Leaps and Bounds: Additive Manufacturing Advances
When it comes to notable technological innovations of the 1980s, people often cite the home computer and the compact disc. Yet, the era also marked the introduction of a new form of manufacturing technology: additive manufacturing (AM). According to ISO/ASTM 52900, AM applies “the additive shaping principle and thereby builds physical three-dimensional (3D) geometries by successive addition of material,” offering an alternative to conventional manufacturing. A less technical way of describing additive manufacturing is: the creation of an object by adding one layer of material at a time. The term “3D printing” is often used interchangeably with AM.
AM applications have been growing since 1984, when American engineer Charles Hull patented the stereolithography apparatus (the first commercial machine for generating 3D objects). From medicine to aviation and a range of industries in between, AM is not just about prototypes anymore.
ASTM International’s committee on additive manufacturing technologies (F42) supports AM in its advancement. Formed in 2009, the committee has over 1,200 members and nine subcommittees, including applications (F42.07). With the applications subcommittee are 10 subgroups focusing on such areas as medical/biological (F42.07.03), construction (F42.07.07), and aviation (F42.07.01).
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An early adopter of AM, the medical field has employed 3D-printed anatomical models in training and preoperative planning since the 1990s. Because they can be customized and made on-demand, these models can mirror specific patients and their pathologies and assist in not only creating but also explaining treatment plans.
Surgical tools and prosthetic devices likewise benefit from AM’s ability to customize. Dental implants and replacement joints such as hips and knees can be crafted to accommodate a patient’s unique size and shape so that the part fits seamlessly.
“With an off-the-shelf part, when you take it into surgery, you open up the patient and then have to do the customization there,” says John Slotwinski, chair of F42. He is also a visiting professor in the materials science and engineering department at Johns Hopkins University. “You literally have tools where you’re making the adjustments to the bone or the joint during surgery to try to get the part to fit right. You won’t get as good a fit as a designed and customized joint. Plus, you’re increasing the time the patient is under anesthesia, when you actually want to try to minimize that time. This reduction of time is another benefit to AM parts.”
Slotwinski adds that, in addition to customization, AM can produce surface porosity much easier than conventional manufacturing can. “This lends itself well to implants because you get the body’s tissue to integrate into that porosity and you get a much better adhesion with the joint and the body,” he says.
Testing the Results
Addressing the use of AM in medicine is the subcommittee on applications – medical/biological (F42.07.03). The subcommittee has drafted a number of work items, including the new test method for additive manufacturing for medical – powder bed fusion (PBF) – assessment of residual powder (WK82776).
“For parts that are used in high criticality areas, particularly for implanted medical devices, there is potential clinical significance if the residual powder were to be released from the part,” says Paul Carpinone, technical lead on WK82776. Carpinone is an applications scientist at Malvern Panalytical and a member of all AM subcommittees. “The FDA has asked for an assessment of residual powder within finished medical devices. At present, while there is a general guide from F3335 [the standard guide for assessing the removal of AM residues in medical devices fabricated by powder bed fusion], there is no normative test method specifically tailored to AM and no standard way of performing and reporting data from this type of assessment. This work item is an important stepping stone to uniform part cleanliness requirements for high criticality AM in medical devices. Any regulations or standards for cleanliness would be built upon this.”
Standards are helping AM revolutionize the aviation industry.
Another work item, the new guide for material process validation for AM of medical devices (WK72659), provides guidance on how to validate novel AM processes used to create medical devices.
“It’s an example of a quality-management system for AM to talk through how you test everything and make sure you’re addressing everything the FDA will be looking for,” says Matthew DiPrima, co-chair of F42.07.03 and materials engineer with the Food and Drug Administration. “It’s not prescriptive. It’s designed to give people getting into AM medical devices a starting point.”
In May 2022, the applications subcommittee published the standard guide for powder reuse schema in PBF processes for medical applications for AM feedstock materials (F3456). Because the powder in PBF processes may be reused, thus reducing waste in production, regulatory bodies such as the FDA have asked companies to outline their reuse process.
“The main intent was to determine how powder reuse would impact the performance of the medical device, but companies were struggling with communicating their powder reuse schema to the FDA,” DiPrima says. “To reduce the burden on stakeholders as well as make the review process smoother, we initiated this as a starting point in how you describe what your powder reuse
schema is. It provides common terminology to simplify the communication between stakeholders and the FDA.”
Building and Construction
While the medical sector has utilized AM for roughly three decades, the construction industry has employed this method of adding, rather than successively taking away, materials for almost a century. An example of early AM construction is American inventor William Urschel’s layered concrete building, made without formwork, in Valparaiso, Indiana in 1939. Five years later, Urschel received a patent for his “wall-building machine,” which, historians note, displayed the same innovations found in today’s large-scale AM. A subsequent two-story structure, created in the 1940s with Urschel’s wall-building machine, still stands in the city today.
Within the past decade, the construction industry has experienced increasing pressure for more housing and structures. “Addressing current construction sector pain points and client-side demand has pushed contractors to look into 3D printing as a viable solution to provide a safe working environment; to be more efficient, productive, and sustainable in operations; and to use more eco-friendly materials,” says Stephan Mansour, associate consultant at Wohlers Associates. He is also vice-chair of F42.07.02 and co-convener of ISO/ASTM TC261 – JG80. “The construction sector is not averse to innovation, but must be reassured that the new technologies and materials are compliant and deliver equal or better performance than what they’re used to. They have a responsibility to deliver structures that withstand time and elements, including seismic and weather conditions and fires.”
With greater demand and innovation comes the need for new standards, which the subcommittee on applications – construction (F42.07.07) addresses through five work items on design and structural integrity. The new specification for AM for construction qualification principles – structural and infrastructure elements (WK77614) defines the requirements for both load-bearing and non-load bearing construction projects in which additive construction is used. When approved, it will be published under ISO/ASTM 52939 and adopted by global standard institutions such as the European Committee for Standardization (CEN and CENELEC) as a CEN ISO/ASTM standard.
“The standard bridges the gap between traditional and 3D-printing operations, making it easier to comprehend the approach and understand which existing ASTM and ISO standards can be used to certify structures,” Mansour says.
The new specification for process characteristics and performance for manufactured polymeric UV-cured structures for residential applications (WK74302) will apply to building components such as a portion of a wall, floor, or roof.
“At Mighty Buildings, we use a fiber-reinforced thermoset composite that cures using light. It allows us to do panelization and achieve the strength of concrete but with significantly less weight,” says Sam Ruben, chair of 42.07.07 and co-founder and senior sustainability advisor at Mighty Buildings. Other companies use various plastics for 3D-printed insulated facades and glass for interiors. In 42.07.07, we want to keep innovation possible with 3D printing while still ensuring that safety and building codes are in place. Safety is paramount, and that’s why construction is one of the most highly regulated industries in the world.”
Two work items, the new practice for additive manufacturing – general principles – design process of additively manufactured building elements (WK81114) and the new practice for additive construction – general principles – standard practice for the evaluation of structural printed elements (WK84415), arose from another work item. This is the new guide for additive manufacturing – general principles – development and road mapping of additive construction standards (WK78110). Serving as a form of gap analysis, the guide indicates a need for printed element testing and evaluation and element design (3D model) conversion, Mansour says.
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“With construction, there’s no one technology that will solve issues of productivity and affordability, but by creating standards to ensure that these technologies can be done safely, we unlock new possibilities for innovation,” says Ruben.
Aerospace and Aviation
Aviation also embraced AM at a relatively early stage and, for over a decade, has been working with 3D-printed prototypes, tools, and parts, including door latches, fuel nozzles, and heat sensors. Through AM, aircraft parts can be made with newer, lighter materials in a shorter amount of time. These lighter parts can lower the plane’s weight and, with that, its fuel consumption, lessening the environmental impact of flight. For older aircraft, for which a conventionally manufactured part may no longer be available, AM allows them to remain safely in operation.
In a field where the simplest part can play a major role in safety and operability, the demand for standards for AM in aviation is great. This is where the subcommittee on applications – aviation (F42.07.01) takes off. In 2022, it published the standard practice for additive manufacturing – general principles – part classifications for additive manufactured parts used in aviation (F3572). The standard enables the creation of a risk metric for engineering, procurement, non-destructive inspection, testing, qualification, or certification processes used for AM aviation parts.
“For aviation in general, most components are a bit more critical than perhaps other industries,” says Jesse Boyer, test methods subcommittee chair. “With over 5,000 aircraft in the sky at peak times, there are many people flying on planes utilizing critical and non-critical components. The benefit of F3572 is that is creates a common part classification across the industry that can be referred to and that allows users to confidently state, ‘This is a flight-critical part. This is a structurally critical part, etc.’ We can ‘bucketize’ components into these different categories and, ideally, assign the required amount of material characterization criteria to be more efficient related to cost and time.”
The aviation subcommittee collaborated on two AM standards with the International Organization for Standardization (ISO). The first is additive manufacturing — system performance and reliability — acceptance tests for laser metal powder bed fusion machines for metallic materials for aerospace application (ISO/ASTM 52941). It details the requirements and test methods for the qualification and re-qualification of laser-beam machines for metal PBF. The standard can be used to verify machine features during inspections or following maintenance and repair activities. It aids in qualifying AM components for general, commercial, and military aviation.
The second standard, additive manufacturing — qualification principles — qualifying machine operators of laser metal PBF machines and equipment used in aerospace applications (ISO/ASTM 52942) details the qualification requirements for operators of laser metal PBF machines and equipment for aerospace. This standard applies to operator qualification testing.
Partnership with ISO
So that ASTM and ISO could work together on developing AM standards for the global market, in September 2011, the two organizations signed a partner standards development organization (PSDO) cooperation agreement. The agreement is expected to shorten the standards-development timeframe and increase availability to users.
“F42 has a unique arrangement with its ISO sister committee TC261, allowing them to co-develop standards and approve each other’s standards,” Slotwinski says. “In Europe, ISO standards eventually become the law in almost every country, so this will give our producers and users equal footing with their European counterparts.” DiPrima adds, “This highlights the committee’s ability to work with a range of international partners and to get the broadest adoption of standards we’re developing. Through this agreement, F42 has an accelerated adoption pathway. We simultaneously ballot a standard in ASTM and ISO so that, once it’s successfully balloted, it can be immediately released as a joint standard. To have a standard balloted simultaneously through both organizations is fairly novel.” ■
Research to Standards: The Additive Manufacturing Center of Excellence (AM CoE)
With an eye toward addressing gaps and challenges in standards, ASTM International established the Additive Manufacturing Center of Excellence (AM CoE) in 2018. The center works with global AM experts from industry, academia, and government to carry out research and development projects, promote AM technology, and present workshops, seminars, and technical expertise. Through its R&D projects, the AM CoE has guided the creation of recent standards such as the guide for AM— feedstock materials — testing moisture content in powder feedstock (F3606) from the subcommittee on test methods (F42.01) and the guide for powder reuse schema (F3456) from the medical/biological applications subcommittee (F42.07.03).
As a result of the AM CoE’s efforts, 36 projects on standards gaps have been initiated to date. They look at such areas as design, data and modeling, processes and post-processes, testing, inspection and qualification, and feedstock, says Mohsen Seifi, Ph.D., ASTM’s vice president, global advanced manufacturing programs division.
“For example, a project on ‘In-Situ Defect Detection and Analysis’ focuses on developing non-destructive testing techniques to detect defects in AM parts during the manufacturing process,” Seifi says. “This project is relevant to all industries that use AM technology, including aviation, construction, and medical/biological applications. Another project, ‘Feedstock Reuse for AM,’ focuses on developing feedstock reuse strategies. This project is important for industries such as aerospace and medical applications. Based on this project, F3456 was recently published, which provides a guide for powder reuse schema. Another example of an industry-agnostic standard is F3530, which is a guide for post-processing of metal PBF-LB.”
He adds that addressing these gaps is critical to the growth of AM. It will enable the increased and widespread adoption of AM in a range of industries, including construction, transportation, and energy.
Along with the committee on additive manufacturing, the AM CoE’s work assists the committees on metal powders and metal powder products (B09), mechanical testing (E28), and non-destructive testing (E07). Seifi notes that these committees are essential to the development of standards for AM powders, evaluating the mechanical performance of AM components, and ensuring the quality of AM parts.
“Overall, the AM CoE’s global network, collaboration and engagement with stakeholders, education and outreach programs, and significant impact on the promotion and advancement of AM technology make it an essential player in the development and promotion of AM standards,”
he says. ■
Kathy Hunt is a U.S. East Coast-based journalist.