UC Davis

The directed energy deposition (DED) process is an additive manufacturing (AM) operation in which highly concentrated energy and metal powder/wire are applied onto a surface to general a metal clad. In this study, experiments were conducted utilizing blown powder DED in which the powder and laser are coaxial to each other in the nozzle housing. Utilizing computer numerical control (CNC), the powder and laser can be moved during the deposition process to generate a continuous clad to create metal objects ranging in geometric complexity. Clad geometry is a function of laser energy flux, powder flux, laser and powder spot diameter, and energy (or temperature) state of the substrate. The working distance between the nozzle and the substrate can fluctuate throughout a deposition which will affect the powder flux and result in changes in the height of the clad. This is due to heat accumulation over time in the deposition piece. The constant laser power results in clads flattening from the heat, leading to the underbuilding of the part. These errors in height may compound over several layers within a deposition. While less evident in short builds, in longer and/or complex builds, the process can become so unstable that the part fails to build any longer. The purpose of developing a height control system that uses a dynamic powder splitter was to manipulate the powder flux to maintain a designated working distance throughout an entire deposition. Monitoring of the working distance was achieved by a camera sensor, changes in powder flow rate (PFR) was achieved by a Dynamic Powder Splitting System (DPSS), and communication between devices was maintained by a microcontroller. Proportional integrative (PI) and proportional integrative derivative (PID) control systems were developed to correct the working distance errors during deposition, and they were compared to finalize the best control to be used in the overall system developed. Thin wall depositions were conducted to analyze the controller’s ability to correct layer-wise height errors. A comparison of the depositions in which the controller was active and inactive showed that each control system could control layer height effectively, resulting in more accurate part geometries. Ultimately, the PID control system created performed better by achieving higher stability and more accurate height control. Due to the development of this control system, more efficient and stable builds can be achieved which will greatly aid in a variety of additive manufacturing applications.