a) Explain why some welds require preheating. b) What role does the additive material play in fusion welding? c) What are the advantages of electron beam welding compared to conventional arc welding? d) Describe typical discontinuities (defects) that can occur in welded material and how can these be avoided? e) Explain what residual stresses that occur in welded structures can lead to. f) Describe two of the most important advantages of cold welding (solid state welding) compared to fusion welding