• How To Make A Safe Trip To The European Sights
    In Times Of Corona

Author: Viola Schick

Nobody would think of describing the Eiffel Tower with its 7300 tons of steel as filigree. But if you try to reconstruct an Eiffel Tower at the ratio 1:8500, a height of 324 m becomes a height of 38 mm.

 

With conventional manufacturing methods it is almost impossible to exactly reproduce the now suddenly very fine detailed structures of the Eiffel Tower. At such orders of magnitude, the limits of additive manufacturing are also reached. We were clearly able to push these limits downwards without interfering with the M290’s hardware. Thus, finally a journey to the most well-known objects of interest of Europe is safe even in times of Corona.

A major advantage of additive manufacturing is that it allows the production of parts that could not be manufactured in this way using conventional methods. If, however, bulk parts and at the same time very filigree structures are to be produced on one system, limits have been reached here too. The shift of these limits, which we were able to achieve, was achieved by using a time-modulated laser.

To illustrate the advantages of the modulated laser, we have built two Eiffel Towers. The left one was built with the standard parameters of the laser in cw mode, the right one with modulated laser.

 

So far, we have identified the following promising advantages:    

  • Fine detailed parts with high resolution are possible: Particularly at the top of the towers, where the structures become extremely fine, it becomes clear that the individual struts are already fused together in the standard process but are clearly resolved in the modulated process. 
  • Support-free build and large overhangs are possible: The Eiffel Towers were built completely without additional support. The lower arches, however, were only made defect-free during the modulated process. Even the extremely filigree handrail of the railing on the first viewing platform could only be built continuously and without errors using modulated laser.
  • As a result of the more fragile structures, it is possible to achieve significantly thinner wall thicknesses. This is of particular interest for lightweight construction.   
  • A very large potential can also be seen in the significantly improved downskins. This makes the modulated process interesting not only for filigree structures, but for all structures with downskins, since less rework is required.    

The starting point for our experiments was the assumption, that with the modulated laser, compared to cw operation less volume is melted due to the regular interruptions, resulting in a thinner melt pool. This was the setup we started with in the first attempts: A M290 with a function generator.

To identify a suitable process window, we started with single tracks on IN718. In order to get as close as possible to the real process and thus obtain the highest possible information value, the single tracks were created under process conditions on an IN718 plate. The following two pictures show images taken with the Keyence Profilometer, which allows the surface profile to be measured, as well as an etched cross section.

These first tests with single tracks were performed using an experimental design in which the laser power, scanning speed, pulse duration and frequency were varied. Important results from these experiments are especially the width of the melt track, but also the continuity of the track. The following graphs show the plots of a regression model for the thickness of the single tracks. The regression model was developed based on the 188 exposure parameters tested.

Based on these results we started our first tests with a real part. During these building tests, which took place with honeycomb structures it turned out that also elevations of the track are critical, since a recoating contact often leads to the destruction of the part.

In the following experiments we focused mainly on the construction of grid structures to determine the wall thickness of the parts using a coordinate measuring machine. It turned out that already in these first tests we succeeded in reducing the wall thickness by 13% compared to the standard cw parameter for thin walls. To achieve these results, it was necessary to switch to soft recoating because the increasingly thin walls vibrate with minimal contact with the coater, leading to holes in the powder bed and, as a result, holes in the part.

In a next step, we were able to transfer the experience we gained in building thin walls to more complex structures. Because our test setup with the function generator could only switch modulation on or off for the complete job, we had to build all parts modulated for our tests. The difficulty here was that these structures also have bulk parts. Therefore, different exposure types are necessary and the hatchdistance comes up as an additional parameter. The following picture shows that this attempt was successful.

That these results are also transferable to other materials is confirmed by tests on Ti64 and AlSi10Mg. The following video shows a high-speed recording of the modulated aluminum process.

In the future this feature will of course also be available for other materials such as 316L, MS1 etc. Currently we are in the process of developing a software with which it is possible to adjust the modulation as exposure parameter.

At EOS were constantly challenging the status quo and strive for perfection. Our customers voice is highly appreciated and we`ll try our very best to develop solutions for your challenges and help you become most successful with your application. If our standard products can`t deliver what you need, we are a top motivated team of creative people that love to think outside the box and go the extra-mile for you.