20) What devices are provided to reflect the light coming to the ends of ruby rod in laser beam welding?

21) Which gas is generally used in gas laser type welding?

22) In which welding process the work pieces are melted and jointed by narrow beam of light source?

23) Which is adjusted in Electron beam welding to eliminate the defect of porosity?

24) What is the approximate revolution of rotating member in friction welding process, to effect the weld joint?