By Norman Quesnel
Senior Member of Marketing Staff
Advanced Thermal Solutions, Inc. (ATS)
Additive manufacturing technologies have expanded in many directions in recent years with applications ranging across numerous industries and applications, including into the thermal management of electronics. As metal 3-D printing techniques have improved and become commercially viable, engineers are using it to create innovative cooling solutions, particularly heat exchangers.
Why are engineer turning to additive manufacturing?
One reason is that additive manufacturing allows for generous cost savings. Companies can reduce 15-20 existing part numbers and print them as a single component. A single part eliminates inventory, additional inspections, and assemblies that would have been necessary when components were produced individually.
As AdditiveManufacturing.com notes, “Some envision AM (additive manufacturing) as a complement to foundational subtractive manufacturing (removing material like drilling out material) and to a lesser degree forming (like forging). Regardless, AM may offer consumers and professionals alike, the accessibility to create, customize and/or repair product, and in the process, redefine current production technology.” 
Developed at the Massachusetts Institute of Technology (MIT), 3-D printing is the most common and well-known form of additive manufacturing. Three-dimensional objects are made by building up multiple layers of material. Thanks to the continued (and rapid) development of the technology and advanced research in materials science, the layers can be composed of metal, plastic, concrete, living tissue or other materials.
In industrial applications, 3-D printing has encouraged creativity. With additive manufacturing, designers can create complex geometric shapes that would not be possible with standard manufacturing processes. For example, shapes with a scooped out or hollow center can be produced as a single piece, without the need to weld or attach individual components together. One-piece shapes can provide extra strength, with few or no weak spots that can be compromised or stressed. 
Making 3-D Printed Heat Exchangers
Heat exchangers are integral to thermal management. Any time heat, cool air, or refrigeration are required, a heat exchanger has to be involved to dissipate the heat to the ambient. This can be as simple as a standard heat sink or a complex metal structure used in liquid cooling. It can be as small as a few millimeters or as large as a building. Heat exchange is a multi-billion-dollar industry touching everything from consumer goods to automotive and aerospace engineering.
Compact heat exchangers are typically composed of thin sheets of material that are welded together. The complexity of the designs, particularly the density of the fin field, makes production both challenging and time-consuming, while the material used for the welding process adds to the overall weight of the part. Heat exchangers produced through 3-D printing techniques (such as those pictured below) can be made quicker, lighter, and more efficiently.
In 2016, a Department of Energy-funded consortium of researchers developed a miniaturized air-to-refrigerant heat exchanger that was more compact and energy-efficient than current market designs. CEEE and 3-D Systems teamed to increase the efficiency of a 1 kW heat exchanger by 20 percent while reducing weight and size. The manufacturing cycle for the heat exchanger was reduced from months to weeks. 
Using direct metal printing (DMP), manufacturers delivered a 20-percent more efficient heat exchanger and an innovative design. It was produced in weeks not months and with significantly lower weight. The one-part, 3-D-printed heat exchanger required minimal secondary finishing operations.
Ohio-based Fabrisonic uses a hybrid metal 3-D printing process, called Ultrasonic Additive Manufacturing (UAM), to merge layers of metal foil together in a solid-state thanks to high frequency ultrasonic vibrations. 
Fabrisonic mounts its hybrid 3-D printing process on traditional CNC equipment – first, an object is built up with 3-D printing, and then smoothed down with CNC machining by milling to the required size and surface. No melting is required, as Fabrisonic’s 6 ft. x 6 ft. x 3 ft. UAM 3-D printer can scrub metal foil and build it up into the final net shape, and then machines down whatever else is needed at the end of the process.
This 3-D printing process was recently given a stamp of approval by NASA after testing at the Jet Propulsion Laboratory (JPL). A report from NASA and Fabrisonic said, “UAM heat exchanger technology developed under NASA JPL funding has been quickly extended to numerous commercial production applications. Channel widths range from 0.020 inch to greater than one inch with parts sized up to four feet in length.” 
There are challenges involved, to be sure. In an article from Alex Richardson of Aquicore highlighting research done at the University of Maryland, researchers discuss the problems that 3-D printing still has competing on price against traditional manufacturing techniques and the difficulties involved with physically scaling a technology up.
In the article, Vikrant Aute of the University of Maryland Center for Environmental Energy Engineering noted that his research team was “considering modularization to overcome the latter issue: Instead of making the exchangers bigger, it might be possible to arrange lots of them together to accomplish the same task.” 
Research Continues to Improve 3-D Printing Process
While there have been numerous advancements in the technology of metal 3-D printing, research is continuing on campuses and in companies around the world to try and improve the process and make it easier to create increasingly complex heat exchangers.
For example, Australia-based additive manufacturing startup Conflux Technology received significant funding to develop its technology specifically for heat exchange and fluid flow applications.  Another example was the University of Wisconsin-Madison, which received a grant from the U.S. Department of Energy (DOE) Advanced Research Projects Agency-Energy (ARPA-E) to build heat exchangers with “internal projections to increase turbulence and facilitate heat transfer. Such intricate shapes are impossible with traditional manufacturing.” 
In 2018, U.K.-based Hieta Technologies partnered with British metrology company Renishaw to commercialize its 3-D-printed heat exchangers. Renishaw used its AM250 system to 3-D print walls of the heat exchanger as thin as 150 microns. The samples were heat treated and characterized to confirm that the laser powder bed fusion process was effective. The process took only 80 hours, was 30 percent lighter, and had 30 percent less volume, while still meeting the heat transfer and pressure drop requirements. [10, 11]
Last month, GE Research announced that it was leading a multi-million-dollar program with Oak Ridge National Laboratory (ORNL) and the University of Maryland to develop compact heat exchangers that can withstand temperatures as high as 900°C and pressures as high as 250 bar. This was also based on funding from ARPA-E, as part of its HITEMMP (High-Intensity Thermal Exchanger through Materials and Manufacturing Processes) program. 
To build the new heat exchanger, GE engineers are using a novel nickel superalloy that is designed for high temperatures and is crack-resistant. University of Maryland researchers are working with GE to create biological shapes that will make the heat exchanger more efficient and ORNL researchers are providing corrosion resistance expertise to develop the materials for long-term use.
These are just some examples of the many ways that 3-D printing has impacted electronics cooling. Researchers at the Fraunhofer Institute for Laser Technology ILT in Germany have demonstrated the feasibility of 3-D printing copper , U.K. researchers 3-D printed “smart materials” for energy storage , a researcher at Penn State (soon to be at MIT) is developing methods for creating rough surfaces through additive manufacturing to enhance boiling heat transfer , and at Virginia Tech researchers developed a new process for 3-D printing piezoelectric materials .
The technology is growing by leaps and bounds each year and is enhancing the options for engineers in the thermal management industry.
For more information about Advanced Thermal Solutions, Inc. (ATS) thermal management consulting and design services, visit https://www.qats.com/consulting or contact ATS at 781.769.2800 or firstname.lastname@example.org. To register for Qpedia and to get access to its archives, visit