One of the major benefits of additive manufacturing is the consolidation of numerous subassemblies into a single component. This reduces the part count of a final assembly, but with the likely result of producing a more complex design with internal features not obtainable by conventional manufacturing.
This design issue, however, can lead to another problem: how do you inspect these items to prove conformity to design specifications? A certain amount of physical measuring and inspection is always going to be required, but inspecting additive parts with hidden and complex features (e.g., internal cooling channels and lattice structures) may require computed tomography (CT) scanning, which can be expensive.
Standardization of requirements for additive parts would help streamline the inspection process (and in some cases reduce the cost) and help improve the overall quality across the board, leading for more demand for additive-produced parts.
The Evolution of Additive Manufacturing
Additive technology, along with the materials used in its production (polymers, ceramics, metals, etc.), is becoming more advanced, and the parts it produces more precise and complex. This begs the question: How much inspection is required at the end of the line? Can the return on investment originate, in part, from an overall reduction in the time allotted for final inspection/testing? Or is more or the same amount of time, in fact, spent on inspecting additive parts versus conventionally produced components?
These are not simple, cut-and-dried questions; the answers are complex and varied. For example, consider the consequences in industries such as aerospace that are subject to catastrophic results if a critical additive component fails.
Creating a New Inspection Standard
It is conceivable that the recognized organizations establishing the benchmarks for testing and inspection (i.e., ASTM International and International Standards Organization) could create a new standard for additive that considers the preciseness of components born of a digital process. Currently, new additive manufacturing standards are being published at a high rate as more companies look to employ them, but it appears that multiple standards are emerging. There is good news— ASTM and ISO are collaborating to produce common benchmarks. On the other hand, SAE International (a worldwide standards-developing organization) publishes its own Aerospace Material Specifications (AMS) additive standards. The U.S. Federal Aviation Administration and European Aviation Safety Agency have also developed their own rules and regulations for metal additive parts in the aerospace sector, and a handful of other standard-setting organizations are publishing their own requirements for additive parts (AFNOR-France, AENOR-Spain, VDI and DIN-Germany).
In addition, individual companies can determine their own set of standards for parts testing, differing perhaps from ISO/ASTM. That can lead to confusion, say for components built in Asia but shipped to the U.S. or the U.K. What inspection level was required at the end of the manufacturing process, and does it match the specifications required in the destination country? Companies in the aerospace industry may eventually develop what they believe is a more “technically complete” standard when it comes to setting inspection benchmarks for parts produced by the additive process.
Yet another factor comes from varying international regulations. What happens when a machine designed to produce additive parts and components in one country does not meet requirements in another? Who makes the required modifications and when? These issues will need to be worked out as the additive method becomes more mainstream and the need for a standard set of construction guidelines becomes a commercial necessity.
Standards are important, but they must be applied in the right applications. For example, in the aerospace world there are three basic classes of parts, highlighting the different levels of inspection needed.
Class 3 (Minor): Example: Cosmetic or interior components. If it falls off the aircraft in flight it does not lead to any major safety issues (except perhaps for some unfortunate person on the ground). Being perfect or applying the same level of specifications as in higher classes may be overkill and costly.
Class 2 (Major): Example: Non-safety or non-structural secondary components. If the part falls off, it is not catastrophic – but the aircraft should land as soon as possible in an abundance of caution.
Class 3 (Critical): Example: Primary structural components or engine parts. A catastrophic scenario could occur if a defective part, however manufactured, fails during a flight.
The classes highlight where a higher degree of standards and required qualification are necessary. Classifications such as this, for any industry, can be a start for creating uniform standards.
There is a great need for a joint effort between OEMs, industry, international standards organizations, national governments and academia to come together in developing and progressing applicable qualification standards for additive manufacturing. This not only applies for aerospace applications, but any area where additive is applied in a range of critical uses; for example, automotive and medical devices.
Standards worldwide for testing and inspection levels will help deliver more believers to the growing world of additive manufacturing.
Neal Polley, Ph.D., has over 20 years of experience working in materials research and development in the defense and aerospace industries, the last seven in the field of additive manufacturing.
