Production Electro mob ility

Risk Protection in Series Production for Alternative Drive Systems A key aspect of the assembly and test planning process for electric vehicles is avoiding the potential dangers ­involved in working with high-voltage components. A concept for preventive risk management developed by MBtech can help to achieve this.

60

Motivation

authors

There is a recognisable trend in the auto­ motive industry towards alternative drive systems. This trend is driven by an increas­ ing environmental awareness, the increas­ ing scarcity of fossil energy sources and new mobility concepts. As a result, the requirements placed on automotive pro­ duction technologies by the markets, the customers and, not least, legislative autho­­ rities have undergone extensive changes. The manufacturing process for hybrid, electric and fuel cell vehicles places in­­ creased demands on the production tech­ niques. Thus contains the assembling vehicles with alternative drive systems involves a significant number of new techniques and additions compared to conventional vehicle production, ❶. Working with the high-voltage compo­ nents requires a comprehensive range of safety measures. The high-voltage safety legislation and standards, which are either currently in planning or have already taken effect, form the basis for these measures. Based on the electronics safety standard ICE 61508, developed in recent years, ISO 26262 forms the basic for the automotive industry. In general, the risk assessment is car­ ried from the perspective of potentially vulnerable people in the manufacturing process. Avoiding exposing the workers to the potential dangers involved in working with high-voltage components is a central aspect of the assembly and test­ ing planning process. A shock current of 200 mA over a duration of only 300 ms can result in ventricular fibrillation. This represents just one example of the poten­ tial risks. Higher currents result in death,

Andreas Büttner

is Senior Consultant at MBtech ­Consulting GmbH, Practice ­Research System in Sindelfingen (Germany).

Wolfgang Triefenbach

is Head of Plant Projects, MBtech Group GmbH & Co. KGaA, Design & Manufacturing Engineering in ­Sindelfingen (Germany).

High-voltage battery

Inverter

HV wiring harness

Hybrid/ electric drive

Converter

03 I 2012

❶ Overview of high-voltage components in the vehicle Volume 12

❷. Preventive measures integrated into

the planning phase of the production processes are critical to reducing the risk. An appropriately designed assembly sequence can largely prevent exposing the workers to risks. For example, this can be achieved by installing the highvoltage bat­­tery and activating the highvoltage system as late as possible in the manufacturing process. Furthermore, the testing strategy and testing procedures must also be expanded to include the requirements of working with high voltages. On one hand, the safety of the high-voltage system must be tested. On the other hand, the commissioning of the complete system must also be guaran­ teed. Repair and reworking resulting from the specific behaviour of the high-voltage components must also be considered in detail in order to identify and eliminate any possible risks. The supporting and indirect areas involved in the manufacturing process represent another aspect of the risk assessment. Handling and transporting the high-voltage batteries throughout the entire supply chain is just one example. Furthermore, the employees are thor­ oughly trained to deal with the potential dangers arising from the modified manu­ facturing process. Work on the on-board energy network and on the high-voltage components during the reworking process, for example, must only be carried out by qualified electrical technicians. The MBtech Procedural Model

As part of the cooperation between MBtech Consulting GmbH and MBtech’s Design & Manufacturing Engineering division, a preventive risk management system was developed during the past three years as a procedural model utilising the “Inno Risk” strategic quality method and implemented in a variety of different pilot projects, ❸. These projects focused on preventively safeguarding the product quality with regard to the internal manufacturing and assembly processes. Along with other aspects, the integrated approach was primarily based on the use of the Failure Mode and Effects Analysis (FMEA) quality method combined with an interdisciplinary maturity management system encompassing the division and development procedures, ❹. This serves

61

Production Electro mob ility

1 1

2

3

4

: No effects – even for longer exposure Ventricular fibrillation probable

10,000

2 Level 2

5000

1000

: 3 bis 5 mA: sensation of pain begins : 10 bis 20 mA: let-go threshold : Usually no hazardous current conduction

Let-go limit

100 50

3

20 Let-go limit above 10 ms

10

0.1 0.2 0.5 1.0 2.0 5.0

10

20

50

Level 3 : Muscle spasms : Respiratory difficulty

Ventricular fibrillation threshold

200

200 mA

500

Perceptible threshold

Time [ms]

: 0.5 bis 2 mA: electricity is perceptible

Ventricular fibrillation probable above 300 ms

2000

: Cardiac arrhythmia : Permanent organ damage generally to be expected 4 Level 4 : Ventricular fibrillation

100 200 500 1000

: Cardiac arrest

Current [mA]

: Respiratory arrest

❷ Potential danger of electric shock

to systematically identify product and pro­ cess risks at an early stage. The potential risks are identified from the very begin­ ning and preventively taken into consider­ ation in the corresponding concepts and planning. An example of an electric vehicle project illustrates the risk evaluation and risk safeguarding procedures in the assembly and logistics areas.

Research & innovation

Level 1

Predevelopment

The procedure began with the system­ atic recording and evaluation of all of the potential risks and weaknesses within the new product project. This was carried out on the basis of a structured procedure for process selection and risk analysis. The FMEA method supported the system­ atic recording and evaluation of the poten­ tial risks in the manufacturing process.

Series development

Process development

Production

Sales

Mortal danger!

The experts from the development, manu­ facturing, quality management, logistics, work safety and after sales areas provided the necessary information. In addition, a knowledge database and the MBtech Group’s own industry and technology expertise also supported this process. The comprehensive inclusion of criti­ cal characteristics of the product and

After sales

Competence training and consulting (process/technology)/coaching Standardisation/strategy consulting Engineering services Standardisation of the method selection and application Competence coaching Method and risk analysis based on info from: : Development : Plant (manufacturing, QA) : After sales : Knowledge data base

Series support

Selection analysis

Method application (e.g. FMEA)

Standards : Toolbox risk management : Defined criteria : Evaluation matrix : Documentation

Central archive of all change versions Reporting and maturity management Interdisciplinary communication

62

Update adaption Trigger : Model update Archiving & : Change year support : Other changes Storage

❸ MBtech procedural model

IMPRI NT

Official Publication of FISITA (International Federation of Automotive Engineering Societies)

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Production Electro mob ility

HV safety

System safety

Process reliability

International standards EUCAR, VDA, USABC etc.

National and international standards DIN/EN/ISO

Preventive safeguarding during product development

Preventive safeguarding of the production and manufacturing processes

Multi-level safety concept

Process FMEA Risk assessment

System/battery level

Process audit

Module level Cell level

Assembly and testing strategy

Design, component and systems FMEA

Employee training and instruction

Maturity monitoring

Work safety/HV officer

Product audits Employee training and further education

❹ System and process reliability

DOI: 10.1365/s35595-012-0123-y

process design, up to and including plan­ ning the quality feedback loops, also made a decisive contribution. The docu­ mentation consistently focused on the safety-relevant aspects involved in work­ ing with high-voltage technologies. The integration of the current development status into the process planning for the production areas formed the basis. Man­ datory measures were defined accord­ ingly as part of the project management, and their implementation was monitored on a regular basis.

Objectives

The objective of the FMEA method was to investigate the overall manufacturing proc­ ess, focusing on high-voltage safety, the prevention of risks to the health and safety of the employees, the safe and fault-free assembly of the high-voltage system and the examination of the reworking volumes, taking into account the different construc­ tion stages of the manufacturing process. The implementation of the risk analy­ sis was oriented towards the following

premises: delivery of 100 % error-free parts with outbound goods inspection by the supplier and a visible status labeling on the high-voltage battery. Furthermore, the wiring paths in the vehicle’s installa­ tion space and the general conditions for the installation process as defined by the development department were also verified. All of the logistical procedures and processes were examined, taking into account the legal regulations and requirements. The results derived from the risk analy­ sis with regard to the process design for the construction of alternative drive systems for hybrid and electric vehicle series are divided into product-related and processrelated measures. The product-related measures include, for example, the classi­ fication of high-voltage plug connections, the insulation requirements for the wiring and the classification of the bolted connec­ tions for all equipotential bonding. They also include an examination of the contact risks for high-voltage components, a safe­ guarded process for activating the highvoltage system on the vehicle and a con­ sideration of low-voltage areas. Examples of process-related measures are the classification of production pro­ cesses and work procedures, safeguarded work processes for commissioning highvoltage systems and a reworking matrix for decision-making when reworking high-voltage components and systems. Further elements in this context include process sequence descriptions, procedural and working instructions, sustainable em­­ ployee qualification and the use of qualified electrical specialists. The procedure described above enabled possible key risk areas to be identified and preventively safeguarded, ❺. The integrated examination and the applied, standardised procedure based on the Inno Risk approach is an important key tool within the preventive risk man­ agement system. The quality of the products and processes is sustainably increased.

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❺ Example of an FMEA difference analysis

64

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