Renishaw recently acquired technology for metals-based additive manufacturing, also using a powder bed of metals that are selectively melted using a laser. Common materials that they provide their customers include forms of Ti6Al4V, TiCP, 17-4 stainless, 316L stainless, and various Inconels.
“There are some challenges with this technology,” said Robin Weston, Global Product Manager for Renishaw. “If you put a standard material through our machine, you do not necessarily get the characteristics of that material as it would be in billet or wrought form.”
The differences in properties might be good for a particular application with, say, better hardness or toughness. “Or it might not be right because it must sacrifice ductility,” he said.
He believes that many designers are not now designing objects that could only be made through additive manufacturing. “Many are designing parts best made using CNC machining from a billet, then using additive manufacturing instead to create the part,” he said, missing the design freedoms accessible through additive manufacturing. “However, some designers have the ambition to capture the advantages of additive manufacturing.”
Others leading in this field recognize the challenge. “We are classifying the material properties that come out of [metals-based] additive manufacturing right now,” said Ben Horine, Director of Advanced Manufacturing, GE Aviation, also noting the different properties from additive manufacturing compared to wrought or billet. He shared that GE Aviation is using a number of materials suitable for the hot side of turbine engines, a particular focus for GE Aviation. “What it really comes down to is what material properties we can get out of this manufacturing technology that is critical to the parts,” said Horine.
Stresses are another concern. They build up in the part because they are essentially welded bit by bit. Internal sections of parts experience heat and thermal expansions that a CNC-machined part would never see. Thicker parts typically see higher stresses and potential distortions. “Every part is stress-relieved right out of the machine,” said Tim Warden, Vice President of Sales and Marketing, Morris Technologies. “We solution heat treat and HIP, depending on some of the materials that we run,” referring to hot isostatic pressing techniques for stress-relieving parts.
Warden is enthusiastic about material advantages. “We are seeing exceptional material properties with the grade of materials we are using, with both EBM and DMLS,” he said. “In a couple of cases, we made parts with Ti6Al4V and Inconel 718 that surpassed wrought properties, after heat treat,” a vast improvement in just the last few years, he noted.
While other industries are certainly using metals-based additive manufacturing, aerospace in particular is embracing the technology, according to Scott Killian, Key Account Manager of Aerospace for EOS.
“There is a company today that is manufacturing parts that are flying,” he said. “Some people are looking at airframe parts, but engine manufacturers are the ones that have found the economies of scale attractive in bringing their complicated parts to production.” Simply put, airframe parts are not particularly challenging geometrically, though some companies are looking at specialized hinge parts and other complicated components. “Parts where they want to avoid wasting a lot of material that is typical in subtractive machining processes,” he said. His company provides primarily cobalt chrome, Inconel 718, and Inconel 625 to engine manufacturers, with Ti6Al4V going more to airframe and structure parts.
Low production rates are also a factor in its popularity in aerospace. “Remember, in aerospace, 50 to 100 parts a year is production, unlike automotive where production means 100,000s of parts,” said Warden.