Many companies have adopted robotic automation to improve or speed up their welding operations. With aluminum, this has been a more difficult endeavor due to a couple of reasons. The first is aluminum is more challenging to weld than other more common materials like carbon steel and stainless steel. Another challenge is making the robotic weld look as good as the previous hand welded parts in most cases TIG welded (GTAW). Read on to see how to improve your robotically welded aluminum application.
How to calculate a weld weave versus weld pulse for a stack of dimes effect.
If you ask a welder to describe a good looking weld, more often then not you will hear the phrase “stack of dimes”. In welding, the stack of dimes look is when the weld freezes (cools) at a different rate in one part of the weld than another. In some cases, the stack of dimes look is a side effect of a physical weave made by a human welder or a robotic welder which could be used for filling larger gaps in the metal. As a secondary benefit, this consistent movement side-to-side or back and forth will create a pattern in the weld bead or a stack of dimes look. Sometimes in robotic welding, there is the opportunity or requirement to focus not only on weld strength but also weld appearance. In this case, there are typically two methods of achieving a stack of dimes look in the weld. The first is the weave pattern or weave motion as mentioned earlier. The weave method moves the weld wire in a pattern as it travels along the weld path. This could be a side-to-side motion (zig-zag), front-to-back motion, figure 8, etc depending on the robot controller options. For a string of dimes affect the back-and-forth option is best or at least the simplest. The weave method has more uses than just creating a stack of dimes look but for the purpose of this blog, we will stick to its use for appearance purposes only. A second method is a process option on some modern welding power sources such as Miller Electric’s Profile Pulse, Fronius’s Synchro Pulse, Lincoln Electric’s Pulse-On-Pulse, and versions from other manufacturers. This process, simplified, changes the weld energy multiple times a second switching between a hotter process and a colder process. This method creates a similar effect as the weave method causing the weld puddle to freeze at two different rates leaving the stack of dimes look. Since, in most cases, the welding process will be a pulsed MIG (GMAW-P) with the second pulse on top of it to create the stack of dimes look. We will just call it the pulse method.
Which tool should you use?
Now in an automated setting, when choosing either the weave method or pulse method, you need to first determine whether you’re going to need the weave. As we said earlier, the weave movement has other uses and may need to be used for other reasons. If so that kinda pigeon holes you into one method. However, if you need to use the weave method on some welds and can use either option on other welds it will be a good idea to calculate the initial parameters so that both welds look similar. With a weld weave the setting is usually dimensional. Meaning, there is a weave length (pitch), weave width, weave shape, and other settings to really fine-tune it to achieve the goal you’re looking for. For the purpose of this blog let’s focus on calculating length and pitch so to predict the look of the dimes whether using a weave or pulse method.
All we have is weave.
Let’s start with the weave again. The weave method causes the weld to freeze in a pattern based on the back-and-forth movement of the weld wire. Each time the weave changes directions it leaves a mark or a change in the weld puddle. The longer the wire stays in one spot the more puddle that is created and potentially the larger the dime in the weld bead. Typically the robot’s controller will create the weave every given distance in inches or millimeters. If you know how fare you want the dimes to be apart you simply put that value in the robot controller and there you have it. Now, remember the robot is still traveling along a path and just moving the wire torch based on the dimension you gave it. If the distances are too great or the weave dimension is not possible you will create problems in the weld or for the robot controller.
Just pulse it!
Now let’s move to the pulse method. The pulse method, again, does not use movement to create the dime effect but a change in weld energy at a given frequency and the amount of wire that is deposited in the weld bead. For instance, with the Fronius Synchro Pulse, the change in energy is created by changing the wire feed speed at a defined frequency. If the base wire feed speed is 150 and we set the wire speed deviation at 60 and 2 cycles per second (Hz), the wire speed will change between 90 and 210 twice every second.
Now for the conversion.
Here is where the two methods can get tricky. With the weave method, we set our weave distance or pitch whereas the pulse method used a frequency. With the weave method if you change the weld travel speed the distance between weave cycles stays the same. However, with the pulse method, the faster the travel speed the further away the dimes will be apart. The reason they are different is that the welding power source is typically controlling the pulse rate and since it does not take into account weld travel speed, it does not know to speed up or slow down. Not to worry. The tables below can help.
To calculate your weave:
Fig 1 below demonstrates the relationship between weave length and frequency at a given travel speed. For instance, if the distance between weave cycles is .125″ and the travel speed is 30 inches per minute, there would be 4 weave cycles per second or a weave every .25 seconds. If the weave length is increased to .25 ” then the frequency will be only 2 cycles per second or .5 seconds. This is important to take note of because this calculation can be used to choose an equal Pulse frequency.
To calculate your pulse:
Fig 2 below demonstrates the relationship between Pulse cycles and visual weld dime pitch at a given travel speed. For instance, if the Pulse frequency is 4 Hz and the travel speed is 30 inches per minute, the distance between dimes in the weld would be .125″. If the Pulse cycles are reduced to 2 Hz then the distance between weld dimes would be .25″. This is important to take note of because this calculation can be used to choose an equal weave length above.
When looking at the weave length table note the frequency as the travel speed increases. Be mindful that the robot controller may have a limit on how fast the weave can be. In contrast, note the pitch of the dimes with the pulse method. As the travel speed increases the pitch increases as well which may not be desired. For a link to the full table click here Weave_Pulse Chart to download. The calculation can be expanded or changed to different units as needed.
When is come to advance robotic welding, THG Automation has decades of experience with difficult application in aluminum, carbon steel, and stainless steel process. Call us at 317-550-4006 to speak with our team about how we can bring your welding presses to their full potential.