Manufacturing

EBAM technology is capable of making full-density, functional metallic components for numerous engineering applications; the technology is particularly advantageous in the aerospace, automotive, and biomedical industries where high-value, low-volume, custom-design productions are required. A key challenge in EBAM is overcoming deformation of overhangs that are the result of severe thermal gradients generated by the poor thermal conductivity of metallic powders used in the fabrication process. Conventional support structures (Figure 1a) address the deformation challenge; however, they are bonded to the component and need to be removed in post- processing using a mechanical tool. This process is laborious, time consuming, and degrades the surface quality of the product. The invented support design (Figure 1b) fabricates a support underneath an overhang by building the support up from the build plate and placing a support surface underneath an overhang with a certain gap (no contact with overhang). The technology deposits one or more layers of un-melted metallic powder in an elongate gap between an upper horizontal surface of the support structure and a lower surface of the overhang geometry. The support structure acts as a heat sink to enhance heat transfer and reduce the temperature and thermal gradients. Because the support structure is not connected to the part, the support structure can be removed freely without any post-processing step. Future work will compare experimental data with simulation results in order to validate process models as well as to study process parameter effects on the thermal characteristics of the EBAM process.

In order for the camera to detect invisible air shocks in an aircraft engine's intake, a fine sheet of laser light is first projected through the airflow. The light is refracted in the densest part of the airflow (the location of the shock), which creates a dark spot that shows up as a dip or negative peak in the pixel intensity profile of the image. The smart camera uses this information to identify a negative going edge and a positive going edge, which is expressed as numeric pixel values within the linear array. Data is output from the circuit as an analog signal or digitally by an onboard microcontroller using a parallel digital bus or a serial interface such as the controller area network (CAN bus), Ethernet, RS-232/485 or USB. Unlike conventional edge detection systems, which rely on both a high-speed camera and a bulky computer or digital signal processor, this innovation uses an analog technique to process images. Its simple, sleek design consists of three basic parts: a linear image sensor, an analog signal processing circuit, and a digital circuit. The result is a smaller, more reliable technology with increased processing frame rates. The design can easily be tailored to the end use, and can be reconfigured to respond to positive and/or negative going edges. Furthermore, the threshold sensitivity can be varied and algorithmically set, making it well suited for a number of other terrestrial applications from transportation to manufacturing.

Via this NASA innovation, a product is first heated to a temperature within the range of 204 to 343 degrees C for an extended soak of up to 16 hours. The product is then slowly heated to a second temperature within the range of 371 to 482 degrees C for a second soak of up to 12 hours. Finally, the product is slowly cooled to a final soak temperature of 204 to 343 degrees C before cooling to room temperature. The product so treated will exhibit greatly improved formability. To date, the low formability issue has limited the use of lightweight Al-Li alloys for large rocket fuel tank dome applications. Manufacturing a dome by stretch forming typically requires multiple panels as well as multiple welding and inspection steps to assemble these panels into a full-scale fuel tank dome. Complex tensile and bending stresses induced during the stretch forming operations of Al-Li alloys have resulted in high rates of failure for this process. To spin form a large rocket dome, the spin blank must be prepared by joining smaller plates together using friction stir welding. However, friction stir welding produces a distinct metallurgical structure inside and around the friction stir weld that makes it very susceptible to cracking during spin forming.

This method provides control over the growth density or tower height of carbon nanotubes (CNTs) on a relatively coarse scale, with density adjustment over several orders of magnitude, using an applied electrical field or voltage difference that is aligned substantially perpendicular to the substrate surface, which is adjacent to the surface during growth. Control or influence of CNT growth density on a finer scale, estimated at a factor of 2 to 10, is provided using temperature control for the CNT growth process. For example, an application of a modest electrical field of between 5 and 20 volts over a transverse electrode- to-electrode gap of about 25 m (electrical field value |E|=(28) x 103 volts/cm) is estimated to change CNT growth density by 1 to 3 orders of magnitude (coarse scale); and variation of CNT source average temperature between 700 degree C and 850 degree C is estimated to change CNT growth density by a multiplicative factor of 2 to 10 (fine scale). A first region may have a first range of CNT densities, and an adjacent region, spaced apart from the first region, may have a second range of CNT densities that partly overlap, or has no overlap at all, with the density range of the first region. The second region has a higher CNT density, and uses variable heating and/or a reduced electrical field to provide the higher CNT density based on an experimentally determined growth curve and experimental configuration of a device. This approach should be distinguished from masking of regions on a substrate, where the result is binary where either a CNT array with a fixed density appears, or no CNTs appear in that region at all. The all-or-nothing approach is fine if the goal is thermal transport because maximum thermal transport benefits if the CNT concentrations are as high as possible. However, if the need is for electron transport (e.g., between adjacent signal processing components on a semiconductor chip), the desired CNT density may lie in an intermediate range, with both a lower bound and an upper bound.

The in situ inspection technology for additive manufacturing combines different types of cameras strategically placed around the part to monitor its properties during construction. The IR cameras collect accurate temperature data to validate thermal math models, while the visual cameras obtain highly detailed data at the exact location of the laser to build accurate, as-built geometric models. Furthermore, certain adopted techniques (e.g., single to grouped pixels comparison to avoid bad/biased pixels) reduce false positive readings. NASA has developed and tested prototypes in both laser-sintered plastic and metal processes. The technology detected errors due to stray powder sparking and material layer lifts. Furthermore, the technology has the potential to detect anomalies in the property profile that are caused by errors due to stress, power density issues, incomplete melting, voids, incomplete fill, and layer lift-up. Three-dimensional models of the printed parts were reconstructed using only the collected data, which demonstrates the success and potential of the technology to provide a deeper understanding of the laser-metal interactions. By monitoring the print, layer by layer, in real-time, users can pause the process and make corrections to the build as needed, reducing material, energy, and time wasted in nonconforming parts.

Friction plug welding is a process in which there is a small rotating part (plug) being spun and simultaneously pulled (forged) into a larger part to fill or repair a hole or join two pieces (functioning like a rivet). Learning from 1,500+ quality &#34known&#34 plug welds, NASA&#146s experts build a load curve that, when combined with the welders&#146 knowledge of strain size, predicts the properties of a plug weld. The software monitors load, spindle speed, torque, displacement speed and distance, and the material properties and dimensions of the sample. The software correlates changes in the process parameters to mechanical testing of ultimate tensile strength. The software works for several Aluminum alloys such as 2015, 2195, and 2219. NASA is using the technology in its current work for closing out the termination hole of some friction stir welds. FPW is also used for repairs and as a potential replacement for rivets.

The process of forming thermal insulation wafer begins with layering a photo resist pattern on an aluminum coated substrate. After the aluminum is etched, a temporary adhesive is applied to the photo resist and substrate. Next, the construction undergoes wafer scale bonding to a silicon insulator. The silicon insulator is then patterned and etched down to the buried oxide layer. The temporary adhesive is then dissolved in acetone. The acetone is diluted with non-polar solvents which are then removed via critical drying. Goddard Space Flight Center has produced multiple arrays of crystalline silicon membranes that were 450 nm thick and were isolated from a silicon support structure by thermal isolation structures that were 30 microns thick and 5 microns long. The largest membranes, among which had 100 % mechanical yield, had an aerial footprint of 1.6 mm x 1.4 mm.

The Pyramid Image Quality Indicator is based on the shape of a tall, 4-sided pyramid. Each side of the pyramid has a pair of vertical trenches which draw closer to each other and get narrower as they approach the tip of the pyramid. Inside the pyramid is a hollowed out conical section which may contain internal features for determining resolution or inserts that can be used for measuring contrast sensitivity. The system can be economically 3D printed and then coated, if need be, with high x-ray absorbing material. When a CT system operator is scanning a part, a specific method for that part which might include a large number of variables such as x-ray voltage, detector-to-source spacing, pixel size, etc. This established method will result in an effective level of detail for the resulting scan. The IQI is used to measure that level of detail. The operator may follow up the scan of the part with an identical scan of the IQI, which will allow a realistic measurement of parameters, like effective resolution or contrast sensitivity. The interior of the Pyramid IQI uses a 3D variant suited for 3D CT scan data tools, known as penetrameters. These penetrameters are a solid disc of material. A stack of discs of different diameters would accommodate a range of different thicknesses. The Pyramid IQI can be easily scaled for either larger or smaller parts. It can also be 3D printed using either plastic or metal additive manufacturing. This allows an end-user to match the material density of the IQI to that of the actual part.

Friction Pull Plug Welding (FPPW) is the process necessary to plug the hole that is left behind as a friction stir weld (FSW) joint is completed and the pin tool of the welder retracts from the joint. FPPW involves a small, rotating part (plug) being spun and simultaneously pulled (forged) into a hole in a larger part. Much work has been done to fully understand and characterize the process and its limitations. FPPW worked very well for building large rocket sections such as the circumferential welds of the upper stages of NASA's Ares rocket, and to repair the external tank. Engineers were challenged to adapt FPPW to accommodate the thicker plates new alloy combinations of the SLS. The new hybrid plug solves the issue of the plugs snapping due to the increase torsion and moment stresses when joining thicker plates. The new hybrid plug, with a steel shank, makes FPPW more practical and robust. The new plug has been used to make space-qualified parts at NASA, and the plug welds are as strong as initial welds.