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8/10/2019 Bosch Automotive

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Automotive IndustryTechnology Update - Welding

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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

~

~

~

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

[email protected]

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

[email protected]

www.boschrexroth.co.uk/automotive

bosch automotive

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