Why is copper wire harder to feed than steel wire?
Because copper-based wires such as CuSi3 or CuAl8 are softer. DVS 0938-1 therefore places higher demands on the feeder, hose package and torch than in steel welding.
In brazing, there is also the fact that the process has little leeway. Brazing is done with a short arc and low power. If the wire speed fluctuates, the arc length immediately fluctuates and with it the heat in the sheet. The result is irregular seams, pores or melted sheet. For periodic seam faults, DVS 0938-3 therefore names as the first step: check the wire feeding.
What does the feeder need?
A drive with constant speed and rolls that do not deform the soft wire. According to DVS 0938-1, the usual four-roll drives with U-groove for steel are not sufficient as they are.
- Feed rolls: rolls with a rounded groove, as for aluminium. Set the pressure only as high as necessary. Too little pressure makes the speed fluctuate, too much squashes the wire.
- Constant speed: the feed motor must hold the set speed even under changing load.
- Power source: if the stick-out changes while the torch is being guided, the power source must readjust quickly. More on this under MIG brazing.
Hose package and torch: when do you need push-pull?
From about 4 m of hose package in manual brazing and from 1.5 m on the robot, DVS 0938-1 recommends a second drive, for example at the torch. Always keep hose packages as short as possible.
- Plastic liner: mandatory for copper wire, no steel spiral. Guide it without gaps as close as possible to the rolls and contact tip; replace worn or dirty liners.
- Robot: water-cooled torches are recommended. In plasma brazing, a drive sits close to the torch; light two-roll drives improve accessibility there.
- Routing: route the hose package without tight loops. Every bend increases the friction.
Older documents still give 3 m for the push-pull torch. The edition of DVS 0938-1 currently in force, from 2012, gives 4 m for manual brazing.
Why are cast and helix so important?
Because they determine how the wire comes out of the contact tip and where it meets the sheet. DVS 0938-1 requires diameter, cast and helix to be closely toleranced.
- Cast: the curvature of the freely hanging wire, measured as the diameter or radius of one full turn. If it is too small, the wire presses hard against the wall of the liner and contact tip.
- Helix: the twist of the wire along its axis, measured as the distance of the wire end from a flat surface. Too much helix makes the wire tip wander.
In addition, the technical bulletin lists defects that must be avoided at all costs: longitudinal scores on the wire, diameter outside tolerance, waviness and welds in the wire. They lead to process faults.
With fast processes such as laser or hybrid brazing, this counts double: at several metres per minute, small deviations shift the position of the wire relative to the focal spot, see Laser and hybrid brazing.
Soft or stiff wire?
For robots with long hose packages, DVS 0938-1 recommends wires with higher strength. They are easier to push and buckle less.
Copper-based wires are supplied in different heat treatment conditions. For special applications, it should be checked whether wires of medium or low strength are suitable. On the filler metals themselves: Filler metals and standard designations.
How do you feed brazing wire from a drum?
With a short, well-routed feed path and, over longer distances, with a low-friction conduit or an additional drive. For drums, DVS 0938-2 explicitly points to the routing of the wire feed.
The principle is the same as with soft aluminium wire: if the wire is pulled through a long hose, the friction rises sharply with every bend. The calculation is on the page Wire feeding for aluminium welding.
- Drawing off: Drum hoods and decoiling aids guide the wire as it is drawn out of the drum.
- Rollers instead of sliding friction: in the Rolliner 3G, Rolliner NG and Rolliner XL2, the wire runs over pairs of rollers.
- Second drive: the pneumatic feed assist DLDA1 or RoboFeed push the wire on over long distances.
All accessories are listed under Wire transport. We are happy to advise on designing the feed path.
Video: Rolliner 3G, the wire conduit with rollers for less friction.
Frequently asked questions
Which liner for CuSi3 wire?
A plastic liner. Steel spirals are not suitable for copper-based wires.
How long may the hose package be in MIG brazing?
Without a second drive, up to about 4 m by hand and up to about 1.5 m on the robot. Beyond that, DVS 0938-1 recommends push-pull.
Why does the brazing wire stutter?
Common causes are a steel liner instead of a plastic liner, dirty or worn liners, wrong roll pressure, tight bends in the hose package, too long a path without a second drive and wire with too small a cast, scores or waviness.
Can you use the same feeder as for steel wire?
Usually yes, but converted: plastic liner, rolls with a rounded groove and adjusted pressure. The motor must hold a constant speed.
Further reading: articles on arc brazing
The series in the order in which the questions arise in practice: from the process via filler metal, gas and base material to the finished seam. For an overview, see Arc brazing.
About the author
Robert Lahnsteiner, Ing., is an International Welding Engineer (IWE) and managing director of MIGAL.CO GmbH. After training in telecommunications and electronics at HTL Braunau, he spent eighteen years in welding technology at Fronius from 1983. Since 2001 he has run MIGAL.CO, the aluminium welding wire manufacturer in Landau an der Isar, together with Martin Erl. His focus is aluminium filler metals, wire manufacturing and wire feeding, and the monitoring of welding processes. Within DVS, the German Welding Society, he has served for around 30 years on technical committee FA03 “Arc welding” and chairs working group 2.4.4 “MIG welding of aluminium”.