Effects of Melt Pool Variables and Process Parameters in Laser Direct Metal Deposition of Aerospace Alloys

Derived from laser cladding, the Direct Metal Deposition (DMD) laser process, is based upon a laser beam – projected powder interaction, and allows manufacturing complex 3D shapes much faster than conventional processes. However, the surface finish remains critical, and DMD parts usually necessitate post-machining steps. In this context, the focus of our work was: (1) to understand the physical mechanisms responsible for deleterious surface finishes, (2) to propose different experimental solutions for improving surface finish. Our experimental approach is based upon: (1) adequate modifications of the DMD conditions (gas shielding, laser conditions, coaxial or off-axis nozzles), (2) a characterization of laser-powder-melt-pool interactions using fast camera analysis, (3) a precise check of surface aspects using 3D profilometry, SEM, (4) preliminary thermo-convective simulations to understand melt-pool hydrodynamics. Most of the experimental tests were carried out on a Ti6Al4V titanium alloy, widely investigated already. Results confirm that surface degradation depends on two aspects: the sticking of non-melted or partially melted particles on the free surfaces, and the formation of menisci with more or less pronounced curvature radii. Among other aspects, a reduction of layer thickness and an increase of melt-pool volumes to favor re-melting processes are shown to have a beneficial effect on roughness parameters.

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Thermal Analysis and Verification for Direct Metal Deposition of 0Cr18Ni9 Stainless Steel

Volume 1: Additive Manufacturing; Manufacturing Equipment and Systems; Bio and Sustainable Manufacturing ◽

10.1115/msec2019-2892 ◽

2019 ◽

Author(s):

Jin Wang ◽

Jing Shi ◽

Yi Wang ◽

Yun Bai

Keyword(s):

Stainless Steel ◽

Additive Manufacturing ◽

Temperature Distribution ◽

Process Parameters ◽

Thermal Stresses ◽

Infrared Camera ◽

Dimensional Accuracy ◽

Metal Deposition ◽

Direct Metal Deposition ◽

Heating And Cooling

Abstract Due to rapid cyclic heating and cooling in metal additive manufacturing processes, such as selective laser melting (SLM) and direct metal deposition (DMD), large thermal stresses will form and this may lead to the loss of dimensional accuracy or even cracks. The integration of numerical analysis and experimental validation provides a powerful tool that allows the prediction of defects, and optimization of the component design and the additive manufacturing process parameters. In this work, a numerical simulation on the thermal process of DMD of 0Cr18Ni9 stainless steel is conducted. The simulation is based on the finite volume method (FVM). An in-house code is developed, and it is able to calculate the temperature distribution dynamically. The model size is 30mm × 30mm × 10.5mm, containing 432,000 cells. A DMD experiment on the material with the same configuration and process parameters is also carried out, during which an infrared camera is adopted to obtain the surface temperature distribution continuously, and thermocouples are embedded in the baseplate to record the temperature histories. It is found that the numerical results agree with the experimental results well.

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An analytical model of the melt pool and single track in coaxial laser direct metal deposition (LDMD) additive manufacturing

Journal of Micromechanics and Molecular Physics ◽

10.1142/s2424913017500138 ◽

2017 ◽

Vol 02 (04) ◽

pp. 1750013 ◽

Cited By ~ 4

Author(s):

Jian Liu ◽

Erica Stevens ◽

Qingchen Yang ◽

Markus Chmielus ◽

Albert C. To

Keyword(s):

Analytical Model ◽

Interaction Model ◽

Source Model ◽

Metal Deposition ◽

Direct Metal Deposition ◽

Single Track ◽

Gaussian Laser Beam ◽

Track Geometry ◽

Geometry Model ◽

Melt Pool

An analytical model was developed for the melt pool and single scan track geometry as a function of process parameters. For computational efficiency, the developed model has simple mathematical forms with essential physics taken into account, without the need for complicated numerical simulation. In this research, a non-diverging Gaussian laser beam and coaxial diverging Gaussian powder stream combination is used to represent the coaxial laser direct metal deposition (LDMD) process. Analytical laser-powder interaction model is used to obtain the distribution of attenuated laser intensity and temperature of heated powders at the substrate. On the substrate, the melt pool is calculated by integrating Rosenthal's point heat source model. An iterative procedure is used to ensure the mass–energy balances and to calculate the melt pool and catchment efficiency. By assuming that the assimilated powder will reshape due to surface tension before solidification, a simple clad geometry model is established. The proposed model is used to simulate the geometry of single track depositions of Ti6Al4V, which shows a good agreement between model prediction and experimental results. This work demonstrates that the developed model has the potential to be used to narrow the parameter space for process optimization.

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Planning the process parameters for the direct metal deposition of functionally graded parts based on mathematical models

Journal of Manufacturing Processes ◽

10.1016/j.jmapro.2017.11.001 ◽

2018 ◽

Vol 31 ◽

pp. 56-71 ◽

Cited By ~ 7

Author(s):

Jingyuan Yan ◽

Ilenia Battiato ◽

Georges M. Fadel

Keyword(s):

Mathematical Models ◽

Process Parameters ◽

Metal Deposition ◽

Functionally Graded ◽

Direct Metal Deposition

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Melt Pool Temperature Control for Laser Metal Deposition Processes—Part I: Online Temperature Control

Journal of Manufacturing Science and Engineering ◽

10.1115/1.4000882 ◽

2010 ◽

Vol 132 (1) ◽

Cited By ~ 37

Author(s):

Lie Tang ◽

Robert G. Landers

Keyword(s):

Temperature Control ◽

Process Parameters ◽

Process Model ◽

Dynamic Balance ◽

Metal Deposition ◽

Time Varying ◽

Laser Metal Deposition ◽

Melt Pool ◽

Melt Pool Temperature ◽

Deposition Processes

Melt pool temperature is of great importance to deposition quality in laser metal deposition processes. To control the melt pool temperature, an empirical process model describing the relationship between the temperature and process parameters (i.e., laser power, powder flow rate, and traverse speed) is established and verified experimentally. A general tracking controller using the internal model principle is then designed. To examine the controller performance, three sets of experiments tracking both constant and time-varying temperature references are conducted. The results show the melt pool temperature controller performs well in tracking both constant and time-varying temperature references even when process parameters vary significantly. However a multilayer deposition experiment illustrates that maintaining a constant melt pool temperature does not necessarily lead to uniform track morphology, which is an important criteria for deposition quality. The reason is believed to be that different melt pool morphologies may have the same temperature depending on the dynamic balance of heat input and heat loss.

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Influence of Process Conditions on the Local Solidification and Microstructure During Laser Metal Deposition of an Intermetallic TiAl Alloy (GE4822)

Metallurgical and Materials Transactions A ◽

10.1007/s11661-021-06139-2 ◽

2021 ◽

Vol 52 (3) ◽

pp. 1106-1116

Author(s):

Silja-Katharina Rittinghaus ◽

Jonas Zielinski

Keyword(s):

Heat Treatment ◽

Additive Manufacturing ◽

Process Parameters ◽

Titanium Aluminides ◽

Metal Deposition ◽

Experimental Investigations ◽

Process Conditions ◽

Laser Metal Deposition ◽

Melt Pool ◽

Temperature Regimes

AbstractTemperature-time cycles are essential for the formation of microstructures and thus the mechanical properties of materials. In additive manufacturing, components undergo changing temperature regimes because of the track- and layer-wise build-up. Because of the high brittleness of titanium aluminides, preheating is used to prevent cracking. This also effects the thermal history. In the present study, local solidification conditions during the additive manufacturing process of Ti-48Al-2Cr-2Nb with laser metal deposition (LMD) are investigated by both simulation and experimental investigations. Dependencies of the build-up height, preheating temperatures, process parameters and effects on the resulting microstructure are considered, including the heat treatment. Solidification conditions are found to be dependent on the build height and thus actual preheating temperature, process parameters and location in the melt pool. Influences on both chemical composition and microstructure are observed. Resulting differences can almost be balanced through post heat treatment.

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