In spite of the many advantages of laser cladding, its industrial applications are still limited. This is not only because of the relatively high cost of laser systems, but also the high sensitivity of this process to disturbances. A small change in absorbed laser power, for example, can cause a large change in the melt pool size. Also, changes in the mass flow of the powder can produce significant variations in the overall geometry and microstructure of the clad. To make the process more stable and less susceptible to disturbances, it is important to understand the effects of involved parameters in the process, and clad quality and dimensions. In Figure 2.7, the important parameters that determine the clad quality are

listed under inputs and process columns. These parameters can be categorized into two groups:

• Intrinsic

• Extrinsic

Intrinsic parameters are those related to the substrate and powder properties. Some of these parameters include absorptivity, thermal conductivity, heat capacity, thermal diffusivity, and workpiece geometry. Extrinsic parameters are those related to the hardware used in the process such as laser, powder feeder, and positioning system. Some of these parameters include laser average energy, laser focal point, powder feeder mass flow, nozzle position and orientation, and relative position and velocity of the laser and substrate. In general, there is no direct control on intrinsic parameters; however, the

effects of changes in intrinsic parameters can be compensated by controlling the extrinsic parameters. For example, change in the absorptivity can be adjusted by controlling the laser average power. The control of extrinsic parameters, on the other hand, is relatively easy for

most of the parameters mentioned above. Commercial lasers, powder feeders, and positioning systems are equipped with built-in controllers that allow the user to set the desired values. This is in fact the approach that is used in many applications. After much trial and error, the parameters that result in a good quality clad or coating for a specific application are obtained. These parameters such as laser average power, focal point, speed, and powder feed rate are then used in an open-loop process control.