Tack vs Continuous Welding

[tomsmith]

Hey all,

I've been welding for a few months now, off and on but still consider myself very new to the process. I use a Lincoln Electric 180HD with flux-cored wire as I want to familiarize myself with flux-cored before I switch to a gas tank.

I find that when I tack weld, the welds are really quite nice, they look like they have nice penetration and are concave. I tack the weld, wait for it to just stop glowing red and then tack again with around a 50% overlap - probably around half a second between tacks.

When I'm continuous welding (that is, welding a long line without interruption), my welds are rather more convex and definitely don't have the 'dime' pattern.

My question is, is tack welding much weaker than continuous welding? My basic knowledge of welding makes me think it isn't because you're still getting penetration and good pool and isn't TIG welding similar to tack welding? You feed the rod in at intervals rather than a continuous feed.

None of my applications are life-threatening ... I've made a metal working table, a stand for a drill press and so on but I want to create my own scissor lift and am wondering if I can get away with tack welding the entire thing or should I hold off until I get my continuous welding technique better?

Incidentally, I tack welded some angle iron at right angles to each other, put it in the vice and whacked it with a 3lb hammer .. the joint didn't crack, even when the horizontal piece of angle started to bend after repeated hits.

Looking for some input/thoughts from the members here and maybe even some science behind the strength between tack and continuous welding

Many thanks!

 

[PAToyota]

One issue with overlapping tack welds with flux-core is that you're running the risk of getting the slag included into the weld - making the weld weaker.

The "stack of dimes" is from the motion of the welding. Depending on the weldor, people will use a "e," "c," or "back and forth" motion. This will push the puddle into the dime pattern you mention. Again, you can get slag included in the weld doing this, but you're less likely to have issues than with the overlapped tacks because the weld you're going back over is still fairly hot and the slag will rise to the top of the new weld.

 

[PAToyota]

This link will show you some of the motions used to attain the dime pattern.

 

[msgross]

tack welding is also good for thinner metals when you need to reduce the heat build up. you would want to space the welds out and continue to move over the entire length of the seam going back to overalap once the previous weld cooled. I use it a lot for sheetmetal on my truck restoration.

 

[AMCguy]

The key to a good weld, weather its cosmetic or actual is the consistent application of the heat, not the filler rod. In other words the rod can be intermittent, but the heat generally must be steady. Think of it as a pre heat. You want the heat there before the rod. Among other things, it floats all the impurities away. When you interrupt the heat and reapply it, you are loosing penetration. The wire will pile up because the parent metal is relatively cool.

With your flux core machine you can get a good weld. It's a matter of the proper heat, wire speed, travel direction, travel speed and gun angle. There is a lot to get right before you will get good looking welds.

I would recommend (if your machine is gas compatible) that you get the basics down using a shielding gas. When you get the hang of it you will find you are better with flux core. Of course you wont want to go back there.

Aside from actual destructive testing of a weld, remember this; A good looking weld may or may not actually be a good weld, but an ugly looking weld can not possibly be a good weld.

 

[MoonRise]

re: TIG welding

Nope, not the same at all. With TIG welding, you have the arc making a puddle of molten 'parent' metal and then you dip the filler rod into that and add a bit of filler into the molten puddle. This addition of added metal from the solid (not liquid molten metal) cools the puddle and thus makes that 'stack of dimes' look.

But the arc from the tungsten is melting the parent metal and making the puddle.

With wire-feed welding (FCAW or GMAW), it is relatively easy to just melt the filler on top of the parent material and not get that desired molten puddle of parent metal going.

Watch the puddle, make the puddle, 'feel' the puddle, Grasshopper, in order to help you on your Zen journey of welding and your journey to turning formerly separate pieces of metal into the Zen 'oneness of being' that is what a weld is supposed to be.

Not just melting some filler metal on top of the parent pieces.

As mentioned, if you are using FCAW and doing a 'zap-pause-zap-pause-repeat' action, you are risking trapping slag (from the FCAW process itself) in between each of those individual 'welds'. Unless you are working on really thin stuff (thin sheetmetal type work), you usually do NOT want to make a whole bunch of zap-pause-zap-pause 'welds'. And especially not with a slag-producing welding process (FCAW or SMAW).

As to welding a scissor-left with a bunch of 'trigger welds', No!

 

[koditten]

I looked into building my own lift years ago. The price of buying vs building was not worth it at all. The difference was only around $200.

Im skilled welder and it would have been a huge fan and welding job to build a lift. Please consider just buying a lift.

Later
Kirk