Global Influences on Power Source Technology
I’ve heard from several users that are curious about the global arc welding market. Globalization of manufacturing is here to stay, but does it affect robotic arc welding which is all about Amps, volts and travel speed?
There are regional differences between continents that affect the development of welding power source technology:
Japan – Low Spatter
Japan uses straight CO2 shielding gas for most of its GMAW welding. This forces short circuit transfer, and Japanese power source technology has been concentrated on reducing spatter with CO2. Argon is approximately 7x the cost of CO2 in Japan and only 3x the cost in the USA. Japan pioneered the “controlled short circuit” technology which is marketed by most companies today (RMD, STT, etc.). When the Japanese do use pulse, it is normally with an 80/20 Ar/CO2 gas mix which is not commonly used in other regions. The fast pace of changing technology means it is often practical to replace power sources when they are less than 10 years old, due to improved performance vs. cost of repair (similar to computers).
Europe – Perfect Pulse
Pulse welding was developed to provide a spray transfer arc at a lower average current. European pulse technology is focused on creating the ideal “one drop per pulse” arc. They use 90%+ mixes of Argon shielding gas and feedback from the arc to pulse current and spray a molten droplet across the arc, while reducing down to a lower background current. The weld parameters are normally set in the power source, and the robot selects schedules or jobs from the power source and then turns the arc on/off during motion. This means the power source has closed loop control of the process, while the robot is just performing motion control. In Asia and the Americas, it is common for the weld parameters to be stored in the robot program itself, and the robot controls the sequence of the weld power.
North America – Faster
Pulse welding and a spray arc do not have spatter; however, the wider spray arc can result in undercut if the travel speed is too fast. The controlled short circuit arc also reduces spatter, but it relies on interaction with the weld pool, and faster speeds create arc instability and generate spatter. US brand welders have multiple pulse modes (with cool names) that operate with shorter arc lengths. They pulse the current and then operate in short circuit mode with recommended gas mixtures around 90/10 Ar/CO2. They will generate spatter, but the pulse modes try to minimize the size and amount of droplets. It results in a balance between faster travels and trying to keep the spatter at a reasonable level.
The power sources from around the world do have some common traits, such as process libraries for algorithms to control the arc based on wire type, size, gas and pulse type. These algorithms are generally developed in a lab for specific conditions. Using an algorithm designed for 1.2 mm dia. wire with a 0.045” wire will normally work, but it may not produce the optimum arc. Regional differences in wire alloys and shielding gas may also contribute to slightly less than ideal conditions.
Does that mean you shouldn’t use power sources from other continents in your plant? Not necessarily. Power source manufacturers can tailor their equipment to regions by including algorithms for local wire and gas mixtures in their process libraries. Manufacturers setting up operations in other parts of the world should be aware of a foreign weld distributor’s ability to support welding standards designed in a different region. In the end, some flexibility in equipment and settings may go a long way toward achieving a quality weld with power source “X” in country “Y”. After all, it’s all about Amps, volts and travel speed.
By Chris Anderson, Associate Chief Engineer