The 6th

edition of the

Interdisciplinarity in Engineering International Conference

“Petru Maior” University of Tîrgu Mureş, Romania, 2012

PRINCIPLES TO ALIGN AN ASSEMBLY LINE (ASSEMBLY

CELL) FOR SPOT WELDING OR RIVETING OF CAR BODY

Lucian MUDURA, Macedon GANEA

University of Oradea, Oradea

str. Universitatii nr. 1, Oradea, Romania

lmudura@yahoo.com, macedonganea@yahoo.com

ABSTRACT The research problem is to measure and align a cell assembly from an assembly line for

spot welding or riveting for car body where this is done by one robot or more robots. The

fixtures can have several working positions, which mean to find the fixture position

according with the robot position. For one fixture can work several robots, which can be

6-axis or 7-axis.

Keywords: fixtures, bodyside welding, measurements, robots, laser tracker

1. Introduction

To meet the requirements on quality, cost and

performance automotive experts concerns were

directed towards practical exploitation of new

technologies arising in their implementation in

manufacturing and assembly, design and

implementation of systems design, testing, repair and

control computer assisted production.

Thus, modern manufacturing faces two main

challenges: high quality at lower prices and improved

productivity. These are the requirements to keep the

major manufacturers in developed countries which

are in direct competition with countries with low-

wage. Other important features of production systems

are flexible and agile manufacturing process because

companies must answer a very dynamic market with

products that have short life cycles due to fashion

trends and global competition. [5]

Therefore, robotic welding is essential for

automatic welding in many industries. The fact is that

25% of all industrial robots are used in welding

processes. Robot welding is used to have a high

quality level of welds in short cycle’s times [5].

Market demands are indicators which

determine what kind of automotive types and variants

has to be made, thus requires the development and

implementation of production systems capable of

processing small batches of parts in terms of quality,

efficiency and high productivity. To fulfill these

requirements is necessary to move from flexible

manufacturing units to their integration into a flow of

materials and information lead by computer.

Flexible manufacturing system can be defined

as a cyber system whose elements are coordinated by

computer for self-regulation and optimization of me-

chanical processing. A flexible manufacturing system

has two or more flexible manufacturing cells connect-

ed by an automated transport (conveyor).

A flexible cell is used in body in white to

assembly of a frame and panels, here the detachable

components are fitted to the body [3].

During the last decades the layout of car

manufacturing plants are changing very often, always

adapted to the new demands and present conditions.

Due to the fact that the terms lean production gains

more importance and the minimization of non-value

activities are taken in consideration, new plant have

to be developed for the future as well [11].

The measurement system has a critical role in

any dimensional evaluation process. In automotive

industries, the measurement system is very important

and his role is particularly influential. The fixture

(tool) suppliers measure most part fixtures in absolute

space (X, Y, and Z coordinates) rather than as relative

distances between points. Absolute space measure-

ments are more complex, particularly for angled

surfaces [1].

The body coordinate system has been widely

used in the automotive industry for drawing of body

parts, product and process design. The origin of the

body coordinate system (OX) is defined at the front

center of a vehicle, its indicates a length of car and

the coordinate system (OZ) is below its underbody

indicates height of car and the coordinate system

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(OY), its starting point is the center of car body

indicates width of car. [1]

In figure 1 and figure 2 we have one assembly

line from Jaguar plant in Castle Bromwich, UK.

Fig.1 - Production line for Jaguar

Fig.2 - Production line for Jaguar

2. Materials and Methods

A flexible manufacturing cell made in GMAB

Consulting is shown in the figure below (fig. 3) [11].

The flexible manufacturing cell is formed by:

� electrical cabinet

� robots and robots controllers (in our

cell are 11 robots)

� Man/machine interface with operator

panel

� spot welding guns fixed on robot wrists

or spot welding guns fixed on the

platform

� grippers for the finishing robots

� tip dressers

� geometrical tools (fixture), turntables

� conveyor for part extraction

� safety device for operation in front of

the turntable

� safety fences

Fig.3 - A flexible manufacturing cell

In a flexible manufacturing cell or line we can

have one or more 7 axis robot. For the robots of the

type IRB 7600, the track motion acts as an integrated

seventh axis, as shown in figure 4.

Fig.4 - Robot on track motion (7 axis robot)

We used a track motion from ABB (fig. 5)

model type IRBT 7003S. The illustration shows the

principle layout of the track motion in the Compact

design [12].

Fig.5 - IRBT 7003S compact.

The component parts of the showing compact

track motion IRBT 7003S are [14]: 1. Gear rack; 2.

Linear guides; 3 & 8. End plates; 4. Side cover; 5.

Motor; 6. Serial Measurement Box / Brake release

box; 7. Carriage; 9. Cable chain; 10. Cable tray; 11.

Gearbox.

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The table below contains technical data

performance for track motion IRBT 7003S (table 1).

Table 1 - Technical specifications

The illustration (fig. 6) shows the length mea-

surements of IRBT 7003S from the front.

Fig. 6 - IRBT 7003S, length measurement [14]

The length of track motion depends on travel

length, in next table are showing how many stands

(quantity N) we need for different travel length. One

stand is 1000mm long.

Table 2 - value of N for different travel lengths

When a 7-axis robot is mounted, this can be

mounted straight on the floor or on frame, if we need

that 7-axis to reach highest points. First is necessary

to fix plates under each stand or frame in the floor, on

these plates the track/frame is welded or bolted.

It is very important that before mounting the

robot on track, this has to be level. It is recommended

to use a laser level in the track motion’s direction of

travel and a spirit level across this to obtain precise

adjustment. Always the measurements are done on a

machined surface such as the linear guide or gear

rack. The accuracy must at least be ± 0,5 mm along

the track length and ± 0,1 mm in height between side

to side.

Geometric leveling of track motion may be

performed according to three different methods:

Method 1: Leveling the track motion by using

a spirit leveler for leveling the carriage horizontally

along the complete travel length.

Method 2: Leveling the track motion by using

position measurement equipment for leveling the

carriage horizontally along the complete travel length.

Method 3: Leveling the track motion by using

a laser leveling instrument based on available

geometric system layout.

We used method 3, using a FARO Laser

Tracker ION as leveling instrument and Metrolog

XG13 as measurement software. Also we place in

position using de datum from layout a several roller

beds, lifters and underbodies.

Usual the origin of the assembly line is same

with origin of the first underbody in line. First we

place the underbody in line, then lifters and roller

beds.

3. Results and Discussion

In the picture below (fig. 7) is represented one

report after leveling the 7-axis. The length of the

track was 6m.

Below I will present the results from zone with

framers where we had to align 3 robots 7-axis, 2

robots 6-axis, and one underbody, one roller bed with

lifter, 2 framers, one fixture for roof (figure 8 and 9)

and one conveyor on track motion (figure 10).

I used the same procedure which I presented in

work paper called “The measurements and

alignment of fixture in a cell assembly for car body” to align the fixture with robots.

Fig. 7 - Leveling report for 7-axis

Fig. 8 - Top view of alignment

Fig. 9 - Left side view of alignment

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Fig. 10 - Conveyor report for leveling

I developed a procedure to align new fixtures

in assembly line which was aligned before and now it

running. In this case I couldn’t measure the flange of

robot because it has mounted tools for rivet. The new

fixtures were for different type of car, which was

shorter than the first car. Because I had the same

origin of the car I could use the old alignment to

position the laser tracker with the old tool then create

the reference for this tool. The robot already has the

position for the old tool, so I could create relationship

between 4 points from the robot in car line and the

old reference. After this I created a new alignment in

the reference of the new tool and generate de 4 points

for the robot for the new fixture, with the new

positions.

4. Conclusions

Is important to have a layout where is present

the position of fixture in the assembly cell or line.

For robots 7-axis is important to know where

is located the origin of the robot coordinate system.

The origin for 7-axis robot is located in manipulator

base frame center (fig. 11).

Fig. 11 - System coordinate for 7-axis robot

When we align an assembly line is important

to use same reference points to place the underbody,

roller beds, lifters and framers. When I create the line

for the middle of the car it has to be longer as

possible, to not have errors put all line together.

In case of having the fixture on the turntable is

important to know the angles for working position

and the turntable is able to rich every time this

position.

Acknowledgment

This work was partially supported by the

strategic grant POSDRU/88/1.5/S/50783, Project

ID50783 (2009), co financed by the European Social

Fund – Investing in People, within the Sectoral

Operational Programme Human Resources

Development 2007-2013.

References

[1] Auto/Steel Partnership Program - Body Systems

Analysis Task Force: Automotive Body

Measurement System Capability.

[2] Richard S. Figliola, Donald E. Beasley (2011):

Theory and Design for Mechanical

Measurements, John Wiley & Sons, Inc U.S.A.

[3] Lorenzo Morello, Lorenzo Rosti Rossini,

Giuseppe Pia, Andrea Tonoli (2011): The

Automotive Body, Volume I – Components,

Design Springer Science + Business Media B.V.

2011, ISBN 978-94-007-0512-8.

[4] Alan S. Morris. (2001), Measurement and

Instrumentation Principles, Butterworth-

Heinemann, A division of Reed Educational and

Professional Publishing Ltd, ISBN 0750650818.

[5] J. Norberto Pires, Altino Loureiro and Gunnar

Bölmsjo (2006): Welding Robots - technology,

systems issues and applications, London

Limited UK: Springer-Verlag.

[6] The ABB website (2012). [Online]. Available:

http://www.abb.com/

[7] W. Schreiber (2004): Planning of a car factory -

Automotive Product Development and

Production.

[8] The Metrologic Group website (2012). [Online].

Available: http://www.metrologic.fr/

[9] GMAB Consulting database with designed

fixtures.

[10] ABB product manual (2006): Product Manual

Track Motion - IRBT 7003S ABB Automation

Technologies AB, Sweden.

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