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Solid Free-Form Fabrication of DOD Weapon System Components from Low-Cost Titaniumby John Krstulich and Corby Anderson
Most future combat vehicles have weight problems. The Army weapons systems of the future will require improvements in transportability, maneuverability, and durability. Micro Unmanned Aerial Vehicles (UAV) have proven invaluable for forward reconnaissance during military operations. Durability, weight, and dimensional features of the components for micro UAV’s could be improved with free-form fabrication using titanium-based alloys. This is just one of the many military applications for this technology. Titanium-based alloys exhibit the exceptionally favorable strength-to-weight ratio, low density, as well as, superior resistance to erosion and impingement attack. It also displays outstanding resistance to a broad range of acids, alkalis, industrial chemicals, natural waters, and marine atmospheres. The current high costs associated with titanium-based alloys remain the main obstacle for widespread use as a material of construction. Although relatively high costs originate in the extraction and refining for the titanium based metal, the highest expenditures can be found in the fabrication of components.
Titanium Fabrication
Due to its high reactivity in the molten state, high melting temperature and low mold filling properties, special techniques must be employed in the titanium casting process. The most common technique is vacuum arc “skull melting” using centrifugal casting. Costs involved with this technique include a high energy requirement to melt the titanium, high cost for manufacturing the mold (including specialized mold materials), and moderately high scrap percentage generated. The design complexities of titanium component make it expensive to machine through conventional milling techniques. A considerable amount of stock must be removed from primary forms such as forgings, plates, bars, etc. In some instances, as much as 50 to 90% of the primary forms’ weight ends up as chips. Near-net-shape fabrication techniques utilizing powder metals have shown the most promise in reducing the cost of fabricating titanium components. Traditional powder metallurgy techniques still require use of a mold, which limits the shape complexity of the titanium component.
Low Cost Titanium coupled with Rapid Fabrication using Three Dimensional Printing
Free form fabrication is a growing technology that can be applied to weapons systems manufacturing. This technology utilizes digital information derived from 3D CAD data or data from 3D digitizing systems. Specialized software converts the 3D data into layered 2D data. This layered data is used by a variety of processes that join liquid, powder, or sheet materials to form parts comprised of plastic, metal, ceramic, or composite parts, in a layer upon layer manner. Titanium-based component fabrication with a three-dimensional printing machine, using of metals powders, and the layer-by-layer methodology, will result in a near-net shape component. For titanium components, the parts will then be subjected to a low-temperature binder removal followed by a high-temperature vacuum furnace sintering and completed by a hot isostatically press furnace stage (see Figure 1). The process holds promise to reduce the fabrication costs for titanium components. This method is a more economical titanium fabrication technique when compared to current casting methods.
The Center for Advanced Mineral and Metallurgical Processing at Montana Tech has been funded by the U.S. Department of Defense through the Army Research Laboratory to explore the use of free form technology for low cost production of complex titanium components. The Army goal is to drastically reduce the cost and time to manufacture of weapon system components, spare parts, and tooling for the fabrication and maintenance of weapon systems. In collaboration with Ex One, we have acquired a titanium compatible printing machine based on Ex One’s Three Dimensional Printing fabrication technology (3DP™). This titanium research initiative will result in the establishment of a national center of excellence. A key thrust of the effort will be to focus on technologies suitable for making titanium and titanium alloys as inexpensive commodity metals for general use, rather than as exotic materials to be used only when their high performance is required despite their present high cost.
Figure 1 – Ex One ProMetal R2 Free-Form Fabrication Process
For the current year, the focus will be on creating a fully-dense part, via thermal processing, by equipment to be procured through project funding. |
