Automotive Bodywork and Rust Repair

by Matt Joseph

  CHAPTE R 8

  One Way to Reduce Heat Problems

  welds ground flat, your weld line should

  look like a perforated tear line.

  Now, the entire seam must be closed.

  This can be done by filling in the gaps

  between the ground tack welds, and

  grinding the resulting welds flat to the

  panel, or by welding a continuous bead

  over the entire seam. In either case, panel

  edge position should be perfect, and heat

  distortion from the whole operation will be

  reduced from what it would have been

  with any approach other than alternate

  tack welding.

  New fender-section metal has been fitted into this old fender with almost

  The same approach works equally

  no fit-up gap, and TIG tack welded into place. MIG welding would have

  well with MIG welding, although our

  required a considerable fit-up gap to handle heat expansion, and would

  example lacks the apparent neatness of

  have produced much more distortion than did TIG welding.

  the same process performed with TIG

  welding. That is because MIG welding is

  Keeping welding heat at the minimum flat to the panel. If you think of each tack not as accurate, controllable, or tidy as is necessary for making good joints is

  weld as a line of continuous and adjacent

  TIG welding.

  critical to joining sheetmetal parts and

  buttons, you want to make tack welds at

  The main point is that this welding

  sections. This limits distortion in the areas

  every second or third button position in

  technique keeps the buildup of welding

  of the welds. One way to accomplish this,

  that line. The actual spacing depends on

  heat way below what it would otherwise

  while ensuring the accurate positioning of

  the situation, and on your personal prefer-

  be, if you attempted to weld continuous

  pieces,

  is

  to

  make

  tack

  welds

  ence. At this point, with the alternate

  beads. This is because it allows more

  incrementally along a seam. This works

  with MIG, TIG, and gas welding

  techniques. Our example uses TIG, and

  then MIG, welding processes.

  You start by making enough tack

  welds to position the pieces that you are

  welding. As you make the first few tack

  welds, at roughly equal distances from

  each other, you can make minor adjust-

  ments in piece positions by prying them

  This is the finished weld bead.

  with a small screwdriver. For example, you

  Note that it is uniform and well

  can keep the edges of the pieces level

  Tack welds were added between the

  penetrated. Also, note how little

  with each other this way, as you fill in more

  existing tack welds, until between

  metal on either side of the bead

  tack welds along the seam.

  1/2 and 1/3 of the seam had been

  has been discolored by heat. There

  When you have filled in most of the

  welded. The tack welds were then

  is no visible distortion in the

  welds, that is, enough to absolutely

  ground flat to the panel, leaving the

  original fender, or in the new metal

  secure the seam, you grind those welds

  seam with a perforated appearance.

  that was welded into it.

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  AUTOMOTIVE BODY WOR K AN D R UST R E PAI R

  W E LDI NG BODY M ETAL

  After grinding and finishing, here is

  the completed fender. It required

  little work to bring it to this point,

  mostly filing and sanding. The

  other photos are of the right

  The underside of this fender repair required even less finishing work than

  fender, while this one shows the

  its topside. A little, light surface grinding and sanding did the job. This is

  left. Its repair was almost identical

  as close to the perfect restoration of metal as you are ever likely to see.

  to that of the right fender.

  The repaired metal is almost indistinguishable from the original.

  cooling and heat-dispersion time between

  riority of the welding in the TIG example.

  equipment and time and skill. Maybe so,

  adjacent short welds. When it is used with

  This work was done by Wayne, at L’Cars

  but it has the potential to restore and

  MIG welding, I prefer to just fill between

  in Cameron, Wisconsin. It represents

  fabricate metal that makes it more like

  the ground welds, and not to weld a con-

  the achievement of perfection in a very

  original metal than any other welding

  tinuous bead over them, because this

  challenging

  job,

  from

  fabrication

  approach. It finishes more easily and

  involves less heat and distortion.

  through welding, and finishing the

  better than any other technique, and

  When you compare these examples

  welds. Some may argue that TIG weld-

  creates far less distortion around welds.

  of MIG and TIG welding, note the supe-

  ing is overkill, in terms of the cost of

  I don’t think that is overkill.

  You can use the same type of

  The welds shown in the previous

  When the seam had been completely

  alternate tack welding approach

  photograph are shown here, after

  welded and ground flat, it was

  with MIG welding as with TIG

  partial grinding. After they were

  finished with a small orbital disc

  welding. This is illustrated here

  ground flat to the panel, it was tack

  sander. The result was a strong and

  with a sample that has been

  welded in the areas between the

  good-looking bond. Note that this

  welded with spaced MIG welds.

  ground welds.

  was a butt-welded joint.

  AUTOMOTIVE BODY WOR K AN D R UST R E PAI R

  79

  CHAPTE R 8

  Actually, you can’t weld with a

  torch by melting and carrying a puddle

  down the seam. The two pieces can’t fill

  the seam without thinning them unac-

  ceptably. For that reason, a steel filler

  rod is applied to, and melted into, the

  puddle as needed to form a bead, as the

  puddle is carried down the seam by

  torch movement in that direction.

  All of this is possible and has

  worked reasonably well for genera-

  tions. On the other hand, MIG and

  TIG welding also have worked much

  better for fewer generations. The first

  disadvantage of torch welding thin

  sections is that it requires consider-

  able skill, more than MIG welding,

  and about the same as TIG welding.

  Note that the considerations and

  manipulations of the TIG electric

  torch and filler rod are somewhat sim-

  Gas welding is difficult to master, due to t
he many operator variables involved

  ilar to those employed in gas welding.

  in its performance. Note the extreme torch angle and the use of filler rod to

  Torch welding also imparts much

  add metal to the puddle and, sometimes, to shield it from excessive heat. Also

  more general heat to a weld area

  note the distortion in this example.

  than either of the common electric

  welding formats. This means more

  great welds in a variety of situations.

  6,300 degrees F at the cone tip of a neu-

  distortion and more fun and games

  As with your personal computer, you

  tral flame. A neutral flame has a perfect,

  chasing collateral damage off the

  can operate a TIG welder without a

  combustible mixture of oxygen and

  welding scene, after welding is com-

  deep understanding of how it works.

  acetylene for complete combustion of

  pleted. For those reasons, torch weld-

  A good welding course at a vocational

  each gas, with no excess of either in the

  ing sheetmetal seams is rarely

  school will have you started down the

  mix. This means that it is possible for

  employed these days. Put simply,

  path of mastering TIG techniques.

  that flame, in sufficient size, to melt the

  you can do better work with much

  surface of steel, which begins to melt at

  less skill, knowledge, and effort with

  Oxy-Acetylene Gas Welding, Brazing

  around 2,700 degrees F.

  electric welding techniques.

  and Braze Welding

  In practice, oxy-acetylene welds

  Brazing and braze welding also

  These are older methods of join-

  are made by moving the flame, with

  have limited use in good autobody

  ing thin metal sections that still have

  its inner cone near the metal to be

  jointure practice. Like torch welding,

  some application in today’s world of

  joined, angled at roughly 45 degrees

  these techniques are performed with

  (mostly) electric welding. In most

  to the surface, and oriented in a fore-

  an oxy-acetylene flame. In this case, a

  cases they will prove inferior, in one or

  handed direction (the direction that

  slightly carburizing flame is preferred.

  more of several ways, to electric weld-

  the weld is being made). The torch is

  That is, a flame with a slight feather

  ing approaches. But there are times

  moved along with a slightly oval or

  around its inner cone, caused by a

  when you may find uses for torch

  circular tip motion to make welds

  richer-than-neutral amount of acety-

  welding and brazing techniques.

  that have characteristics indicated by

  lene in the oxygen/acetylene mixture.

  The oxy-acetylene flame, generated

  the approved ripple appearance in

  Brazing is somewhat like solder-

  by mixing oxygen and acetylene gases

  their weld beads. All of that takes

  ing with tin/lead-based and silver-

  to fuel a torch, is infernally hot—about

  some coordination and practice.

  based solders, but is done at higher

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  AUTOMOTIVE BODY WOR K AN D R UST R E PAI R

  W E LDI NG BODY M ETAL

  temperatures (around 1,000 degrees

  F) and with filler rod that is a brass

  alloy or, less commonly, a bronze-

  based alloy. Note: Brass alloys are

  based on copper and zinc, while

  bronze alloys are based on copper

  and tin. Like soldering, brazing does

  not produce a fusion joint; that is,

  the molecules at the surfaces of the

  metals do not intermingle as they do

  in true fusion processes, like MIG,

  TIG, and torch welding. Instead, the

  brazing material is attracted by capil-

  lary action between the sections

  being brazed together. There is some

  surface mingling of braze and base

  metal molecules, but nothing like

  the alloying action that occurs in

  true fusion welding.

  You might think that brazing

  is the low-temperature and low-

  distortion solution to the challenges

  of joining thin-metal materials. It

  might seem that all you have to do is

  bring joints up to a relatively low

  temperature, and flow brazing rod

  into the space between the pieces.

  The weld on the left is a pretty good gas weld. The one on the right is a MIG

  And because brazing rod is very cor-

  weld. Note how much smaller the heat-affected zone is in the electric weld.

  rosion resistant, it should automati-

  This translates into less warping and distortion.

  cally seal areas like lap joints.

  Alas, it isn’t that simple. Brazing

  be done in production, but usually is

  (or bead) of brazing material in braze

  materials typically don’t have the

  very difficult in repair and custom

  weld areas. This type of joint is

  strength required for making sound

  fabrication situations. Another prob-

  stronger than simple brazing, but has

  butt welds, so their use is reserved for

  lem with brazing is the flux that is

  all of brazing’s other drawbacks,

  lap and offset lap joints. In fact, in

  used. It is most often borax based,

  mentioned above. There are some

  years past, some automobile manu-

  and it can be persistently difficult to

  places where brazing and braze weld-

  facturers used some brazed lap joints

  remove from finished joints. If some

  ing have application in sheetmetal

  in their original constructions of cars

  is left behind after cleaning, it does

  work, particularly when they are used

  and trucks. However, for most pur-

  not take on primer and paint well.

  to repair or to replace factory joints

  poses, butt joints are more desirable.

  Finally, brazing fluxes have a ten-

  that were originally brazed or braze

  That eliminates brazing them.

  dency to cause hydrogen embrittle-

  welded. In the main, however, brazed

  Even with lap joints, the fit-up

  ment in the metal adjacent to brazed

  and braze welded joints are perilously

  for brazing is critical to getting the

  joints, and this can cause cracking in

  close to being substandard tech-

  right capillary flow of the brazing

  that metal, as panels vibration cycle

  niques for most panel jointure pur-

  material into the joint. Without this

  over miles and time.

  poses today. While these techniques

  factor, brazed joints tend to be too

  Braze welding, unlike brazing,

  once may have seemed attractive,

  weak for automotive panel jointure.

  goes beyond capillary action and

  modern electric welding approaches

  Maintaining
proper fit-up gaps can

  deposits a strengthening thickness

  have supplanted them.

  AUTOMOTIVE BODY WOR K AN D R UST R E PAI R

  81

  CHAPTE R 8

  Six Welding Shop Tricks and Tips

  There are hundreds of little tricks,

  habits, and minor ploys that will help

  you make great welds. Some of them are

  in books devoted to welding, and others

  in books, DVDs, and seminars by

  advanced professionals in the sheetmetal

  and welding crafts. Still others can be

  garnered by watching seasoned body

  shop welders at their work. Here are six of

  my favorites:

  Tip #1

  The edges of the sheetmetal that you

  weld are often somewhat jagged, from

  contact with the likes of saws and

  aviation-type snips. If you take a minute

  to run an inexpensive hand-deburring tool

  over these edges, before you weld them,

  you will improve your welding results by

  making them more uniform. It is a small

  Behold the screwdriver trick for keeping edges in alignment as you tack

  weld them. The heat from tack welding can cause edges to lose lateral

  alignment as you add tacks. Some judicious prying with a small-blade

  screwdriver can reestablish alignment, before more tack welds are added.

  point, but it is so easy to deburr edges

  this way that it is a good idea to add this

  trick to your routine preparations for

  welding autobody metal.

  Tip #2

  Sometimes, despite your best efforts

  to keep surfaces properly laterally posi-

  tioned to each other, the heat of tack

  welding or seam welding causes them to

  An inexpensive edge-deburring

  move out of position. When this happens,

  tool can improve your welding

  it can be corrected as you go along by

  when it is applied to the sheet-

  prying edges back into alignment with a

  Cooling welds with compressed air,

  metal edges that you weld. The tool

  small screwdriver or other prying tool. I

  right after you make them and as

  is drawn along an edge to cut off

  tend to keep a cheap, small screwdriver in

  you go along, reduces heat buildup

  any minor defects that may have

  my left hand for this purpose as I weld

  and hardens the metal in the welds

  been created when the edge was

  sheetmetal tacks and seams, probably

  and weld area. Both of these

  originally cut.

  because I am right-handed.

  results are highly desirable.

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  AUTOMOTIVE BODY WOR K AN D R UST R E PAI R