Nya Svetsaren 1, 1999. - Luleå University of Technology

nipulation for the adjustment ofparts, elaborate positioning proceduresusing expensive, complicatedtools can be replaced bysimple tools and the final accuracywill be produced by laser adjustment[Table 1].It is clear that laser processingin the electronics industry has becomea mature technology and alarge number of parts can only bemanufactured using this technology[Fig. 5]. Using solid state laserswith high beam quality, it ispossible to create weld sizes inthe 100 µm range. By adaptingthe beam geometry and pulseshape for each individual weldingapplication, it is possible to minimizethe distortion as well as thecontamination of the welded part.Welding plasticsThe application of lasers hascreated new opportunities in thewelding of thermoplastic components,which until now has primarilybeen performed usingultrasonic or vibration welding.For this area of application,Nd:YAG and diode lasers, offeringradiation near a wavelengthof 1 µm, are suitable for use becauseof the absorption characteristicsof plastic materials. Theseabsorption characteristics in thematerials to be welded are veryimportant when using laser. Theabsorption and thereby the penetrationdepth of the radiation is afunction of the laser beam andmaterial composition. Plastic materialsabsorb the CO 2 radiationin the surface layer and cause thevaporisation of the material. TheNd:YAG and diode radiationpenetrates into the polymer sampleand produces a melting volumewhich is necessary for thewelding process. The absorptionproperties can be influenced bythe content of pigment in theplastic material. So black partscan be welded together, becausebeing black to the eye differsfrom being black or absorptivefor the laser.Virtually all thermoplastic materialscan be laser welded. Thejoining of two different materialsis possible if the material combinationis weldable, i.e. the temperatureranges in which the materialsare liquid must overlap.Fluorinated and temperatureresistantmaterials can be weldedwith lasers, as well as PMMA andABS, or plastic to metal. In acombination of increasing interestto the automotive industry,TPEs can easily be joined withthermoplastics using laser radiation[Fig. 6].A keyless entry product has ablack keypad overlap-weldedonto the black case [Fig. 7]. Thekeypad is coloured with a pigmenttransparent to laser radiation,while carbon is used as theabsorptive pigment for the case.Welding these keyless entry casesis the first example in which thelaser is being used in an industrialapplication. Laser welding waschosen because the keypad is thefinal part of the assembly and iswelded after all the electronic circuitsare mounted. Other weldingprocesses would have led to increasedscrap rates. Ten diode laserswith an output power of 30W each are used to perform thewelding process and the weldingspeed is in the range of 5 m/min.Using the laser also permits excellentquality control of the weldseam during production. Modernelectronics and sensor technologyprovide the means for on-linemonitoring and process control ofFigure 8: Principal layout of a diode laser bar for an HPDL.Figure 6: Diode laser welded specimensof TPE/thermoplastics.Figure 7: Laser welded polymer keycasing with integrated electronic components.48 Svetsaren No.1–2 1999