The 3D printing industry was alight with the news that one of the world's largest manufacturing conglomerates, GE, had acquired two key manufacturers of metal 3D printers, Arcam and SLM Solutions. Now that GE will be shifting from metal 3D printer user to both printer producer and user, surely this is a sign that the technology is mainstream.
However, metal additive manufacturing (AM) still has barriers to overcome before it is widely adopted as a method for reliable production of end parts. The chief concerns of potential customers of metal 3D printers are the interrelated variables of cost, productivity and quality. If a system can reliably produce quality parts, it might very well justify the six or seven figure price tag to purchase a metal 3D printer.
As it stands, pulling quality out of a metal 3D printer is heavily based on trial and error, as machine operators struggle to optimize the printing parameters for every given object, material and build. While companies like 3DSIM aim to tackle this issue through the development of advanced simulation software, Stratonics, in Lake Forest, Calif., is focused on the technology that actually monitors the printing process.
With a suite of sensors and software, Stratonics is providing predictability to 3D printing by measuring the thermal data during a print job and generating actionable data that can be used either to optimize subsequent builds or implement in-process quality control mechanisms. The technology has proven so successful that Stratonics has worked with most of the big names in aerospace and was chosen by Oak Ridge National Laboratory (ORNL) to research 3D printing quality control.
ENGINEERING.com spoke with President of Stratonics James Craig to learn not just how the technology works and how it's being used in the industry today, but also how bringing quality to metal 3D printing could push the industry further forward with dramatic innovation in design and reduction in cost and delivery.
Measuring Heat
Ensuring that the temperature produced by the energy source within a 3D printer is accurate isn’t as easy as sticking a thermometer into a holiday ham. Those unfamiliar with metal AM may be surprised to learn that most metal 3D printers don’t feature actual thermometers for measuring the heat of an energy source as it interacts with the metal 3D printing material. Instead, they often rely on advanced cameras that capture photos of the build area, from which measurements are made of the light intensity emitted from, say, a laser hitting metal powder.
Stratonics' ThermaViz sensor system, in contrast, achieves thermal imagery with high resolution and absolute accuracy based on two-wavelength, true temperature measurement technology. The company produces three different sensors based on this technology for both directed energy deposition (DED) and direct metal laser sintering (DMLS) processes. Two of these sensors are for measuring the temperature of a meltpool, where the energy source melts the printing material and adds it to the deposit. The third sensor measures the global temperature of the entire deposit. Together, the meltpool and global temperature provide a thermal picture of a deposit, including how the material responds when heated and melted, as well as how it cools.
With this information, a machine operator can determine how the parameters of the machine will affect the final printed part. The four biggest parameters a user might be interested in include the power of the laser, the system's scanning speed, the distance between scans and the thickness of the powder layer when it is recoated with each subsequent layer.
Light vs. Temperature
Rather than measure only the intensity of light that cameras see emitted from a meltpool, the ThermaViz system actually measures the temperature throughout the build area. As a result, it’s possible to continuously obtain accurate information about the power that a laser or other energy source is applying to a print—vital information for ensuring that a printer is operating properly.
A variety of variables might interfere with the interpretation of the camera-based measurement of light intensity. For instance, soot from the printing process might begin to cloud the camera lens or window, thus making it look as though the laser is emitting less light and, therefore, less power. “You'd say, ‘Well it looks to me like the meltpool is getting smaller, so I need to turn up the power needs to be increased to recover the original melt pool size,' but actually, the window just got dirty,” Craig explained.
Some 3D printing systems do use pyrometers, but they may only capture one wavelength, limiting the range of data that the sensor measures. As a result, single-color pyrometers may not be as accurate and are highly sensitive to the material that is being printed, according to Craig.
“The pyrometers just give you an average temperature over some large spot area, which is an indicator of temperature, but not necessarily an absolute measurement of temperature,” Craig said. As a 3D printer operator fine-tunes the parameters of a machine for a given material through trial and error, the operator essentially has to start the empirical process over again when switching to a different metal. This characterization process can end up becoming quite costly for the machine owner.
Craig, however, suggests that Stratonics' sensor systems can move from Inconel to stainless steel to titanium, Ti-6Al-4V and other high-temperature metals used in aerospace without the same issues.
3D Printing Quality Parts
The data that is collected by these sensors is fed into accompanying ThermaViz software, which can either help machine operators improve printing parameters for subsequent prints or in-process quality control.
By generating reports and temperature videos, the software makes it possible to analyze past builds. Real-time temperature data, however, also allows an operator to adjust parameters, such as the power of a laser, while the print is taking place.
Ideally, this process will be fully automated so that, through a combination of software and hardware, a 3D printer can automatically adjust a range of necessary operating parameters during a build. Before it can do that, it’s necessary to understand what parameters will lead to a quality print. Stratonics has achieved a prototype-level of control under its Navy SBIR program, using an Optomec LENS 3D printing platform at Penn State University. Real-time thermal imagery was used to control the heat in the deposit, providing improved uniformity in material properties and high precision in thermal reproducibility.
The research will not only enable those using 3D printers to qualify their processes for fabricating parts that meet the specifications of aerospace manufacturers, but, in the future, make it possible to integrate quality control mechanisms within 3D printing technology.
“After you learn how to make a good deposit,” Craig says,” the next step is to develop methods to make sure the melt pool stays in that configuration throughout the component build. Now, you’re building a hundred components, you want to build them all the same way so that the thermal cycle is reliably repeated at every layer thus ensuring the quality of every part.”
An initial measure to ensure reliability is to integrate controls within a printer that alerts a user to whether or not a print has gone off track. Once alerted, a machine operator could stop the build to prevent any further material waste. In the long term, it’s possible to imagine printers capable of monitoring a print and, using the collected data, automatically adjusting settings to maintain a quality build.
Obstacles to Metal 3D Printing
Qualifying parts and processes for large manufacturers, such as those in defense and aerospace, can be costly, further making it difficult to incorporate metal 3D printing into mainstream manufacturing. For this reason, quality control mechanisms such as those offered by Stratonics and the actionable data produced by research like that being conducted with ORNL could begin to lower the cost of qualifying metal 3D printing.
However, improved quality control and predictability is beginning to make its way into the industry. A number of companies and researchers have already begun to bring ThermaViz in house. Stratonics has incorporated its sensors into DED technology from RMP Innovations, as well as DMLS machines from Concept Laser, EOS, and 3D Systems, with SLM Solutions on the way. In addition to being incorporated into Optomec’s LENS systems, large aerospace and defense companies such as Honeywell, Boeing and Aerojet, as well as Texas A&M University, Mississippi State University and the Applied Research Lab at Pennsylvania State University, have begun using Stratonics’ technology.
With that in mind, it’s only a matter of time before metal 3D printing reaches its full potential and not only will GE be a massive player in the metal 3D printing industry, but so too will the other large manufacturers on the planet.