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Joyce Yeung

Metrology

Fast-Track Certification and Qualification for Additive Manufacturing

A Q&A with Barnes Group Advisors’ Laura Ely and VELO3D’s Zach Murphree

Published: Monday, March 9, 2020 - 13:03

Additive manufacturing (AM, aka 3D printing) is increasingly accepted as an end-product manufacturing method, rather than just for prototyping. However, ensuring the final quality of parts for use in critical applications such as medical, and particularly aerospace, can still be a labor- and cost-intensive process. AM machine makers have most recently been concentrating on improving the actual printing technology of their equipment, and monitoring build progress in situ, so that printed parts not only perform as expected, but also can meet the various standards set by different industries.

Such proof generally comes in two forms: certification of the final product and qualification of the equipment, software, and materials used to produce that product. Two industry experts—Laura Ely from the Barnes Group and Zack Murphree, from AM equipment and software provider VELO3D—define and discuss these issues, and other important related ones, in the Q&A below.

What’s changed in additive manufacturing that makes certification more important these days?

Laura Ely: Our goal at The Barnes Group Advisors is to help industrialize AM, which includes helping customers along their path to making or using production AM components. AM has progressed from prototyping and tooling; it’s moving into production, and that requires tying into certification and qualification activities. We need to define these terms a bit more because sometimes they get a little confused. We also need to talk about the critical role that leaders in the AM industry, such as VELO3D, can play in supporting their customers with the certification process.

So, what is the difference between qualification and certification?

Ely: Certification is when a component meets design intent and is also fit for service in a system. For example, a component may meet all the design criteria specified by its designers, but can it be taken off the production line and placed in the machine it was designed for and work every time? It really doesn’t matter what industry you are in, whether it’s aerospace, medical, oil and gas, or a less heavily regulated industry; there will always be some level of requirements. An independent authority will review the data presented and certify whether a component is good to go in an airplane, in an automobile, or in some other system.

Qualification, on the other hand, is a critical process that supports certification. This process not only needs to take care of the machine, the process, and the material, but also the entire manufacturing system to get to the point where you can certify a component.

What are the key elements of certification?

Ely: When we talk about certification, it is helpful to use the Five Pillars of Certification, a modified version of the principles of the late John W. “Jack” Lincoln’s pioneering work in aircraft structural integrity. These divide the process into very clear categories required for a product to progress from initial design to final implementation.

 

Certification is best explained using a modified version of the general principles of the late John W. Lincoln’s work in aircraft structural integrity as an outline. Photo credit: The Barnes Group of Advisors.

 

The first pillar is requirements and design criteria. A design for a component may be beautiful and elegant, but it is of no value if it cannot meet the established performance requirements when it is placed in a system. It won’t get certified if it can’t do the job it was originally specified to do.

The second pillar is producibility. This is a key phase, as the process and equipment must be capable of manufacturing the part without excessive scrap and rework. Closely linked is the fourth pillar, stability, robustness, and repeatability, which essentially means that every part in production meets the requirements demonstrated by the parts used for initial certification.

The third and the fifth pillars, characterized properties and predictability of performance, mean that the material properties and the material to process parameter relationships are well understood, and the designer can confidently use the performance data to design a part.

What are some of the challenges facing AM when trying to get a part or process certified?

Ely: The problem that we have right now with AM is that it is not as mature as traditional processes. With traditional manufacturing processes, the material to process relationships are very well known, the data have been around for many years, and components have been in service for a long time. So, confidence in those processes is very high. AM, due to its less mature status, requires a lot more data to support the five pillars of certification with independent authorities.

Once again, AM is not at the same point as classic manufacturing, which often uses statistical mechanical properties (i.e., A, B, and S-basis allowables) to support predictability of performance. Many AM manufacturers are doing part certifications, which is a path to say this one individual part is suitable for performance in a system. The goal as an industry is to move toward process qualifications, where a process is deemed suitably stable, robust, predictable, and characterized to be a faster and less expensive platform from which multiple-part or part-family certifications can be achieved. This qualification process is where companies like VELO3D come into play.


Sapphire printer from VELO3D Click image for larger view.

 

How can companies like VELO3D help streamline the qualification process?

Zach Murphree: This is really an important thing for an AM provider like VELO3D to be involved in because we can do a lot to make life easier for manufacturers that use AM if we focus on the qualification process from the beginning. When we were initially looking at the five pillars that Laura was talking about, the first one that involves a manufacturer like us is producibility.

Producibility is something that VELO3D set out to address from the outset. When we were initially looking at producibility, we began with the intent to expand the geometries that could be printed using AM. For example, our Sapphire printers can print geometries that extend below 45° to 0° without supports. This has a significant effect on which parts can actually be produced by our customers and results in an improved manufacturing process that is more readily qualified.

How has VELO addressed characterized properties?

Murphree: I’ll give you an example. In conjunction with The Barnes Group Advisors, we did a study that looked at the average mechanical properties of Inconel 718 when printed on our system. We evaluated how AM compared to castings and wrought materials. We also looked at statistical mechanical characterization, or how stable the mechanical probabilities are across a full data set.

Velo3D and The Barnes Group of Advisors worked together to conduct a materials study of Inconel 718, evaluating the mechanical properties of AM vs. castings and wrought materials. Photo credit: The Barnes Group of Advisors. Click image for larger view.

 

We looked at data from five different machines printing two laser paths, each for a total of 10 different laser paths and about 100 samples. We examined how the statistics vary across the build plate, across builds, across machines, and across lasers. This is imperative because it gives you confidence in the next pillar that we focus on: stability, robustness, and repeatability.

In our study, 99.7 percent of the parts we sampled were within the specified levels for yield strength, ultimate tensile strength, and percent elongation. That is well over ASTM specifications, so we are definitely making significant progress.

Tell us more about stability, robustness, and repeatability. Why is this important, and how do you address it?

Murphree: When you think of this fourth pillar in the certification series, you have to ask, “Can I print the same part over and over while I’m varying the inputs, and still get the same result?” The important aspect here is varying the inputs, something which is not taken into enough consideration when you’re looking at stability, robustness, and repeatability. The reason I say that is when you start a print, you don’t necessarily know the state of the machine. Usually AM machines are calibrated by a field service engineer every three to six months, but you really don’t know what is going on in between these service dates.

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Velo3D’s quality assurance capabilities enables the Sapphire printer to be calibrated before every build. This image is taken directly from the Sapphire machine interface: If laser alignment is out of spec, a single click of a button will bring it back in spec. Photo credit: Velo3D

 

One of the things we set out to do at VELO3D in terms of our metrology was the ability to do calibrations in situ and to do them before every build from a single-button click interface. This gives you the confidence that your machine is in a good state when you start the build.

All of these features improve the performance of the AM process in terms of stability, robustness, and repeatability, and help lead manufacturers toward qualification of their processes and certification of their component parts.

What about the final pillar, predictability of performance?

Murphree: One of the things that VELO3D has been really focused on is making metrics that have a direct correlation to the probability of porosity. With our software, our customers are able to correlate the metrology that we’re taking live during the print to porosity. Porosity is one of the main causes of defects and poor mechanical properties in metal AM prints.

With this capability and others, we’ve made the path to qualification and certification a lot easier.

Aerospace comes to mind as an industry for which certification and qualification are critical. Any thoughts on that?

Ely: We are seeing more time spent in certification and qualification in aerospace as the industry moves more into AM for flightworthy parts. Of course, there’s the high-level map of what certification looks like, and there are all the qualification activities that stack up to that. Aerospace is starting to get to the point of creating those paths with more successful part and system certifications. There’s still a lot of activities focused on the issue of developing the robust data for AM, and there’s a general process that must be followed to have confidence in your results. You must have a stable process before you go and create a whole bunch of mechanical property data, for example.

Murphree: What we’re seeing right now is often people buy an AM machine and think they’re ready to go to the races, so to speak. But then they realize their process is not yet in control to the point that they can get there. So, there’s a lot of time spent in process development, and robustness and stability, before they can get to the next step.

I think that, whether it’s VELO3D or any of the other suppliers, when you are helping your customers with those things, and you already have the process stability and a level of characterized properties from the get-go, your customers are much further along in the race from the start. And hopefully that will then push more of those activities toward getting certified components into critical applications like aerospace and others.

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Four key aspects to qualification: The facility, machine/process, part, and finally, lot acceptance. Having a printing process that demonstrates stability and control, and is repeatable, is critical to passing qualification. Photo credit: The Barnes Group of Advisors

 

Ely: Streamlining the qualification process in any industry boils down to data. Once you have those known data pools, and you have a known process, the qualification and certification process will go much faster. The hardest thing is to certify a component the first time with a new process. Once we’ve got these layers and layers of data, I think we’ll start moving very quickly, especially from a process qualification standpoint. Cracking the code on process qualifications could shorten part and system certifications by 50 percent or more.

About Laura Ely and Zach Murphree

Laura Ely joined The Barnes Group of Advisors to support its mission to accelerate the industrialization of AM. Ely is well known in AM circles after her latest role as head of technology at GKN Aerostructures, where she oversaw the GKN-Oak Ridge National Laboratory partnership to develop directed energy deposition AM techniques for aerostructures. Ely has a bachelor of science degree in metallurgical engineering from the University of Missouri-Rolla (now Missouri S&T).

Zach Murphree is VELO3D’s vice president of technical partnerships. In previous roles with VELO3D, Murphree served as the director of business development, head of product and applications, and head of the hardware engineering group. His background includes engineering roles for energy companies, where he was in charge of introducing metal AM technology to a Fortune 500 energy company. Prior to joining VELO3D, Murphree led North American sales for Concept Laser. He earned bachelor of science and Ph.D. degrees in aerospace engineering from the University of Texas and has been granted more than 35 patents.

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About The Author

Joyce Yeung’s picture

Joyce Yeung

Joyce Yeung is director of marketing at Velo3D, where she is responsible for their thought-leadership programs. Prior to Velo3D, she held a variety of marketing roles at Concept Laser and GE Additive