Northeastern University Background
Cold spray is an additive manufacturing technology used for building metal and cermet (metal/ceramic mix) materials onto solid surfaces, repairing high value components, and printing metal and composite 3D structures. Metal and cermet particles of 1 to 150 micrometers are accelerated through convergent-divergent supersonic nozzle to achieve very high velocities. Particles deform and adhere to the targeted surface and to each other and generate low porosity and high strength depositions. Nozzle manipulation with a robot allows to build material in a desired geometry to perform repairs of worn/eroded surfaces, build coatings, or additively manufacture components. This process is followed for repairing, coating, and component manufacturing.
A major challenge in cold spray processing for materials that require high impact velocities is caused by tendency of some powder materials (e.g. Ti-6Al-4V powders) to wear or clog the supersonic spray nozzles when high gas temperatures and pressures are used.
Aluminum powders tend to clog nozzles made of hard materials when cold spray process gas temperatures are sufficiently high in high pressure systems. Thermoplastics are generally used for cold spraying aluminum powders. However, thermoplastics (such as PBI “polybenzimidazole”) have temperature limitations (425 °C) and nozzles wear quickly when used near glass transition temperatures.
Internally Cooled Aerodynamically Centralizing (ICCN) nozzles perform well in both keeping nozzle internal wall surfaces cool while drastically reducing particle-nozzle interactions by forcing particles away from the nozzle walls. Hence, this design is a viable and realistic option to resolve clogging and wear problems experienced in the deposition of a number of materials including nickel, titanium, and aluminum. The ICCN nozzle design produces very low internal nozzle temperatures where high velocity particles will come in contact with the nozzle wall. This keeps particulates away from the nozzle internal surfaces by aerodynamically forcing particles towards the center of the nozzle.
The capability of these nozzles to aerodynamically centralize particles to produce small footprint depositions will allow cold spray users to build 3D structures with high resolution. This will also allow for additively manufacturing smaller cold spray deposited structures and components.
In addition, single or multiple set of cold gas injection channels can be machined into cold spray nozzles to form a cold gas skin inside the nozzle and keep hot gas separated from the nozzle surfaces.
This invention will enable the cold spray systems to produce coatings and components that were previously problematic.
Controls injection location and injection rate to centralize particles and produce small footprint depositions for additive manufacturing of 3D structures with high resolution
Dynamically changes the effective orifice size by increasing/decreasing coolant injection rate near the nozzle throat providing more control over gas/particle flow conditions.
Increases manufacturing rates while decreasing labor time and material waste
Reduces the thermoplastic nozzles wear rapidly and the resultant unpredictable deposition properties
Enables the cold spray systems to produce coatings and components that were previously problematic
Useful in military equipment, biomedical applications, electronics manufacturing and 3D printing of metal parts