Guilan Wang

Fundamental study on plasma deposition manufacturing

Direct fabrication of metal or end-use-material components has become one of the most interesting fields in the R&D of materials additive manufacturing (MAM) at present. Plasma deposition manufacturing (PDM), as an emerging MAM technique derived from plasma powder surfacing, has the capacity and predominance of producing fully dense metal or high performance specialty material parts with complex shapes. This process starts with a CAD model and automatically assembles materials to a designed configuration without the need of molding or tooling. The present paper reports initial pilot study of PDM process, and some existing problems and further study are also discussed in detail.

Rapid hard tooling by plasma spraying for injection molding and sheet metal forming

Abstract Amidst the harsh competition over the development of new products around the world, rapid prototyping, especially rapid tooling methods have received widespread attention. Amongst the rapid hard tooling methods, thermal spraying can manufacture metal molds without limitation of pattern size. However, it has the disadvantage that only soft metals with low melting points such as zinc alloy can be sprayed to original mold, such as a rapid prototyping model or a natural material pattern, due to their lack of heat resistance and shrinkage of spray metals. So the wear resistance of spray tool is poor, it can be used only for trial or small-lot production. In this study, attempts were made to improve the heat resistance by using composite materials made of ceramic and metal powders as the sprayed original mold materials, and using stainless steel, tungsten carbide alloy, iron–nickel–chromium alloy with excellent wear resistance as spraying materials, respectively. The results show that injection molding spray mold and sheet metal forming spray die can be made by transferring from natural patterns and rapid prototyping models. As the durability and dimensional accuracy of the sprayed tools has sharply improved, the tools can be used for mass production.

Numerical simulation of coating growth and pore formation in rapid plasma spray tooling

Rapid plasma spray tooling (RPST) is a process that can quickly make molds from rapid prototyping or nature patterns without limitation of patterns size or material. In this paper, the process of coating growth and pore formation in RPST has been analyzed by numerical simulation. The objective of this work was to determine the porosity in plasma sprayed coatings and verify the developed computer model, which might serve for future thermal residual stress studies of plasma sprayed coatings. The analysis was divided into two steps: particle flattening and coating growth. In the analysis, a ballistic model was used for modeling the in-flight powder particles. The method allows for the calculation of off-normal spray angle, which is common in plasma spraying of engineering components. Also, a set of rules for coating growth as well as pore formation in the coating has been proposed. Based on these works, a computer program was developed to calculate the effects of process parameters, such as gun scanning velocity, spray angle, etc., on the porosity of the coating. Finally, an experiment was carried out to verify the effects of spray parameters on the porosity. The results agree with the prediction of the model.

Numerical simulation of multiphase transient field during plasma deposition manufacturing

A transient solid/liquid/vapor unified mathematical model for plasma deposition manufacturing was developed to investigate the fluid flow and heat transfer of the molten pool and deposition layer. The level-set approach was adopted to deal with the liquid/vapor interface boundary conditions, which considered surface tension gradient (the major driving forces for the melt flow), interface curvatures, buoyancy, and convection heat loss. The mixture continuum model was applied to describe melting and solidification processes at the solid/liquid interface. Moreover, the effects of main processing parameters on the thickness of the deposition layer, full depth of the molten pool and penetration depth of the substrate have been studied further. The experiments agree well with the simulation results.

Effects of scanning path on the deposition process in rapid plasma spray tooling: Modeling by homogenization theory

Rapid plasma spray tooling (RPST) is a kind of process that can quickly make a mold from rapid prototyping or nature pattern without limitation of pattern’s size or material. In a previous investigation of the authors, the process of coating growth, pore formation and its effect on coating’s properties in RPST has been analyzed numerically. The objective of this work is to calculate temperature and stress field during plasma spray process when using a different kind of scanning path. In mesoanalysis, two-scale asymptotic homogenization theory is introduced to predict the effective properties of plasma sprayed coatings with porous. Based on this, in macro process simulation, a FEM software developed system has been used to analyze the effects of gun scanning path on the temperature and stress field. The numerical examples for the four kinds of gun scanning paths are presented. In the scanning paths of s-shape (H), spire in, spire out and s-shape (≤), characteristic of the temperature field under spire out path is the best, and the maximum stress and deflection under spire out path are the smallest after the model cool. 2003 Elsevier Science B.V. All rights reserved.

Fabrication and electrochemical performance of solid oxide fuel cell components by atmospheric and suspension plasma spray

Abstract The theory of functionally graded material (FGM) was applied in the fabrication process of PEN (Positive-Electrolyte-Negative), the core component of solid oxide fuel cell (SOFC). To enhance its electrochemical performance, the functionally graded PEN of planar SOFC was prepared by atmospheric plasma spray (APS). The cross-sectional SEM micrograph and element energy spectrum of the resultant PEN were analyzed. Its interface resistance was also compared with that without the graded layers to investigate the electrochemical performance enhanced by the functionally graded layers. Moreover, a new process, suspension plasma spray (SPS) was applied to preparing the SOFC electrolyte. Higher densification of the coating by SPS, 1.61%, is observed, which is helpful to effectively improve its electrical conductivity. The grain size of the electrolyte coating fabricated by SPS is also smaller than that by APS, which is more favourable to obtain the dense electrolyte coatings. To sum up, all mentioned above can prove that the hybrid process of APS and SPS could be a better approach to fabricate the PEN of SOFC stacks, in which APS is for porous electrodes and SPS for dense electrolyte.

Numerical Simulation of Transient Multiphase Field During Hybrid Plasma-Laser Deposition Manufacturing

The hybrid plasma-laser deposition manufacturing (PLDM) process is developed based on the plasma deposition manufacturing (PDM) technology. PLDM belongs to the three-dimensional (3D) welding technology and involves the laser power as an augmented heat resource. Compared to PDM technology, the PLDM process has many advantages such as a higher power density, higher processing precision, refined microstructure, and improved mechanical performance of forming components. There exist complicated physical and metallurgical interaction mechanisms due to the combination of PLDM along with the rapid melting and solidification process. Moreover, the interaction between the laser and plasma arc also directly influences the forming quality and precision of the 3D metal components. Therefore, the proposed work is a preliminary attempt to study the transport phenomena in the PLDM process, in which the heat transfer, fluid flow, and molten powder depositing processes have been investigated in detail. The numerical study is performed by using a pressure-based finite volume difference technique after making appropriate modifications of the algorithm. The associated solid/liquid phase transformation process is involved by using an enthalpy-porosity method, and the level-set approach is introduced to track the evolution of weld surface of the deposition layer with powder feeding. An experimentally based hybrid heat input model is developed to involve the influence of the interaction of laser and arc plasma on the redistributed energy absorption by the material. Corresponding experiments of the PLDM process are performed using the same parameters as in the computations, showing a good qualitative agreement.

Optimization of plasma deposition manufacturing parameters using a hybrid ANN-GAs method

Summary form only given, as follows. Plasma surfacing is an important enabling technology in high performance coating applications. Recently, it is being applied to rapid prototyping/tooling to reduce development time and manufacturing cost for the development of new product. In this technology, a plasma arc beam is used as thermal energy source, metal powders are preheated in plasma arc and deposited in melt pool on the base plate or deposited layer synchronously, with the movement of plasma gun and/or worktable controlled by CNC according to CAD slice model in computer, deposition layer grows gradually along z direction until the total part is fabricated. However, this technology is in its infancy, it is essential to understand clearly how process variables relate to deposit microstructure and properties for plasma deposition manufacturing (PDM) process control. In this article, the microstructure, mechanical properties and coating appearance for single surfacing and multiple surfacing under different parameters, such as plasma power, powder feedrate and scanning speed, etc., were studied in detail, and then a hybrid BP artificial neural network (ANN) and genetic algorithms (GAs) method which can overcome the shortcoming of BP neural network and obtain a global convergence result, was presented to optimize processing parameters. Using the optimized parameters, metal parts with complex shape and excellent mechanical properties and microstructure were fabricated successfully.

Numerical Simulation of Electromagnetic Flux Leakage in Application of Internal Defects Prediction of Metal Parts

Metal products were widely used at a variety of industry, so it is essential to predict the security and the usability without the destructive testing for the desired production efficiency under the different their working conditions. Recently, the plasma deposition dieless manufacturing process (PDM) is an innovative and promising application of plasma heat source with extensive industrial potential for refractory and intractable material part or prototype, rebuilding of worn components and especially the direct rapid fabrication of functionally graded materials (FGMs). However, Residual stress and distortion induced by the highly localized transient heat and strongly nonlinear temperature distributions would likely promote undesired and unpredictable warps and cracks in this process. Thus, to distinguish the internal defect from the significant discontinuities during the nondestructive testing of the metal parts, in this paper, the finite-element method (FEM) was applied to predict the electromagnetic distribution. According to the difference the magnetic flux leakage analysis, distinction threshold was built by the ratio of the peak-to-peak amplitudes of the raw inspecting signal anomaly. Computational results show that it is potential to decrease the testing period and improve the security of metal parts, in particular, the micro-raw and hole in the metal parts can be predicted, thus the possiblyintended breakage would be improved.

Robotic Digital Manufacturing of FGM Component

In this paper, a robotic digital manufacturing process for fabrication of FGM (Functionally Graded Materials) component was presented. Firstly, the construction procedure of robotic FGM digital manufacturing process was described. Then a method of transforming CL (cutter location) code trajectory into robotic trajectory instruction format was proposed. As the key apparatus for FGM component fabrication, a new flexible numerical synchronously controlled FGM powder feeder system and its superior computer control program was developed. Finally a functionally graded PEN (positive electrode/ electrolyte/ negative electrode) of SOFC (Solid Oxide Fuel Cell) was fabricated to evaluate the manufacturing process. The Scanning Electron Microscopy (SEM) observation indicated that the variation of PEN composition was continuous functionally gradient transition as expected.