Automotive Welding
Last updated 2007-09-18 11:12 PDT

Potentially Helpful Tips and Charts for Automotive Welding

Disclaimer

While I can weld decently, have studied welding, and have read a few books on the subject, I shouldn't be taken as an absolute authority. I have, however, tried to provide some data that might prove useful and some thoughts that might help someone. Your corrections, suggestions, and critiques are appreciated (see bottom).

Some Thoughts on Safety

Gloves

Welding is "joining metallic or nometallic material in a relatively small area by heating the area to the welding temperature." Therefore, the first danger that confronts the welder is that of excessive heat. Leather gloves should always be worn. Thinner gloves are preferred for gas and TIG welding because of the manual dexterity that filler rod demands. Gauntlet-length gloves should be used in TIG, Arc (stick), and MIG welding to protect your arms from flying sparks. The heat of Arc and MIG welding, in particular, make thicker leather with insulation necessary and there is no filler rod to worry about in these processes.

Protective Clothing and Footwear

Above the gloves, the clothes worn while welding, particularly when welding out of position, should cover the skin and be of non-synthetic fabric. Cotton (heavy) is usually the best bet. Cotton blends with polyester or rayon, etc, are particularly susceptible to smouldering/fire. There are flame-retardant coveralls for those particularly concerned. In addition to making sure you're not welding in nylon/polyester running shorts, check for open pockets and cuffs which will catch hot sparks and heat, unknown to you, until you smell your pocket-protector burning, or worse. Frayed cuffs of jeans also have an amazing ability to light from even the tiniest spark and are to be avoided. Also have a look at your shoes. Really low cut footwear (and sandals) are to be avoided although you might not want to lace your boots too tightly. Should a spark get in your shoe, (and someday they will!) getting them off quickly without your hands can save you from a nasty burn. Burning feet make a mind forget awfully quickly how to untie shoes.

Eyewear

Now that you've protected your body and are moving closer to being ready to weld you should think about your eyes. What a lovely blue they are, I'm sure... keep them seeing by always protecting them from both harmful radiation and flying spatter. Goggles are "recommended" for oxyfuel welding but good (dark) sunglasses will often work just as well. Any arc welding (TIG, MIG, Arc) requires a welding hood with the proper shade. These shades protect your eyes from the truly catastrophic damage that can occur. The ultraviolet and infared rays that electric arcs emit will cause burns (like sunburn) after frying your eyes. A welding hood protects your face and eyes from all of these dangers and the additional danger of spatter on the face. A cap (welder's cap, bicycler's cap, yarmulke, or anything else thin that will cover your head) keeps both sparks and the nasty straps of some welding hoods out of your hair. For those still having nightmares about starting welds "in the dark," new photochromic welding hoods are starting to be quite inexpensive. They are also much nicer and easier to use. Some are even (dubiously) "stylish!"

Ventilation

Adequate ventilation is an absolute necessity when welding. Fumes from certain types of chemicals in flux and metals are toxic. Among them are cadmium, chromium, lead, zinc, and beryllium. Particularly caution should be paid to arc welding electrodes, which often produce hazardous fumes.

As always, shop saftey should include awareness of fire hazards, things about to smash your feet, electrical hazards, etc.

Danger: Hazardous Materials and Containers

One final note to remember: do not try to weld or cut a container that holds or has held flammable or hazardous materials. Consult a certified welder and refer to American Welding Society ( AWS) Standard F4.1:1999, Recommended Safe Practices for the Preparation for Welding and Cutting of Containers That Have Held Hazardous Substances.

Skip directly to specific processes/techniques:

Arc

TIG

MIG

Arc (SMAW)

This is where I would talk about Arc welding but I decided not to because I am so incredibly bad at it. If I felt like there was demand, I might have someone else (Eric?) write something but I doubt that many are reading this page. If you'd like to protest, email me at the bottom.

TIG (GTAW)

TIG, Tungsten-Inert-Gas (or Gas Tungsten Arc Welding), welding is the most versatile welding technique. (Note: TIG is sometimes refered to as "heliarc welding.") TIG is technically an arc welding process because it creates heat from an arc between the nonconsumable tungsten electrode and the base metal. To protect the weld pool from atmospheric contaminants, the TIG torch also releases an inert gas. Because the weld pool is always shielded, TIG is a very clean process.

A good TIG machine gives the welder a choice between DCEN, DCEP, and AC current. DCEN will provide the deepest penetration (about 70% of the heat will be in the base rather than the electrode). DCEP requires a larger electrode than DCEN for the same current because 70% of the heat is now in the electrode. This creates a wide, shallow bead. An advantage of DCEP is the cleaning action it creates on aluminum on magnesium. ("The heavy gas ions strike the surface and cause the oxides to break up near the weld bead.") AC welding, which starts and stops the arc 120 times per second, has the cleaning action of DCEP and penetration in between the other two. Heat is distributed evenly between electrode and base metal.

TIG torches can be water- or air-cooled. Water-cooled torches should be used when currents over 200A are desired.

Two inert gasses are used for shielding TIG: argon and helium. Either gas can be used individually or in combination. Helium allows a hotter arc (and therefore faster travel) but is more expensive. Starting and maintaining an arc is easier with argon and less gas is required because argon is heavier than air and will cover the weld area better (though it would seem that this would only be true in flat welding and not in overhead).

Another choice (there are so many) in TIG is the electrode. Different results will come from varying electrode: type, diameter, tip shape. Electrodes come as pure tungsten, 1 or 2% thoria (or thoriated [actually thorium dioxide]), .15 to .40% percent zirconia (zirconium oxide), 2% ceria (cerium oxide), or 1% lanthana (lanthanum oxide). Pure tungsten can be used for DC welding but is not optimal. It is recommended for AC welding and forms a ball on the end when heated (which is nice). Thoriated tunsten allows electrons to flow more easily and is easier to start. It is recommended for DC and can carry more current than pure tunsten. Zirconia tungsten is like pure tungsten but is easier to start. It can carry about the same current as thoriated tungsten but can only be used for AC. I have no idea about ceria or lanthana (other than that they exist). When welding steel or stainless use a thoriated electrode. My book recommends pure or zirconium electrodes for aluminum with AC but I'd suggest trying it with thoriated. See if you like it better. Here are some tables.

AWS Tungsten Electrode Classifications and Color Codes

AWS Classification Defined Color
EWP Pure Tungsten Green
EWTh-1 1% Thoria Yellow
EWTh-2 2% Thoria Red
EWZr-1 0.15-0.40% Zirconia Brown
EWCe-2 2% Ceria Orange
EWLa-1 1% Lanthana Black
EWG Other Gray

TIG Welding Mild Steel with DCEN

Metal Thickness Joint Type Electrode Diameter Filler Rod Diameter Amperage Argon Flow (cfm)
1/16" Butt/Corner 1/16" 1/16" 60-70 15
1/16" Lap/Fillet 1/16" 1/16" 70-90 15
1/8" Butt/Corner 1/16-3/32" 3/32" 80-100 15
1/8" Lap/Fillet 1/16-3/32" 3/32" 90-115 15
3/16" Butt/Corner 3/32" 1/8" 115-135 20
3/16" Lap 3/32" 1/8" 140-165 20
3/16" Fillet 3/32" 1/8" 140-170 20
1/4" Butt/Corner 1/8" 5/32" 160-175 20
1/4" Lap 1/8" 5/32" 170-200 20
1/4" Fillet 1/8" 5/32" 175-210 20

TIG Welding Aluminum with AC and High Frequency

Metal Thickness Joint Type Electrode Diameter Filler Rod Diameter Amperage Argon Flow (cfm)
1/16" Butt/Corner 1/16" 1/16" 60-85 15
1/16" Lap 1/16" 1/16" 70-90 15
1/16" Fillet 1/16" 1/16" 75-100 15
1/8" Butt 3/32-1/8" 3/32" 125-150 20
1/8" Lap/Fillet 3/32-1/8" 3/32" 130-160 20
1/8" Corner 3/32-1/8" 3/32" 120-140 20
3/16" Butt/Corner 1/8-5/32" 1/8" 180-225 20
3/16" Lap/Fillet 1/8-5/32" 1/8" 190-240 20
1/4" Butt/Corner 5/32-3/16" 3/16" 240-280 25
1/4" Lap/Fillet 5/32-3/16" 3/16" 250-320 25

TIG Welding Stainless Steel with DCEN

Metal Thickness Joint Type Electrode Diameter Filler Rod Diameter Amperage Argon Flow (cfm)
1/16" Butt/Corner 1/16" 1/16" 40-60 15
1/16" Lap/Fillet 1/16" 1/16" 50-70 15
1/8" Butt/Corner 3/32" 3/32" 65-85 15
1/8" Lap/Fillet 3/32" 3/32" 90-110 15
3/16" Butt/Corner 3/32" 1/8" 100-125 20
3/16" Lap/Fillet 3/32" 1/8" 125-150 20
1/4" Butt/Corner 1/8" 5/32" 135-160 20
1/4" Lap/Fillet 1/8" 5/32" 160-180 20

One of TIG's strengths is its ability to weld aluminum cleanly. TheFabricator.com has a useful article (and probably a lot of others) with a nice, step-by-step approach. Aluminum is difficult because it does not change color when heated. Steel has a progressive color shift as it heats which allows a welder with even a minumum of experience to gauge its temperature. The only way to gauge a piece of sheet aluminum's temperature is its liquidity. Watching for a pool rather than color is a tricky thing to get used to at first and the tendency for aluminum to melt through at the first opportunity doesn't really help. A foot pedal (for remote control), which comes with many modern machines but was often absent on older models, is a convenience for any TIG welding but a near necessity for aluminum. For welding aluminum I know of two techniques: "Pedal to the Metal" and "Foot Stompin' Fun" (ok, I just made those names up, but they work pretty well). Both "Pedal" and "Stompin'," which I first saw a guy on TV do while welding a motorcycle frame, can be used on metals other than aluminum, although "Pedal" works best on AL. Both techniques start with laying out your pieces (perhaps tacking), bringing the tungsten quite near (but not touching!) the metal, and lowering your hood (duh). "Pedal" begins with the welder slamming the foot pedal all the way to the floor (which makes the choice of current more important). Get the aluminum hot. When it starts to pool, back-off to about 50-75% throttle and move the tip of the tungsten in small circles until the pool is big enough. Begin dipping the filler in the pool and progressing along the weld (prolly to your left) with constant throttle position (still 50-75%). After reaching the halfway-point in your weld (although this varies drastically with length of weld and thickness of material), begin backing off the throttle while continuing to dip the filler material. You may need to increase speed (and size of dip) as you near the end of the weld (while decreasing throttle). When you get to the end you should be as low on the throttle as possible while still keeping an arc. The aluminum will be very hot even with little current because of the high thermal conductivity of aluminum*.

MIG (GMAW)

MIG, Metal-Inert-Gas (or Gas Metal Arc Welding), welding is commonly used when speed is at a premium. Here's a good description from TWI. MIG welding uses a consumable electrode (a wire spool) to provide both the filler material and the electrical connection (and arc). This means that it is by far the easiest process. It is good with steel and generally bad with aluminum. The absolute best use for MIG is a series of tacks on thin material.

Approximate Transition Current Levels for Various Electrodes

Wire Electrode Type Wire Electrode Diameter Sheilding gas Minimum spray arc current (A)
Mild Steel 0.030"/0.76mm 98% argon-2% oxygen 150
Mild Steel 0.035"/0.89mm 98% argon-2% oxygen 165
Mild Steel 0.045"/1.14mm 98% argon-2% oxygen 220
Mild Steel 0.062"/1.59mm 98% argon-2% oxygen 275
Stainless Steel 0.035"/0.89mm 99% argon-1% oxygen 170
Stainless Steel 0.045"/1.14mm 99% argon-1% oxygen 225
Stainless Steel 0.062"/1.59mm 99% argon-1% oxygen 285
Aluminum 0.030"/0.76mm 100% argon 95
Aluminum 0.045"/1.14mm 100% argon 135
Aluminum 0.062"/1.59mm 100% argon 180
Deoxidized Copper 0.035"/0.89mm 100% argon 180
Deoxidized Copper 0.045"/1.14mm 100% argon 210
Deoxidized Copper 0.062"/1.59mm 100% argon 310
Silicon Bronze 0.035"/0.89mm 100% argon 165
Silicon Bronze 0.045"/1.14mm 100% argon 205
Silicon Bronze 0.062"/1.59mm 100% argon 270
Note: Spray transfer will only occur when high percentages of argon or helium are used. (from the AWS)

Suggested Shielding Gas Flow Rates for Use with Various Metals and Thicknesses

Metal Joint Type Thickness
in mm
Weld Position Argon Flow
Cfm Lpm
Aluminum and Aluminum Alloys All
1/16 1.6
3/32 2.4
1/8 3.1
3/16 4.8
1/4



6.4



3/8



9.5



3/4

19.0

F
F,H,V,O
F,H,V,O
F,H,V,O
F
H,V
O
F
H,V
O
F
H,V,O
25 11.8
30 14.2
30 14.2
30 14.2
40 18.9
45 21.2
60 28.3
50 23.6
55 26.0
80 37.8
60 28.3
80 37.8
Steel and Stainless Steel
Butt
Butt
60° Bevel
60° Double Bevel
Lap, 90° Fillet
1/16 1.6
1/8-3/16
3.2-4.8
1/4-1/2 6.4-12.7
1/2-5/8 12.7-15.9
1/8-5/16 3.2-7.9
30 14.2
35 16.5
35 16.5
35 16.5
35 16.5
Nickel and Nickel Alloys All
Up to 3/8 Up to 9.5
25 11.8
Magnesium Butt
0.025-0.190 0.6-4.8
0.250-1.000 6.4-25.4
40-60 18.9-28.3
50-80 23.6-37.8

*Here are some thermal conductivity numbers in W/m*°C:

3003 Aluminum 233.64
1199-H18 Aluminum 240 (!)
6061-T4 Aluminum 154
6063-O Aluminum 218
7079-T6 Aluminum 121.10
AISI 304 Steel 16.27
AISI C1020 Steel 46.73
B 120VCA Titanium 7.44
Iron 83.50

For further reading, the Army has a textbook online that is extremely helpful and informative. It goes into much more depth than I could ever attempt and has quite a few charts and figures. Highly recommended.

Here is a good primer into both welding symbols and the layout of different welds. They use the correct nomenclature but I do not.

If, by some odd perversion, you want to know more about the thermal conductivity of aluminum here is a huge chart of the characteristics of all (?) of the alloys.Update (1/29/04): I've found a better place to research metal characteristics.

If you wanted to learn about Oxy-Acetylene Welding try looking here.

If you missed it above, TheFabricator.com has an quite an index of articles. Also, some helpful facts sheets are available from the AWS.

 
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