H
idden inapicturesque landscape
between lakesandsurrounded
by forests is thesouthSwedish
townofOlofström–approxi-
mately twohours from the international
air traffichubof Copenhagen.Here, away
from the industrial centresof Stockholm,
GothenburgandMalmö, lies themost
important bodyworkplant of theVolvo
group, a factorywhich issteeped in trad
ition. In the18thand19th centuries, the
factory–at that timenot yet under the
nameofVolvo–manufactured inparticular
wrought ironandsemi-finishedproducts
suchassteel pipesand ironplates. Since
1927, theOlofström factoryhasbeen
producingcarbodyparts forallVolvo
models.
Today, five trainswith280 containers full
of car bodyparts leaveOlofströmevery
day, heading for theVolvoassemblyplants
inGothenburgandGhent, Belgium,where
theyareassembled to form complete
bodies. Thisamounts to50million com-
ponentsannually.
Competency inspotwelding
“Most ofwhat you canseeof aVolvo
comes fromOlofström,”explainsLeif
Winberg, theplant engineer in chargeof
resistancewelding in theVolvoOlofström
factory. This includes load-bearing com-
ponents like theA, BandC columns, the
ASwedish recipe
that reallyhits thespot
The fact that spotwelding isbecomingever faster andmore reliable
is illustratedbya
customer-specific solution installedatVolvo inSweden. The ingredientsof thisspecial
Swedish recipeareelectricdrive technologyandvisionsystems from Festo, linked to the
automationplatformCPX. Thismeansmore reliability in theproductionof thesheet-metal
components forVolvo car bodies, andmoresafety for theplant operators.
Automotive industry:milling theelectrodesofweldingguns
bumper reinforcement, the front side
members, theside impact beams, the
crossbeamsand the roof archand roof
rail, togetherwithdoorsand frames. All
these componentsareproduced indiffer-
ent versions for thevariousVolvomodels,
ranging from the compactV40 through to
theS60saloonsand the largeSUVwith
thenameXC90.
Akeyelement inbodyworkproduction is
resistancewelding, since correctlywelded
sheetmetal componentsplaya crucial
role in thepassivesafetyof avehicle.
Within theweldingprocess, there isgreat
potential for increasedproductivity in the
millingof electrodes. Theelectrodesof
weldinggunsbecomeblunter as theyare
used tomakespotweldsandmust there-
forebemilledafter approximately150
spotweldsso that theyonceagainenable
accuratespotwelding. “Electrodemilling
operateson thesameprincipleas the
sharpeningof ablunt pencil,”explains
weldingexpertWinberg.
Joint development
“In recent yearswehave foundsolutions
whichhaveenabledus tocut thecycle
times for electrodemillingbywell over
half,”continuesWinberg. “There isalso
again insafety, sinceplantoperatorsno
longerhave toenter the robot cellsafter
milling inorder toadjust theelectrodes to
thecorrectposition for thespotwelds,”
addsLeif Lindahl,BusinessDevelopment
ManagerAutomotivewithFestoSweden.
For staticweldingguns, Festodeveloped
a customisedpivot armexactlyasper
thespecificationsofVolvoandABBwhich
brings theelectrodemillingdevice, theso-
called tipdresser, to theelectrodesafter
150spotweldshavebeen completed.
Thepivot arm ispreciselypositionedby
Festoelectric cylindersDNCE. Thanks to
freelyprogrammablepositions, these
electric cylindersareflexible in termsof
motionandaccelerategently. The com-
plete ready-to-install electrical package
suppliedby Festo includessteppermotor
EMMSandmotor controllersCMMS. The
motor controllersaresafely integrated in
acontrol cabinetwith theautomation
platformCPX.TheCPXcommunicateswith
themotor controllersandwith themaster
control system for the robot installation
viaProfinet.
Electrodemilling controlledby
visionsystem
Mobile tipdressersarenot necessary for
theweldinggunson theABBarticulated
robots. These robots can feed their elec-
trodes themselves to theelectrodemilling
deviceafter 150spotwelds. This freedom
ofmovement of theweldinggunsopens
completelynewhorizons. Inafirst step,
thearticulated robot brings thewelding
gun to the tipdresser. This thenmills the
electrodes. In thenext step, the robot
swings itselectrodes in front of the lens
of the FestovisionsystemSBO… -Q. “The
systemproducesan imagewhichsupplies
the robot systemwithall thedataneces-
sary inorder toposition theelectrodes
correctly toweld thenext sheetmetal
components,”saysWinberg. “Thevision
system isalsoeasy to integrateandsimple
to commissionviaparameterisation.”The
system includesnot only thesensor sys-
tem for theacquisitionof imagedatabut
alsoa completeelectronicevaluationunit
and the interfaces (Ethernet/CAN) required
for communicationwithhigher-level con-
trollers (PLCs). Thevisionsystem itself is
accommodated inahousingwhich isno
bigger thanaone-litre cartonofmilk.
Cycle times reduced toaquarter
Ina fractionof asecond, the image from
thevisionsystemprovidesdataon the
alignment of the contact surface, the
lengthandangleof theelectrodeand the
startingpoint on thesheetmetal. The
visionsystemsends thisdata to the robot
controller,whichsets the robot for the
next spotwelds. “Thishasallowedus to
reduce the cycle times for electrodemill-
ing from35seconds to justnineseconds,”
saysWinbergenthusiasticallyabout the
newsystem. “Thismeans thatwe can
almost achieve thesame cycle timeasa
machining rotary indexing table,which is
six seconds.”Considering that thereare
300welding robots installed inOlofström,
thismarksa furthermilestone in thehunt
for shorter cycle timesand thushigher
productivity.
Tipdresser for articulated-arm robots:
On the right the twoholes for
electrodemilling, andon the left the compact housingwith thevision
systemwhichprovides thedata for repositioning theelectrodes.
For staticweldinggunsystems:
A fast andprecisepivot arm
brings theelectrodemillingdevice, theso-called tipdresser,
to theelectrodesafter 150spotweldshavebeen completed.
VolvoCarCorporation
Olofström, Schweden
Areaof business:
Vehiclemanufacture
ABBAB
Västerås, Schweden
Areaof business:
Energytechnology, factory
andprocessautomation
At the camera-controlledelectrodemillingdevice:
LeifWinberg, Plant
Engineer forResistanceWeldingatVolvo inOlofström (left) andLeif
Lindahl, BusinessDevelopmentManagerAutomotivewith FestoSweden.
Faster andmore reliable:
Volvo is constantly improving its
weldingprocesses.
Photo:©Volvo
1.2014
trends inautomation
Synergies
24
–
25
