New Directions for Additive Manufacturing
Choose metal or polymer. Define the object with a computer-aided design file and send it to print. And use a production process such as laser sintering, electron beam melting, selective deposition lamination, or inkjet printing. End with a new product.
Whether you call it 3D printing or additive manufacturing, it means building things layer by layer.
With additive manufacturing, or AM, a plane engine fuel nozzle can be produced that is more geometrically complicated than possible with traditional manufacturing.
Or, for surgery, AM can make a cutting guide specific to the individual patient. During a knee replacement, for example, the surgery can then be more precise, and the end result a better functioning artificial joint.
AM is a growing field. According to Wohlers Associates in a report issued earlier this year, the additive manufacturing industry surpassed $5.1 billion (U.S.), and the “industry grew by $1+ billion for the second consecutive year.”
Yet along with these benefits for such diverse applications — frequently aerospace and medical these days — come questions about how long that metal nozzle will last or whether that cutting guide is as clean as it should be.
“We’re on the threshold of another industrial revolution,” says Steven Daniewicz, Ph.D., head of mechanical engineering at Mississippi State University, “We have to make sure that structural integrity is there to go along with the complicated geometries we now have the ability to make.”
Jon Moseley, Ph.D., senior director of applied research at Wright Medical Technology, says, “To fully realize the potential of this technology you have to understand both the benefits and the pitfalls.”
To explore AM benefits and challenges, recent ASTM workshops, sponsored by Committees F04 on Medical and Surgical Materials and Devices, and E08 on Fatigue and Fracture, were held during the May committee week in San Antonio, Texas. The programs brought together more than 100 professionals to each event from the aerospace and medical industries; other industries that are starting to use or considering AM; labs; regulatory bodies such as the U.S. Food and Drug Administration and the Federal Aviation Administration; and academics and researchers. As a result, new ASTM programs and standards development will address challenges and maximize opportunities for innovation.
AM medical devices run the gamut from cutting guides to bone augments, artificial joints, hearing aids, and dental crowns.
AM’s flexibility opens up a realm of design possibilities, notes Moseley, who co-chaired the workshop on medical applications. A computed tomography or magnetic resonance imaging scan can be converted into a 3D model that meshes with device design to become a plate for someone’s head following tumor removal or after trauma, for example.
And these days, “Just about everyone in academia and industry in medical devices has some program going in AM,” he says.
The workshop focused on both how AM can make a difference for patients and how the approach still needs additional work. One presentation reported how models helped plan successful complex joint replacement surgery. Others considered the cleanliness of AM devices and the techniques used to remove excess oil or process material. Still others looked at device surface finishes and their polishing.
The workshop raised four issues in particular about AM medical devices:
Of the last, Moseley says industry needs to figure out when it makes sense to use AM, and where it’s economical. “If there’s no advantage and it’s more expensive, then we’re not likely to do it,” he says.
In the workshop, the need for standards was raised, including cleaning and process control validation.
Attendees noted that they want Committee F04 to complement work going on in Committee F42 on Additive Manufacturing Technologies. F04 members involved in both committees can bring any raw material, characterization, or processing approaches or needs to F42.
Moseley, who is active on the F04 implant cleanliness task group housed in F04.15 on Material Test Methods, will be involved in developing relevant cleanliness standards that will cover the removal of residual oils and material particles to help prevent adverse reactions. Moseley will be working on and helping to coordinate two planned standards efforts coming out of the workshop:
FDA and F42 representatives, among others, have expressed interest in being part of the work, he says, and he anticipates that scope statements, and perhaps a draft standard, will be ready for consideration sometime this fall.
In aviation and aerospace applications, AM metal parts such as turbine blades, engine parts, and pumps, among others, are becoming more common.
The workshop on mechanical behavior of AM components, like the medically focused program preceding it, raised questions about process control and validation, as well as fatigue strength, strain life, and crack growth.
“The AM community has been growing very rapidly, but there hasn’t been a lot of attention paid to structural integrity and strength,” says Daniewicz, who co-chaired the workshop. “We feel that there is fatigue-related work that needs to be done to increase the trustworthiness of additively manufactured parts.”
Co-chair Nima Shamsaei, Ph.D., assistant professor of mechanical engineering at Mississippi State University, agrees. “That’s one of the major barriers to the broad adoption of additive manufacturing for structural applications.”
Daniewicz and Nik Hrabe, Ph.D., a metallurgist at the U.S. National Institute of Standards and Technology, and workshop co-chair, discovered each had been planning a program to delve into AM for metals, and the specific challenges around their mechanical behavior.
Attendees expressed that it is essential that nondestructive test methods find any defects in AM parts, that the fatigue life be right for the use, and that additional tests be available to determine and characterize flaws and damage tolerance. Presentations covered alloy use in both medical devices and aviation structures as well as current research on testing material properties of AM parts.
Hrabe says that with the workshop, “We started a conversation. It will eventually lead to many things, including standards development and a better understanding of AM in general.” As a result, a symposium on the topic with Daniewicz and Shamsaei as co-chairs has already been scheduled for the latter part of 2017.
ASTM and Its Work on Additive
Additive manufacturing is an ongoing focus at ASTM.
In June, 3MF — a consortium of GE, Materialise, Microsoft, Siemens, and others working on a 3D printing format that will allow companies to focus on innovation — signed a liaison agreement with ASTM. The agreement between ASTM and the 3MF Consortium is the beginning of a potential collaboration on data exchange formats for additive manufacturing. The partners aim to share information and develop standards that will help advance additive manufacturing.
With the 3MF Consortium partnership, “We have the opportunity to improve 3D content representation technology for a wide range of users and industries,” says David Rosen, Ph.D., professor and research director, Singapore University of Technology and Design.
At ASTM, that’s just the latest step in AM-related work that launched with the 2009 organization of the committee on additive manufacturing technologies (F42). Following the signing of a memorandum of understanding between ASTM and the Society of Manufacturing Engineers, F42 was established as the home for AM standards development.
More milestones followed. America Makes, the National Additive Manufacturing Innovation Institute, signed a memorandum of understanding with ASTM for standards development. And a Partner Standards Developing Organization agreement was signed by ASTM and the International Organization for Standardization (ISO).
To date, F42 members have completed 11 standards, including a terminology standard, a guide for characterizing metal powders used in AM, a specification for the titanium aluminum vanadium alloy often used in AM, test methods that support the spec, and more.
Through the ASTM/ISO collaboration, two standards have been developed for broad industry use; these are also European Norms and mandatory in the European Union. The standards are:
More is coming. One proposed standard (WK48649) describes existing features for solid modeling, informationally complete 3D geometric models, which supports ISO/ASTM 52915. Rosen says, “Solid modeling is particularly important for engineering and medical imaging applications. In contrast to solid modeling, surface models represent only the bounding surfaces of 3D models and lack an ‘understanding’ of which side of the surface is ‘inside’ the object and which side is ‘outside.’” WK48649 will address this difference and should improve solid modeling representations as well as make them easier to use. Several additional draft standards will guide AM design and design rules, mechanical properties, and AM processes.
F42 is looking and planning ahead with a road map and a strategic approach to what standards it develops. The plan will support the expansion of AM technologies into additional industries and making AM mainstream.