Jianzhong Ruan

Automatic Process Planning and Toolpath Generation of a Multiaxis Hybrid Manufacturing System

With the integration of multiaxis layered manufacturing and material removal (machining) processes, a hybrid system has more capability and flexibility to build complicated geometry with a single setup. Process planning to integrate the two different processes is a key issue. In this paper, an algorithm of adaptive slicing for a five-axis Laser Aided Manufacturing Process (LAMP) is summarized that can generate uniform and non-uniform thickness slices. A method to build a non-uniform (thickness) layer that utilizes two processes is presented, and an overall algorithm for integration is described. The newly developed algorithm implemented in the process planning helps the hybrid system build parts more efficiently.

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.

Part Repairing Using a Hybrid Manufacturing System

At present, part remanufacturing technology is gaining more interest from the military and industries due to the benefits of cost reduction as well as time and energy savings. This paper presents the research on one main component of part remanufacturing technology, which is part repairing. Traditionally, part repairing is done in the repair department using welding processes. However, the limitations of the traditional welding process are becoming more and more noticeable when accuracy and reliability are required. Part repairing strategies have been developed utilizing a hybrid manufacturing system in which the laser-aided deposition and CNC cutting processes are integrated. Part repairing software is developed in order to facilitate the users. The system and the software elevate the repairing process to the next level, in which accuracy, reliability, and efficiency can be achieved. The concept of the repairing process is presented in this paper, and verification and experimental results are also discussed.Copyright

Direct Three-Dimensional Layer Metal Deposition

Multi-axis slicing for solid freeform fabrication manufacturing processes can yield nonuniform thickness layers or three-dimensional (3D) layers. The traditional parallel layer construction approach to building such layers leads to the so-called staircase effect, which requires machining or other postprocessing to form the desired shape. This paper presents a direct 3D layer deposition approach that uses an empirical model to predict the layer thickness. The toolpath between layers is not parallel; instead, it follows the final shape of the designed geometry and the distance between the toolpath in the adjacent layers varies at different locations. Directly depositing 3D layers not only eliminates the staircase effect but also improves manufacturing efficiency by shortening the deposition and machining times. Simulation and experimental studies are conducted that demonstrate these advantages. Thus, the 3D deposition method is a beneficial addition to the traditional parallel deposition method.

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.

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.

A Multi-Axis Slicing Method for Direct Laser Deposition Process

With multi-axis capability, direct laser deposition process can produce a metal part without the usage of support structures. In order to fully utilize such a capability, the paper discusses a slicing method for multi-axis metal deposition process. Using the geometry information of adjacent layers, the slicing direction and layer thickness can be changed as needed. A hierarchy structure is designed to manage the topological information which is used to determine the slicing sequence. Its usage is studied to build overhang type structure. With such a character, some overhang features such as holes, can be deposited directly to save the required machining operation and material cost, which improves the efficiency of the metal deposition process. Combined with direct 3D layer deposition technique, the multi-axis slicing method is implemented.Copyright

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.

A process planning strategy for multi-axis hybrid manufacturing process

This paper outlines a process planning strategy for a multi-axis hybrid manufacturing process that includes a metal deposition system and a multi-axis CNC machining system to rapidly manufacture precision metal parts. Different from the current layered manufacturing processes of which build direction is fixed throughout the process, the orientation of the part can affect the non-support buildability in the multi-axis hybrid manufacturing process. However, each orientation that satisfies the buildability and other constraints may not be unique. In this case, the final optimal orientation is determined based on build time. The build time computation algorithm for multi-axis hybrid system is presented in this paper. To speed up the exhaustive search for the optimal orientation, a multi-stage algorithm is developed to reduce the search space. A case study is used as an example to show the process planning strategy.