How can one accurately and constistently control the depth of penetration when welding thin guage aluminum? Are there specific signs or aspects of the puddle that I should be watching for that will tell me that it isn't deep enough or it is about to be too deep?
Currently it feels like the only way I know if it will have worked or not is to turn it over and look to see if it melted the back or just caused heat discoloration or minor texturing, then try changing my technique to increase or decrease it based on that, also trying to watch the puddle size on the second try compared to the first try. I'd like to be able to know before, not after, welding. If it dramatically starts melting through I can see it sag on the front, but of course that's way too late. I can see when the puddle starts to get dramatically too hot or isn't hot enough and roughly correct for that near the beginning and end of the joints, I'm more concerned about the bulk of the weld in the middle and fine-tuning it.
Background info if it helps: Just started learning to TIG weld aluminum within the week, and yesterday I was attempting T-joint fillet welds in the flat and horizontal positions using pieces of 11-guage aluminum about 2 inches by 6 inches with filler rod. (will soon be trying 16-guage, all positions, other joint configurations as well.) I don't know the exact alloys of the stock or filler rod as it is just whatever happens to be placed in the bins for practice, but is most likely going to be whatever is most commonly available.
I'm sure this has been discussed elsewhere too, haven't been able to locate it yet though; perhaps I'm just looking in the wrong place though, so feel free to point me to another discussion if this has already been answered.
Thanks for any info!
#1 tool for limiting penetration on thin aluminum is to clamp a heat sink to the back side of the work you are doing.
Tee joints in the horizontal have a natural heat sink on the piece laying on the table, a heat sink clamped to the vertical piece will help.
The overall profile of the bead can (in time with practice) become a good indicator of penetration as well. If the profile of the bead is high and the transition at the weld toes is steep, there is a chance that you have limited penetration.
You can also limit penetration (if that is what is necessary) by increasing your (push) torch angle, the heat goes where the electrode is pointed. This means with an increased torch angle that your puddle will be oblong and not penetrate as deep. The drawback here is that if you go too steep with the angle, the heat from the arc will melt your filler wire too sooon and it will ball up at the end.
Increased penetration will come with a technique that brings your torch angle closer to perpendicular to the axis of the weld. A sharpened end with a blunted tip on your tungsten electrode (rather than a balled tip prep) will provide a slightly more directional arc which can provide a bit more penetration and directional control in fillets.
I'm sure some of the other folks here have other good pieces of advice to add as well.
Keep the questions comming.
Hello sriesch, to add further to Lawrences always great responses. Heat sinks of copper or stainless steel work really well. If you are filling holes or adding to missing pieces, edges, corners, ears, or other instances where you are trying to fill or add to aluminum pieces; stainless steel backing works really well for that purpose. If your power source has a balance control this can be used to increase and decrease penetration to a certain degree. You will notice that most of these balance controls will list one side of the knob as increased penetration and the other side of the control will generally refer to increased cleaning action of the arc. When this control is set towards the cleaning action portion, the balance will dwell longer on the reverse polarity side of the AC wave and when the control is concentrated onto the penetration side of the control it will dwell longer on the straight polarity side of the AC wave. The lesser penetration will be achieved when the control is set towards the increased cleaning side. Machines with variable hertz controls can provide a narrow, deep penetrating arc when they are adjusted to a higher HZ. setting or a wider, shallow penetrating arc when they are set to a lower HZ. setting. The pulsing features on machines can also help with penetration and burnthrough control issues due to the hot/cool characteristic of the welding puddle as it is controlled by increasing/decreasing the application of amperage, controlling the hi/lo amperage differences, controlling the length of time that hi/lo amperage settings are applied and a number of other puddle control parameters depending upon the specific machine and it's capabilities.
A few examples of the inverter tigs with the variable hertz and balance controls might be as follows: Lincoln Invertec, Miller Dynasty, Thermal Arc ArcMaster, HTP Invertig, there are a number of others as well. Likely others will have additional comments for you. Good luck on your leap into the TIG arena. Best regards, Allan
Watch the weld pool; it will sink as the penetration starts.
Mechanically (Scrape w/stainless steel tool) Clean oxides from all joint surfaces; face, root and groove face. Position material 1/8" off any "heat sink". IMHO use a sharpened ceriated tungsten; no balling, focus the arc, its easier to see what is happening in the weld pool. If your machine has a "Squarewave AC Balance Control"; set it to 65-75% time at negative or "max penetration" which most machines have 60-70% time at negative as "Max Pentetration". Inverter type machine with AC frequency control; 90 - 120 hertz. If your machine has a pulse control; thin material is where this really shines, use it to break the weld pool's surface tension.
Thinner material - smaller diameter electrodes; 16 gauge Al, 1/16" or 0.040" diameter tungsten. Thinner material - smaller diameter filler wire; 16 gauge Al, 0.047", 0.035" or 0.030" diameter Al GMAW wire.
>Watch the weld pool; it will sink as the penetration starts.
>...
>The overall profile of the bead can (in time with practice) become a good indicator of penetration as well. If the profile of the bead is high and the transition >at the weld toes is steep, there is a chance that you have limited penetration.
How much of a change in the profile of the weld pool am I looking for? Is it something obvious where it will suddenly sink and flatten out at the toes when I have reached the right level of penetration, or is it a gradual change? Am I looking for the exact moment when it starts to sink, or do I need to let it sink a specific amount? If it isn't obvious, is there any chance there are good photos/drawings of profiles showing not penetrating enough, just right, and too far that I can use for reference to get an initial feel for it?
Watch the weld pool form a shiny mirror like pool; when the surface tension breaks and begins to sink; you are penetrating. It takes practice & practice & practice & more practice to achieve even/consistent penetration. Keeping the weld pool as narrow as possible helps make seeing what is happening with the surface tension of the weld pool. The variables of Torch travel speed and the addition (speed & amount) of filler wire all will affect the penetration.
Welding sheet aluminum is perhaps the most difficult thing I have ever had to learn. Everything has to be clean: cleaner than clean. Aluminum is unforgiving to the point that you really have to teach yourself entirely different techniques for holding lead angle, work angle and tip to work distance. You also have to teach yourself to simultaneously increase speed of travel while decreasing current, all while feeding filler at just the right tempo to keep bead sizes consistent. All that, and I still love to weld aluminum with TIG more than any other material or process. As stated, it requires years of practice. Everything can be an indication of your progress, from the appearance of the molten puddle to the sound of your HF. Keep learning. Weld, weld, weld. It is the only way you will know that you are making sound welds in one of the most difficult materials ever made by man.
As far as the question of attaining penetration that is "just right" goes, well now that's all a question of code, and design, and other requirements of the job. Do you have a requirement to produce a weld which only partially penetrates the base metal? With thin sheet, this will be difficult. It will be interesting to watch where this thread goes. What a good topic!
>Do you have a requirement to produce a weld which only partially penetrates the base metal?
Not at this time; I'm just learning, and was simply assuming this was something I would need to be able to do if asked.
One tip on welding thin aluminum is to use more current than you would think and travel as fast as you can. Many try to weld using low current and are forced to "hang around" while you develop a molten pool Due to the high heat conductivity of aluminum, you will have a problem with burning through as you progress down the plate. Use fairly high current to get a molten weld pool as quickly as possible and then move along to stay ahead of the heat that moves down the plate, while backing down on the current to the minimum required to maintain the molten pool.
Back in my "good old apprentice welder days" at PSNS (WA state) I was assigned to the sheet metal shop fabricating HVAC ducting for navy ships from thin aluminum. What a nice clean job, sitting in a soft chair with the very clean components sitting in front of me. Good memories!
I probably welded in the same exact area you did for some years, from '01-'05. Yeah, nice shop. I didn't get to weld very much in there, unfortunately.
Topic Welding Industry / Technical Discussions / controlling GTAW (TIG) aluminum sheet penetration depth
