Todd E. Sparks

The Investigation of Gravity-Driven Metal Powder Flow in Coaxial Nozzle for Laser-Aided Direct Metal Deposition Process

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.

Automated Slicing for a Multiaxis Metal Deposition System

A multiaxis adaptive slicing algorithm for multiaxis layered manufacturing, which can generate optimal slices to achieve deposition without support structures, is presented in this paper Different from current adaptive slicing, this technique varies not only layer thickness but also in slicing/building direction. Aware of potential problems of previous research on slicing, the work in this paper focuses on innovative geometry reasoning and analysis tool-centroidal axis. Similar to medial axis, it contains geometry and topological information but is significantly computationally cheaper. Using a centroidal axis as a guide, the multiaxis slicing procedure is able to generate a three-dimensional layer or change slicing direction as needed automatically to build the part with better surface quality. This paper presents various examples to demonstrate the feasibility and advantages of centroidal axis and its usage in the multiaxis slicing process.

Vision-based defect detection in laser metal deposition process

Purpose – Laser metal deposition (LMD) is a type of additive manufacturing process in which the laser is used to create a melt pool on a substrate to which metal powder is added. The powder is melted within the melt pool and solidified to form a deposited track. These deposited tracks may contain porosities or cracks which affect the functionality of the part. When these defects go undetected, they may cause failure of the part or below par performance in their applications. An on demand vision system is required to detect defects in the track as and when they are formed. This is especially crucial in LMD applications as the part being repaired is typically expensive. Using a defect detection system, it is possible to complete the LMD process in one run, thus minimizing cost. The purpose of this paper is to summarize the research on a low-cost vision system to study the deposition process and detect any thermal abnormalities which might signify the presence of a defect. Design/methodology/approach – Durin...

Stereo vision-based repair of metallic components

Purpose This paper aims to investigate a stereo vision-based hybrid (additive and subtractive) manufacturing process using direct laser metal deposition, computer numerical control (CNC) machining and in-process scanning to repair metallic components automatically. The focus of this work was to realize automated alignment and adaptive tool path generation that can repair metallic components after a single setup. Design/methodology/approach Stereo vision was used to detect the defect area for automated alignment. After the defect is located, a laser displacement sensor is used to scan the defect area before and after laser metal deposition. The scan is then processed by an adaptive algorithm to generate a tool path for repairing the defect. Findings The hybrid manufacturing processes for repairing metallic component combine the advantages of free-form fabrication from additive manufacturing with the high-accuracy offered by CNC machining. A Ti-6Al-4V component with a manufacturing defect was repaired by the proposed process. Compared to previous research on repairing worn components, introducing stereo vision and laser scanning dramatically simplifies the manual labor required to extract and reconstruct the defect area’s geometry. Originality/value This paper demonstrates an automated metallic component repair process by integrating stereo vision and a laser displacement sensor into a hybrid manufacturing system. Experimental results and microstructure analysis shows that the defect area could be repaired feasibly and efficiently with acceptable heat affected zone using the proposed approach.

Aerospace applications of laser additive manufacturing

Abstract Additive manufacturing (AM) has been used in aerospace applications from the beginning. It not only plays a role as a rapid prototyping technology for saving capital and time during the product development period but also brings profound influences on product design, direct part fabrication, assembly, and repair in the aerospace industry. Because of recent developments, AM has rapidly become a strategic technology that will generate revenues throughout the aerospace supply chain. In this chapter, we analyze the characteristics of aerospace components favoring AM, discuss different aerospace applications benefit from different AM processes, and describe the repair applications for aerospace components. Examples of aerospace applications both from commercial and academia areas are also analyzed. Finally, this chapter discusses the challenges of applying AM to the aerospace industry and potential future aerospace applications.

Numerical and Analytical Modeling of Laser Deposition with Preheating

Laser deposition allows quick fabrication of fully-dense metallic components directly from CAD solid models. This work uses both numerical and analytical approaches to model the laser deposition process including actual deposition and preheating. The numerical approach is used to simulate the coupled, interactive transport phenomena during actual deposition. The numerical simulation involves laser material interaction, free surface evolution, and melt-pool dynamics. The analytical approach is used to model heat transfer during preheating. The combination of these two approaches can increase computational efficiency with most of the phenomena associated with laser deposition modeled. The simulation is applied to Ti-6Al-4V and simulation results are compared with experimental results.Copyright

Multi-axis tool path generation for surface finish machining of a rapid manufacturing process

This paper proposes a completely automated, integrated tool path planning for the finish machining of freeform surfaces as a part of the hybrid metal additive manufacturing and CNC machining. This planning capability spans from a generation of b-spline freeform surfaces, to surface finish optimisation, to collision detection, to tool path generation. Two scallop height methods have been used to compare the optimal tool path strategy. Both collision detection of a tool with neighbouring surfaces and collision correction for a tool are solved using a novel extension of the bounding box, which uses body diagonal points for computation. This paper proposes a multiple screening technique to improve the computational efficiency of tool path generation calculations.

Development of low‐cost imaging system for laser metal deposition processes

– The melt pool created by a laser is one of the most important factors affecting the quality of the deposit in a laser metal deposition (LMD) process. The high‐intensity infrared (IR) radiation emitted by the melt pool saturates a conventional camera sensor preventing useful data acquisition. The purpose of this paper is to discuss the development of a low‐cost vision system to monitor the size of the melt pool for in‐process quality control of the deposit., – According to the black body radiation theory, there is no radiation emitted in the ultraviolet (UV) region from the melt pool created in the LMD process. IR radiation and visible light are the only radiations inherent to the LMD process. UV illumination is utilized along with narrow band pass filters on a USB camera to achieve a clear image of the melt pool while IR radiation of the process is blocked out. The melt pool size and shape were closely monitored during the deposition process., – A clear image of the melt pool was obtained using a relatively low‐cost imaging system during laser deposition process., – Traditional approaches to vision systems in high‐intensity processes use a high‐speed video camera fitted with IR filters to prevent saturation of the camera sensor. Such systems are usually complex and expensive to run and maintain. This paper demonstrates an alternative and lower cost method to achieve in process monitoring in an LMD process.

Layer-to-layer height control of Laser Metal Deposition processes

A Laser Metal Deposition (LMD) height controller design methodology is presented in this paper. The height controller utilizes the Particle Swarm Optimization (PSO) algorithm to estimate model parameters between layers using measured temperature and track height profiles. The process model parameters for the next layer are then predicted using Exponentially Weighted Moving Average (EWMA). Using the predicted model, the powder flow rate reference profile, which will produce the desired layer height reference, is then generated using Iterative Learning Control (ILC). The model parameter estimation capability is tested using a four-layer deposition. The results demonstrate the simulation based upon estimated process parameters matches the experimental results quite well. The experimental deposition using this methodology demonstrates good tracking of the height reference in terms of the finished track.

Realisation of robot ink deposition on a curved surface

In the robot ink deposition system proposed in this paper, an Additive Manufacturing AM concept-based method generates an ink deposition path, and the developed adaptive compensation algorithm allows the robot to deposit ink on a curved surface based on B-spline surface theory. This method gives the robot arm more flexibility to print characters or to graph on a curved surface, and it affords the robot system a larger working envelope for ink deposition. A letter-printing experiment was conducted in a laboratory using this method. The results show that writing letters on the ink deposition path generated based on the AM concept is much easier than doing so on paths generated using existing methods, and that the adaptive compensation algorithm for printing letters on a large curved surface is effective.