bosch automotive
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Automotive IndustryTechnology Update - Welding
Electric Drivesand Controls Hydraulics
Linear Motion andAssembly Technologies Pneumatics Service
Automotive Solutions from Rexroth
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Automotive RelatedTechnologies, Poducts & Solutions
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What is Medium Frequency (MF) Welding?
Medium frequency (1000Hz) resistance welding works by rectifying
a three-phase 50Hz AC current and supplying it to an inverter, which
converts the current to a frequency of 1000Hz and passes this through
a transformer/rectifier, typically integrated into the welding gun, so
that the welding current is always DC.
Compared with AC welding at 50Hz, the use of direct current MFwelding offers a number of technical and operational advantages:-
Balanced Phases
Since the MF welder draws from all three phases, it is less demanding on
the electrical distribution network, resulting in reduced electricity bills.
More Tolerant
It is also more tolerant of mains disturbances, as energy is supplied via
the inverter rather than directly.
More Efficient
Rexroth estimates that for a given welding application, power savingsof around 25% are achievable against a single-phase AC system.
Thanks to the higher operating efficiency, even the MF transformers
are lighter and more compact than AC types, especially where larger
currents are required, making them particularly suited to robotic
applications. This means robots can be smaller so less energy is
expended in moving the welding gun.
Weld Faster
MF means that weld times are 15% shorter too, because there are no
current fluctuations. Furthermore, due to the 1000Hz output from the
inverter and its more compact waveform, weld times can be controlled
to the millisecond, giving twenty times more accuracy than is possible
with a 50Hz AC supply. Also, unlike AC systems where there is inherent
resistance in the welding arm, there is no resistance to overcome,allowing different arm lengths and tip characteristics to be specified,
without affecting weld times. Tip life is also extended, resulting in
considerable savings on tip dressing and consumables.
Weld Cleaner
With MF systems, peak voltage is virtually the same as RMS voltage,
which helps to obtain high quality welds, with none of the splash or
sparks that are characteristics of AC welding.
More Material Options
The controllability of MF also makes it ideal for difficult-to-weld
materials like high strength steel, aluminium, exotic alloys, laminatedsteel/polymer composites, coated steels, multi layer applications, etc.
The PS 6000 Series
The PS 6000 Series is a comprehensive range of AC and Medium
Frequency welding controllers with some of the most advanced
features found in any weld controller on the market today. With
a complete power range covering anything from small welding
application, through general purpose, welding aluminium and all the
way to high power applications such as seam welding.
All welders offer excellent connectivity options which include Ethernet,Profibus, Interbus, DeviceNet.
The range is completed with a line of compact class leading MF
welding transformers and optional adaptive control / quality assurance
option modules (covered opposite).
20 ms
t t
u
t
i
~
single phase thyristor 50 Hz AC
Conventional AC Welding
t
1 ms
t
u
t
~
~
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3 phase invertor 1000 Hz DC
Medium Frequency (MF) Welding
The PS 6000 Series consists of AC and MF welding controllers,
MF transformers and associated user interfaces.
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Welding Controls for Land Rover
Bosch Rexroth, the European market leader in medium frequency
(MF) DC welding technology, is the system supplier of around
400 welding control panels used in the production of Land Rovers
all-new Discovery 3 and Range Rover Sport at its plant in Solihull,
Birmingham. The contract is based on Rexroths latest PS 6000
integrated MF welding controls, comprising inverter, weld timer and
I/O board, which are housed in custom-made cabinets. To date, some
200 automatic panels for robot applications and 175 manual panels
have been supplied.
The all new Discovery 3 is the first Land Rover to be built using
the companys new and unique integrate Body-frame structure a
structure that has also been tailored for the recently launched Range
Rover Sport. Both models are produced along the same line at the
Solihull manufacturing plant.
Rexroth has built its reputation in this field based on equipment
reliability, providing permanent on-site engineers and its strong
commitment to ongoing technical and training support. Rexroths UK
headquarters is in St. Neots, however many contracts including this
one are also handled out of its sales and service centre in Cirencester.
Land Rover is the worlds pre-eminent manufacturer of 4WD vehicles
and the Range Rover is the original, luxury sports utility vehicle. The
company is part of PAG, alongside Aston Martin, Jaguar and Volvo,
with Ford as its parent and employs some 11,000 people in the UK, at
Solihull and its state-of-the-art headquarters and engineering centre in
Gaydon, Warwickshire.
Rexroth has supplied PS 6000-based welding controls for use in
automated and manual welding stations on the T5 project. Since first
receiving an order for 60 medium frequency DC welding stations from
Volvo, Rexroth has supplied more than 1,000 such systems to PAG sites
worldwide. Quality-conscious automotive manufacturers recognise
that MF welding technology is less demanding on plant power systems,
allows shorter, more precisely controlled weld times, yields savings on
welding consumables and delivers consistently improved quality.
Used for controlling spot and projection welding in Land Rovers
new body-in-white manufacturing facility, the PS 6000 systems are
all based on 100KVA MF inverters, to allow standardisation of parts
and the flexibility to handle different weld applications, incorporate a
high level of protection at 1000Hz and employ a common InterbusS
fieldbus link for programming and I/O communication.
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In welding there can be many process concerns that lead to defective
welds. The normal way to find these defects is to look at the weld
after the event (via destructive or non-destructive testing) and then
change the process parameters to stop future defects.
Adaptive Quality Control
Variation offorce
Variation ofsheet thickness
3 - sheetwelding
Bad tipsGlueVariation ofcoating
ShuntingBad fitting ofsheets
Let Us Help Your Welding
Medium Frequency welding and Adaptive quality control are not
just the preserve of large multi-national automotive manufacturers.
Even if your manufacturing only uses a single pedestal welder, these
solutions can help you improve your quality, traceability and the
types of materials you can weld. If we can help, regardless of your
application size, please contact us and one of our skilled weldingspecialists will assist you.
Automotive Tel: 0870 8502103
www.boschrexroth.co.uk/automotive
This technology uses an ultrasonic sender and receiver mounted
on the welding gun. As the weld begins the system uses transverse
ultrasonic waves to sense the liquid weld nugget developing. This data
is then used to control the weld very precisely to ensure consistent
nugget size. This technology has been used with great success with
difficult to use materials such as aluminium and hard steels.
With UIR the voltage, current and resistance are closely monitored.
If the weld begins and the observed variables differ from normal,
adaptive closed loop control is used to ensure a good weld. This is
achieved by varying the current and duration of the weld.
The ultrasonic solution offers the greatest possible weld control, but
the UIR approach offers many of the benefits at a lower cost.
PS 6000 Series Weld Controller all carry an expansion port (located
on right hand side) that can accommodate either the USR or UIR
Adaptive Control option modules.
Ultrasonic Transmitter
Ultrasonic Receiver
Current
SecondaryVoltage
Rexroth have developed two key MF technologies to avoid this
expensive and wasteful approach. They both share the same basic
principal of using a closed loop adaptive control strategy. If a
condition arises that is not normal, the weld profile is modified
dynamically so as to ensure a good weld every time. Also, the data of
every weld is available to make the process more visible, reducing the
need for additional destructive/non-destructive testing.
Option 1: Ultransonic Control (USR) Option 2: Voltage/Current/Resistance (UIR)
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Printed in UK
RR855 09/2005
Bosch Rexroth Ltd.
15 Cromwell Road
St Neots
Cambridgeshire
PE19 2ES
Great Britain
Tel: +44 (0)1480 223200
Fax: +44 (0)1480 470789
Automotive Tel: +44 (0)870 8502103
www.boschrexroth.co.uk/automotive