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In Focus - Archives Septembre 2011
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Shape and modulation of the laser should be adapated to the individual requirements.
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If the pulse parameters are not individually adjusted to
the material, cracks and pores may occur.
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Thermal pulse forming
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17.09.2011 -
Laser welding technology is second-to-none, regardless of whether you are dealing with gears and injection molds or delicate and challenging welding works. When conventional cw lasers and many Nd:YAG-lasers reach their limits, modern process strategies can help to machine demanding welding metallurgies, different types of materials, or micro components process reliably and efficiently. Laser welding is particularly used if components have to be joined at a high welding speed, because slim welding seams, and a low thermal distortion are required. Compared with other welding techniques, the energy during laser welding fully penetrates into the material.
Pulsed lasers can be perfectly adjusted to the materials
Based on their signal type, lasers can be categorized into two types: While the beam of conventional continous-wave lasers (cw lasers) always show a continuous beam, pulsed lasers emit the energy pulse by pulse. Therefore more process parameters are available for influencing the solidification characteristics of the materials, than with cw lasers, particularly when machining challenging materials and material combinations. With plused neodym-designated yttrium-aluminum-granat lasers (Nd:YAG lasers) the pulse-to-pause ratio, and therefore the setting behavior of the material can be influenced. Moreover, the pulse can be adjusted with the thermal pulse forming to the temperature-dependent absorption behavior of the material. This way, the melt bath can be stabilized, and the material can be preheated and cooled down at a defined temperature. At the same time, the pulse can be modulated for mixing the weld bath, and for specifically influencing the crystal growth. Both pulse versions significantly influence the welding result. It particularly pays off to know the effect and how far the pulse can be influenced, if challenging materials are concerned, and how to benefit from this knowledge.
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Laser welding machine PSM 400 from SCHUNK
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Structure with pulse forming
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Structure without pulse forming
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Thermal pulse shaping minimizes cracks and pores
In contrast to laser welding with a rectangular pulse, where the whole pulse power is always actuated, the performance during the whole pulse shaping process can be adjusted with the thermal pulse forming. Therefore, surplus capacities and an overheating of the melt bath can be avoided. The quality of the welded surface improves, and in case of copper alloys splashes can be avoided that can form during a sudden phase transition.
Pre-pulse phases have proven in case of copper and aluminum alloys for injecting the laser beam into the material, and thus improves the reproducability of the welds. In case of other materials, oxide layers can be removed during the per-pulsing phasis, and the formation of pores can be avoided. However, the post-pulse phases have a homogenizing effect. They can prevent the formation of pores by improving the degassing of the material, and can circumvent hot cracks, or in case of high carbon-containing materials, hardness cracks.
Pulse modulation generates a homogenous structure
By means of the pulse modulation, the temperature of the melt bath can be influenced and stabilized. This effect is used for achieving a high rate of nucleation during solidification, and thus a fine-grained homogeneous structure. Moreover, the modulation of the laser power can help influencing the melt bath dynamics, and in turn, the morphology of the solidification. If different types of materials are welded, such as titanium and aluminum, the formation of cracks can be avoided by increasing the plastic deformation (ductility) of the connection. The combined pluse forming and modulation are of particular importance, if refractory metalls, such as alloys made of titanium, zirconium, tantalum or molybdenum are welded. If their melt bath is specifically supercooled by pulse modulation, a fine-grained structure and thus an excellent quality of the weld can be achieved.
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A turbine blade made of nickel based alloy is repaired on a PSM 400 laser welding machine.
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This turbine blade made of nickel-based alloy has been welded without any cracks and pores.
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Melt bath supercooling
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Additional materials make the impossible possible
If no satisfactory result is achieved by adjusting the pulse characteristics and parameters of the material, the metallurgy can be influenced with additional materials. This process plays a significant role if high levels of chronium-nickel steel are concerned, or aluminum alloys are alloyed with silicon and magnesium. Therefore high level chromium-nickel steels are used for laser welding, where a filler wire made of a nickel-base alloy is used. This makes the material corrosion-resistant, and is normally used in the medical technology or food processing industry. Due to the plastic expansion behavior of this tough material, most of the shrinking stress can be absorbed, which occurs during the welding process, and thus prevents a hot crack formation.
Pure aluminum can be perfectly welded by means of optimized pulse forming, while aluminum alloys with silicon, magnesium, lithium or copper have the tendency of forming hot cracks.This particularly concerns aluminum alloys with a magnesium concentration between 0 and 3.5%. Due to its excellent mechanical and metall-cutting properties, it is often used in industrial applications. Together with a filler wire from the low-melting eutectic alloy AlSi12, they can be alloyed and welded together crack-free. The same applies for the material AlSi1, which is prone to hot cracks and is used in the automotive and areospace industry.
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The PSM 400 from SCHUNK is equipped with a pulsed Nd:YAG laser.
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This injection mold has been machined on a PSM 400 laser welding machine.
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Perfect results from micro to macro
Modern pulsed Nd:YAG lasers offer numerous possibilities for ensuring optimum joining of the challenging materials and material combinations. With the multi-purpose PSM 400 laser welding machine from SCHUNK Lasertechnik, the welding process can be efficiently influenced, and can be adapted to the solidification characteristics of the material. Since most of the Nd:YAG lasers on the market allow laser pulses between 20 and 60 ms, the PSM 400 achieves laser pulses of 100 ms, and therefore is setting standards. Particularly in machining brittle materials, such as castings, high-carbon steels and superalloys, the user benefits from the overlong laser pulses, which considerably improve the weldability and reduce the effort of remachining works. The PSM 400 Blade Welder is even more efficient. It has been particularly designed for welding high-temperature resistant nickel or cobalt base alloys, as they are used in modern gas turbines. Its pulse duration can be extended to 200 ms. The BladeWelder is equipped with highly efficient fibers, which can absorb reflections so that the laser beam won’t damage the fiber of highly reflective materials, materials such as copper. Both machines ensure an adaptive closed-loop control to ensure that the laser is stable and is working precisely. Via a freely scalable pulse forming and modulation, the laser parameters can be adjusted to the specific features of the materials. Once defined, they can be deposited in the control unit, and can be quickly activated when needed again. Based on metallurgical tests, SCHUNK can check and prove the quality of the welding results in its own material science laboratory.
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12.2011
Clamping solutions for automated mass production
Efficient manufacturing means automated manufacturing. This particularly applies if large series are machined. This is when the clamping vises, which are the direct interface to the workpiece, playing an important role. In only a few seconds, they have to mount the components, safely and precisely align them, clamp them with-out deformation, and after machining they have to be reliably released. In view of the several million clamping cycles, which have to be carried out by many clamping vises being exposed to chips and coolant, process reliability is one of the decisive factors of success.
 Pour en savoir plus…
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11.2011
Modularity the factor of success
When designing gripping systems for handling and assembly applications, standardized modular systems will play an increasingly important role in the future. They reduce the necessary time for project planning and commissioning, and lower the investment costs. Due to the standardization, they offer optimum preconditions for stable processes. Since modular designed units can be flexibly modified and enlarged, they can be re-configurated for any changes that come up in the future.
Pour en savoir plus…
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10.2011
Producing more efficient
For a number of years, everybody was talking about the energy efficiency issue. Increasing energy costs, a growing environmental awareness, and the political guidance were all triggers for many companies to highlight the energy consumption of machines and components in their communication with the public. Efficiency is much more than simple energy efficiency now, especially when considering the
time- and cost aspects in regards to efficiency. When all these factors have been considered in a holistic way, the full potentials for modern machining and production become visible. The modern clamping devices and gripping systems make it clear how complex the possibilities are.
Pour en savoir plus…
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09.2011
Welding demanding materials crack- and pore-free
Laser welding technology is second-to-none, regardless of whether you are dealing with gears and injection molds or delicate and challenging welding works. When conventional cw lasers and many Nd:YAG-lasers reach their limits, modern process strategies can help to machine demanding welding metallurgies, different types of materials, or micro components process reliably and efficiently. Laser welding is particularly used if components have to be joined at a high welding speed, because slim welding seams, and a low thermal distortion are required. Compared with other welding techniques, the energy during laser welding fully penetrates into the material.
Pour en savoir plus…
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08.2011
More than a "Stopgap":
Intermediate sleeves ensure safe clamping and precision
They appear to be unimposing - but they are located at a decisive interface in the chain of the metal cutting process. Between toolholder and workpiece, the intermediate sleeves influence reliability and precision of the clamping operation. The thin-walled, mostly slotted precision sleeves cover the difference between the clamping diameter of the toolholder, and the workpiece which has to be clamped. Functioning like reduction inserts, they multiply the fields of application of the toolholders or arbors, compensate tolerances, and ensure safe and gentle clamping of gear wheels. The newest sleeve design can do even more. Intermediate sleeves with nozzle effect extend the tool service life and increase the volume machining.
Pour en savoir plus…
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07.2011
Changing, machining, compensating -
current trends in robot accessories
In dealing with industrial robot efficiency cycle rate and process reliabilty largely depend on their front ends, the grippers and other tools, but also from the effectors’ interfaces to the robot arm. Robot accessories have a great influence on the robot’s performance, flexibility and fields of application. Latest developments of quick-change systems, driven tools, compensation units, and power sensors show that the potentials of modern accessory components are enormous. Experts assume that their importance for handling, assembly and manufacturing will continuously increase.
Pour en savoir plus…
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06.2011
Deformation-free clamping:
From the plastic chuck jaw to the hybrid chuck
In case of rings, housings and other workpieces which are highly deformable dur-ing processing, conventional 3-jaw chucks quickly reach their limits. If the clamping forces are too low, there is no secure hold. If they are increased, workpieces de-form, and precision is reduced. A comparison shows the alternatives, the differ-ence between them, and how users can achieve an optimum result.
Pour en savoir plus…
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05.2011
Service robotics is the future key market
Insiders are convinced that golden times lie ahead for service robotics. Around the world companies and institutes have recognized the potential of robots as helpers for humans, and are working on everyday solutions. All different kinds of businesses are interested in service robotics, from large companies, to innovative startups, and also conventional manufacturers of industrial robots, electronic and automation components.
Pour en savoir plus…
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04.2011
Having set-up times under control
You cannot earn money with a turned off machine. However, in many companies the workpieces are still set-up in a complicated and time-consuming way on a grooved table while the plant is turned off. But solutions exist, which optimize the machine tool load. Modern quick-change pallet systems demonstrably accelerate the machining process, and at the same time, ramp up the precision and process reliability score. This leads to a reduction of set-up costs of up to 90%.
Pour en savoir plus…
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03.2011
Toolholders for micro cutting
Clamping tools used for micro cutting have their own rules. The subtle tools, the high spindle speeds, and the extreme precision requirements are a challenge for every tool manufacturer and user. Those who want to achieve continuously precise results, need mountings with a high run-out accuracy and balancing grade. Moreover, they should be as slim as possible and resistant to dirt. Furthermore, they have to assure that even small tools can be precisely adjusted and exchanged.
Pour en savoir plus…
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02.2011
Leight-weight design increases efficiency of Gripping Systems
Light-weight modules are now playing an increasing role in the area of gripping systems. Integrated into the system, they are saving energy at the same efficiency, or achieve a considerably higher efficiency at the indentical energy consumption. In both cases, the efficiency of the whole system is increasing. This is why the lightweights are so interesting for plant manufacturers, system integrators, and users. Since light-weight solutions had the reputation of being overly expensive in the past, recent developments now show that efficiency and cost control can go hand-in-hand. Modern designs, materials and techniques are paving the way to lighter solutions, which are rigid and robust, too. This also offer many more advantages.
Pour en savoir plus…
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In Focus - 2013
In Focus - Archives 2012
In Focus - Archives 2011
In Focus - Archives 2010
In Focus - Archives 2009
In Focus - Archives 2008
In Focus - Archives 2007
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