Mega-casting in the automotive production system: Expert interview-based impact analysis of large-format aluminium high-pressure die-casting (HPDC) on the vehicle production

개요

연구의 핵심 목적: 본 연구는 자동차 생산 시스템에서 대형 알루미늄 고압 다이캐스팅(HPDC)을 이용한 메가캐스팅의 파괴적 잠재력을 분석하고 자동차 생산 시스템에 미치는 영향을 평가하는 것을 목적으로 한다. 특히, 메가캐스팅의 경제적, 환경적, 사회적, 전략적, 기술적 잠재력을 평가하고 생산 시스템의 각 티어 수준에 대한 기회와 과제를 전문가의 시각에서 제시하는 것을 목표로 한다.

주요 방법론: 본 연구는 메가캐스팅에 대한 최신 정보를 수집하기 위해 체계적인 인터넷 검색(SIR), 문헌 연구(SLR), 특허 연구(SPR)를 수행하였다. 연구 간극을 바탕으로, 자동차 생산 시스템 전반에 걸친 33개 기업 및 기관의 전문가 63명을 대상으로 심층 인터뷰를 실시하여 메가캐스팅 생산 개념과 의사결정 지원 모델을 개발하였다. 근거 이론과 코딩 방법론을 사용하여 데이터를 분석하였다.

핵심 결과:

메가캐스팅 생산 시스템 개발: 전문가 인터뷰를 바탕으로, 메가캐스팅 생산을 위한 제품-공정-생산설비(PPS) 프레임워크를 개발하였다. 기존의 다양한 재료를 사용하는 다중소재 혼합(MMM) 방식의 차체와 메가캐스팅을 적용한 차체 설계를 비교 분석하였다. 1+1 개념(알루미늄 다이캐스팅 언더바디 + MMM 상부 차체)을 가장 유망한 생산 개념으로 제시하고, 공정 체인과 설비를 구체적으로 제시하였다.

잠재력 분석: 메가캐스팅의 경제적, 환경적, 사회적, 전략적, 기술적 측면에 대한 잠재력을 분석하고 기회와 과제를 도출하였다. 경제성은 높은 초기 투자비용과 운영비용으로 중간 수준으로 평가되었고, 환경적 측면은 높은 CO2 배출로 낮게 평가되었다. 사회적 측면은 일자리 감소와 증가가 동시에 발생하여 중간 수준으로, 전략적 측면은 원자재 공급망 의존성으로 중간 수준으로 평가되었다. 기술적 측면은 높은 잠재력을 가진 것으로 평가되었다.

생산 시스템 영향: 메가캐스팅의 도입은 자동차 생산 시스템의 각 티어에 상당한 영향을 미칠 것으로 예상된다. 특히, Tier 1 및 2 공급업체에는 상당한 변화가 예상되고, OEM은 주조 공장을 직접 운영할 필요성이 증가할 것으로 예상된다.

의사결정 지원 모델: 메가캐스팅 도입 여부 결정을 돕기 위해 의사결정 지원 모델을 개발하였다. 해당 모델은 인프라, 구동 방식, 차량 종류, 투자 규모 등의 요소를 고려하여 생산 시스템의 적용 가능성을 평가한다.

주요 Figure:

• Figure 1: 연구 방법론을 보여주는 흐름도 (SIR, SLR, SPR, 전문가 인터뷰, 잠재력 분석, 생산 시스템 영향 분석, 의사결정 지원 모델 개발)
• Figure 3: 메가캐스팅 제품 스펙트럼(1+0, 1+1, 2+2, 3+1 개념)을 보여주는 그림. 다양한 개념의 부품 구성과 차체 제작에 미치는 영향을 보여준다.
• Figure 4: 기존 자동차 차체 생산 공정 흐름도
• Figure 5: 메가캐스팅 1+1 개념과 기존 MMM 방식의 차체 제작 공정 비교
• Figure 6: 메가캐스팅 1+1 개념과 기존 MMM 방식의 차체 조립 공정 비교
• Figure 9: 전문가 인터뷰를 통한 메가캐스팅 도입의 기회와 과제 분석 결과
• Figure 10: 메가캐스팅이 자동차 생산 시스템의 각 티어에 미치는 영향 분석 결과
• Figure 11: 의사결정 지원 모델 개발 방법론
• Figure 12: 의사결정 지원 모델 흐름도 (1+1 개념에 중점)

연구진 정보:

• 소속 기관: 시겐 대학교 국제생산공학 및 경영학과, 아헨 공과대학교 기계공구 및 생산공학 연구소(WZL)
• 저자명: Peter Burggräf, Georg Bergweiler, Stefan Kehrer, Tobias Krawczyk, Falko Fiedler
• 주요 연구 분야: 국제 생산 공학, 생산 관리, 기계 공구 및 생산 공학

연구 배경 및 목적:

해당 연구가 필요한 산업적 배경: 전기 자동차 시장의 성장과 새로운 경쟁업체의 등장으로 인해 자동차 생산 시스템의 혁신이 필요해졌다. 기존의 복잡한 차체 제작 공정을 단순화하고 생산성을 높이기 위한 새로운 방식이 요구된다.

구체적인 기술적 문제점 과제: 기존의 자동차 차체 제작 방식(MMM)은 부품 수가 많고 복잡하며, 조립 공정이 어렵고 시간이 많이 소요된다. 경량화와 비용 절감을 위한 새로운 기술이 필요하다.

연구 목표: 메가캐스팅이 자동차 생산 시스템에 미치는 영향을 분석하고, 경제적, 환경적, 사회적, 전략적, 기술적 측면에서 그 잠재력을 평가한다. 메가캐스팅 생산 개념을 제시하고 각 티어별 기회와 과제를 분석하고, 메가캐스팅 도입 여부 결정을 위한 의사결정 지원 모델을 개발한다.

결과 및 성과:

정량적 결과: 전문가 인터뷰 결과를 통해 메가캐스팅 도입의 기회와 과제를 정량적으로 분석하였다. (Figure 9 참조)

정성적 결과: 메가캐스팅 생산 개념, 공정 체인, 설비에 대한 구체적인 내용을 제시하였다. 전문가 인터뷰를 통해 도출된 잠재력 분석 결과(경제적, 환경적, 사회적, 전략적, 기술적 측면)를 제시하였다. 메가캐스팅이 자동차 생산 시스템 각 티어에 미치는 영향을 정성적으로 분석하였다. (Figure 10 참조)

기술적 성과: 메가캐스팅 생산 시스템을 위한 PPS 프레임워크를 개발하고, 기존 MMM 방식과 비교 분석하였다. 메가캐스팅 도입 여부 결정을 위한 의사결정 지원 모델을 개발하였다.

결론:

본 연구는 메가캐스팅의 자동차 생산 시스템에 대한 영향을 다각적으로 분석하였다. 메가캐스팅은 높은 기술적 잠재력을 가지고 있으나, 경제성, 환경적 영향, 사회적 영향, 전략적 리스크 등을 고려해야 한다. 개발된 의사결정 지원 모델은 OEM의 메가캐스팅 도입 결정에 도움을 줄 수 있을 것으로 기대된다. 향후 연구는 비용 구조 분석, 지속 가능한 생산, 수리 개념, 혼합 메가캐스팅 개념 등에 대한 추가적인 연구가 필요하다.

저작권 및 참고 자료

본 자료는 Peter Burggräf, Georg Bergweiler, Stefan Kehrer, Tobias Krawczyk, Falko Fiedler의 논문 "Mega-casting in the automotive production system: Expert interview-based impact analysis of large-format aluminium high-pressure die-casting (HPDC) on the vehicle production"을 기반으로 작성되었습니다.

DOI: [DOI URL] 본 자료는 위 논문을 바탕으로 요약 작성되었으며, 상업적 목적으로 무단 사용이 금지됩니다. Copyright © 2025 CASTMAN. All rights reserved.

Abstract

Since the revolutionary invention of the conveyor-belt production by Henry Ford in 1913, market player mainly evolved a unique selling point through E-Mobility. Mega-Casting promises a revolutionary simplification of the automotive production system using large-format high-pressure die-cast (HPDC) aluminium structural components in the automotive car body. Through 35 cross-industry expert interviews in the automotive production system, the paper's study has the aim to (1) present first time the analysis of the disrupting Mega-Casting automotive production concept. Based on grounded theory and coding methodology, the economical, ecological, sociological, strategical, and technical potential of Mega-Casting has been assessed to identify its differences and thus the impact on the automotive production system. (2) Expert view on opportunities and challenges of Mega-Casting for each TIER-level in the production system through a detailed Mega-Casting production concept case study.

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Keywords

• Tesla
• Giga casting
• Cast shop
• Body shop
• Foundry
• Giga press
• E-mobility
• Gigacasting
• MegaCasting
• Unboxed process

1. Introduction

1.1. Motivation

A paradigm shift in automotive production is taking place due to the E-Mobility transition and new market player can easier participate. These new players can realign their corporate structure and rethink and simplify car manufacturing. Some of those players have the vision to simplify the automotive production with the idea to produce cars like electronic devices or toy cars. These ideas are especially arising due to the green field status, which, in contrast to established OEMs, enables more freedom for new ways of manufacturing. Tesla's 2018 patent [1, p. 1-3] shows such an approach to simplify the highly complex press and body shop by a die-cast under body and conventional upper body. This approach could enable new player in product and production, which causes an interest in determining the technical, economic, and environmental potential of Mega-Casting. The term Mega-Casting is used in this paper to describe the production of large high-pressure die-casting applications on high-pressure die-casting machines with a locking force of over 5,000 kN.

1.2. Automotive production and high-pressure die-casting (HPDC) application

A car is produced step by step along the press shop, body shop, paint shop, and assembly shop [2, p. 43;4, p. 17]. Sheet metal parts are formed from coils of steel or aluminium [4, p. 15] with cost-intense part-specific tools in external suppliers or internal press shop and then joined in the highly-automated and thus complex body shop [4, p. 19]. These parts can also be manufactured by suppliers. In the following paint shop, pre-treatment and application of the paint layers are carried out [4, p. 23]. Finally, parts manufactured by supplier as well as the OEM, that are not part of the body-in-white are assembled to the painted body-in-white in the assembly shop [4, p. 25–30].

Conventional concepts for the production of the body-in-white can be differentiate i.e. by the product architecture and production characteristics. For example, the space frame is made of extruded aluminium profiles and is economically for small series [5, p. 223]. Despite high investment costs for equipment, economical production at high volumes is possible due to low cost of materials (steel or aluminium) and low cycle time [5, p. 222]. Efforts in lightweight design are increasingly leading to multi-material-mix (MMM)-design with the coexistence of steel and aluminium [5, p. 223] with up to 700 individual parts, which are joined in a multi-stage process with over 900 robots [2, p. 6]. This multi-stage-process consist mainly of one or more main lines, where the body-in-white is produced sequentially by adding more and more parts in several joining stages (J1-J3) [6, p. 7]. In addition to the robots, there are usually hundreds of harmonised fixtures in use. Furthermore, complexity arises due to the diversity of manufacturing techniques applied [4, p. 20], whereby resistance spot welding (RSW) is one of the most common joining processes [3, p. 1] with up to 5000 RSW spots per car [5, p. 179].

The application of die casting in car bodies has been limited so far to aluminium structural cast parts as shock towers used mainly in sport vehicles, sport utility vehicles (SUV), upper mid-range and luxury class segments, Buehler shows on its website on April 5, 2024. Aluminium structural cast parts are produced on various die casting machines and finally joined together with conventional car parts [1, p. 1].

The manufacturing process of die-casting means primary forming from the liquid state [7, p. 11] by using permanent moulds [8, p. 503]. For die-casting, a distinction can be made between the cold chamber and the hot chamber process [8, p. 503]. The cold chamber process is used for aluminium, brass, and magnesium because the separation of furnace and machine in the cold chamber process means that metals with a high melting temperature and high chemical activity can be processed with low thermal and chemical stress on the machine [7, p. 24]. However, magnesium can also be used in the warm chamber process [10, p. 4].

In the automotive industry, development trends are currently emerging among OEMs to produce Mega-Casting body components. Tesla and Volvo show on their websites as on May 5, 2024, that they are pursuing approaches to the production of Mega-Casting aluminium components in the underbody of the car body [1, p. 1;10, p. 61]. A Tesla patent from 2018 describes the invention for optimised production of aluminium die-cast car bodies by using improved die-casting machines and associated methods with the aim to reduce i.a., cycle time as well as operation, manufacturing, and tooling costs [1, p. 1]. Other companies that plan to use Mega-Casting are Mercedes Benz, which calls the technology Bionic Cast, and Chinese OEMs such as XPeng and Nio. This information can be seen on the websites of the OEMs.

This research paper follows a mixed-method approach where we show how Mega-Casting influences automotive production and processes. In particular, the aim of the paper is to (1) present first time the analysis of the disrupting Mega-Casting automotive production concept. Based on grounded theory and coding methodology, the economical, ecological, sociological, strategical, and technical potential of Mega-Casting has been assessed to identify its differences and thus the impact on the automotive production system. (2) Expert view on opportunities and challenges of Mega-Casting for each Tier level in the production system through a detailed Mega-Casting production concept case study.

2. Methodology

The methodology in this work starts with a systematic research of the internet, literature, and patents to identify and analyse relevant information on Mega-Casting. Based on the derived research gap, cross-industry expert interviews unveil further information, which give a basis to develop a production concept and a decision aid model. The described methodology in this paper is depicted in Fig. 1.

2.1. Method of systematic internet research (SIR)

To gain a first overview on the current state on Mega-Casting, a systematic internet research (SIR) was conducted in accordance to the procedure of the systematic literature review (SLR). With the same key words than the SLR, internet research engines have been used as databanks and the relevant results has been summarized in an excel sheet and PowerPoint slides. Moreover, with Mega-Casting associated company websites, newsletter, internet forums, and intern/extern conferences has been especially screened. The objective of the SIR was to gather broad information on Mega-Casting, which is rather non-scientific and industry-related, where this current trend has its origin.

2.2. Method of systematic literature research (SLR)

The basis of scientific research is the combination of existing and new knowledge [12, p. 2; 13, p. 333]. The condition for this is to create an overview of already existing and relevant literature [14, p. xiii]. Thus, a systematic literature research (SLR) was conducted on the topics of automotive body shop, aluminium die-casting, and technology management. The procedure of the SLR is based on the STARLITE (Standards for Reporting Literature) methodology [15, p. 425] and the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) methodology [16, p. 1006].

2.3. Method of systematic patent research (SPR)

A high relevance of Mega-Casting was determined as a part of the SIR, which lead to the motivation what intellectual property (IP) might have been claimed. Based on the key words used in the SLR and the known parent patent of Tesla (patent reference multi-directional die-casting), a systematic patent research (SPR) was conducted in two approaches: first, the parent family was analysed concerning forward and backward citation analysis and secondly, related key words and patent classifications has been used to analyse the patent databanks.

2.4. Method of cross-industry expert interviews

The conducted SIR, SLR, and SPR showed that Mega-Casting is due to its novelty in an early stage of research. Consequently, relevant information and sources are not yet available in sufficient quality and quantity. Therefore, the expert interview and specifically the guided interview was used as qualitative method for further data collection. It enables the collection of expert's knowledge on a predefined topic by a guideline of non-binding question formulations [17, p. 41].

The approach of the conducted expert interviews includes the steps preparation, implementation, and post processing.

At the step of preparation, the aim was to select experts for interviews in a manner that they form a representative sample for a holistic investigation on Mega-Casting. The supplier pyramid of the automotive industry has been utilized as a framework for defining all necessary player [18, p. 2;18, p. 27]. In addition, this visualisation offers the possibility of illustrating results such the influence on companies, institutions, and sectors of the production system that result from Mega-Casting. In total 63 experts of 33 companies or institutions were interviewed. A nomenclature was introduced for the anonymise designation of experts which consists of two numbers combined: For example, E31 designates the first expert of the third interview, while the second expert of the fourth interview is designated E42. Appendix 1 gives an overview of all experts that participated in the interviews.

Simultaneously with the selection of the experts, the content for the interviews was prepared, a guideline with leading questions as well as a first set of slides with the main topics were created. The interview guideline is structured with several chapters that deal with individual topics, such as the Mega-Casting production with focus on the process chain and machines and tools. The guideline was designed according to Lamnek and Krell [20]. To be able to comprehensively document and evaluate the valuable contents of the expert interviews and match the ethical requirements, preparations were made for recording and a declaration of consent was drawn up. In the declaration of consent, the experts agreed that their statements could be recorded, transcribed, anonymised, and published anonymously. All interviewed experts received a summary of the survey and they have further the possibility to get access to the transcribed interviews on request.

The post-processing of the expert interviews is aiming for an evaluation for generation of theory and for development of concepts from the interview transcription [21, p. 80]. Therefore, an approach is chosen which is based on the steps of evaluation according to Meuser und Nagel [22, p. 83]. In a first step, the recorded interview contents are transcribed, and the experts, companies, institutions, and contents are anonymised to match ethical requirements. The “reconstruction of an overall picture” [21, p. 80] for generation of theory out of the interview contents is conducted by coding text passages according to Grounded Theory [21, p. 72]. The text passages are transferred to an Excel table for evaluation and headings are assigned to the individual text passages. These headings are defined both ex ante and during the evaluation process [17, p. 47]. For cross-passage and cross-interview topic comparison, these headings are also given consistent codes [23, p. 86;20, p. 79]. The coding with headings and codes is done in orientation to the main topics. Thus, filtering the text passages according to these headings and codes enables the previously not available informational basis for the development of the production concept and the analysis of the potential of Mega-Casting.

2.5. Method of development of production concept

The aim of the production concept is to create a suitable reference for analysing the potential of Mega-Casting based on the expert interviews. Based on the derived requirements for Mega-Casting as well as for the identification of relevant criteria for the analysis of its potential from the expert interviews, a product-production-system (PPS) for Mega-Casting is developed. The PPS is a framework, which systemize a production system in three dimensions: product, process, and production equipment [24, p. 86]. Each of these three dimensions is described below for the implementation of a Mega-Casting concept. In the first step, all possible Mega-Casting concepts are defined from product-view. For the most promising concept, the production concept is developed and the resulting differences compared to the reference car body design in MMM are identified. The process chains of the production with Mega-Casting are developed and the necessary machines and tools are characterised. In addition, a factory layout for the implementation of automotive production with Mega-Casting is presented and used to describe the processes in production and to show cycle times. For the production-side of Mega-Casting, opportunities and challenges are identified and the potential is analysed and evaluated based on different criteria. Finally, the influence on the production system is examined. The design of a roadmap for the industrialisation of Mega-Casting summarises the results of the present work and provides an outlook into the future of automotive car body production. OEM and supplier considering Mega-Casting as a relevant alternative, but they are confronted with a lack of information and unstructured decision aid process. This paper aims to provide a decision aid model that guides through the important steps on assessing Mega-Casting as a concept. To provide this model, decision-making criteria and the developed production concept are chosen as the starting point. In a first step, the criteria are sorted in a decision sequence. Then, the possible decision points and possible outcomes are formulated. In the last step, the decision aid model is executed.

3. Results

This chapter describes the results of the previously described contents of the methodology. Parts of the results of the expert interviews has been presented in the automotive circle conference in September 2022 [25, p. 1–25].

3.1. Result of the systematic internet research (SIR)

SIR unveiled that Tesla speaks of Giga-Casting during the Battery Day 2020, while Volvo uses the term Mega-Casting on their website. The manufacturer of die-casting machines Buehler uses both terms. The terms are therefore to be understood as synonymous and describe the production of aluminium die-cast components with a locking force of the die-casting machines that exceeds the locking forces already in use. Buehler refers on their website to systems that achieve a locking force of over 5000 tons.

The SIR yields an overview of the companies already using Mega-Casting, such as Tesla has application in a structural component containing the front and rear body of the Model Y at the gigafactory in Texas. Research on the news websites of Electrek an Insideevs shows that in the future, Mega-Casting will also be used in Tesla's Cybertruck and that Volkswagen has announced to consider Mega-Casting for the E-Mobility-Project VW Trinity. Volvo also wants to use Mega-Casting in the rear part of electric cars, although it is not yet known which models will be produced with Mega-Casting. Idra states on its website as of May 5, 2024, that it has already sold 24 Gigapress (Idras die-casting machine for Mega-Casting). Mega-Casting has already been investigated for opportunities and risks on vehicle production [26, p. 580–584] and influence on the automotive supplier industry [27, p. 26–29]. Online reports show that Tesla produced an entire under body in one Mega-Casting piece for the first time in September 2023 and could use it in the future to produce an affordable small car [28]. The largest existing die-casting machine was shown online by LK with a locking force of 16,000 tons [29].

3.2. Result of the systematic literature research (SLR)

According to the guidelines of the STARLITE methodology, a comprehensive sampling strategy is followed and all online available sources within the selected databases are considered. Relevant key words were derived from the papers objective and associated synonyms were identified. Table 1 shows a matrix of combination these keywords combined by using Boolean operators to build meaningful search strings and the achieved hits in total and relevant per databank.

Table 1: Overall results of the conducted SLR with defined search strings and hits.

According to Moher et. al the phases identification, screening, and result systematically reduce the number of hits [16, p. 1009]. At the beginning, literature available online from the predefined databases (Science Direct, Springer Link, University Library of RWTH Aachen University, and Web of Science) were identified by means of the search strings and resulted in the total number of hits n_total. At this phase, hits from other sources available offline were also integrated. After adjusting the hits of duplicates, an initial selection took place based on a review of the titles. After this, topic and branch relevance were ensured by checking the abstract and summary, thus further reducing the number of hits. Finally, these hits n_relevant have been considered in a detailed literature review. Systematic online research on Mega-Casting has produced few articles due to the new topic. In a Chinese publication, the production of super-sized high pressure die casting components was shown on machines with a locking force of 8880 tons using magnesium alloys [30].

3.3. Result of the systematic patent research (SPR)

The SPR on Mega-Casting unveiled many patents related to Tesla, die-casting technology as well as machines, and Mega-Cast car body structures and alloys. Based on the paper's objective, following patents are most relevant and are summarized as followed.

On the product-side, an aluminium alloy with castability for Mega-Casting has been published in 2021, which has enough strength and ductility without following heat treatment [31, p. 1–2]. Another patent shows how the challenge of shock absorbing in front bodies can be integrated in large monolithic structures, such as in Mega-Casting. The example shows a complete die-cast front body, where energy absorbing works through plastic deformation of special cast pillar [32, p. 1–5]. Another patent describes the application of thin-walled die-cast honeycomb structures for an automotive car body, which consists of many hexagonal tubes [33, p. 1–6].

On the production-side, the patent “Multi-directional unibody casting machine for a vehicle frame and associated methods” describes for the first time how a Mega-Casting machine for an entire car body can look like. In comparison to conventional die-casting machines, this machine concept seems to have five moveable dies, which form in closed position the cast car body [1, p. 1–5]. In addition, a modular die-casting mould design has been published by General Motors, which addresses the challenges in dies thermal management through active cooling and heating features [34, p. 1–5].

In conclusion, the extensive analysis of the Mega-Casting associated state of the art by performing a SIR, SLR, and SPR unveils insufficient information on Mega-Casting with respect to the paper's objective. Although there is literature on aluminium die-casting and patents on Mega-Casting, general information on the concept, its potential, and how to design such a PPS, is missing.

3.4. Result of cross industry expert interviews

The results of the expert interviews allow the design of such a PPS, which will be used and compared with the conventional body, leading to the development of new process chains. The analysis of the interview results starts with deriving of requirements on Mega-Casting and the definition of criteria for the potential analysis of the PPS. After that, a PPS for Mega-Casting is designed. The analysis of the potential is done by describing opportunities and challenges, which lead to the evaluation of the potential.

3.4.1. Derived requirements and criteria

In the following, requirements on Mega-Casting are described and relevant criteria for analysing its potential are presented. The requirements and criteria are derived from the literature on the one hand and from the content of the expert interviews on the other.

Requirements

Filtering the 121 codes defined in the Excel table provided all the relevant text passages on requirements mentioned in the transcribed and analysed expert interviews. Fig. 2 presents the requirements mentioned by the experts in the interviews, as well as their number and share of the total number of the code requirements. The experts mention requirements for joining technology most frequently. E61 explains that “aluminium die-casting is challenging in terms of joining technology […] and this becomes even more complex when the structures become larger. The reason for this is that the properties will fluctuate over the component.” After joining technology, competences in carrying out the casting process and the need for a foundry in the OEM's production hall are regularly mentioned.

Criteria

For a sustainable performance of companies, different perspectives must be considered. These perspectives can be described by the FESG-Factors. These factors are intended to take into account the financial perspective (Finance), the ecological perspective (Environmental), the social perspective (Social), and the steering perspective (Governance) [35, p. 10]. In the same way as Boos, Hall also classifies the criteria in a similar manner [36, p. 111]. For the categorisation of the criteria to be identified in the context of this work, the FESG-Factors are used and extended by the technical perspective (Technical). Therefore, in the following these factors are called FESGT-Factors. As a basis for argumentation for the expert interviews, initial criteria were identified in advance based on the literature. These preliminary considerations included the explanations of the criteria grid according to Hall as well as influencing factors according to Kampker et al. [37, p. 163]. These exemplary criteria were used to stimulate discussion among the experts. The results of the expert interviews on criteria and its allocation to the FESGT-Factors are presented in Table 2.

Table 2: Categorisation of the criteria identified according the FESGT-Factors for subsequent potential analysis.

The evaluation of the expert interviews shows that most of all criteria mentioned can ultimately be attributed to the financial perspective. In addition, the issue of sustainability must be considered. This will “in future [...] almost become a finance [...] criterion, because [...] CO₂ will [probably] become the new euro” (E51). “Finance is certainly the most fundamental thing [...], so it must make economic sense that [one] wants to allow oneself this leap at all” (E51).

3.4.2. Developed Mega-Casting production concept

In the following, the detailed development of a suitable production concept as well as the identified changes compared to conventional body shop are shown. For this purpose, the framework conditions and assumptions are described by defining the concepts within the product spectrum. This is followed by the detailed development of the production concept for the technically most promising concept alternative, with additional alternatives also being referred to at suitable points.

Description of the framework conditions and assumptions

The framework conditions and assumptions are determined by the expert interviews content and supplemented by further assumptions. Table 3 provides an overview.

Table 3: Framework conditions and assumptions for the development of the production system for Mega-Casting.

Definition and identification of concepts within the product spectrum

To develop the production concept of die-cast car bodies, product concepts are needed as input. For this, the conventional body-in-white MMM concept serves as reference. It consists of many deep-drawn sheet metal components (steel and aluminium) as well as a few structural cast parts. According to Tesla's patent [1, p. 2], the MMM is challenged by a Mega-Casted electric vehicle made from a single component. Thus, the term 1 + 0-Piece-Concept is defined for this variant. These two extremes of MMM and 1 + 0-Piece-Concept build the product spectrum, see Fig. 3.

The evaluation of the expert opinions on the concept alternatives within the product spectrum is shown in Appendix 2. Most of the experts have a positive attitude towards the 2 + 2-Piece-Concept and the 3 + 1-Piece-Concept. For example, E71 can imagine three large-format die-cast components in the platform, because the parts are relatively similar. A high degree of feasibility can therefore also be assumed for the 1 + 3-Piece-Concept. E101 sees the 1 + 0-Piece-Concept as visionary, but expects further development of machinery, which can produce larger die-cast components in the future.

Consequently, for the development of the production concept, the 1 + 1-Piece-Concept is defined. It consists of a one-piece die-cast aluminium underbody and an upper body with MMM. For the PPS with the 1 + 1-Piece-Concept, a decision aid model is given for the application.

After the determination of the framework conditions and the choice of the 1 + 1-Piece-Concept, the detailed development of a production concept is shown. To describe the product, a very simplified approximation of the weight is used. A weight of approximately 250 kg can be assumed for the body-in-white with MMM of a mid-range car [5, p. 226]. Very low wall thicknesses of at least 0.7 mm are possible for the sheet metal components. In die-cast design, E251 assumes the wall thicknesses to be between two to three millimeters. This results in a factor of the order of three. In contrast, aluminium has a considerably lower density than steel. An OEM body designer (E251) assumes: “could not work out such presumed weight advantages.” Other experts expressed similar views during the interviews. E81 doubts that the body will be lighter, as structural parts of the body, which must perform well in the event of a crash, must be designed differently than before. E141 also does not see any weight savings, meaning that lightweight construction is not a motivation for Mega-Casting, but rather cost savings in production. According to Pischinger and Seiffert, the density ratio of steel to aluminium is also a factor of three [5]. The effects described above compensate for each other, thus a weight of 260 kg is also assumed for Mega-Casting in the following. The authors therefore assume that Mega-Casting will have a minor impact on the car body weight.

In the 1 + 1-Piece-Concept, the one-piece die-cast aluminium underbody should account for about 60 % of the body-in-white weight, which is approximately 150 kg. The weight of the upper body with MMM is assumed to be about 100 kg.

3.4.3. Developed process chains of the Mega-Casting production concept

The production of Mega-Casting car bodies with the 1 + 1-Piece-Concept results in changes in the process-chains, compared to the production of car bodies with MMM. In the following, the influence of production of Mega-Casting car bodies on the stages of the automotive production, shown in Fig. 4, is described and new process chains for all stages are designed.

Aluminium supply

The raw materials in conventional car body design are supplied in the form of coils [38, p. 15]. The supply of raw materials will be greatly change by the production of Mega-Casting car bodies. In conventional body shop, most components are manufactured from steel using deep-drawing and forming processes. Only small components, such as suspension struts, are already made of aluminium castings. Specific aluminium alloys are used as for Mega-Casting car bodies. These have characteristics, that are suitable for the die casting process, such as a lack of heat treatment. In a patent published by Tesla on aluminium alloys used for Mega-Casting, alloys with a silicon content of 6 % (3C1) to 7 % (3C3) are mentioned. Other components include copper, manganese, iron, vanadium, and magnesium [31]. The aluminium can be supplied either in solid or liquid form. According to E91, liquid delivery is “easily feasible” over a transportation period of up to five hours. E201 also speaks of a maximum transport distance of 500 km. This delivery is better in terms of energy, because it is no longer necessary to melt the raw material during production. This means that liquid delivery requires the production site to be located close to the raw material manufacturer. In the case of solid delivery, the raw material is supplied in the form of ingots. The transport of solid aluminium is implemented in 30 packages, each weighing up to 1000 kg (E91). Delivery in a liquid state is excluded, due to the high energy input required during transport to keep the aluminium liquid. In addition, the solid delivery of aluminium requires intermediate storage at the production site without the need for additional energy (E201). Liquid delivery takes place in a supply chain that is susceptible to traffic disruptions or delivery failure due to accidents or breakdowns (E91). In such cases, production may be interrupted due to a lack of raw material. The loss of production is avoided by storing the raw material temporarily during solid delivery. With the introduction of Mega-Casting, the production of aluminium is initially still heavily dependent on primary aluminium, as there are still few vehicles with aluminium bodies in operation, that can be recycled.

Component manufacturing in the foundry and in the press shop

The process chains for component manufacturing in the foundry and in the press shop are changing when using Mega-Casting. On the one hand, MMM is characterised by many forming process chains to produce shell components for the car's underbody, the crash structures, the upper body, and the hang-on parts. The process chains of forming are composed of deep drawing, trimming, punching, and postforming [39] and are supplemented by logistics. On the other hand, there are already some die-casting process chains to produce structural components such as die-cast suspension domes, side members, and cross members. Fig. 5 shows the process chain of the conventional body shop in the upper part. In the 1 + 1-Piece-Concept, die-casting of the underbody in a large-format component results in a single process chain in the foundry. It consists of the conventional approach with a smaller number of process steps, as the use of self-hardening aluminium alloys means that the heat treatment process after the casting process can be omitted [40]. Recent research shows, that the application of paint baking on non-heat treatable aluminium alloys has similar effects on the properties of aluminium alloys as conventional heat treatment [41, p. 11]. The step of transport remains but requires different logistics due to the in-house foundry and the larger component dimensions. Likewise, due to the elimination of many deep-drawn components in the 1 + 1-Piece-Concept, a reduction of the process chains in the press shop can be achieved. The process chain of the production of a die-casting underbody in the 1 + 1-Piece-Concept is shown in the lower part of Fig. 5.

Joining process in the body shop

The process chains for the joining process in the body shop are also changing when using Mega-Casting. If the 1 + 1-Piece-Concept is realised, almost all process steps can be omitted in joining stage 1 (J1). Casting the underbody in a single component makes them obsolete. Only the steps for connecting elements of crash structures should still be considered in the underbody. For example, E42 speaks of the need for crash performance elements in the front part and rear part. Similarly, E63 assumes that these crash elements cannot be replaced by a die-cast component due to their specific requirements. Joining stage 2 (J2) will not be characterised by any significant change, as the upperbody will continue to be produced with MMM according to the definition of the concept. The same applies to the steps of joining stage 3 (J3). In a series production of die-cast car bodies, “the cycle time [...] is very decisive because [...] die-casting is a batch process, component after component” (E121). For the casting of a one-piece front part or a one-piece rear part, a cycle time of about 100 s was confirmed by the experts (E32). Changes in the process chains by the implementation of Mega-Casting body production can be seen in Fig. 6.

To produce the die-cast one-piece underbody in the 1 + 1-Piece-Concept, a cycle time of 180 s is assumed by E231 due to a longer dosing, injection phase, and solidification time. For post-processing, 180 s are also assumed. The common cycle time in the body shop of 60 s (E71) is reduced to 45 s due to an expected reduction in the number of components to be joined. This value can be confirmed by the information provided by a video at the Tesla open day in October 2021 [39]. In the following, a rough estimation of the annual production of Mega-Casting car bodies is shown. Fig. 7 shows the planned cycle times of the production of a car body with Mega-Casting and a calculation of the annual car body production, without considering downtime during maintenance and scrap parts, that cannot be used. A 3-shift operation with six working days per week and 12 public holidays per year results in 300 working days per year [42]. This means that 1920 car bodies can be produced per day and the targeted annual number of 576,000 vehicles can be achieved. According to E291, a tool change must be carried out after 20,000 produced car bodies. E291 estimates the duration of a tool change as one work shift. From this, it can be assumed, that a total of 29 tool changes per year must be carried out for the production concept shown. The quantity of car bodies that are not produced due to the downtime is calculated as 18,560. This value is deducted from the total production, so that 557,440 car bodies can be produced, considering maintenance and tool changes. According to E191, a scrap rate of at least 10 % must be expected, reducing the quantity of produced bodies to 501,700.

Paint shop

The process chain of the paint shop in Fig. 8 remains the same in the production of die-cast car bodies, but there are changes in the process steps.

The quest for cost savings in production that can offset high investment costs through Mega-Casting in the foundry makes the use of the “Paintshop-Of-The-Future”, presented by the company Dürr, attractive for painting Mega-Casting car bodies. In this concept, the body is no longer painted in a line, but with the help of multiple paint shop boxes, that carry out the conventional painting steps.

Assembly

The statements made by the experts in the interviews do not indicate big changes in assembly due to Mega-Casting. This can be attributed to the fact that after both conventional body shop and in Mega-Casting, a finished car body with the same dimensions and same body parts is transferred to the assembly. According to E261, there is a trend of battery installation shifting from stations 80 to 120 towards the first station. Most of the changes take place in the chassis line. All components relating to a combustion engine as a drive are omitted or replaced by new components. The assembly of the fuel lines is omitted, as is the tank module. The assembly of the drive unit, which is an electric motor in the new concept, is retained and is also pre-assembled in a secondary line. Along the finish line, the process step in which the operating materials are filled is shortened, as no fossil fuel is filled in. The exhaust gas test is omitted from the scope of testing.

3.4.4. Design of factory layouts

The production process is described in detail below using a newly developed factory layout. This consists of a press shop, a foundry, the body shop, and the paint shop. Appendix 3 shows the design of a newly developed factory layout for Mega-Casting.

Press shop.

The design of the press shop is based on well-known press shops used in the automotive industry. In the first production cell (see I), the laser blank cutting machine cuts the desired geometry of the components in sheet metal. The raw material is rolled up in coils which, due to their weight of up to 30 tons, are transported from the storage location to the decoiling station with the help of an overhead crane. The coils are transported directly to the warehouse using a heavy-duty-transporter.

Due to the weight of the coils, the crane must be able to have a load capacity of 40 tons and be able to move over a length of around 15 m from the coil store to the decoiler. In addition, the crane must be able to reach every point of the coil store, which implies the crane must be able to move along a length of around 40 m along the coil store. The crane is used to unload delivered coils from transporters, which can drive up to the warehouse via the logistics area. Due to the overhead crane, a ceiling height of 20 m is selected, which is also required for the foundry hall, as an overhead crane is also used here. The cutting process in the cutting machine takes place on a moving conveyor belt, so that no robots are required for handling the sheets from the coil to the finished sheet. The waste material produced during the process is collected underneath the cutting machine so that it can be transported for recycling. The cut sheets are transported via automated guided vehicles (AGV) to an intermediate storage area. This allows different cycle times in the production cells. From the storage areas, the sheets are delivered in special load carriers (SLT) to the second production cell with the help of AGVs. The two-bin principle is used when stacking the sheets after the cutting machine. A filled SLT, which is on its way to the warehouse with the AGV, is immediately replaced with an empty SLT at the end of the cutting machine so that new sheets can be transported from the cutting machine at any time.

In the second production cell (see II) is the press line, which consists of six presses, with a robot in between the presses that passes the blanks on to the next press [43]. Two robots at the start of the press line place the sheets in the first press. At the end of the press line two robots place the sheets into a SLT. The SLT with the manufactured sheet-metal components is transported by an AGV to the high rack where the components are immediately placed in the desired level by the AGV. On both sides of the press line, space is provided for the storage of spare tools and tool changes, whereby logistics areas are outside these areas [43]. In total, the press shop with all components and logistics will have an area of 9200 square metres and a storage area for raw materials of 1600 square metres. The width of all logistics areas is assumed to be 10 m according to a calculation with VDI 2510 [44].

Foundry

In the foundry, four production cells are provided, each with a die-casting machine arranged around a centrally located post-processing line. With this arrangement, both the cycle time of the post-processing line and simple and fast logistics of the components from the die-casting machines to the post-processing centre can be achieved, while producing multiple parts at the same time to achieve the goal of 500,000 cars per year. Each production cell also contains supplemental machines as a melting furnace, a trimming press, a cooling bath, and a shredder. In addition, each die-casting cell contains two robots on linear axes for handling. The design and sequence in the die-casting cells are based on the Buehler Carat 920 die-casting cell for Mega-Casting [45]. The aluminium is delivered in the form of ingots, which are grouped together in aluminium stacks. The stacks are transported from the storage area to an intermediate storage area at the die-casting machine. The required aluminium mass per die casting machine can be determined in a rough calculation from the cycle time determined in chapter 3.4.3 and the mass of an aluminium die-casting underbody determined in chapter 3.4.2. Each machine produces 450 underbodies per day, each having a mass of approximately 150 kg. This results in an aluminium mass of about 70,000 kg per day. Considering the 10 % scrap rate, the required aluminium mass is reduced to 63,000 kg. After completion of the die-casting process, a robot on a linear axis transports the component from the machine to the first quality control and then to the cool-down station and the trimming press. Another robot on a linear axis removes the component from the trimming press. The second robot moves the component to a second quality control and then places the component on the deposit table. The defective components are moved to the shredder by the robot at the post-processing centre. In the shredder, the components are shredded and transported back to the melting furnace by means of a conveyor belt. The post-processing centre is connected to the melting furnace by a conveyor belt to enable the aluminium to be transported back to the furnace at each production cell there is a robot that travels along a linear axis and transfers the die-cast components, which are approved by the quality control, from the deposit table to the post-processing centre. The robots travel along this linear axis with the component to the start of the post-processing centre. In addition to the production cells, areas are provided for storing the replacement tools. Around the tool set, space is provided for machining the tool. Due to the size and weight of the tools, an overhead crane is required for tool changing. The load capacity of a crane is given by E271 as 150 tons and hall height of 20 m, resulting from the information provided by crane manufacturers. In the post-processing centre, there are four machines for deburring, straightening, machining, and cleaning the components [40]. Between the machines are a total of three robots that pass the component on to the next machine. At the end of the post-processing centre is a robot that places the final machined component on an AGV. The AGV transports the underbody directly to the body shop. For the foundry, the layout results in an area of 14,950 square metres and a storage area of 2,600 square metres.

Body Shop

The body shop is divided into three joining stages J1, J2, and J3, with J1 consisting of six joining stations and two stations with quality control. J2 and J3 each contain ten joining stations and two stations for quality control. Each joining station contains an average of four robots and has a length of 6 m and a width of 12 m. Two metres are provided for the area between two stations. Storage areas are provided on all sides of the production lines for the delivery and intermediate storage of the components. The components from the press shop as well as supplied components are taken from the high racks by AGV. From these racks, the components are delivered to the corresponding storage areas on both sides of the joining stations. In J1, the die-cast underbodies are delivered directly from the foundry to J1 by the AGV. The underbody is transported through the production line on the AGV. In the following stations, the underbody is joined with components of the crash structures at the sides, front, and rear. This is followed by two stations for quality control. After J1, the body is transported on AGVs to J2. In the ten stations of J2, the A-pillar, side panels and roof components are joined. Quality control is carried out in the last two stations. In J3 hang-on parts such as flaps and doors are joined. The complete body is handed over to the paint shop at the end of J3 via AGV.

Paint shop

The layout of the paint shop for production with Mega-Casting is to be realised according to the “Paintshop-of-the-Future”-concept, as already described. Here, the car bodies are painted in several painting lines at the same time. Each of these painting lines consists of several boxes, whereby one painting step of the conventional paint shop is carried out in each box. According to the Dürr Group, a box has a length of 12 m and a width of 5 m. For a painting line, this results in a length of 96 m. The AGV first transports the body to a high rack warehouse, where the bodies are temporarily stored to compensate for different cycle times. With the help of control software, each body can be assigned a storage location in the high rack warehouse. If there is a paint order for a body, the body is transported to a paint line with the help of an AGV. At the paint line, the body is removed from the AGV by robots and placed on a transport lane, which moves the body through the paint line. Once all steps of the painting process have been completed, the body is transported by an AGV to a different high rack warehouse and stored. As soon as the assembly order is in the system, the body can be picked up by an AGV and delivered for assembly. There are large areas between the painting lines on which the AGVs can move and at the same time keep sufficient distance from each other. The size of the paint shop depends on the variable number of paint lines and can be assumed to be 44,200 square metres for ten paint lines and two high-bay warehouses as well as an AGV loading station.

Tool shop

Car body production with Mega-Casting has an impact on toolmaking. E271 gives an insight into the changes in toolmaking due to Mega-Casting. The increasing size of the tools leads to a segmentation of the tools into a mould frame and the mould insert. This is due to challenges in hardening the steel during heat treatment. The mould insert, which consists of several parts, is subject to increased wear compared to conventional moulds and is replaced several times within the mould frame. E271 assumes up to four new mould inserts before the mould frame needs to be replaced. The segmentation of the moulds also makes it easy to adapt the mould to change requirements by replacing only individual mould inserts. The market for tool manufacturers is small in Mega-Casting. E121 currently sees only four companies worldwide ready to produce tools for Mega-Casting. Small tool manufacturers cannot produce the tools for Mega-Casting because of the high investment in plant technology and transport. Many small companies are not willing to take this economically risky step and are waiting for the Mega-Casting trend to develop. Large tool manufacturers can outsource the production of small tool segments to small tool manufacturers who can produce parts of this size and concentrate themselves on design and project management. For tool manufacturers that produce tools entirely in-house, the need for a larger machining centre with cranes and presses arises. The experts see a trend towards globalisation of tool manufacturing due to the few companies with competences in building Mega-Casting tools and supplying tool segments.

3.4.5. Identification of machines and tools

This chapter characterises the machines and tools required for the production of die-cast car bodies. The required machines and their tools to produce the 1 + 1-Piece-Concept are, as described in the previous sections, determined by the requirements of the product and the process. To produce deep-drawn components for the upper body and the hang-on parts, a press line in the press shop or a supplier will still be required. This can consist e.g. of two machines on the input side for cutting and six presses for forming the sheet metal, shown on the website of the Schuler Pressen GmbH as of May 5, 2024. In the 1 + 1-Piece-Concept, the same tools will be required as in the conventional concept, as there will be no change to the components for the upper body and the hang-on parts. The press line will be smaller than in the conventional concept, as the output quantity is lower due to the omission of the components for the mega-casted underbodies. The specifications of the die-casting machine are determined by the area of the part and the locking force. E251 describes, that the locking force of the machine depends on the surface area of the component. Die-casting machines with a locking force of approx. 6000 tons are required for Mega-Casting of a front or rear part (E121). To produce a complete underbody from one die-cast component, a simplified assumption is made that three times the surface area is required for a component if the rear body, front body and middle part are assumed to be approximately the same size. This corresponds to a triple locking force of 18,000 tons. The current developments of die-casting machines show that in the medium-term die-casting machines with the necessary technical specifications will be available on the market. The LK Group has produced machines with a locking force of 12,000 tons and has already developed a machine with a locking force of 16,000 tons. To avoid interruptions in the casting process, according to E121 three tool sets per die-casting machine are considered as a minimum, whereby one tool set is in the machine, another is ready to be changed, and the third is in the tool shop for reworking. For the time of production of a mould set by the tool manufacturer, E271 assumes seven to nine months after design freeze. E271 also sees the possibility of a post-processing centre at the car manufacturer's plant that can perform mould insert changes. Data for the dimensioning of the die-casting machines can be derived from the developed factory layouts. The machine sizes are determined by linear extrapolation of the machine data from known die-casting machines from Bühler AG, assuming the use of a machine with a locking force of 12,000 tons.

Table 4: Estimation of the dimensions of a die casting machine with a locking force of 12,000 tons based on known machine data of the die casting machines of Bühler AG.

3.4.6. Identification of opportunities and challenges

The text passages from the interviews with the code opportunities and challenges are evaluated and summarized in Fig. 9. These codes form the basis of the following potential analysis. Parallel to this work, the topic of “Mega-Casting” was analysed in further work at the WZL of the RWTH Aachen University. Among other things, a SWOT analysis was carried out to classify the opportunities and risks of Mega-Casting based on strengths and weaknesses [26, p. 582–584].

Production

The simplification in production is mentioned as the greatest opportunity and thus E173 sees a “significant reduction in the number of parts” leading to a reduction in joining effort. Other opportunities are identified in logistics (LOG), raw material (RM), data management (DM), space requirements (SR), and complexity (COM). The biggest challenge, according to experts, is in raw material. E131 sees the significant increase in raw material demand as challenging. The casting process (CP), complexity (COM), logistics (LOG), and data management (DM) are named as further challenges. Regarding machines and tools physical challenges due to the size of the components are mentioned. E301 mentions the difficulty of the fluidity of the liquid aluminium in the casting process, which leads to inhomogeneities in the component. Regarding the tooling, some experts address tool wear, which can lead to high tooling costs if the wear is too high. Regarding the process chain, the joining technology is mentioned as the biggest challenge. E162 evaluates the joining of castings as difficult and new technologies must be found for joining such Mega-Castings. However, E311 also evaluates this as an opportunity for joining companies. Change requests (CR) and scaling (SC) are also seen as an opportunity and a challenge. Other challenges, according to experts, are post-processing (PP), feasibility (FE), handling (HA), energy costs (EC), and cycle time (CT).

Product

At product level, the experts rated the question of repair concepts for Mega-Casted bodies as the biggest challenge. Other challenges refer to the product quality (QA), crash performance (CP), model variants (MV), product weight (WE), repairability (RE), and tolerances (TO). The possibility of functional integration is most frequently mentioned among all opportunities. This relates especially to the integration of the battery components or interfaces for outer shell parts.

3.4.7. Potential analysis and evaluation along the FESGT-factors

The Mega-Casting production concept has high investment costs due to the equipment in the foundry, especially the die-casting machines and tools. In addition, there are high energy costs due to the operation of the melting furnace. On the other hand, operating costs and investment costs can be saved by eliminating robots and joining operations in the body shop. Therefore, the economic potential of the 1 + 1-Piece-Concept is rated as medium. From an ecological point of view, the potential can be assumed to be low, as the extraction of raw materials and production are associated with high CO₂ emissions. Therefore, recycling of aluminium is necessary to a high degree. From a sociological point of view, the potential can be rated as medium, since jobs are lost through the simplification of production and the automation of production is further advanced. On the other hand, the foundry will create new jobs that can be filled by retraining personnel from the body shop. The strategic view can also be rated as medium, because there is a fear of dependence on certain and small group of suppliers due to the raw material aluminium and the Mega-Casting machinery. The production concept has high potential from a technical point of view. Due to the expected further development of die-casting machines, it can be assumed that the necessary plant technology will be available in the future. The product has challenges such as reparability and crash performance, for which concepts or ideas exist. In addition, the concept offers the potential to simplify the product and production through function integration, which offers further economic advantages.

3.4.8. Investigation of the influence on the production system

The influence of Mega-Casting on the production system is presented by the framework of the supplier pyramid and is expanded with the participants of the interviews. In another work on the subject of “Mega-Casting” at the WZL of the RWTH, a Porter analysis was carried out in which the influence of Mega-Casting on all tier-level of the supplier pyramid was examined [19; 27, p. 26–29]. In the interviews, the experts were asked to classify themselves into tier-levels. This is shown in Fig. 10, which is based on the supplier pyramid mentioned in 2.4. The numbered black circles represent companies that are assigned to one or more levels. The numbered grey circles show companies that are parallel to all levels, as they are suppliers to all levels.

Various internet sources discuss the influence of Mega-Casting on companies in the automotive industry. On gwcast.com, Mega-Casting enable the opportunity to rethink traditional supply chain and production [46]. In a presentation at the Automotive Circle, the results of the expert study were shown and the influence on the companies in the supplier pyramid was evaluated [25].

Among the experts of OEMs, E51 sees a positive influence if the greenfield approach is pursued and a negative influence for established structures. Other factors such as sustainability in relation to the raw material also need to be clarified before an assessment can be made regarding the influence. E251 sees “ definitely no negative influence.” Experts from research institutions do not see large influence so far, as German OEMs have been cautious about the topic. As described in the requirements, it is necessary for the OEM to operate its own foundry at the facility to produce die-cast car bodies in order to be able to implement an economically viable operation of the production system with Mega-Casting. This forces the OEM to increase the depth of added value in production. This has an impact on all companies in the value chain. Through Mega-Casting, the OEM builds up competences in the production of cast components. Furthermore, the OEM retains competences in the production of steel components, as the operation of a press shop is still necessary to produce car bodies and mostly hang-on parts.

For Tier 1 suppliers, there is almost no change in the depth of value creation, as the core business will continue to be the supply of facility technology and robotics, even for Mega-Casting. Some Tier 1 suppliers already have expertise in aluminium die-casting. A new market is emerging, particularly for equipment manufacturers in aluminium die-casting [25]. There are major changes in value creation for component suppliers whose core business in conventional car bodies with MMM is the manufacturing of steel components. The substitution of steel components with Mega-Casting components necessitates a shift in value creation. In addition, the development of competences in the die-casting sector is necessary to be able to supply Mega-Cast structural components or to be able to produce spare parts for repair concepts. In the developed production concept, competences in the production of car bodies are shifted to the OEM through the die-cast body produced in the factory of the OEM. This eliminates business cases for the suppliers and requires adaptations of their business. For component suppliers who previously had a “build-to-print” competence, there is the possibility of transformation into solution providers. This means that the execution of build orders specified by the customer is replaced by the acquisition of competences in developing components and solutions for design challenges.

Demand for small body components is expected to decline among Tier 2 suppliers. As a result, significant development progress in the direction of aluminium die-casting is necessary to benefit from this development [25].

A major impact is expected for Tier 3 suppliers. The surveyed suppliers of facility technology see a positive influence by Mega-Casting. E221 sees the influence as positive because they are already participating in the trend and have won orders as a result. In joining technology, new equipment will be necessary due to the larger size of single components of the car bodies. E301 sees the development as a die-casting machine manufacturer as positive overall because there is a high demand for the machines. Tier 2 supplier E171 sees a clear negative influence. The production of die-cast car bodies is seen as a substitution technology that significantly reduce the need of sheet metal parts and thus replaces E171's business basis. The large decrease in body shop operations due to a decrease in the traditional production of metal sheet parts, joining applications in body shop and component handling may lead to the replacement of small and medium suppliers whose business is based on traditional body shop operations. E161 sees a negative influence because as a supplier of welding equipment, the use cases decrease due to less joining technology. The possibility of switching to mechanical joining technology is also rated as a negative influence, since it is technically too different. A supplier for aluminium evaluates the influence neutrally, as they supply aluminium “no matter to whom, if the price is right” (E91). For the manufacturers of raw materials, there will be almost no change in value creation. The demand for raw materials will continue to exist. The demand for steel in the automotive sector will decrease and the demand for aluminium will increase.

Internet sources see a rising interest in Mega-Casting, but also emphasize, that it remains to be seen, if Mega-Casting replaces conventional MMM car bodies [47].

3.4.9. Roadmap for the industrialisation of the Mega-Casting process

The developed production system is classified in a roadmap, which can be used as a tool in the systematic product development. Roadmaps show existing technologies and important events in the technology development [48, p. 1] and provides insights into future development steps. Appendix 4 shows the designed roadmap with horizontally plotted timeline. The period from 1990 to 2030 is chosen for the evolution of die-casting in the automotive industry, as this period is relevant for the development of Mega-Casting. Technical developments are shown vertically and are classified in the levels product, process, machines and tools, and production system. The content of the roadmap is based on the performed expert interviews. The maturity level of die-cast car bodies was assessed by the experts as level six to seven according to the Technology Readiness Level (TRL) of NASA [49]. Based on the results of the interviews, it was estimated that level eight would be reached in 2025 and that large-format die-cast car bodies, such as the 1 + 1-Piece-Concept would be ready for series production in 2030.

3.4.10. Development of a decision aid model for mega-casting process

After a PPS has been developed for the application of Mega-Casting, this chapter will provide an aid to support an OEM in the question of selecting a PPS. The extensive upheaval caused by the industrialisation of the Mega-Casting concept challenge OEM with a difficult and responsible decision-making process.

The development of the decision aid model consists of several decision steps, which are elaborated and graphically represented in the following Fig. 11. The model is used to answer the question of whether the application of the developed PPS with the 1 + 1-Piece-Concept is an option for the OEM or not.

First, all possible Mega-Casting concept alternatives are defined based on the OEM car model concept strategy and presented for the decision support. From the product spectrum in chapter 3.4.2, the 2 + 2-Piece, the 3 + 1-Piece and the 1 + 1-Piece are adopted as possible concepts in addition to the conventional MMM concept. The decision model is focused on the question whether the 1 + 1-Piece-Concept can be a possible PPS for the OEM. The other concepts, that are shown in chapter 3.4.2, can represent alternatives that can be applied if one or more criteria are not agreed to.

The next step is to define the criteria that will be considered in the decision-making process. These criteria are also based on the framework conditions developed in chapter 3.4.2. The following criteria are applied:

• •Infrastructure (Greenfield or brownfield approach, die-casting in use)
• •Drive concept (Electric, combustion, or hybrid)
• •Vehicle segment (compact class, middle class, or luxury class)
• •Investments (Machines and robotics)

The decision-making process can be illustrated with the flow chart in Fig. 12. The criteria are evaluated one after the other in several decision-making steps. In the application of the decision tree, one of the options is selected at each decision level, considering the company's requirements and the intended application. A tree diagram is chosen as the form of representation, as it offers a high degree of clarity. Each criterion is placed at a decision level (D1, D2, D3, D4) by giving two or more options for action. Each action option leads to a new state on the status levels (S1, S2, S3). For this, it is necessary to determine the order of the decision levels. The decision points and states are numbered in the decision tree and called nodes. The decision levels are numbered so that the first number indicates the number of the decision level and the second number indicates the number of the node in the decision level of the decision tree. Node 34 is therefore the fourth node in the third decision level. The decision levels result in several status levels, which are designated with letters. Every status node is given a different letter to differentiate all status levels (A, B, C). In the first decision level D1, a decision is made between brownfield or greenfield approach, as this is the most fundamental decision in the design of the PPS. Here, consideration must also be given to whether, in the case of a brownfield approach, the site is suitable for the installation of Mega-Casting equipment, for example in terms of the load-bearing capacity of the floors and ceiling height. Likewise, there need to be considered whether the OEM's competencies are sufficient to operate a casting shop at the OEM's site or whether an alternative concept needs to be developed. The second decision level D2 differentiates between the production of electric vehicles or conventional drive concepts. This product-related decision is concretised in the third decision level D3 with the choice of vehicle segment. In a final decision level D4, the investment volume is considered. The investment refers to the system technology, which either already exists or must be purchased. In this way, the special importance of the economic requirement, which was elaborated in chapter 3.4.1, is integrated into the decision-making process. Fig. 6 shows the path of the decision tree leading to the 1 + 1-Piece-Concept only, because this paper focusses on the 1 + 1-Piece-Concept. The decisions follow from the Mega-Casting-Concept developed in chapter 3.4.2. Deviations from the decisions shown can lead to the choice of alternative Mega-Casting-Concepts such as the 3 + 1-Piece-Concept.

4. Conclusion and future work

The E-Mobility transition fundamentally changed the automotive industry. In this work, the potential of Mega-Casting for the car body design, the production system, and the production processes were analysed. A systematic literature research was performed to identify relevant knowledge and information on car body design and the production process of aluminium die-casting. It was revealed that, due to the actuality of Mega-Casting, there is not yet sufficient information in the literature for a comprehensive analysis of its potential. Therefore, the expert interview has been selected for further data collection. In a first step, production requirements and relevant criteria for analysing the potential of Mega-Casting were identified. These were categorised according to various factors to enable a holistic analysis from different perspectives. Most of the criteria mentioned could be traced back to the financial perspective in their origin. For the subsequent development of a suitable production concept, a product spectrum of conceivable concept alternatives for Mega-Casting was first drawn up based on the experts' statements. From this, it was concluded that the 1 + 1-Piece-Concept should be the focus for the development of the production concept. This concept consists of a one-piece die-cast aluminium underbody and an upper body with multi-material-mix (MMM)-design that can still be manufactured using conventional car body design. Process chains were developed for the foundry and press shop, body shop, and paint shop. Machines and tools were identified, production cells were designed, and factory layouts for the press shop, foundry, and body shop were drawn. For the analysis of the potential of the production of die-cast car bodies, opportunities and challenges were first identified from the expert interviews. The evaluation showed that the experts see significantly more challenges than opportunities for Mega-Casting. The subsequent analysis and evaluation of the potential was carried out from economic, ecological, sociological, strategic, and technical perspectives. For the developed production concept of the 1 + 1-Piece-Concept, a low potential was identified from an ecological perspective. From an economic, sociological, and strategic perspective, a medium potential could be identified, whereby a technical potential was rated as high. The impact on companies and the production system were described as significant and positive or negative depending on the Tier-level and branch in the case of an implementation of Mega-Casting. Afterwards, a roadmap for the industrialisation of Mega-Casting was designed. To this end, relevant events relating to die-casting in car body design and in the production system were classified in terms of time, and development trends and future action steps were identified. Due to the high level of technological maturity of die-casting technology, production of large-format die-cast car bodies can be expected in the next few years. Finally, a decision aid model was provided to support OEMs in the question of selecting a production system for the application of Mega-Casting. The extensive upheaval caused by the industrialisation of the Mega-Casting concept in car manufacturing presents OEMs with a difficult and responsible decision-making process. The process of the decision aid model consists of several decision steps, which are elaborated and graphically represented. The model is used to answer the question of whether the application of the developed production system with the 1 + 1-Piece-Concept is a worthwhile option for the OEM.

Further actions in the topic of Mega-Casting can be the following. A supplementary quantitative online survey would be useful to substantiate the identified qualitative data with more concrete values for further studies on the analysis and evaluation of the potential of Mega-Casting. For this survey, a larger sample would be conceivable due to the lower effort required to conduct it compared to the expert interviews. In order to analyse and quantitatively evaluate the potential, the cost structure of the production concept should be examined in further detail. For this purpose, a cost model can be set up that considers the investment costs of all relevant plants, machines, and tools, as well as the operating costs. An extended view on Mega-Casting with respect to the complete life cycle, starting from a sustainable production with recycled aluminium, life extending with repair and remanufacturing concepts, and circularity in case of recycling should be taken into account. Further potential can be analysed in hybrid Mega-Casting concepts, which combines the benefits of complex Mega-Casting castings and standardized aluminium profiles through a fixtureless connection with component-integrated fixture features [50].

Credit authorship contribution statement

Peter Burggräf: Supervision, Resources, Project administration, Conceptualization. Georg Bergweiler: Supervision, Resources, Project administration, Methodology, Investigation, Funding acquisition, Conceptualization. Stefan Kehrer: Writing – review & editing, Writing – original draft, Visualization, Validation, Methodology, Investigation. Tobias Krawczyk: Writing – review & editing, Writing – original draft, Visualization, Validation, Methodology, Investigation. Falko Fiedler: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Software, Resources, Methodology, Investigation, Formal analysis, Conceptualization.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Appendix 1. Interviewed experts with Tier-level, category of company respectively institution, position All experts work in Germany except E301 (Italy) and E292 (England)

Appendix 2. Identification of the concept alternatives from the expert interviews

Appendix 3. Design of factory layouts for the press shop, foundry, and body shop

Appendix 4. Roadmap for the industrialisation of Mega-Casting

Appendix 5. Supplementary data

Download: Download spreadsheet (690KB)

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