Again and again, orange-red flashes sparkle, coming closer, making a couple of loops, and receding again. Olaf Rehme from Siemens Corporate Technology observes the seemingly chaotic whirl of sparks that is taking place behind the window of a 3D printer. He watches a laser beam as it moves along, drawing the cross-section of a component into a layer of powdered metal. In doing so, the laser welds the fine particles of metal together. The platform, on which the component is located, drops lower so that a fresh 0.05-millimeter-thick layer of powder can be spread on top. The laser beam then recommences its dance. Layer by layer, the outline in the dark gray powder grows to become a three-dimensional structure. A virtual 3D model provides the template for the laser’s path.
From Powders to Finished Products
3D printers are now being used in manufacturing. They are revolutionizing spare parts management and opening the door to new designs for complex components.
Lasers are increasingly being used in places where objects were previously forged, milled or cast. Laser beam welding creates objects layer by layer. 3D printing has been around since the 1980s. Originally, only rapid-hardening plastic was used for the process, which was ideal for making prototype parts that would later be mass-produced by conventional stamping or injection molding machines.
“But things haven’t stood still,” says Rehme. “Now, 3D printers are not making just the models and molds for individual parts, but the parts themselves. At Siemens, we are even printing burner tips for use as replacement parts in gas turbines.” The all-new technique reduces repair times for certain turbine models by around 90 percent, because the replacement burner tip no longer has to be laboriously welded together. Instead, the new burner tip is simply printed onto the body of the burner, reducing repair costs by a considerable amount.
Some of the parts inside turbines have to operate for a very long time between maintenance intervals. Gas turbine blades, for example must run for 25,000 hours, despite being subjected to temperatures of around 1,300 degrees Celsius. Plastic parts would be inappropriate for such applications, as they would immediately melt. Siemens therefore prints the parts from powdered steel. “We use nickel-based alloys for high-temperature applications in turbines. These types of steel are especially durable and heat-resistant,” says Rehme.
Locally Produced Parts
Burner tips are one of many examples of how 3D printing could revolutionize the supply of spare parts. Today, such parts are stored and delivered individually whenever they are needed. In a worst-case scenario, a factory or plant might have to be switched off until an urgently needed part arrives. “In the future, a network of small 3D printers could create spare parts based on digital blueprints. They would make the parts precisely where they are needed: close to the customer,” explains Rehme.
From New Geometries to Better Turbines
In addition, 3D printing can create shapes that other production methods can’t. For example, it would allow the creation of complex geometries for components that optimally whirl the gas-air mixture to improve combustion. Another example would be the blades in expansion turbines. “Turbine blades contain filigree ventilation ducts to provide cooling,” says Rehme “At present, such ducts still have to be drilled or cast, but these methods are now reaching their limits. Turbine blades could probably be cooled better if we could print them in one piece.”. Better cooling of the blades would reduce the amount of cooling air that turbines need, enabling greater efficiency.
Extremely High Centrifugal Forces
“However, we have to make more progress before this will be possible,” says Rehme as he takes a brush to sweep the fine powder off of a finished component. “It still takes a relatively long time to print each part. Depending on the object’s size, it can take anywhere from a few hours to several days,” he explains. Rehme and his colleagues also have to further develop the materials used in the printing process. Turbine blades must be capable of withstanding extreme conditions. At high rotational speeds, for instance, the tips of the blades move faster than a pistol bullet and must endure centrifugal forces comparable to the weight of 20 cars. Printed metal parts are still not strong enough to be used under such conditions.
As a result, factories will continue to forge, mill, and cast components. This is especially true with regard to mass-produced parts, for which high production speeds and low unit costs are essential. On the other hand, 3D printing will most likely supplement existing techniques, while providing an economical solution for products that must be produced in small batchesand unusual shapes. To speed up this process a bit more, the latest printer models include up to four lasers that simultaneously “dance” across a layer of powdered metal.