Tham khảo tài liệu 'process selection - from design to manufacture episode 2 part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 204 Selecting candidate processes Quality issues High quality welds possible with little or no distortion. No flux or filler used. Integrity of vacuum important. Beam dispersion occurs due to electron collision with air molecules. Out-of-vacuum systems must overcome atmospheric pressures at weld area. Beams can be generated up to 700 mm from workpiece surface for high-vacuum systems can be reduced to less than 40 mm for out-of-vacuum. Precise alignment of work required and held using jigs and fixtures. Hazardous X-rays produced during processing which requires lead shielding. Vacuum removes gases from weld area . hydrogen to minimize hydrogen embrittlement in hardened steels. Localized thermal stresses leads to a very small heat affected zone. Distortion of thin parts may occur. Surface finish excellent. Fabrication tolerances a function of the accuracy of the component parts and the assembly jigging method. Joints gaps less than mm required. Therefore abutment faces should be machined to close tolerances. Laser Beam Welding LBW 205 Laser Beam Welding LBW Process description Heat for fusion is generated by the absorption of a high power density narrow beam of light commonly known as a laser. Focusing of the laser is performed by mirrors or lenses see . Schematic of Laser Beam Welding LBW Laser beam welding process. Materials Dependent on thermal diffusivity and to a lesser extent the optical characteristics of material rather than chemical composition electrical conductivity or hardness. Stainless steel and carbon steels typically. Aluminum alloys and alloy steels difficult to weld. Not used for cast iron. Process variations Many types of laser are available used for different applications. Common laser types available are CO2 Nd YAG Nd glass ruby and excimer. Depending on economics of process pulsed and continuous wave modes are used. Shielding gas such as argon sometimes employed to reduce oxidation. Laser beam machines can also be used for .
