three basic categories of welding
- Fusion welding
- Solid-state welding
- Brazing and Soldering
- What is fusion welding?
- What are the different types of fusion welding?
- Using heat(chemical or electrical) to join materials with or without the use of filler metals
- Consumable/non-consumable electrode arc welding and high-energy-beam welding
What is Oxyfuel-gas welding
- What is a common gas used?
- roughly what temperatures can be reached?
General term describing a welding proceses using a fuel gas combined with oxygen to produce a flame
- Acetylene
- 3300degrees celsius
What is arc welding?
- roughly what temperatures?
Welding with the use of electrically sourced heat- can be both non or consumable
- 30000 celsius: as such, a shielding gas is needed to prevent oxidation at weld zone
What is DCEN and DCEP
- what is the advantagesof each?
- Direct current electrode positive: workpiece is negative and electrode is positive. DCEN is the opposite
- When workpiece is negative, the penetration is less, but the diameter is wider
What is the equation for het transfer in arc welding
H/l=(eVI)/v
H=Heat input l=weld length I=current v=welding speed V=voltage applied e=efficiency
Equation for total melted volume from a heat input
H=u(Vm)=uAl
u=specific energy for melting
Vm=volume of material melted
A=cross-section of weld
Common types of consumable electrode welding
- Shield metal arc welding
- Gas metal-arc welding
What is shield metal arc welding
also called stick welding(electrodes come in stick shapes)- touch electrode to surface before moving to distance close enough to maintain electron flow. Very common, very old style
- Electrode coating deoxidizes weld area and provides shielding gas to protect from oxygen in environment
What is Gas metal-arc welding(GMAW)
Weld area shielded by inert atmosphere of argon, helium and Co2. Consumable bare wire fed through nozzle of weld arc by a wire feed motor
- low temperatures produced
- suitable for ferrous metals and thin welds
What is the electrode usually made of in nonconsumable elctrode arc welding
- pros of non-consumable arc welding
tungsten
- constant distance easy to maintain
- no flux used
- uses noble gases for shielding, but very expensive as a result
- Very high quality finish- because of stable arc gap
Pros of electron beam welding
- Usable on almost every metal
- distortion and shrinkage is minimal
- small heat-affected zones
- high depth to width ratios
- can be very accurately controlled with automation and can be high speed
Design aspects of welding
- unless automated, welding can be costly, and should be minimized
- Places of excessive stress magnitude or concentration should be avoided for welding
- locatioin shouldn’t interfere with firther processes
- Weld bead size should be as small as possible
What is solid state welding?
- basic categories in this type of welding?
joining takes place without fusion- as such, no liquid phase in the joint at any point
- Diffusion bonding
- Cold
- Ultrasonic
- Friction
- Resistance
- Explosion welding
What are the basic parameters of solid state welding?
Heat, Pressure, Relative interfacial movement
What is friction welding
- heat made via friction. One workpiece is stationary while the other is rotated at high speed while force applied. Then brought to quick stop to prevent shearing while axial force increases
What is friction stir welding
- Advantages?
third body is rubbed against the two joining surfaces. Spinning causes heating and mixing
- Less heat
- very high quality
- minimal pores
- no shielding gas or surface cleaning required
What is resistance welding
Running a current through the metals, heat welds together. comes in two forms, spot welding and seam welding
What is diffusion bonding
- what parameters affect it?
- movement of atoms across the interface joins them
- Pressure, temperature, time of contact, how clean surfaces are
- often used to join disimiliar metals, or reactive metals
- slower than other processes
What is brazing and soldering?
Brazing:
Filler metals, but lower temperatures than welding
Soldering:
Same, but with even lower temperatures
- In both cases, filer metal between pieces and melted to temps that is lower than melting temp of workpiece
- Generally, can make strong bonds between disimiliar metals
