Question 1

Regarding weld testing - if I’m qualifying 5086 to 5086 and 5086 to 5083 do I need 2 procedures or if I stay in 5xxx series am I good with 1 procedure?

Accepted Answer

Both 5086 and 5083 have the same M number (25) as listed in the current AWS
D1.2. Looking at the section, "Limitations of Essential Variables of a WPS Table
3.1", Base-Metal Alloy section states "A change from one M-number group to
another M-number group or to an alloy that does not have an M-number" (as an
essential variable). Since there is no change in the M-number, therefore, only one
procedure is needed for these alloys.

Question 2

I'm seeing some cracks in the weld pool at the end of the weld; however, they are not being detected until after the product goes out for a clean and Alodine process. My question is twofold, could these cracks be subsurface and are being uncovered during the light etching in the cleaning process? Or do you think the cracks are just missed by the inspector before going out to process? The structure we are welding is basically a sheet metal box with bracing about 12’ long by 4’ x 4’ square. 6061 material with 4043 filler diameter 0.035” shielding gas is 100% Argon with a flow of 30 - 50 CFH."

Accepted Answer

First where exactly is the crack? If it is in the center of the weld, then cracks are often a function of "Base Metal Dilution". This issue is common when welding 6XXX Series base alloys since it is one of the most crack sensitive alloy groups in aluminum. As the weld terminates during that last fraction of a second while filler alloy is being delivered into the puddle, residual heat continues to melt the base thereby diluting the puddle with
more base alloy. Filler alloys such as the 4043-product used in your operation, are designed to flood the puddle with an alloy that in this case is higher in Silicon (Si). The added Si dilutes the puddle out of the crack sensitive range. The best solution is to develop a crater filling technique or utilize a "canned" program in the welding equipment. The techniques for
crater filling differ although the basics are the same. Colder wire must inter the puddle as the arc is reduced. This is done by "back-stepping", increasing travel speed at the end of the weld, "stuffing the arc" (the method of pushing the torch close to the puddle while releasing the torch trigger), or any combination of these.

Question 3

Do contact tips get larger or smaller when they are heated in operation?

Accepted Answer

If you think of the copper tube as a straight bar that has been bent into a circle, it’s reasonable to believe that the bar will get longer since there is more mass in the length than in the width. While the copper does expand in all directions, there is also more mass to expand in the out portion than the inner portion, which makes the hole either stay the same size or get larger, depending the ratio of the hole to the outer diameter of the contact tip. The bottom line is the hole never gets smaller. The wire can get bigger although it must become almost molten to do so since its traveling thru tip for such a short time.

Question 4

My welding operators have recently switched from steel to aluminum. They claim to have switched all the right parts although we are constantly throwing away the bottom layers. We have a standard four-roll drive 8ft. push gun and the welds look great expect those last layers. What is causing the problem?

Accepted Answer

There is a key point to this problem! It is that bottom half of any spooled wire product. As the spool diameter changes from the top layers, about 12 inches (305mm) to the bottom, around 6 inches (150mm), the force to pull the wire changes as well. Let’s say there is 5 pounds of force at the top of the spool (which by the way is excessive). By the time it is down to the bottom layers that force has increased 4 times! There would be 20 pounds
of force required, which certainly would put undue stress on the motor, drive rolls, and not to mention cause slippage problems thereby making the arc erratic. Most machines have some type of adjustment on the hub that allows the static brake system to be reduced. There only needs to be enough force to keep the wire from falling off the spool. Sometimes less is
a good thing!

Question 5

Our company uses only one size wire for everything from 1/8” (3mm) to 1” (25mm). We don’t want a bunch of wire sizes lying around having our welders drive costs. This just seems easier for storage and our purchasing people. What are some of the pros and cons of doing this?

Accepted Answer

Certainly, having one size limits some issues around storage and product usage (through-put). It is important to note that using too small of wire can burn out some of the constituents such as magnesium in 5XXX series wire alloys. This can reduce strength. If a customer has repeatable welds, it certainly makes sense to use the largest wire possible since it’s often less expensive, can increase travel speeds, improve strength, reduced feeding issues, and reduce heat input (distortion). With the use of improved power supplies on today’s market, larger wire diameters can be used on thinner welds where costs can be reduced. Most welders like the control of a smaller weld wire and there are some advantages
in penetration resulting from current density. Although the bottom line for wire manufacturers is to make a quality product while turning a profit. Through proper weld development, testing of welders, and proper training, welders tend to prefer the larger diameters.

Question 6

Different articles and suppliers are recommending various liners spiral steel to plastic composites. Which works best?

Accepted Answer

First thing to consider is what size of wire is being used. Again, one size does not fit all! In a push system, the “slop” between the wire and the liner can allow as much as an inch or two (depending on the length and gap) of wire length. This means that when the wire is cut and pulled, such as after a weld or when the ball is removed, the wire can be pulled back and forth. The slack is then taken up when the wire is fed and the slack can cause a burn-back on the start-up. Therefore, the smallest gap will help prevent this problem. Second thing to consider is that even aluminum wire is abrasive although against steel, shavings will develop. There are steel liners that have plastic coatings although these are thin and there is no real way to know if they are worn until shavings develop. The ends of steel liners (if they must be used) have sharp edges that can cut wire easily and these should be polished or ground.
Disqualifying metal liners, this leaves some sort of plastic product.
 
The difference between Teflon and Nylon is two-fold. Teflon has the lower coefficient of friction than Nylon although is softer. Nylon, the harder of the two is not cut as easily, which helps reduce imbedded shavings (such as shop dust/particles) from causing wire scratches and shavings. Nylon has another hidden advantage; it is much cheaper than Teflon! Some manufactures have developed two-part liners, an outer liner that is stiff and an inner liner that has a lower coefficient of friction. The characteristics of the liner that actually touch the wire still exist while the cost is probably higher. Composite products also have advantages in lubricity although if they cut easily, they still have the opportunity to embed particles (as describe earlier). The last thing to consider is the temperature requirements of the liner. The liner often comes into contact with the contact tip and/or gas diffuser, which can melt
liners. Some liners come with a metal coiled “jumper-liner” made from brass, copper or even steel. These metal (jumper) liners can also cause shavings just as those constructed completely from metal. One alternative is a liner cap that has a high heat tolerance. Consider the cost of changing liners frequently, the materials used, shop conditions they serve, heat range, and the diameter of the wire when choosing a liner. Remember, down time is a lot more expensive than preventive maintenance!

Question 7

To those of you trying to pass tensile strengths on weld tests:

Accepted Answer

It is a good idea to verify the strength of the base plate (in the annealed condition) prior to making your test. The reason is that the range in chemistry can be below the minimums resulting in a failed test.
 
The surface coating or residue can certainly affect the quality of the weld. Some of these coatings are affected by the temper of the base material. This results from the heating of the product after initial fabrication (to change the temper). Here’s why: When the aluminum plate is rolled, lubricants are used to reduce friction where these lubricants are not removed either right after manufacturing or by normal cleaning methods at the user. These lubricants are also very tenacious! So, looking at the temper can influence these coatings by the heat that
is used to change the temper such as going from an H12 to an H32. The difference is simply that the base material has been heated in an oven after cold working the product. The heat dries out the volatiles in the lubricant making the residual easily removed using mechanical methods. Grinding or cutting on products that still have a “gooey” surface coating simply causes a “smearing” of the coating which then causes lack of fusion, porosity, and/or cold lapping on the weld. It’s best to check with your base metal supplier to best understand the tempers and coatings used to make your product and to be aware when substitutions are offered!

Question 8

What's the difference between a quality welding torch and a quality wire? Specifically, how does one choose one over the other?"

Accepted Answer

As with most things, “you get what you pay for”! When choosing a weld torch, spend a few extra dollars can prevent tons of downtime. First, the distance from the feeder to the area being welded needs to understood. Feeding only 6 to 8 feet allows a push style, while feeding wire 25 feet should require a push/pull gun. The cost for the later can dramatically increase and raise the complexity as not all push/pull guns will work with all feeders. The next choice is whether the torchshould be water cooled, which also requires a water cooler and coolant! This certainly raises the cost although it increases both the duty cycle and can minimize the weld downtime. As with all welding guns, it is a fact that consumables will need to be replaced. Items such as liners, gas cups, contact tips, gas diffusers, connectors are routinely changed while things like triggers and cables are replaceable but not often (that depends on how well the gun is taken care of). It is also handy to know that there are after market replacement parts although these again can fall into the “good, better, best” category and sometimes these parts will change the performance/parameters in the operation. Also, look to make sure that if you are working on aluminum, that the gun has suitable parts for this operation. The bottom line on welding torches is to evaluate it on the type of work that it will be performing and within the amperage range desired. It is fair to say that not all welding guns are easy to hold, consider having to heft this thing around for 8 hours a day if you’re a production welder and what effects to production that will have on your workers. Also note that duty cycle changes dramatically when using Argon. Therefore, welding aluminum, which usually uses Argon for a shielding gas, can drop the duty cycle in half of many welding torches.

THOM BURNS CONSULTING

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