Ralph B. Dinwiddie

The U.S. Department of Energy's Office of Scientific and Technical Information

To reduce the uncertainty of build performance in metal additive manufacturing, robust process monitoring systems that can detect imperfections and improve repeatability are desired. One of the most promising methods for in situ monitoring is thermographic imaging. However, there is a challenge in using this technology due to the difference in surface emittance between the metal powder and solidified part being observed that affects the accuracy of the temperature data collected. The purpose of the present study was to develop a method for properly calibrating temperature profiles from thermographic data to account for this emittance change and to determine important characteristics of the build through additional processing. The thermographic data was analyzed to identify the transition of material from metal powder to a solid as-printed part. A corrected temperature profile was then assembled for each point using calibrations for these surface conditions. Using this data, the thermal gradient and solid-liquid interface velocity were approximated and correlated to experimentally observed microstructural variation within the part. This work shows that by using a method of process monitoring, repeatability of a build could be monitored specifically in relation to microstructure control.

Researchers from Manufacturing Demonstration Facility (MDF) at Oak Ridge National Laboratory (ORNL) worked with Applied Optimization (AO) to understand and evaluate the propensity for defect formation in builds manufactured using DM3D-POM laser direct metal deposition. The main aim of this collaboration was to understand the character of powder jet behavior as a function of the nozzle parameters such as cover gas, carrier gas, and shaping gas. In order to evaluate the sensitivities of the parameters used in model, various experiments were performed with in-situ monitoring of the powder stream characteristics using a high speed camera. A wide variety of conditions while keeping the hopper motor rpm constant, including laser power and travel speed were explored. The cross sections of the deposits were characterized using optical microscopy.

A well-established method for determining the thermal diffusivity of materials is the laser flash method. The work presented here compares two analysis methods for flash heating tests on anisotropic carbon bonded carbon fiber. This material exhibits a higher conductivity in the direction in which the fibers are oriented than in the direction perpendicular to the fiber orientation. Of the two analysis methods used, one method uses the temperature data from the entire surface of the sample by examining 201 temperature histories simultaneously, with each temperature history originating from an individual pixel within a line across the middle of the sample. The other analysis method uses only the temperature history from a single pixel in the center of the sample, similar to the data that is traditionally generated using the classical flash diffusivity method. Both analysis methods include accommodations for modeling the penetration of the laser flash into the porous surface of the carbon bonded carbon fiber material. The robustness of the method using the single-pixel temperature history shows that anisotropic thermal diffusivity can be measured using standard flash diffusivity instruments, if modeled properly, avoiding the additional complexity associated with the use of a thermal imaging camera.

Both mid-wave and long-wave IR cameras are used to measure various temperature profiles in thermoplastic parts as they are printed. Two significantly different 3D-printers are used in this study. The first is a small scale commercially available Solidoodle 3 printer, which prints parts with layer thicknesses on the order of 125μm. The second printer used is a “Big Area Additive Manufacturing” (BAAM) 3D-printer developed at Oak Ridge National Laboratory. The BAAM prints parts with a layer thicknesses of 4.06 mm. Of particular interest is the temperature of the previously deposited layer as the new hot layer is about to be extruded onto it. The two layers are expected have a stronger bond if the temperature of the substrate layer is above the glass transition temperature. This paper describes the measurement technique and results for a study of temperature decay and substrate layer temperature for ABS thermoplastic with and without the addition of chopped carbon fibers.

Non-destructive, in-line quality control methods were adopted for evaluating the thickness and homogeneity of wet and dry lithium secondary battery electrodes. Laser caliper and infrared (IR) thermography methods were implemented in a systematic fashion for the first time to evaluate the quality of electrodes during the coating process on a slot-die coater. Laser caliper sensors were mounted, aligned, and subsequently calibrated at the oven inlet of the coating line in order to examine the thicknesses of different cathodes and anodes. The effect of various factors such as substrate vibration, temperature, surface reflectivity and laser positions on the thickness measurement during slot-die coating were evaluated. The setup was used to monitor the wet thickness of the cathode and anode, and the precision of the in-line laser thickness measurement was determined to be less than ±2%. Thickness deviation for cathodes was typically ±2.0–2.3%, and for anodes it was typically ±2.2–2.6%, which confirms excellent precision of the measurement. The homogeneity of the dried electrodes was also evaluated by IR thermography at the oven outlet of the coating line. Temperature profiles from thermography images of dry electrodes were carefully examined to detect any flaws and inhomogeneity present in the electrodes. An increase or decrease in the temperature profiles indicated defects/flaws in the electrodes that could not be observed in optical images. The techniques applied in this work will be helpful for detection of electrode flaws and contamination during large-scale manufacturing and to identify flawed product prior to lithium-ion cell assembly.

Oak Ridge National Laboratory (ORNL) has been utilizing the ARCAM electron beam melting technology to additively manufacture complex geometric structures directly from powder. Although the technology has demonstrated the ability to decrease costs, decrease manufacturing lead-time and fabricate complex structures that are impossible to fabricate through conventional processing techniques, certification of the component quality can be challenging. Because the process involves the continuous deposition of successive layers of material, each layer can be examined without destructively testing the component. However, in-situ process monitoring is difficult due to metallization on inside surfaces caused by evaporation and condensation of metal from the melt pool. This work describes a solution to one of the challenges to continuously imaging inside of the chamber during the EBM process. Here, the utilization of a continuously moving Mylar film canister is described. Results will be presented related to in-situ process monitoring and how this technique results in improved mechanical properties and reliability of the process.

An extended-range IR camera was used to make temperature measurements of samples as they are being manufactured. The objective is to quantify the temperature variation of the parts as they are being fabricated. The IR camera was also used to map the temperature within the build volume of the oven. The development of the temperature map of the oven provides insight into the global temperature variation within the oven that may lead to understanding variations in the properties of parts as a function of build location within the oven. The observation of the temperature variation of a part during construction provides insight into how the deposition process itself creates temperature distributions, which can lead to failure.