future view

Ammunition from a printer

12 September 2017 • 4 min reading time

Designing gunpowder, rocket engines, and explosive charges with a 3D printer. By combining expertise in energetic material and 3D printing, it can be done. TNO envisages a future in which entire items of ammunition with the desired effect come rolling out of printers in the required quantity. It is an innovation that is driven by the need for product security, improved performance and cost reduction.

The production of ammunition is an intensive process that requires safety measures. That means that production, storage and transport may not cause unnecessary risks to those involved or to third parties. In addition, work is constantly ongoing into improving performance and flexibility. 3D printing has the potential to play a major role in this. The formability of the manufacturing process allows for greater performance levels using less material, and for integrating flexibility. The production process is also safer, which means that in the distant future, it will be possible to print ammunition on site, according to demand. As a result, the logistical footprint will be reduced, and ultimately, the Ministry of Defence will benefit from lower costs.

3D printing formability

“As well as meeting the ever-present need for ammunition that performs better, TNO is permanently engaged in responding to the demand for smaller and lighter instruments that the troops have to carry,” explains Joost van Lingen, Team Leader Energetic Materials at TNO. “This means that ammunition has to perform better while being lighter in weight. However, there comes a point when you reach the limitations of existing product technologies. That is where 3D printing came in. The formability it offers opens up new opportunities. Four years ago, we decided to explore the potential of printing energetic materials. We selected the most challenging type of 3D munition printing, deliberately choosing to focus on a niche area.”

“The formability of the manufacturing process with 3D printing allows for greater performance levels using less material, and for integrating flexibility”

Printing techniques

“We started by making an index,” says Van Lingen. “What printing techniques and energetic materials were already available, and could they be matched up? We came to the conclusion that TNT was the only explosive material we could print ‘just like that’. Wherever possible, we used ‘off-the-shelf’ printing techniques. Our research focused on increasing the energetic content of printable materials.”

Pressure behind the bullet

After several years of investigation, TNO researchers succeeded in making a product from a non-optimized lump of TNT that is similar, in terms of performance, to standard gunpowder. The first three patents will shortly be publicized. One concerns the composition of the print material. Another deals with the shape, which in the case of gunpowder, is crucial when it comes to improving performance. Van Lingen explains, “By adding several layers of gradient to the material, it burns more and more quickly, with the pressure behind the bullet becoming a kind of plateau rather than an inefficient curve. The third patent is about the bulk density.”

“For the future, we also envisage being able to print the housing, together with the energetic material, in-built sensors and so on”

Shape of a smartie

“Usually, gunpowder particle cylinders are cut perpendicular to the direction of extrusion in larger weapons systems, such as those on Dutch reconnaissance aircraft,” Van Lingen continues. “If you shape them more like a smartie, you can get a lot more particles and therefore much more weight in the same volume. That improves performance. The barrel has to be able to cope with that, but it does produce more pressure with regard to the velocity of the projectile. Extra bulk density to the tune of 18%, for example, results in around 10% more kinetic energy.”

Unique combination of fields of expertise

The idea for linking expertise on energetic materials with that on 3D printing came about at TNO in Ypenburg. Van Lingen explains, “We have been the in-house laboratory for the Ministry of Defence for seventy years and we accept orders for the international defence industry. It was only logical to ‘shop around’ among other TNO employees elsewhere in the country for knowledge of 3D printing. Our colleagues at AMSYSTEMS Center in Eindhoven and the Brightlands Materials Center in Geleen have twenty years’ experience with 3D printing. It is thanks to this unique combination of fields of expertise that we are the leaders in this area.”

Challenges

There are still many challenges ahead in relation to 3D printing. “The more energetic material you add to the binder system, the better the effect, but the more problems you get with viscosity. The mass must remain fluid. Also, many processes are based on the melting of material. One challenge here is that the temperature must not get too high. This should be no more than 300ºC for TNT and 80ºC for normal gunpowder. If the melting point is too close to the ignition point – which is usually the case – then the material is rejected. Another process parameter is pressure. Gunpowder particles are traditionally produced by extrusion, with ductile material being pressed through a matrix. This involves subjecting the material to considerable forces in order to mix it. However, the pressure should not be too high. To improve these processes and materials further, TNO is continuously on the lookout for partners.”

“Thanks to our unique combination of fields of expertise on energetic materials and 3D printing we are the leaders in this area”

Interest and investment

With the right investments, the first real products could be realized in five years. “But things could move more quickly,” believes Van Lingen. “Until now, it has mainly been the Ministry of Defence that has invested in the sustainability and security of this innovation. But we have recently started to receive significant funding from the US for research. There is also interest from industries in which the new gunpowder is to be produced for the time being. At present, the Ministry of Defence has no 3D printers that could be used to print energetic materials, but I expect that to change in the foreseeable future. We also envisage other developments in the future, such as the printing of the housing using energetic material and in-built sensors. I will be very pleased to hear from readers who would like to know more and from businesses seeking to develop a business case.”

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