ME 330
Manufacturing Processes
WELDING PROCESSES
(cont.)
Principle of the process
Structure and configuration
Process modeling
Defects
Design For Manufacturing (DFM)
Process variation
Weld Joints: Five Types
(a) Butt joint, (b) corner joint, (c) lap joint, (d) tee joint, and (e) edge joint
Weld Types: Fillet Welds
(a) Inside single fillet corner joint;
(b) outside single fillet corner joint;
(c) double fillet lap joint;
(d) double fillet tee joint
Filler metal is used
Weld Types: Groove Welds
(a)
(b)
(c)
(d)
(e)
(f)
square groove weld;
single bevel groove weld;
single V-groove weld;
single U-groove weld;
single J-groove weld;
double V-groove weld (for thicker sections)
Filler metal is used
©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Weld Types: Plug Weld and Slot Weld
(a) Plug weld and (b) slot weld
Filler metal is used
Weld Types: Spot Weld and Seam Weld
Fused section between surfaces of two sheets or plates:
(a) spot weld and (b) seam weld
 Used for lap joints
 Used commonly with resistance welding
 No filler metal
Weld Types: Flange Weld and Surfacing Weld
(a) Flange weld;
(b) Surfacing weld used not to join parts but to deposit filler metal
onto surface of a base part
Principle of the process
Structure and configuration
Process modeling
Defects / quality control
Design For Manufacturing (DFM)
Process variation
Typical Fusion Welded Joint
Cross section of a typical fusion welded joint:
(a) principal zones in the joint, and (b) typical grain structure
Weld Quality
Motivation:
Obtaining a weld joint that is strong and absent of defects
Topics:
1. Residual stresses and distortion
2. Welding defects
3. Inspection and testing methods
Residual Stresses and Distortion
Shrinkage
Butt welding
Residual stress
warping of weldment
Principle: Rapid heating and cooling in localized regions during fusion welding result
in thermal expansion and contraction that cause residual stresses, and stresses
cause distortion and warpage
Techniques to Minimize Warpage
 Welding fixtures to physically restrain parts
 Heat sinks to rapidly remove heat
 Tack welding at multiple points along joint to create a rigid structure
prior to seam welding
 Selection of welding conditions (speed, amount of filler metal used,
etc.) to reduce warpage
 Preheating base parts
 Stress relief heat treatment of welded assembly
 Proper design of weldment
Weld Defects: Welding Cracks
 Welding cracks: On weld or near weld
 Very serious because strength is reduced significantly
 Caused by low
of weld and/or base metal combined with high
stresses during contraction
Welding Defects: Cavities
Two defect types:
1. Porosity - small voids in weld metal formed by gases
entrapped during solidification, caused by inclusion of
atmospheric gases, sulfur in weld metal, or surface
contaminants
2. Shrinkage voids - cavities formed by shrinkage during
solidification
Welding Defects: Solid Inclusions
Nonmetallic material entrapped in weld metal:
1. Most common form is
generated during
arc welding processes that use flux. Instead of floating to
top of weld pool, globules of slag become encased
during solidification
2. Other forms: formation of metallic oxides, such as Al2O3
when welding aluminum
Welding Defects: Incomplete Fusion
A weld bead in which fusion has not occurred throughout
entire cross section of joint. Forms of incomplete fusion are
shown below:
Weld Profile in Arc Welds
(a) Desired profile for single V-groove weld joint,
(b) undercut - portion of base metal melted away,
(c) underfill - depression in weld below adjacent base metal
surface, and
(d) overlap - weld metal spills beyond joint onto part
surface, but no fusion occurs
Inspection and Testing Methods: Visual Inspection
 Most widely used welding inspection method is manual
examination for:
1. Conformance to dimensions, warpage
2. Surface defects, such as cracks, cavities,
incomplete fusion
 Limitations: Only surface defects are detectable
Inspection and Testing Methods:
Nondestructive Evaluation (NDE) Tests
1. Ultrasonic testing - high frequency sound waves through specimen to
detect cracks and inclusions
2. Radiographic testing - x-rays or gamma radiation provide
photographs of internal flaws
3. Dye-penetrant and fluorescent-penetrant tests - to detect small
cracks and cavities at part surface
4. Magnetic particle testing – iron filings sprinkled on surface reveal
subsurface defects that distort the magnetic field
Inspection and Testing Methods:
Destructive Testing -- Mechanical Tests
(a) Tension-shear test,
(b) fillet break test,
(c) tension-shear of spot weld, and
(d) peel test for spot weld
Inspection and Testing Methods:
Destructive Testing -- Metallurgical Tests
 Metallurgical tests – to examine metallic structure, defects,
extent and condition of heat affected zone, presence of
other elements, etc. of the weldment
 Microscopy is an example of this
Weldability
 Capacity of a metal or combination of metals to be welded
into a suitable structure, and
 For the resulting weld joint(s) to possess the required
metallurgical properties to perform satisfactorily in
intended service
 Good weldability characterized by
1. Ease with which welding is accomplished
2. Absence of weld defects
3. Strength, ductility, and toughness in welded joint
Weldability Factors: Welding Process
Some metals or metal combinations can be readily welded by
one process but are difficult to weld by others
Example: stainless steel readily welded by most arc welding
and resistance welding processes, but difficult to weld by
oxyfuel welding
Weldability Factors: Base Metal
1. Some metals melt too easily; e.g., aluminum
2. Metals with high thermal conductivity transfer heat away
from weld, which causes problems; e.g., copper
3. High thermal expansion and contraction in metal causes
distortion problems
4. Dissimilar metals pose problems in welding when their
physical and/or mechanical properties are substantially
different
Other Factors Affecting Weldability
 Filler metal. Must be compatible with base metal(s)
 Surface conditions (how clean)
1. Moisture can result in porosity in fusion zone
2. Oxides and other films on metal surfaces can prevent
adequate contact and fusion
Principle of the process
Structure and configuration
Process modeling
Defects
Design For Manufacturing (DFM)
Process variation
Design Considerations in Welding
 Minimum parts - welded assemblies should consist of
fewest number of parts possible
Example: usually more cost efficient to perform simple
bending operations on a part than to weld an assembly
from flat plates and sheets
 Design assembly to allow for welding gun access
 Assembly should allow for welding from above