Laser beam diagnostics for metal working applications

The Materials Fabrication Division (MFD) of Lawrence Livermore National Laboratory (LLNL) has three pulsed Nd-YAG lasers dedicated to metal working. Figure 1 shows one of the units, a Raytheon SS-500, positioned on a Computer Numerical Controlled machine tool base capable of four axis control. The units are used for welding, brazing, cutting, and drilling. The MFD facility is a job shop fabricating prototypes of design concepts. For the most part these fabrications represent one-of-a-kind parts. When a design does prove successful, we are required to produce additional units for testing. We have found that by following a standard setup procedure in our initial fabrication, carefully measuring the significant parameters, and maintaining a thorough record of these data, we can reproduce desired results in subsequent parts with a minimum of setup time. Careful control of all operating parameters is essential; however, the control of the mode of the laser beam, the stability of the mode, and the symmetry of the laser beam is the key to reproducible results. This paper will review the procedure used for set up and operation of the laser metal working systems with particular emphasis on the methods used to define and control the mode, stability and symmetry of the laser beam.