Research highlights from Fraunhofer IWU, Dresden Branch of the Institute

Manufacturing beyond the limits of today’s processes – additive manufacturing

The laypersons calls it 3D printing, the expert talks about additive manufacturing. Strictly speaking, nothing is printed, but built up layer by layer using various materials. For example, plastics are melted and pressed as a liquid through a nozzle before they solidify again. In addition, complex and very large metal components can be manufactured by additive processes, for example in industry. Scientists at Fraunhofer IWU proved this to work.

The researchers applied laser (beam) melting, thus choosing new paths for developing and manufacturing innovative components. Based on computer models, they are built up directly, for example using powder of stainless steel, aluminum, titanium or cobalt-chromium. A laser beam successively melts this powder entirely. When it hardens again, it results in a microstructure that is almost 100 percent dense. Since the components are generated layer by layer and without using any tools, this process offers nearly unlimited freedom of design and construction, and it allows for any complex metal structure.

This includes tools used for forming presses to shape metal sheets for car body production. The engineers of Fraunhofer IWU have special competencies in this area. Using laser beam melting, they developed tool inserts with new functions. For example, they manufactured components with delicate channels through which coolants can flow. This method allows for considerably faster cooling down of the tools to the correct operation temperature for the next pressing cycle. Thus, more parts can be produced in a shorter period of time, the workpiece quality is improved and resources can be saved. The molds and workpieces produced by additive manufacturing are absolutely robust and highly stress-resistant, which was proven by the IWU scientists under conditions of mass production.

Smart facade with energy-saving effect – project house smart³

Almost 40 percent of the total energy consumption in Germany is attributed to buildings. Heating, cooling, airing of residences, office buildings and public buildings is cost intensive. Energy is mainly wasted by buildings with extensive glass facade. Within the framework of the BMBF-Zwanzig20 innovation initiative “smart³”, researchers of Fraunhofer IWU together with the Department of Textile and Surface Design of the Weißensee Academy of Art Berlin are developing facade components that react independently to sun exposure and the arising heat, thus reducing the energy consumption.

In order to control the facade element, thermal energy of the sun is used exclusively. The demonstration unit “Solar Curtain” based on the draft by a design student, consists of a matrix of 72 individual textile components that look like blossoms. Shape-memory actuators are integrated into the textile modules. They are thin, 80 mm long wires of a nickel-titanium alloy that remember their initial shape upon heating. If the facade is heated by the striking sunlight, these wires are activated. They contract, thus opening the textile components without any sound. The open surface of the facade element closes and the sunlight cannot enter the room. If the sun disappears behind clouds, the elements close again and the facade is transparent again. The effect is based on a special lattice structure in the material. If the wire is bent and heated, it “remembers” the original design that it had before bending and resumes it.

The facade element can be imagined as a membrane that adapts to the daily and seasonal weather conditions, offering the ideal shading for every position of the sun.

The sun screen designed for extensive glazing can be installed later without any problems and offers numerous design possibilities. Patterns, geometry, color and reaction temperature of the individual blossom modules can be adapted and specific areas can be shaded individually. Due to the modular design the “Solar Curtain” can also be adapted to curved glass surfaces. The design is independent of the type of building.

Precisely adapting artificial hip joints – medical engineering

In Germany more than 200,000 people need a hip prosthesis every year. So far, the physicians have relied on the measuring tape and their trained eye to adapt the artificial hip joints to their patients’ leg length. The consequence of this process, which is not very precise: After hip surgery, the affected leg can be up to two centimeters shorter or longer than before. If problems occur with the vertebral column, only arch supports will help to balance this difference.

The scientists of Fraunhofer IWU developed a solution for this problem, together with their project partners, the Leipzig Clinic for Orthopedics, Trauma Surgery and Plastic Surgery of the University Hospital Leipzig, the University of Applied Sciences Zwickau and their Research and Transfer Center Association, the AQ Implants GmbH and the MSB-Orthopädie-Technik GmbH: a precise measuring process combined with an adjustable implant.

The principle of the measuring method: the physician attaches a plastic box containing two LEDs onto the shin of the laying patient. Then he grabs the overstretched leg at the heel and moves it upward. Due to the circular motion, the light points describe an orbit that is recorded by a camera located about one-and-a-half meters next to the patient. This resembles a compass: the hip joint, where the leg is “hinged”, would be the needle and the LEDs would represent the pencil. If the distance changes because the leg becomes longer or shorter, so does the orbit that the LEDs describe.

The measurement is conducted by the physician directly before the surgery and a second time, after the implant has been inserted tentatively – the box remains on the leg during the surgery. A software compares the two orbits and determines whether the leg is as long as it was before the operation. If necessary, the physician adjusts the artificial hip. Currently, clinical trials of the measuring system are running.

A smart drive repairs itself – adaptronic

Ball screw drives are the drive systems most commonly used in machine tools. A spindle is driven via a motor or gears and belt drives. Between spindle and nut balls move in grooves. These balls move along the axis when the spindle is rotated. In the ball-return track of the spindle nut the balls are returned again, thus closing the movement circuit. Rotational movements are transformed into linear movements. The advantage of a ball screw drive is its high efficiency and its energy efficiency. If it is defect, the repairs can cost several thousand euros. And if it fails during running operation, further machine components can be damaged in the worst case.

Another challenge: in order to position the drive as precisely as possible, a high mechanical preload is set up, i.e. the clearance between spindle and nut is reduced to few micrometers. This leads to increased friction, fatigue and finally to wear. This expands the clearance between nut and spindle, and the preload and the machining accuracy of the machine tool drops permanently. The ball screw drive has to be exchanged or, if possible, a new preload has to be applied.

Within the framework of the project “LastPass”, funded by the Federal Ministry of Economy, scientists of Fraunhofer IWU managed together with industrial partners to integrate shape-memory actuators into a ball screw drive. This “smart drive” varies the preload itself by using the heat arising between the rolling contacts for activating the integrated actuators. In order to vary the pre-load, a ring-shaped actuator element was integrated between the two washers. Due to the frictional heat the shape-memory actuators expand up to a predefined degree, thus increasing the preload force permanently. This elongation stays after onetime activation and does not need any further energy supply. In first trials the preload was increased by an average of 60 percent. The researchers are already thinking ahead: The system shall be monitored via sensors in a next step in the sense of Industry 4.0.

Joining of thick sheets – joining technologies

In boxing clinch means a tight clinch of the opponent from which he can hardly break lose. A very tight connection is also the meaning of clinching in terms of joining technology. Sheets are joined without supplementary material, i.e. without welding, riveting or bolting them – this offers an economic advantage.

Clinching is a forming process, since the joining takes place via forming of the sheets. The tool that joins the sheet consists of a die and a punch. The latter forms the materials to be joined into the die, which is designed in such a way that a shape similar to a push-button arises. The sheets form an undercut which holds them together. This method is often used in automotive production to join car body components. It joins materials that cannot be joined by spot welding. This process has also been established in the equipment industry and the electrical industry. Thin sheets with thicknesses of a single sheet of up to two millimeters are used here. For a long time concepts have been missing to apply this efficient joining technology also for industrial sectors using thick sheet processing, such as rail construction, ship building, manufacturing of commercial vehicles or structural steel engineering.

This is what the scientists of Fraunhofer IWU are researching. Using computer simulations, they develop tools with which thicknesses of single sheets of an average of up to one centimeter can be joined by clinching. The application of this process in industrial production is demonstrated by the engineers in a project with the escalator manufacturer Schindler. They clinched stiffening braces to the top and bottom chords of an escalator framework.

Since the process can easily be automated and due to its high joining speed, it has advantages compared to welding, and above all, thermally caused deformations in the workpiece can be avoided and preliminary work and supplementary material can be saved.

More quiet on the rail via simulation – technical acoustics

Environmental noise has a decisive influence on health and quality of life. For this reason traffic noise plays an important role, particularly in cities. Thus the acoustical requirements are continuously increasing regarding road vehicles, rail vehicles and water crafts. In rail vehicles, a significant sound source is the drive unit consisting of the electric drive and the transmission. The noise emissions of these components have a characteristic sound with a defined frequency which can easily be perceived and which are highly irritating.

In a project of Fraunhofer IWU scientists developed a simulation-based method for acoustic optimization of gear elements. It was evaluated using a single stage spur gearbox of a rail vehicle. A dynamic simulation model was used to determine acoustically critical rotational speeds and loads. Thus the scientists found two approaches that enable acoustic optimization when applied in parallel: the improvement of the microgeometry of the individual gear components and a structural reworking of the gearbox.