Aug 4, 2015 | By Alec

While we owners of desktop FDM 3D printers rarely realize it, metal 3D printing isn’t all fun and fantastic either. One often heard complaint is the limited number of available materials and inefficient manufacturing. However, one team of scientists at the Virginia Polytechnic Institute and state University has now developed a Binder Jetting 3D printer that could make copper, one of the most sought after metal materials, available in an efficient manner.

A perfect and inexpensive conductor of heat and electricity that also does very well in alloys, copper is one of the most widely used metals in the world – especially in electronics. However, being relatively soft, it has so far been quite a hurdle in 3D printing terms. One of the particular problems it faces it that 3D printing creates microscopic pockets of air into the parts, something that is detrimental to the parts’ strength (which isn’t very high to begin with). However, this new machine by Associate Professor Christopher Williams and PhD student Yun Bai, seems to successfully deal with all these issues.

As the researchers explain in a recent paper on the subject, this project grew out of a limitation of current metal 3D printing, especially in an efficient way to conduct heat. Copper would obviously be perfect. ‘ However, advances in the design of highly efficient thermal management systems are somewhat stymied by an inability to Additively Manufacture complex structures with copper material. To release this design constraint, [we] are investigating the use of Binder Jetting to process copper. This layer by layer fabrication process offers the utmost design freedom in the realization of complex geometries,’ they explain.

‘What we are doing that’s different, is that we are printing copper,’ Williams explains to reporters. ‘It’s a really tricky metal to create. We are working with a process called binder jetting. In that process, you’re using an ink jet head to actually selectively jet glue into a bed of (copper) powder, one layer at a time. Once the part is created in that fashion, we then take it to a furnace to then sinter or fuse the particles together to make the metal part.’ That is, in a nutshell, what their entire project and custom 3D printer is all about.

The machine they developed therefore features an additional inkjet printhead that adds an extra layer of binder during 3D printing. ‘Once a layer has been printed, the powder feed piston raises, the build piston lowers, and a counterrotating roller spreads a new layer of powder on top of the previous layer. The subsequent layer is then printed and is stitched to the previous layer by the jetted binder. The remaining loose powder in the bed supports overhanging structures and is removed with compressed air in post processing,’ they explain in more detail. The parts are then cured at a higher temperature, before sintering the copper to achieve the required strength and density.

Not only does this process fill the air pockets between the copper layers, Binder Jetting is also exceptionally suited for complex copper parts because it doesn’t require any support structures and is scalable to just about every printer size. ‘These large part sizes are possible as Binder Jetting is free from the powder bed thermal management constraints typically found in direct-metal AM processes. Furthermore, Binder Jetting systems have a relatively high throughput: a 100 nozzle printhead can create parts at up to ~200 /min,’ they explain.

All these tests were done on with ExOne’s standard binder (PM-B-SR-1-04), which is a widely used binding agent for many metal. The polymer inside hardens upon heating to provide a satisfactory strength, before sintering follows. So far, the tests were very successful, with three parts being printed on an ExOne R2 3D metal printer. ‘In the temperature range from 1060 °C to 1090°C the sintered density and shrinkage is proportional to the temperature. The reducing sintering atmosphere can achieve a purity of up to 97.3%,’ they reveal.

But most importantly, they have also come up with a way of dealing with the air pockets. The team is currently working on a way of adding a nanosuspension binder into the polymer glue to fill these microscopic parts on each and every layer. While slightly complicating the entire process, this will greatly increase the part density and opens the way for a wide number of 3D printed copper applications. ‘“We hope [the binder glue will] improve its sintering performance and its mechanical performance and its electric conductivity,’ Williams told reporters. ‘We hope that we’ll be able to share these results, and enable engineers and designers to design new copper products for energy applications, thermal applications, structural applications with any kind of complexity that you can imagine.’

This promising copper 3D printer is thus reaching new milestones, but there’s only one downside to it. Williams expects that it will take at least five years before this unique process can be integrated into commercial machines. However, it definitely paves the way for long term innovations in a wide variety of fields – from consumer electronics all the way to aerospace applications. In short, it is well worth the wait.

 

Posted in 3D Printing Technology

 

 

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