However, TRUMPF is also strengthening its portfolio at the lower-power end of the spectrum. The new picosecond lasers from the TruMicro Series 2000 are entry-level models for micro-processing materials in the low-average-output range. Together with their high beam quality, this makes them suitable for applications such as cutting polyimide and structuring glass. TRUMPF also offers this series in green and infrared wavelengths.

TRUMPF is expanding its spectrum of TruMicro picosecond lasers – in the upper, medium and lower power ranges and in regard to the wavelengths – gallery

Ultra-short-pulse lasers for scientific research

At the trade fair, TRUMPF Scientific Lasers is unveiling for the first time the prototype of a laser pump source for scientific applications in the femtosecond range. The lasers in this SDL series deliver pulses of one picosecond and pulse energies of up to 50 millijoules. This makes them an ideal basis for optical parametric amplification stages (OPA), which are used to generate high-energy femtosecond pulses. These OPAs will shortly join the TRUMPF portfolio as lasers that are well suited to scientific applications, such as spectroscopic examinations.

New marking laser capabilities

TRUMPF is presenting a world first in Munich with its new TruMark Series 1000. The new infrared-wavelength marking laser has an extremely compact design: the beam source, power supply unit, computer, and even the scanner all fit inside a box which is the size of a shoe box and weighs only around ten kilograms. This makes it easy to integrate the laser into both existing and new production lines.

Although the marking laser represents an affordable entry point into the world of laser marking, it also bears comparison with the TruMark Series 3000 and 5000 in terms of quality and functionality, as readily testified by the automatic focal position control of TruMark 1000. But TRUMPF is also expanding its marking laser portfolio at the higher end of the output scale. The new fiber laser from the TruMark Series 5000 is suitable for the rapid processing of high quantities of both metal and plastic parts.

TRUMPF presents the new TruMark Series 1000 – Compact entry-level units for laser marking – gallery

Compact direct diode lasers

Another highlight is the new direct diode laser generation with output powers of up to six kilowatts for brazing and cladding. The new TruDiode 6006 impresses with its energy efficiency of 40 percent and extremely low operating costs in general. This is all down to a simple, space-saving laser concept, making TruDiode 6006 the most compact diode laser in its power class available on the market. Moreover, it offers excellent value for money thanks to its simple and smart laser design.

The new TruDiode generation made by TRUMPF scores points with greater energy efficiency and lower operating and investment costs – gallery

New generation of disk lasers

Also on exhibit at the trade fair is the new generation of TruDisk disk lasers, which deliver laser output powers of up to six kilowatts from a single disk. This facilitates an even more compact design and leads to a significant reduction in operating costs of up to 25 percent. Special attention was devoted to bringing down energy consumption. The efficiency of the new generation is as high as 30 percent. A redesigned control system with intelligent energy management ensures that the laser is always in an optimum energy state, even during breaks in operation.

The new generation also scores highly for being robust even under extreme environmental conditions. The youngest member of this series is the new TruDisk 2000, which is being exhibited for the first time in Munich. Its outstanding beam quality makes it ideally suited to cutting and welding operations.

Diffusion-cooled CO2 lasers

Introducing the new TruCoax 1000 generation, TRUMPF presents a compact and robust CO2 laser for processing metallic and non-metallic materials. TruCoax 1000 achieves very good beam quality of over 1.1 M2 and a peak pulse output of up to several kilowatts, enabling extremely fast and precise processing.

Furthermore, the geometrical and optical specifications of TruCoax 1000 ensure outstanding beam and output stability and hence reproducible application results even at high speeds and during the whole service life. The coaxial laser works with a transistor-driven high frequency generator, which fits under the hood of the laser.

This makes TruCoax 1000 an energy-efficient and compact laser that customers can easily integrate into their own individual systems. Uniquely for lasers in its class, TruCoax 1000 is completely maintenance-free, so there is no need to replace premix gas or HF tubes or even for a refurbishment. Operating costs are therefore minimal. These qualities make TruCoax an extremely reliable and cost-effective laser for industrial manufacturing.

Their short pulse duration can trigger and even control processes with extremely fast dynamics, while their superb spatial coherence makes for outstanding pulse focusing properties. Femtosecond lasers also enable intensive spatial and temporal focusing of the light energy. That paves the way for extreme light-matter interactions — which has laid the basis for numerous experiments in attophysics and nonlinear optics.

Unverzichtbar für die Forschung

In recent years, ultra-short pulsed lasers have made inroads into the fields of biology, chemistry, material sciences and medicine. They are used to measure mental processes in neural networks, investigate the dynamic processes and response mechanisms of catalysts, make detectors more compact, and help us to understand nanomaterials.

Research with, and into, ultra-short pulsed lasers will continue to be a fascinating topic. Simpler, more compact and more economical ultra-short pulsed lasers will increase the acceptance of this technology and open up new areas of interest.

Diode-pumped solid-state lasers will replace more complex, ultra-short pulsed lasers such as titanium sapphire lasers. And an increase of several orders of magnitude in average output power and repetition rate will make it possible to develop innovative systems in many fields.

Hochspannend für die Industrie

These developments are of great interest to industry, too, since new materials such as fiber-reinforced matrix composites, high-strength steels, temperature-sensitive biomaterials and tempered thin glass are difficult to machine with conventional tools. Ultra-short laser pulses can interact with materials via multiphoton absorption, thus performing what is known as “cold machining”, a process in which the energy pulses are absorbed in a tiny layer, leading to a direct sublimation from solid to gas.

This prevents damage to the surroundin material and enables precise structuring in the nanometer or micron range. Traditional material parameters such as homogeneity, absorption properties, vaporization temperature and hardness only play a subordinate role in this process which, in principle, can be used for high-precision machining of any material.

Enormes Potenzial für Massenanwendungen

Yet it was only recently that ultra-short pulsed lasers started to be used in industrial production. The breakthrough came in the form of diode-pumped solid-state lasers which offered enough output power and stability to make their use cost-effective. The potential is huge. Conceivable applications include structuring low-friction surfaces for efficient engines, machining carbon fiber reinforced plastics, generating microstructures in small batches for medical applications, and many, many more.

Femtosecond lasers will expand into many other markets in the years ahead. One particularly promising area involves sensor systems that make use of optical frequency combs. A single laser can generate tens of thousands of ultra-stable wavelengths simultaneously — a revolutionary step forward for spectroscopy and measurement techniques. Although femtosecond lasers are currently too expensive and complex for high-volume applications, new technologies such as ultra-short pulsed semiconductor lasers offer enormous potential for mass-volume applications in biotechnology, medicine and environmental technology.

It currently stands at 80 attoseconds, but a team in the USA recently reported a laser pulse of just 67 attoseconds.

What drew you to this field of research and why do you find it so fascinating?

I enjoy making processes visible which we once believed nobody would ever see. Everyone knows how difficult it is to capture rapid motion, whether in photography or television. And people are fascinated by sequences of snapshots that show things like an object smashing through a pane of glass.

So when I first encountered short pulse lasers I was immediately struck by a thought: If capturing images of fast-moving objects in the macroscopic world is so exciting and interesting, then it would surely be even more fascinating to do something similar in the microscopic world — a realm in which everything happens at even more extraordinary speeds. But that requires a light source capable of emitting pulses of sufficiently short duration. So that’s been the focus of my research ever since I did my thesis at the University of Budapest in 1985, in which I developed a technique for measuring ultrashort laser pulses. I was immediately hooked and was never tempted to try any other line of work!

It sounds like you have the kind of enthusiasm that could motivate other people, too.

My curiosity spurs me on and makes it easier for me to motivate the young people I work with. And that’s essential in today’s research environment, because the era of scientists working in isolation is over. What we need is a team that brings together people with different kinds of experience and very specific, specialized knowledge — that’s the only way we can make progress nowadays. It is extremely important to get young, talented scientists interested in your field of research. If you don’t do that, then your research is destined to fail.

What does it take to work in attosecond physics ?

Young researchers need patience, endurance and staying power. The more ambitious our goals, the more we need to demonstrate patience and the ability to get through lean periods. That’s one of the key points I emphasize in the first interview with people who are looking to join my team. It’s important that the people who join us are not just looking for quick successes. In our team, you don’t measure your own performance by the number of publications, but rather on how much closer you are getting to the goal from one month to the next. There are very few opportunities to publish interim results on the way to reaching that goal, and some people find that hard to accept.

Have you experienced lean periods yourself ?

Of course. Let me give you one example: We established the experimental conditions for generating the first attosecond pulses back in 1997. Those pulses were the shortest pulses that were physically possible because light is a wave and a wave must oscillate at least once. The duration was just a few femtoseconds, and that was a new world record. Theorists then showed us ways of using this as a basis for generating attosecond pulses. But of course direct measurement of the pulse duration was out of the question. It took us four whole years, until 2001, to reach the point at which we were finally able to perform the measurements. Four years — that’s the same amount of time it takes to produce a thesis.

Nevertheless, your own career has been nothing short of lightning fast by the standards of university research!

I have to admit that I don’t see my career as having been particularly remarkable. I just know how lucky I am to have found a job so early on in which work doesn’t really feel like work, but is just something I enjoy doing. Since then things have just flowed naturally onwards.

How have things unfolded since those first attosecond achievements?

Our 80 attosecond record was really a kind of by-product. As soon as we generated the first light pulses of a few hundred attoseconds a whole new world opened up for us. All of a sudden we were able to observe the motion of electrons. If you’ll permit me to compare it to photography, the attosecond pulses gave us a camera fast enough to capture this ultrafast motion, and that was something totally new.

Electrons play a fundamental role. They ensure that the molecules in our bodies perform the functions they need to perform — and of course no electrical device would work without electron dynamics. That’s why understanding and observing this particle is something that is both fundamental in a theoretical sense and also very relevant in practice. That was what really enthralled us, far more than just the idea of generating ever shorter pulses, which was essentially the means to an end. Our research focus embraces a far greater number of exciting scientific questions which are coming within the reach of our experiments for the first time. It also includes the development and validation of the measurement technology used in pertinent research.

So do your results already have a certain degree of practical relevance?

If you are intrigued by the issue of practical relevance, you’ll probably be interested to know that, in collaboration with TRUMPF, I have founded a company to translate our research findings into products and solutions. At the moment, however, we’re not focusing on attosecond pulses, but rather on the femtosecond lasers that we need to generate the pulses.

How did that come about?

It was back in 2004 when we started investigating how we could push the boundaries of laser technology. We quickly came up with an answer. Instead of using titanium sapphire as a gain medium, we wanted to experiment with optical parametric amplification. The problem was that we didn’t have any reliable pump sources. We tried using our own resources to develop the picosecond lasers we needed as pump sources, based on disk lasers, but that was tremendously challenging.

So we got in touch with TRUMPF in Schramberg and they presented us with a fully mature disk laser module which gave us the breakthrough we needed. Using this picosecond laser as a pump source, we pushed ahead with our research until we finally fulfilled our expectations. That intense and successful period of collaboration built up trust and yielded a business concept.

What lies at the heart of your joint business concept?

The idea is for TRUMPF Scientific Laser to use our research on optical parametric amplification when developing market-ready femtosecond laser systems. These systems will primarily be aimed at the scientific market. Once these laser systems have been fully developed, we will also look into the possibility of applications in medicine and industrial manufacturing.

Our experiments in the 1990s showed us that any further reduction in pulse duration only makes a difference — though undoubtedly a major difference — if you are processing dielectric materials. The shorter the pulse duration, the more delicate the structures you can reproducibly generate. In the case of our new femtosecond lasers, that means we can carry out materials processing at the nanometer level. That opens up a whole range of new possibilities in materials processing, both in regard to materials and applications.

You’re investigating a new world – does that fill you with pride?

It’s more a sense of privilege than an object of pride. The thing I am proud of is the extraordinary team I have working with me, and the ability of this team to get the best researchers from all over the world to join our team or cooperate with us on our various projects. By constantly delving into new areas, this team has managed to steadily push back the boundaries of experimental physics. If we are eventually able to trigger some truly fundamental developments, that will make everything even more worthwhile.

And what if you don’t succeed in producing fundamental changes on a practical level…?

Even then, cutting-edge research is still immensely valuable. The fact that it produces such highly skilled professionals for academia and business would in itself be enough to justify every euro spent on top-level research. And that’s before you even start analyzing the benefits of the research results. Just look at researchers such as the duo who founded TRUMPF Scientific Laser, for example. They were both members of my team for many years. Their qualifications and professionalism show just how important cutting-edge research is to the prosperity of Germany and Europe and their future as key industrial locations. I wanted to stay in close touch with them even after they decided to move into the world of business, and that was one of the main reasons behind my decision to initiate and support the founding of the venture.

Research has become an international affair. Does it make any difference nowadays where research is conducted?

Yes, it does. For one thing, researchers need to be somewhere where talented people are emerging who can form part of their teams. And you also have some situations that simply offer the ideal conditions. For me, that was the Max Planck Institute combined with the chair in Munich, a combination which is probably unbeatable anywhere in the world. And fortunately we still enjoy a unique situation in Germany where taxpayers and politicians are still willing to spend money on basic research.

Englmaier: In 2010, we had a concrete application problem. We wanted to produce finer structures in stainless steel and obtain perfectly burr-free cuts. So we did a few tests at TRUMPF using an ultra-short-pulse (USP) laser. In the end, the results for this material were no better than with the fiber lasers we had been using up to then. But we immediately saw other potential in the USP laser that would enable us to develop entirely new applications. Not long after this, we took the decision to invest in the new technology.

Wasn’t that a risky investment? After all, the processes involved are still very new and you had no way of knowing for certain whether it would help you to win new customers.

Kleemann: We classified the risk as medium. While it is true that we were venturing into virgin territory and had no means of estimating the exact demand for this type of service, it was nonetheless clear that it would give us access to a new market.

E.: Our company makes its living by developing innovative solutions for its customers, and that means remaining at the forefront of technological evolution. To hold onto this position, it is essential that we invest in new technologies. It was never a question of simply installing a USP laser system and starting production immediately. We have spent the past two years testing it in the laboratory.

If it’s only being used in the laboratory, it’s purely for research purposes?

E.: No, not at all. We are actively marketing our services in this domain and using the system in commercial applications. But we are also conducting our own research projects to develop new machining processes, which we can then present to customers as a better, alternative solution to their requirements.

K.: At present, we are focusing exclusively on low-volume batch production. We eventually plan to be able to offer solutions for continuous, 24-hour industrial processes, but this is not yet possible with the systems we have at present.

Who are your present customers?

K.: We have customers in many different industrial sectors, and their requirements are correspondingly diverse. But in most cases they turn to us for applications requiring ultra-precise machining and for solutions to problems with heat input. Standard lasers generally don’t generate much heat, but sometimes even this is too high. I can cite an example from the watchmaking industry where, a few years ago, we wanted to use a laser-cutting process to produce a hair spring for a second-hand movement. Due to the heat generated by the laser, this filigree part was always slightly out of tolerance. We tried to remedy the problem by adjusting the geometrical parameters, but this made the process more difficult to control and the results were not always stable. So this obviously wasn’t the right solution. But once we started using a USP laser, we could do the job without any problems. The laser cutting of filigree, precision-engineered components is thus a market segment in which we see great potential.

USP lasers can cut filigree precision-engineered parts without distortion. The picture shows a hair spring for the second-hand movement of a wristwatch, made of 0.05-millimeter stainless steel.

E.: I can cite another case of a concrete application requiring extreme precision. The customer needed a solution that would enable a single layer of a fuse wire to be ablated at a specific point along its length, without damaging the underlying material. The USP laser enabled us to meet this challenge.

The production of pinhole diaphragms, for instance for automotive fuel supply systems, is a further example. This application involves drilling holes to very precise tolerances, a task that the USP laser can easily accomplish because it produces extremely sharp, totally burr-free ablated edges.

K.: Another advantage of the USP laser is that it enables us to process a wider range of materials than before, including glass and other transparent materials, sapphire, and high-performance polymer films.

Are you actively promoting the USP laser in your customer advertising?

K.: Obviously, it forms part of our advertising strategy. We are approached by certain customers precisely because they aware of the advantages of USP laser technology. They say: “We’ve heard you have a USP laser. We need it to drill this special type of glass.” That means there are customers out there who design components from the outset with this machining technique in mind. But the majority of customers come to us because we have a reputation of being able to do things that no-one else has the capability to do. And it has taken us a long time to build up this reputation. Our investment in USP laser technology is simply another step in the process of living up to this promise. So the USP laser certainly helps to attract new customers, but in the end what counts is the ability to establish long-term customer relationships based on their confidence that we can tackle any job, by whatever means are appropriate.

What potential does the USP laser hold for service companies like yours?

K.: As I already mentioned, the greatest interest lies in applications requiring precise, targeted material ablation or a defined heat input – in other words, the production of precision-engineered parts or the ablation and structuring of vapor-deposition and sputtered coatings.

And then of course there are the more challenging tasks where the USP laser allows us to do things that wouldn’t be possible with standard laser tools. This applies in particular to the machining of notoriously hard-to-process brittle, transparent, and hard materials such as ceramics, glass and sapphire. For example, the new technology allows smooth-walled holes without micro-fissures to be drilled in sapphire wafers for aerospace applications.

E.: We also estimate that the USP laser has great potential in the machining of high-performance polymers. We’ve obtained good results with Kapton film used to insulate electrical cables. We’ve barely started our investigations in this area, but we can say that as a general rule, regardless of the material, ultra-thin films are far easier to cut using a USP laser, and handling is simplified too.

Looking back: How did you adapt to working with the USP laser?

Precision-cut contact strip made of 0.1-millimeter stainless steel

K.: It was something of a challenge, partly because we had decided we needed a customized solution that would enable us to integrate different optics. It was our own idea to combine a multi-axis system with an ultra-short-pulse laser. TRUMPF supported us with know-how and practical information about the laser, but we dealt with the construction of the actual system, including calibration and software development, ourselves.

Another challenge was working out the parameters for different materials. Here, too, we benefited from TRUMPF’s experience, at least for the basics, but after that it was up to us to learn how to use the new machine and discover how the USP laser actually works in practice.

With other types of laser, it is often a case of “the more you give the more you get” – by increasing the laser output you automatically speed up the process. You can forget that when working with USP lasers. Here, the pulse width is given and the processing time depends on optimizing the relationship between feed rate and laser output. We had to learn to live with the fact that certain applications require a certain amount of time, and that there is no way of accelerating the process.

E.: The high-precision structures that we can now produce using the USP laser also meant investing in a 3D microscope, without which we wouldn’t be able to verify their dimensions.

Ablation of copper using the USP laser, producing areas of different ablation depths with sharp edges

What was your first real-life application?

K.: It was a task we deal with regularly, namely cutting ultrathin copper foils. We used to do this with a standard laser cutting machine, but because it operates with compressed air we had to go to extreme lengths to fix the foils in place, to stop them from being blown away. With the USP laser, all we have to do is lay the foils on a glass substrate and run the program. It didn’t bring us additional business – all we did was to transfer the task from one laser to another – but it was an improvement because it simplified our work.

E: That’s usually what happens when you get a new tool. You start by using it to do the work you already have and only later begin to tackle new jobs that weren’t possible before.

What is your verdict so far?

K.: The verdict as far as the capabilities of the USP laser are concerned is unquestionably positive. And it has met our expectations concerning its suitability to process new materials. After two years gathering experience with the new technology, we now have sufficient know-how to really get the ball rolling. That makes us supremely confident that we will soon start reeling in contracts for a whole load of new applications.

In 1965, Intel cofounder Gordon Moore presented to the semiconductor industry his prediction that the number of transistors incorporated in a chip could be expected to double approximately every 18 months.

Since then the industry has been fighting for every square nanometer in a titanic, billion-dollar struggle. A transistor in a modern smartphone CPU is roughly the same size as a flu virus. Soon the transistors will be so small that they will only come up to a virus’s knee, and not long after that the virus will be stepping on transistors and thinking “Where did these crumbs come from?”

But how much smaller can transistors really get? A whole lot smaller, says the extraordinarily innovative semiconductor industry — but we need more light!

Read here how the laser is conquering the chip fabrication chain, from lithography to the drilling of PCB contacts.

Laser in microchip production

EUV lithography

Extreme ultraviolet light is the lithographic key to tomorrow’s tiny circuit patterns – all thanks to TRUMPF CO₂ lasers. read…

Low-K-Grooving and Wafer Dicing

The going is getting tough for the saw. Using a picosecond laser to cut wafers is faster and cleaner and can produce up to 50 percent more chips. read…

Marking microchips

Marking ever more information onto an ever smaller space on a microchip is something only lasers can do. Plus, they raise profit in the quality control process. read…

PCB contacts drilling

A thousand holes per second, with 30-micron precision in both depth and breadth – mechanical drilling methods in PCB have reached their limit whereas lasers are just getting started. read…

The various process steps would normally require multiple manufacturing stages with different lasers — but Dow Corning had other ideas, as Guy Beaucarne, head of the Solar Cell Department, explains: “Modern solar cell manufacturing lines make extensive use of laser processes. For our R & D activities, we wanted a compact laser workstation that not only could execute some laser processes that have become common in the industry, but also could provide a wide research flexibility, enabling us to apply more advanced laser processes required for emerging solar cell technologies.” With this concept in mind, the project manager decided to call up TRUMPF.

Project Engineer Jörg Smolenski recalls what happened next: “We were fascinated and fairly sure we could come up with a solution for the laser components. But we needed a systems partner capable of designing the complex automation package that the lasers would require.”

Three jobs in one

Smolenski placed a call to IPTE in Belgium. TRUMPF and the systems integrator have a long history of working together on automation projects. His call was answered by Kris Smeers, Business Development Manager Automation at IPTE: “We’re very familiar with the production stages because we do a lot of work in the photovoltaic industry. And we were immediately tempted by the challenge of squeezing an entire fab into the smallest possible space and controlling it with micron precision.”

Take a look in the gallery to see how the miniature fab is set up.

To ensure the system would be able to handle all the processes involved in the laser manufacturing of solar cells as well as have additional built-in flexibility for upcoming R & D projects, Dow Corning asked for three wavelengths emitted by non more than two beam sources: 1,030 nanometers (infrared), 515 nanometers (green) and 343 nanometers (ultraviolet).

In addition, it was essential for Guy Beaucarne to have the option of carrying out additional modulation of the light and working with pulse lengths in the nano and picosecond range. That’s the only way in which the beams can ablate the various substrates while still supplying enough energy to cut the material. A key goal of Dow Corning’s design concept was to maintain flexibility with regard to the sequence of the process steps.

“It wouldn’t have made sense to choose anything else”

Guy Beaucarne, head of the Solar Cell Department at Dow Corning

The TRUMPF application engineers proposed using two beam sources, one of which would be a marking laser: “The TruMark lasers are reliable, compact systems, so it wouldn’t have made sense to choose anything else,” says Smolenski. With its green 532 nanometer light and a pulse repetition frequency of between 25 and 100 kilohertz, the TruMark 6230 proved to be the perfect tool for marking silicon.

But the main workhorse in this miniature fab is a TruMicro Series 5000 ultrashort pulse laser. Depending on the application, it delivers pulses as short as 10 picoseconds, pulse energies up to 250 microjoules and an average laser output of up to 100 watts. Parameters, which would also allow for a conversion of its light into the green and ultraviolet spectral ranges. TRUMPF used it as a basis for creating a triple frequency solution.

A special “box” developed by the company Xiton Photonics, based in Kaiserslautern in Germany, in collaboration with TRUMPF plays the role of the frequency conversion module. It either lets the infrared light through or converts the laser pulses into either green or ultraviolet laser light as required, each of which is sent through its own individual scanner optics.

High-precision system engineering

Kris Smeers, Business Development Manager Automation at IPTE

To control the box, scanner and overall system, IPTE developed a special automation solution: “The biggest challenge for us was the level of precision required in positioning the wafers under the lasers,” says Kris Smeers. In some cases, the all-in-one system has to position the wafers with an accuracy surpassing 10 microns while still being able to handle a broad range of different formats.

Kris Smeers and his team decided to implement a high-precision image capture system: “As long as the machine can see what workpiece is coming and how it is positioned, then the exact shape doesn’t matter,” says Smeers, explaining how they reached their decision.

The camera used for image acquisition offers a resolution of 12 x 12 megapixels and the positioning drives utilize fully adjustable motors and high-precision encoders. To ensure that no external factors interfere with this precision work, IPTE limits human interaction to the programming of the process steps through the user-friendly interface — plus of course the constant provisioning of fresh wafers to the machines. This is one area where the miniature fab clearly differs from its larger counterparts: In bigger machines, IPTE also automates the process of loading the silicon wafers.

The solar industry’s future tool

Jörg Smolenski, Project Engineer at TRUMPF

The system has been up and running in the research center since fall 2012. In response to the question as to why it specifically needed to be a laser system, Guy Beaucarne explains that he sees the laser as one essential tool of the future for the solar industry: “Lasers are very flexible, fast and reliable. They are easy to control and they ensure a reproducible process. At the same time, they can offer a smaller footprint and lowertotal cost of ownership than alternative patterning and machining methods,” he says. “Many in the solar industry see the laser as a necessary tool for advanced solar cells”.

This applies not only to the miniature fab that Dow Corning is using for its research, but also to these same processes on an industrial scale: “IPTE and TRUMPF have managed to create an extremely flexible tool that we can use for multiple different process steps,” says Guy Beaucarne, emphasizing Dow Corning’s satisfaction with the miniature fab.

Hundreds of millions of laminated cores will be needed to build electric motors for the millions of electric, hybrid electric, and fuel-cell vehicles that will one day populate our roads.

The construction of a laminated core is relatively simple. The more urgent challenge is finding a cost-efficient manufacturing process that limits the exposure to stress during manufacture and guarantees a long life in the operating environment, where they must withstand crushing magnetic forces.

Is laser superior to TIG?

Arc welding techniques – especially tungsten inert gas (TIG) welding – are commonly used to produce laminated cores for automotive drives. Processes that employ several torches operating in parallel are comparatively cost-efficient. But they impose limits on factors such as process speed, accessibility, choice of materials, and the mechanical properties of the laminated core, which together make arc welding a less-than-ideal solution for the projected volumes required for future electromobility applications.

To investigate the idea that laser welding might provide a better solution, four companies – C.D.Wälzholz KG (CDW), Laser Cut AG Densbüren (LCD), Trumpf Laser GmbH + Co. KG (TLS), and SWD AG Stator- und Rotortechnik – set up a joint project team. The project was concluded in 2011 and the results first published in ATZ – Automobiltechnische Zeitschrift.

The experimental phase

The project team performed welding tests on cold-rolled non-grain-oriented, final-annealed electrical sheets with temperature-stable paint insulation produced by CDW.

To achieve welding results as close as possible to production standard, the project team used laminated disk packs punched from sheets. The geometry of the punched stacks was configured in such a way that twelve weld seams were made on the square stack with in each case three different types of seam preparation – two different bumps and a concave trough.

Three different triangular weld cross-sections were aimed for in the welding tests:

• Large: seam width at top approx. 2.5 mm x depth approx. 1.5mm = approx. 2.0 mm2
• Medium: seam width at top approx. 1.5 mm x depth approx. 0.6 mm = approx. 0.6 mm2
• Small: seam width at top approx. 0.8 mm x depth approx. 0.3 mm = approx. 0.15 mm2

The welding parameters such as welding speed, focus position, single/double focus and laser power output were selected so as to achieve good-looking welds on the various electrical sheet grades and seam geometries with the desired weld cross-sections.

Good-looking means crack-free and without visible open pores. The tests were intended to determine the maximum attainable welding speed at which good weld seams can still be achieved.

Weld geometry: trough or bump?

In arc welding, the paint insulation between the individual disks combusts and escapes as gas from the welding zone. Laser welding produces a similar reaction and considerable smoke is emitted.

The high vapor pressure additionally forces the evaporating paint components in between the individual disks of sheet, so that these gases exit the welding zone at the edge of the seam. The residues leave a black fringe. The evaporating paint also causes considerable spatter, limits the attainable welding speed and can lead to pore formation in the weld seam.

A higher welding speed and better seams can be attained in the trough because fewer cracks occur when no bumps are present. However, bumps facilitate outgassing in laser welding too, while allowing burnt paint residues to be avoided by using shielding gas.

The welded cross-section can be varied by the irradiated energy density and the welding speed.

Sheet grades and welding speed

Parameter studies on welding the different electrical sheet stacks showed that each electrical sheet grade requires an adjustment of the welding parameters and that the maximum attainable welding speed also varies for the different sheet grades.

On laminated cores of M270-50A good welds were produced at a maximum speed of up to six meters per minute. On M270-35A five meters per minute were attained and on M800-50A four meters per minute. In the test where the high welding speeds were applied to a greater number of parts it was found that the quality of the welds was not constant and the surface in some cases exhibited visible pores and cracks.

In order to more reliably control the welding process, the welding speeds had to be reduced in some cases to 50 per cent of the maximum values. In the future it will be possible to distinctly improve production reliability even at higher speeds by extensively optimizing the parameters.

It was observed that materials with a higher silicon content have a slightly greater tendency toward crack formation, whereas the insulating coating and its pigments, and the compressive force with which the stack was clamped for welding, did not appear to influence the welding result.

The sheer strengths measured on some of the specimens exhibited a wide distribution of values, especially in the presence of pores that reduce the area of the welded cross-section.

Laser versus gas metal arc welding (MIG/MAG) – which is the better choice?

To avoid cracks and pores, arc welding can only be used on sheet grades with a thin paint coating of up to about 1.5 micrometers and bumps as weld seam preparation. Also, arc welding only attains maximum speeds of 0.9 nine meters per minute.

Sheets with a thicker paint coating and the thinner electrical sheet NO20 can only be welded with considerable deterioration in quality. The reason for this is the pronounced formation of pores. In arc welding the introduction of heat and the welded cross-section can only be varied to a small extent. In addition, the shear stresses of the laser-welded specimens are in all cases higher than the stresses of the TIG-welded specimens.

As in other applications, manufacturing costs per unit are lower when using laser processes because they permit higher welding speeds, require fewer operators, and offer significantly better reproducibility than comparable arc welding solutions.

Disk lasers and high-power diode lasers as the beam source considerably reduce the energy input compared with CO₂ lasers. What’s more, with an output power of four kilowatts and equipped with multiple beam guides the beam source can weld four seams on one laminated core simultaneously.

This reduces the cycle time and the distortion occurring on the component without any risk that the simultaneously performed welds mutually influence each other with currents and magnetic forces in the way arc torches do when working in parallel.

Major shipbuilders in Europe are systematically implementing hybrid laser welding. The technology generates enormous savings. Cruise ship manufacturer Meyer Werft, for example, has reported reducing total build time by 30 percent due to implementing hybrid laser welding.

Ed Hansen, product manager at ESAB

What’s prevented more widespread adoption?

Early adopters have been very secretive owing to the strong competitive advantage the technology creates. Without published case studies and data on economic return, it’s been difficult to grow awareness and acceptance of the technology.

What are the economic benefits?

In one automotive industry example, we showed a reasonable, four-year amortization on the costs incurred when adding the technology to their existing production. But if the company were to redesign the product, amortization would take less than a year, thanks to reduced material use. In another example, one redesigned rail car’s weight was reduced by 30 percent. This translates into 30 percent more payload for each rail car.

What particularly cost-effective applications have you seen?

Hybrid laser welding is particularly well suited for mass production welding at high capacity utilization. Depending upon the application, hybrid laser welding can be three to ten times faster than conventional processes. The technology can lower heat input by as much as 90 percent and this reduces the typical macroscopic distortion. Additionally, we’ve seen benefits in weight-sensitive applications, We’ve also seen significant fatigue life improvement in products exposed to cyclical loading, such as car suspensions, pressure vessels, and bridge components.

What developments in laser technology haven influenced hybrid laser welding?

The continued development of high-power solid-state lasers with smaller form factors, greater efficiency, and lower cost has had a big effect on hybrid laser welding. Our transition to solid-state lasers in 2001 made it feasible to apply the technology to industrial settings. New technologies, particularly fiber delivery, let us integrate the process into conventional motion systems — robots, gantries and automation — which increased acceptance. Many laser improvements benefit other applications more than ours. We’re currently limited in how much laser power or brightness we can use productively. But in the future I see less expensive, compact lasers which are easier for us to incorporate into existing production operations.

What does the future of process control look like?

So far, most advances in process control have focused on visible surface features. In the future, we’ll look inside the weld and manage the process based on what we see below the surface, using a closed-loop, real-time control system. Improving weld stability inside the material and preventing the creation of discontinuities inside the weld will enhance quality control and allow us to reliably apply the process to thicker, larger sections.

Every technology has its limits. Which are the current limitations of hybrid laser welding?

The thinnest application we’ve seen is around one millimeter. The fastest is a pressure vessel, three to four millimeters thick, welded at 6.1 meters per minute. This by the way makes it almost seven times as fast as conventional butt welding. There’s a big advantage to one-sided welds, particularly inside pressure vessels like those used for petrochemical tanks, hot water heaters, and in power plants. Using laser-augmented welding with filler wire, we can weld thicker segments with a non-penetrating hybrid laser variant. Our thickest one-sided, single-pass application was in half-inch thick steel, butt welded at 2.3 meters per minute.

What applications show the most promise?

We’ve seen significant interest from the energy industry. Over the next twenty years, production will be increased and many pipelines will be replaced. Many of these applications use high-strength materials and manufacturers will have to automate to keep up with demand. Promising opportunities exist in bridge building, where designs are moving toward more cable-stayed suspension and long span bridges. Weight is critical here. As manufacturing moves to lighter products, structures get thinner and distortion becomes a bigger problem.

How is this technology expanding in automotive manufacturing?

Transportation — shipbuilding, rail cars, truck trailers, mobile equipment, automobiles — offers the biggest area of growth. New efficiency standards and high fuel prices are driving higher structural efficiency. Hybrid laser welding is an enabling technology for the distortion reduction, mass reduction, and high-strength alloys important in steel and aluminum vehicle construction. In one recent project, an automotive manufacturer redesigned a product for hybrid laser welding and high-strength material. It not only improved the structure’s crashworthiness; it also reduced the weight by 40 percent. Generally, automotive manufacturers find the cost per pound goes up when using high-strength materials, but when the overall weight drops, so does the total cost.

What role will hybrid laser welding have in the future?

It’s exciting to think about the global effect hybrid laser welding can have in creating lighter, high-strength structures and reducing material consumption. Hybrid laser welding will change the way structures are built. I think we’ll see larger scale adoption of the technology, particularly as costs drop and more welding codes incorporate the technology.

ESAB

Uwe Stadtmüller, the founder and managing director of Stadtmüller GmbH, presses the start button. The door of the laser welding system — developed by Stadtmüller himself — closes, the wire cross braces and wire rings are pressed into position on a simple clamping mechanism, and the robot-controlled, camera-assisted scanner optics weld 760 wire joints and four slide-in connectors.

After five minutes, the robot raises its head, swivels around 180 degrees and begins work in the second of the two adjacent cells. The optics system — a PFO 3D by TRUMPF with the light of a TruDisk 5302 from a 200 micron fiber — hovers over the next workpiece, which had been prepared while the laser was working in the other cell.

As the process starts up again, the first cell opens and the machine ejects a freshly made fan guard unit, ready for painting.

A product, that nobody wants but everybody needs

This grate-type fan cage is one of those wire mesh casings used in industrial fans as protective screens and fan motor mountings. It is a product which Stadtmüller’s customers are determined to get for the lowest possible price. “The fan guard is necessary, somebody has to produce it, and whoever does it quickest and cheapest wins,” he says.

In 2000, Stadtmüller won for the first time. Back then Stadtmüller developed a resistance welding technique which joined the several hundred intersection points with a single burst of energy. This approach represented a huge leap in productivity for his entire process. Fan guards are typically produced from two sub-assemblies which are “wedded” in a third step and completed with some additional wire rings in a fourth step.

The first sub-assembly is the supporting frame, for which the outer flanges, support braces and motor flanges are joined in an arc welding process. The second sub-assembly is the actual wire cage consisting of the criss-crossed wire braces and rings.

Uwe Stadtmüller, founder and managing director of Stadtmüller GmbH

Twelve hours retooling for a few hours of production

“It was a good technique – at least for a few years,” says Stadtmüller. But nowadays the market is forcing his customers to provide fan systems in an increasing range of sizes. Twelve years ago, Stadtmüller GmbH was producing wire guards for 400 different types of fan units.

Today that figure has climbed to almost 1,200. At the same time, average batch size has fallen from 1,500 pieces to fewer than 100. Stadtmüller was forced to invest more and more money in welding tools and to retool ever more frequently – with retooling taking up to 12 hours for each machine. “That was eating away at the productivity of my welding systems.”

It was also clear that the thermal distortion generated by the welding process was steadily becoming a major cost issue. “My choice was clear: I either had to raise my prices or come up with an innovative solution,” says Stadtmüller.

Laser welding would be just the thing, but…

That solution turned out to be a laser process which he hoped would provide three key advantages: A system that could complete all the welds in a single pass, eliminate welding distortion, and achieve maximum flexibility, since lasers do without type-specific tools and require virtually no retooling time.

Remote welding was an absolute must right from the start,” says Stadtmüller. “Only a scanner system is capable of moving the focus quickly enough from one weld spot to another.” And the three-dimensional shape of the parts makes the optics’ job even harder: “The focal distance changes from one weld spot to the next. That’s why we need a PFO 3D, which has the ability to move the focus spot in all three dimensions with tremendous precision.”

Yet even with a remote process, Stadtmüller was unable to switch to laser welding without having a clear idea of how exactly to carry out the individual welds. The intersection points are indeed tiny, yet welding all these points from the side with fillet welds would require the robot to change position far too often and would eliminate the speed advantage of the scanner optics. So Stadtmüller decided on a more direct route, approaching the weld vertically from above and along the brace straight through the wire ring.

“This is not going to work”

His ideas were initially met with skepticism. “The feeling in the automotive industry — and indeed industry in general — is that robot-controlled scanner welding is a process that is only worth using in largescale, fully automated applications,” he says. “But I felt differently.”

His goal was not to increase the speed of his welding process, but rather to compress the process as a whole: “Scanner welding with the PFO 3D was never the ultimate objective — it was just the right means to the end.”

Productivity calculations revealed that condensing the process into a single step and the flexibility gains alone would be sufficient to recoup the investment. All that remained was to find a solution for the weld spots.

Welding the intersections from above meant cutting through the thin wire rings and then re-welding them. “The solution we came up with was contact pressure,” Stadtmüller recalls. The resulting “yoke”, a fixture lowered onto the flanges, wire braces and wire rings to hold them in place, also presses them into the melt during the welding process.

Aiming precisely

The third challenge was rather more unexpected: “I had imagined that we would simply program the system with the CAD data, press the start button and watch the finished fan guards pile up,” says Stadtmüller.

Yet in the welding tests the laser kept missing its target, often by more than a millimeter, as Stadtmüller explains: “The PFO 3D itself was focusing just as accurately as we had hoped. But it turned out the target was not properly positioned in the focus spot. A robot arm always has a certain amount of play. Normally that is fairly minimal and doesn’t affect the job in hand, but in our case it was clearly a problem.”

The process only works if the laser hits the wires within 0.1 millimeters of the target spot. Yet the accumulated tolerances of the robot and workpiece meant that the targets were frequently deviating from the CAD coordinates.

Teaching would have been the standard solution, but with 760 weld spots this was clearly impossible. So Stadtmüller tried a different approach. Instead of guiding the robot to each welding point, he decided to use the PFO 3D system’s optional image capture function. This involves the scanner optics moving to their working position and focusing on all the intersection points in the working area without actually welding them.

The software – developed by the specialist for industrial image processing i-mation – uses the image data to identify the points at which the rings and braces intersect and then compares this information against the CAD data to determine the actual target coordinates.

And this was just the beginning

The new laser system has now become an integral part of the production process. The fan guard units are consistently within tolerance and Stadtmüller has even eliminated the need for sandblasting thanks to the fact that the laser does not leave behind any scaling or spatter.

He is certainly satisfied with the results: “When we switch production to a different model it only takes us an hour or less to change the clamping mechanism and get back online, so we save 11 hours of downtime on every switchover.”

One thing that fascinates him is the design potential that the process offers: “We have started to redesign the fan guards and we can already see that the laser technique will open up a whole new range of options for our customers. That’s our next innovation project!“

Scanner systems are also nothing new in industrial applications: the small, lightweight mirrors incorporated in these systems are used to move the focus spot over the surface of workpieces at extremely high speed. But now scientists at the Max Planck Institute for Solid State Research have created something that really is new: a successful technique that combines the PLD concept with scanner technology. Their ‘Combining Laser Deposition (CLD)’ method substitutes scanner optics for the fixed focus of the PLD technique.

Pico-scale lunar landscape

In the PLD process, the usable area on the target is very small, and it gets rougher each time a laser pulse hits it, forming a pico-scale lunar landscape from which the laser blasts out increasingly uneven ‘chunks’. Larger particles begin to be deposited on the substrate as droplets. Since the target can only supply the material for a single coating layer, multilayered coatings are produced in multiple process steps.

Alternatively, the laser can be focused on alternating targets in a single process step, though each change of target is reflected as an unevenness in the coating. Coatings combining multiple elements can either be produced using a ‘pre-mixed’ target or by quickly alternating between individual targets consisting of the pure elements. However, in both these cases the elements often accumulate in a slightly different ratio to that at which they are ablated from the targets.

The CLD process

On the target on can see how the layers are arranged.

In the CLD process, one target supplies all the components for all the layers of a coating system. In addition, the technique generates composite layers during the process. This is achieved by arranging the elements for the coating system in a suitable geometry.

In the CLD process, the scanner directs the laser pulses over the target line-by-line. This lets the process use the entire target surface while simultaneously coating large areas of the substrate with a continuous and complete coating system. It is even possible to form gradients with evenly increasing or decreasing concentrations of the coating components within a single layer.

The Max Planck Institute investigated and developed this new technique as part of a project to coat sapphire substrates with an aluminum-titanium-niobium coating system. The target they used consisted of a titanium disk into which wedge-shaped segments had been inserted and a niobium disk in the center. The experiments were performed at target temperatures of between 25 and 500 degrees Celsius employing a femtosecond laser

Schematic illustration of the set-up: (1) laser, (2) scanner, (3) segmented target, (4) motor, (5) substrate, (6) vacuum chamber, (7) optical window.

The laser struck the target at a wavelength of 516 nanometers, pulse energy of between 0.3 and 0.6 millijoules, and pulse frequency of one kilohertz. The researchers subsequently examined the ablation of the target and the deposition and composition of the coating layers on the substrate samples.

No droplet formation

This series of experiments showed that one of the biggest difficulties of PLD — droplet formation — does not even occur. Overall, the new CLD technique transfers more material, thanks to the higher pulse frequency of the femtosecond laser. Yet the ultrashort pulses ablate smaller quantities of material moreevenly with each pulse.

In addition, the focus spot migrates across the target instead of constantly firing at the same point, which results in the surface actually being smoothed by the laser.The substrates used in the experiments featured evenly mixed Al-Ti-Nb coatings with particle sizes of between 20 and 200 nanometers. There were negligible differences between the substrates coated at 25 degrees and those coated at 500 degrees Celsius.

Homogeneous coating: droplet formation does not even occur.

All three components accumulate in their crystalline phase at all temperatures, without forming alloys. The desired component ratio of 1:1:1 was achieved across the entire coating. The researchers also discovered that the ratio of the components in the deposited coating changes immediately and in exactly the same proportion whenever the target ablation ratio is changed.

In addition, the scientists found that the ablation of the components can be directly controlled by the position of the scan lines, and an examination of the deposited coatings showed that ablation and deposition also change in proportion to the laser power employed — a change that is immediate and ‘drag-free’. As a result, the laser output power, the position of the scan line on the target, and the movement of the target can all be harnessed as precisely controllable process parameters.

Laser as joker

The laser smoothes the Titanium layer. Here before and after laser ablation.

The joker in the pack in this process is the laser: experiments performed at TRUMPF with a TruMicro have shown that a productive and stable coating process can even be achieved with an industrial picosecond laser. And everything suggests that the process could be accelerated even further by using more powerful lasers, shorter pulses, and higher repetition rates, while still retaining full control over the process.

Start Movie

On the target on can see how the layers are arranged.

Contact

Dr. Dieter Fischer
Email: d.fischer@fkf.mpg.de

This article was first published in winter 2011.