The nonheat-treatable alloys offer excellent ductility when using matching fillers, though lower ductility results from welds made with 4XXX series. Heat-treatable alloys do not exhibit high ductility, and post-weld heat treatments generally reduce ductility.
Taking Metallurgy to the Next Level
Now that we have some background on aluminum metallurgy, we now want to apply that knowledge to the actual welding of the alloy. To do this, we will first take a look at technology that produces outstanding welding characteristics on aluminum, combating common problems such as poor penetration, high spatter levels, burnthrough and porosity.
Today’s quick response inverters using Lincoln’s patented Waveform Control Technology™ precisely control welding waveforms for more efficient control of droplet transfer. This reduces the amount of spatter caused by the low density of aluminum while a high-energy pulse peak insures proper penetration.
In addition, since variations in chemistry dramatically change an alloy’s physical properties, these custom waveforms can be designed for specific alloys to best suit the physical properties of what is being welded.
Because aluminum has a high maximum solubility for hydrogen in its liquid state and a low solubility at its solidification point, pulsing output waveforms are further designed to minimize arc length by trimming the output as low as possible and reduce the likelihood of porosity.
Lincoln has recently taken custom waveforms to the next level with Wave Designer Software®. The software allows welding engineers and operators to manipulate and modify welding waveforms on their PCs as communicated from welding equipment in real time. This creates high quality, tailored performance, when used in conjunction with inverters.
New Welding Methods
The use of Constant Current power sources for the gas metal arc welding of aluminum has a long and very successful history. The use of “drooper” output has assisted in the delivery of a high energy axial spray transfer mode for aluminum that responds evenly and consistently with the proper welding current despite changes in arc length. The result of constant current is consistent penetration throughout the length of a given weld.
The evolution of the control of the arc has lead recently to the development of software controlled inverter power sources. The use of software to “optimize” arc characteristics for aluminum GMAW has been taken to a new level at Lincoln Electric and it is known as Waveform Control Technology. A modified constant current output is employed in a very high speed synergic pulsed output that incorporates many of the benefits of Constant Current GMAW for Aluminum. These benefits include the high energy input that occurs during the pulse peak. The pulse peak helps to provide a consistent penetration profile throughout the length of a given weld and the advantages of pulsing also includes reduced spatter levels, improved puddle fluidity with an increase in effective travel speeds, and reduced heat input and lower distortion levels.
Lincoln Electric’s Waveform Control Technology™ takes pulsing to the next level. This technology allows welding waveforms to be manipulated to form the “perfect”, user defined, waveform for a particular application. This Waveform Control Technology and the tailoring it provides, can be found in highly developed software such as that found in Lincoln’s Power Wave inverter power sources. The Power Wave can be utilized in either one of two ways. Operators can select pre-programmed waveforms for welding aluminum or, engineers can create their own tailored, waveforms using Lincoln’s Wave Designer Software. These waveforms, which are created on a PC, can be programmed into the Power Wave.
Anatomy of a Waveform
But what exactly is the waveform control technology provided by Wave Designer Pro? With this technology, the power source responds to changes demanded by the software instantaneously. Keep in mind that the “waveform” is the means for determining the performance characteristics of a single molten droplet of electrode. The area under the waveform determines the amount of energy applied to that single droplet. Current is raised to a level higher than the transition current for spray transfer for a few milliseconds. During this time the molten droplet is formed, detached, and it begins its excursion across the arc. Additional energy can now be applied to the molten droplet during its descent that allows it to maintain its fluidity or increase its fluidity. The pulse is now moving to a low background current that sustains the arc which cools the cycle but prepares for the advancement to the next pulse peak.
Lets look at the waveform in detail. The front flank (A) is the rise to peak, measured in amps per millisecond, where the molten droplet is formed at the end of the electrode. As the molten droplet reaches peak it detaches. A percent of current “Overshoot”, (B), provides arc stiffness and it assists with the detachment of the molten droplet from the end of the electrode. The time spent at peak, (C) determines the droplet size; less time results in larger droplets and more time results in smaller droplets. From here the detached molten droplet is affected by energy supplied by the rear flank. The rear flank is comprised of tailout, (D), and stepoff, (E). Tailout can add energy to the molten droplet if it is increased. It can assist with puddle fluidity especially when the tailout speed is decreased. Stepoff is the place where tailout ends but it has impact on the stability of the anode and manipulation of stepoff can result in the elimination of fine droplet overspray. From this point the waveform moves to the background current, (F), where the arc is sustained. The time at the background current as it decreases has the effect of increasing the pulse frequency. The higher the pulse frequency, the higher the average current will become. Increasing frequency will result in a more focused arc.
Superimposed, in a selective fashion, over the waveform is the “Adaptive” characteristic of synergic pulsed GMAW. Adaptive, or, adaptivity refers to the ability of the arc to maintain a specific length despite changes in electrical stickout. This is an important enhancement for weld bead consistency and sound weld metal.
