contribution to validation and testing of seatbelt … · also for today’s belts the car...

BULETIN ŞTIINłIFIC, Seria C, Fascicola: Mecanică, Tribologie, Tehnologia ConstrucŃiilor de Maşini SCIENTIFIC BULLETIN, Serie C, Fascicle: Mechanics, Tribology, Machine Manufacturing Technology ISSN 1224-3264, Volume 2014 No.XXVIII

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Contribution to Validation and Testing of Seatbelt Components

Paul Andrei IMRE 1,*

- Radu COTETIU2

Abstract: In this article an account of the different phases involved in seatbelt component development and testing are

explained. This will include a short introduction about the 3 point seatbelt and its components, the different tools and

needed in each validation phase: concept, product and serial production. In the concept phase the impact of different

external factor on the development process is listed as well as the tools used by the development team such as CAD,

FMEA, FEA, MBS etc. For the product phase the different departments involved in this step as well as the test to be

performed are listed, and in the serial life phase the tools for quality and production control are listed such as the SPC

and COP.

Keywords: seatbelt development, concept validation, product validation

1. INTRODUCTION

The first seatbelts were introduced in 1930, when doctors in the USA observed that a lot of deaths resulted from car crashes and could be prevented by an occupant retention system in the seat. So they mounted 2 point lap belt in their vehicles [2].

The factory mounted seatbelt on cars was introduced by Volvo in 1956, it was also a 2 point lap belt and because the statistics showed a significant improvement in deaths and serious injuries as a result of car crashes, the European law regulated as mandatory the mounting of the seatbelt for front car seats in 1965 [2].

There is a significant difference in the safety offered by a 2 point lap or chest belt in comparison to a 3 point belt. For example the 2 point lap belt would hold the occupant, but it would allow his chest to travel forward and potentially hit the staring wheel. And for the 2 point chest belt there is a great risk of submarining [4].

Today it is mandatory for all car manufacturers to equip their cars with 3 point seatbelt systems for all seats in the vehicles. A 3 point seatbelt system can be observed in figure 1.

The seatbelt is comprised of the following elements, as shown in figure 1: retractor; webbing; pillar-loop; tongue; buckle and 3rd point anchor. To improve safety some modification can be made to this standard seatbelt system, such as: replacing standard retractor with a retractor with pre-pretensioning and pretensioning capabilities; standard tongue with the crash-locking tongue, standard buckle and 3rd point anchor with pyrotechnical pretensioners; also to improve comfort you can add a height-adjuster. All this options are chosen by the car manufacturer depending on the wanted safety classification for the car in the NCAP tests. In order to be able to meet this demands the seatbelt manufacturer has to test and validate each seatbelt as a system and also each component [4].

Also for today’s belts the car manufactures have different ways to improve the seatbelt system in terms of comfort or in terms of safety, for example to improve the loads on the occupant body in the crash a pre-pretension system or a pretension system could be added, the dynamic locking tongue also helps to improve safety.

And the comfort may be improved by using an electric height adjuster [5].

Fig. 1. Three point seatbelt and its components [3]

2. FROM DEMAND TO CONCEPT

For any new car platform, the same platform could be used form multiple car models, the manufacturer will make a design goal document (DGD) in which he defines and lays-out all the important information for the component manufacturers. The important information for seatbelt design is defining the safety and comfort requirements, this will include: positioning of each seatbelt component; the vehicle destination market, as each market has their own set of standards for car safety systems (ex: ECE-R16 for Europe, FMVSS 208 and 210 for North America, CCC for China, etc.).

The positioning of the elements is important because the retractor for example could be placed in the B-pillar of the car or under the seat, the 3rd anchor point position is influenced by the number of doors the car has, etc. The legal requirements that the seatbelt performance has to adhere to depend on the destination market and this will have a big impact on the testing requirement of each seatbelt component. Also the seatbelt interaction with other car components such as the trim and seat has to be taken into account, as these components might pose a risk to the integrity of the webbing and other components.


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3. COMPONENT CONCEPTS AND CONCEPT

VALIDATION

Based on the information described above the

seatbelt manufacturer can decide what system best suits the needs of the car maker and offer existing products or develop new ones if needed. In this paper we will only consider the option of developing a new component.

In a new concept development the first necessity is to form a specific development team capable of delivering a product from concept to market, in the concept phase the core of the team will be formed by the development department, in the next phases the involvement of other departments such as purchase, quality, manufacturing and logistics will increase as the product gets closer to serial production.

The most important “limitations” for the development team are: the budget, this is influenced also by the customer (i.e. the car maker) as he may finance the development or nor; also the second important factor is the timeline for the new platform.

After the initial concept is laid out the team must first prove this concept, the easiest way is to generate CAD models and see how the components fit together and how they would interact with the environment, for this the programs that are mostly used in the industry are CATIA and UG.

If the concept is proven the team must create a list of the possible issues that the new product might have, this list is called a Failure mode and effects analysis (FMEA), it is used to better classify each identified risk and assigned a risk priority number (RPN), this number is obtained by first assigning a number from 1 to 10 for each of the following 3 categories: severity, occurrence and detection, and then multiplying them. The roadmap for the FMEA can be seen in figure 2.

Fig. 2. FMEA roadmap [4]

Based on this list each point which is considered to be a significant risk should be improved, in terms of RPN. To better understand the severity of each rick simulations can be performed to better verify assembly and movement collisions in multi-body dynamics (MBD), perform finite element analysis (FEA) as shown in figure 3 etc.

Fig. 2. FEA analysis on seatbelt tongue [7]

After the resulted information from the simulations is factored into the concept design the first rapid prototypes can be produced using 3D printers and rapid prototyping tools. After this initial validation of the concept is performed the testing of the concept can start.

For this step components are built to be more robust so they can endure more test in order to be able to validate the real-life function of the concept. This testing phase will be short and will comprise of only a few function tests as listed below for the different elements of the seatbelt:

• Retractors: webbing extraction, sensor function, durability, etc.;

• Height-adjusters: durability, assembly tests, etc.;

• Buckle: tongue insertion force, buckle function, push button force, etc.;

• Pretensioning elements: performance test, integrity test, etc.

4. PRODUCT VALIDATION

The phase starts when the concept is considered

robust and mature enough for serial life. For this part the full team is involved.

Purchase department is needed to be able to find the right suppliers for the components needed for the seatbelt assembly. These suppliers have to meet criteria’s regarding: quality, delivery time, cost per part and also offer long term sustainability.

The quality department has to make sure all the requirements are fulfilled by the components and by the system, with all the necessary legal documentation and in accordance with the latest standards. This department is split into different functions: supplier quality (SQ), production quality (PQ) and customer quality (CQ).


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The logistics department has to make sure that all components are registered in their system and place the order in time so the parts arrive just in time (JIT). Also there must always be sufficient stock and fluctuating levels in the assembly process must be taken into account.

Manufacturing and industrial engineering department have to come establish the process lay-out for the assembly process, and also take the necessary precautions together with the development team to assure that the risk identified in the FMEA list are taken into account and monitored [8].

The development and engineering department has to approve all the components form the nominated suppliers and also validate the assembly process. The ideal situation for this would be to use components from the serial manufacturing tool and built in the serial process. For this validation extensive testing in necessary to prevent any possible failures to pass unnoticed and undocumented to the serial product, as the investigation and correction costs would increase tenfold by then. For all test the statistical prediction tools of the six-sigma process are used, to be able to predict the performance of the product in the long-term.

The requirement for the results is to be at least in the 3σ range of the specification or 3 standard deviations (SD) from the mean, as this will assure a chance that the product will be 99,7% of the time within required limits. In figure 4 the relation between the SD and the probability that a part would be outside the specified limits is shown.

Fig. 4. Six sigma probability with normal curve [9]

First the measuring system has to be validated trough a measurement system analysis (MSA) which takes into account not only the machine, but also the interaction between machine, operator, measured part, measured dimension etc. After in order to determine the preliminary process capability (ppk) a range of software can be used, like MiniTab, QS-Stat see figure 5 etc.

Fig. 5. QS-stat graphs of data from samples [9]

In the case that a defect or a signal can be observed in the data range the cause for that must be found, for this a design of experiment (DoE) can be used to be able to obtain the most data with the smallest number of tests considering all the relevant factors.

5. SERIAL PROCESS CONTROL

Based on the tests and results obtained during the

product validation phase the verifications and tests to be performed in the product serial life are established, also the frequency of the test need to be taken into account because some of the tests are destructive so no matter how critical this test would be to the validation of the product performance you need to rely on an SPC process.

And if during the first two phase there is a chance that the car maker will pay for some of the investigations in serial life all the costs have to be supported by the manufacturing plant. The SPC is a quality tool and is used to determine how stable and predictable the process is in regards to the limits imposed by the customer.

The data used for this capability study is long term data (cpk) and it predicts how the process will behave in the future using 2 methods: sum of squares or moving range; because each process has variations in time due to a cumulus of factors: material, machine, method, man, environment and measurement, each of this could have an influence on the final product.

Using the data to establish control limits for the process, you could also determine any trends, shifts, or signals in the recorded values, an example of this can be seen in figure 6. All this factors would indicate that the process is not stable and predictable and without a stable and predictable process you can’t make any predictions regarding the values that will be obtained in the future [1].


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Fig. 6. Graphs of data groups showing a not stable and

not predictable process.

a) Shifts; b) Trends in process; c) Signal values outside

of process limits From the 3 factors listed above that would make

the process not predictable and not stable the signals could be treated as outliers, but only if there is a explanation for that value, for example: a maintenance intervention, a different measuring or testing method, etc.

6. CONCLUSIONS

For each new product a multidepartment team is

needed in order to allow a smooth transition of the product from concept to market. The development team needs to take into account not only the customer requirements but also legal and other imposed restriction such as budget and time limitations.

The number of performed test on the product will have a big impact on its reliability in serial life, so a good tracking of the RPN resulted from the FMEA list is needed. Also in the product validation phase it is important to have good communication between all departments in order to avoid unnecessary quality issues.

A range of development and quality tools can be used to help save time and reduce cost in all the phases of the project. Also the most important thing is to monitor the product throughout its serial life in order to increase your know-how and document the lessons

learned in order to better improve the next product and its manufacturing process.

REFERENCES

[1] Benneyan, JC., (1998). Use and interpretation of

statistical quality control charts. Int J Qual Health Care. 1998 Feb;10(1), pp. 69-73.

[2] Håland, Y., (2006). The evolution of the three point

seat belt from yesterday to tomorrow. IRCOBI Conference, Madrid, 20-22.09.2016. pp.3-5.

[3] Hesseling, R.J., Steinbuch, M., Veldpaus, F.E., Klisch, T. (2006). Identification and control of a

vehicle restraint system. Proceedings of the

Institution of Mechanical Engineers. Journal of Automobile Engineering 220(4), 401. ISSN 0954-4070

[4] Paul, Imre, (2013). Stadiul actual al dezvoltării

sistemelor de pretensionare în domeniul centurilor

de siguranŃă pentru automobile. Raport de cercetare nr. 1 la doctorat. Universitatea Tehnica din Cluj-Napoca. Centrul Universitar Nord din Baia Mare.

[5] Paul, I., Nasui, V., CoteŃiu R., (2014). Current

development of seatbelt pretensioning technologies

in the automotive industry. 15th International Scientific Conference. Automation in production planning and manufacturing, Zilina-Oscadnica, Slovak Republic, 19-21.05 2014. pp. 91-95. http://kavs.uniza.sk. ISBN 978-80-554-0878-1.

[6] Kan, S.H, Some basic measures. Retrieved on 18.07.204, from flylib.com/books/en/1.428.1.33/1/

[7] *** (2014). 3D software for inspection and reverse

engineering. Retrived on 18.05.2014, from www.otto-jena.de/3D_software.html

[8] *** (1995). Potential Failure mode and effect

analysis reference manual. Automotive Industry Action Group (AIAG).

[9] *** (2006). Statistik-Software (SPC) zur

Qualitätssicherung Q-DAS. Retrieved on 18.05.2014, from www.brigel.ch/messtechnik/q-das.htm

Author’s addresses 1Paul, Imre, ing., Universitatea Tehnica din Cluj-

Napoca Centrul Universitar Baia Mare, street Unirii,

no. 11/22, phone +40723779080, [email protected] 2Radu Cotetiu, prof. univ. dr. ing., Universitatea

Tehnica din Cluj-Napoca. Centrul Universitar Baia

Mare, Victor Babeş, no. 62/A, phone +40262401265; e-

mail [email protected]

Contact person *Paul,Imre, Drd. Ing.,

phone +40723779080, [email protected]

contribution to validation and testing of seatbelt … · also for today’s belts the car...

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