Process Parameters Optimization in Multilayer Laser Solid Freeform Fabrication Process Using a 3D Transient Numerical Model

2007 ◽  
Author(s):  
Masoud Alimardani ◽  
Ehsan Toyserkani ◽  
Christ P. Paul
Keyword(s):  
Process Parameters ◽  
Solid Freeform Fabrication ◽  
Parameters Optimization ◽  
Fabrication Process ◽  
Main Process ◽  
Thin Wall ◽  
Aisi 304L ◽  
Freeform Fabrication ◽  
Modeling Approach ◽  
Laser Solid Freeform Fabrication

This paper presents a 3D transient numerical approach for thermal and strain/stress modeling of the multilayer laser solid freeform fabrication process, by which correlations between the main process parameters and their effects on the final build-up properties can be studied. This model can be used to optimize the process parameters to increase the controllability of the geometrical and metallurgical variations resulted from the thermal and stress fields. Using this modeling approach, the geometry of the material deposited as well as temperature and thermal stress distributions across the process domain can be predicted based on the process parameters such as powder feed rate, process speed and laser power, assuming the interaction between the laser beam and powder stream is decoupled. The main process parameters affected by a multilayer deposition due to the formation of non-planar surfaces such as powder catchment are also incorporated into the modeling approach. To verify the proposed method, fabrication of a four-layer thin wall of stainless steel AISI 304L on a low carbon steel substrate is modeled with the same process parameters throughout the build-up process. The results show that the temperature and stress slightly increase at the end-points of layers 2, 3, and 4 which cause over deposited materials and micro-crack formations at these regions. The results are then used to discuss optimum process parameters which can be used to have a buildup with better geometrical and physical qualities. The reliability and accuracy of the model are experimentally verified.

Effect of Preheating on the Delamination and Crack Formation in Laser Solid Freeform Fabrication Process

2008 ◽  
Author(s):  
Masoud Alimardani ◽  
Ehsan Toyserkani ◽  
Jan Paul Huissoon
Keyword(s):  
Thermal Stresses ◽  
Crack Formation ◽  
Solid Freeform Fabrication ◽  
Fabrication Process ◽  
Experimental Results ◽  
Stress Fields ◽  
Thin Wall ◽  
Freeform Fabrication ◽  
Micro Cracks ◽  
Laser Solid Freeform Fabrication

This paper presents a numerical-experimental investigation on the effects of preheating the substrate on the potential delamination and crack formation across the parts fabricated using the Laser Solid Freeform Fabrication (LSFF) process. For this purpose, the temperature distributions and stress fields induced during the multilayer LSFF process, and their correlation with the delamination and crack formation are studied throughout the numerical analysis and the experimental fabrication of a four-layer thin wall of SS304L. A 3D time-dependent numerical approach is used to simulate the LSFF process, and also interpret the experimental results in terms of the temperature distribution and the thermal stress fields. The numerical results show that by preheating the substrate prior to the fabrication process, the thermal stresses throughout the process domain substantially reduce. Accordingly, this can result in the reduction of potential micro-cracks formation across the fabricated part. Preheating also decreases the transient time for the development of a proper melt pool which is an important factor to prevent poor bonding between deposited layers. The experimental results are used to verify the numerical findings as well as the feasibility of preheating on the reduction of the micro-cracks formed throughout the fabrication process.

Effect of Thermal and Stress Fields on the Microstructure of a Thin Wall Built Using Laser Solid Freeform Fabrication Process

2007 ◽  
Author(s):  
Masoud Alimardani ◽  
Christ P. Paul ◽  
Ehsan Toyserkani
Keyword(s):  
Temperature Distribution ◽  
Stress Field ◽  
Thermal Stresses ◽  
Solid Freeform Fabrication ◽  
Experimental Results ◽  
Thin Wall ◽  
Stress Concentrations ◽  
Aisi 304L ◽  
Freeform Fabrication ◽  
Laser Solid Freeform Fabrication

Temperature distribution and consequent rapid cooling determine the microstructure and final physical properties of a part fabricated using laser solid freeform fabrication (LSFF). As well, in this technique, thermal stresses are the main cause of any possible delamination and crack formation across deposited layers. In this paper, the temperature distribution and the stress field induced during the LSFF process are studied throughout the fabrication of a thin wall up to four layers. The thin wall is fabricated of stainless steel AISI 304L using a 1 kW Nd:YAG pulsed laser. Variations of the microstructure and geometry of the wall are studied. A 3D dynamic numerical model of the multilayer LSFF process is used to interpret the experimental results in terms of the temperature distribution, stress field and microstructure. The experimental results show that the stress concentrations at the end points of the wall, which are due to the higher temperature gradient at these regions, are the locations for possible delaminations and crack formations. Different types of microstructures are observed at the various locations within the same layer due to the different cooling rate. While numerical results confirm the experimental findings, they also show that it is possible to reduce the maximum stress by preheating the substrate.

Dynamic Geometrical Modeling of Deposited Material in Multilayer Laser Solid Freeform Fabrication Process

2006 ◽  
Author(s):  
Masoud Alimardani ◽  
Ehsan Toyserkani ◽  
Jan Paul Huissoon
Keyword(s):  
Process Parameters ◽  
Solid Freeform Fabrication ◽  
Numerical Results ◽  
Thin Wall ◽  
Absorption Factor ◽  
Freeform Fabrication ◽  
Melt Pool ◽  
Proposed Model ◽  
Laser Solid Freeform Fabrication ◽  
Modeling Strategy

In this paper, a novel algorithm is proposed to develop a 3D transient finite element model of multilayer laser solid freeform fabrication (LSFF) process. The proposed model predicts the clad geometry as a function of time and process parameters including laser power, traverse speed, powder jet geometry, and material properties. In the modeling strategy, the interaction between the laser beam and powder stream is assumed to be decoupled, therefore, the melt pool boundary on the moving substrate is obtained in the absence of the powder stream. Once the melt pool boundary is calculated, a deposited layer is formed based on the powder feed rate, elapsed time, and intersection of the melt pool and powder stream. After the deposition of each layer, the effect of this geometrical change into the thermal distribution within the model is considered for thermal analysis of the next layer deposition. In the numerical simulation, the effects of a non-planar surface on the process parameters such as powder efficiency and absorption factor are taken into account. Geometrical aspects of a thin wall of steel AISI 4340 with four layers are numerically simulated by the developed modeling strategy. Numerical results show that with the growth of the number of layers in the wall, the powder efficiency increases while the absorption factor decreases. Experimental and numerical results are compared to verify the accuracy and reliability of the proposed model.

Effects of Process Parameters on Surface Finish in Laser Solid Freeform Fabrication

2009 ◽  
Author(s):  
Masoud Alimardani ◽  
Mehrdad Iravani Tabrizipour ◽  
Amir Khajepour
Keyword(s):  
Process Parameters ◽  
Surface Finish ◽  
Laser Power ◽  
Solid Freeform Fabrication ◽  
Experimental Investigations ◽  
Main Process ◽  
Layer By Layer ◽  
Freeform Fabrication ◽  
Quality Aspects ◽  
Laser Solid Freeform Fabrication

Laser Solid Freeform Fabrication (LSFF) is a flexible rapid prototyping technique in which a laser beam is used to melt and deposit the injected powder in a layer-by-layer fashion to form 3D components. In this paper, the effects of the main process parameters such as laser power and traverse speed on the surface finish of the parts fabricated using the LSFF process are investigated. Since these process parameters and their variations determine the microstructure and other resultant physical qualities of the fabricated parts, they should carefully be selected to increase the surface quality without compromising other quality aspects of the outcomes. For this purpose, along with the experimental analyses, an experimentally verified 3D time-dependent numerical model is employed to comprehensively study the temperature distributions, thermal stress fields, and their variations resulted from different process parameters and consequently different surface finishes. The experimental investigations are conducted through the fabrications of several thin walls of AISI 303L stainless steel using a fiber laser with a maximum power of 1100 W. The numerical and experimental results show under a constant power feed rate by increasing the process speed while optimizing the laser power, the surface finish of the fabricated parts can improve without compromising the melt pool conditions.

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