Additive manufacturing delivers a great deal of freedom when designing and developing parts. You are not always confined to a build platform, though. Some machines and processes deliver what may be the ultimate freedom—free-form fabrication.
By Leslie Langnau, Managing Editor
The freedom to build any geometric shape you desire, especially with metal materials, is one of the advantages of Additive Manufacturing (also known as 3D printing—3DP) over more traditional forms of part production, such as CNCs and injection molding.
Developers of additive manufacturing (AM) machines are coming up with highly creative and innovative ways to build objects, a few involving novel ways to move about X, Y, and Z planes.
Many AM processes for metal materials use a type of powder bed fusion. Here, though, you are still limited by the size of the build table and chamber. What if you didn’t need to worry about height? What if, like a bird flying in the air, you could twist and turn about the X, Y, and Z planes to build objects?
A process known as Blown Powder additive manufacturing can deliver such freedom. Available for a number of years, it differs from powder bed methods in that you do not use a vat of powder which a laser moves across to solidify a specific pattern, layer by layer.
Instead, a powder delivery system, consisting of nozzles that precisely regulate mass flow, blows powder to a central point that intersects with a laser beam. At the point of intersection, the powder is sintered as it is deposited onto a substrate. This substrate can be several things, including the beginning layers of an object or part being built, or an existing part having metal added to it to repair wear or damage.
Optomec is a developer of blown powder AM systems. The Optomec LENS technology is housed in a hermetically sealed chamber purged with argon to keep oxygen and moisture levels below 10 parts per million to prevent oxidation.
The table in the machine can be tilted and rotated, delivering five axis coordinated motion: X, Y, Z, tilt, and rotate. For larger parts that won’t fit on a table, the machines include a rail system, which the blown powder delivery nozzles move about. The largest of Optomec’s machines has a process work envelope of 900 X 1500 X 900 mm (35.43 by 59.06 by 35.43 in.)
The company’s LENS technology builds parts with mechanical properties that are equivalent to wrought for many applications. For example, using this process the Titanium alloy Ti 6-4 has a fatigue strength that matches wrought annealed material based on independent testing. This process is compatible with a number of metals, (stainless steel, tool steels, titanium alloys, cobalt alloys, ceramics, refractory metals, and so on), which can be supplied by a number of vendors. Surface finish ranges from 12 to 25 µm Ra.
The water-cooled deposition head deposits sintered powder at a rate of about 0.5 kg/hr for standard steels, titanium and nickel alloys. Metal objects can be built with a porosity of less than 100 µm. An integrated camera and optics helps you to see the process in operation.
Once you have converted your CAD design into an STL file, the control of the AM machine uses the geometric information in the solid model to automatically build the component layer by layer. The machine control and software convert the STL data into a G code tool path using user-specified layer height and hatch patterns. The part is constructed layer by layer under the control of software that monitors parameters to ensure geometric and mechanical integrity.
Parts can be built fully dense. You can also use this process to add metal material to existing structures, such as metal fan blades or industrial parts to repair them from wear or minor damage, or rework them to correct defects. Or, you can easily use this process to simply add material to make the part larger.
When the build is complete, the component can be removed from the chamber and can then undergo other processes as needed, such as heat-treating, Hot Isostatic Pressing, machining, or finishing in any customary manner.
The LENS technology is the only AM technology to date that is available as a turnkey system configuration or as a modular print engine that can be integrated into existing or new CNC machine tools. This flexibility gives you the ability to deposit metal and machine in the same system.
Combining electronics in a 3DP build
Another use of blowing material to additively create an object is to combine electronics into the AM build. An example is Optomec’s Aerosol Jet Technology.
Aerosol Jet printing can be used to create miniature electronic circuits and components. The process works with a range of functional materials, including conductors, semi-conductors, resistors, dielectrics, and encapsulation materials. These materials can be printed onto virtually any surface material. The fine feature sizes allow novel packaging of discrete SMDs such as integrated circuits, MEMS and sensors onto 3D parts.
The Aerosol Jet process uses aerodynamic focusing to precisely and accurately deposit functional inks. The directions for deposition come directly from the CAD programs. The inks can consist of metals, polymers, ceramics, and even biomaterials.
The ink is placed into an atomizer, which creates a dense aerosol of droplets between 1 and 5 µm in diameter. Aerosol droplet density can approach 10-µm drops per cubic mm. Drops larger than 5 µm cannot overcome the force of gravity and so drop back into the ink and are recycled.
The aerosol is carried by a gas flow to the deposition head. Within the deposition head, the aerosol is focused by a second gas flow (sheath gas), which surrounds the aerosol as an annular ring. When the sheath gas and aerosol pass though the profiled nozzle, the mixture is compressed, which focuses the aerosol. The resulting high velocity converging particle stream is deposited onto the substrate creating the fine features.
Once the materials are deposited, thermal or chemical post-treatments can be done to attain final electrical and mechanical properties and adhesion to the substrate. Aerosol Jet printed electronic systems can locally process the deposition using a laser treatment process that permits the use of substrate materials with very low temperature tolerances, such as polymers. The end result is a high-quality thin film (as fine as 10 nm) with excellent edge definition and near-bulk properties.
During deposition there is no physical contact between the material being printed and the nozzle. This helps to keep the critical area of the print system clean and free of material build up allowing long run times and stable operation.
The use of a process like Aerosol Jet lets you print complex circuits onto 3D structures. But some parts produced on 3DP/AM systems exhibit features that complicate the integration of 3D electronic systems. These features, which Optomec engineers have identified, include:
• Rough and porous surfaces
• Low thermal stability of the powder materials
• High substrate Coefficient of Thermal Expansion (CTE).
Rough and porous surfaces have relatively high surface energy making it difficult for the printed ink to form a clean, even deposit. This is especially true when the surface roughness is much larger than ink thickness.
The relatively low-temperature capability of many polymer-based 3DP/AM materials can also make it difficult to get good electrical properties from the deposited inks.
Like the LENS system, Optemec makes the Aerosol Jet technology available as either a turnkey system or as a modular print engine that can be integrated into automation platforms. The modular architecture is scalable and is designed to enable quick swap out of the Aerosol Jet Print Cassettes from the Print Heads for routine cleaning and ink refill.