Frank W. Liou

Variable Powder Flow Rate Control in Laser Metal Deposition Processes

This paper proposes a novel method, called variable powder flow rate control (VPFRC), for the regulation of powder flow rate in laser metal deposition processes. The idea of VPFRC is to adjust the powder flow rate to maintain a uniform powder deposition per unit length even when disturbances occur (e.g., the motion system accelerates and decelerates). Dynamic models of the powder delivery system motor and the powder transport system (i.e., 5 m pipe, powder dispenser, and cladding head) are constructed. A general tracking controller is then designed to track variable powder flow rate references. Since the powder flow rate at the nozzle exit cannot be directly measured, it is estimated using the powder transport system model. The input to this model is the dc motor rotation speed, which is estimated online using a Kalman filter. Experiments are conducted to examine the performance of the proposed control methodology. The experimental results demonstrate that the VPFRC method is successful in maintaining a uniform track morphology, even when the motion system accelerates and decelerates.

A SOA Approach to Improve Performance of Metal Additive Manufacturing Simulation

Metal additive manufacturing (AM) processes are very complex and the process parameters required to fabricate quality parts can be very complicated and challenging to determine. For this reason, there is a continuous demand for AM simulations which can assist users to determine optimal process parameters in a timely manner. However, current commercial simulation packages are expensive and not designed with AM processes in mind, which makes it challenging to simulate an AM process. In addition, they are computationally intensive and usually require some high performance computing (HPC) system to run effectively. Besides, they take relatively more time, usually from several days to months, to simulate an AM process. This paper presents additive manufacturing simulator (AMS), a simulation tool built specifically with AM processes in mind, to address the challenges with current AM simulation tools. AMS is based on a three-tier client-server architecture, coupled with service oriented architectures (SOA) publication and subscription model. It has the ability to scale to utilize available computational resources and automatically balances computational resources among multiple processors. Compared with current AM simulation systems, AMS improves performance of AM simulation considerably and can run on not only HPC systems, but also low-cost desktop computers.

Analysis of the Powder Flow Characteristics for the Direct Laser Deposition Process

Direct laser deposition process is one of the advanced technologies in the current industrial and research scenario. In this process, metal and/or alloy powder is directly fed into the melt pool created by the laser to form the solid parts. The powder flow characteristics play an important role in the laser aided deposition. The melting of the powder depends mostly on the laser beam spot size and the powder flow from the nozzle. The intention of this contribution is to study this basic parameter of the powder flow in detail with respect to the coaxial deposition nozzle. Different nozzle dimensions are used to analyze the different flow patterns of the gravity fed powder in a cold stream. Rapid prototyping technique is used to make this analysis cost and time efficient. This analysis lays down the benchmark for the coaxial nozzle design used for the laser aided deposition process in a productive manner.Direct laser deposition process is one of the advanced technologies in the current industrial and research scenario. In this process, metal and/or alloy powder is directly fed into the melt pool created by the laser to form the solid parts. The powder flow characteristics play an important role in the laser aided deposition. The melting of the powder depends mostly on the laser beam spot size and the powder flow from the nozzle. The intention of this contribution is to study this basic parameter of the powder flow in detail with respect to the coaxial deposition nozzle. Different nozzle dimensions are used to analyze the different flow patterns of the gravity fed powder in a cold stream. Rapid prototyping technique is used to make this analysis cost and time efficient. This analysis lays down the benchmark for the coaxial nozzle design used for the laser aided deposition process in a productive manner.