The graceful, sweeping lines of the node developed through additive manufacturing were the result of efforts to achieve maximum efficiency in the process, not improve aesthetics. © Davidfotografie
Additive manufacturing of steel shows promise in producing small, complex steel components for building projects.
June 24, 2014—A team of engineers in the Netherlands was recently faced with a challenge. As they developed the design for tensegrity structures on a lighting project in The Hague, the complex network of struts and cables was to be angled and irregular. This meant that all of the nodes that would connect the elements would be slightly different—1,200 nodes, all unique.
“As you can imagine, it is a bit of a task to produce,” says Salomé Galjaard, an engineer and senior designer in the Amsterdam office of the engineering firm Arup.
The team worked diligently to devise alternatives, but ultimately released the project to the contractor with the 1,200 distinct nodes. Once the project was complete the team began to question whether, for future projects, there was a better answer to be found in the nascent field of additive manufacturing, commonly known as 3-D printing.
“We thought this is probably going to happen more often, so could we make this into an internal research project? Is there a better way of producing all these slightly different elements?” Galjaard says.
The 3-D printing of concrete is in the early stages but is advancing within the building industry. Researchers have built specialty curved panels, intricate sculptures, and even small structures with the technology. Several methods are being developed simultaneously. One method involves spraying a catalyst on a special cementitious mix of sand and polymers. Another team is developing a process that deposits layers of special wet cement on already formed layers.
Additive manufacturing of metal and steel is quite different. Galjaard explains that in the method currently being investigated and used, a thin layer of metal alloy powder is placed on the base of a cube-shaped chamber measuring 40 cm to a side. A laser passes over the powder, applying heat only to the sections dictated by a computer model used for the project. More powder and more laser passes follow. Each pass of the laser not only melts the powder, but the already formed metal beneath it, fusing the new layer with the previous layers.
The finished product is then removed from the chamber. The unused powder is collected and can be reused anywhere from 10 to 100 times, depending on the formula. The ultimate recycling rate is limited because although the loose powder hasn’t been exposed directly to the laser, it has been exposed to heat in the chamber.
The aviation and aerospace industries are pioneering development of the technology because it eliminates superfluous material, resulting in the strong, lightweight components prized in those applications.
“Our challenge was to find out how to design for this production method,” Galjaard recalls. “We didn’t want to take the originally designed node and print it. The original design was developed for traditional production methods. So we started from scratch, with new boundary conditions, trying to define the essence of the functionality of the node and then see how we can design it in a way that was as optimized as possible.”
The team started with the basics: what was the function of the node and what forces would it need to support? The team was able to remove material from the node in many places where it was not functional. But a key challenge of the additive manufacturing process is supporting horizontal surfaces above voids. This required the careful design and placement of supports.
A project requiring 1,200 traditionally produced nodes, each of
them unique, inspired the engineers to consider additive
manufacturing in the future. © Davidfotografie
“You can print any sort of shape, but it could happen that you have to print support structures that you later have to remove,” Galjaard says. The team was trying to avoid this postprocessing of the node with a design that was “smart and smooth and economical.”
Galjaard says that the process was a delicate balancing of new freedoms in design and new rules from the additive manufacturing process. “For us, as engineers, it’s very interesting to try to free your mind and design without too many restrictions that we [experience in] our traditional processes,” Galjaard says.
Even though the team initially thought they had taken advantage of the new design freedoms, when production started they realized they were needlessly restricted by their experience with traditional production methods. “You limit yourself to all the things you’ve learned over the years,” Galjaard explains. “I think the challenge with additive manufacturing is to give yourself a lot of design freedom and to try to really get the most out of the qualities of the production technique.”
The resulting node from the process is an elegant, sweeping structure with small branch-like supports extending to an upper horizontal plate. The team did not, however, consider aesthetic appeal in the design.
“It’s not beautified. It’s actually more functional than the original node. We just put the material where it is needed, where the forces are running through,” Galjaard says. Although the team didn’t consider aesthetics, she says the technology offers the design freedom to enhance the visual appeal of structural elements.
“Maybe it results in more visible structures. In that sense, I think, it could have an influence on our industry in the way we design that we don’t even realize yet. Maybe buildings are going to be turned inside out, where the structure is no longer hidden, but [become] the most visible part of the building,” Galjaard says.
For now, however, the team is redesigning the node and will likely simplify it greatly. The prototype was designed to be formed from stainless steel. Because the manufacturer had only maraging steel in stock, the node is likely four times stronger than necessary.
Although the strength of the node hasn’t been tested directly, the research team did test steel rods made through additive manufacturing and found them to meet the expected specifications. “That was good initial feedback,” Galjaard says. “But before we really start implementing this technique and start applying it for full-scale buildings, there is a lot more material research to do and a lot more experience to gain.”
Currently, additive manufacturing of steel is more expensive than steel produced via conventional methods. Because of this, Galjaard does not foresee a time when the process will be used on large, simple components such as rods and beams. Rather, she sees engineers utilizing the technology on small, complex components, such as the node in the research project.
“In the building industry you create an element [and] you connect it to something else with another element. And you can end up with a lot of different elements that need to be installed and connected on-site,” Galjaard says. “This technique ...provides the option to integrate those different products and their functionalities in one product, which is printed in one go.”
This has the potential to reduce installation costs greatly by both reducing the number of components and the complexity of the installation process. Other benefits of additive manufacturing can be less material waste in manufacturing, and the resulting components will be lighter, requiring less energy to transport. In certain projects, these benefits might have the potential to offset the added expense of additive manufacturing, Galjaard says.
“We looked at the complete life span of the product. The direct costs are still high, absolutely. But, for example, in our structure you could say [that] if all these nodes are reduced in weight, the weight of the entire structure goes down. All the other elements can be produced smaller and lighter and cheaper, and that has a positive influence on costs, as well,” Galjaard says.
“There are quite a lot of factors that should be taken into account. It’s a bit difficult now to map them exactly, but we think for the right projects, it could be financially interesting to use a production technique like this,” she adds.
For now, the Arup team is redesigning the node and considering a second, small-scale project on which to test additive manufacturing. “Every time, it is a surprise. You come up with an idea and you think about production and you think, ‘This is not possible.’ And then later on you think, ‘Why haven’t I thought of that?’ It’s a bit of an adventure in that sense,” Galjaard says.
“It’s quite inspiring, but also interesting to see how much you know and how that influences the solutions and ideas you come up with. It will be an interesting process for the engineers and designer here to go through,” she adds.