modularity as key enabler for scalability of final assembly units in the automotive sector

Peer-review under responsibility of the scientific committee of the 49th CIRP Conference on Manufacturing Systems doi: 10.1016/j.procir.2016.11.039 Procedia CIRP 57 2016 224 – 228 Sci

2212-8271 © 2016 The Authors Published by Elsevier B.V This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/)

Peer-review under responsibility of the scientific committee of the 49th CIRP Conference on Manufacturing Systems

doi: 10.1016/j.procir.2016.11.039

Procedia CIRP 57 ( 2016 ) 224 – 228

ScienceDirect

49th CIRP Conference on Manufacturing Systems (CIRP-CMS 2016) Modularity as Key Enabler for Scalability of Final Assembly Units in the

Automotive Sector Jakob Webera*, Markus Stäblera, Sebastian Thielena, Kristin Paetzoldb

a Daimler AG, TecFabrik, HPC F151, 71059 Sindelfingen, Germany

b Universität der Bundeswehr München, Werner-Heisenberg-Weg 39, 85577 Neubiberg, Germany

* Corresponding author Tel.: +49-7031-90-83779; fax: +49-711-3052-164757 E-mail address: jakob.weber@daimler.com

Abstract

This paper presents a novel approach to design assembly units steplessly scalable according to their degree of automation, where the core idea involves substituting and reconfiguration of different manual assembly steps with automated solutions For this reason assembly units are modularized in relation to their specific functional assembly steps For each assembly function a manual and an automated solution or so called

“functional module” is generated Recombining these different solutions allows an almost infinitely variable scalability and a variety of diverging overall solutions can be generated for these production units The procedure consists of designing a fully manually operated assembly unit which can be upgraded to a semi-automated or automated assembly unit by adding gradually functional modules This has mainly two benefits: Firstly, in context of changeable production units this procedure helps to easily adapt the assembly unit to unforeseen changes of the production environment Secondly, in the case of implementing the assembly unit at different places in a global production network, redesigning and over-engineering can be avoided by simply reconfiguring prepared functional modules The presented approach is demonstrated for a use-case within the automotive sector The conceptual work for a scalable cockpit assembly is shown and advantages according minimized engineering efforts are pointed out

© 2015 The Authors Published by Elsevier B.V

Peer-review under responsibility of Scientific committee of the 49th CIRP Conference on Manufacturing Systems (CIRP-CMS 2016)

Keywords: Scalability, Modularity, Changeability, Assembly, Axiomatic Design;

1 Introduction

The capability to react on turbulent environment conditions

is a central issue for original equipment manufacturers

(OEMs) in order to remain competitive in globalized markets

In this context, changeability of production units is a main

target for companies within the automotive sector

Particularly in final car assembly, conventional fully

automated production units, which often are firmly fixed and

inflexible, make it difficult to reach this goal of changeability

Therefore, during the design process of changeable

production units several enablers for changeability have to be

considered to counteract these shortcomings For assembly

these enablers are “automatibility”, “convertibility”,

“scalability”, “mobility” and “modularity” [1] This paper

presents an approach to reach scalability for most

semi-automated and semi-automated assembly units by the use of

modularity and reconfigurability of functional modules (see Fig 1) The basic idea is to scale a parameter of an assembly unit (e.g output) by adjusting the degree of automation

Fig 1 Scalability through reconfiguration of functional modules

© 2016 The Authors Published by Elsevier B.V This is an open access article under the CC BY-NC-ND license

( http://creativecommons.org/licenses/by-nc-nd/4.0/ ).

Peer-review under responsibility of the scientifi c committee of the 49th CIRP Conference on Manufacturing Systems

There are several works about enabling changeability in

assembly The results of these are the so-called

Reconfigurable Assembly Systems (RAS) as a new class

besides of conventional assembly systems However, these

works are often validated for small and medium-sized

enterprises (SMEs) [2] or for workpieces of small dimensions

compared to cars [2, 3, 4, 5] As a consequence, these

approaches often provide only a minor transferability to tasks

of companies of the automotive sector

With the aim of increasing changeability in assembly units

and therewith scalability of an OEM, the key aspect of this

paper is the modularization according to assembly functions

Starting with the analysis of a conventional assembly unit all

identified assembly functions are translated to functional

modules For each functional module a manual and an

automated solution is designed which can be configured and

also reconfigured arbitrarily In consequence, an almost

infinitely variable scalability of the degree of automation is

achieved

2 Previous Work and Research Gap

In order to concretize the research area, an outline of

previous work on changeability in context of assembly is

given Furthermore a short explanation on considering

changeability in design methodology is provided

2.1 Changeability in Assembly

The term changeability describes the possibility to react on

unforeseen environmental changes caused by e.g

technological developments, politics, and world economy

[6, 7, 8] In more detail, changeability can have different

characteristics on different hierarchical levels of a global

production system In accordance with [1, 7, 9] there is a

classification of changeability reaching from station level,

where only single part elements are machined, to production

network level involving the whole product portfolio of a

company In context of this paper, where the focus lies on

single assembly units, the corresponding level can be seen in

system level On this level changeability is expressed by

flexibility on the one hand and reconfigurability on the other

hand Flexibility describes the possibility of enabling logical

changes like re-programming, re-routing and re-scheduling

On the contrary reconfigurability means the ability to fulfil

physical changes of the structure of manufacturing processes

like adding, removing or modifying machine modules [1]

More precisely, a system’s reconfigurability is preset by its

initial configurability This configurability is in turn based on

a modular design resulting in a modular construction set of

production unit [10]

In conformity with this definition there are two production

paradigms: Flexible Manufacturing Systems (FMS) and

Reconfigurable Manufacturing Systems (RMS) The

differentiation of both paradigms is given by the degree of

flexibility [11] A FMS shows a high general flexibility,

which can be advantageous and disadvantageous at the same

time The high and beneficial degree of flexibility results from

much built-in functionality which leads to high and

detrimental investment costs of the systems [12, 13] In contrary, an RMS only shows a customized and limited flexibility [11] An RAS is defined analogously to an RMS with the difference of having the focus on assembly instead of manufacturing

For achieving a changeable assembly several enablers of changeability have to be considered, as already mentioned In context of assembly the most important enablers are modularity, scalability, convertibility, mobility and automatibility [1] A key role in order to reach a changeable assembly can be seen in enabling modularity The importance

of modularity is emphasized because major research takes place in the field of modularization methods of changeable production systems [14, 15, 16, 17] Although this research is

on production system level, it is a hint for modularity being important on the lower level of production units [18, 19]

2.2 Design Methodology

In [20] a design approach for changeable manufacturing system design is proposed Thereby a central idea is the assumption that factories are products for which product design theories can be applied in the design process According to this it can be stated that there is an extensive amount of usable design methods, methodologies and theories One of these is Axiomatic Design (AD) Theory by Suh which inter alia seems particularly suitable for the design and development of changeable production systems and production units The theory mainly consists of two axioms with a special focus on independence of functional requirements of a design task [21]

Exemplarily, in [23, 24] two new approaches and applications of AD in context of changeable production systems are introduced The emphasis of these papers lies on challenges of SMEs in context of changeability

Another approach for using AD for the development of changeable production units is given in [25] With this a way

is shown to consider enablers of change in this theory and to apply this theory in the setting of a large company like an OEM

2.3 Research Gap

The mentioned solutions and approaches for RAS are proper solutions for the specific problem definitions These approaches are often dedicated to assembly systems which are hardly or not at all comparable to final car assembly This can

be explained with different dimensions of the produced work pieces as well as with completely different conditions regarding the assembly system Conventional final car assembly is characterized by many manual and a small proportion of automated processes The area of automated processes can be divided like follows: on the one hand there is fixed and inflexible conveyor technology, on the other hand,

in some cases assembly tasks like the joining of cockpits are realized with fixed automations involving large industrial robots A major challenge is to find a way to introduce changeability to final car assembly particularly for automated processes and to satisfy the given constraints at the same time

With the focus on automations with industrial robots the

research questions can be formulated as follows:

1 Can modularity be seen as key enabler for scalability of

assembly units in final car assembly?

2 How can reconfigurability of production units be

considered in final car assembly?

3 Approach

The following approach can be used to answer the stated

research questions The central idea is to pursue a strict

modularization according to functions of an assembly unit in

order to improve changeability and therewith scalability In

Fig 2 the three main steps are depicted, starting with an

analysis of a conventional assembly unit, a synthesis step and

ending with the configuration of a changeable assembly unit

Fig 2 Design procedure for changeable assembly units

3.1 Analysis

Starting point of the analysis step is a conventional

assembly unit The analysis of a unit like this provides the

possibility to identify the main functional requirements which

have to be fulfilled by the assembly unit The aim is to

combine several functional requirements in a favorable

manner to an assembly function which fulfills one single

assembly task Moreover, it might be possible that there are

functional requirements which are not assignable to one

specific assembly function On the contrary they might be

relatable to two or more assembly functions These functional

requirements can be brought together in a sort of basic

function This is later on a common basis for all different

solutions of the scalable assembly unit

A suitable tool in order to gather and to structure the

requirements represents Axiomatic Design Theory The

provided domain model and hierarchical presentation of

functional requirements can help to identify and to cluster the

assembly functions

Thus, the result of the analysis step is a listing of functional requirements which are bundled to a basis function and to several assembly functions The physical solution to these assembly functions is generated in the following synthesis step

3.2 Synthesis

The synthesis step serves to generate physical solutions for each required assembly and basic function The aim is to find

a manual and an automated solution for each function To allow an arbitrary combination and substitution of these modules, it is very important to keep all functional modules physically and conceptually independent Only if this claim for independence is fulfilled, scalability of the overall assembly unit is enabled A variety of design theories is about dependencies and also about minimizing dependencies Here,

as already mentioned AD Theory also is a very useful tool, because one of the two central axioms of this theory is about keeping functional requirements independent

As a result of this step, there is a catalogue of a basic module and several functional modules This catalogue contains an automated and a manual solution for each functional module which are functionally independent and therewith randomly exchangeable

3.3 (Re)configuration

The last step is configuring or reconfiguring an assembly unit For a new unit the different modules can be freely configured to an overall solution In this way it is possible to generate new assembly units which provide tailored solutions for each application Influencing factors for the selection process of the modules can be various They might be ranging from the country where the assembly unit will be used to requirements which occur from corporate policy

Moreover, for an existing assembly unit the possibility of reconfiguration is important Through strict modularity it is possible to reconfigure the assembly unit according to changing environmental conditions Reconfiguration means adding, removing or substituting single elements of an assembly unit Accompanying with this it is possible to substitute single functional modules either with the automated

or with the manual solution With consequent modularity the reconfiguration can be done with little effort regarding time and investment costs

4 Conceptual Work: Cockpit Assembly

In order to proof the benefits of the presented approach, an assembly unit is redesigned under aspects of modularity and therewith scalability The carried-out conceptual work is presented in the following paragraphs

4.1 Initial Situation

The cockpit assembly unit of an OEM is favored for several reasons Firstly, it is a unit with the assembly task of joining the cockpit into the car to be produced So, it is

obviously a task which has to be carried-out for every car in

every plant within a global production network In

consequence there are many applications of cockpit assembly

units with varying environmental conditions regarding labor

costs, qualification of the workers, cycle time and so on

Secondly, cockpit assembly units are quite common and

there is already a variety of solutions ranging from manual

processes to fully automated solutions Hence, the possibility

of joining the cockpit manually with the same quality as with

an automated process is proven Concretely, three different

solutions for joining the same type of cockpits can be

identified:

x manual process with two workmen with handling device

x semi-automated process with one workman with handling

device

x fully automated process with industrial robot

4.2 Analysis

The analysis process provides a broad variety of functional

requirements which have to be satisfied by the assembly unit

Structuring and clustering them results in a total of five major

assembly functions which have to be fulfilled An exemplary

cockpit module is depicted in Fig 3 with different colors

assigned to the different functions

Fig 3 Identified assembly functions

The first assembly function is to grip the cockpit which is

going to be joined into the car For this reason the cockpit has

to be first picked up from the transport rack Thereafter the

orientation and position has to be maintained during the

cockpit is moved into the car Finally the workpiece has to be

released in order to enable the joining of cockpit and car

Fully pre-assembled cockpits are provided on transport

racks Furthermore the cable set is already installed and is

delivered in a kind of box which also is provided on the

transport rack and has to be gripped, too The functional

requirements are analogous to the handling of the cockpit with

the difference that the transport box has to be returned to the

transport rack after joining the cockpit and placing the cable

set in the car

As a third assembly function the function of moving the

cockpit and the cable set box is identified Therefore it has to

be possible to move and orientate both items in three rotatory and three translational dimensions

In context of moving the cockpit the fine positioning in the car is another assembly function This function secures the fitting of the cockpit in the car and ensures quality of the overall cockpit assembly process

Most recently, the cockpit has actually to be joined into the car For this purpose there has to be an assembly module to fasten the cockpit in place by screws More functional requirements of this assembly function are for example to pick the screws, to monitor the screwing and to document the quality of the screwing process

4.3 Synthesis

The main task of the synthesis step is to generate proper solutions for the requirements, which are identified in the analysis step According to the five explained assembly functions, five functional modules with a manual and an automated solution each are designed An overview of the conceptual solutions for the specific functional modules is given in Table 1

The basic frame of the manipulator can be seen as a joint basis or basic module Therewith the design of the basic frame itself and of the interface between the modules and the frame

is essential The linking has to be easy to use and must allow adding, substituting or removing modules easily It is very important, that the interfaces of a manual and an automated solution of the same functional module are compatible

Table 1 Overview of conceptual solutions for functional modules

Functional Module Manual Solution Automated Solution Cockpit gripper Manual tensioner Pneumatic cylinder Cable set box gripper Manual tensioner Pneumatic cylinder Moving unit Flange for handling

device

Flange for industrial robot

Fine positioning unit Linear track Actuator Screwing unit Handheld screwdriver Automated screwdriver

4.4 Configuration of the Assembly Unit

The configuration of the assembly unit is done by combining the different solutions of the functional modules With two solutions for each of the five modules there are in summary ten solutions Because of the possibility of arbitrarily combining the solutions there are a total of 32 possible overall solutions of the assembly unit This allows a very fine scaling of the degree of automation and therewith of associated output values e.g the output in jobs per hour

4.5 Expected Effects and Lessons Learned

The application of the presented approach during the conceptual work already indicates several advantages For example there seems to be no more or just a negligible effort regarding costs for the development and implementation of the modular concept of the assembly unit On the contrary, with providing a catalogue of already finished modules the

follow-up costs for additional cockpit assembly units can be

reduced Indeed, for the first time there is a bigger effort for

designing all possible solutions, therefore the engineering

costs for further applications will be low Compared to the

current situation the engineering costs will be lower, because

the variety of solutions is limited to the solutions of the

catalogue

Another positive effect can be seen in the possibility to

carry out changes with little effort The modularity helps to

save engineering time in advance and maintenance time

during the reconfiguration of an existing unit It also helps to

reduce costs because only single modules are affected without

requiring the whole unit to be re-engineered

Furthermore, one insight can be gained for the design of

comparable assembly units: the biggest potential lies in the

modularization of the manipulator whether handled by a

handling device or an industrial robot

5 Discussion

The electrical point of view allows a critical assessment of

the proposed approach The whole modularization approach

works only if the electrical compatibility of the single

modules is guaranteed Corporate intern standards might help

to reach this goal

Moreover, another critical point of view can be seen in the

purpose of the fine scalability of the degree of automation

Not all combinations of automated and manual functional

modules may be useful Nevertheless, the presented approach

gives the opportunity for this fine scaling If it is not

necessary some automated or manual solutions for single

functional modules can be omitted if it is not helpful to

provide them

6 Conclusion and Outlook

This paper presents a novel approach to introduce

scalability of assembly units by consequently applying

modularity principles By reconfiguring functional modules

with automated and manual solutions a fine scaling of the

degree of automation of the assembly unit can be achieved

The proposed approach was applied during the conceptual

phase of the design of a cockpit assembly unit Five identified

functional modules with a manual and an automated solution

for each module provide a total of up to 32 possible overall

combinations of the assembly unit with varying degree of

automation This is advantageous in sense of reduced costs for

additional assembly units because of reduced engineering

effort as well as in sense of reconfiguration of an existing unit

with the aim to scale key performance indicators Future work

involves applying this approach to other assembly

applications

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