Presentation on theme: "Arc Welding Processes. Lesson Objectives When you finish this lesson you will understand: The similarities and difference between some of the various."— Presentation transcript:
Lesson Objectives When you finish this lesson you will understand: The similarities and difference between some of the various arc welding processes Flux and gas shielding methods Advantages and disadvantages of the arc welding processes Need to select between the processes Learning Activities 1.Read Handbook Pp 1-16, 2.Look up Keywords 3.View Slides; 4.Read Notes, 5.Listen to 6. lecture 7.Do on-line workbook 8.Do homework Keywords Welding Flux, Inert Shielding Gas, Shielded Metal Arc Welding (SMAW), Gas Metal Arc Welding (GMAW), Metal Transfer Mode, Flux Cored Arc Welding FCAW), Submerged Arc Welding (SAW),
Arc Welding Processes l Welding processes that employ an electric arc are the most prevalent in industry Shielded Metal Arc Welding Gas Metal Arc Welding Flux Cored Arc Welding Submerged Arc Welding Gas Tungsten Arc Welding l These processes are associated with molten metal Electric Arc
Protection of the Molten Weld Pool l Molten metal reacts with the atmosphere Oxides and nitrides are formed Discontinuities such as porosity Poor weld metal properties l All arc welding processes employ some means of shielding the molten weld pool from the air
Welding Flux l Three forms Granular Electrode wire coating Electrode core l Fluxes melt to form a protective slag over the weld pool l Other purposes Contain scavenger elements to purify weld metal Contain metal powder added to increase deposition rate Add alloy elements to weld metal Decompose to form a shielding gas
Shielding Gas l Shielding gas forms a protective atmosphere over the molten weld pool to prevent contamination l Inert shielding gases, argon or helium, keep out oxygen, nitrogen, and other gases l Active gases, such as oxygen and carbon dioxide, are sometimes added to improve variables such as arc stability and spatter reduction Argon HeliumOxygen Carbon Dioxide
Turn to the person sitting next to you and discuss (1 min.): What would happen if there was no flux on the wire to decompose into gas or no inert shielding gas was provided? What would the weld metal look like?
SMAW Advantages l Easily implemented l Inexpensive l Flexible l Not as sensitive to part fit-up variances Shielded Metal Arc Welding
Advantages l Equipment relatively easy to use, inexpensive, portable l Filler metal and means for protecting the weld puddle are provided by the covered electrode l Less sensitive to drafts, dirty parts, poor fit-up l Can be used on carbon steels, low alloy steels, stainless steels, cast irons, copper, nickel, aluminum
Quality Issues l Discontinuities associated with manual welding process that utilize flux for pool shielding Slag inclusions Lack of fusion l Other possible effects on quality are porosity, and hydrogen cracking Shielded Metal Arc Welding
Limitations l Low Deposition Rates l Low Productivity l Operator Dependent Shileded Metal Arc Welding
Other Limitations l Heat of welding too high for lead, tin, zinc, and their alloys l Inadequate weld pool shielding for reactive metals such as titanium, zirconium, tantalum, columbium
Turn to the person sitting next to you and discuss (1 min.): Wood (cellulose) and limestone are added to the coating on SMAW Electrodes for gas shielding. What gases might be formed? How do these gases shield?
GMAW Modes of Metal Transfer Spray Globular Short Circuiting Pulsed Spray Gas Metal Arc Welding
GMAW Filler Metal Designations ER - 70S - 6 Electrode Rod (can be used with GMAW) Minimum ultimate tensile strength of the weld metal Solid Electrode Composition 6 = high silicon Gas Metal Arc Welding
Shielding Gas l Shielding gas can affect Weld bead shape Arc heat, stability, and starting Surface tension Drop size Puddle flow Spatter Ar Ar-He HeCO 2 Gas Metal Arc Welding
GMAW Advantages l Deposition rates higher than SMAW l Productivity higher than SMAW with no slag removal and continuous welding l Easily automated Gas Metal Arc Welding
Quality l Spatter Droplets of electrode material that land outside the weld fusion area and may or may not fuse to the base material l Porosity Small volumes of entrapped gas in solidifying weld metal Gas Metal Arc Welding
Limitations l Equipment is more expensive and complex than SMAW l Process variants/metal transfer mechanisms make the process more complex and the process window more difficult to control l Restricted access GMAW gun is larger than SMAW holder Gas Metal Arc Welding
Turn to the person sitting next to you and discuss (1 min.): When comparing processes that have spray and globular metal transfer, which type of transfer mode do you thnk results in more spatter? Why?
FCAW Electrode Classification E70 T - 1 Electrode Minimum UTS 70,000 psi Position Flux Cored /Tubular Electrode Type Gas, Usability and Performance Flux-Cored Arc Welding American Welding Society Specification AWS A5.20 and AWS A5.29.
Advantages l High deposition rates l Deeper penetration than SMAW l High-quality l Less pre-cleaning than GMAW l Slag covering helps with larger out-of-position welds l Self-shielded FCAW is draft tolerant. Flux-Cored Arc Welding
Limitations l Slag must be removed l More smoke and fumes than GMAW and SAW l Spatter l FCAW wire is more expensive l Equipment is more expensive and complex than for SMAW Flux-Cored Arc Welding
Turn to the person sitting next to you and discuss (1 min.): What do you suppose would happen if the powder inside the core did not get compacted good?
SAW Flux / Filler Metal Compositions F7A2-EM12K l F indicates flux 70-95 ksi UTS, 58 ksi minimum yield strength, 22% elongation A - as welded; P - postweld heat treated 2 - minimum impact properties of 20 ft-lbs @ 20°F l E indicates electrode (EC - composite electrode) M - medium manganese per AWS Specifications 12 - 0.12% nominal carbon content in electrode K - produced from a heat of aluminum killed steel Submerged Arc Welding
Advantages l High deposition rates l No arc flash or glare l Minimal smoke and fumes l Flux and wire added separately - extra dimension of control l Easily automated l Joints can be prepared with narrow grooves l Can be used to weld carbon steels, low alloy steels, stainless steels, chromium- molybdenum steels, nickel base alloys Submerged Arc Welding
Limitations l Flux obstructs view of joint during welding Flux is subject to contamination porosity l Normally not suitable for thin material l Restricted to the flat position for grooves - flat and horizontal for fillets l Slag removal required l Flux handling equipment Submerged Arc Welding
Do Homework Assignment 2, “Arc Welding Processes” from the Assignment Page of the WE300 Website. Turn in next Class Period.