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22-june-2020

How to weld aluminium? - Good Practices

Technology, Welding

With the increase in the demand for aluminium parts, is expected an increasing curiosity about how to automate welding operations for this material. This article gives you some good practices of this technique.

Robotic aluminium welding applications are growing:

  1. Clients seek to manufacture lighter and more efficient parts
    - For example, trucks and cisterns’ manufacturers use aluminium because the weight of the structure has a direct impact on vehicle consumption;
    - Following the COVID-19 pandemic, several companies are producing metal disinfectant dispensers in aluminium because its lighter to move and easier to sanitize.
     
  2. Technological advances in robotic solutions
    - Smaller torches provide access to previously inaccessible chamfers in more complex geometries;
    - Lighter robots with greater load capacity allow the use of additional technology (such as joint tracking) without compromising the size of the robot;
    - Better gas distribution mechanisms and more developed welding machines allow greater control over the welding process.

Therefore, it is expected to increase curiosity about how to automate aluminium welding operations.

So, how do we start?

First... Process, process, process!

The key priority is to decide which process to use. There are many, but the most common are MIG (GMAW) and TIG (GTAW).

  • In most TIG applications, no material is added to the part. Therefore, using this process requires very precise joints and high part repeatability. In other words, all the processes before welding (cutting, handling, among others) must be very precise in order to guarantee that the parts keep the same characteristics. This is easier said than done, which is why, historically, robotic system integrators tend to avoid applications with TIG. However, with the democratization of fiber laser cutting systems in the last years, the repeatability of the parts is increasingly easy to achieve, so the decision between MIG and TIG is not obvious (as it was before), at least in terms of automation.
  • MIG has adition of material. A welding wire is added continuously so there’s a high propensity for the existence of welding projections, which gives a less "aesthetic" aspect to the finished piece. But, the fact that thicker materials are more difficult to heat (with TIG the materials need to melt before weld), makes MIG the best process to use the greater the thickness is.

Assuming we are going to use MIG as the process (the most common process on the market), what can we do to optimize robotic aluminuim welding?

  • Process: Dual Pulse. Although pulsed welding is used to weld aluminium, this variation of the process, where there’s an alternation between high and low current, creates the appearance of a TIG welding bead (overlapping “coins”) because aluminium solidifies faster than carbon steel. This can be an advantage for some customers given the more appealing aesthetic aspect of welding, but for others it can cause an adverse effect, since this type of finish has a greater potential to accumulate grease and residues over time, which weakens the welding.
  • Wire Feed Configuration: Push / Pull. Although there may be some financial or process constraints on using a wire feed system like this, it is still the most suitable for welding aluminium. It guarantees the greatest possible control over the beginning and end of the welding process and also greater control over the continuous feed of the wire.
  • Torch: Water cooled. Since the aluminium welding process is pulsed, there is a tendency for the wire to heat up, which can cause it to swell and stick to the nozzle. For this reason, the use of a refrigerated torch can help with wire feeding problems.
  • Contact tip. Unlike what is used to weld carbon steel, in order to improve the gas coverage, we must use a retracted contact tip if the access to the chamfer allows it.

At last, let’s talk about some good practices:

  • Clean the metal - removing oils, powders and other residues helps to obtain good results and lower porosity risks.
  • Remove aluminium oxide layer - aluminium oxide acts as an insulator due to its high melting point and can cause problems at the beginning of the welding arc. High temperatures will be required to weld through the oxide layer, which will cause the material to burn until the base wich results in some porosity, since the oxide layer also tends to retain some humidity.
  • Storage - keeping the material at stable temperatures helps to prevent that humidity creates condensation on the aluminium.
  • Check the consumables - In order to reduce porosity, we must use new and in good condition tube and make sure that all connections are tightened in order to be watertight. It is also important to use suitable rollers and rows. Using plastic material when welding aluminium helps to prevent the wear of the aluminium wire and that residues clog or complicate the wire supply to the torch.
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