wm026001.pdf

© 2003 EWM HIGHTEC WELDING GmbH 1/6 WM026001.doc; 10.03

Figure 1 Phoenix, complete, welding with accessories and options

Welding and brazing vehicle bodywork made easy

by Franz Krämer, Köln, Heinz Lorenz and Bernd Budig, Mündersbach, Germany Introduction With over 50 million motor vehicles in Germany, bodywork repair is an important sector of the car industry. In future there will be recognised qualifications for bodywork and car mechanics and for bodywork and vehicle technicians in Germany. The main emphasis is on accident repair work for cars and HGVs. Very high demands are placed on staff and workshop equipment in order to meet manufacturer repair guidelines. The different materials used in vehicle construction necessitate using the following processes: MIG/MAG and MIG brazing. The PHOENIX CAREXPERT 300 welding machine (Figure 1) from EWM is a future-proof solution for using these welding processes in bodywork repair. Vehicles can only be repaired correctly if the right choice is made from the variety of new joining techniques for the modern materials and low sheet thicknesses which have been used in recent times to manufacture new vehicles. Some of the innovations in this sector are described below. New materials being introduced into the vehicle construction sector For environmental and economic reasons, there is a requirement to keep the vehicle mass as low as possible to reduce energy consumption. However, vehicle safety and driving comfort must not be compromised. This requires the use of suitable materials to achieve the optimum lightweight design. Steel materials The steel materials in use today are required to have a high degree of strength and corrosion protection, alongside good deformation properties. Bodywork panels with strength values of up to 1300 MPa with zinc plate thicknesses of up to 20 µm are commonly used in modern bodywork. When repairing an accident-damaged vehicle, this requires a repair technique providing passengers with the same level of safety as before the accident. Manufacturer anti-corrosion warranties of up to 13 years represent a significant challenge for repair shops in terms of corrosion protection. Aluminium The use of aluminium is on the increase. Although there are at present only a few manufacturers offering cars with bodywork entirely of aluminium, the proportion of aluminium in vehicles is on the increase through its use in doors, bonnets and wings. This also demands new repair procedures which have only recently been introduced to the sector.

Welding techniques in bodywork repair Looking at the two main areas of bodywork repair, structural parts and outer skin, the welding machine being used needs to offer both MIG/MAG welding processes and MIG brazing, and must be capable of joining panels with a thickness range of 0.8mm to 5mm. This dictates the use of a welding machine which fully meets these tasks for all areas, without time-consuming setup procedures. MAG welding Until recently, MAG welding was the ultimate joining procedure alongside resistance spot welding. However, the melting temperature of the additive of around 1500°C creates a very high heat level in the area being welded. In modern steel materials, this results in a loss of strength, and the high internal stresses cause the bodywork surface to collapse in that area, which in turn necessitates additional, expensive reworking. With zinc-plated panels, there is a high level of zinc vaporisation and combustion, resulting in insufficient corrosion protection. However, the repair guidelines from many car manufacturers prescribe the use of this welding process in structural areas in particular, with the result that this process still needs to be used in repair work. MIG welding The use of aluminium in all-aluminium bodywork requires MIG welding when joining sections with cast links. This welding process is less commonly used for


Replaced part, (side panel,

rocker panel, column)

Door hinges,

fixing parts

Floor area,

structural areas

Body shell

Reshaping of

deformed panels

Replaced part on

the body shell

Replaced part, (side panel,

rocker panel, column)

Replaced part on

the body shell

Lap weld

Butt weld

Fillet weld

Raised-edge weld

Tack weld

Plug weld

Slot weld

Fillet weld for tie rod

outer skin work, but deformed areas which are only accessible from one side can be reshaped by welding on dent pullers. In the case of HGV repairs, the work extends to HGV bodies and tippers. MIG brazing Modern steel materials necessitate a reduction in heat feeding in the area of the weld. MIG brazing is especially well-suited for this purpose. Unlike MIG or MAG welding where additives of the same or similar material are used, MIG brazing uses bronze wires which are fused using shielding gases with a high argon content. The melting temperature of brazing additives is much lower compared to that of the parent metal. The melting range of silicon, tin or aluminium bronzes is not much above 1000 °C, see Table 1. Unlike welding where deeper fusion penetration is desirable, in arc brazing the bond is created solely via diffusion and via adhesion processes in the brazing area.

Grade DIN code Alloy base Melting

range °C

Silicon bronze SG-CuSi3 Cu + 3% silicon 910-1025

Tin bronze SG-CuSn6 Cu + 6% tin 910-1040

Aluminium

bronze

SG-CuAl8 Cu + 8%

aluminium

1030-1040

Table 1 The most important brazing materials in arc brazing

This is achieved thanks to the low melting point of the solder and a forehand torch motion which directs the arc less onto the parent metal and more onto the weld pool. This produces lower heating of the joint zone compared to MAG welding, which avoids losses in strength with higher-strength and high-strength steels. In the same way, vaporisation and combustion of the metallic surface coating is minimised and the typical spatter formation produced in MAG welding on zinc-plated surfaces does not occur.

Figure 2 The main weld types in bodywork repair


These advantages of brazing have increasingly resulted in MIG brazing being used more often than MAG welding in both new manufacture and in vehicle repair. Weld shapes in bodywork repair Primarily lap, butt, raised-edge and fillet welds are used in MIG brazing and MAG welding. Figure 2 shows the most important weld shapes in vehicle repair, and Figure 3 shows typical brazing seams that may be used in repairing door sills. Plug and slot welds are used for fixing outer skin parts. Tacking bodywork components and fixing dent pullers complete the range of welds used. For one panel, this means that up to 8 weld types may be required for the bodywork repair. Lap welds where one panel is on top or which has a “shoe” on the inner side (3-panel weld), is used with structural parts and the outer skin area in sectional repairs. This type of weld simplifies the complete joining of the panels and at the same time prevents the bodywork surface collapsing. In edge areas, plug welds and slot welds are used to join bodywork components. This may be both for structural parts and in the outer skin area. Dent pullers can be brazed on to reshape bodywork components using a pulling hammer or using hydraulic straightening equipment. This avoids the dreaded situation of bodywork components breaking. In addition, the puller is used to connect a lifting tool which can be used to pull out dents in bodywork components.

Setting optimum welding parameters for MIG brazing using the PHOENIX CAREXPERT 300 The weld types and panel thicknesses which occur demand different brazing data. Naturally, account needs to be taken of the special heat requirements of the different weld shapes. With zinc-plated panels, the zinc loss should be kept as low as possible, but without hindering adequate “alloy formation” in the weld area. When brazing the outer skin, it is important to ensure that a brazed seam root is produced with butt welds as surface finishing of the weld seam will be carried out later on. With butt welds, the ideal has been shown to be a brazed joint with a gap of 0.8 mm. This brazed joint is possible thanks to a cutting off wheel from the grinding equipment manufacturer Rhodius which has only been on the market for a few months. In this thin panel range up to 1.2 mm thickness in particular, this combination has proven to be virtually indispensable. Setting optimum brazing parameters requires significant experience on the part of the bodywork professional, which is further complicated due to the large variety of different vehicles for repair. Test brazing on vehicles is out of the question and test brazing on sample panels does not reflect the actual conditions on the component. Including the options for 5 panel thickness variations and 8 weld shapes, there is a total of 40 setting options each for MAG welding and MIG brazing. The settings in conventional MIG/MAG machines is also made harder in that with manual setting, the speed of the wire feed, which determines the current intensity and therefore the output, and the arc length, which gives the voltage, have to be matched precisely.

Figure 3 Typical brazing types when repairing a door sill


A new type of MIG/MAG welding system (PHOENIX 300 CAREXPERT) Figure 4, which has been developed especially for the bodywork trade, solves all these problems in an intelligent way. The welding machine is designed for the following tasks:

• MAG welding for all steel panels in the bodywork sector

• MIG brazing on plated and unplated panels

• MIG welding of aluminium thin panels

The machine stores characteristics for the optimum data for the most important welding/brazing work and weld types in bodywork repair. All the welding/brazing operative needs to do is call them up. This data is based on the expertise of the machine manufacturer as well as the experience of well-known bodywork companies. Efficient setting parameters have been determined using comprehensive tests on bodywork panels and genuine bodywork components. In addition, data issued by the car manufacturer for welding and brazing tasks can be set for many vehicle types. Exactly how all this works is described in the next section.

User-friendly adjustment provides a great variety of options The adjustments are carried out by pressing pushbuttons on the operating panel on the front of the power source. This setting can be made for MAG and MIG welding and for MIG brazing. The procedure for MIG brazing is described below. To call up the manufacturer data stored on the power source, first select the brazing wire (CuSi 3) and shielding gas (argon) to be used in the central part of the operating panel shown in Figure 5, in the far left row. The wire diameter 0.8 mm is set next to this. The panel thickness depends on the area on the vehicle being repaired. The settings are displayed using LEDs. This completes the basic settings for the operator. The other settings can now be made simply using the specified weld shapes. The self-explanatory symbols given on the machine and on the welding torch are used for this purpose, see also Figure 2. The rocker switch and display on the welding torch can be used to call up these weld shapes directly. It is no longer necessary to leave the site of work to make

any corrections required, which means that the welder can concentrate fully on the brazing process. In addition to the stored data, the voltage and thus the arc length can also be changed using the central rotary dial in Figure 6 in a range of +/-2 Volt. However, this is rarely necessary in actual operation.

Figure 4 View of the Phoenix 300 Car Expert Pulse MIG/MAG system

Figure 5 Right-hand section of the operating panel

Figure 6 Left-hand section of the operating panel


This setting method has the following advantages over previous machines:

• The application area covers MIG/MAG welding and MIG brazing

• User-friendly setting options are provided

directly on the welding torch

• The settings are ideal for the relevant weld type in terms of the strength of the joint

• Minimal heat feeding in the weld area

possible for thin panels Well-known vehicle manufacturers have produced their own repair guidelines which need to be followed by their contracted workshops for the relevant repair work. If you press the car symbol to the right of the display, you can search for the vehicle type being repaired using the up and down buttons. The left-hand car symbol in Figure 5 can then be used to set the data for the welding and brazing tasks for the relevant vehicle type. Updates for entering specific manufacturer data for new vehicle types can be carried out at any time. For special cases, a “customised setting” can also be used. This setting can also be used with joining tasks not specific to bodywork. On the left-hand display, either the set panel thickness, the wire feed speed used or the current intake of the wire feed motor can be displayed in addition to the current intensity. Current intensity also indicates whether or not the wire feed unit is running correctly. Too high a current intake could indicate that the wire feed paths are blocked, for example. In the right-hand part of the display, either the set arc voltage or the manufacturer and type of the vehicle being repaired can be displayed. Other setting options, such as the operating mode, welding type (standard/pulse), gas post-flow time, etc. complete the excellent overall features of the system. When using a special torch (Figure 7) there is the option of calling up programs 1-8 directly on the torch, in addition to entering settings on the operating panel. Documentation of the joint parameters The weld data documentation software Q-DOC 9000 in Figure 8 guarantees the seamless documentation of all welding data as required, so that you can provide evidence of correct repair work at any stage.

Overall system (Figure 1): The welding system is attached to a trolley at the optimum working height. This means that the basic settings can be made without the usual “bowing down” in front of the machine. A large storage area on the machine combined with additional storage space means that the needs of the professional have been fully taken into account. Conclusion: There have been wide-ranging developments in bodywork construction in recent years. Modern materials are being used and when joining thin, coated steel panels, the focus is increasingly on competent, yet cost-effective repairs. To simplify the work of bodywork repair technicians in repair workshops when welding and brazing, and to maintain a high quality standard, a shielding gas system has been specially developed to make setting and operation work much easier for operatives. The software for the power source stores the manufacturer’s expertise and that from leading

Figure 8 EWM Software Q-DOC 9000

Figure 7 “CAR CONTROL” MIG welding torch


bodywork outfits. Settings specified by renowned vehicle manufacturers can also be called up. When the bodywork repair technician is working with this database, he can always be sure of using the optimum setting to make the welding/brazing process as easy as possible, meaning that he can fully concentrate on moving the torch in the joint. The end result is high quality repairs. In the shape of the PHOENIX CAREXPERT 300, EWM is able to offer a machine for the future. It can be used for metal shielding gas welding processes and for MIG brazing, tailored especially to the needs of bodywork repair workshops for car manufacturers and independent bodyshops.

wm026001.pdf

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