What is TIG Welding?

http://www.wisegeek.com/what-is-tig-welding.htm
Change the paragraph to the Present or Past Perfect.

Tungsten inert gas (TIG) welding __________ ______________ (is) the process

of blending together reactive metals such as magnesium and aluminum.

The TIG welding method __________ ______________(became) popular and useful in

the early 1940s and, as a result, has greatly propelled the use of aluminum for welding and structural processes.

TIG welding _________ _____________ (is)commonly used for both high quality
and manual welding.

During the process of TIG welding, an arc __________ _______________ (is)

formed between a pointed tungsten electrode and the area to be welded. As a

result of the gas shield, a clean weld __________ _______________ (is) formed.
This prevents oxidization from occurring.

The type of gas shielding typically used for TIG welding __________

_______________ (is) argon, helium, or a combination of both. When combined,

these two gases can ensure a higher welding speed and welding penetration.

Argon __________ _______________ (is) the preference of most welders when

it comes to TIG welding. It __________ _______________ (is) often used simply

because it is heavier than air and provides better coverage when welding.

With TIG welding, one can perform a variety of weld types on several different

metals. Steel and aluminum, however, are the two most widely used metals.

The filler rod is another important aspect of TIG welding.

Usually made from the same material as the base metal, it __________

_______________ (is) used for reinforcing joints and welding heavy metals.

There __________ _______________ (are) several different types of joints

designed for use with TIG welding. These include the butt joint, lap joint, corner

joint and t-joint. The butt joint can be welded without the assistance of a filler rod.

With this type of joint, two pieces of metal __________ _______________ (are)

joined together along the seams.

With a lap joint, the top edge__________ _______________ (is) welded to the

bottom piece in an area between the two overlapping metals. A corner joint

involves welding one piece of metal at a right angle to the edge of a second piece

of metal in order to form a corner. To create a t-joint, a filler rod is necessary.

The t-joint __________ _______________ (is) created by placing one piece of

metal perpendicular to another piece of metal to form a T shape. This type of TIG

welding __________ _______________ (is) done along either side of the

perpendicular seam.