Research Article – IJAAT – 2017 – 22

International Journal of Advances on Automotive and Technology http://dx.doi.org/10.15659/ijaat.17.07.529 Promech Corp. Press, Istanbul, Turkey Manuscript Received October 14, 2016; Accepted May 15, 2017.

Vol.1, No. 3, pp. 131-136, July, 2017

This paper was recommended for publication in revised form by Co-Editor Yasin Karagoz

LIGHTWEIGHT DOOR RING SOLUTION IN BODY DEVELOPMENT

*Evren Altınok Hakan Kayserili TOFAŞ, Turkish Automotive Company TOFAŞ, Turkish Automotive Company R&D Center R&D Center Bursa, Turkey Bursa, Turkey

Ahmet Mert Serkan A. Altınel TOFAŞ, Turkish Automotive TOFAŞ, Turkish Automotive Company R&D Center Company R&D Center Bursa, Turkey Bursa, Turkey

Keywords: Ring, Hot Stamping, Boron Alloyed Steel, A-, B-Pillar, Rocker, Body Light Weight, Frontal Crash, Lateral Crash Phone: +90 224 261 03 50, Fax: +90 224 261 0408 E-mail address: [email protected]

ABSTRACT manufacturers in order to reduce CO2 emission that causes Lightweighting has become a target for car manufacturers greenhouse effect, the main reason for climate change. To in order to reduce CO2 emission that causes greenhouse effect, lessen vehicle load is aimed to increase fuel efficiency, provide the main reason for climate change. 40% of average weight occupant protection and environmental factors. distribution of a vehicle arises from the parts that belong to the The statistics show that fuel consumption may decrease 6- body. With a door ring design developed differently from 8% if the lightweight effect of full vehicle reaches 10% [1]. As standard methods, around 3 kg/vehicle weight reduction was the automotive structure possess about 40% weight of full achieved. Rocker which currently a couple of part was vehicle, the weight reduction in body structure is one key way converted to single part and the number of operation applied in to achieve fuel efficiency, harmful emissions reduction and raw production line was reduced. By this means the structure was material saving [2]. Moreover, crashworthiness is the other made more rigid. B-Pillar was designed as a lightweight part important issue that focuses on occupant protection to reduce suitable for the system. The weight reduction was obtained by the number of fatal injuries. The body is the suitable place to optimizing the parts without compromising vehicle safety reinforce structures to reduce effect of crashes. Hence, the objectives and by changing the loading method for welding ability of the vehicle to absorb energy comes into prominence process. By supporting designs with virtual analysis design for body design. Using resisting materials in design, providing validation was conducted. structural rigidity are the basis studies to increase stability for accidents. Especially the door ring that absorb energy in lateral crash must be designed without compromising vehicle safety objectives. INTRODUCTION The door ring (in Fig.1) is designed with three crucial parts Environmental problems that are increasing day by day which are A-Pillar that supports the , B-Pillar that canalize the most of industrial areas like automotive industry to play a key role providing strength to the midsection of the new researches. Lightweighting has become a target for car

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vehicle and Rocker that is located along the sides of the vehicle between front and rear wheel. In this paper, a new door ring was designed by developing differently from standard methods for a stronger and lightweight body structure. As a result, around 3 kg per vehicle weight reduction was achieved and new door ring design was verified by supporting with numerical analysis. The new door ring design method was developed according to FCA (Fiat Chrysler Automobiles) product development FIG.2 – PRODUCT DEVELOPMENT PROCESS process (Fig.2). The relevant process consists of four main phases which are concept, definition, execution, industrialization. RESULTS AND DISCUSSION Design Optimization The design of the door ring that is known as a life cage of the vehicles in side impact and the loading method of the door ring was developed in order to be more competitive without compromising vehicle performance. Problem Description and Alternative Solution: The standard door ring design is shown in Fig. 3. As can be seen in the figure, the standard design includes three important parts which are A-Pillar, B-Pillar and Rocker.

FIG.1 – A-PILLAR, B-PILLAR, ROCKER PANEL IN A CAR BODY DESIGN

FIG.3 – STANDARD DESIGN The new design was started in execution phase that includes technical development and tooling development process. In main design activities of technical development Gas metal arc welding (GMAW) is supposed to be applied stage that are packaging controls, virtual validations, on the back side of the door ring in order to avoid visual manufacturing feasibility and process simulations were made by pollution in the standard design. In addition to that GMAW design team. In addition to that the mathematic models were must be applied because of the Rocker which consists of two created in the CAD release level. In tooling development stage, parts (Fig.4). The same GMAW application must be used on the mathematic models were released by project team and the joint of A-Pillar and B-Pillar. previous design activities which are in technical development stage were continued in this stage too. Finally, in industrialization phase that is the final stage of development process, process verification, durability, VLO (vehicle layout controls), plant manufacturing process readiness, design validation and pre serial production were conducted by project team.

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The necessity of GMAW usage was eliminated as producing a new single Rocker part. Instead of that, spot welding is adequate in order to join Rocker and B-Pillar before loading the door ring to the body. Hence, B-Pillar was optimized as removing unnecessary portions of part that is used for GMAW on B-Pillar (Fig. 6).

FIG. 4– GMAW AREA ON THE DOOR RING

FIG. 6 – SPOT WELDING AREA ON THE DOOR RING Each part of the door ring is loaded to the body separately. Therefore extra welding applications are required on joint The number of operation applied in production line was regions. Production process is extended due to many number of reduced whereby the new door ring is designed. Around 3 kg operation. The new design process was launched based on these per vehicle weight reduction was achieved due to form A- and problems eventually. The new door ring design can be seen in B-Pillar with hot stamping and due to remove unnecessary Fig. 5. portion of parts. The effect of hot stamping on weight reduction is an expected result. Hot stamping offers considerable potential for minimizing component weight by reducing sheet thickness and the number of components needed. Hot stamping technology can be used for A- and B-Pillar reinforcement roof rails, side wall members and beams for crash management structures [3]. Tolerancing and Loading to Body: In the standard design, single part tolerances are used so that each part of the door ring are loaded to the body separately. The parts cannot be loaded to the body that will be experienced in case of unsuitability of the new door ring tolerances. Loading simulations were made in order to determine proper tolerances. The tolerance studies are applied on the new door ring design can be seen in Fig. 7. Moreover, the tolerance values were validated as making loading simulations.

FIG.5 – NEW DOOR RING DESIGN

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FIG.7 – TOLERANCE STUDIES OF THE NEW DOOR RING DESIGN

FIG.8 – SIDE IMPACT ANALYSIS IMAGE FOR EURO NCAP

Optimization Process The goal of this study is to obtain more rigid and stronger The data which is taken after a car that is moved at 50km/h door ring design by reducing the reinforcement parts and is crashed to a stable testing vehicle were compared with without increasing overall weight. It is more important to know performance criteria. The deformation effect on B-Pillar that is the safety performance of the vehicle which parts are affected observed in side impact simulation is in Fig. 9. The data is by lateral crash. Structural and mechanical characteristic of obtained from the simulations results were determined in door ring is crucial for the safety performance of the vehicle. accordance with the criteria by the safety center of FIAT. The door ring should have good energy absorption characteristic and high mechanical properties in order to be protected safety door ring. Generally these characteristics are obtained by using functionally graded strength (FGS). FGS structures are found by optimizing all of the crashworthiness and its deviation by the time of the crash impact (peak forces, max-min acceleration of the deformation, max displacement of the related zone in safety cage etc.) [4]. In optimization process, stampability analysis, side impact simulations, NVH tests, chemical composition and micro structure analysis were made on the new door ring design and optimal door ring design solution was obtained successfully. Side Impact Simulations (Lateral Crash Tests): Research has shown that side impacts are relatively uncommon, but they represent a disproportionately high level of fatalities FIG.9 – SIDE IMPACT SIMULATION RESULTS FOR [5]. Euro NCAP- European New Car Assessment Programme EURO NCAP added a pole test to demonstrate passenger safety. Euro NCAP’s pole test has seen several updates, including the test dummy, NVH Tests: Recently, various structural and mechanism performance criteria and scoring [6]. The image of side impact analysis techniques have been applied to vehicle development analysis according to Euro NCAP standards can be seen in contributing to simplification of prototyping and reduction of Fig.8. labour time required for vehicle development [7]. Thus, the finite element model of the door ring that is designed for change of concept was created for NHV test that is one of these analysis techniques (Fig.10).

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FIG.11 – STAMPABILITY SIMULATION RESULTS

FIG.10 – FINITE ELEMENT MODEL OF THE NEW DOOR RING DESIGN

The flexural mode that is obtained after the modal analysis is evaluated and is determined in accordance with criteria by the relevant department.

Stampability Analysis: Hot stamping process consists of austenitizing and quenching stages. The first process in hot stamping is heating of the blank up to its austenitization FIG.12 – STAMPABILITY SIMULATION RESULTS temperature that is between 900 and 950 °C for 4 to 10 min. The blanks are inside a continuous-feed furnace and transferred to cooled die set in 3 seconds. The cooling rates must be faster CONCLUSION than 30 °C/s to avoid undesirable bainite or even ferrit-pearlit In this study, around 3 kg per vehicle weight reduction was transformation. This process provides an advantage of low flow achieved with a door ring design developed differently from stress of boron alloyed steel in austenitization temperature and standard methods. In addition to that, the number of operation allows the manufacturing of parts with minimum springback applied in production line was reduced whereby the new door and high strength. ring is designed. Hence, loading time of the door ring to the Stampability analysis provides valuable feedback on key body was decreased in production line. The contribution of hot stamping quality issues and rapid geometry modification. The stamping to weight reduction was experimented as well as simulations of hot stamping parts can be seen in Fig. 11 and gaining experiences about hot stamping. The performance of Fig. 12. According to sectional thinning that is observed in developed new design and the suitability to the system were simulation results some improvements was made on the die verified by Euro NCAP side impact tests, NVH tests, designs and obtained optimal geometries. Above all, stampability analysis, loading simulations and tolerancing background and manufacturing information about hot stamping studies. Thus, academic research about hot stamping and was obtained thanks to this study. lightweighting for vehicles was done for next projects that was

prepared a substructure.

ACKNOWLEDGEMENTS This study is supported by TÜBİTAK (The Scientific and Technical Research Council of Turkey) with 3150096 Project Number. We would like to thank TÜBİTAK for its financial support throughout the project.

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NOMENCLATURE REFERENCES [1] Joseph C, B.K. Light metals in automotive applications. Light Austenitinization to heat the iron, iron-based metal, or Metal Age, 2000, 58(10), 2. steel to a temperature at which it changes crystal structure from ferrite [2] LONG Jiangqi, L.F., Chen Jiking. New Technology of Lightweight to austenite [8] and Steel-aluminum Hybrid Structure Car Body. CHINESE JOURNAL OF MECHANICAL ENGINEERING, 2008, 44(6), 9. Bainite a plate-like microstructure or phase (Chinese). morphology (not an equilibrium phase) that forms in steels at [3] T. Altan, Hot-stamping boron-alloyed steels for automotive parts, Part II: Microstructure, material strength changes during hot stamping, temperatures of 250–550 °C January18, 2007. (depending on alloy content) [9] [4] S. Bruschi, A. Ghiotti, Hot Stamping, Reference Module in Ferrite α-ferrite (α-Fe) or alpha iron, is a Materials Science and Materials Engineering, from Comprehensive solid solution of limited amounts of Materials Processing, Volume 3, 2014, Pages 27-54, Current as of 28 carbon in iron with a body-centered October 2015. cubic (BCC) crystal structure. It is this crystalline structure which gives [5] D. Otte, R. Sferco, R. Schaefer, et al. Assessment of Injury Severity steel and cast iron their magnetic of Nearside Occupants in Pole Impacts to Side of Passenger in European Traffic Accidents - Analysis of German and UK in-depth properties, and is the classic example DataProceedings of the International Technical Conference on The of a ferromagnetic material [10] Enhanced Safety of Vehicles (ESV). Stuttgart (2009).

NVH noise, vibration, harshness [6] M. Ratingen, A. Williams, A. Lie, A. Seeck, P. Castaing, R. Kolke G. Adriaenssens, and A. Miller, the European New Car Assessment Pearlite two-phased, lamellar (or layered) Programme: A Historical Review, Chinese Journal of Traumatology, structure composed of alternating Volume 19, Issue 2, April 2016, Pages 63–69. layers of ferrite (88 wt %) and cementite (12 wt %) that occurs in [7] Kurisu, Fujikawa, Miyauchi, Koizumi, Hirobe, Fukushima: Application of ADAMS mechanism analysis software to powertrains, some steels and cast irons [11] Mazda Technical Review, No. 22, p44-49 (2004).

[8] Nichols R. "Quenching and tempering of welded carbon steel tubulars, The Fabricator, July 29, 2001.

[9] Honeycombe, RWK (1981). Steels: Microstructure & Properties. ISBN 0713127937.

[10] Maranian, Peter (2009), Reducing Brittle and Fatigue Failures in Steel Structures, New York: American Society of Civil Engineers, ISBN 978-0-7844-1067-7.

[11] R. Asthana, Materials Processing and Manufacturing Science: Chemistry, Chemistry, 1st Edition, 2016, ISBN 9780750677165.

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