Fraunhofer (17)

In the past, selective laser melting (SLM) technology has been cost effective only for manufacturing components with relatively small volumes. In an innovative breakthrough that combines SLM with casting, now the Fraunhofer Institute for Laser Technology ILT has developed a cost-effective method for manufacturing solid, large-volume components using SLM.

Injection molding is used to make the majority of plastic components. With additive manufacturing techniques such as SLM, it is possible to integrate complex conformal cooling channels into the tool inserts required for injection molding. These channels allow the tool mold to be heated up during the injection process, and the melt to cool down quickly and evenly – resulting in rapid, distortion-free manufacturing. However, the manufacture of large-volume tool inserts using SLM is very cost-intensive, because the main production costs are volume-dependent.

To tackle this problem, scientists from Fraunhofer ILT have teamed up with the Foundry Institute at RWTH Aachen University and partners from industry in a bid to combine SLM and casting methods. In the “GenCast” project, which is funded by the German Federal Ministry of Education and Research as part of the Central Innovation Program SME (or “ZIM” in German), the project partners have worked together to build up the requisite process understanding and developed the process chain for the combined method.

The idea behind combining the two methods is to manufacture the shell of the tool insert from hot work steels (1.2343 or 1.2709) using SLM. During this process, cooling channels with complex geometries are still integrated in the exact places where they are needed to heat or cool the component. The shell built up using this technique serves as a casting mold, which is rapidly and cost-effectively filled with gray cast iron (e.g. GJL-200) or highly thermal conductive copper in a subsequent casting process. This cuts production times by up to 80% compared to components made using SLM alone. The bigger a component is, the more the advantages of this combined method come into play. It can be used cost-effectively from part sizes of only half a liter upward.

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When manufacturing products, the coating technology is a key innovation driver for almost all areas of daily life – for example, for making scratch-proof displays for smart phones or anti-bacterial surfaces in refrigerators. Other coatings protect components from corrosion or aging, for example in a solar cell module or a car engine, without the end user noticing their existence. In industry today, wet chemical processes or vacuum plasma processes are primarily used for coating applications. Both have drawbacks. Vacuum units are expensive, limited to smaller components and applying a coating takes a relatively long time. Wet chemical processes often involve high resource and energy consumption with the corresponding environmental damage and can also cause difficulties in the handling of material combinations for lightweight construction such as plastics/ metals or aluminum/steel.

“There has to be another way”, thought Dr. Jörg Ihde and Dr. Uwe Lommatzsch from the Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM in Bremen. Together with Plasmatreat GmbH, the IFAM team developed a new kind of plasma coating process that works at ambient pressure, that is to say, in an open atmosphere. “And that poses a major challenge”, explains Jörg Ihde. “Because the pressure is more than 10,000 times higher and the absence of a vacuum reactor, we had to stop unwanted particles from forming and embedding in the coating. That was the key to developing robust and efficient industrial processes using the new plasma system.

One nozzle – various functional coatings

The central element is a plasma nozzle. The nozzle is no bigger than a typical spray can. Yet it contains a highly complex coating system. “In the nozzle, an electrical discharge generates small flashes - a plasma that is expelled from the nozzle in the form of a jet. We systematically feed into the nozzle outlet those materials that are excited and fragmented in the plasma and then deposited out of the plasma jet as a functional nano-layer onto the surface”, explains Uwe Lommatzsch. “We achieve extremely high deposition rates, enabling fast and cost-effective production processes to be realized.”

The use of a nozzle allows the coating to be applied very precisely and only where it is needed, thus conserving resources. “We can control the processes so that the same nozzle can be used to apply coatings with various functionalities, for corrosion protection or for increasing or reducing adhesion, for instance”, adds Jörg Ihde. Only very small amounts of coating material are required and practically all materials and material combinations can be coated. The process offers, in addition to the coating qualities and functionalities, even more benefits: it can be easily integrated into an inline production process, requires little space and is easy to automate, meaning it can be controlled via a robot. Yet another advantage: low investment costs and easy on the environment. The positive characteristics benefit industrial production: depositing an adhesion-promoting coating on a car window edge before gluing it in, to replace environmentally damaging chemicals or as a substitute for thick protective paint on printed circuit boards, which improves heat dissipation and hence prolongs service life. The process is already employed in the automotive industry and the energy sector to provide protection against corrosion and aging.

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Fiber-reinforced plastics are the most talked-about class of materials in lightweight construction. In mobility lightweight components can both lower fuel consumption as well as increase the vehicle's operating range. But still the market penetration of complex lightweight components is very low while their manufacturing costs are very high. To tackle this issue, the Fraunhofer Institute for Laser Technology ILT is working together with industry and research partners to develop cost-effective methods of production that will significantly increase the usability of lightweight components in mass-market applications.

Recent years have seen soaring demand for lightweight components worldwide. Typical lightweight construction materials include aluminum, high-strength steels, magnesium, titanium and, above all, fiber-reinforced plastics (FRPs). FRPs consist of an organic matrix reinforced either with carbon fibers (CFRP) or glass fibers (GFRP). The production of FRP products is currently hindered by long cycle times and low levels of automation – two factors that pose significant obstacles to mass production – and methods are now being sought to produce FRP products more efficiently. The EU project FibreChain and the InProLight project, which is funded by the German Federal Ministry of Education and Research (BMBF), have set themselves the goal of developing various integrated process chains ranging from sophisticated specialist solutions to the mass production of fiber-reinforced thermoplastic composites. Fraunhofer ILT’s primary task within the scope of these projects is to optimize methods of cutting and joining lightweight components.

Structural joining by laser beam welding
Drawing on the characteristics of the raw material, Andreas Rösner and his colleagues have developed a method of structurally joining lightweight components. These have traditionally been joined by adhesive bonding or riveting – two comparatively expensive methods that require extensive preliminary work and extended process time. Rösner has overcome these drawbacks by joining the components using a laser. In this time-efficient process, the energy is deposited directly into the joining zone. Thus, complex components consisting of several individual parts can be produced. Furthermore, the process enables the production of persistent structures, creating selective reinforcements. As an extension of this process, the joining of plastics with metal was realized in a special two-stage laser process. Rösner first structures the metallic component with a high-brilliance laser beam, and in a second step he heats it by using a diode laser. The softened plastic then penetrates into the structured metal which leads to an excellent mechanical clawing between the joining parts.

Cutting without damaging the edges
In addition to joining FRP components and producing plastic-metal connections, another step that appears multiple times in the process chain is cutting. As well as cutting the raw material itself, it is also necessary to trim the components and cut out the required holes and sections. One of the key goals of the cutting process is to minimize any damage to the edges of the material. However, conventional laser cutting techniques often produce poor results due to the size of the heat affected zone. Frank Schneider and his colleagues, therefore, decided to develop a series of new cutting methods, one of which uses an innovative short-pulse CO2 laser. By reducing the heat input, they were able to significantly reduce the thermal damage inflicted on the material. The Aachen researchers achieve a nearly complete elimination of thermal damages by using a high power ultrashort pulse laser. Even highly sensitive material combinations in aeronautics can be processed economically by these lasers at a performance of up to 500 Watt.

Many potential applications for FRP components
For the first time, these new laser welding and cutting methods will make it possible to automate the production of FRP components to create a production process that is simplified, fast and cost-effective. To demonstrate this new method’s practical feasibility, the Fraunhofer scientists have already successfully applied it to car seat backs made by the company Weber.
Lightweight components are the preferred technology for any application where a reduction in weight offers the opportunity to cut operating costs, from auto and aircraft manufacturing to shipbuilding and spaceflight engineering. Economical and versatile forms of lightweight design are also becoming increasingly popular for highly dynamic machines and civil engineering projects as an alternative to construction with standard components.

Our experts will be attending the JEC Europe 2012 Composites Show from March 27–29 in Paris to showcase a selection of FRP components produced using the new methods they have developed. These will include car seat backs, front-end components and other examples of lightweight construction applications that rely on laser technology.

Laser Lightweight Construction Center
One example of Fraunhofer ILT’s commitment to research in the field of lightweight construction is the Laser Lightweight Construction Center, which is currently being set up in the Institute's laser machine facility. This will be presented as part of the “Laser Technology Live” event at the International Laser Technology Congress AKL’12 on May 11, 2012. The new Center will bring together various laser systems under one roof, including a gantry system for fiber-coupled machining of 3D sheet metal and FRP components and a 2D laser machine with acceleration parameters of up to 5g. Fraunhofer ILT’s Lightweight Construction Centre will also include a machine with 3D capabilities and a CO2 laser for the machining of FRP components. Rounding out the center’s facilities are high power ultrashort pulse lasers that are able to process CFRP components in particular with an ablation and cutting quality unattained until now.

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Wednesday, 18 April 2012 12:25

Shooting at ceramics

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Producing thin ceramic components has until now been a laborious and expensive process, as parts often get distorted during manufacture and have to be discarded as waste. Researchers are now able to reshape the surfaces of malformed components by bombarding them with tiny pellets.

In corrosive, high-temperature environments, metals quickly lose their elasticity. Beyond certain temperatures the material fails and its properties are compromised; metallic springs stop working if heated above 500 degrees Celsius, for example. But what to do if these are exactly the conditions a production process requires? One way of avoiding the problem has been to make components out of ceramic, a material that is lightweight, rigid, corrosion-resistant and able to withstand high temperatures. Yet this only offers a partial solution, as producing thin ceramics for parts such as leaf springs, lightweight mirrors for optical and extraterrestrial use, or membranes for sensors and fuel cells is both time-consuming and expensive. This is because ceramics can only be machined using costly diamond tools, and the process itself creates tensions within the surface of the material which cause the finished part to distort as soon as it is removed from the machine. Reshaping the components after manufacture has never been a viable option before as the material is too brittle, and so the large amounts of waste that are generated push the costs up.

Precisely calculated paths guide the way

Researchers at the Fraunhofer Institutes for Mechanics of Materials IWM in Freiburg and for Production Systems and Design Technology IPK in Berlin have now found a way to straighten out distorted ceramics using shot peening, a process by which small pellets, known as shot, are fired at the surface of a component with a blasting gun. The shot strikes the surface and alters the shape of the thin, outermost layer of material. By moving the gun over the ceramic part along a precisely calculated path, scientists are able to counteract any undesired warping or create lightly curved mirrors out of thin, even ceramic plates. “Shot peening is common practice for working metals,” says Dr. Wulf Pfeiffer, who manages this business unit at the IWM, “but the technique has never been used on ceramics because they are so brittle – they could shatter, like a china plate being hit with a hammer. This meant that we had to adapt the method to the material with great precision.” The researchers began by analyzing which size of shot would be suitable for use on ceramics, as the surface could be destroyed by pellets that were too big. Pellet speed is another critical factor: hitting the material too fast causes damage; too slow and the shape of the surface is not altered enough. They also discovered that it is important not to bombard the same spot too often with too much shot. Before producing a new component, the scientists first conduct experimental analysis to determine what can be expected of the particular ceramic involved. They fire a beam of shot at it and then measure the resultant stresses to see what sort of deformation is possible and how the beam should be directed.

The experts have already produced various prototypes, including a ceramic leaf spring and a concave mirror. For manufacturing simple components, the technique is now advanced enough to be used in series production. The IWM scientists have recently gone one step further and are developing a computer simulation that will allow components to be worked in multiple axes. Meanwhile their colleagues at the IPK are working on automating the process using a robot.

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Wednesday, 15 February 2012 12:45

A robot sketches portraits

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An industrial robot as artist? From March 6-10, 2012, researchers will be presenting what may at first seem to be a contradiction at CeBIT in Hanover, Germany (Hall 9, Stand E08). There, interested visitors can view the metal painter in action and can even have it sketch their own faces.

Artists are often colorful personalities. This one, though, comes across as cool, precise and metallic – and is anything but extravagant. No wonder – after all, it’s an industrial robot, one that will convert the Fraunhofer stand at CeBIT into an art studio. Its artistic genius only emerges if someone takes a seat on the model’s stool positioned in front of the robot: first, its camera records an image of its model; then it whips out its pencil and traces a portrait of the individual on its easel. After around ten minutes have passed, it grabs the work and proudly presents it to its public. This robot installation was developed by artists in the robotlab group, at the Center for Art and Media ZKM in Karlsruhe, Germany, some of whom are now employed at the Fraunhofer Institute for Optronics, System Technologies and Image Exploitation IOSB in Karlsruhe.

But how does this technical production aid manage to provide an authentic rendering of a person’s facial expressions? “We have used an image-evaluation process that essentially equips the robot with the sense of sight,” explains Martina Richter, a scientist at IOSB. “There is a camera mounted on the robot’s arm that it uses first to take the person’s picture.” Edge-processing software seeks out the contrasts in the image and translates these to robot coordinates: to movements of the robot’s arm.

For the researchers and artists, the main difficulty was to adjust the algorithm for image processing so that the sketched image would leave the impression of a portrait – and so that the high-tech artist would overlook the tiny wrinkles but would still render the eyes. “We attach great importance to the artistic look of the drawings that results, but on the other hand, we have also equipped the robot with an automatic system that enables it to carry out all of the steps itself. With this installation, we have created an interface between art, science and technology,” Richter is convinced.

The robot’s everyday routine is less artistic, however: ordinarily, researchers at IOSB use it to analyze the optical reflection properties of various materials. They shine light on an object - a reflector of the kind mounted on children’s school bags or jackets, for instance - from various directions. The robot’s arm circles the material sample in a hemispheric pattern, measuring how the object reflects light. Experts refer to this as a material’s spatial reflection characteristics. This helps design objects such as reflectors so that they return light in the most bundled way possible to the direction from which it comes – to a car driver, for instance. Then the reflector emits a bright flash that draws the driver’s attention to the child. The objective is different when it comes to paint effects on a car’s own surface: The aim there is to display different hues to the observer depending on the direction of view.

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Friday, 13 January 2012 12:30

Sky light sky bright - in the office

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Working under the open sky – it sounds enticing, but it’s seldom really a practical option. Now, a dynamic luminous ceiling brings the sky into office spaces by creating the effect of passing clouds. This kind of lighting generates a pleasant working environment.

As the wind swiftly blows clouds across the sky, the light is in a constant state of change. The feeling of spaciousness and freedom we experience outdoors is exactly what researchers from the Stuttgart-based Fraunhofer Institute for Industrial Engineering IAO replicate indoors: a luminous ceiling that extends across the entire room simulates lighting conditions which resemble those produced by passing clouds – conveying the impression that you are sitting outdoors.

The innovative luminous ceiling, which was developed by the Fraunhofer researchers in close collaboration with their partners at LEiDs GmbH, consists of 50cm by 50cm tiles. “Each tile comprises an LED board with 288 light emitting diodes (LEDs),” states Dr. Matthias Bues, head of department at the IAO. “The board is mounted on the ceiling. A diffuser film in matt white is attached approximately 30cm beneath the LEDs and ensures that the individual points of light are not perceived as such. This diffuser film creates homogenous lighting that illuminates the room throughout.” The researchers use a combination of red, blue, green and white LEDs in order to produce the full light spectrum. This combination makes it possible to generate more than 16 million hues. What’s more, the white LEDs are more energy efficient than the colored lights, which keeps the energy costs to a minimum.

The main focus in developing the virtual sky was to simulate natural lighting conditions on a cloudy day. To achieve this goal, the researchers carefully examined natural light to find out how – and how quickly – the light spectrum changes when clouds move across the sky. “The LEDs allow us to simulate these dynamic changes in lighting in a way that is not directly obvious to the naked eye. Otherwise the lighting might distract people from their work. But it does need to fluctuate enough to promote concentration and heighten alertness,” says Bues. The results of a preliminary study indicate that users find this dynamic lighting to be extremely pleasant. The study involved ten volunteers who carried out their daily work over the course of four days under these lighting conditions with a lighting surface of 30cm by 60cm. Throughout the first day, the lighting remained static. On the second day, it fluctuated gently, and on the third day the fluctuations were rapid. On the fourth day, the participants could choose which type of lighting they wanted, and 80 percent opted for the fast, dynamic lighting.

A prototype of this virtual sky has now been developed that contains a total of 34,560 LEDs spanning an area of 34 square meters. At full power, the “sky” lights up with an intensity of more than 3,000 lux, but 500 to 1,000 lux is sufficient to create a comfortable level of lighting.

From March 6 -10, 2012 at the CeBIT trade fair in Hannover, the researchers will be exhibiting a 2.8m by 2.8m virtual sky at the joint Fraunhofer booth in Hall 9, Booth E 02. Initial inquiries regarding the new lighting have already come in, mainly for use in conference rooms. The virtual sky currently costs approximately 1,000 euros per square meter, but this price will come down, since the more units are produced, the more cost-effective each luminous ceiling will be.

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Thursday, 22 December 2011 09:55

Electronics made of plastic

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The "Deutscher Zukunftspreis 2011" was won by a team comprising existing and former Fraunhofer researchers. Professor Karl Leo, Dr. Jan Blochwitz-Nimoth and Dr. Martin Pfeiffer were honored for their pioneering achievements in the field of organic electronics.

When the concept was first proposed, it was dismissed as being unrealizable: “It’ll never work,” commented one expert assessor of an application for research funding. Today, 15 years later, the physicist Professor Karl Leo and two of his colleagues have been presented with the "Deutscher Zukunftspreis", one of Germany’s most prestigious research awards, for what was once a highly controversial idea. Leo, director of the Fraunhofer Institute for Photonic Microsystems IPMS in Dresden, has devoted most of his career to organic electronics. Until now, most electronic components have been made of inorganic silicon. The brittle material is a good semiconductor, but its manufacture requires a highly sophisticated process. It involves growing large crystals at high temperatures and then cutting them into thin slices known as wafers.

The more elegant solution is to use an organic material, a type of dye commonly used in the production of road signs. Such materials have the advantage that they can be applied as a coating on flexible films and other substrates. This gives rise to endless new possibilities, such as displays that can be rolled up and carried in a vest pocket or switchable window panes that light up at night to illuminate rooms while hardly consuming any electricity. On the other hand, organic dyes are poor electrical conductors. But this is where the once-mocked ingenious idea comes into play: their less-than-satisfactory conductivity can be increased by doping, i.e. adding a small amount of another chemical substance. After years of experiments, the researchers have succeeded in creating materials with an electrical conductivity a million and more times greater than the original dyes, with a doping ratio of no more than one percent.

The "Deutscher Zukunftspreis 2011", endowed with 250,000 euros, has been awarded by the President of the Federal Republic of Germany every year since 1997. It honors outstanding innovations that have made the transition from the research laboratory to industrial practice, thus helping to create jobs. Fraunhofer is a frequent winner of this prize, no doubt because it operates precisely at this interface between the world of research and the commercial market. This time, the jury chose to honor organic electronics, which Leo describes as a technology “that will revolutionize our lives”.

The ultrathin semiconductor coatings have already made their way into mass production. They are equally versatile as the silicon chips that preceded them, for instance converting electrical energy into light just as easily as they convert sunlight into electricity. Novaled AG has adopted the first approach, using the technology to produce materials for displays and lamps, while Heliatek GmbH has chosen to focus on photovoltaics. Both of these companies are spinoffs created by former members of Professor Leo’s research team. By now they employ a total of nearly 200 people, and work closely together with other Dresden-based companies in a technology network. This year’s Zukunftspreis is shared by the founders of these two spinoffs, Jan Blochwitz-Nimoth (Novaled) and Martin Pfeiffer (Heliatek), and their mentor Professor Leo. Novaled AG is slightly further ahead in terms of marketing: the company is already mass-producing materials for cellphone displays. In two or three years’ time, it intends to start supplying materials for ultraflat TV screens that display true-to-life colors and consume a minimum of energy. “OLED displays combine the best qualities of LED and plasma screens, the two technologies currently available,” says Blochwitz-Nimroth. They are more energy-efficient than plasma TVs and deliver sharper images than LED technology, because they don’t need backlighting.

Solar cells made of organic materials have not yet reached the mass market. Heliatek GmbH expects to start production sometime next year. The company’s latest prototypes have an efficiency of ten percent, which is not yet high enough to compete with conventional silicon cells. “But in the longer term we will reach efficiencies approaching 20 percent”, Professor Leo states. Moreover, organic cells have other advantages compared with silicon technology, foremost among them a simpler – and therefore cheaper – manufacturing process.

The method employed by Karl Leo and his prize-winning former colleagues involves depositing microscopically thin layers of the organic material on a substrate. These coatings have a thickness of no more than one fifth of a micrometer – one thousand times thinner than in conventional solar cells. Only about a gram of semiconductor material is needed to coat a surface area of one square meter – in a process that takes place at room temperature, not at the 1,000 or so degrees Celsius required to produce inorganic cells.

This not only saves energy but also allows PET films to be used as the substrate, instead of the heat-resistant glass that was previously the only option. PET is the same plastic used to make bottles for soft drinks. It is cheap, light and flexible. The prize-winners have developed a continuous process based on roll-to-roll technology that enables the solar cells to be manufactured cheaply in large numbers. The resulting lightweight modules can be installed on roofs too weak to support the weight of standard photovoltaic panels.

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North Rhine-Westphalia’s 2011 Innovation Award in the "Innovation" category has been awarded to Professor Reinhart Poprawe M.A. (57), Director of the Fraunhofer Institute for Laser Technology ILT, and his team of laser experts comprising Dr. Andres Gasser (52), Dr. Ingomar Kelbassa (38), Dr. Wilhelm Meiners (47) and Dr. Konrad Wissenbach (56). The award, which carries a cash prize of 100,000 euros, will be presented to the winners by Svenja Schulze, North Rhine-Westphalia’s Minister for Innovation, Science and Research, at a ceremony to be held on November 14, 2011, at the K21 museum of contemporary art in Düsseldorf.

The Fraunhofer ILT research team has been driving forward progress in the field of additive manufacturing for over 20 years, developing techniques that help to save energy and resources in the production environment. The institute’s specialists have systematically evolved laser processes for use with different materials and in different applications, paving the way to their implementation on an industrial scale. Dr. Poprawe and his team are the world’s leading experts in the technique of selective laser melting (SLM), a field in which Fraunhofer ILT has led the way since its inception. SLM enables customized components such as medical implants or functional parts for machine tools to be manufactured cost-effectively and extremely rapidly in small batches on the basis of 3-D CAD data, following the just-in-time principle. This has opened the door to entirely new business models in the manufacturing industry, including mass customization, open innovation and co-creation, which allow end users to participate in the design process or even take over a large part of the design work themselves.

Over the past 20 years, the team of experts at the Fraunhofer Institute for Laser Technology ILT and the associated Chair for Laser Technology LLT at RWTH Aachen University has expanded additive manufacturing from a niche role as a rapid-prototyping application to an enabling technology with a major impact on future industrial manufacturing processes. This view is illustrated by the words of Professor Reinhart Poprawe: "In a few years’ time, the way spare parts are manufactured for an established supplier of hydraulic components will be radically different. Instead of keeping hundreds of variants of spare parts in stock, the manufacturer will simply store the 3-D CAD data of all components that have been produced in the past. Then, when an order is received, the appropriate part can be produced on demand using the selective laser melting process and shipped promptly to the customer."

The scope offered to designers of customized parts is significantly wider in terms of geometrical freedom and function integration when components can be constructed layer by layer. The selective laser melting process enables 3-D CAD data to be directly transformed into the real component. Dr. Ingomar Kelbassa, vice and academic director of the Chair for Laser Technology LLT at RWTH Aachen University and department head at Fraunhofer ILT, emphasizes the unique opportunity this offers to product designers: "Designers are liberated of almost all restrictions related to the production process, and can freely express all of their creative ideas in the product. Everything else is taken care of by our 3-D printing process." Things were very different 20 years ago; at that time, while prototypes could be built using plastic or paper, manufacturing metallic versions of these components was simply not possible.

Rapid prototyping took on an entirely new dimension when Fraunhofer ILT in Aachen developed the technique of selective laser melting. "For the first time, designers and product managers were able to present a demonstration model or even a functional prototype in metal based purely on CAD data with no more than a day’s notice. In the past, that used to take days or even weeks, for example when designing new tool inserts," relates Dr. Wilhelm Meiners, group manager Rapid Manufacturing at Fraunhofer ILT. He and his team invented the selective laser melting process for metallic materials, which they patented in 1996. It was to be the first in a whole family of patents. "We have since moved on to the next important stage," says Dr. Wilhelm Meiners confidently, »which is to take the rapid prototyping approach further and develop it into rapid manufacturing, enabling customized products to be manufactured rapidly in batches of any size, and at reasonable cost.« More and more companies are integrating additive manufacturing techniques in their production strategies.

Dr. Konrad Wissenbach, competence area manager Additive Manufacturing and Functional Layers at Fraunhofer ILT, offers a convincing argument: "The 3-D construction technique used in additive manufacturing processes reduces production costs across the board, regardless of the complexity of the component. In contrast to conventional ablation processes, additive manufacturing techniques have no need of additional resources such as costly tool modifications to produce undercuts, internal cooling channels or complex support structures, for example."

In addition to SLM, a technique developed from the outset by the laser experts in Aachen, the Fraunhofer ILT research team is also promoting the use of Laser Material Deposition LMD in manufacturing MRO, repair and modification activities. The main applications at present are the repair of aircraft engine components and tools for a wide range of industrial sectors. Dr. Andres Gasser, group manager Laser Material Deposition at Fraunhofer ILT, explains the difference between SLM and laser material deposition: "In SLM, the component is built up by melting particular areas of successive layers of powder using a laser source that fuses the material in a pattern corresponding to the final product. By contrast, in LMD, the components are produced by laser melting powder material projected by a nozzle onto specific areas of the component. SLM is capable of generating the finely detailed structures of complex components. LMD is more suited to the manufacture of large-area components and to repairs."

The members of the Fraunhofer innovation cluster "Integrative Production Technology for Energy -Efficient Turbomachinery – TurPro", which benefits from over ten million euros in overall budget, include leading aircraft manufacturers and energy providers in addition to the Aachen-based Fraunhofer Institutes for Laser Technology ILT and for Production Technology IPT. It is here that concepts for manufacturing cost-intensive nickel-alloy components such as BLISKs, or blade-integrated disks, for aircraft engines are developed. "Laser material deposition beats all other processes for repairing and manufacturing BLISKs in terms of precision and flexibility," claims Dr. Andres Gasser. The core competencies of Fraunhofer ILT are by no means restricted to manufacturing processes: they also extend to systems engineering. The services provided by the institute to its industrial partners also include the development of powder nozzles and optical heads for optimized component processing, process control units for quality-optimized process control, and manufacturing concepts based on optimized machining processes. In the framework of Aachen’s Cluster of Excellence "Integrative Production Technology for High-Wage Countries" in close collaboration with an interdisciplinary team of engineers, material scientists, physicists and economists, Prof. Poprawe develops industrial production systems for future mass customization.

Additive manufacturing processes, based on Selective Laser Melting (SLM) and/or Laser Material Deposition (LMD), open the door to entirely new business models in the manufacturing industry, including mass customization, open innovation and co-creation, which allow end users to participate in the design process or even take over a large part of the design work themselves. The ability of the new technology to process a wide variety of materials is one of the most important factors in its growing popularity across a variety of business sectors. Professor Poprawe and his team first demonstrated an additive process for the manufacture of metallic components in their laboratory in 1996. The revolutionary aspects at the time were that it allowed the use of commercial powder materials and that the laser beam fully melted the powder particles. Hence the name given to the process by the Aachen-based scientists: "Selective Laser Melting" or SLM. The technique enables a component density of nearly 100 percent to be achieved. This feature enables the mechanical characteristics of SLM components to approach those specified for the processed material. SLM is meanwhile being marketed under many proprietary brand names. The range of materials that can be processed in this way has grown over the years, and now includes stainless steel, tool steel, aluminum, copper, ceramics and bioresorbable materials used in medicine. The milestones generated by this diversity of Fraunhofer ILT services are eloquent:

• The industrial use of additive manufacturing processes for die and tool making, with the implementation of near-net-shape cooling channels. The improved temperature-control of the tools significantly reduces injection-molding cycle times for plastics and improves their quality. (2001)

• The additive manufacturing of metal dental restorations. The first implementation of a mass customization concept based on metallic components produced by means of additive manufacturing. (2002)

• The qualification of volume-produced aluminum components for road vehicles. (2006)

• Patients implanted with replacement hip joints created using additive manufacturing processes. (2008)

• Use of bio-resorbable materials for bone implants created using additive manufacturing processes. (2009)

• All-ceramic dental bridge produced using an additive manufacturing process. (2010)

The processing speed of additive manufacturing techniques has meanwhile been multiplied by 10 compared with the first variants, opening the way to entirely new fields of application. With this significant increase in efficiency, it is now possible to deploy additive manufacturing techniques in the implementation of functionally optimized structural components, for example in the automotive and aerospace industries. Users can expect to realize far greater efficiency in their use of resources and energy throughout the entire product lifecycle.

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Friday, 04 November 2011 12:59

Simulating real-world surfaces

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These days, cars are developed on computers, and to assist with this, designers want processes which generate realistic surfaces such as seat covers. Researchers have now developed high-resolution scanners which copy objects and fabric samples in a few minutes, converting them into virtual models. The light effects are startlingly realistic.

When buying a car, customers are not just interested in its fuel consumption. They rather turn their attention to the car’s appearance. The interior fittings should have a quality look, the pattern on the seat covers should be subtle and understated and the leather-look dashboard should add a sense of luxury. That is why designers want to know at an early stage how a piece of fabric or imitation leather will look in the new car cockpit. Models used to be manufactured by hand, but that was time-consuming. And although computer simulation is faster, it takes time as well: real-world objects must first be scanned at high resolution and then translated to the virtual world. Researchers at the Fraunhofer Institute for Computer Graphics Research IGD in Darmstadt are now hoping to accelerate this process. They have developed two scanners which capture images of real objects with micrometer precision and use the data to generate deceptively lifelike virtual images. The first device, the HDR-ABTF scanner, is specifically designed to capture images of materials such as textiles and leather, lit from different directions, precisely and especially quickly. Computers can then be used to simulate how an object – for instance a car seat – covered in that material will look in changing light conditions. The second device, the meso scanner, captures high-resolution images of three-dimensional objects. Unlike conventional systems, it even records finest surface details with yet unmatched precision.

Both scanners have been developed from established processes which are more expensive or which take longer. “For industrial applications, though, we need fast and affordable devices with high resolution,” explains Martin Ritz, a developer at Fraunhofer IGD. This is what the HDR-ABTF scanner delivers. A single-lens reflex camera installed in the device looks down on the object from above. The material is lit successively by several LEDs arranged in a quadrant arc, so that the surface is lit from various different angles and photographed in varying light conditions. The end result is a series of exposures for each light direction, which can then be integrated on a PC to produce high-resolution HDR images. A vehicle designer can then combine the image data with the computer model of a car seat and observe the material’s behavior when lit from any angle. There are already similar processes that use multiple cameras and considerably more light sources, but working with the equipment developed by Fraunhofer IGD is both simpler and faster. Within the period of just ten minutes, a new material can be scanned and translated to a virtual model.

The meso scanner captures images of small three-dimensional objects. Conventional 3-D scanners project a relatively coarse pattern of stripes onto an object and the software infers the three-dimensional shape from the distortion of the stripes. This innovative new scanner instead projects a much more detailed pattern of black and white stripes onto the object, each of which is just about a third of a millimeter or so across. Using a special lens in front of the projector, this pattern is moved across the object with sub-pixel accuracy, which is to say it is shifted in individual steps of 1/25 of a pixel or less. This means that the object is scanned in much greater detail than before, achieving high resolution. Any hollows or wrinkles can be recorded with a depth measurement which has an accuracy of around 30 micrometers – which is two to three times more accurate than without the lens-shifting system.

As Ritz points out, “The meso scanner isn’t just interesting for car development. There’s also scope for museums to use it to scan rare exhibits such as jewelry or coins with high precision.” Another possible application for the device would be in the computer gaming industry. Researchers will be showcasing the initial prototypes of the new scanners at the booth of the Fraunhofer Additive Manufacturing Alliance at the Euromold trade fair (Hall 11, Booth C66a) from November 29 to December 2, 2011 in Frankfurt am Main.

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Thursday, 03 November 2011 09:05

High-tech spider for hazardous missions

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Spiders are very agile, and some can even jump. They owe this capability to their hydraulically operated limbs. Researchers have now designed a mobile robot modeled on the same principle that moves spider legs. Created using a 3-D printing process, this lightweight can explore terrain that is beyond human reach.

Enviably agile and purposeful, the mobile robot makes its way through grounds rendered off-limits to humans as the result of a chemical accident. Depressions, ruts and other obstacles are no match for this eight-legged high-tech journeyman. Its mission: with a camera and measurement equipment on board, it will provide emergency responders with an image of the situation on the ground, along with any data about poisonous substances. Not an easy task; after all, it must be prevented from tipping over. But this risk seems a minor one as it confidently and reliably picks its way through the area. As a real spider would, it keeps four legs on the ground at all times while the other four turn and ready themselves for the next step. Even in its appearance, this artificial articulate creature resembles an octopod. And no wonder – the natural specimen provided the model for researchers at the Fraunhofer Institute for Manufacturing Engineering and Automation IPA. This high-tech assistant is still a prototype, but future plans envision its use as an exploratory tool in environments that are too hazardous for humans, or too difficult to get to. After natural catastrophes and industrial or reactor accidents, or in fire department sorties, it can help responders, for instance by broadcasting live images or tracking down hazards or leaking gas.

With its long extremities, the spider has a range of ways to get around. Some models can even jump. This is possible using hydraulically operated bellows drives that serve as joints and keep limbs mobile. With no muscles to stretch their legs, these creatures build up high levels of body pressure that they then use to pump fluid into their limbs. Shooting fluid into the legs extends them. “We took this mobility principle and applied it to our bionic, computer-controlled lightweight robot. Its eight legs and body are also fitted with elastic drive bellows that operate pneumatically to bend and extend its artificial limbs,“ explains Dipl.-Ing. Ralf Becker, a scientist at IPA. The components required for locomotion, such as the control unit, valves and compressor pump, are located in the robot‘s body; the body can also carry various measuring devices and sensors, depending on the application at hand. Hinges interoperate with the bellows drives so that the legs can move forward and turn as needed. Diagonally opposed members move simultaneously, too. Bending the front pairs of legs pulls the robotic spider‘s body along, while stretching the rear extremities pushes it.

The special aspect of this high-tech helper: not only very light, it also combines rigid and elastic shapes in a single component; with just a few production steps, it can also be produced at low cost. To date, designs such as the mobile robot have been generated using conventional mechanical-engineering technologies – a time-consuming and costly undertaking. Researchers at IPA, on the other hand, rely on generative production technologies, and specifically on selective laser sintering (SLS) of plastics, a 3-D printing process. In this process, step by step thin layers of a fine polyamide powder are applied one at a time and melted in place with the aid of a laser beam. This way, complex geometries, inner structures and lightweight components can be produced – with structures optimized much as if produced by Nature herself. The experts at IPA have a great deal of latitude in the design of their mobile robot; the leg modules, for instance, can be designed with infinitely variable load-bearing characteristics.

“We can use SLS to produce one or even several legs in a single operation; this minimizes assembly effort, saves materials and reduces the time it takes to build a robot. With the modular approach, individual parts can be quickly swapped as well. Our robot is so cheap to produce that it can be discarded after being used just once – like a disposable rubber glove,“ Becker points out. A prototype of the robot can be seen at the EuroMold 2011 trade fair in Frankfurt, at the joint stand of the Fraunhofer-Gemeinschaft (Hall 11, Stand C66), from November 29 through December 2.

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The Fraunhofer Institute for Laser Technology ILT has developed a method of structuring the metallic surfaces of tool inserts by laser remelting. For the first time, this method makes it possible to structure materials without resorting to ablation and at the same time to polish them to a brilliant gloss finish. This gives tool manufacturers greater scope to adapt their production processes to incorporate novel structures and design elements while also saving them time and money. Another new technique can additionally be used to provide tools and products with a dual-gloss effect.

From steering wheels to toothbrush handles, we have become accustomed to the look and feel of structured surfaces on components we encounter in virtually all areas of our lives. Injection molding tools made from metal are often used to give these components their structure, and one method that is commonly used to produce the desired structure on the tools themselves is photochemical etching, where specific regions of the tool insert are structured by etching away the unwanted regions. However, this is a costly and time-consuming process which requires the use and disposal of large quantities of environmentally hazardous acids.

A more environmentally-friendly alternative is the technique of laser structuring by ablation, which has been used successfully for more than ten years. This method can achieve ablation rates of 1-10 mm3/min in processes designed to create structures > 10 µm, but in many cases the workpiece subsequently requires further treatment to remove the melt residue which accumulates during ablation. In addition, the laser requires some ten passes to achieve a structure depth of 200 µm, which means that the laser-based structuring of large surfaces through ablation is generally not a cost-effective option for tool manufacturers.

Remelting instead of ablation

Fraunhofer ILT has now developed a method of structuring tools using laser remelting. The laser beam travels over the workpiece and the resulting heat input melts the metal surface. At the same time, the laser power is modulated in order to continuously change the size of the melt pool at defined points. "This modulation causes the material to be redistributed, creating mountains and valleys: half of the resulting structure lies above its initial level, while the other half lies below it," says André Temmler, project manager at Fraunhofer ILT. Thanks to surface tension, when the uppermost layer of the molten material solidifies, it exhibits uniformly low roughness, and the surface is left with a brilliant polished finish. Unlike laser structuring by ablation, the novelty of laser structuring by remelting is its ability to directly produce finished surfaces which do not require any post-processing. For a structure depth of approximately 200 µm, this method can achieve processing rates of up to 75 mm2/min, enabling a volume redistribution rate of 15 mm³/min in a single pass. A further advantage of this new method is that it consumes less energy and fewer resources than conventional laser-based structuring by ablation. Less energy is required for melting than for sublimation, the process requires significantly fewer passes, and there is no loss of material. Depending on the material and batch size, these benefits can yield considerable time and cost savings for tool manufacturers. For flat surfaces and single-curved component geometries, the laser technique of structuring by remelting is already available for industrial use. Temmler and his team are now working on applying the technique to freeform surfaces.

Dual-gloss effect by selective laser polishing

In cases where an additional dual-gloss effect is required for end products such as decorative elements or an entire product surface, the first step is to apply a matt finish to the whole surface of the tool, which is generally achieved through blasting with glass beads or sand. Selected regions are then remelted using a laser beam. These regions solidify from the melt with a polished finish – in other words, the selective laser polishing creates a contrast between the matt, untreated areas and the brilliant, laser-polished areas. Depending on the intensity of the dual gloss, this can even produce a 3D effect in which the polished points appear to protrude from the surface. One example of how selective laser polishing can be used is to provide structured tools designed to apply a leather grain structure to plastic components with a dual-gloss effect which is then transferred to the end product during the molding process. For the first time, this selective polishing technique can now be applied on an industrial scale for both flat and freeform surfaces.

Visitors to the joint Fraunhofer Booth C66 in Hall 11 at EuroMold 2011 will have the opportunity to see components produced with workpieces which were laser structured by remelting. Our experts will also be presenting a selection of sample objects molded in plastic by selectively laser-polished tools.

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Tuesday, 13 September 2011 12:45

Blood Vessels from Your Printer

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Researchers have been working at growing tissue and organs in the laboratory for a long time. These days, tissue engineering enables us to build up artificial tissue, although science still hasn’t been successful with larger organs. Now, researchers at Fraunhofer are applying new techniques and materials to come up with artificial blood vessels in their BioRap project that will be able to supply artificial tissue and maybe even complex organs in future. They are exhibiting their findings at the Biotechnica Fair that will be taking place in Hannover, Germany on October 11-13.

There were more than 11,000 persons on the waiting list for organ transplantation in Germany alone at the beginning of this year, although on the average hardly half as many transplantations are performed. The aim of tissue engineering is to create organs in the laboratory for opening up new opportunities in this field. Unfortunately, researchers have still not been able to supply artificial tissue with nutrients because they do not have the necessary vascular system. Five Fraunhofer-institutes joined forces in 2009 to come up with biocompatible artificial blood vessels. It seemed impossible to build structures such as capillary vessels that are so small and complex and it was especially the branches and spaces that made life difficult for the researchers. But production engineering came to the rescue because rapid prototyping makes it possible to build workpieces specifically according to any complex 3-D model. Now, scientists at Fraunhofer are working on transferring this technology to the generation of tiny biomaterial structures by combining two different techniques: the 3-D printing technology established in rapid prototyping and multiphoton polymerization developed in polymer science.

Successful Combination
A 3-D inkjet printer can generate 3-dimensional solids from a wide variety of materials very quickly. It applies the material in layers of defined shape and these layers are chemically bonded by UV radiation. This already creates microstructures, but 3-D printing technology is still too imprecise for the fine structures of capillary vessels. This is why these researchers combine this technology with two-photon polymerization. Brief but intensive laser impulses impact the material and stimulate the molecules in a very small focus point so that crosslinking of the molecules occurs. The material becomes an elastic solid, due to the properties of the precursor molecules that have been adjusted by the chemists in the project team. In this way highly precise, elastic structures are built according to a 3-dimensional building plan. Dr. Günter Tovar is the project manager at the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB based in Stuttgart. When we caught up with him, he described the latest work: The individual techniques are already functioning and they are presently working in the test phase; the prototype for the combined system is being built.

When ink becomes an artificial vessel system
You have to have the right material to manufacture 3-dimensional elastic solids. This is the reason why the researchers came up with special inks because printing technology itself calls for very specific properties. The later blood vessels have to be flexible and elastic and interact with the natural tissue. Therefore, the synthetic tubes are biofunctionalized so that living body cells can dock onto them. The scientists integrate modified biomolecules – such as heparin and anchor peptides – into the inside walls. They also develop inks made of hybrid materials that contain a mixture of synthetic polymers and biomolecules right from the beginning. The second step is where endothelial cells that form the innermost wall layer of each vessel in the body can attach themselves in the tube systems. Günter Tovar points out that »the lining is important to make sure that the components of the blood do not stick, but are transported onwards.« The vessel can only work in the same fashion as its natural model to direct nutrients to their destination if we can establish an entire layer of living cells.

Opportunities for Medicine
The virtual simulation of the finished workpieces is just as significant for project success as the new materials and production techniques. Researchers have to precisely calculate the design of these structures and the course of the vascular systems to ensure optimum flow speeds while preventing back-ups. The scientists at Fraunhofer are still at the dawn of this entirely new technology for designing elastic 3-dimensionally shaped biomaterials, although this technology offers a whole series of opportunities for further development. Günter Tovar acknowledges »we are establishing a basis for applying rapid prototyping to elastic and organic biomaterials. The vascular systems illustrate very dramatically what opportunities this technology has to offer, but that’s definitely not the only thing possible.« One example would be building up completely artificial organs based on a circulation system with blood vessels created in this fashion to supply them with nutrients. They are still not suited for transplantations, but the complex of organs can be used as a test system to replace animal experiments. It would also be conceivable to treat bypass patients with artificial vessels. In any event, it will take a long time until we will actually be able to implant organs from the laboratory with their own blood vessels.

This is a project that the Fraunhofer Institute for Applied Polymer Research IAP in Potsdam, Germany, the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB in Stuttgart, Germany, the Fraunhofer Institute for Laser Technology ILT in Aachen, Germany, the Fraunhofer Institute for Manufacturing Engineering and Automation IPA in Stuttgart, Germany and the Fraunhofer Institute for Material Mechanics IWM in Freiburg, Germany are all participating in. They are exhibiting a large model of an artificial blood vessel printed with conventional with rapid prototyping technologies and samples of their current developments in Hall 9, Stand D10 at the Biotechnica Fair.

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Thursday, 01 September 2011 12:09

Components based on nature’s example

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They are lightweight and yet strong and resilient: straw, bamboo, bones and teeth owe their surprising strength to their cleverly designed internal structures and a judicious combination of materials. The same principles can be applied to produce lighter and more durable plastic products.

The exceptional strength of certain biological materials is due principally to their complex structure. Long bones, for instance, consist of a compact, solid outer casing filled with spongy tissue, which makes them particularly strong and resilient. Researchers from the Fraunhofer Institutes for Mechanics of Materials IWM and for Environmental, Safety and Energy Technology UMSICHT are collaborating on a project entitled “Bionic Manufacturing”, which aims to develop products that are lightweight but strong and economic in their use of materials – imitating the perfected structures found in nature. The IWM scientists in Freiburg have taken on the task of identifying the best internal structures for manufactured components. “We have set ourselves the challenge of working as efficiently as nature: The finished component must not weigh more than necessary and yet still be able to perform its mechanical function reliably,” explains Dr. Raimund Jaeger of IWM. This approach can be combined with a high degree of creative freedom: “Such components can be used to produce consumer goods with a high aesthetic value, such as designer chairs,” adds Jaeger. And if by chance one of these bionically designed objects should break as the result of excessive loading, it will do so in a benign way – collapsing smoothly in localized areas rather than shattering into sharp splinters.

Whereas natural materials have evolved over numerous generations to reach the level of perfection we see today, engineers and product designers have to work much faster. The Freiburg research team has therefore developed a new design method. They start by constructing a virtual model of the future workpiece on the computer, filling out its contours with almost identical, cube-shaped, elementary cells. If the numerical simulation reveals that the grid structure does not satisfy requirements, the cell walls (trabecular microstructure) are refined accordingly. “We make them thicker if they are too weak and thinner if they need to be more pliable, or align them with the force lines along which the load is distributed,” explains Jaeger. This method enables many different shapes to be designed around an inner cell structure that can then be evaluated and optimized using the simulation tool. To complement the simulations, the researchers carry out tests on real-life components to verify the structure’s mechanical properties.

Jaeger reports that the method has worked very well every time they have used it to design any type of workpiece based on two-dimensional templates that can be pulled into the desired shape using the computer simulation. The same applies to components with a relatively regular shape. Despite their light weight, all of these components are very strong and resilient and capable of absorbing even substantial shocks. According to the scientists, they have potential applications wherever there is a need for products that combine a high level of mechanical stability and aesthetic appearance with low weight – for example medical orthopedic devices or anatomically formed body protectors such as lumbar support belts for skiers.

Fraunhofer UMSICHT is responsible for the technical implementation of the bionic design principles. The solution chosen by the project managers in Oberhausen involves the use of additive manufacturing techniques – in this case selective laser sintering of polymer materials.  This technique enables workpieces to be fabricated by laying down successive layers of a fine polyamide powder, which are fused together in the desired configuration using a focused laser beam. It is the ideal method for creating complex internal structures and, at a later stage, components with a distributed pattern of material properties, which experts refer to as functionally graded materials. The resulting structures are similar to those observed in nature.

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Tissue engineering pursues the aim of replacing natural tissue after injuries and illnesses with implants which enable the body to regenerate itself with the patient’s own cells. So that tissue can be produced to replicate the body’s natural tissue, knowledge of the interaction between cells in a three-dimensional framework and the growth conditions for complete regeneration is essential. Using a special laser technique, research scientists at the Fraunhofer Institute for Laser Technology ILT and other Fraunhofer Institutes have succeeded in producing hybrid biomimetic matrices. These serve as a basis for scaffold and implant structures on which the cells can grow effectively.

If tissue has been badly damaged by disease or due to an accident or if parts of the tissue have been completely removed, the body is often unable to regenerate this tissue itself. What’s more, in many cases no endogenous material is available for transplants. As a result, demand in the medical field is increasing for implants which enable complete regeneration to take place. But the current artificially produced implants are often not adequately adapted to the environment in the patient’s body and are therefore of limited use as a tissue replacement. The main reason for this lack is the missing knowledge on how cells react to a threedimensional environment. Scientists at Fraunhofer ILT in cooperation with other Fraunhofer Institutes, however, have developed a process for producing biomimetic scaffolds which closely emulates the endogenous tissue. This process allows the fabrication of specialized model systems for the study of three dimensional cell growth, for the future generation of optimal conditions for the cells to colonize and grow. For this purpose the Aachen-based research scientists have transferred the rapid prototyping technique to endogenous materials. They combine organic substances with polymers and produce three-dimensional structures which are suitable for building artificial tissue.

Laser light converts liquid into 3-D solids As the basis the research scientists use dissolved proteins and polymers which are irradiated with laser light and crosslinked by photolytic processes. For this they deploy specially developed laser systems which by means of ultra-short laser pulses trigger multiphoton processes that lead to polymerization in the volume. In contrast to conventional processes, innovative and low-cost microchip lasers with pulse durations in the picosecond range are used at Fraunhofer ILT which render the technique affordable for any laboratory. The key factors in the process are the extremely short pulse durations and the high laser-beam intensities. The short pulse duration leads to almost no damage by heat to the material. Ultra-fast pulses in the megawatt range drive a massive amount of protons into the laser focus in an extremely short time, triggering a non-linear effect. The molecules in the liquid absorb several photons simultaneously, causing free radicals to form which trigger a chemical reaction between the surrounding molecules. As a result of this process of multiphoton polymerization, solids form from the liquid. On the basis of CAD data the system controls the position of the laser beam through a microscope with a precision of a few hundred nanometers in such a way that micrometer-fine, stable volume elements of crosslinked material gradually form.

"This enables us to produce scaffolds for cell scaffolds with a resolution of approximately one micrometer directly from dissolved proteins and polymers to exactly match our construction plan," explains Sascha Engelhardt, project manager at the ILT. "These biomimetic scaffolds will enable us to answer many aspects of threedimensional cell growth." For this purpose the team of research scientists uses various endogenous proteins, such as albumin, collagen and fibronectin. As pure protein structures are not very shape-stable, however, the Aachen-based researchers combine them with biocompatible polymers. These polymers are used to generate a scaffold which in a subsequent step provides a framework for the protein structures that have been produced. This new process makes it possible to create structures offering much greater stability. The scaffold can be seeded with the patient’s own cells in a medical laboratory. The colonized scaffolds can then be expected to produce good implant growth in the patient’s body. The long-term aim is to use the process to produce not only individual cell colonies but also complete artificial tailor-made organs. That would represent a huge medical advance!

The Fraunhofer ILT research scientists are currently engaged in work to optimize the process. For example, they want to greatly increase the production speed by combining the fabrication process with other rapid prototyping methods, in order to reduce the time and cost involved in producing tailor-made supporting structures for synthetic tissue.

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The era of gas guzzlers that clatter through streets and pollute the air is over. Cars rolling off the assembly line today are cleaner, quieter and – in terms of their performance weight – more efficient than ever before. Nevertheless, development continues. Ever-stricter environmental regulations and steadily rising fuel costs are increasing the demand for cars that further reduce their impact on the environment. But customer demands are often tough for manufacturers to meet: car bodies should be safe yet light-weight and engines durable yet efficient. Year after year, new models must be developed and built that can claim to be better, more efficient, and more intelligent than the last.

The race against time and competitors places high demands on manufacturers and their suppliers. Lasers can help them win the race. Resistant to wear and universally applicable, laser light is an ideal tool in the manufacture of vehicles. Lasers can be used to join, drill, structure, cut or shape any kind of material. Surfaces can be engineered for motors and drive trains that create less friction and use less fuel. Lasers are not only a decisive key towards faster, more efficient and economical production, but also towards energy-saving vehicles. At Laser 2011, Fraunhofer scientists will demonstrate how we can use lasers to save time, money and energy.

A weight-loss program in automotive manufacturing

Extra pounds cost energy. They have to be accelerated and slowed down every time you drive – over the entire lifespan of the car. To reduce weight, manufacturers are increasingly turning to the use of fiber-reinforced plastics, which are 30 to 50 percent lighter than metal. The disadvantage, however, is that these new materials are difficult to process. Fiber-reinforced plastics are brittle, meaning cutting and drilling tools are quickly worn out and the conventional assembly techniques used for metal components are often not appropriate. "Lasers represent an ideal alternative here," explains Dr. Arnold Gillner of the Fraunhofer Institute for Laser Technology ILT in Aachen. "Lasers can cut fiber-reinforced plastics without wear and can join them too. With the appropriate lasers, we can cut and ablate components with minimal thermal side-effects. Lasers can also be used for welding light-weight components – a viable alternative to conventional bonding technology. We can even join fiber-reinforced plastics to metals with laser welding. The laser roughens the metal surface, while the plastic, briefly-heated, penetrates the pores of the metal and hardens. The results are very stable."

Weight reduction can also be achieved with high-strength metallic materials. These, however, are difficult to process. "Joining combinations of various materials allows us to make optimal use of the individual materials' specific properties. But this proves to be difficult in many cases," explains Dr. Anja Techel, Deputy Director of the Fraunhofer Institute for Material and Beam Technology IWS in Dresden. Her team believes in lasers: "With our newly-developed integrated laser tools, we can now even weld together combinations of materials, free of fissures or cracks." At Laser 2011, Fraunhofer scientists will present, for the first time, a new welding head capable not only of focusing with extreme precision but of moving back and forth across the seam with high frequency to mix the molten materials. When they harden, they create a stable bond.

Laser replaces chemistry

Lasers also save time and money in tool design. The molds used in the production of plastic fixtures and steering wheels, for example, have to be structured to give the finished component a visually and tactilely appealing surface. Most car manufacturers order a design from their suppliers, whose surface typically has the appearance of leather. Until now, the negative pattern used to create the design has been etched out of the steel tools used in injection molding – a tedious and time-consuming process. "With lasers, the steel surface can not only be patterned more quickly, but also with greater scope for variety," explains Kristian Arntz of the Fraunhofer Institute for Production Technology IPT. "We can transfer any possible design directly from the CAD model to the tool surface: What will later become a groove in the plastic is preserved as a ridge, while the surrounding material is vaporized. The process is efficient, fully automatic, and highly variable."

Saving energy with low friction motors

Laser technology is also in demand in engine optimization. Engineers strive to keep friction as low as possible in order to improve efficiency. "That is true not only for the electric engines currently being developed, but also for classic internal combustion engines and diesel motors, as well as transmissions and bearings," says Arnold Gillner of the ILT. Ceramic, high-performance coatings are especially desirable, because they are not only resistant to wear but also smooth, which generates less friction. Coated metal components have until now been prohibitively expensive, being produced in plasma chambers in which the ceramic was vaporized and applied to the surface of the components. Fraunhofer scientists have now developed a less expensive and faster method in which work pieces are coated with ceramic nano-particles, then treated with a laser. This finishing process has already been applied to gear wheels and bearings.

Lasers can even be used to make specific modifications to the properties of engine parts. "Friction between the cylinder wall and piston is responsible for a big part of a motor's energy consumption. That is why we try to minimize it. This is especially important for engines featuring modern, automatic start-stop functions that are stressed by frequent ignition," says Gillner. "To protect them, we have to ensure that the cylinder is always coated with a film of oil. Laser technology can help reduce friction with special structuring processes that improve oil adhesion." Fraunhofer researchers aim to increase the engine's life-span and reduce energy consumption in this way.

Fitness program for electric cars

Lasers can even increase the efficiency and life-span of electric batteries. That is good news for manufacturers and owners of electric cars, since batteries continue to be extremely expensive. The engineers and scientists at Fraunhofer are currently working on various solutions to make batteries more durable and less expensive. One approach is to increase the surface area of the electrodes with appropriate coating in order to increase their efficiency. Another approach involves analyzing and optimizing production processes. Manufacturers produce batteries using one anode and one cathode cell, which they then connect. In theory that sounds pretty simple, but in practice the fusing of copper anodes with aluminum cathodes creates brittle connections that break easily. That presents a problem for application in cars that sometimes drive on cobblestone or dirt roads. With the help of lasers, researchers at the ILT have succeeded in forming durable connections between electrodes without creating the culprit brittle alloys. Researchers at the IWS in Dresden have developed an alternative solution in which a laser warms the surfaces and rollers press them together. "Using roll plating with lasers and inductive pre-heating, we were able to create very stable connections with high electrical conductivity, with only a minimal loss of power," reports Anja Techel. "The finished batteries are very efficient. And since only small amounts of electrical energy are transformed into heat, these batteries do not require as much cooling."

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Up to now it was not possible to use Selective Laser Melting (SLM) on copper alloys. Now, however, research scientists at the Fraunhofer Institute for Laser Technology ILT have solved the technical problems that prevented this by enhancing the technique. The new method opens up new possibilities, for instance in plastics processing.

Rapid Manufacturing is making triumphant progress in industrial production as it enables digitized design engineering data to be directly and quickly translated into workpieces. In this context, SLM is particularly suitable for producing metal components of complex shapes which cannot be manufactured using conventional technology or can only be produced at very high cost. In the InnoSurface project, which is funded by the German Federal Ministry of Economics and Technology (BMWi), a research team at Fraunhofer ILT in Aachen has succeeded in modifying the SLM process to make it suitable for copper materials. This opens up new opportunities, for example in the manufacture of tools for plastics processing.

In SLM the workpiece is built up layer by layer on a platform from powder material. Basically, the process functions like a printer working in three dimensions. Directed by the computer-generated design data for the planned workpiece, the metal powder is deposited in layers and then melted at the required points by a laser beam. As a result, it bonds with the already produced part of the object. Material tests have shown that steel or light-metal components produced in this way exhibit the same mechanical properties as conventionally produced parts.

Owing to the high thermal conductivity of copper and copper alloys, however, it has not been possible up to now to use SLM on these materials. Although copper has a lower melting point than steel, it also exhibits lower laser light absorption and higher heat dissipation. As a result, the melting track interupts and tiny balls of molten metal form. This creates cavities and thus reduces the density of the component. To compensate for the high heat dissipation and the low laser light absorption by the copper during the melting process, we use a 1000-watt laser instead of the 200-watt laser that is currently the norm in SLM, explains project manager David Becker. To achieve satisfactory results, he chose a laser that produces a particularly even beam profile. Meanwhile Becker and his team modified the entire installation to prevent the high energy input from causing disruptions. For example, they changed the inert gas control system and the mechanical equipment. Tests with the copper alloy Hovadur K220 are already showing excellent results, Becker continues, with workpiece density reaching almost 100 percent. The technique is therefore ready for industrial use.

It is the high thermal conductivity of copper and its alloys that makes them suitable for many applications. Inserts of these materials in steel injection molding tools for the manufacture of plastic parts ensure rapid heat removal at critical points. SLM makes it possible to integrate conformal cooling channels in these copper inserts to carry a coolant such as water. Cycle times and warping are reduced by fast and even cooling of the entire tool.

In the near future the Aachen-based research scientists intend to go a step further and process not only copper alloys but also pure copper to make dense components. The thermal conductivity of pure copper is almost twice as high as Hovadur K220. This makes for an interesting challenge!

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Monday, 03 January 2011 22:27

Impregnating plastics with carbon dioxide

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Everyone has heard that carbon dioxide is responsible for global warming. But the gas also has some positive characteristics. Researchers are now impregnating plastics with compressed CO2 in a process that could lead to new applications ranging from colored contact lenses to bacteria-resistant door handles.

CO2 is more than just a waste product. In fact, it has a variety of uses: the chemical industry makes use of this colorless gas to produce urea, methanol and salicylic acid. Urea is a fertilizer, methanol is a fuel additive, and salicylic acid is an ingredient in aspirin.

Researchers at the Fraunhofer Institute for Environmental, Safety and Energy Technology UMSICHT in Oberhausen are pursuing a new idea by testing how carbon dioxide can be used to impregnate plastics. At a temperature of 30.1 degrees Celsius and a pressure of 73.8 bar, CO2 goes into a supercritical state that gives the gas solvent-like properties. In this state, it can be introduced into polymers, or act as a “carrier” in which dyes, additives, medical compounds and other substances can be dissolved. “We pump liquid carbon dioxide into a high-pressure container with the plastic components that are to be impregnated, then steadily increase the temperature and the pressure until the gas reaches the supercritical state. When that state is reached, we increase the pressure further. At 170 bar, pigment in powder form dissolves completely in the CO2 and then diffuses with the gas into the plastic. The whole process only takes a few minutes. When the container is opened, the gas escapes through the surface of the polymer but the pigment stays behind and cannot subsequently be wiped off,” explains Dipl.-Ing. Manfred Renner, a scientist at Fraunhofer UMSICHT.

In tests, the researchers have even managed to impregnate polycarbonate with nanoparticles that give it antibacterial properties. E-coli bacteria, placed on the plastic’s surface in the institute’s own high-pressure laboratory, were killed off completely – a useful function that could be applied to door handles impregnated with the same nanoparticles. Tests conducted with silica and with the anti-inflammatory active pharmaceutical ingredient flurbiprofen were also successful. “Our process is suitable for impregnating partially crystalline and amorphous polymers such as nylon, TPE, TPU, PP and polycarbonate,” states Renner, “but it cannot be applied to crystalline polymers.”

The process holds enormous potential, as carbon dioxide is non-flammable, non-toxic and inexpensive. Whilst it shows solvent-like properties, it does not have the same harmful effects on health and on the environment as the solvents that are used in paints, for example. Painted surfaces are also easily damaged and are not scratch-resistant. Conventional processes for impregnating plastics and giving them new functions have numerous drawbacks. Injection molding, for instance, does not permit the introduction of heat-sensitive substances such as fire retardants or UV stabilizers. Many dyes change color; purple turns black. “Our method allows us to customize high-value plastic components and lifestyle products such as mobile phone shells. The best about it is that the color, additive or active ingredient is introduced into layers near the surface at temperatures far below the material’s melting point, in an environ mentally friendly manner that does away with the need for aggressive solvents ,” says Renner. The process could, for example, be used to dye contact lenses – and lenses could even be enriched with pharmaceutical compounds that would then be slowly released to the eye throughout the day, representing an alternative to repeated applications of eye drops for the treatment of glaucoma. According to the scientist, this new impregnation method is suitable for a broad range of new applications.

Source: Fraunhofer-Gesellschaft

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