Automotive Bodywork and Rust Repair

by Matt Joseph

  ing is still sometimes used. MIG,

  clips, screw clamps, and various Cleco

  to be pretty bulky and cumbersome.

  TIG, and resistance (spot) welding are

  devices. Each of these represents a

  Beyond that reach, other methods of

  the main approaches covered here.

  class of fixturing devices, and each

  fixturing must be employed.

  comes in a great variety of styles, sizes,

  Edge clips are limited to holding

  Stick Welding

  and configurations. Each also has

  the edges of panels and patches, but

  This method was once used to

  application to most types of seams—

  have the advantages of being quick

  join autobody panel metal, both in

  butt, lap, and offset lap.

  to apply and to remove, and of offer-

  production and for repair. This prac-

  Locking pliers are often referred to

  ing very little obstruction to or inter-

  tice involved using small-diameter,

  by the name given to this tool by the

  ference with adjacent parts.

  coated welding rods that were

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  CHAPTE R 8

  years, car manufacturers sometimes

  supplement spot welds with adhe-

  sives and anti-corrosion treatments to

  add bonding strength, and to protect

  joints that are welded this way.

  Some of the spot welders used in

  repair and restoration do not squeeze

  the weld area between two elec-

  trodes, but apply spot welding force

  and heat to one piece of metal that is

  grounded through the other piece to

  be joined to it. These devices are par-

  ticularly handy where access to both

  sides of a spot weld area are difficult

  or impossible to achieve. There are

  Spot welds are not very strong individually, but in numbers they gain strength.

  also numerous attachments for MIG

  The key to making good spot welds is getting the welding duration right, so as

  welders that mimic the strength,

  to not under-weld weak attachments or burn through with excessive weld

  appearance, and configuration of

  times. Clean contact and mating surfaces are also critical.

  resistance welds.

  Another technique for duplicat-

  specifically designed for sheetmetal

  and considerable squeezing pressure

  ing the appearance and function of

  work. Both AC and DC formats were

  on the two outer surfaces of the weld

  spot welds is button hole welding.

  employed. Stick welding sheetmetal

  area by the welding electrodes, melts

  This technique employs torch, MIG,

  required

  considerable

  skill,

  and

  the spot into a fusion weld. Spot

  or even TIG welding to join two sec-

  yielded results that were often less

  welds are quick and easy to make, and

  tions together, one on top of the

  than great. The main problem was

  reasonably neat and strong. Modern

  other, by welding through the top

  that when stick welding was per-

  light vehicles depend on as many as

  thickness of metal and into the sur-

  formed with the machines commonly

  3,000 or 4,000 spot welds to hold

  face of the metal under it. This must

  associated with it, the process pro-

  their structures together. In recent

  be accomplished without overheat-

  duced excessive heat for thin-section

  ing the whole area, and ending up

  jointure, resulting in excessive drop-

  with an unsightly and embarrassing

  out and distortion. The time required

  hole through both pieces. One trick

  to finish stick welds in sheetmetal was

  to avoid this is to do a pseudo-

  excessive, by today’s standards. This

  button-hole weld by drilling a hole

  practice is obsolete.

  through the top section, and weld-

  ing its rim to the metal under it.

  Resistance or Spot Welding

  Spot welds are often vulnerable

  This has been a mainstay of auto-

  to corrosion because the places

  motive construction since the 1930s.

  where they are used are prone to

  It uses no flux or filler, and is accom-

  attracting moisture between the

  plished by applying a concentrated

  joined pieces of metal through capil-

  short circuit, and strong physical pres-

  lary action. This problem is made

  sure, to a small spot on as many as

  This type of spot welder allows you to

  worse by the fact that spot welding

  three thicknesses of body metal to be

  make welds from one side of a panel.

  tends to vaporize many of the steel

  joined. A combination of intense

  This can greatly ease access

  treatments, like galvanizing, that are

  heat, created by maintaining a very-

  problems. It takes high electrode

  employed to protect sheetmetal. This

  high-amperage short circuit at the

  pressure and clean metal for this type

  problem is mitigated by using a

  point of the weld for a short interval,

  of weld to work well.

  weld-through primer between pieces

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

  W E LDI NG BODY M ETAL

  Applying a good weld-through primer

  to the surfaces between spot welds

  goes a long way to protecting them

  from corrosion. This technique can

  also be used with MIG and TIG

  Today, MIG welding is the mainstay of most autobody welding. It is relatively

  welding, but is less effective in those

  easy to learn this technique. It is being used here to fill weak spots in a

  cases than with spot welding.

  sheetmetal floor.

  that are spot welded. Such primers

  reason than that everyone uses and

  the short circuit. However, it is

  contain a very high percentage of

  understands them.

  quickly reestablished, as more wire is

  zinc in their solids. This makes them

  In the MIG process, a welding

  fed into the puddle, creating the

  conductive, and thus able to carry

  wire is continuously fed into the

  short arc cycle that is the basis of

  spot welding currents, and protects

  weld area—the puddle—as it is

  MIG welding. This all occurs at about

  finished welds with ions from the

  drawn along the weld seam. The wire

  100 to 150 cycles/second, and pro-

  zinc particles in the coating after a

  carries current, and is surrounded at

  duces the famously characteristic fry-

  weld is made.

  the weld, by an inert shielding gas

  ing egg sound that is associated with

  that is fed there through the welding

  MIG welding.

  MIG Welding

  h
ose and gun, along with the wire.

  The most-often botched aspect

  This has become the most com-

  C-25 is the most common gas used

  of MIG welding is fit-up, the distance

  mon type of repair and custom auto-

  for sheetmetal welding, in a 25-

  between the edges of the metal

  body welding. Its name derives from

  percent CO2 and 75-percent argon

  pieces that are being joined. In lap

  the term metal inert gas, which is

  mixture. The gas acts like the heat-

  and offset lap joints, fit-up is not an

  really a misnomer. After all, so-called

  vaporized rod coating in stick weld-

  issue because the joints are overlaps.

  TIG welding (for tungsten inert gas)

  ing. It shields the weld puddle and

  But in butt welding, it is critical to

  is also a metal-inert-gas welding

  the cooling weld from most of the

  leave

  adequate

  fit-up

  distance

  process. Properly, what is called MIG

  oxidation corrosion that would

  between butted edges. This space is

  should be called—according to the

  occur if the weld was made and

  consistently in the range between

  American Welding Society (AWS)—

  cooled in a normal air environment.

  the thickness of a dime and a nickel.

  GMAW for gas metal arc welding.

  The actual MIG process involves

  It may sound more difficult to carry

  TIG is properly designated as GTAW,

  a cycle. As the mechanically fed wire

  a weld puddle down such a gap than

  for gas tungsten arc welding. I’m

  contacts the puddle, it creates a

  down two more closely fitted edges.

  glad to get all of that sorted out,

  direct

  short

  circuit

  with

  the

  However, this is not the case.

  thank you. Now, please forgive me,

  grounded work piece. The heat gen-

  What is beyond difficult, in fact all

  while I continue to use the vernacu-

  erated by the short melts off the

  but impossible, is to get a good MIG

  lar terms, MIG and TIG, for no better

  wire’s end, into the puddle, ending

  butt weld when edges are fitted up too

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  CHAPTE R 8

  These welds, with their fronts shown on the left and their backs on the right, represent (top to bottom: 1) a finished

  weld done with alternate tacking and grinding, 2) a bead, welded with trigger on/off segments, and 3) a weld bead

  comprised of automatically stitch-timed segments.

  closely or in actual contact with each

  Amperage is set by setting the wire

  ting wire speed and voltage properly

  other. This is because the expansion

  feed speed. Different wires and differ-

  for MIG welding. Some machines set

  from welding heat inevitably distorts

  ent thicknesses of metal require dif-

  one, or even both, of these variables

  too-closely-fitted metal edges so badly

  ferent speeds. Manufacturers supply

  automatically. While many welds do

  that it is very hard to weld them. It is

  recommendations for this setting

  not allow for practice, some do. If

  also very difficult to straighten out

  with their machines. It is, however,

  you can duplicate the conditions of a

  panels welded that way.

  rough data, and you should plan to

  difficult weld with scrap metal that is

  There are several issues to master

  modify it for your own situations and

  similar to the material in the sections

  in order to do good MIG welding. You

  according to your own experience.

  that you will be welding, and prac-

  need to figure out ideal gas flow for

  Voltage settings are also critical.

  tice your difficult weld, it would be

  your work. This is set with a regulator

  The best MIG machines have contin-

  to your advantage to do so.

  as the volume of shielding gas deliv-

  uous voltage settings, while less-

  Some MIG welding machines

  ered. Try to use a two-stage regulator

  expensive ones rely on step settings.

  have fine controls for things like

  that employs a volume indicator in its

  In either case, the voltage setting in

  stitch welding, that is, weld time on

  second stage. About 10 to 20 CFM (at

  MIG welding is somewhat analogous

  and time off, and burnback control,

  atmospheric pressure) is a good range

  to how long an arc you hold in stick

  which is the time that the wire elec-

  in which to work when you are weld-

  welding. It controls the format of the

  trode remains energized after the

  ing body metal with .023- to .025-inch

  weld bead and thus its height, shape,

  gun trigger is released. These are

  wire. Practice and experimentation are

  and, to some degree, its penetration.

  handy features that can improve the

  your best guides in this matter.

  Somewhere between your gen-

  convenience and quality of work,

  Amperage settings are critical

  eral experience and getting frequent

  but they are not essential to doing

  when MIG welding sheetmetal.

  practice, you will get the hang of set-

  good MIG welding.

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

  W E LDI NG BODY M ETAL

  One thing that is essential is to

  use good wire. MIG welding wire

  varies in quality. Some wires are

  junk, barely good enough to weld

  with, while others are a pleasure to

  use. Today, most of the major wire

  brands perform well. Still, different

  wires often have different features

  and advantages. For example, one

  wire may produce welds that are eas-

  ier to grind, while another may lay

  down more uniform beads. Again,

  these are things with which you

  should experiment.

  Other

  variables,

  like

  torch

  approach (forehand or backhand),

  distance from work, position, and

  angle, are best dealt with in manuals

  and other sources that are specifi-

  cally devoted to MIG welding

  instruction.

  TIG Welding

  TIG welding is probably the most difficult welding technology to master.

  This is probably the most skill-

  However, it pays the reward of being the best way to join sheetmetal pieces

  intensive type of welding, but pre-

  and panels, when quality is the prime objective.

  sents an odd dichotomy. It can be

  understood in very complex and

  nology, but knew how to weld with

  sus thumb wheels, and so forth, are

  technical terms, but it can be per-

>   it, instinctively and superbly.

  hot topics. Also, there is specializa-

  formed beautifully with little knowl-

  The point is: You can interpret

  tion in TIG welding particular metals

  edge of its technical aspects.

  TIG welding in many ways and at

  and alloys.

  Here is an example: Back in the

  many levels, comprehending and

  Unfortunately, is not possible to

  age when TIG welders did not have

  mastering as much or as little of the

  offer instruction in TIG welding in

  the modern sophistication of solid-

  underlying technical issues as the

  this book. However, if you are inter-

  state-generated square-wave forms

  spirit grabs you. Some people revel in

  ested in doing ultimate-quality weld-

  and slope control, they relied on car-

  the complexities of TIG waveforms

  ing work on a variety of metals, from

  bon bundle frequency generators for

  and the possible adjustments to them.

  stainless and common steel to alu-

  superimposed high-frequency cur-

  Others are greatly concerned with the

  minum, TIG welding provides the

  rents to keep their arcs from stalling

  shape of the TIG electrode and/or of

  best results. It takes some consider-

  at the AC wave turnover point. I

  its ceramic. Others almost intuitively

  able commitments of money for

  knew a man who operated one of

  know or remember how to make the

  equipment and of time to learn to use

  those primitive TIG machines. He

  best choices in these matters.

  it, but you should at least consider

  would not have understood much of

  TIG is the most individualistic

  making those commitments if ulti-

  the technical sentence above, but

  welding format that exists. Some

  mate welding quality is your objec-

  with the equipment of that period,

  operators prefer air-cooled torches;

  tive.

  Don’t

  let

  the

  imposing

  he could deposit a uniform and well-

  others prefer liquid-cooled units. The

  technicalities of TIG welding scare

  penetrated weld bead on the business

  merits of each are often debated for

  you off if you are interested in this

  edge of a razor blade. It was no small

  jobs that involve the same materials

  format. You do not have to under-

  feat. He understood little of TIG tech-

  and similar welds. Foot controls ver-

  stand it in technical detail to make

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