Source: Jiangsu Laser Alliance
Vanderbilt University graduate Neeley, who recently earned a PhD in mechanical engineering, has created a welding material for extreme conditions that minimizes hazards for the equipment and operators needed.The material is a safe, stable aluminous paste that can be used as a portable, programmable heat source for use in space, underwater and battle zones.The slurry is 3D-printed and deposited in a pattern called a reactive material framework, which can be controlled and guided.
Traditional welding or brazing requires skilled operators and heavy equipment and is difficult to power, maintain and transport in harsh environments.In order to overcome the cost and complexity of traditional methods, high-energy materials are used as heat sources, often called exothermic brazing.Exothermic brazing USES the heat generated by solid or near-solid reactions to melt the filler material used in the connection process.It can be used to create joints in isolated environments or in physically complex or inaccessible joints.
Previous studies have demonstrated the success of exothermic brazing in space and underwater.Exothermic brazing has also been successfully used for pipeline brazing and exothermic brazing of hydraulic fittings in aircraft.However, this work is limited by the complex fixed demands for energy in and around the joints.With the development of additive manufacturing technology, it is now easy to generate structurally sound energetics with complex geometric shapes.The energetics of digital fabrication tools, known as reactive materials Architecture (RMA), allow for new field connectivity technologies.
RMA is a structure that controls reaction rate and heat by geometric features, not just chemical composition changes.An example of such control is the production of solid rocket fuel particles using additive manufacturing technology, which enables the combustion rate of printed fuel particles to be comparable to that of cast fuel particles.Additive manufacturing techniques can also be used to create unique geometric shapes that cannot be created by casting (such as draping, undercutting, and filling porosity).For chip level conjugations, there have been some APPLICATIONS of RMA in nano level conjugations, but for macro level conjugations there is a need for macro level architectures.
The high-energy material selected for this experiment is a highly viscous aluminothermic slurry consisting of iron oxide (Fe2O3) with a mass ratio of 3:2:2, aluminum powder, and calcium hemihydrate (CaSO4·0.5H2O).All samples were ignited with a small amount of aluminum-thermite and magnesium powder with a magnesium fuse and were printed using a Hyrel Engine SR printer with a SDS-60 injector print head.
Each joint consists of two 2 × 2 × 0.040 “copper sheets arranged in a lap joint.Each joint is cleaned with acetone and then prepared with flux.Four 2-inch solder (KappZapp4, copper with 96Sn/4Ag solid wire solder) are placed at the lap joint.Place the printed sample of thermite on top of the joint and place the entire unit on the sand layer.A metal gasket is placed under the top copper sample to indicate solder melting so that the top and bottom copper samples are parallel after ignition.See Figure 1 below.Another control sample was prepared and prepared in the same manner, except that it was placed in an oven at 240℃ for 2 hours.
The strength of the resulting aluminum-iron joints was similar to that of the control joints. The strongest aluminum-iron joints broke under 4497N load, which was 63.8% of the maximum parent strength sample.Average joint strength is 2212N.Joint strength appears to be primarily determined by solder dispersion at the joint.Figure 3 shows the solder coverage of four samples, three experimental samples and one control sample.Sample 1, as seen in Figure 3B, has excellent joint strength and almost complete coverage, very similar to the control sample seen in Figure 3A.Figure 3C shows sample 3 with medium solder coverage.This is very consistent with the 2760 N binding strength of the sample.Figure 3D shows an example of defective solder coverage.The strength of the corresponding sample (sample 5) is only 1225N, and the distribution of solder is controlled by the heat source and joint setting.
In addition, Neely combined two interests in her graduation project, 34D printing and high-energy materials.The extra dimension is time.The 4D material changes over time, reacts to environmental stimuli such as humidity or temperature and changes shape.She credits Alvin Strauss, a professor of mechanical engineering, and Kevin Galloway, an assistant professor of mechanical engineering, as well as Vanderbilt’s doctoral advisers, with giving the green light to the idea.
Their study Soldered copper Lap Joints using Reactive Material Architectures as a Heat Source was published in Manufacturing Letters in April 2020,”Additively Manufactured Reactive Material Architectures as a Programmable Heat Source” has been released in 3D Printing and Machining Manufacturing in August 2019.
This article source: https://doi.org/10.1016/j.mfglet.2020.02.002