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Direct metal printing helps manufacture lean and green heat exchanger

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article image Direct metal printing removes the complexity involved in manufacturing

Direct metal printing by 3D Systems, On Demand Manufacturing helped the University of Maryland’s Center for Environmental Energy Engineering (CEEE) develop a more efficient heat exchanger while meeting their ‘lean and green’ manufacturing objectives.

The CEEE is working with Oak Ridge National Laboratory to develop the next generation of miniaturised air-to-refrigerant heat exchangers for HVAC and refrigeration applications. For this project, funded by the US Department of Energy’s Building Technologies Office, only one type of manufacturing could satisfy CEEE’s lean and green mandate: direct metal printing (DMP) using 3D Systems' On Demand Manufacturing service.

Greater efficiency in less time

CEEE provides innovative solutions and technology transfer to meet industrial research and development challenges. 3D Systems On Demand Manufacturing is the world’s leading provider of unique, custom-designed parts, offering instant online quotes, expertise in 3D design and printing, and proven manufacturing services support.

CEEE partnered with 3D Systems to increase the efficiency of a 1kW heat exchanger by 20 percent while reducing weight and size. Thanks to the DMP approach, the manufacturing cycle for the heat exchanger was reduced from months to weeks.

Making it manufacturable

Heat exchangers are used widely across the world in any application where heat, cool air or refrigeration is required. At a global level, heat exchange is a multi-billion-dollar industry touching everything from consumer goods to automotive and aerospace engineering.

CEEE’s extensive experimental and theoretical research has led to automated design algorithms for creating unique shapes for tubes and fins used in heat exchangers. In addition to achieving an optimal air-side thermal resistance, key objectives also included minimising the size and weight of the heat exchangers. However, these innovative designs require new ways of manufacturing.

Vikrant Aute, director of CEEE’s Modeling and Optimization Consortium, explains that most of these optimised designs are simply not economically manufacturable today as they are too complex technically with small feature sizes and extremely thin material thicknesses.

This is where the unique capabilities of direct metal printing come into play – by removing the complexity.

Direct metal printing, in this case 3D Systems’ ProX DMP 320 system enabled CEEE to prototype its heat exchanger with non-conventional, variable shapes that weren’t possible to manufacture using traditional forming techniques such as extrusion or stamping. According to Aute, DMP allowed them to manufacture highly unusual tube shapes in the form of a hollow droplet to carry the refrigerant.

3D Systems On Demand Manufacturing provided input into the design of the heat exchanger to ensure that it could be manufactured efficiently.

Jonathan Cornelus, business development manager at 3D Systems On Demand Manufacturing says the ProX DMP 320 allows them to deliver open-channel diameters and feature sizes as small as 250 microns in a reliable and repetitive way. He adds that high pressure and leak-tight exchanger walls can be built as thin as 200 micrometres, which is a true game-changer for heat exchanger applications.

Better design in one part

Working together, CEEE and 3D Systems optimised the heat exchanger design so it could be printed as a single part that requires minimal secondary finishing operations. Manufacturing can be completed in weeks instead of months, enabling CEEE to test designs much earlier and more often during the research program. The one-part design also helps ensure greater reliability.

Observing that assembly by brazing extremely thin tubes to a manifold using conventional manufacturing technologies can be painstaking with very low reliability when it came to leakages under high pressure conditions, Aute says DMP technology eliminates any need for assembly since the part is produced in one continuous operation, no matter how complex the parts or how delicate the features.

The ProX DMP 320 not only handles very complex parts at no extra cost, but also meets CEEE’s lean and green goals.

Pre-set build parameters developed by 3D Systems based on the outcome of nearly half-a-million builds, provide predictable and repeatable print quality for almost any geometry.

A totally new architecture simplifies set-up and delivers the versatility to produce all types of part geometries in titanium, stainless steel or nickel super alloy. Titanium was chosen for the CEEE heat exchanger project, based on its lack of porosity and the ability to provide extremely thin, but very strong walls.

Exchangeable manufacturing modules for the ProX DMP 320 system reduce downtime when moving among different part materials while a controlled vacuum build chamber ensures that every part is printed with proven material properties, density and chemical purity. The small portion of non-printed material can be completely recycled, saving money and providing environmental benefits.

CEEE performed extensive testing on the new heat exchanger design, using infrared cameras to verify that heat was dispersed uniformly over the exchanger and that all the narrow, droplet-shaped exchanger channels were open and functioning fully. Results showed that the DMP-manufactured heat exchanger performed as expected.

Adding mean to lean and green

The unique capabilities of direct metal 3D printers such as the ProX line are rapidly turning the DMP technique from an experimental prototyping tool into a mainstream production asset for manufacturers worldwide.

3D Systems' Cornelus says DMP is being used in new applications as well as massive improvements for existing projects in upper-end aerospace and industrial equipment markets, especially in cases where reduced space, low weight and high efficiency are critical concerns.

He adds that CEEE’s heat exchanger application exemplifies the importance of DMP in the lean manufacturing space for creating low-volume, high-complexity metal components. These parts are now performing critical functions under challenging conditions such as continuous stress, high pressure, repeated use and extreme temperatures.

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