Lecs 22-26 Flashcards
(33 cards)
LEC 22 AM & RP
What are four additive manufacturing techniques?
1) Liquid monomers (stereolithography)
2) Powders, sintered or melted
3) Molten materials (e.g. fused deposition, plastics
4) Laminating sheets
What’s the typical layer thickness for stereolithography?
0.005 to 0.150 mm. Super thin.
What are some advantages to RP and RTM?
Rapid prototypes. You can have your thing in front if you within hours, instead of months. And RTM allows you to make things fast.
LEC 23: Fusion Welding
What are three benefits to fusion welding?
1) It’s permanent
2) It’s economical
3) It can be done in the field
Two welded parts become one entity,
What are four drawbacks to fusion welding?
1) Manual labor - can be costly.
2) High temperatures - dangerous
3) Permanent
4) Hard to assess quality of weld
What are the faying surfaces?
The two parts of metals that you wish to join.
What are the two categories of welding?
1) Fusion welding. Base metals are melted for coalescence.
2) Solid state welding. Metals don’t become molten, and no filler metal is added.
What is arc welding, and what are the two types?
A fusion welding process that uses arcs between an electrode and the material to melt the faying surface. Arcs can get as hot as 5500C sometimes.
The two types are consumable and non-consumable.
Consumable has filler metal by nature, but filler metal’s not required for non-consumable.
Tell me more about electrodes in arc welding.
Non-consumable electrodes are made of tungsten, which resist melting. But they still vaporize, so they need to be changed every once in a while.
Consumable electrodes come both in the form of sticks and of spools of wire.
Why is arc shielding important, and what are two ways to accomplish that?
At high temperatures, metals tend to react with the oxygen, nitrogen, and hydrogen in the air, which can degrade the joint.
Two ways to accomplish this are with shielding gas (argon, krypton), or with flux material on the surface.
What is flux, and how can it be applied?
A substance that either prevents the forming of oxides and other impurities, or dissolves and evacuates them.
It can be applied in a granular fashion, or it can be present as a coating or core in a consumable electrode.
What’s the difference between D/C and A/C welding?
A/C is cheaper, but D/C provides better arc control.
What are the five consumable electrode fusion welding processes?
1) SMAW Shielded Metal Arc Welding
2) GMAW Gas Metal Arc Welding
3) FCAW Flux-Cored arc welding
4) EGW Electrogas welding
5) SAW Submerged arc welding
What is SMAW?
SMAW consists of a consumable electrode covered in flux. When exposed to high temperatures, the flux gives off gases that shield the weld from oxidation.
SMAW is cheap and versatile and popular.
What is GMAW, and how is it better than SMAW?
GMAW uses gas to shield the weld zone, and uses an electrode wire.
It can be fed using a continuous spool.
What is FCAW, and how is it better than SMAW? Is it shielded?
FCAW has flux at its core. It also uses a spool of continuous consumable electrode.
It can be shielded or not, depends on you.
What is electrogas welding?
There’s more to it, but the basic difference you can see is that it fills crevices.
What is SAW?
Submerged Arc Welding is when a bare electrode wire is used, and granular flux is introduced ahead of the weld pool.
Name the four non-consumable arc welding processes.
1) GTAW Gas-tungsten arc welding
2) PAW Plasmac arc welding
3) CAW Carbon arc welding
4) SW Stud welding.
What is GTAW, and what are its pros and cons?
Gas-Tungsten arc welding uses a tungsten electrode and a shielding gas.
It provides high quality welds with no need for clean-up, but it’s slower and more expensive.
What is PAW, and what are its pros and cons?
Plasma arc welding. It’s a specialized form of GTAW, where the inert gas is directed into the arc region to create an intensely hot plasma, reaching up to 28000C.
Super clean, can join almost any metal, can move fast, but it’s expensive.
What is OFW?
Oxyfuel gas welding. A combination of oxygen and a flammable gas to create a flame.
Acetylene is the most popular, because it’s a two stage reaction that produces an inner cone and an outer cone.
What is EBW, and its pros and cons?
Electron beam welding. It can create deep narrow welds with a limited heat affected zone, but it’s expensive, requires precies lining up, and requires vacuum chambers, which take a while to heat up.
What is LBW, and what are its pros and cons?
Laser Beam welding. High energy density too, but it’s shallower and requires shielding gas.
