No question: aluminum welding is the premier class of welding. In a previous blog we explained in detail what a manufacturing company should pay attention to when welding aluminum by hand. But what do you do when the quantities are so high that one welder alone can no longer handle them? If hiring an additional welder for aluminum welding is not an option or you simply cannot find a suitable welding specialist? Can you possibly also weld aluminum in industry with a cobot – i. e. a collaborative robot – or is it too difficult to program a cobot to achieve the same results as when welding aluminum manually.
First of all: if you consider the following 7 things, you will achieve top results in your company when welding aluminum with a cobot.
When welding aluminum, it is essential to work cleanly – both in terms of cleanliness on the workpiece and a clean environment. The first point is a basic requirement, of course, when you want the welding result to be of good quality. This principle applies equally to manual welding, welding with an industrial welding robot and welding aluminum with a cobot. Oil, grease or even water need to be kept away from the workpiece surface. Oil on a steel surface is not a problem when welding because the oil simply burns. However, it is different if carbon gets into an aluminum weld: A connection between the workpiece and additional material is no longer possible with carbon inclusions. If a weld seam is formed with carbon inclusions, it is very likely that it will tear later. Aluminum welding must therefore be carried out cleanly. It is even best to weld aluminum in a separate room, if the circumstances permit.
In addition to cleanliness with regard to grease and oil in preparation for the welding process – not only in automation – the oxide layer must of course also be removed. As is well known, it forms immediately on the aluminum surface as soon as it is exposed to oxygen and appears as a silvery-white coating. This aluminum oxide layer must be removed mechanically before welding, for example with a plastic fleece. This contains particles bound in the plastic, which ensure gentle removal, because scratches on aluminum definitely have to be avoided. Since this oxide layer forms again within a few minutes, this must be taken into account when preparing the workpieces and this process may have to be repeated. But even in the welding process itself when using MIG AC welding, the layer is broken up by the positive half-wave in the alternating current.
Another recommendation is to deburr the edges of the workpieces, as dirt can just as easily stick to them. The cleaner a workpiece is for the welding process with the cobot, the more reliable is the consistently good quality of the weld seam.
In addition to the material itself, the shielding gas used for aluminum welding must also be free of moisture. Sometimes moisture builds up in the loop piping systems that transport the gas to the process. Moisture in the gas leads to the inclusion of hydrocarbons, which in turn creates pores in the weld seams and pore formation means rejects. Special test devices that are connected to the gas tapping point can measure the humidity in gas pipes. If moisture is found in the gas pipe, it must be flushed with gaseous nitrogen until the moisture content is a maximum of 200 ppm.
The structure of the loop piping system plays a major role when it comes to moisture inclusion. Sometimes you can see that interfaces or junctions are sealed with hemp, but this should be avoided. Due to its natural properties, hemp at the connection points can let oxygen and thus moisture into the gas line. PTFE adhesive tape is more suitable for sealing gas pipes with screw connections. However, crimped connections are now being used more and more frequently. There is also the option of soldering the connection points, but this is more time-consuming and costly.
In addition to pore formation, moisture can also lead to black spots in the weld seam – regardless of whether it comes from the line that supplies the shielding gas, remains on the base material or was introduced with the welding wire. This is not desirable for components made of aluminum, where visible seams are mainly produced.
Of course, cleanliness is also important for the wire when welding aluminum with a cobot. Wire must not be too old. For example, if a spool of aluminum wire has been lying around for several years without protection such as the foil around the spool or in an open barrel in a production hall, the wire can no longer be used. It was exposed to ambient oxygen for too long and has now built up an oxide layer that no longer cannot be removed. The only thing that helps is proper disposal. Correct storage must therefore also be ensured with aluminum wire. If the wire has only been lying in place for a few days or weeks, unwinding and removing the top wire layer will help.
There are no special requirements on the power source itself. It goes without saying that it should have special characteristics for aluminum welding. However, careful attention must be paid to the correct equipment of the power source for aluminum welding. The same applies to the equipment of the welding torch. In the following, we have put together the most important points to be observed for the power source and welding torch:
Wire feed rolls in the power source
While steel wire is fed with a V-groove on the wire feed rolls, a U-groove is required in the feed roll for aluminum welding. This semicircular groove forwards the soft aluminum wire smoothly and reliably to the cable assembly and without deforming it. Choosing the wrong groove shape can have the consequence that particles of the aluminum wire literally peel off. These chips get stuck in the wire feed spiral and result in wire hangers. It is best to speak to your welding distributor about this.
Special PTFE liner/MIG cable liner
Due to the very smooth surface of the PTFE liner, aluminum wire can be fed very easily and very smoothly from the machine-side connection of the welding torch through the cable assembly and to the process. The front part of this MIG cable liner, however, consists of a piece of copper spiral, which ensures that the PTFE does not burn – which would inevitably happen if it were also used in the part of the liner that leads through the torch head and thus directly to the process. The combination of PTFE and copper makes this special liner a combination wire feed liner in common use of this word in general language.
Special contact tips and gas nozzles
To ensure that the soft aluminum wire can be guided safely, the inner diameter of the contact tip – also called contact nozzle – must be larger. For example, if the aluminum wire has a diameter of 1.2 mm, the contact tip used should be approx. 0.2 mm larger in the inner diameter than it would be used for steel wire. In addition, there are specific contact tips for welding with aluminum wire. Contact tips made of E-Cu are suitable for this, as the aluminum wire itself is not as conductive as a copper-plated wire and the contact nozzle then takes on the task of transmitting current. Current tips made of CuCrZr are also well suited for aluminum welding.
Just like the contact tip, the gas nozzle must also have a larger inside diameter to ensure better gas coverage. The diameter of the gas nozzle when welding aluminum should be at least 16 mm.
The longer the cable assembly of the welding torch, the more resistance for the wire. Because aluminum wire is very soft, the cable assembly should be as short as possible when welding aluminum with a cobot, if you are working with a simple drive for the wire feed. We recommend a maximum length of 3 meters for the cable assembly on the cobot for aluminum welding.
Very important: aluminum welding with a cobot works best with a liquid cooled welding torch. The reason for this is simple: the liquid cooled cable assembly is more stable. At the same time, the wear parts have a longer service life because they are cooled better and thus the adhesion of spatter is reduced. This in turn ensures a reliable laminar flow of shielding gas.
There is always soot produced when welding aluminum. In order to prevent this soot from getting into the weld pool, forehand welding is recommended. During forehand welding, the cobot holds the torch at an angle of 20° to the welding direction. The arc hits the base material, which has not yet melted. The resulting soot always runs in front of the weld pool and burns again immediately. The result is a flat seam profile, a smooth seam and a shallow penetration depth.
If the torch is held in a neutral position, soot gets into the weld seam because the arc burns onto the weld metal, which is visible as small black dots when brushing over the seam after welding. When welding the torch directed towards the finished part of the weld – the so-called backhand welding – the result is even worse, because then the entire weld seam is sooty, which cannot be brushed out. In addition, backhand welding results in deeper penetration and the seam is also higher. Therefore, forehand welding is generally the correct welding direction for aluminum welding.
Aluminum always has to be welded with a root, not only in automation. This means that the weld seam must be full penetration welded in order to achieve a solid connection between the material and the additional filler material. If aluminum is not welded full penetration, a notch is created on the back and the welded workpiece can break at this point. The desired stability is only achieved by welding a root in aluminum welding.
Last but not least, the welder uses his specialist knowledge to decide how well the result is when welding aluminum with a cobot. In many cases, there is still a widespread fear that a cobot will take away a skilled welder's job. This fear of losing a job can be quickly refuted. A cobot is only as good as its programmer, an experienced welder. It is true that programming a cobot does not require the programming knowledge and time required to program a welding robot, but the programmer of the cobot must be a specialist in welding.
When programming a cobot, the welder inputs all his specialist knowledge and skills into the system of the collaborative robot so that in the end every component has the desired result. Once programmed, an employee without specialist knowledge can then equip the collaborative robot. The trained welder thus has extra time for more demanding work that requires all of his know-how. In this way, on the one hand, higher quantities can be produced with consistent quality, because once programmed, a cobot welds without a break. On the other hand, a cobot even creates jobs in the company, because components have to be prepared accordingly, made available to the collaborative robot and made ready again for further processing.
Aluminum welding with a cobot means more efficient welding with consistent quality and is ideal for larger quantities.
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