Means of reducing and controlling weld distortion are described, covering b) tack weld one end, then use back-step technique for tacking the rest of the joint. It is a weld progression utilized to minimize distortion. Backstep welding is a technique to avoid distortion while welding on thin sheets. This technique involves a continual stalling of the forward travel motion by traveling backwards slightly, into the previous deposited weld. This technique has two.

Author: Garan Baran
Country: Niger
Language: English (Spanish)
Genre: Literature
Published (Last): 25 January 2015
Pages: 33
PDF File Size: 7.6 Mb
ePub File Size: 12.19 Mb
ISBN: 934-4-11629-146-5
Downloads: 21071
Price: Free* [*Free Regsitration Required]
Uploader: Mikashura

The time now is Copper tubes are brazed or soldered to copper holding clamps, and the water is circulated through the tubes during welding.

By continuing to use this website, you agree to their use. This site uses cookies. And for a PDF full letter size version click here.

There are occasions, however, when stress relief is necessary to prevent further distortion from occurring before the weldment is finished. In a welded joint, these same expansion and contraction forces act on the weld metal and on the base metal. And if you have are too fast you may not have enough heat input. So we do what is called multipass welding.

Shrinkage caused by each pass tends to be cumulative, thereby increasing total shrinkage when many passes are used. Plan the welding sequence A well-planned welding sequence involves placing weld metal at different points of the assembly so that, as the structure shrinks in one place, it counteracts the shrinkage forces of welds already made.

Here’s another multipass welding example on. This separation is most pronounced as the first bead is laid. Distortion is basically when your metal warps. One might expect this stress to cause considerable movement or distortion after the welded part is removed from the jig or clamps. For example, depositing a given-size weld on thick plate with a process operating at amp, 25 volts, and 3 ipm requires 87, joules of energy per linear inch of weld also known as heat input. You are commenting using your Facebook account.

Anticipate the shrinkage forces Presetting parts at first glance, I thought that this was referring to overhead or vertical welding positions, which is not the case before welding can make shrinkage perform constructive work. Results 1 to 7 of 7. When welding heavy plate over 1 inch thick bevelling or even double bevelling can save a substantial amount of weld metal which translates into much less distortion automatically.


The potential problems that can occur from poor weaving techniques is that you can undercut the weld bead edge as well as have bad fusion. When a pipe welder starts a pass he will usually strike on the side of the joint move forward to get a puddle then back to fill in the crater.

There are quite a few welding techniques you will use in your welding. The two actions coincide, and the welded plates assume the desired flatness.

Back stepping may not be effective in all applications, and it cannot be used economically in automatic welding. Beginning welders and even those that are more experienced commonly struggle with the problem of weld distortion, warping of the base plate caused by heat from the welding arc.

It takes practice to control heat input.

Weld Distortion

It’s also good for other types of welding like surface welds. If the restraints clamps that hold the workpiece, or an opposing shrinkage force are removed, the residual stresses are partially relieved as they cause the base metal to move, thus distorting the weldment. What is Weld Distortion? As the bar is uniformly heated, it expands in all directions, as shown in Fig.

As the weld metal solidifies and fuses with the base metal, it is in its maximum expanded from. The weld made with the higher heat input generally results in a greater amount of distortion. Thus the completed weld is slightly longer than it would be if it had been made on the flat plate.

Weld Distortion

Generally speaking, the parent metal will take in less heat the faster you weld. As a matter of fact there are many problems that can occur as you weld, and this is covered here. If there is too little heat input there is poor penetration. Click the image for a larger view or to print. There are no problems.

The residual stresses that would tend hechnique distort the weldments are thus minimized. And multipass requires you to use a weaving technique after you lay a stringer bead.


Back step welding

A good weld, whether it’s a stringer bead or a weave bead will The first weld you learned is a string bead which is a continuous weld in a straight line. You use this motion to make cover welds over stringer beads multipass welding. When you start a weld you get a lot of heat and not much metal and the zone is subject to cracking.

Gamble, See the provided link. There is no weaving or motion other than dragging or pulling. To find out more, including how to control cookies, see here: This does not occur, however, since the strain unit contraction from this stress is very low compared to the amount of movement that would occur if no restraint were used during welding.

Backstep Technique for TIg Welding

If you are welding in the flat position or the vertical welding position you can try this technique. For example, as the temperature of the weld area increases, yield strength, elasticity, and thermal conductivity of the steel plate decrease, while thermal expansion and specific heat increase Fig. You start your weld move forward then back to fill the crater, the same when you finish a weld you leave a crater of heat with no metal so you go back over the weld to fill in the crater.

The use of mechanized welding equipment reduces welding time and the amount of metal affected by heat and, consequently, distortion. This is a simplified explanation of basic cause of distortion in welding assemblies. In the back-step technique, the general progression of welding may be, say, from left to right, but each bead segment is deposited from right to left as in figure. Clips are welded to the edge of one plate and wedges are driven under the clips to force the edges into alignment and to hold them during welding.

Water-Cooled Jig Various techniques have been developed to control distortion on specific weldments.