Welding Processes - LBW/ESW/PAW 808

Filler metals used for Brazing would melt above what Temp

840 deg F or 459 deg C

Definition of Air Carbon Arc Cutting (CAC-A)

A very effective cutting process in air carbon cutting. This equipment for CAC-A consists of a special electrode holder which is attached to a constant current power source and a compressed air supply. This special holder grasps the carbon electron in copper jaws, one of which has a series of holes through which the compressed air passes. To achieve a cut, the carbon electrode is brought close to the work to create an arc. Once the arc melts the metal, the stream of compressed air is initiated and blows away the molten metal to produce a gouge or cut. While its primary applications for the cutting of non-ferrous metals, PAC is also useful for the cutting of carbon steels. Advantages include the ability to cut metals which can not be cut with OFC, the resulting high quality cut, and increased cutting speeds for carbon steel. One limitation is that the kerf is generally quite large and the cut edges may not be square.

Definition of Oxyfuel Gas Cutting (OFC)

An oxyfuel flame to heat the metal to a temperature at which it will readily oxidize, or burn. The temperature needed is referred to as the kindling temperature, and for steels, it is about 1700 deg F (925 deg C). A pressure stream of cutting oxygen is directed on the heated surface to produce an oxidation reaction. This stream of oxygen also tends to remove the slag and oxide residue which is produced by this oxidation reaction. Therefore, OFC can be thought of as a type of chemical cutting process.

Primary Shielding gas used with PAW

Argon

PAW is similar to what other welding process

GTAW

Description of EBW

Is a fusion process that produces coalescence of materials with heat obtained by impinging a beam of high energy electrons onto the joint to be welded. The heat of the electron beam welding process is the electron beam gun/column assembly. Used a focused beam of electron as a heat source for fusion welding.

Definition of Resistance Welding (RW)

Is a group of welding processes that produces coalescence of the joining surface with heat obtained from resistance of the work pieces to the flow of welding current in a circuit of which the work piece are a part, and by the applications of pressure. It is typically used for sheet metal applications, up to about 3mm thick.

Description of ESW

Is characterized by the joining of members which are placed edge to edge so that the joint is vertical. The welding is done in a single pass such that the progression is from the bottom to the top of the joint, without interruption. Even though the welding progresses vertically up the joint, the position of the welding is considered flat due to the location of the electrode with respect to the weld puddle. During welding, the molten metal is supported on two side by water cooled shoes.

Definition of Brazing

Joining of two materials without the melting of the base metals.

Limitations of EBW

Joints must be accurately positioned under the beam. Square butt joints are required. Work piece must often be forced together. The fast cooling rates can produce cracking and embrittlement in the heat affected zone and can trap porosity in the weld metal. Equipment is expensive, typically in the 1 million dollar range.

Description of LBW

Laser Beam Welding (LBW) is a fusion process that produces coalescence of materials with the heat obtained from a concentrated beam of coherent, monochromatic light impinging on the joint to be welded. The high energy of the laser beam causes some of the metal at the joint to vaporize, producing a keyhole which is surrounded by molten metal. As the beam is then advanced along the joint (or the part is moved under the beam), molten metal flows form the forward position of the keyhole around it periphery and solidifies at the rear to form weld metal. The equipment is fairly complex. LBW is a non-contact process, and thus requires no pressure be applied. Inert shielding gas is often employed to prevent oxidation fo the molten pool, and filler metal is occasionally used.

Advantages of EBW

Low overall heat input results in less grain growth in the heat affected zone and less work piece distortion. High depth to width ration (on the order of greater than 10:1) are attainable when the weld is made in the keyhole welding mode. Single pass electron beam welds have been made in steels up to 4" (102 mm) thick. A high purity environment (vacuum) for welding minimizes contamination of the metal by oxygen and nitrogen. Rapid travel speeds are possible because of the high melting rates associated with the concentrated heat source. Hermetic closures can be welded with the high or medium vacuum modes of operation while retaining a vacuum in side the compartment. The beam of electron can be magnetically deflected to produce various shaped welds; and magnetically oscillated to improve weld quality or increase penetration. The focused beam of electrons has a relatively long dept of focus, which will accomodate a broad range or work distances. Full penetration, single pass weld is with nearly parallel side, and exhibiting nearly symmetrical shrinkage, can be produced. Dissimilar metal and metals with high thermal conductivity such as copper can be welded.

Advantages of LBW

Low overall heat input results in less grain growth in the heat affected zone and less workpiece distortion. High depth to width ratios (on the order of 10:1) are attainable when the weld is made in the keyhole welding mode. Single pass laser welds have been made in materials up to 1 1/4" (32 mm) thick. The laser beam can be focused on a small area, permitting the joining of thin, small, or closely spaced components. A wide variety of materials can be welded, including combinations of materials with dissimilar physical properties. The laser beam can be readily focused, aligned and directed by optical elements, thus the laser can be located away from the work piece and the laser beam directed around tooling and obstacles to the work piece.

Advantages of PAW

PAW becomes the choice where applications warrant the use of more localized heat source. It is used extensively for full penetration welds up to 1/2" thick.

What is PAW

Plasma Arc Welding is a defined as an ionized gas.

List 3 major Resistance Welding Processes

Resistance Spot Welding (RSW) Resistance Seam Welding (RSEW) Projection Welding (PW)

ESW is similar to what other weld process

SAW since they both use a granular flux which becomes molten.

Examples of Mechanical Cutting

Shearing Sawing Grinding Milling Turning Shaping Drilled Planing Chipping

2 Factors why Brazing can develop a strength equal or greater than the base metal even though the braze material may be much weaker than the base metal

The brazed joint is designed to have a large surface area. The clearance of gap between the two pieces to be joined is kept to a minimum.

How is PAW and GTAW similar

The equipment required is similar Same Power source Same non-consumable electrode (tungsten)

Limitations of ESW

The extensive time required to set up and get ready to weld. There is tremendous amount of time and effort required to position the workpieces and guides before any welding takes place.

Definition of Stud Welding (SW)

The stud welding method is used to weld studs, or attachments, to some metal surface.

Difference between Brazing and Soldering

They are differentiated by the temperature at which the filler metal melts.

Definition of Plasma Arc Cutting (PAC)

This process is similar to most respects to PAW except that now the purpose is to remove metal rather than joining pieces together. Higher power requirements than PAW. Used to cut metals that can not be cut with OFC.

List Brazing Processes

Torch Brazing - TB Furnace Brazing - FB Induction Brazing - IB Resistance Brazing - RB Dip Brazing - DB Infrared Brazing - IRB

History of EBW

Was initially used as a commercial welding process in the late 1950's, the process has earned a broad acceptance by industry. The process was initially strictly to operation in a high vacuum chamber, however a system was soon developed that required a high vacuum only in the beam generation portion. This permitted the option of welding in either a medium vacuum chamber or a non vacuum environment. This advancement led to its acceptance by the commercial automotive and consumer product manufacturers.

The main difference between PAW and GTAW

the PAW torch has a copper orifice within the ceramic nozzle.