This Small Business Innovation Research (SBIR) Phase I project seeks to advance manufacturing processes in the dissimilar metal/impact welding industries via an aluminum/water reaction that chemically produces hydrogen energy. Ideally, the energy in the form of about 100 kpsi-200 kpsi, could be the source of power for a small high-velocity impact bonding machine to metallurgically bond dissimilar metals. Current impact bonding methods such as explosive welding have not led to machines for bonding near-net-shaped parts, but rather a process of preparing large raw materials to be cut into the desired smaller parts. Disadvantages associated with explosives include safety issues, long lead-times, high costs, material waste, and reliance on imports. A high-velocity impact bonding machine could revolutionize the manufacturing of smaller, discrete parts opening new avenues for design engineers. Experiments will be conducted to establish the ideal conditions for impact induced interlocking micro-bonds, e.g., between Copper and Stainless Steel. The variable test parameters of this project include: (a) flyer velocity (implicitly determined by hydrogen pressure), (b) impact angle between the flyer plate and the anvil or base material, (c) standoff distance between flyer and anvil material, and (d) surface topography. The results will lead to optimized conditions for wavy-joint morphology of dissimilar metals
The broader impact/commercial potential of this project is attributed to the utilization of a new energy source that will transform how some manufacturing processes are powered. The advancement of an aluminum/water reaction to replace explosives or complex pressure, heat or electrical sources for electrical, friction, heat or impact bonding methods of manufacturing dissimilar metal components will prove to have many benefits by developing a safe, user-friendly and environmentally-friendly bonding machine. Additionally, impact loading for other processes such as forging and hydroforming that use high pressure fluid will capitalize on these benefits as well. The introduction of this machinery will provide a versatile assembly-line manufacturing capability with advantages to include: (a) substantial cost savings, (b) motivating small U.S. manufacturing companies to produce discrete parts within the U.S., (c) potential for new designs of customized parts otherwise infeasible, (d) a low skilled operation for small facilities eliminating long lead-times, and (e) the potential for other manufacturing processes that could use this platform technology. Dissimilar/bi-metallic parts are in high demand in the chemical, automotive, aircraft, marine, and nuclear industries due to their high conductivity and galvanic corrosion resistance and favorable mechanical properties contained in one part.
This research project incorporates an innovative technique of utilizing chemically produced hydrogen energy by reacting aluminum powder and water for impact bonding of dissimilar metals. Advanced Hydrogen Technologies Corporation (AHTC) has developed a cartridge based system that can produce enormous hydrogen power instantly via aluminum-water reaction. The AHTC Cartridge for the Generation of Hydrogen was used as the source of energy to impact copper flyers into stainless steel billets at a sufficient velocity to remove the oxide coating on the metals being bonded and create an intermetallic bond. Figure 1 shows the experimental setup which consists of a bonding chamber, barrel, cartridge, 9-volt battery, and copper and stainless steel samples. A 9-volt battery was used to heat a micro-filament embedded inside a chemical igniter within the cartridge thereby rapidly raising the temperature to initiate the Al-H2O reaction. Upon initiation, the aluminum powder and water reacted to release large amounts of high pressure hydrogen gas in small fractions of a second. The hydrogen gas was the source of the acceleration that caused the flyer to reach velocities comparable to those of flyer plates used in explosive welding. As a result, an impact bond was achieved that showed wave morphology at the joint. The bonded samples and cartridge are then removed and replaced for the next cycle. The near-net-shape bonding of copper and stainless steel billets, shown in Figure 2, was carried out by AHTC, while the analyses of the bonded parts were carried out by North Carolina State University. The integrity of an impact bonded joint can be assessed, in part, by the morphological structure of the bond. Figure 3(i) shows a sector cut from a bonded sample. Along the marked locations A to I, optical micrographs were taken to study the bond morphology. As seen in Figure 3(ii-iv) the bond exhibits wave morphological patterns, which indicate a good and strong bond. Shear tests were then conducted that confirmed the relation of bond strength to the exhibited wave morphology. The wave morphology observed in all experiments carried out in this study is such that the wave sizes (amplitude and wave length) increase gradually away from the center. Therefore the center of the specimens exhibits smaller waves whereas large waves are observed away from the center (Figure 3iv). The result presented in Figure 3 is for copper flyers with a flyer angle of 9°. The wavelengths varied from 60µm to 290µm, while the wave amplitudes varied from 40µm to 80µm. The experiments have also revealed that increase in flyer angle results in a substantial increase in the wave size. The flyer angles investigated in this study were 9°, 12° and 15°. A novel technique for bonding dissimilar metals using hydrogen energy has been developed. Impact bonding experiments were successfully carried out for copper and stainless steel cylindrical billets. One of the advantages of this technique over the explosive welding method is that bonding via hydrogen energy does not involve explosive substances. The conclusions drawn from this study are: (a) There is a potential to develop a machine for bonding of near-net-shape of discrete parts based on energy produced by reacting aluminum powder and water, (b) The wave morphological structure, which is one of the indicators of a successful bond by correlating with shear strength tests, was observed on all specimens bonded, and they varied in size as a function of location and flyer angle. Another advantage of this technique is that near net to net shapes can be achieved. This advantage drastically reduces or eliminates material waste and machine time. Tests were successfully conducted to restrain the material from distorting in the direction perpendicular to the impact. The planned future work for this investigation includes; carry out impact bonding experiments using different materials; study the influence of billet size and constraining factors on bond morphology and investigate the relationship between billet size and hydrogen energy expended. The ultimate goal of the authors is to develop an automated production machine that will be used for net-shape bonding of discrete parts using hydrogen energy. The development of AHTC's non-explosive bonding process through use in a bonding machine will create an advanced manufacturing technique for joining dissimilar metals. It will allow engineers to fabricate parts on the spot without long lead times in new configurations that were previously not possible. This will positively impact automotive, aerospace, defense, nuclear, marine, and other industries by allowing them to optimize transition joints, use lightweight or stronger materials, create parts in-house, easily conform to safety standards, and save money and time in the process. Society will benefit by having better products formed from this new wave of manufacturing possibilities.
