Prevention and Control of Distortion in Arc Welding

Prevention and Control of Distortion in Arc Welding


In many fields of modern industry,
electric arc welding is accomplishing miracles of production. Powerful diesel-electric locomotives
are being made lighter and stronger, by using arc welds in place of bolts, rivets
and castings. These penstock tubes at Shasta Dam were arc welded, to eliminate all joints which
might otherwise leak or corrode. New methods of ship construction have
resulted from the use of arc welding, which speeds up production, and produces
a lighter, more rigid ship. In the manufacture of aircraft — arc
welding on engine mounts, fuselages and landing gear ensures maximum strength,
with the minimum of weight. But the successful application of arc welding depends on the use of proper
welding methods. Here is what happens when improper
welding methods have been used. Distortion has caused this job to warp
out of shape. The same thing has occurred to this metal tray. The purpose of this film is to show how all distortion can be controlled,
and prevented. But first of all, we must understand
what causes distortion. Let’s start with this ordinary steel bar. If the bar is heated thoroughly and uniformly
throughout its entire volume, considerable expansion in all directions will take place. Now, if the bar is allowed to cool evenly
without restraint of any kind, we know that it will contract to its original
shape and size without distortion. However, if we place the two ends of the
bar in a vise, and then heat the bar uniformly, expansion in these directions
will be prevented by the vise, and expansion can only occur in these
other directions. As the bar cools, it contracts evenly
in all directions. The result, is a shorter bar, with a
greater thickness. Now let’s go back to our original bar, and see what happens when we heat only
one side. Getting up close, we see that expansion
in this case is localized, and uneven. The surrounding cool metal acts similar to the vise — and restrains expansion
in these directions. But there is no resistance to expansion
in this direction. It is obvious that this uneven expansion
causes an unnatural displacement of metal. When this area starts to cool and contract, a small amount of that
displacement becomes permanent. In other words, there was no control;
and the final result is distortion. Now several steel bars side by side,
is much the same as a steel plate; showing that uncontrolled contraction
always causes distortion. Let’s see what actually happens when
we make this butt weld. Now keep the picture of that steel bar
in mind; because the bar’s behavior when heated is very similar to the weld bead
we’ll form to join these two plates. As the weld progresses, we can see that the molten weld metal begins to cool,
and contract immediately. But at the same time, the heat of the arc itself is causing considerable expansion
ahead of the contraction. Looking at the end view, we can see that
the intense heat of this molten weld metal, plus the heat of the arc itself,
is being transmitted to the surrounding areas. It is important to understand that while
the weld metal is cooling, and therefore contracting, the temperature of the
surrounding plates is rising and therefore causing considerable uneven expansion. As these plates cool, they will also contract. When we allow expansion and contraction to
occur without any control, the result is bound to be distortion — caused by this
tough looking villain, Mr. Shrink himself! He thinks he is pretty powerful; but we can show that Shrink is all bronze, and
no brains. We know that on any welding operation,
Shrink is always right on the job. Look at him pull! And look at the distortion! Now that the damage has been done, let’s
slice off a piece of the plate, and examine a typical cross-section of the weld. The over-welding here is a waste of time
and money, adds nothing to the strength and performance of the joint, and in this
case caused abnormal distortion. Let’s find a rule we can apply in a
situation of this kind. Rule #1: To prevent distortion, reduce
the effective shrinkage force. In other words, always use as little weld metal as possible, and make better use of
the weld metal you need. We can also reduce the effective shrinkage
force through proper edge preparation. This amount of bevel would require more
weld metal than necessary. To obtain proper fusion at the root of the weld with a minimum of weld metal,
the bevel should be 30 degrees. But proper fitup is also important; so space the plates 1/32″ to 1/16″ of an
inch apart [0.794mm to 1.59mm]. You will then need only a minimum amount
of weld metal to produce a strong joint. Using fewer passes is another way of
controlling distortion. For example, on plates that are free to move, distortion in this direction is
always a problem. In this case, if we use one or two passes with large electrodes, we will greatly
reduce distortion. In welding any structure, it is always
important to consider the neutral axis. With a conventional fillet, the weld is
so far off the neutral axis, that Shrink has plenty of leverage to pull the
plates out of alignment. But use of the *incoherent* fillet method
places the weld close to the neutral axis greatly reducing the leverage so that
Shrink cannot pull the plates out of line. Your own experience and ingenuity will
uncover other methods. For example, intermittent welds frequently
give all the strength required. In this way, you can use 2/3rds less weld metal, and reduce the effective shrinkage
force by that much. On this bulkhead, good engineering design
permitted the use of intermittent welds which meet all strength requirements, and
at the same time, minimize distortion. When a continuous weld is required, we
can control distortion if we first understand how expansion affects the
plates. Notice how expansion from the heat of
the weld along the edges causes the plates to spread, as shown in the magnified circle. As the weld progresses, the spreading
continues: and the plates become locked in this position by the cooling and
contraction of the weld metal. Welding speed will determine the amount
of this spreading action. But we can control this action and prevent
distortion by the use of back-stepping; whereby each successive bead is laid from
right to left; but the direction of your welding progresses from left to right. To illustrate this method, very short
welds are used here. But in actual practice, each bead is
laid with one stick of electrode to allow time for the heat of each weld to
distribute evenly throughout the plates before beginning the next bead. When we use backstepping, notice how
heat from the first weld causes expansion which temporarily spreads the plates. But as the heat moves out across the
plates, the expansion in these outer areas, acting against the bead which
has cooled, forces the plates together. Each weld becomes a rigid section by
the time the next weld is started, so that the spreading action becomes
less and less which each succeeding bead until the weld job is completed
without further spreading or distortion. Rule #2 gives us a little different
slant on this fellow Shrink. To prevent distortion, make shrinkage
work for us. This is simply another way of saying
that Shrink is plain dumb, and is just as willing to work for us as against us,
providing we’re smart enough to use him to our advantage. On a “T” weld like this, we can anticipate
Mr. Shrink’s tendencies, and tip the perpendicular plate slightly away from
the weld side. Now, see how quickly Shrink goes to work for us, and straightens this part up to
its true position. Another adaptation of Rule #2 is the
spacing of parts before welding. In welding these searchlight trunnion arms
which be very accurately spaced when the welding is completed, allowance is made
for the amount of shrinkage which will occur. Before welding, the parts are spaced
like this. Then when the welding is completed,
watch how controlled shrinkage brings the two arms into the correct position
and perfect alignment. We can also make shrinkage work for us by prebending or springing the parts
involved. For example, when these two plates are
sprung away from the weld side, the counterforce exerted by these clamps
holding the plates firmly, overcomes the shrinkage tendency of the weld metal,
causing it to yield. But we can still use Mr. Shrink after
the clamps are removed. Now all he needs to do is give the plates a slight pull to eliminate any
signs of distortion. Prebending may be applied to any number
of welding operations. Here, it is being employed on these steamshovel dipper sticks to make sure
the parts will be straight after welding. So far, we have illustrated several methods by which we can control and
prevent distortion. First, by reducing the effective shrinkage force: and second, by making
shrinkage work for us. But on certain types of weld jobs, we may find that we still have a distortion
problem. Then we must use other methods. We’ll call this Rule #3. To prevent distortion, balance shrinkage
forces with other forces. This rule applies automatically in welding this machine base, for its own structural
nature provides rigid balancing forces. But when these natural balancing forces
are not present, we can place Shrink in the position of using his own powerful
force to balance itself. Here’s how: Use proper welding sequence. By welding alternately on both sides
of the neutral axis of these two plates, watch what happens to Shrink: first he
has to pull on this side. Then rush around to pull on the other side. And back again! And over again! Phew! It’s a much harder pull each time, until finally we have Shrink tired out
completely. – *bong* The result? No distortion. Here’s another application of the same
principle: Staggered intermittent welds applied in this sequence: 1… 2… 3… 4. Proper welding sequence permitted the
construction of this crane boom to proceed without delay and without distortion. The operation was throughly planned
beforehand, so that each cross-arm was tack-welded to the main members to first
make the entire crane a rigid structure. Following this, one set of cross-arms was
welded on one side. Then, one set on each opposite side; always
balancing one shrinkage force with another. Step by step right on up to the end, so that the final result was a perfectly
straight crane boom. The use of peening is the application of a balancing force to prevent distortion
in a different sense of the word. By peening the bead, we actually stretch the weld metal, counteracting its tendency
to shrink as it cools. When we use peening, Shrink really takes
a beating. -*hammering sounds* Look at him! He’s groggy already. Peening takes the fight right out of him. But don’t overdo it; too much peening may
damage the weld metal. The most important method of overcoming
distortion problems is the use of clamps, jigs or fixtures to hold the work in a
rigid position during welding. In this way, we balance the shrinkage forces of weld metal with sufficient
counter-forces to prevent distortion. For example, when we weld these two
plates, we know that when the weld metal cools, the plates will distort, like this.
-However, if we hold the plates perfectly rigid with clamps or jigs, the restraining
forces here prevent the plates from moving. Consequently, the weld must
stretch as it cools. Now after removing the clamps, we see that almost all distortion has been
eliminated. But in most cases, the plates to be
welded are merely parts of a structure, and other sections will continue to hold
the plates as rigid as if they were clamped permanently, thereby reducing
distortion to a minimum. Here is a practical application of this
principal. These heavy fixtures clamp the aircraft tubing of this fuselage so rigidly that
distortion is impossible. The type of jig or fixture required will be determined of course by the nature of
the welding job. Here’s the setup where we have every
possible shrinkage force balanced with other forces: the more Shrink pulls,
the more exhausted he becomes. *bonk* *bonk* *bonk* *drumroll* Well — that’ll take the starch out
of him for awhile! Remember that controlled shrinkage
prevents distortion, so be sure to apply one or all of these three rules
to every welding job. Reduce the effective shrinkage force; make shrinkage work for us; balance
shrinkage forces with other forces. Arc welding is the truly modern method
of fabrication, it is one of the great tools with which the leaders of modern
industry today are building a new world of tomorrow.

52 thoughts on “Prevention and Control of Distortion in Arc Welding

  1. You can't beat these old instructional videos. Produced at a time when this nation had a bright and unlimited future based on its seemingly unlimited industrial power. Too bad it is not like that any more…

  2. I don't know for sure, but isn't "Make shrinkage work for us" not really used much at all today? I mean I haven't really heard of that anywhere else. Can anyone think of a modern application for that?

  3. This is awesome! I was shown this video in trade school and I've been looking for it since. Thank you very much for posting this!

  4. "Too bad it is not like that any more…"

    It is too bad and sad as you can see the results of what was Detroit via the outsourcing and offshoring of our jobs and plants because the Americans citizens voted for the GOP-Dem Corporate cabal whom in very bipartisan cooperation sold our jobs to non-Americans….Americans can have all sorts of reasons and excuses on why they did that but the fact is America doesn't want real jobs or a job at all….Sad but true…..

  5. people would be surprised to see how little has changed since then and now. in the sense that all these rules still apply. it's crazy

  6. as good today as it was then ,,, you canna change the laws of physics , captain ,,, as a well known scotts engineer has been heard to say.

  7. Many people are welding from left to right as its "easier". But i was taught by way more experienced welders to ALWAYS go right to left and from the bottom to top for better penetration values. Im not that experienced but i was lucky to get a job in a company which produces sections for coal mines which are installed 1100 m under the ground. Im assembling and welding "details", but every night when i have some free time i always sit in the cabin and trying my best to become a much better welder.

  8. I started thinking it was funny old times stuff and ended I could not believe my eyes. it's so useful because it's the same today. but there is a very important thing they did not say or explain well: we call it "making points", it's when you weld deeply just one point on another side of the main first welding, where it could hold the piece like it was clamped. yeah they said that about that complex tower structure, but they should explain well how it can be used also on simple pieces to weld.

  9. Thanks for posting this.  I will post this for my weldability class.  It is more fun than than still images in the textbook.  I still show part of an old Disney/AISI video on steelmaking with Donald Duck doing the heavy labor.  I like Mr. Shrink here.

  10. I must say that you have done a superb job at being an audio video archaeologist recovering and restoring old teaching information so it may remain in our archives forever. Thank You from a new to welding, 60 year old student.

  11. Nothing makes a class of adult women and men break the serious air of a learning environment faster than a personified Shrink falling on their ass.

  12. These vids should be taught in school all around the world …… I'm from the Caribbean and theses vids makes more sense than my teacher lol

  13. 16:38
    Please explain me how that one works. You weld top and bottom flanges – they will pull flanges inwards, reducing distance between flanges. Now you introduce gussets between flanges and weld them as shown (inside), so they'll pull flanges even further inside… i am confused….
    I'd rather weld gussets on the outside…

  14. i love these old videos they make way more since then all the scientific explanations. theirs alot more of these videos on youtube too

  15. They appear to be referring to "fleet-fillet welding" in the "incoherent" spot on the video at 7:31.

    You can find a description at http://delibra.bg.polsl.pl/Content/18436/P-779_1942_Vol110_No22.pdf

    The relevant pages are 70, 72, 100 & 101. These correspond to the numbering in the pdf file of 46, 48, 76 & 77 (hint: printing only those pages of document as a pdf produces a pdf that is easier to read than the original 33 MB document).

  16. Where can I speek to u about my problem of warpage in SS job v r doing, I am Sanjeev Sehgal,from India and available at 09810681806

  17. world war two welders saved the day. they made a new fleet of ships in record time. and we were able to fight on two fronts. Pacific theatre and European theatre. our welders made ships and therefore we won the war.

  18. Got a project to do where I suspect warpage will be a factor. This is exactly what I was looking for. Perfect, thanks!!

  19. I was sceptical about this video when I started watching it, but its very informative and explains in great detail the problem I was seeking to overcome. Thanks for posting it!

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