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There is a lot of information about MIG welding aluminum on the web and here on the Glen-L Forum too but not in one place so this post is an attempt to get some basics about MIG aluminum in one place.

I'm not going to cover the differences in the welding types, or show those diagrams but I will attempt to give a short how-to, in order help others see how simple it can be to weld marine aluminum alloys with Metal Inert Gas ('hot' wire feed) welding equipment.

This topic comes from the Chine Bars topic because we began to discuss MIG seams both as they relate to the Scrambler and other designs in the Glen-L catalog. The purpose here is to give a 'sight picture' and some rules of thumb for the new welder who may not have built before, and who may need to review some of the basics as they practice before welding on their boat.

FULL DISCLOSURE: I have welded for a long time, I use expensive welding equipment and have built hundreds of welded aluminum boats; but I am not 'the last word' on anything presented. Further, I don't sell designs, teach welding, or advocate any specific brand of welding power supply for others. The information presented is my personal opinion, not authorized or advocated by Glen-L and is presented solely to help folks learning to weld to understand more about what they're learning to do.

With that said, I'd like to clear up some legacy misunderstandings. First welded aluminum is a 'new' boat building material and is not as fully and widely understood as some other boat building materials. That has lead to many people in many locations doing 'things' differently than the that work is done else where - and a very sailor-like bit of language has been used in the 'brisk' discussion about the relative merits of the differing methods! Not to mention more than a few remarks about each others' mother's and their 'pedigree' or lack there of! So if you read something here that is opposite of your understanding and practice (?) it would help the Glen-L Forum most if you were able to present the 'other side' in a manner that would allow the readers to understand the differences (in our opinions) and not have to deal with aspersions on my heritage!

What I'm going to illustrate focuses on basic weld prep, bead methods and adjustments using sight pictures you can use to help your practice. I'm not a very good photographer and I haven't marked up the images with all the arrows I could have used. I hope the information is useful as it is, and not just raising more questions instead of giving answers?

Brief review. MIG (Metal Inert Gas or GMAW Gas Metal Arc Welding) is done with three different wire feeders or guns. One is a hollow handle and copper 'contact' tip where the wire is fed from a cabinet to the torch handle and welding is done by pushing the wire only. This is most widely known as a MIG gun.

Next model has the wire spool of filler mounted in a small case on the gun itself. This model is called a 'spool gun' and the wire is fed into the contract tip by a motor in the handle and the gun looks like a pistol so it is sometimes referred to as a pistol grip style gun. This MIG gun is useful for aluminum but the push only model is not used (to speak of) for aluminum MIG.

The last type of MIG gun has a cabinet and a large roll of wire with a motor to push the wire 20-30' to the pull gun which pulls the wire and feeds it to the contact tip. This type of gun is most widely used in production aluminum welding and is most expensive of all the MIG welding torches.

The reasons are: Pushing aluminum more than a few inches allows it to flex into a 'spring' and then surge to the tip in push only system so the puddle is not reliable in push only Aluminum applications. The spool gun (one pound gun/ pistol style) is push only but the distance is so short the wire is steady. These are more expensive than push only but less expensive than push-pull.

What is needed is a steady uniform and exactly controlled wire feed. If you don't have that, your MIG aluminum will suffer.

Push-Pull systems draw on a large 15lb roll of wire and therefore can weld many more feet before tending the wire roll as would be done regularly in a spool gun with its 1lb, and therefore much shorter, roll of filler.

Next I'll try to get some images up.

Cheers,
Kevin Morin
Kenai, AK

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Kevin Morin

First, some tools prep and products, doesn't matter if you use the exact same stuff but there is a need for each item here.


Acetone is a solvent, that cuts all greases, and other hydrocarbons which can contribute to gas pockets in MIG welds if not removed prior to welding.

Vixen files or 'body putty' files are used for non ferrous metals and in this case to deburr the saw and sanding burr left on the edge of one of the pieces in this test. If this burr is not removed then it forms a 'burned' up strip of aluminum oxide that can result in gas entrapment in the weld, leaving the weld weaker.

SS wire brushes, power and hand are used consistently in aluminum MIG to remove mill scale and to prepare the oxides to lift easier and more completely prior to MIG welding.

The power wheel is critically important in the size of the wires on the wheel. Do not under any circumstance use wire wheels with wire that is larger in diameter than 0.014" or you will gouge and smear the aluminum. The SS alloy is usually 304 and the soft wire will abrade the mill scale off, and score the oxide film but will not gouge or excavate the parent metal.

The hand brush is similar but since you're using it with your arm not a motor the bristle size is not a critical as it is with a 4" power brush.


there is mill scale on this scrap but the burr has been filed off with a few strokes of the Vixen file used as a block plane in the palm of a gloved hand.


the two weld test pieces have been power brushed for most of their lengths and the vertical marked in four areas/zones. Right most is an area where the mill scale is mostly intact, next toward the right is an area where mill scale is gone.

The third zone has a beveled lower edge to provide more penetration under the vertical parent metal and the left most segment will be back welded where the others will only be welded from one side.



I'm using a fume extractor to lift the welding smoke away from me, and I know they're very expensive but I've only got the two lungs and no spares so.... if you're going to weld much make your own choice. The Optrel autodarkening hood is a good product and the push-pull gun is the MK Python powered by a Lincoln 350 MP Power MIG.

[Yes, these are expensive tools in this picture, but I'm not advocating you need these tools just introducing what I'll be using to get the following weld images.]

So I've used the power brush to clean the weld zones of mill scale, and after tacking the two pieces up, I"ll continue to use the hand brush immediately before welding.

Cheers,
Kevin Morin

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Kevin Morin

First an old test scrap from the pile since I could just grab it to show some concerns and examples.


This is 1/4" welded to 1/4" no bevel and the wire is 0.045" 5356 but the reason for the image is the cold start indication. Notice the rounded over bulge of the start area at the black arrow? This indicates the beginning of the MIG weld continuing to the left was 'cold' that is the wire built up too fast to fuse into the parent metal and the symptom is the tucked under edges. There is no fusion of flowing of the puddle edges into the parent metal until a puddle or two to the left along the weld.

So this means that area could be a cold lap where metal is deposited onto the parent surface but is not fused- its not welded. [The underlying bead is MIG and goes to the right and then a TIG weld was done onto of the first MIG bead.]

Next the weld continues on to the left and the top and toe of the individual puddle steps (sometimes called a "stack of dimes") are flowing into the parent metal. The tips of the overlap area is about the center of the previous puddle/dime/step (?) and the puddle steps are mostly rounded and not pointed. These are all decent indicators of the amperage/voltage combination as well as travel and hand/torch movement being in balance.

If the top and bottom curl under that weld is likely too cold' if the puddles' steps or dimes are pointed the movement is not 'rounded' (like a lower case c or e) or the heat is too high; or both of those conditions is true. Its a question of balance.



Here is a race track reminder of the weld pattern for stand alone beads that will be used to stitch stringers and longitudinals to hulls and is a good thing to understand and recall.

The weld is initiated inside the final weld area and very rapidly moved back then forward along the final weld track ending by back stepping once puddle or two. If you have a crater fill feature on your welder that can be discussed separately, so can the more advanced technique of 'wiping off ' the end of seam stitch weld, but we're not at that stage of the discussion yet.

This just tells use where I'm about to put in a short weld to test the settings and my 'hand'. I'll begin under the left end of the right hand arrow and follow the path and end at the right hand tip of the left arrow.



Path for this weld is above; the weld has a clean zone along the top, decent fusion of top and top into the parent metal and decently rounded puddle conformation showing the balance of welding wattage and movement and travel.



Cleaned of soot the weld tells us a lot about improving the settings for this parent metal and wire combination. First the welds are more pointed than needed and this is because of my motion being less smooth, not amperage/voltage because the build up in the center of the puddle shows I'm pausing where the 'tip' is formed.

Next the overlap is just a bit long, not as tight as needed so I'm moving more along the weld in my 'whip' or lower case e movement than around. This is a practice and rhythm issue that means I need to practice! (or warm up)

Edge fusion shows little too much ridge/rim/raised shape so the amperage should be up a bit or the wire speed down, or the stick out a little longer, all of which would increase the wattage/heat of the weld and cause better fusion shown by less edge formation.



Here is another old scrap with a stitch on it but we can see the weld and improve the settings and movement from this image. The weld is closer, step by step, so it's smoother but they're just getting pointed so the voltage/wattage/heat is just a bit high for the amount of 'whip' I used. I could make a more pronounced C or turn down a little and achieve a better shape with just as much top and toe fusion and not loose anything in strength.

There is a relationship between speed of pattern movement, travel along the weld, the wattage/heat of the weld, stick out or the distance of the wire contact tip to the work, gas coverage and the lead or trail angle that effects the results of MIG welding in aluminum.

I'm showing this group of welds to focus on the points we can see that will improve the settings and methods used to get a more uniform and better quality weld.

hope we're heading in the right direction?

Cheers,
Kevin Morin

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Kevin Morin

Thank you for all the time you spent for this helpful example. I appreciate your expertice. Awsome and what i needed!!! Very helpful! Keep on smiling!

Wayne

OK, lets look at some other aspects of this topic so you can continue practicing with a little more detailed look at MIG in aluminum.

Patterned MIG welds do accomplish several welding goals that are desirable. They are wider, without being proportionally thicker so the root face is 'bigger' but the weld deposit is not double that of a drag weld. That is a gain.

Patterned or whipped welds, usually use a transition between short arc and spray to increase wetting and then deposit a pure, porosity free, 'top layer' in the short arc mode, and last they allow a higher wattage weld to be applied without increasing the travel speed of the weld to 'machine' or robotic speeds.

But.. they are not the only game in town. Drag welds or non-patterned welds work fine and they need to be mentioned.


if you're familiar with welding with a coated electrode or 'stick' welding then you've probably welded a fillet between two 90deg pieces by just following the natural V formed between the two pieces? That is a fillet but if there is no pattern to the weld bead, so that weld could be performed by just 'dragging' the electrode. The term -drag weld- is used for a bead formed by moving uniformly along the weld area, even if you 'lead' the weld as in aluminum MIG. I'm not being intentionally inconsistent as these are terms widely used, so please let me know if this is (too) confusing?

Leading is to lean the cup to the right while welding toward the left or... leaning the cup to the left while welding to the right. Dragging a weld with a MIG gun would be to lean the gas cup to the right and weld to the right. [Just to get some terms clear, in case I use them in a confusing manner.]

this bead is a drag bead even if I put it down leading the weld from right to left (I'm a right handed welder) and then back stepped one puddle to 'crater out'. [More on crater/cratering out/weld ending coming]



This is just a close up view of the previous image but it contains info we can use. The clean zone looks inadequate but the last puddle is 'clean'? What's up with that? Well the weld was done with a constant lead and at a higher rate of travel than a 'stepped' or patterned weld so the gas cleans as you weld but the evidence or clean zones or white tracks are not as evident. What we do see is a toe and top fusion that is relatively even, not built up and the arc patterns are reasonably round and uniform inside the puddle.

All this indicates that we're approaching a decent balance of wire feed speed, wattage of weld power, travel, angle of the torch to work and gas coverage that ends in a reasonable bead profile.



wire brushing that same weld shows the fusion at toe and top is not a perfect as we could get. At the top there are tiny droplets of aluminum that were 'splashed' on to the parent metal showing that the wire speed was just tiny bit to slow, so the arc was more spray mode and there were some droplets that were 'stray' and they show along the boundary of this weld.

This is not a bad weld, I'm just trying to guide the reader to the better MIG bead. The arc contours are round, and that is a good indication of balance. However, the top of weld boundary area does show I could have added just a bit more wire speed to shorten the arc length , by a very small amount, to reduce this splash and thereby increasing the quality of my bead.

Drag or 'stringer' bead welds are very important skill to master in building welded aluminum boats. They are applicable to welds that do not lend themselves to patterned or wider, somewhat slower travel speed, welds. They are very useful to avoid distortion in some internal welds and are difficult to master since the amount of practice plate and argon required is high- (read expensive).

I wanted to make sure we don't ignore this important MIG bead in our discussion. I do realize it takes a bit more effort to learn this bead at the speeds implied by 0.045" wire if you weld on 0.125" or thinner material. Therefore, I would suggest this welding technique be used with 0.035" wire for 0.160" or thinner material OR... 0.190" thick material or thicker parent material with 0.045" wire.

What the combination of wire diameter and parent metal thickness does, as given above, is to confine the welder to a set of more nearly matched wattage and rate of deposition that are easier to put down. You can, use 3/64" wire on thinner material but the movement is very high to create a drag that is proportional to the parent metal. [I would say that speed would come with the second 1000 hours of welding.]

Next let's look at the beads on the scraps prepared above.

Cheers,
Kevin Morin

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Kevin Morin

Since MIG wire has to be running to create the arc, melting the parent metal and also depositing the filler (wire melted in the arc); starting a MIG weld is not the best state of balance.

The parent metal is cold compared to what it will be heated by the arc. The wire has to being running out of the contact tip to form the arc or the tip will 'burn back'. As the arc begins and the parent metal comes to the heat of fusion/melting point I've shown above a method of beginning inside the eventual weld track/bead and going back one step to begin the final weld, therefore you'd weld over the start.

This is done with a quick movement like a stepped puddle but is best done while the trigger is being pulled so the arc is washed over the area and the parent metal is heated without as much wire being deposited. This technique reduces the cold lapped lump but sometimes this is not enough to create a clean and smooth weld initiation.



Here are two different 'die grinders' with carbide burrs mounted. Each burr has 'teeth' like the Vixen file's wide, long cutting edges that will cut aluminum and then fling the chip free without loading. ( If used for long periods of time- these bits can be sprayed with Pam (tm) or other generic frying pan spray to release the cut metal more reliably.)

If you use the finer tooth steel or SS burr(s), usually cross hatched teeth like a steel file's teeth, the very fine chips will heat up and melt coating the burr and then further cutting is very limited until the burr is cleaned.

The larger tool turns at 14k rpm and has the 'tear drop' burr while the smaller tool turns at 20k rpm and shows a round burr end on to show the 'teeth' or cutting ridges more clearly.


Here is how most full time welders deal with MIG starts AND stops. They're cut out using some carbide cutting tool and leaving a cleanly cut depression where the next bead can be started or stopped. Still the technique of back stepping one puddle at the start or stop would be used but the tie in point of both welds adjacent to the final weld would have these end preparations.



The weld to the left is a TIG bead, the weld to the right is a stepped MIG bead and the middle weld is the drag bead put down above, this image was staged just to show a way to make longer seam welds more uniform. By gouging out the potentially cold start area, and the potentially crater cracked or porous end puddles, carbide burrs offer the boat builder a more controlled way to tie welds on longer continuous seams, like chine, keel and sheer welds, by stitching together MIG beads regardless if they are stepped or drag style weld beads.

There are other tools that can be used to do this work but I feel these are the most controllable and safest choice so I've only shown this one method.

Now we'll look at the test panel weld(s).

Cheers,
Kevin Morin

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Kevin Morin

What I'd intended in creating this test coupon was to show how you should confirm your own weld integrity before welding on your boat(s). One of the four experimental conditions failed to deliver the results I had hoped to show because of the power supply I'm using and because I didn't take the time to go back over that segment to make sure I could show the failure I wanted to illustrate.

Please keep this in mind when you look at these images.


as shown above, I've cut two pieces of scrap and brushed a section where I'll weld, then I labeled the vertical section for the four types of weld conditions I want to show. The right side is where my experiment failed to deliver the results I'd hoped to show. The 'failure' is that I was not able to get the results to be different in the right hand two sections. I've labeled them as 'scale intact' (right most), 'no bevel' (next to the right end segment) and the next two are beveled with the left most back welded instead of single sided.

What I'd hoped to show but did not get, was the right most segment to cold lap on the mill scale to illustrate how poorly the weld penetrated the scale.


both pieces were tacked from the back to hold the vertical for the welds to that side first.


just before welding a SS, hand 'tooth brush' was used to abrade the right side two weld areas of the coupon.


The weld was from the right to the left using the 'race track' or wrapped ends method. So the first arc was about 1/2" inside the right end and a back-step was made to fuse the end moving to the right. Then the weld progressed to the left and ended at the back step over the next to last puddle to leave the 'crater on top'- hopefully avoiding leaving a crack in the underlying weld.

[Always clamp the ground with a firm grip -never use welding cable ground clamps they create extra resistance and arcing on the clamp face. If you have to use a spring loaded ground clamp put a clamp on it to make the electrical connection decent.]

First glance shows some clean track along side the bead, mostly rounded patterns, back step and e or c pattern was mainly 1/2 lapped and therefore about right.



Zoomed in a little closer the clean track shows OK. The pattern is reasonably uniform and the fusion line at the toe and top is even so there was a match between the speed of travel with the speed of the e or c movement (whip) and wire feed speed.


This end of the test piece has a bevel on the lower edge of the vertical scrap. The bevel will allow a deeper root penetration of the weld and increase the surface area of the joint without increasing the weld size outside the Heat Affected Zone (HAZ). This means the joint will be stronger for the same relatively welding effort, cost and time.

This bead shows a slightly more V shaped puddle edge because the weld wattage was dissipated less because of the beveled edge of the vertical. That small reduction in mass of the vertical piece moved/conducted/cooled heat in the weld zone just a bit less that the full edge of the previous weld. That small change in the rate of heat movement from the HAZ, resulted in a slower chill rate or slower freeze rate of the weld. That slower freeze is shown by the just slightly more 'pointed' or side ways V shape of the weld steps.

This is not a bad weld, I'm not saying its going to fail, I was pointing to this visual indicator to illustrate this weld could have been turned down (wattage) just a bit and still give good fusion. Also I could have increased my e or c pattern speed (whipped faster) and the arc time in each puddle would have resulted in less net heat to any given section of the weld; resulting in a compensation for the reduced mass of the joint to dissipate heat and then delivering a rounder more uniform weld pattern.


Zoomed in on the second weld done under the beveled vertical piece shows I did try to speed up! what I must have seen was the pointed versus rounded puddle steps and then I moved farther between steps! Instead of making more rapid e's or c's I moved farther between puddle steps. Both worked to compensate for the fact I failed to turn the weld wattage down. But the result is this more pointed step profile.

The gas and soot are less defined here because I held the gas cup farther off the parent metal and that increased the weld voltage too. A better position to have welded this would have been positioning my body to the left of the weld instead of over the gun so I could have seen into the gas coverage from the left, and not held the gun's gas cup so far off the weld zone.

I'm trying to illustrate the relationships between the variables of MIG welding in aluminum by showing visual indications of the effects of these differences. Of course you'll have to dial in your own power supply, MIG gun and gas flow settings to get close enough to begin refining your welds.

Next we'll break these welds open to see what effects each of the four weld sections have on final strength.

Cheers,
Kevin Morin

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Kevin Morin

I forgot the back weld on the last (left most) beveled section of the test coupon.



Notice the more rounded and full steps? there is no bevel on this side so the weld piles up more, and is somewhat 'cooler' since the opposite siden now has a full weld bead added to the beveled area making that side 'thicker' and more of heat sink. So now, the movements being used resulted in the more balanced bead shown. Decent top and toe fusion, a clean track, but the weld transitions in the first three or four steps- beginning with some overspray and then stopping that condition.



Cleaning the weld of soot with a hand brush gives a closer look at the bead.

What I'm pointing out is the over spray or splashing of droplets near the bead to the right where it began. These stop about four steps into the weld, moving to the left.

I added some wire feed speed to the controls and the increased wire speed shortened the length of the arc, making the spray less wide and more focused and therefore reduced or almost eliminated this overspray or splash of molten aluminum.

Not all welders like to remove the wire speed control tension O ring. I use the MK Python with a wire speed pot under the gripping hand's ring finger and move it when welding. This allows me to slow the wire to start and stop and to speed it up or 'tune the speed' as I travel to compensate for small changes in residual heat in the parent metal.

I'm not saying everyone (anyone!) needs to adopt this technique, I'm illustrating the effects of tiny adjustments to wire feed speed on the resulting bead that is deposited.

If you're beginning your MIG learning curve, being aware of this image's information is enough; don't bother to add remote wire feed speed to your gun's features or hand controls until you've become familiar enough with your welds to need this level of fine tuning as you weld.

Now we'll break these welds.

Cheers,
Kevin Morin

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Kevin Morin

Hi Kevin,

Very helpful thank you. Although my welds do not have the years and hours behind them they are getting better as my project goes along. I am sure this will be very helpful to many for years to come.

Wayne

The simplest test for all aluminum welders is to back break the fillet or butt weld on test material that is most like their boat's. That is done by preparing a weld, welding then cutting the weld into bend coupons and bending them until they break.

When the welds break you can look inside and learn about penetration, root face fusion, porosity, and the bend and break will show you a lot about the strength of the welds.

I mentioned above that I'd hoped to create a cold lapped weld on the mill scale intact (right most) segment of the test, but that didn't happen as well as I'd have liked. Still noting this here to remark that I have seen welds that looked OK but were just pure cold lapped on mill scale and failed because of lack of preparation by the welder/fitter/builder of those boats.


Four segments band sawn into T's that I can break with a wrench while clamped to the bench.



Typical break bend test for aluminum MIG, not complicated but very informative.


This is the segment I'd hoped would be least fused and it was to some degree but not a full cold lap. This segment broke at this angle shown, and will be opened in an upcoming image. This weld broke at less than 45deg bend and was fully loose at 70 degrees and came free of the weld, the weld broke down its centerline.


all the four different prep conditions broken or bent. As we'd expect the beveled welds were most strong with the back welded end nearest the camera 'beating the metal'.



here is a look inside the root and the break lines of the welds.



there is not that much porosity, the root face is what is most important here. The weld does not fuse fully in the last or inner most 1/4 of the root face !@!!!!@#$)!Q@#$%!@#$*(.... ! That is why the beveled welds were so much stronger- the thinner parent metal at the inner most edge of the weld joint was heated and fused more easily when that cross section is thinner than full thickness.

This is shown by the darker root line that is not broken weld- there is not fusion to break! That cold lapped area is why weld prep and setting all the related rates is so critical to aluminum MIG. There are a lot of things to 'go wrong' or be ignored and the results are weaker than needed welds.

The bevel sections performed better because they have more root fusion and more nearly fuse the entire two parent metal edges.


Back welding allows the weld to avoid loading at the cold fused root and therefore the main stress failure is on the face of the opposite side weld. Here that allowed the two welds to hold to the parent metal enough to bend the parent metal completely before the weld failed. So if the boat were twisted into a complete pretzel the welds would hold.

This also shows the edge burr that is removed by the Vixen file or sanding, or other debrurring operation prior to welding as mentioned above in the preparation post(s).

There is a very small void in the root of this weld coupon but the weld did hold the metal for the bend.



The weld face shows little distortion or strain cracking and there are no stress risers running along the parent metal above the top of weld on the bend vertical leg. The marks shown are hand brush striations/scratches and the metal bent outside the HAZ where is was softened by the weld heat and the force of the lever of the wrench.



finally, the back bend is done to see if the material will fracture when the weld is bent back the other way, and here the other leg of the coupon bent and the weld remains intact.

This allows a welder to practice and then confirm their welds' integrity. The methods and this entire post tries to give a summary of these concepts and show images that may help tune your welds as you practice.

If the material leads to confusion please post the questions so I can try to clarify, the purpose in this post is solely to educate practicing aluminum MIG welders not to confuse.

I think building boats in the Miracle Metal is the most enjoyable boat building there is. My goal is to support the Glen-L builders that are interested in building the designs in this fine catalog, by Mr.'s Witt and Hankinson, in aluminum; to produce the best boats they can.

Cheers,
Kevin Morin

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Kevin Morin

Kevin,

Have you written any "beginning welding" books?

That might be the next Glen-L listing!

Thanks

STeve

Love the tests, Well done!!
You make me want to go do some TIG !
Thanks again! Randy

I wrote this to Kevin in a private message because I did not want to distract or contradict anything he said. He suggested I post it in the forum. He is very knowledgeable and there is a wealth of good info in this thread. I have been teaching welding for 24 years after working in the field for 15 yrs. I am also a certified welding inspector and do a lot of work with aluminum. However as far as metallurgy in regards to aluminum I would defer to him. A very knowledgable poster and one we are lucky to have on this forum. So please do don't disregard anything he has posted, I am just posting a couple of things I have encountered doing inspection work and teaching my trade to others.
Kevin,
Good stuff in the mig welding thread. You really do a great job of showing the relationship of wire speed and voltage and the effects on a weld puddle. I am sending this to you as a private message because I don't want to do or say anything which will distract from your thread.
However I do somewhat disagree with you on the step method being a better method for new welders for a couple of reasons. First,, I think I have mentioned I teach welding at a tech center in Fl. My main method of instruction is the "kiss" theroy (keep it simple stupid). Whether the welder uses the step method or the push method they still have to develop the ability to see the legs of the weld tie in top and bottom as well as break down the center of the joint for adequate pen. I have found students seem to grasp this quicker just using a push method so all they look for is the leg tie ins and the bead width. With the step method they are also have to learn to look at the back of the puddle to keep the bead uniform, keep from overly increasing the stickout as they move out of the puddle and bring it back in to the right length as they move back to deposit the weld metal.

Another issue I have run into on a couple occasions recently is this. We have a large naval experimental dive unit in our area and as such a lot of contractors doing naval project work. I was hired by one of the contractors to help determine why they were having weld failure on some weldements after they were accepted by the navy. The welds were all on 1/4" up to 1/2" 5086 aluminum welded with 5052 .045-.052 wire. and all fillet welds of various designs. What I found was a lot of underbead porosity caused by the stepping technique. We set up several test in the shop with their welders and welding equipment. We did all the necessary cleaning a prep work. The welders all laid nice beads with the stepping method that bent with no problems. However when we sheared or cut the welds we found a lot of underbead porosity. I then had the same welders repeat the welds using a full spray and a straight push method. The welds all bent as they should but upon cutting or shearing we did not find the porosity.

Another thing I had the company do after we determined eliminating the stepping method would eliminate the porosity was to add some helium to the gas mix and use a low pre-heat on the 1/2" stuff. They have had no more issues with weldement failure after making the changes. I really wish Lincoln would write a program for the heluim mix to use on the MP350s.

Again I am not wanting to distract from the work you have done in this thread but thought I would share what I have found. I always enjoy "talking" with you about welding. It is nice to have someone who knows what he is talking about.
Eric
Subject: MIG welding Aluminum

mcmbuilder,
I don't think the stepped weld is 'better' than the straight drag bead, I was responding to other welders here who had shown stepped beads in their posts. Sorry if I gave that impression- not my intent to imply one bead is better, they each have a use where one is more suited than the other.

Stepped beads can provide some advantages in thinner (relative term) metal over drag beads in the same application. That advantage is the bead size versus the root face of fusion and related distortion. If the drag bead is put in, of the same root face size/width, the travel would have to be much higher and most welders cannot produce that proportion/related rate and this is one reason many welders use stepped welds.

In heavier plate, I can definitely understand the use of a large section drab/stringer style bead where the travel and bead sizes are not in the same proportion as two 3/16" pieces or 1/8" and 3/16".

Yes, I agree, stepped welds are more difficult to learn since they require two sets of movements to perform. First you have to pull/push/move the torch along the weld path and second while doing the first movement evenly you have to put the pattern on the weld; either a 'c' or 'e' or some use a horizontal 'j' movement.

So just making the first movement the main focus of the weld, especially of the newer welder, makes the most 'muscle' sense as there are fewer movements at one time to master. Also, there is nothing wrong with a push bead or stringer bead/drag bead weld and the wire speed vs travel speed related to the weld wattage settings are easier to tune.

Porosity has plenty of causes all of which should be tested by the individual welder for themselves. Since the gases that are being expelled from the weld zone only have a short time to escape the puddle before the molten aluminum 'freezes' or re-solidifies, its easy to see how the drag/push bead with its continuous location of the arc and molten aluminum deposition will have less gas than a patterned weld. By nature the patterned or stepped weld has move arc movement, travel plus the pattern while traveling, so the amount of time (very short) for the gases to bubble off and be expelled by the hot argon is shortened by comparison.

In thinner metal, say 0.190-3/16" down to 0.100" I'd suggest that 0.035" wire be used for most work, because regardless of the bead type, the travel speed could be lower with 0.035" compared to 0.045" Hopefully this will lead to longer arc time in any given part of the bead and more gas release and cleaning than the heavier wires?

You mention a very good point that I did not cover at all and that is; where should you eyes focus when you 'watch the weld'? The most experienced welders, I think, watch the top and toe or "12&6" as the weld is lead along a 3:00 to 9:00 track. (discussing a horizontal weld)

This is critical to 'tuning' the wire to voltage/wattage versus travel speed and lead angle relationships as you weld. If the top and bottom edges of the puddle a built up and not fused, or the overall 'wetting' of the lead edge of the puddle is not even the potential for cold lap, and the gas trapping that would go along with that condition, will be high and the most welds substandard.

Hopefully, if any GLen-L builders have direct questions they'll post them here and we can try to answer to make the many aspects of aluminum MIG clear?

thanks for the reply
Cheers,
Kevin Morin

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Kevin Morin

Kevin, do you use the pulse or pulse on pulse modes for any of your alumunim work any? I build a lot of fuel tanks in the 80-135gal range for a local shop which does a lot of boat restoration projects. I primarily use .125 5052 for the material. For a long time I tigged the tanks out totally which on the 135gals usually took about 2 1/2-3 hours. It took me a lot of practice and adjusting parameters to get enough confidence to trust the pulse method to use the procedure on the outside corner joints. However with enough tweaking and practicing I starting welding the tanks out using the procedure. Gives perfect penetration and makes a very nice looking weld also. Best thing about it, my weldout time is now in the 30 min range. I still use TIG for welding the fittings on because of the moverment speed required to get around the round fittings it is easier to control with TIG. If you are not using it give it a try sometime.