In recent years, the usage of additive manufacturing (AM) provides new capabilities for component repair, which includes low heat input, small heat-affected zone, and freeform near-net-shape fabrication. Because the geometry of each worn component is unique, the automated repair process is a challenging and important task. The focus of this paper is to investigate and develop a general best-fit and shape-adaption algorithm for automating alignment and defect reconstruction for component repair. The basic principle of using features for rigid-body best-fitting is analyzed and a multifeature-fitting method is proposed to best fit the 3D mesh model of a worn component and its nominal component. The multifeature-fitting algorithm in this paper couples the least-squares method and a density-based outlier detection method. These two methods run alternately to approach the best-fit result gradually and eliminate the disturbance caused from the defect geometry. The shape-adaption algorithm is used to do cross section comparison and defect reconstruction based on the best-fitted 3D model. A “point-line-surface” fracture surface detection method is proposed to construct fracture surface and the fracture surface boundary is dilated to trim the nominal 3D model to obtain defect geometry. Illustrative examples with typical components and different kinds of defects are used to demonstrate the flexibility and capability of using multifeature-fitting and shape-adaption algorithm developed in this paper.

A hybrid manufacturing system integrates computer numerical controlled (CNC) machining process and layered deposition process and achieves the benefits of both processes. An integrated process planning framework, which includes every module of the hybrid manufacturing process is critical for making the building of functional parts feasible and reliable. In this paper, the hybrid manufacturing system is introduced and the integrated process planning framework, which aims to automate the hybrid manufacturing is investigated. Critical components of the process planning, including decomposition of the computer-aided design (CAD) model, improvement of the toolpath generation pattern, and collision detection algorithms, are discussed. The interfacing and integrating process between deposition and surface finish machining is also studied. The goal of integrated process planning is to realize the automatic hybrid manufacturing process without much human interference. Experiments are implemented to validate the feasibility and reliability of the integrated process planning framework.

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.

The quality and efficiency of laser-aided direct metal deposition largely depends on the powder stream structure below the nozzle. Numerical modeling of the powder concentration distribution is complex due to the complex phenomena involved in the two-phase turbulence flow. In this paper, the gravity-driven powder flow is studied along with powder properties, nozzle geometries, and shielding gas settings. A 3-D numerical model is introduced to quantitatively predict the powder stream concentration variation in order to facilitate coaxial nozzle design optimizations. Effects of outer shielding gas directions, inner/outer shielding gas flow rate, powder passage directions, and opening width on the structure of the powder stream are systematically studied. An experimental setup is designed to quantitatively measure the particle concentration directly for this process. The numerical simulation results are compared with the experimental data using prototyped coaxial nozzles. The results are found to match and then validate the simulation. This study shows that the particle concentration mode is influenced significantly by nozzle geometries and gas settings.

This paper presents an approach for modeling powder delivery system dynamics in low flow rate applications. Discrete particle modeling (DPM) is utilized to analyze the motion of individual powder particles. In DPM, an irregular bouncing model is employed to represent the powder dispersion in the powder delivery system induced by non-spherical particle-wall collisions. A three-dimensional friction collision model is utilized to simulate the interactions between particles and the powder delivery system walls. The modeling approach is experimentally verified and simulation studies are conducted to explore the effect of powder delivery system mechanical design parameters (i.e., tube length, diameter, and angle, number of tubes and meshes, and mesh orientation and size) on the powder flow dynamics. The simulation studies demonstrate that the powder delivery system dynamics can be modeled by a pure transport delay coupled with a first order system.

This paper discusses the microdeposition technologies used in the fabrication of meso- and microscale structures. The ability to process a wide range of materials and the flexibility to build functional and geometrically complex structures in meso- and microscale gives the microdeposition method some advantages over micromachining or lithography methods investigated extensively in the past. In this paper, work on deposition technology is reviewed, including material, supply of material, powder flow rate, and manipulation of particles and microdeposition technologies. The advantages and disadvantages of each technology are summarized at the end of the paper.