It seems the whole materials testing industry is talking about Additive Manufacturing, but what does this mean for materials testing? Join MTS experts Mike Shepard, PhD and Mark Menzuber, MBA, as they discuss the basics of Additive Manufacturing, what makes it different from 3D printing and how it will affect the future of Materials testing.
What is Additive Manufacturing (AM) and what are its advantages?
Shepard: Well I can’t possibly do the technology justice with a short answer, but Additive Manufacturing is driving a revolution in design and manufacturing. The technology lets us directly create parts from a solid drawing, using a wide and growing range of Additive Manufacturing methods. In the best cases, properties can compare favorably to conventional manufacturing processes. The various techniques are applicable to metals, polymers, and even composites and ceramics. Generally speaking, you build up the part directly, layer by layer. Parts that have tight tolerances or are load-bearing may need some finish machining steps or heat treatment, but in some cases the parts can be used right out of the additive manufacturing system.
The advantages of this technology are numerous. First, you get incredible freedom to design shapes and structures. Designers can optimize for weight, heat transfer, space and other properties. Second, in terms of material use, it can be very efficient—you are not turning a big block of metal into chips to create a small, complicated part. This is why Additive Manufacturing is described as having an excellent “buy-to-fly ratio.” Meaning, most of the material you buy actually goes into the component, versus being turned into chips or scrap. The supply chain can also be shortened dramatically. Multiple manufacturing steps and vendors can potentially be reduced to a single, albeit complex, manufacturing process—in a single location. The logistical advantages in terms of shorter lead times and consolidated logistical chains are obvious.
What industry trends are driving the need for AM and which industries are leading in the use of AM?
Menzuber: Most companies that are engaging with additive are really attracted by the ability to trim weight and add performance in various ways. There’s also a lot of interest in the potential to simplify their supply chain and cut lead times by using Additive Manufacturing onsite in place of multiple production steps, possibly at other locations. Finally, Additive Manufacturing offers new efficiencies for small to midsize production runs, which can facilitate more economical customization and shorten product development timelines.
Additive Manufacturing technologies, as they mature, have the potential to be pretty disruptive. Everyone is considering additive manufacturing, but I see the most energy and investment in Aerospace and Biomedical applications. These industries have very high value-added applications, with low to moderate volumes. Applications in these industries tend to be highly optimized and tested extensively, so emerging manufacturing processes like Additive Manufacturing can be integrated as their value proposition is clear. Automotive applications are also really coming on strong, but there is a higher level of cost sensitivity in that industry.
What is the difference between 3D printing and AM?
Shepard: These terms are still commonly used interchangeably, especially in the mainstream media and consumer market space. In my opinion, additively manufactured parts are typically used in end use applications. Since the part will be used in a product, AM requires a robust process, suitable for a production environment, that can be completed with reasonable efficiency.
In a rapid prototyping application, the parts would generally not see any type of significant service. Strength might not be too high and properties may not be uniform. You would want to be careful using these parts for any practical application, especially where any load was involved. The printing process itself might be pretty slow. All that being said, a rapidly available physical prototype can really help design engineers understand how a part is going to function and interact with other parts. These printed prototypes are also extremely helpful for demonstrating fit and function to collaborators and customers. I consider these 3D printed prototypes as the next step up from visualizations that you might create with 3D CAD software.
Does MTS use Additive Manufacturing?
Shepard: Oh, yes. As it turns out, MTS has a long history in additive manufacturing, starting in the mid-90’s. We were a little ahead of our time for the market, but working with a number of partners we were able to refine our Laser Additive Manufacturing (LAM) process to the point where we could successfully produce aerospace quality Ti-6Al-4V parts. Some of those parts may still be flying on F-15s. That experience gave us tremendous insight into what it takes to qualify an additive manufacturing process and the parts that come from it, especially the mechanical testing aspects.
More recently, we’re excited about the design possibilities and efficiencies of additive for the same reasons as our customers are interested in this technology. We have an in-house Additive Manufacturing system we use for rapid prototyping and some production parts. When we’re designing custom systems, we use rapid prototyping as part of our R&D process. 3D CAD is amazing and we use it extensively but nothing beats being able to hold the parts and see how they fit together and function. Our customers appreciate it as well. When we’re designing a new unique system for them, it is really helpful to have a full or subscale model that will allow them to see the mechanical concept of operations firsthand.
We also use Additive Manufacturing for some low-volume, high complexity, non-load bearing parts. For these parts, AM gives us competitive cost and short lead times that are very attractive logistically. In the past, these parts had to be fabricated using multiple steps, sometimes using vendors outside our factory. Now we just upload the solid model of the component, apply standard practices for our AM process settings and come back later when the part is finished. The additively manufactured component can sometimes go right into the build, with no secondary manufacturing steps.
How does AM affect materials testing?
Menzuber: There are a number of important elements. First, it may be challenging to get standard specimens machined out of additively manufactured components, so you might need to use subscale specimens or a different type of test. We’re pretty experienced dealing with these variables. We have a wide range of load frames and fixturing that will allow you to apply the right level of force to a correctly configured specimen to help you assess the properties you care about. We’re also sensitive to the fact that different customers are going to be interested in running different types of tests and will need solutions at different capabilities and price points.
You also need to keep in mind the nature of Additive Manufacturing processes and how that influences the uniformity of materials properties in a part. Generally speaking, Additive Manufacturing’s chief attribute is that you go directly to finished or nearly finished parts, layer by layer. You don’t make a big block of relatively uniform material and then machine a part out of that. The layer-by-layer nature of additive manufacturing can leave you with material properties that are not necessarily isotropic, meaning they are not uniform depending on direction in the part. In particular, properties perpendicular to the additive layers, usually termed Z direction are of the highest interest. One should plan to run some extra tests make sure they understand how uniform the material is in the parts. Also, depending on how mature the particular Additive Manufacturing process is, one may need to run tests to understand the impact of the various processing parameters on mechanical properties to better understand the safe processing region for production. These processes can be extremely complex, with lots and lots of variables.
Testing witness coupons is particularly valuable as part of an additive production process. You can build a small testing coupon before and after a complicated build to make sure the system is performing generally as expected. We have a range of smaller, modestly priced systems that are perfect for this. They are easy to use and can sit right next to the Additive Manufacturing system if you like. These systems can give you immediate feedback as to whether or not the system is producing good material from a mechanical properties perspective. Coupons cut directly from components can give a more direct indication of process stability and component quality.
What are some important considerations when selecting test equipment for AM specimens?
Shepard: Logically, the testing community is trying to make use of existing equipment and standardized testing methods as much as possible. Unfortunately though, the material in an additively manufactured article may not have uniform properties. In many cases, you simply can’t get standard specimens out of these manufactured components. This is a fun challenge for us. We have comprehensive families of load frame technologies (servohydraulic, electromechanical, electrodynamic) as well as fixturing (grips, three-point bend, clevises, etc.) that allow us to deal with subscale and unusual specimens without excessive difficulty. We also have load frames that are sized well for smaller scale testing, if that is required.
Depending on the types of tests that are needed, you may be best served by different types of systems. On the top end, for the highest level of performance and flexibility, you probably want a servohydraulic system. Those are especially well-suited to dynamic tests like fatigue and fracture and can easily do more routine testing, such as tensile testing. Some customers may have simpler requirements and may just need to be able to run tensile tests. These customers might be best suited to an electromechanical system. Electromechanical systems can be quite affordable and are ideal for testing witness coupons as part of a production process.
In recent years there’s another option too. Electrodynamic systems offer a lot of dynamic performance and don’t require a hydraulic pump. These systems are especially attractive if you need to operate in a particularly clean environment or if you are new to testing and need some dynamic capability, but would prefer to avoid the complexity and expense of a hydraulic installation.
How is MTS involved in the Additive Manufacturing community?
Menzuber: Well first, we’re a user of the technology and have a long history in the technology area, so we have some firsthand knowledge of the advantages and challenges associated with Additive Manufacturing methods. Second, we have really close relationships with our customers. They each have their own ways of integrating new materials and processes into their products and we partner closely with them to support. That could mean helping them develop design data, generate parameters for their materials models, testing witness coupons, all the way up to testing components and full-scale systems. Third, we’re engaged with the standards organizations that are developing Additive Manufacturing testing standards, especially ASTM and ISO. It’s important for MTS to participate in these organizations so that we can support the technical community with our testing expertise and bring forth the needs and experiences of our customers.