Form v Function - Why Not Both?


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How laser plastic welding is leaving a mark (and a good looking mark at that) on car tail light innovation.

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Form v Function - Why Not Both?

  1. 1. L a s e r Te c h n o l o g y SPECIAL The robot guides the laser beam and the halogen light along the contours of the workpiece (photos: LPKF) Robot-guided Halogenand Laser LightPlastics Hybrid Welding. Car headlights and other automotive lights in sheetmetal and glass are a thing of the past. Today, it is plastics that dictate automotivedesign. A ready-to-use hybrid welding system has now opened up new scope forthe size and design of the lights. The concept behind the system incorporates thefull welding technology in an industrial robot – including the quality assurance. Inthis way, the rapidity and flexibility of the six-axis robot can be exploited by thewelding cell in its entirety. RALF HÖGEL Laser contour welding overcomes the ABS or blends of ABS+PC to the trans- limits of traditional plastics welding parent PMMA lens. High-grade 3-D hat would modern cars be like processes and is particularly suitable for welds can be achieved while imposing justW without their sophisticated plas- tic lights? The productionprocesses available to date, however, have joining today’s standard light housings in low mechanical stresses on the parts – the secret lies in a precisely tuned energy in- put. But there’s an even better solutionimposed tight limits on designers in re- i Contact still: working together with the Bay-spect of size and shape. Low-stress join- erisches Laserzentrum, LPKF Laser &ing was only possible for parts up to a cer- LPKF Laser & Electronics AG Electronics AG, Erlangen, Germany, hastain size and with relatively flat geome- D-91056 Erlangen developed the robot-based laser hybridtries using the standard vibration and hot Germany welding process, which it has been tryingplate welding processes that were avail- TEL +49 9131 61657-10 out on a number of test systems sinceable. It was also necessary to hide irregu- > 2005. And this patented process has alsolar welding seams by means of black in- shown its capabilities in series productionjected-on edges on the transparent Stäubli Tec-Systems GmbH already. For some time now, the very largePMMA lens. Robotics tail lights on the Hyundai Equus have D-95411 Bayreuth been joined by means of laser welding. Germany The further development of this tech-Translated from Kunststoffe 1/2011, pp. 24–26 TEL +49 921 883-0 nology, employing an integral articulat-Article as PDF-File at www.kunststoffe- > ed arm robot (type: Stäubli TX60L),; Document Number: PE110638 presented at Fakuma 2009. In the current >Kunststoffe international 1/2011 11
  2. 2. SPECIAL L a s e r Te c h n o l o g y series solution for its light production, trols operations inside this air-condi- accuracy,” explains LPKF Product Man- LPKF uses an encapsulated six-axis robot tioned, hybrid welding cell with a rotary ager Manuel Sieben. “The TX90L fulfills (type: Stäubli TX90L) and a rotary table. indexing table. Its precisely guided hand this condition with a path repetition ac- This means that the fully automatic directs the laser beam and the halogen curacy of ±0.035 millimeters, and is also LPKF TwinWeld3D welding cell is light onto the workpiece. While the robot very compact with a reach of 1,200 mil- equipped to achieve shorter process times follows the contour of the workpiece, the limeters even in the “L model”, despite the and considerably lower tooling and ma- pneumatically-sprung tensioning roller specified payload capacity. The open VAL3 terial costs, in addition to ensuring a flaw- applies forces of up to 300 N to ensure a control system also satisfies our stipula- less appearance and additional freedom precise positive-locking fit between the tions for integration in the cell. This en- of design in plastics welding. two plastic parts being joined. The result ables us to supply our clients with an all- is a low-stress, precise and slim weld with round, highly user-friendly system.” Laser Welding in a Thermal no fraying at the edges, which is even wel- Field come as a decorative strip in the visible Sixth Axis for Pneumatically- section of the part. sprung Tensioning Roller By contrast to pure laser welding, in the “Realizing hybrid welding is only pos- hybrid process the heat energy is applied sible with the flexibility provided by a six- Only at first glance does the high speci- not only to the laser-absorbing lower axis robot with an extremely high path fied payload of almost 15 kg seem sur- component but also to the transparent upper component. To do this, the mono- chromatic laser beam, which cannot heat the transparent joining partner directly, is combined with long-wave polychro- matic halogen light. This means that the temperature selected for the welding process can be precisely aligned to the ma- terial-specific melting points of the two parts being joined. This combination of energy sources increases the speed of the process and ensures good-looking, low- stress welds. The more uniform heating and cooling of the two parts being joined makes it possible to get by without the an- nealing process that is needed to elimi- nate stresses in the other plastics welding processes The advantages set out above – and, in addition to these, the feasibility of joining very big plastics lights with bold freeform surfaces – have now prompted three au- tomotive suppliers to order turnkey Twin- The fully automatic TwinWeld3D welding cell shortens process times, making for a flawless look Weld3D systems. The Stäubli TX90L con- and increased freedom of design in plastics welding prising. A look at the robot in the weld- ing cell reveals all – in addition to the high pressing force applied by the tensioning roller, the robot also has to shoulder the entire welding system. It carries the laser energy source with its high-performance cooling setup so as to dispense with long In addition to the high fiber-optic cables and all their drawbacks. contact pressure to “This kind of machine concept would be applied, the robot have been impossible only two years ago, has to shoulder the because back then the cooling alone of a entire welding tech- comparable laser was still the size of a 19′′ nology rack,” says Manuel Sieben.“A customized wrist created by the Stäubli development engineers made it possible to mount a complex welding head with a circular halogen source onto the fifth axis instead of a co-rotating housing. This and the laser beam which shines through the cen- ter are imaged at infinity via a complex, gold-coated reflector. The two radiation12 © Carl Hanser Verlag, Munich Kunststoffe international 1/2011
  3. 3. L a s e r Te c h n o l o g y SPECIAL parameters. With the database obtained er they set new benchmarks, with only in the course of this process, it is possible around 30 seconds processing time to to get by without a subsequent tightness weld an average tail light, and complete- test in many cases. ly saving the around 30 minute annealing Manuel Sieben: “A large number of procedure. mathematical calculations are carried out The hybrid welding process and inno- during the welding process to control the vative system concept, which integrates power output of the laser and the halo- the complete state-of-the-art welding gen light dependent on the welding speed. technology package in the robot, opens A PLC with interfaces to the PC control up the way to an almost completely un- acts as the master that actuates all the restricted design of automobile tail lights. movements. This, in turn, communicates Since the lights can even be fitted with with the robot control. The results are sta- LEDs prior to welding, models of this ble processes with very high levels of user- type will doubtless influence the design friendliness via the system touch panel. of the whole vehicle more frequently in This gives a top view of the product en- future. abling operators to very quickly re-teach the robot path points – as can happen THE AUTHOR fairly frequently depending on the RALF HÖGEL, born in 1960, is the owner of Indus- amount of dimensional deviation of each trie Kommunikation Högel, Stadtbergen, Germany. batch of plastic components. The Stäubli manual controller can also be used if nec- essary.”A customized wrist created by the developmentengineers made it possible to mount a complex No Upper Die Kunststoffe -international.comwelding head with a circular halogen sourceonto the fifth axis instead of a co-rotating hous- Unlike other plastic welding methods, this Collections of articles about specificing system needs no upper die because the topics (construction, automotive, electri- whole welding head, including the ten- cal/electronics, packaging, medical,sources are then focused onto a single sioning roller, is integrated in the robot. temperature control) can be found atpoint by a shared lens. These are the new The only component-specific tool costs very sophisticated features of this sys- are associated with the lower die which is dossierstem,” explains Sieben. constructed by LPKF as part of the design The tensioning roller needed for the support activities. The speed and flexibil-laser welding technique is also located in ity of the six-axis robot is therefore passedthe hand of the Stäubli robot – on its sixth on to the welding cell as a whole. Togeth-axis – and generates the vertically actingclamping force on the components. Thisis made up of a toothed wheel with plan-et gears which drive a pneumatically-sprung gear rim with an arm for thecooled clamping roller. The roller is de-coupled from the rotary movements ofthe welding head. The integrated pneu-matic-springing guarantees the gentle,surface-protecting guidance of the roller– even where there are large componenttolerances.Integrated Quality AssuranceA process control system based on an as-sessment of the component’s reflectionproperties can be integrated directly inthe welding head. The system measuresthe height of the component on the onehand and assesses the quality of the weldproduced, on the other. The key featureof this system is that the measurement canbe made at the full process speed of 80 to150 mm/s. This measurement allows tol-erances in each of the components to be LPKF product manager Manuel Sieben: “Realizing hybrid welding is only possible with the flexibilitycompensated by influencing the control provided by a six-axis robot with an extremely high path accuracy.”Kunststoffe international 1/2011 13