Artistic photograph of a component that illustrates the fine resolution in stereolithographic printing

forschung leben – The Magazine of the University of Stuttgart

Mobility in the field of 3D printing

The University of Stuttgart and the Karlsruhe Institute of Technology are working together on the transformation of mobility. The goal is to use 3D printing to produce any components with specific properties according to requirements. This is intended to bring production back to Central Europe and sustainably conserve resources.
[Photo: b&b eventtechnik/Gregor König]

Leap-frogging innovations and new technologies are set to make the car production state of Baden-Württemberg into a showcase of contemporary and sustainable mobility. To this end, the University of Stuttgart and the Karlsruhe Institute of Technology (KIT) have joined forces with the “Mobility of the Future” (ICM) innovation Campus.

Prof. Thomas Graf focuses on his work on the laser beam.
Prof. Thomas Graf of the IFSW adjusts the laser beam.

“Essentially,” says Dr. Max Hoßfeld, Managing Director of the ICM in Stuttgart, summing up the problems of today's mobility behavior, “we still drive the same kind of cars as Bertha Benz”. The car pioneer Bertha Benz personally took the wheel on her first successful long-distance journey in a car from Mannheim to the center of her native town of Pforzheim. “Basically, no city planner wants back these days,” says Hoßfeld. This is because, private transport, as we all know, takes up a lot of space and produces exhaust gases and noise pollution. Yet, getting on top of these problems is also an issue in a state whose key industries depend on people buying a new car every few years.

But vehicle sales had started to falter even before and especially during the Covid-19 crisis, which has drastic consequences in terms of corporate profits and the labor market. “The conventional automotive industry business model will only last for another one or two vehicle generations at most,” says Hoßfeld, describing the challenges, “after which we will need different solutions.” What we need is a transformation of mobility culture and its related products and business models, but also of our current globally fragmented value chains.

Dr. Max Hoßfeld in Forschungsumgebung
Dr. Max Hoßfeld

We have to bring value creation back to Central Europe to reduce global dependencies, and, to achieve that, our production system has to become more flexible and efficient.

Dr. Max Hoßfeld, Managing Director of the ICM

It’s all about “advanced Manufacturing.” Researchers at the ICM are pursuing the vision of a universal production technology or “universal machine” to take this to a new level, which will combine currently separate serial production processes in a single system technology. Once set up, this flexible all-purpose system will be able to accept direct CAD data input and then produce practically any component on site as required, even if the batch size is 1. 3D printing, which can not only be used to produce high-quality (lightweight) components, but also components with novel integrated functions, will be a key technology in this context.

A leading role for lasers

“Most 3D manufacturing processes are laser-based,” explains Volkher Onuseit of the University of Stuttgart’s Institute of Laser Technologies (IFSW), which is involved in various ICM projects. This process involves melting metal wires or powder by laser to build up the workpiece and its contours layer by layer. The problem with this is that the surfaces of components produced in this way are relatively rough and insufficiently precise for accurate fitting with other components or to guarantee such properties as adhesion or friction, which means that they have to be reworked by removing part of the material prior to further processing.

The three researchers each hold components in their hands as if they were exchanging technical information about their properties.
Prof. Hans-Christian Möhring (IfW), Dr. Max Hoßfeld (IFSW) and Prof. Thomas Graf (IFSW)

“This raises certain questions,” explains Onuseit: “how much more material do I have to build up to ensure that the post-processing process produces the desired result? How and with which tool can the part be produced? How could the processes be regulated?” Such questions can only be answered in an interdisciplinary manner. That’s why researchers from the fields of Automotive Engineering, Product Development, Production Engineering, Chemistry, Materials, Electrical Engineering, Aircraft Design and Machine Tools are collaborating in the ICM. The relevant topics are being dealt with by research teams from Stuttgart and Karlsruhe. “This works extraordinarily well,” says Hoßfeld, who is also responsible for the operational collaboration between the two locations.

The complementary competences of the researchers from Stuttgart and Karlsruhe in both basic research and technology transfer complement each other perfectly.

Dr. Max Hoßfeld

A better understanding of interactions

The University of Stuttgart’s Institute for Machine Tools (IfW), the IFSW, the Institute for Control Engineering of Machine Tools and Manufacturing Units (ISW) and the Institute for Materials Testing, Materials Science and Strength of Materials (IMWF) are therefore collaborating in a pilot project to investigate final, contour-optimized production as well as the optimization of additively manufactured component properties. The KIT Institute of Production Science (wbk) is involved.

Dr. Becker (left) and Steffen Boley (right) together hold a test component in their hands and look at it while testing.
Dr. Becker and Seffen Boley, research associates at the IfW, examine a test component.

One particular challenge in the optimization of the final contours is the interplay between 3D manufacturing and finishing. “Melting powder or metal influences the material properties within the component,” explains the Director of the IfW, Prof. Hans-Christian Möhring, “the residual stress for example.” Removing material during post-processing changes these conditions again. “We want to gain an understanding of this complex chain of effects and model the component properties.”

As an initial step, Dr. Dina Becker, an academic employee at the IfW, has the IFSW produce small cylinders of aluminum wire using the laser cladding technique. Her goal is to discover how many lengths of wire must be laid out to achieve a certain material thickness, as well as how wide the melting band becomes and what effects this has on the component shape accuracy.

Dr. Dina Becker holds a cylindrical component in each hand and checks whether they fit together.
Dr. Dina Becker checks the shape accuracy of a cylindrical test part.

“We have already been able to define a minimum wall thickness during our tests at the IFSW,” she says, “but, initially, the accuracy and surface quality of the cylinders were not optimal. We need a homogeneous wall thickness.” So, in the next step, Becker varies the post-processing parameters and analyzes how these affect the material properties. The research being carried out on comparatively simple components, such as cylinders, will later be applied to complex component geometries.

Our objective is to understand the entire process of additive-subtractive manufacturing such that we will be able to adjust individual processes even for complex components and achieve certain properties in a conscious manner.

Prof. Hans-Christian Möhring, Director of the IfW

Optimizing 3D printing

However, additive manufacturing (3D printing) has one disadvantage – it is slow and expensive. The objective of another project, in collaboration with the Institute of Aircraft Design (IFB), the Institute of Polymer Chemistry (IPOC), the IFSW and the Karlsruhe-based wbk, is, therefore, to increase productivity, whereby the speed of production is one of the key variables. “We want to use ultrashort pulsed laser beams to increase the production of high-precision components in resin-based additive manufacturing processes from the current few cubic millimeters per second to cubic centimeters per second to achieve relevant production volumes for future mobility applications,” explains Tristan Schlotthauer, a research associate at IFB. The researchers are investigating how dynamic laser beam shaping based on two-photon polymerization could be used to decouple the production process from the layered production that has been used to date. A second variable would be not only to print individual components, but complete assemblies which would dispense with subsequent assembly tasks. Various things , such as metallic inserts for particularly stressed areas or mechatronic components that perform sensor and actuator functions can also be integrated into the components during printing. “This has not been possible until now, or was only possible at great expense,” says Volkher Onuseit of the IFSW.

Photo of the test setup
Blue light caused by the two-photon polymerization effect in the resin basin at the Institute for Aircraft Design.

Unimagined degrees of freedom

This can also result in the creation of new component types that give designers in the mobility sector unimagined degrees of freedom, which Prof. Nejila Parspour of the Institute for Electrical Energy Conversion (IEW) believes will be of particular benefit in the field of electric mobility. Together with the IFSW and the Karlsruhe Institutes for Product Development (IPEK) and for Vehicle System Technology [de] (FAST), the IEW is searching for ways to better solve one of the basic problems of electromobility using 3D-printed components: “Electric motors” she explains, “have to be lightweight and compact whilst also achieving extremely high levels of efficiency in urban traffic and on the freeway, i.e., in very different speed ranges.” A magnetic field, which converts electricity into speed plays a key role in this. There are three influencing variables that can optimize this conversion process, which include the design, which consists of mathematical algorithms, the controller and the “ingredients”, such as hard and soft magnets.

Prof. Nejila Parspour is using 3D-printed soft magnets.

Our research makes new types of motors possible, from which we expect much higher levels of efficiency.

Prof. Neijla Parspour, Director auf the Institute of Electrical Energy Conversion

Parspour and her team came across chemists at Aalen University who produced such magnets using 3D printing almost by chance and were inspired, and not only because magnets can be produced in large quantities and with special structures using 3D printing. “The real breakthrough,” she explains, “is that, similar to knitting, 3D printing enables each layer to be designed differently. One can integrate air or other materials into the soft magnet layers,” which is exciting because the magnetic field always follows the path of least resistance and is attracted to areas of good conductance whilst avoiding air pockets. Therefore it is possible to integrate areas with different levels of conductivity in soft magnets to channel the magnetic flux in the desired direction, which “makes new types of motors possible, from which we expect much higher levels of efficiency,” as Parspour says with enthusiasm.

But 3D printing can also be used to produce solid magnets in a more differentiated manner. To stabilize their thermal behavior, these contain rare earth elements, which are currently expensive and are also often extracted under questionable conditions. “3D printing,” Parspour explains, “enables us to incorporate rare earth elements into components in a very targeted manner, i.e., depositing more in areas that get warm and less elsewhere.” This will not only benefit future mobility but also the general conservation of the environment.

Text: Andrea Mayer-Grenu

 

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Andrea Mayer-Grenu

Scientific Consultant, Research Publications

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