Chapter 7: Welding Flashcards
Why is joining/assembling (welding) necessary
- Impossible or uneconomical to manufacture a product as a single piece
- Easier to manufacture as components, then assemble
- Product may have to be taken apart for maintenance
- Transportation of part as individual components may be easier/economical
What is Joining vs What is Assembling
Joining includes processes that form a permanent joint between parts (welding, brazing, soldering, and adhesive bonding)
Assembly involves mechanical methods of fastening parts together
What is welding
A joining process in which two or more parts are coalesced at their contacting surfaces by application of heat and/or pressure
Why is welding important
- Provides a permanent joint
- Usually the most economic way to join parts
- not restricted to a factory environment
Limitations and drawbacks of welding
- most performed manually resulting in being expensive in terms of labor cost
- most welding utilizes high energy which is dangerous
- Welded joints do not allow for convenient disassembly
- Welded joints can have quality defects that are difficult to detect
What are the safety issues associated with welding
- high temperatures of molten metals
- in gas welding, fuels are a fire hazard
- Many welding processes use electrical power, so electrical shock hazard
What are the 5 types of weld joints and describe them
- Butt Joint - two parts joined parallel creating a groove between the two parts
- Corner joint - two parts are joined perpendicular at their edges to create a corner
- Lap joint - two parts are parallel with on top of the other creating a stair effect
- Tee joint - two parts are joined perpendicular with one part in the center of the other creating a T shaped part
- Edge joint - two parts (usually curved) are joined parallel with a lot of overlap
What are the types of welds
- Fillet Weld
- Groove Weld
- Plug and Slot Welds
- Spot and Seam Welds
What are fillet welds used for
Used to fill in the edges of plates by creating corner, lap, and tee joints
Filler metal in fillet welds takes what shape
right triangle
Most common weld type in arc and oxyfuel welding
Fillet Welds
Type of weld that requires minimum edge preperation
Fillet Weld
Type of weld that requires part edges to be shaped into a groove
Groove welds
What are the shapes grooves can take
Square, bevel, V, U, and J, in single or double sides
What type of joints are groove welds most associated with
Butt joints
What does spot welding and seam welding accomplish
A fused section between surfaces of two sheets or plates
What is spot and seam welds used for
Lap joints
What are spot and seam welds most associated
resistance welding
This type of welding melts the base metal
Fusion Welding
This type of welding does not melt the base metal
Solid State Welding
What are the three types of solid state welding
Diffusion welding
Friction Welding
Ultrasonic Welding
What are the 3 types of fusion welding
Arc Welding
Resistance Welding
Oxyfuel Welding
What are the two classifications of arc welding
consumable electrode welding
non-consumable electrode welding
What are the two types of consumable electrode arc welding
SMAW - Shielded Metal Arc Welding
GMAW - Gas Metal Arc Welding
What are the two types of nonconsumable electrode arc welding
GTAW - Gas Tungsten Arc Welding
PAW - Plasma Arc Welding
What are the types of Resistance Welding
RSW - Resistance Spot Welding
RSEW - Resistance Seam Welding
What is the type of oxyfuel welding
Oxyacetylene welding
Benefits of a filler metal
added strength and bulk
What is a fusion weld with no filler metal called
Autogenous weld
What is arc welding (AW)
melting of metals is accomplished by an electric arc
What is resistance welding (RW)
Melting is accomplished by heat from resistance to an electrical current between fraying surfaces held together under pressure
What is oxyfuel gas welding (OFW)
Melting is accomplished by an oxyfuel gas such as acetylene
Problems with manual welding
Weld joint quality
Productivity or arc time
Non-consumable electrodes are made of what
Tungsten
What is arc shielding and why is it needed
In AW processes, the mechanical properties of the joint can be degraded by chemical reactions with the air due to high temperatures. So, arc shielding is using shielding gases or flux to protect the operation
What is flux
A substance that prevents the formation of oxides and other contaminants in welding or dissolves them and facilitates removal
What are the power sources available in Arc welding
Alternating Current (AC) or Direct Current (DC)
Benefits and limitations of AC in arc welding
less expensive but restricted to ferrous metals
Benefits and disadvantages of DC in AW
can be used on all metals and better arc control but more expensive
What is Shielded Metal Arc Welding SMAW
- Called stick welding
- uses a consumable electrode consisting of a filler metal rod coated with flux for shielding
What is Gas Metal Arc Welding GMAW
Uses a consumable bare metal wire as an electrode with shielding by flooding the arc with gas
GMAW advantages over SMAW
- Better arc time - no sticks
- Better use of elctrode filler metal
- Eliminates slag removal
- Can be automated
What is Gas Tungsten Arc Welding GTAW
Uses a non-consumable tungsten electrode and an inert gas for shielding
- filler metal is added seperately
Advantages and Disadvantages
Advantages:
- High-quality welds
- No spatter because no filler metal through the arc
- little to no post-weld cleaning because no flux
disadvantages:
- generally slower and more constly
What is Plasma Arc Welding PAW
A special form of GTAW in which a constricted plasma arc is directed at weld area
Adv and diadv of PAW
Adv: good arc stability and weld quality and almost any metal
disadv: high cost and large torch size
What is the principle RW process
RSW - Resistance spot welding
Components in RSW
- Parts (usually sheet metal)
- two opposing electrodes
- means of applying pressure
- power supply
pros and cons of RW
Pros:
- no filler metal
- high production rates
- low operator skill
- good reliability
Cons:
- high equipment cost
- limited to lap joints
Primary Characteristic of RSEW
Uses wheel electrodes to create lap joints
What is oxyfuel gas welding OFW
Group of fusion welding operations that burn various fuels mixed with oxygen
What is Oxyacetylene Welding OAW
Fusion welding performed by a high temperature flame from combustion of acetylene and oxygen
What is diffusion welding DFW
coalescence is achieved by holding two surfaces together under pressure at elevated temperature (not melting)
What is friction welding FRW
coalescence is achieved by heat of friction (not melting)
What is ultrasonic welding (USW)
coalescence achieved by ultrasonic oscillating motion under pressure
What is weld quality
concerned with acceptable weld joints that are strong and absent of defects
What are Residual Stresses a result of
Rapid heating and cooling in localized regions during FW result in thermal expansion and contraction that cause residual stresses
What do residual stresses result in
distortion and warpage
Techniques to minimize warpage
Welding fixtures - physical restraint of parts
Heat sinks - to rapidly remove heat
Tack welding at multiple points along joint to create a rigid structure prior to seam welding
Techniques to minimize warpage
- selection of welding conditions
- preheating base parts
- stress relief heat treatment
Welding defects
cracks
cavities
solid inclusions
incomplete fusion
Weld profile in AW
What are cracks, what problem do they create, and why are they caused. How are they fixed
Cracks are fracture-type interruptions in weld or base metal. Results in a discontinuity that reduces strength. Caused by embrittlement or low ductility of weld or base metal. Must be repaired
What are the two defect types of cavities and what are each caused by
- Porosity - small voids in weld formed by gases entrapped during solidification
- Shrinkage Voids - formed by shrinkage during solidification
What is incomplete fusion
A weld defect in which fusion has not occurred throughout the entire cross-section of joint
What are the 3 weld profile defects in AW
Undercut- portion of base metal melted away
Underfill- depression in weld below the adjacent base metal surface
Overlap- weld metal spills beyond joint onto part surface but no fusion occurs
What are the forms of inspection and testing
visual inspection
Nondestructive Evaluation NDE
Destructive Testing
Mechanical Tests
What is visual inspection? What are limitations
Most widely used. Human inspector visually examines for conformance and surface defects. Only surface defects are detectable
types of nondestructive evaluation
Ultrasonic - high frequency soundwaves to detect cracks and inclusions
Radiographic - x-ray or gamma ray provides photos of internal flaws
Dye-penetrant and fluorescent-penetrant - to detect small cracks and cavities at part surface
Magnetic particle - iron fillings sprinkled on surface reveal defects by distorting magnetic field
Types of destructive testing
mechanical tests- conventional testing methods such as tensile and shear tests
Metallurgical tests - preparation of metallurgical specimens of weldment to examine metallic structure, defects, extent and condition of heat affected zone
