model has been conceived. It is basically oriented to the process models of [17, 22] and extends these approaches for the application in SMEs operating in GPN. Similar to existing approaches, the model comprises five phases (initialization, analysis, conceptualization, realization, demonstration) which are depicted in Fig. 2. As a more detailed explanation in the following sections will show, the initialization phase focuses on the problem definition and project planning, while the analysis phase records the status quo and reveals potentials for improvement. The conceptualization phase, moreover, aims at developing an I4.0 solution for the identified problem, which is then implemented in the realization phase. Within the demonstration phase, finally, the solution is transformed into a showcase which can serve as an inspiration for other companies on their way towards I4.0. For guaranteeing user-friendliness and comprehensibility, all of these phases are supported by dedicated methods, documents and milestones (Fig. 2) .
The process model thereby starts with the initialization phase (Fig. 2). Apart from a careful preparation that aims at avoiding risks, this phase also includes project planning . This entails the definition of a higher-level project plan and time schedule . Here, all executive and management personnel from areas such as IT, logistics, production and quality have to be involved. Once the project team is fixed, its members are asked to develop an initial knowledge on I4.0 (e.g. by a literature review). This serves as a basis for a precise problem definition during the kickoff meeting where a precise field of action is agreed upon within which the derived I4.0 solution can contribute to improved product qualities or logistics performances. Such a field of action might be the lack of traceability of WIP or parts which leads to delayed deliveries and hence low customer satisfaction rates.
Thereafter, the status quo of the identified field of action has to be thoroughly recorded in order to elaborate core potentials and weaknesses and to develop initial solution approaches. For a structured recording of the status quo, the developed approach proposes two methods that support the project team in observing the field of action: The value stream analysis, on the one hand, examines affected GPN processes  to identify potentials for improvement in terms of process control (e.g. superfluous process steps). Since the classical value stream analysis is usually limited to a door-to-door-modelling for a single plant , further symbols (e.g. for manual and automatic processes, scrap, small load carriers as well as for internal and external material flows) were added to conduct a network-based analysis.
The Industry 4.0 Maturity Model, on the other hand, supports the assessment of the actual state and helps to unveil potentials that might address weaknesses discovered during the value stream analysis with an I4.0 focus. As mentioned before, the toolbox developed by  serves as a basis. To meet the requirements of a cross-company assessment, however, it has been adapted and complemented by the GPN perspective. Therefore, the model differentiates between the “supplier” perspective which separately evaluates all suppliers within a GPN and the “GPN” perspective that analyses the I4.0 maturity levels of the network as a whole. Since the focus of the paper lies on improving supplier quality in terms of their processes without explicitly addressing the improvement of products in terms of usability and customer value, the supplier perspective does not differentiate between the production and the product dimension proposed by . Instead, aspects such as the machine–machine-communication are adopted from  and particularly supplemented by aspects such as the avoidance of errors, hence explicitly allowing for a comprehensive overview of the supplier quality in terms of their production processes. The obtained model is shown in Figs. 3 and 4.
After the weaknesses in the field of action have been elaborated by means of the value stream analysis, they have to be analyzed and subdivided into their original root causes. Therefore, the problem analysis (e.g. Ishikawa) offers a structured approach. Based on that, the I4.0 maturity assessment might unveil potentials how certain root causes might be eliminated or reduced by means of a stronger focus on I4.0. The maturity assessment therefore serves for identifying potential initial solution approaches.
Based on the analysis phase, the conception phase aims at developing a concept for an I4.0 use case which paves the way to solve the selected problem according to its root causes. Therefore, a structured one-day workshop is suggested in which I4.0 ideas are generated, prioritized and conceptualized. The workshop concept is divided into four major agenda points:
I4.0 keynote: The keynote motivates the workshop participants and provides incentives for an increased I4.0 implementation. Besides, by repeating the acquired knowledge on I4.0, it ensures a common understanding for all participants.
Presentation of results on value stream analysis, maturity assessment and problem analysis: During this agenda point, the results from the value stream analysis, the I4.0 assessment and the problem analysis are presented and further serve as a basis for the creativity part.
Creativity part: The creativity part consists of four steps, which are carried out using the metaplan technique. This way, all workshop participants make a contribution and more ideas might be uncovered . As shown in Fig. 5, the first step of the creativity part comprises an individual working part aiming at the generation and transcription of ideas for solving the selected problem by means of I4.0 according to the respective root causes. After having written the ideas down, all participants present their proposals to the remaining participants. Based on this, ideas are clustered to measures on a metaplan board and then discussed and analyzed by the whole team. Finally, the measures are prioritized using evaluation points which are pinned to the favorite measures on the board. The measure with the highest priority (highlighted in red in Fig. 5) is then conceptually developed into a use case.
Conceptual development of the use case: The conceptual elaboration of the use case forms the central part of the workshop. It aims at further developing the measure into a use case concept (e.g. holistic traceability solution to track WIP and parts in progress). For supporting the development of the conceptual design, the project team is provided with a template which can be understood as a concise project profile (see Fig. 6). It contains the most important facts and serves both as a documentation of the conception phase and as an information basis for the realization phase. The template is divided into three levels and ranges from idea and realization to evaluation. On the idea level, the as-is situation and the target state of the use case are recorded. Besides, it is described how the target state shall be achieved. The realization level ensures that the concept can be carried out in a targeted manner. Therefore, necessary prerequisites and requirements must be recorded. Subsequently, both the milestones of the use case and the responsible persons as well as the planned project duration are captured. On the evaluation level, possible opportunities and risks can be noted. Moreover, an initial cost estimation or limit can be recorded.
Since the majority of SMEs wishing to implement I4.0 solutions on their shopfloors depends on externally purchased technology or know-how , the realization phase is designed for the assumption that a new machine, technology or IT system has to be purchased to implement the use case concept. In this context, the model offers assistance in order to be able to carry out the specification and selection process in a structured manner. Accordingly, the procedure is subdivided into the four steps “requirements catalogue”, “market overview (longlist)”, “pre-selection (shortlist)”, and “final provider selection” shown in Fig. 7.
As Fig. 7 indicates, the creation of a requirements catalogue is the essential first step, which aims at transferring the requirements from the project profile (Fig. 6) into concrete requirements including their importance or prioritization. In addition to general requirements, the catalogue can, especially for technical use cases (such as the introduction of RFID tags within the GPN), also contain technical requirements, infrastructural requirements or system requirements. Based on the catalogue, as many providers as possible are identified who might be considered for the desired solution. Therefore, a rough screening has first of all to be conducted which results in a market overview (longlist). Exhibitor directories of relevant industrial fairs or internet research might thereby serve as adequate means. After the compilation of all potential providers, the longlist might have a considerable scope, which should be reduced to 10–15 providers (shortlist) by means of a pre-selection. For this purpose, the catalogue of requirements can be used to successively compare the information published on the provider websites with the determined requirements. According to their respective degrees of requirements’ fulfillment, the providers are then put into a lexicographical ranking and the ones with the highest ranking are included in the shortlist. Aiming at a final provider selection, these providers are then contacted with the requirements catalogue and asked for a statement regarding the requirements. The two to four providers whose feedback appears most promising with regard to the fulfilment of the requirements are then invited to a provider workshop. The workshop thereby aims at getting to know the remaining providers and their solution concepts in detail. In this context, it is important to pre-define the objectives of the workshop in order to be able to evaluate solutions, appearances and knowledge of the providers as accurately as possible. The subsequent evaluation of the providers should thereby include non-monetary as well as monetary aspects: Non-monetary aspects will, on the one hand, be compared by means of a cost–benefit analysis. The investment calculation, on the other hand, will reflect monetary aspects. Both results are finally consulted by the management for making a decision. Afterwards, the provider has to draw up a functional specification according to which the purchase contract is finalized. With the final implementation of the I4.0 measure, the realization phase is considered to be successfully completed.
Building upon the realization phase, the demonstration phase aims for transforming the realized I4.0 application into an I4.0 showcase that serves as an inspiration for other enterprises to enhance I4.0 penetration in SMEs in GPN by simultaneously promoting the innovation performance of the company. For reaching this, the present model refers to a questionnaire proposed by the VDMA, which can be seen as an application document and as an instrument of assistance for transforming the I4.0 use case into a showcase for the Platform Industrie 4.0—an extensive and valuable collection of practice-oriented I4.0 applications . Since the platform is used as a popular source of information by institutions and companies alike, both its multiplication effects as well as its use as a source of information for companies are good reasons to promote the showcases on the platform .