West Dundee, IL

HiETA develops metal additive manufacturing (AM) methods for the production of complex, lightweight structures for heat management applications. Parts manufactured include combustion components for micro gas turbines, phase-change heat exchangers for fuel cells, and components for internal combustion engines.

The build chamber of the RenAM 500M metal additive manufacturing system.

Traditionally, heat exchange products are made up of thin sheets of material that are welded together. The complexity of the designs makes production both challenging and time-consuming, while the material used for the welding process adds to the overall weight of the part. Prior to the work at HiETA, little research had been undertaken into the use of AM for the manufacture of heat exchangers. The initial challenges were to confirm that AM could successfully generate sufficiently thin walls of the required quality and then to produce a complete component with the complexity of a typical heat exchanger. The third challenge was to use the knowledge and experience developed to move the process from the manufacture of samples and prototypes into low-volume production.

HiETA chose Renishaw’s AM250 system across a range of projects. First, HiETA worked with Renishaw to develop specific parameter sets for the production of leak-free thin walls in Inconel down to thicknesses of 150 microns. Both companies produced samples using a variety of settings on the AM250. The resulting samples were heat-treated and then characterized. The test results enabled the companies to confirm the optimum parameters on the machines for thin-walled structures and also allowed HiETA to develop a design guidebook with parameters for heat transfer in heat exchangers manufactured using laser powder-bed fusion technology.

Having achieved a leak-free integral wall, the next stage was to move to a complete, full-sized unit that could be completed in a reasonable build time. Two projects were undertaken; the first was a cuboid heat exchanger (recuperator) to be used as a range extender for electric vehicles. The second aimed to take the design of the components to higher levels of complexity beyond the traditional cuboid shape. More complex shapes can improve product performance and cycle efficiency, give benefits in packaging, and reduce costs. The design chosen for this stage was a recuperator of annular form that could be wrapped around other components and contain integrated manifolds to give a more compact overall system. As well as allowing further optimization of the Renishaw equipment to handle the larger samples, HiETA used these projects to develop an extraction process for removal of excess powder material from the cores of the heat exchangers.

The first result of the partnership between HiETA and Renishaw was to produce the basic data needed to set up the AM equipment to produce thin-walled structures successfully and to provide the parameters needed to predict the performance of heat exchangers manufactured with the Renishaw equipment. The thermal transfer and fluid flow data that resulted has been incorporated into the CFD and finite element analysis programs used by HiETA. These programs can be used for an initial assessment of the likely performance of new component designs and confirm that the proposals have the potential to meet the customer’s requirements. At the same time, Renishaw has added software improvements, both to facilitate processing of the large amounts of data when the complete recuperator is sliced into thin layers and to create the build instructions needed for the complete part.

The first attempt at making a complete product on the AM250 system generated a successful component but needed a build time of 17 days. Following improvements to the hardware and software, this was reduced to 80 hours. Detailed testing showed that the component would meet the requirements in terms of pressure drop and heat transfer, with a weight and volume approximately 30% lower than an equivalent part made by conventional methods.

“With almost all of our projects, we are trying to lightweight components and solve thermal management issues,” explained Stephen Mellor, Lead Project Engineer at HiETA. “Through our partnership with Renishaw, we have produced components that are typically around 40% lighter and smaller by volume than anything equivalent that is available on the market. This is possible because with the Renishaw technology, we can design and manufacture many novel and high-performing surfaces integrated into a single component.”

Following the success with the Renishaw AM250, HiETA invested in the more powerful RenAM 500M system to enable more cost-effective production of commercial components in low volumes.

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