Mumbai University > Mechanical Engineering > Sem 3 > Production Process 1

Marks: 5M

Year: May 2015

• It is a fusion welding technique in which coalescence is produced by heating the work piece due to impingement of the concentrated beam of stimulated electrons coming from the laser source.
• LASER SYSTEM: It is a device that produces a concentrated coherent light beam of single frequency by stimulated electronic or molecular transitions to lower energy levels.
• Laser is an acronym for Light Amplification by Stimulated Emission of Radiation.
• In the LBW process, the laser beam is directed by flat optical elements such as mirrors and then focused to a small spot (for high power density) at the work piece using either reflective elements or lenses.
• It is a non-contacting pressure requiring no pressure to be applied.
• Inert gas shielding is generally provided to prevent oxidation of the molten pool and filler metals may be occasionally used.
• The electric discharge style CO2 gas lasers are the most efficient type currently available for high power laser beam material processing.
• These lasers employ gas mixtures primarily containing nitrogen and helium along with a small percentage of carbon dioxide
• An electric glow discharge is used to pump this laser medium
• Gas heating produced in this fashion is controlled by continuously flowing the gas mixture through the optical cavity
• Thus, carbon dioxide lasers are usually categorized according to the type of gas flow system which they employ.

Advantages:

• Heat input is close to the minimum to the required to fuse the weld metal, thus heat affected zones are reduced and work piece distortions are minimized.
• No electrodes are required; welding is performed with freedom from electrode contamination, indentation or damage from high resistance welding currents.
• LBW being a non-contact process, distortions are minimized and tool wears are eliminated.
• Welding in areas that are not easily accessible with the means of welding can be done by LBW, since the beams can be focused, aligned and directed by optical elements on a very precise area.
• Laser beam can be focused on a small area, permitting the joining of small, closely spaced components with tiny welds.
• Wide variety of weld materials including various combinations can be welded.
• The burn back is quite often noticed in arc welding for small and thick sections.
• No vacuum or X-ray shielding is required.
• Aspect ratios (i.e. depth-to-width ratios) of the order of 10:1 are attainable in LBW.
• High accuracy
• Accurate control
• High speed

Limitations:

• Joints must be accurately positioned laterally under the beam and at a controlled position with respect to the beam focal point
• In case of mechanical clamping of the weld joints, it must be ensured that the final position of the weld joints is accurately aligned with the beam impingement point.
• The maximum joint thickness that can be welded by LBW is limited.
• High reflectivity and high thermal conductivity of materials like Al and Cu alloys can affect the weldability with lasers.