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WELDING TECHNOLOGY

definition and classification

For details go to my website: http://www.subhankar4students.blogspot.com
Definition and Classification

Welding is a process of permanent joining of two metal pieces usually. It is done by inserting a third metal known as filler material between the two workpieces. Tremendous amount of heat is then supplied to melt the two metal pieces to be joined as well as the filler material localisedly to produce a molten mixture of work metal and filler material. When the mixture is allowed to be cool enough to be solidified, it produces a strong joint in between the two work pieces thus joining the metals rigidly having sufficient strength to bear different types of load.

What are the responses of materials to Welding processes?

Defects in the Weld
Micro-structural changes
Stresses and Distortions
Heat-Treatment of parent metals and welds

POROSITY:

Restart Porosity
Surface Porosity
Crater Pipes

INCLUSIONS

LACK OF FUSION AND PENETRATION

CRACKS

Hydrogen Embrittlement
Lameller Tearing
Reheat Cracking
Solidification Cracking

POROSITY:

Uniform porosity from exsolution of dissolved gases
Restart Porosity: from unstable arc at weldstart (incomplete protection and poor welding techniques)
Surface Porosity: from excessive contamination (grease, dampness, atmosphere)or sometimes high sulpher in consumables
Crater Pipes: from shrinkage crater at the end of weld run

REDUCTION OF POROSITY

Proper selection of electrodes and filler materials
Improved welding techniques

Preheating
Increasing heat input

http://www.webcitation.org/5lpDLc6Iw


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