In recent years it has become far easier to switch from conventional welding methods to laser processes. This is thanks to technological innovations that include the increasing flexibility of laser welding robots, the development of automatic laser focusing systems, and advances in the design of modular clamping devices.
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TRUMPF Medizin Systeme GmbH
The medical systems engineers in the Thuringian town of Saalfeld have been gathering experience in laser welding since 1993, when the company was still operating under the name of Blanco Med. The company was acquired by TRUMPF in 1998. TRUMPF Medical Systems has two production sites in Germany where it develops and manufactures solutions for operating rooms, intensive care stations and auxiliary services, including operating tables, surgical and examination lighting systems, video solutions and supply units.
With the TruSystem 7500, TRUMPF has redefined the distinguishing qualities of top-class operating table systems. This system meets the very highest requirements in terms of functionality, user-friendliness, material properties and design. Moreover, it accords with TRUMPF’s philosophy of assuring backward and forward compatibility with other repositionable operating tables driven by electric motors. A simple solution with a guaranteed return on investment.
The TruLaser Robot 5020 cell is a turnkey solution. This highly integrated system can serve as a node in a TRUMPF LaserNetwork for the processing of complex seam geometries. It is built using industry-standard components that are freely available on the market. Thanks to its outstanding flexibility, the TruLaser Robot 5020 is a cost-optimized solution for all manufacturing scenarios, even for small-batch production.
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When the company now operating as TRUMPF Trumpf Medizin Systeme GmbH in Saalfeld (TRUMPF Medical Systems) first adopted laser materials processing, such accomplishments were still a far-off dream. At the time, the company hadn’t yet joined the TRUMPF Group: “We were the first company in Thuringia to investigate the possibilities of laser welding, well before the universities and research institutes had begun to study its applications,” reports Helmut Zapf, the head of production at TRUMPF Medical Systems in Saalfeld.
Zapf recalls the early days when the company first started using laser materials processing in its operating-table manufacturing operations. It was a big change but they embraced it readily. “When I look back now,” he comments, “I would say that in 1993 we plunged in at the deep end, because our first purchase was a combined laser cutting and welding machine. We’d chosen this solution because we wanted to cut and weld 3D profiles in sheet metal and tubes.”
The machine they purchased was one of the first 3D laser processing systems marketed by TRUMPF, which used a Cartesian coordinate system to define the displacement along the X, Y and Z axes. This meant that the beam had to be guided with great precision through a series of mirrors, lenses and prisms. As Zapf explains, “The slightest deviation at the beginning of the path had a major impact on the final result. It all became much easier when we installed a TruLaser Robot 5020 welding cell eight years ago, followed by a second four years later. With a fiber-optic cable, the laser beam can be directed everywhere we want.”
Today’s operating tables are examples of high technology in its purest form. “They are based on a modular design and consist of 500 to 800 different components including sheet-metal parts, precision motors, and electronic and hydraulic units,” says Arnd Schreiber, head of the sheet-metal processing unit at TRUMPF Medical Systems.
The medical product regulations applicable to operating tables impose binding standards relating to their safety under defined static and dynamic loads. In order to support a patient weighing 360 kg, which is the maximum requirement, operating tables must be designed to withstand four times that weight. Schreiber adds: “This means that our welded assemblies, too, must offer this safety margin.”
Helmut Zapf describes an incident many years ago that caused him to question traditional working practices: “An operating table pedestal in a hospital broke. In those days, the parts were joined manually by specialized and experienced welders in a certified workshop. The incident prompted our decision in 1993 to switch to laser cutting and welding.”
Highly accurate parts are essential
Once the production specialists in Saalfeld had familiarized themselves with the laser cutting and welding machine and tested its capabilities and limits, the product development department was brought in on the action. Zapf relates: “We gave our development engineers advice on how they might adapt the design of different parts to make them better suited to the requirements of automated laser welding.”
Laser welding differs from manual welding in that it imposes stricter requirements on the dimensional accuracy of parts and requires the use of a suitable clamping device to ensure that the parts are positioned accurately.
These two points have turned out to be very important. “We achieve the required tolerance of approximately 1/10 of the gap width on the one hand thanks to clean laser cuts and on the other hand by insisting that our suppliers deliver parts of a very high quality,” says welding expert Schreiber.
The robotic tool welds metal sheets inside the TruLaser Robot cell from a distance of 70 millimeters. The large working distance enables the beam to reach difficult-to-access areas. (Photo | TRUMPF)
An inconspicuous but important element: the clamping device plays a significant role in the final result. As well as ensuring perfectly accurate weld seams, its design also determines the speed at which the machine can operate. (Photo | TRUMPF)
TRUMPF Medical Systems uses two TruLaser Robot 5020 cells to weld assemblies for operating tables. (Photo | TRUMPF)
Laser welding reveals its huge advantages
In the years since the company started using lasers to weld the components of its operating tables, the production department has identified a whole series of advantages that laser welding offers compared with manual techniques. Zapf cites an example: “Due to the high energy input and the ability to precisely focus the laser beam, the effective welding speed is 100 times higher than when welding by hand.”
“With conventional methods, I have to prepare the weld seam,” explains Schreiber, “for instance by filing a groove that I then have to fill with wire. This step isn’t necessary in laser welding.” And Zapf adds: “I can create a deep weld, without contact and without additional material, and obtain a very strong joint. No other technique allows me to do this.”
The experts relate that their colleagues in quality assurance initially found it hard to believe that the narrow, well-defined weld seams obtained with the laser could be as stable as the fatter and wider seams produced by hand. To prove that this was true, they welded one part manually and another with the laser, and sent both to the test laboratory for load testing. To everyone’s amazement, the hand-welded part split at a pressure of one metric ton, while the laser-welded part remained intact up to a pressure of four metric tons.
The repeatability of the results is another major advantage of laser welding, according to the two experts, because the machine produces welds of a consistently high quality. This in turn increases the reliability of the process. In many cases there is no need for downstream finishing steps because, as the production team in Saalfeld has frequently observed, laser weld seams are generally thinner and smoother than those produced manually.
“A further advantage is that there is less distortion of the material due to stress, which eliminates the need for downstream corrective measures,” says Schreiber. And as Zapf points out: “Such finishing stages can drive up costs substantially.” The automatic laser focusing system that TRUMPF developed some years ago enables welding robots to switch easily from deep penetration welding to conductive heat resistance welding. As a result, it is possible to produce internal welds in areas of complex parts that are inaccessible to manual welding tools.
Novel modular clamping system saves time
The necessity of custom-building clamping devices for each individual component is often one of the greatest hurdles that prevent manufacturers from abandoning conventional welding techniques in favor of laser welding. TRUMPF engineers are well aware of this problem, and are therefore continually working on improvements to laser material processing systems such as the TruLaser Robot 5020.
Component of an operating table after laser welding. (Photo | TRUMPF)
The same component in the clamping device (Photo | TRUMPF)
No finishing required (Photo | TRUMPF)
Close-up of the weld seam (Photo | TRUMPF)
“The efficiency of laser welding depends on the availability of appropriate clamping devices.” This is one of the main cost factors, hence the importance of close collaboration between product designers and production engineers at an early stage of the planning process, in order to obtain the best fit between the product and the clamping device.
This explains the recent introduction of a flexible, modular clamping system for parts of different shapes and sizes, from simple sheet-metal parts to bent profiles. This solution helps to save time, especially in short-run manufacturing and prototype-building.
Today, the Saalfeld laser-welding facility is equipped with two TruLaser Robot 5020 welding cells supplied by TRUMPF Laser and System Technology, Ditzingen, and in the past six months this facility has handled 6000 manufacturing jobs involving 1700 different parts. As Zapf confirms, “I can’t remember having to deal with a single product failure since we introduced the laser welding process, hence our confidence in its quality.”