What happens at the point of welding iron? What is the physics behind welding iron? It is obviously the electricity that causes the two metal parts to fuse but what is the role of the welding rod and why is it said to damage your eyes when you look at the spark. Is it just the brightness, or does it radiate a specific wavelength that is more damaging, such as UV rays?
 A: Based on your mention of electricity, and of a "welding rod", I will assume you are talking about arc welding.  From Lincoln Electric:

"Arc welding is one of several fusion processes for joining metals. By applying intense heat, metal at the joint between two parts is melted and caused to intermix - directly, or more commonly, with an intermediate molten filler metal. Upon cooling and solidification, a metallurgical bond is created. Since the joining is an intermixture of metals, the final weldment potentially has the same strength properties as the metal of the parts. This is in sharp contrast to non-fusion processes of joining (i.e. soldering, brazing etc.) in which the mechanical and physical properties of the base materials cannot be duplicated at the joint.
"In arc welding, the intense heat needed to melt metal is produced by an electric arc. The arc is formed between the actual work and an electrode (stick or wire) that is manually or mechanically guided along the joint. The electrode can either be a rod with the purpose of simply carrying the current between the tip and the work. Or, it may be a specially prepared rod or wire that not only conducts the current but also melts and supplies filler metal to the joint. Most welding in the manufacture of steel products uses the second type of electrode."

Regarding the danger to your eyes by looking at the electric arc, it is the Ultraviolet Radiation (wavelength 200 to 400 nm) that causes the damage.  Obviously the intensity (brightness) is also a factor, but the visible (400 to 700nm) and infrared (700 to 1400 nm) radiation from the welding arc is, for the most part, harmless.

"Certain types of UV radiation can produce an injury to the surface and mucous membrane (conjunctiva) of the eye called "arc eye," "welders' eye" or "arc flash." These names are common names for "conjunctivitis" - an inflammation of the mucous membrane of the front of the eye. The symptoms include:

*

*pain - ranging from a mild feeling of pressure in the eyes to intense pain in severe instances

*tearing and reddening of the eye and membranes around the eye

*sensation of "sand in the eye" or abnormal sensitivity to light

*inability to look at light sources (photophobia)

"The amount of time required to cause these effects depends on several factors such as the intensity of the radiation, the distance from the welding arc, the angle at which the radiation enters the eye, and type of eye protection that the welder or bystander is using. However, exposure to just a few seconds of intense UV light can cause arc eye. These symptoms may not be felt until several hours after exposure."

The above quote is from Canadian Centre for Occupational Health and Safety ... See there for a good, and more complete, description of the hazards of arc welding on the eyes and skin.
A: Welding is the fusing of two materials using a filler material.General welding processes super heat the parent metals into a liquid state, then the filler material is ‘melted’ into the parent metals to create a welded joint.
