Reading Assignment

31.1 Oxyfuel-Gas Welding
31.4 Arc Welding
31.5 Consumable-Electrode Arc Welding
31.6 Nonconsumable-Electrode Arc Welding
31.7 Welding Equipment

Outline

Oxyfuel Gas Welding

Equipment

Fuel Gas Cylinder
Oxygen Cylinder
Regulators and Gauges
Hoses and fittings
Flashback arrestors
Check Valves
Welding Torch

Fuels

MAPP Gas
Acetylene
Propane
Natural Gas
Propylene

Flame Temperature, Total Heat (BTU per cubic foot)

Flame Types

Carburizing
Neutral Flame
Oxidizing

Torches

Controls (oxygen, fuel valves)
Tip Sizes

Advantages

Control over:
- the rate of heat input
- the temperature of the weld zone
- the oxidizing or reducing potential of the welding atmosphere.
Filler metal is added independently of the welding heat source.
Ideally suited to the welding of:
- thin sheet
- tubes
- small diameter pipe.
- It is also used for repair welding.
But, thick section welds are not economical.

Safety

The following is a list of some safety items that should be followed when using an Oxy-Acetylene outfit.

Never use Acetylene gas at a pressure over 15 psig.
Never use damaged equipment.
Never use oil or grease on or around Oxygen equipment.
Never use Oxygen or fuel gas to blow dirt or dust off clothing or equipment.
Never light a torch with matches or a lighter. Always use a striker.
When opening a Oxygen or fuel cylinder valve, always crack it open first.
Always make sure regulators have their adjusting screws released by turning them counter clockwise till free before opening cylinder valves. Stand to the side of a regulator, not in front of it when opening cylinder valves.
Always wear the proper welding goggles, gloves and clothing when operating Oxy-Acetylene equipment. Pants should not have cuffs.
Always have a fire extinguisher handy when operating Oxy-Acetylene equipment.
Always replace cylinder caps when finished using cylinders.
Do not rely on the color of the cylinder to identify its contents as some suppliers may use different color codes.
Always use the proper regulator for the gas in the cylinder.
Always use cylinders in the upright position only.
Never store cylinders in temperatures over 130deg. F.
Always keep the valve wrench on the Acetylene cylinder valve when in use. Only open valve a maximum of 1 1/2 turns.
Do not carry lighters, matches or other flamable objects in pockets when welding or cutting.
Always be aware of others around you when using a torch.
Becareful not to let welding hoses come into contact with torch flame or sparks from cutting.

See Safe Welding and Cutting with Oxy-Fuel (video)

Arc Welding Processes

Uses an electric arc between an electrode and the base material to melt the metals at the welding point. A generic term that is casually used to refer to SMAW, but actually refers to a class of processes.

AC
DCEN – Straight Polarity
- Faster melting of electrode
- For thinner workpiece
DECP – Reverse Polarity
- provides deeper penetration

Shielded Metal Arc Welding – SMAW

Commonly called “stick welding” or “arc welding.”

In SMAW, the arc is created between a flux-covered metal electrode and the base metal. As the flux melts, it produces a shielding gas that protects the weld area.

Electrodes (consumable)

An electrode covering may serve any or all of the following purposes:

Add filler metal to the weld
Create a protective gas shield around the arc and molten metal.
Create a flux to clean impurities from the molten metal.
Create a hard slag covering to protect the molten bead as it cools.
Improve mechanical and chemical properties of the weld by adding alloying elements to the weld material

Electrode Identification

The American Welding Society (AWS) numbering system

The prefix “E” designates an arc welding electrode.
The first two digits of a 4-digit number and the first three digits of 5-digit number indicate tensile strength.

For example, E6010 is a 60,000 psi tensile strength electrode while E10018 designates a 100,000 psi tensile strength electrode.

E	60	1	“10”
Electrode	Tensile strength	Position	Type of Coating and Current

The next to last digit indicates position. The “1” designates an all position electrode, “2” is for flat and horizontal positions only; while “3” indicates an electrode that can be used for flat, horizontal, vertical down and overhead. The last 2 digits taken together indicate the type of coating and the correct polarity or current to use.

Gas Metal Arc Welding (GMAW)

Commonly called “MIG” or “wire welding.”

Electrode is consumable.

Shielding gas comes from a tank.

Argon
Helium
Carbon Dioxide
Gas affects penetration and weld shape

Metal Transfer

The method by which the filler metal is transferred from electrode to the weld puddle.

Short circuiting transfer
Globular transfer
Spray transfer
- Used for metal > .125 thick. Requires shielding gas that is at least 80% argon or helium.

Wire Feeder

A wire feede pulls the electrode wire smoothly from the spool and pushes it to the welding gun.

Backing

Sometimes used on large welds to produce consistent penetration

Flux Cored Arc Welding (FCAW)

Flux-cored arc welding is similar to GMAW. Flux-cored arc welding is a welding process in which metals are joined by heating them with an electric arc between the baes metal and a continuous consumable electrode. Shielding gas is obtained from the flux inside the tubular electrode. Additional shielding may be provided by a shielding gas.

Advantages

Can be used where shielding gas is impractical
Can be used with existing GMAW equipment

Disadvantages

Produces smoke and spatter
Requires post-weld cleaning of slag

Gas Tungsten Arc Welding (GTAW)

Also known as “TIG” or “Heliarc” welding.

GTAW is a process that joins metals together by heating them with an arc between a nonconsumable tungsten electrode and the work. The electrode andweld area are shielded with an inert gas or gas mixture. Filler metal may or may not be used.