^ Image 3. Aviation structural mechanic cleans and inspects a heat exchanger (Photo Credit: US Navy). Brazing and welding produce toxic substances such as Trichlorethylene, Hydrofl uoric acid, and Hexavalent chromium, most of which are banned by environmental agencies. Source: VELO3D

Will Hasting, Director of Power Turbine and Aviation Solutions, VELO3D

 Next-generation AM systems
Image 1 (a,b,c,) Next-generation AM systems provide advanced features, such as high aspect ratios and ultra-thin walls, that revolutionize what’s possible with heat exchanger geometries. Source: VELO3D

A typical commercial jet needs four to six heat exchangers per engine to function properly, as well as heat exchangers for refrigeration and other purposes. As a result, the average commercial craft can contain more than 20 heat exchanger units overall.

Most heat-exchangers made for aviation are still assembled largely by hand, requiring many hours of skilled labor and multiple production steps. It is a costly and timeconsuming process. And the ability to innovate beyond traditional heat exchanger design is actually limited by conventional manufacturing and the brazing technology (first employed by the ancient Egyptians around 2400 B.C.) still widely used to manufacture them

Revolutionary: enhancing thermal efficiency

As additive manufacturing (AM, aka 3D printing) started becoming a proven industrial technology in recent decades, a few forward-thinking engineers began applying it to the design and production of heat exchangers—particularly for aviation and aerospace.
Where applied, additive manufacturing has been revolutionary for the supply chain. The ability to consolidate multiple parts into a single, unifi ed component with 3D-printing dramatically reduces assembly times, eliminates expensive tooling, fixtures, pre-cleaning and the use of environmentally hazardous chemicals (such as hexavalent chrome).
Traditionally manufactured heat exchanger designs are limited by the extrusion, corrugation and other metal forming processes. Additive manufacturing has allowed for the surface area per unit volume to be increased far beyond what traditional manufacturing can achieve, enhancing thermal efficiency. Design cycles per iteration can be reduced from 12-18 months to as little as a few weeks, which allows for more design iterations to occur and enables a faster time to market.

The benefits of advanced AM systems

3D-printed heat exchanger
Image 2. This 3D-printed heat exchanger shows precision and fine features that cannot be achieved through traditional, subtractive manufacturing. Photo: VELO3D.

As promising as this first generation of AM technology was, it was still a work-in-progress. But recent developments have now taken the industry to new levels. The most-advanced laser powder-bed fusion (LPBF) metal AM systems are uniquely suited to helping manufacturers design and produce high-performance heat exchangers unlike any developed before.

These newer machines include a non-contact, powderrecoater technology that enables greater design flexibility with the ability to print higher aspect ratio (thinner) walls, surfaces down to zero-degree print angles (which break the 45-degree limit that many current AM machines still must adhere to), interior channels (up to 100 mm diameter) – all printable with fewer support structures that require postprocess removal.
The tighter process control, along with optimized parameter recipes, contributes to a smoother surface finish straight out of the build chamber with no need for elaborate refinishing. Surface roughness in additively manufactured heat exchangers does increase the turbulence and thermal effi ciency. However, the part surfaces produced by most current AM equipment can be so rough that it causes the pressure drop in the heat exchanger to be unacceptably high, and a non-starter for the application. The smoother surfaces produced with next-gen systems provide a better balance to optimize thermal efficiency while minimizing the pressure drop to enable optimum system performance.
A key aspect to having high production yield is ensuring the printer is calibrated prior to starting the build. Newer printers have a variety of sensors that verify that the printer is in spec, and this process is initiated with the push of a button by the operator. Metrics such as laser distortion mapping, laser focus, beam stability, and powder-bed quality are verified in real time. If the printer is out of spec, the machine can self-calibrate without the intervention of a field service engineer.

Agility and responsiveness

nTopology’s generative-design
Image 4. nTopology’s generative-design software was used to create this novel heat-exchanger design with a complexgyroid inner structure that enhances thermal performance. Printed on a VELO3D Sapphire AM system. Source: nTopology.

The development of first-generation additive manufacturing machines made it possible to start manufacturing traditional plate-fin heat exchangers with 3D printing. Not all heat exchanger designs could be reproduced with AM, however, and many manufacturers simply could not justify making the switch. Now, with the advent of the more advanced AM systems, 3D printing can be used to create solutions that were not even considered possible before. Not only can these systems deliver on more innovative designs, they can do so while reducing costs, minimizing time-to-market, decreasing weight, and improving performance.

If you are considering changing your heat-exchanger production methodology from conventional methods to AM, you are likely thinking about the new variables and risks involved. Here are some thoughts: Each weld joint likely costs you about $100—but what does it cost you if that joint fails? What is the cost of quality in production of leaking braze joints? What is the cost of a braze joint failure in the field? What if you could deliver highestquality 3D-printed parts to your customers—with tighter packaging, higher thermal performance and lower pressure drop—with higher yields and in much less time?

Recommendations

For those heat-exchanger manufacturers interested in trying advanced additive manufacturing, it’s recommended to consider
a part where there is difficulty sourcing components, poor yield, or a need for improved thermal performance. Discuss metrics with your customer and consider trying out the new generative-design software that will create the most innovative results possible while delivering on the goals of thermal performance, pressure drop, cost & weight. Material choice is important, as components that can be manufactured with materials that lend themselves to the AM process — F357 and IN625—are most common for heat exchangers, but IN718, Ti-64, or Hast-X are available as well.
Manufacturers who are thinking about moving to AM for heat-exchanger production should be aware that, while brazing will continue to be used by some, the availability of the new advanced metal AM systems is starting to revolutionize the industry. There are now opportunities to move ahead of the competition by designing and producing high-performance products with additive manufacturing technology that meets the expectations of the most demanding aerospace and aviation customers.

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