A numerical investigation of thermal property effects on melt pool characteristics in powder-bed electron beam additive manufacturing

2016 ◽  
Vol 232 (9) ◽  
pp. 1615-1627 ◽  
Author(s):  
Bo Cheng ◽  
Kevin Chou
Keyword(s):  
Thermal Conductivity ◽  
Electron Beam ◽  
Thermal Properties ◽  
Additive Manufacturing ◽  
Melting Point ◽  
Thermal Property ◽  
Manufacturing Process ◽  
Powder Bed ◽  
Melt Pool ◽  
Melt Pool Size

Powder-bed electron beam additive manufacturing has the potential to be a cost-effective alternative in producing complex-shaped, custom-designed metal parts using various alloys. Material thermal properties have a rather sophisticated effect on the thermal characteristics such as the melt pool geometry in fabrications, impacting the build part quality. The objective of this study is to achieve a quantitative relationship that can correlate the material thermal properties and the melt pool geometric characteristics in the electron beam additive manufacturing process. The motivation is to understand the interactions of material property effect since testing individual properties is insufficient because of the change of almost all thermal properties when switching from one to the other material. In this research, a full-factorial simulation experiment was conducted to include a wide range of the thermal properties and their combinations. A developed finite element thermal model was applied to perform electron beam additive manufacturing process thermal simulations incorporating tested thermal properties. The analysis of variance method was utilized to evaluate different thermal property effects on the simulated melt pool geometry. The major results are summarized as follows. (1) The material melting point is the most dominant factor to the melt pool size. (2) The role of the material thermal conductivity may outweigh the melting point and strongly affects the melt pool size, if the thermal conductivity is very high. (3) Regression equations to correlate the material properties and the melt pool dimension and shape have been established, and the regression-predicted results show a reasonable agreement with the simulation results for tested real-world materials. However, errors still exist for materials with a small melt pool such as copper.

On Process Temperature in Powder-Bed Electron Beam Additive Manufacturing: Model Development and Validation

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
Bo Cheng ◽  
Steven Price ◽  
James Lydon ◽  
Kenneth Cooper ◽  
Kevin Chou
Keyword(s):  
Thermal Conductivity ◽  
Electron Beam ◽  
Additive Manufacturing ◽  
Thermal Characteristics ◽  
Pool Size ◽  
Process Temperature ◽  
Thermal Imager ◽  
Powder Bed ◽  
Melt Pool ◽  
Melt Pool Size

Powder-bed beam-based metal additive manufacturing (AM) such as electron beam additive manufacturing (EBAM) has a potential to offer innovative solutions to many challenges and difficulties faced in the manufacturing industry. However, the complex process physics of EBAM has not been fully understood, nor has process metrology such as temperatures been thoroughly studied, hindering part quality consistency, efficient process development and process optimizations, etc., for effective EBAM usage. In this study, numerical and experimental approaches were combined to research the process temperatures and other thermal characteristics in EBAM using Ti–6Al–4V powder. The objective of this study was to develop a comprehensive thermal model, using a finite element (FE) method, to predict temperature distributions and history in the EBAM process. On the other hand, a near infrared (NIR) thermal imager, with a spectral range of 0.78 μm–1.08 μm, was employed to acquire build surface temperatures in EBAM, with subsequent data processing for temperature profile and melt pool size analysis. The major results are summarized as follows. The thermal conductivity of Ti–6Al–4V powder is porosity dependent and is one of critical factors for temperature predictions. The measured thermal conductivity of preheated powder (of 50% porosity) is 2.44 W/m K versus 10.17 W/m K for solid Ti–6Al–4V at 750 °C. For temperature measurements in EBAM by NIR thermography, a method was developed to compensate temperature profiles due to transmission loss and unknown emissivity of liquid Ti–6Al–4V. At a beam speed of about 680 mm/s, a beam current of about 7.0 mA and a diameter of 0.55 mm, the peak process temperature is on the order around 2700 °C, and the melt pools have dimensions of about 2.94 mm, 1.09 mm, and 0.12 mm, in length, width, and depth, respectively. In general, the simulations are in reasonable agreement with the experimental results with an average error of 32% for the melt pool sizes. From the simulations, the powder porosity is found critical to the thermal characteristics in EBAM. Increasing the powder porosity will elevate the peak process temperature and increase the melt pool size.

On Process Temperature in Powder-Bed Electron Beam Additive Manufacturing: Process Parameter Effects

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
Steven Price ◽  
Bo Cheng ◽  
James Lydon ◽  
Kenneth Cooper ◽  
Kevin Chou
Keyword(s):  
Electron Beam ◽  
Additive Manufacturing ◽  
Surface Morphology ◽  
Recent Work ◽  
Thermal Characteristics ◽  
Beam Current ◽  
Process Temperature ◽  
Powder Bed ◽  
Melt Pool ◽  
Melt Pool Size

Build part certification has been one of the primary roadblocks for effective usage and broader applications of metal additive manufacturing (AM) technologies including powder-bed electron beam additive manufacturing (EBAM). Process sensitivity to operating parameters, among others such as powder stock variations, is one major source of property scattering in EBAM parts. Thus, it is important to establish quantitative relations between the process parameters and process thermal characteristics that are closely correlated with the AM part properties. In this study, the experimental techniques, fabrications, and temperature measurements, developed in recent work (Cheng et al., 2014, "On Process Temperature in Powder-Bed Electron Beam Additive Manufacturing: Model Development and Experimental Validation," ASME J. Manuf. Sci. Eng., (in press)) were applied to investigate the process parameter effects on the thermal characteristics in EBAM with Ti-6Al-4 V powder, using the system-specific setting called “speed function (SF)” index that controls the beam speed and the beam current during a build. EBAM parts were fabricated using different levels of SF index (20–65) and examined in the part surface morphology and microstructures. In addition, process temperatures were measured by near infrared (NIR) thermography with further analysis of the temperature profiles and the melt pool size. The thermal model, also developed in recent work, was further employed for EBAM temperature predictions, and then compared with the experimental results. The major results are summarized as follows. SF index noticeably affects the thermal characteristics in EBAM, e.g., a melt pool length of 1.72 mm and 1.26 mm for SF20 and SF65, respectively, at 24.43 mm build height. SF setting also strongly affects the EBAM part quality including the surface morphology, surface roughness and part microstructures. In general, a higher SF index tends to produce parts of rougher surfaces with more pore features and large β grain columnar widths. Increasing the beam speed will reduce the peak temperatures, also reduce the melt pool sizes. Simulations conducted to evaluate the beam speed effects are in reasonable agreement compared to the experimental measurements in temperatures and melt pools sizes. However, the results of a lower SF case, SF20, show larger differences between the simulations and the experiments, about 58% for the melt pool size. Moreover, the higher the beam current, the higher the peak process temperatures, also the larger the melt pool. On the other hand, increasing the beam diameter monotonically decreases the peak temperature and the melt pool length.

scholarly journals Feedback Control of Melt Pool Area in Selective Laser Melting Additive Manufacturing Process

Processes ◽  
2021 ◽  
Vol 9 (9) ◽  
pp. 1547
Author(s):  
Syed Zahid Hussain ◽  
Zareena Kausar ◽  
Zafar Ullah Koreshi ◽  
Shakil R. Sheikh ◽  
Hafiz Zia Ur Rehman ◽  
...  
Keyword(s):  
Additive Manufacturing ◽  
Feedback Control ◽  
Selective Laser Melting ◽  
Manufacturing Process ◽  
Thermal Model ◽  
Laser Melting ◽  
Powder Bed ◽  
Melt Pool ◽  
Melt Pool Size ◽  
Pool Area

Selective laser melting (SLM), a metal powder fusion additive manufacturing process, has the potential to manufacture complex components for aerospace and biomedical implants. Large-scale adaptation of these technologies is hampered due to the presence of defects such as porosity and part distortion. Nonuniform melt pool size is a major cause of these defects. The melt pool size changes due to heat from the previous powder bed tracks. In this work, the effect of heat sourced from neighbouring tracks was modelled and feedback control was designed. The objective of control is to regulate the melt pool cross-sectional area rejecting the effect of heat from neighbouring tracks within a layer of the powder bed. The SLM process’s thermal model was developed using the energy balance of lumped melt pool volume. The disturbing heat from neighbouring tracks was modelled as the initial temperature of the melt pool. Combining the thermal model with disturbance model resulted in a nonlinear model describing melt pool evolution. The PID, a classical feedback control approach, was used to minimize the effect of intertrack disturbance on the melt pool area. The controller was tuned for the desired melt pool area in a known environment. Simulation results revealed that the proposed controller regulated the desired melt pool area during the scan of multiple tracks of a powder layer within 16 milliseconds and within a length of 0.04 mm reducing laser power by 10% approximately in five tracks. This reduced the chance of pore formation. Hence, it enhances the quality of components manufactured using the SLM process, reducing defects.

Thermofluid Properties of Ti-6Al-4V Melt Pool in Powder-Bed Electron Beam Additive Manufacturing

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
M Shafiqur Rahman ◽  
Paul J. Schilling ◽  
Paul D. Herrington ◽  
Uttam K. Chakravarty
Keyword(s):  
Electron Beam ◽  
Additive Manufacturing ◽  
Heat Source ◽  
Thermal Behavior ◽  
Source Parameters ◽  
Three Dimensional ◽  
Full Density ◽  
Layer By Layer ◽  
Powder Bed ◽  
Melt Pool

Electron beam additive manufacturing (EBAM) is a powder-bed fusion additive manufacturing (AM) technology that can make full density metallic components using a layer-by-layer fabrication method. To build each layer, the EBAM process includes powder spreading, preheating, melting, and solidification. The quality of the build part, process reliability, and energy efficiency depends typically on the thermal behavior, material properties, and heat source parameters involved in the EBAM process. Therefore, characterizing those properties and understanding the correlations among the process parameters are essential to evaluate the performance of the EBAM process. In this study, a three-dimensional computational fluid dynamics (CFD) model with Ti-6Al-4V powder was developed incorporating the temperature-dependent thermal properties and a moving conical volumetric heat source with Gaussian distribution to conduct the simulations of the EBAM process. The melt pool dynamics and its thermal behavior were investigated numerically, and results for temperature profile, melt pool geometry, cooling rate and variation in density, thermal conductivity, specific heat capacity, and enthalpy were obtained for several sets of electron beam specifications. Validation of the model was performed by comparing the simulation results with the experimental results for the size of the melt pool.

Thermal Modeling of Electron Beam Additive Manufacturing Process: Powder Sintering Effects

2012 ◽  
Author(s):  
Ninggang Shen ◽  
Kevin Chou
Keyword(s):  
Electron Beam ◽  
Additive Manufacturing ◽  
High Energy ◽  
Maximum Temperature ◽  
Beam Diameter ◽  
Moving Heat Source ◽  
Metal Powders ◽  
Melt Pool ◽  
Metallic Parts ◽  
Melt Pool Size

In recently developed Additive Manufacturing (AM) technologies, high-energy sources have been used to fabricate metallic parts, in a layer by layer fashion, by sintering and/or melting metal powders. In particular, Electron Beam Additive Manufacturing (EBAM) utilizes a high-energy electron beam to melt and fuse metal powders to build solid parts. EBAM is one of a few AM technologies capable of making full-density metallic parts and has dramatically extended their applications. Heat transport is the center of the process physics in EBAM, involving a high-intensity, localized moving heat source and rapid self-cooling, and is critically correlated to the part quality and process efficiency. In this study, a finite element model was developed to simulate the transient heat transfer in a part during EBAM subject to a moving heat source with a Gaussian volumetric distribution. The developed model was first examined against literature data. The model was then used to evaluate the powder porosity and the beam size effects on the high temperature penetration volume (melt pool size). The major findings include the following. (1) For the powder layer case, the melt pool size is larger with a higher maximum temperature compared to a solid layer, indicating the importance of considering powders for the model accuracy. (2) With the increase of the porosity, temperatures are higher in the melt pool and the molten pool sizes increase in the depth, but decrease along the beam moving direction. Furthermore, both the heating and cooling rates are higher for a lower porosity level. (3) A larger electron-beam diameter will reduce the maximum temperature in the melt pool and temperature gradients could be much smaller, giving a lower cooling rate. However, for the tested electron beam-power level, the beam diameter around 0.4 mm could be an adequate choice.

Thermal Analysis of Electron Beam Additive Manufacturing Using Ti-6Al-4V Powder-Bed

2017 ◽  
Author(s):  
M. Shafiqur Rahman ◽  
Paul J. Schilling ◽  
Paul D. Herrington ◽  
Uttam K. Chakravarty
Keyword(s):  
Electron Beam ◽  
Additive Manufacturing ◽  
Three Dimensional ◽  
Vital Role ◽  
Full Density ◽  
Rate Variation ◽  
Layer By Layer ◽  
Powder Bed ◽  
Part Quality ◽  
Melt Pool

Electron Beam Additive Manufacturing (EBAM) is one of the emerging additive manufacturing (AM) technologies that is uniquely capable of making full density metallic components using layer-by-layer fabrication method. To build each layer, the process includes powder spreading, pre-heating, melting, and solidification. The thermal and material properties involved in the EBAM process play a vital role to determine the part quality, reliability, and energy efficiency. Therefore, characterizing the properties and understanding the correlations among the process parameters are incumbent to evaluate the performance of the EBAM process. In this study, a three dimensional computational fluid dynamics (CFD) model with Ti-6Al-4V powder has been developed incorporating the temperature-dependent thermal properties and a moving conical volumetric heat source with Gaussian distribution to conduct the simulations of the EBAM process. The melt-pool dynamics and its thermal behavior have been investigated numerically using a CFD solver and results for temperature profile, cooling rate, variation in density, thermal conductivity, specific heat capacity, and enthalpy have been obtained for a particular set of electron beam specifications.

scholarly journals A Single Crystal Process Window for Electron Beam Powder Bed Fusion Additive Manufacturing of a CMSX-4 Type Ni-Based Superalloy

Materials ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 3785
Author(s):  
Julian Pistor ◽  
Christoph Breuning ◽  
Carolin Körner
Keyword(s):  
Additive Manufacturing ◽  
Single Crystal ◽  
Single Crystals ◽  
Process Window ◽  
Powder Bed Fusion ◽  
Powder Bed ◽  
Melt Pool ◽  
High Fraction ◽  
Scanning Strategies ◽  
Melt Pool Size

Using suitable scanning strategies, even single crystals can emerge from powder during additive manufacturing. In this paper, a full microstructure map for additive manufacturing of technical single crystals is presented using the conventional single crystal Ni-based superalloy CMSX-4. The correlation between process parameters, melt pool size and shape, as well as single crystal fraction, is investigated through a high number of experiments supported by numerical simulations. Based on these results, a strategy for the fabrication of high fraction single crystals in powder bed fusion additive manufacturing is deduced.

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