Research Article Modelling the Heating Process in ...downloads.hindawi.com/archive/2016/3824065.pdfResearch Article Modelling the Heating Process in Simultaneous Laser Transmission

Research ArticleModelling the Heating Process in Simultaneous LaserTransmission Welding of Semicrystalline Polymers

Christian Hopmann and Suveni Kreimeier

Institute of Plastics Processing (IKV) RWTH Aachen University 52074 Aachen Germany

Correspondence should be addressed to Suveni Kreimeier suvenikreimeierikvrwth-aachende

Received 31 July 2016 Revised 12 September 2016 Accepted 19 September 2016

Academic Editor Yeong-Soon Gal

Copyright copy 2016 C Hopmann and S Kreimeier This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

Laser transmission welding is an established joining process for thermoplastics A close-to-reality simulation of the heatingprocess would improve the understanding of the process facilitate and shorten the process installation and provide a significantcontribution to the computer aided component design For these reasons a thermal simulation model for simultaneous weldingwas developed which supports determining the size of the heat affected zone (HAZ) The determination of the intensity profileof the laser beam after the penetration of the laser transparent semicrystalline thermoplastic is decisive for the simulation Forthe determination of the intensity profile two measurement systems are presented and compared The calculated size of the HAZshows a high concordance to the dimensions of theHAZ foundusing lightmicroscopyHowever the calculated temperatures exceedthe indicated decomposition temperatures of the particular thermoplastics For the recording of the real temperatures during thewelding process a measuring system is presented and discussed

1 Introduction

Since the 1980s laser transmission welding of plastics partsplays an increasing role in industrial mass production dueto advancements in process and machine technology Forexample for welding of vibration sensitive componentswhere conventional techniques meet their procedural limitsthe benefits of laser transmission welding become apparent[1ndash3]

Extensive research on thermal modelling of laser trans-mission welding has been presented since the mid-1990sParallel to the first industrial applications of the laser trans-mission welding the analytical description of the heatingphase was analyzed [4ndash8] To be able to make these calcu-lations several simplifications had to be accepted regardingthe optical properties of the welding partners the scatter-ing of the laser light or the temperature dependence ofthe material properties The first comprehensive thermalmodelling of the laser transmission welding process usinganalytical methods was performed by Russek [9] Compar-ing the experimental and simulated results of contour and

simultaneous welding tests a good accordance could beshown However a statement regarding to what extent thecalculated temperatures match the real temperatures is stillmissing

First approaches to leverage a finite element analysis(FEA) as a numerical simulation of the heating phase duringlaser transmissionwelding can be found in [5 10ndash19] Grewelland Benatar for example presented the implementation of acoupled squeeze flow and intermolecular diffusion modelwhich was used to predict the quality and size of micro weldsin thermoplastics The simulation results had a good accor-dance with the experimental values although there was somedeviation between the experimental data and the simulationmodel for different parameters Grewell and Benatar statedthat this was due to the temperature-dependent materialproperties as well as optical aberrations [16] Mayboudi et alpresent a three-dimensional unsteady thermal model of thelaser transmission welding process solved using FEA Theirthermal model includes the heating and cooling stages in alaser welding process with a shifting laser beam consideringthe heat conduction along the beam travel direction [17]

Hindawi Publishing CorporationJournal of PolymersVolume 2016 Article ID 3824065 10 pageshttpdxdoiorg10115520163824065

2 Journal of Polymers

Reflectedlaser radiation

Transmittedlaser radiationTransmitting

component

Absorbingcomponent

Heat affected zone Heat transfer Q

Q

Q

Figure 1 Principle of radiation fluxes during laser transmission welding

In [20] the thermal simulation model for the calculationof the temperature distribution in the weld seam duringthe laser transmission welding process of thermoplastics ispresentedOne focus of this paper is the topic of ldquodeterminingthe energy input in the welding zone during weldingrdquoThereforemeasurements with a spectrometer were comparedto measurements with an integrating sphere For the mea-surements with the integrating sphere a new measurementsetup is presented Furthermore the topic ldquooptical interfacesrdquois considered for portraying the simplifications which havebeen made in the simulation Finally a first attempt for athermomechanical simulation has been presented Based onthe calculated temperature distribution thermally inducedresidual stresses have been calculated

Today still most of the model simplifications are maderegarding the input parameters in the simulation As a resultbased on the thermal model in [20] here temperature-dependentmaterial properties and the influence of the degreeof crystallinity on the optical properties are considered in theheating simulation In addition significant effort was spentto determine these material properties experimentally Inorder to determine the shape of the intensity distribution ofthe laser beam after passing the laser transparent part twomeasurement systems are introducedMoreover ameasuringsystem to determine the maximum temperature in the weldline is presented

2 Principle of the Laser Transmission Welding

In laser transmission welding the heating of two plastics partsand the joining operation of the two partners occur in a singlestep [21ndash23] For this reason the welding technique of lasertransmission welding requires joining partners with differentoptical properties One joining partner is required to have ahigh transmittance for the laser radiation whereas the otherone needs to have a high absorbance at the wavelength of thelaser In Figure 1 the process is shown schematically

The laser radiation irradiates the laser transparent joiningpartner and is absorbed and converted into thermal energynear the surface of the laser-absorbing partner This resultsin heating up the material above the melting temperatureThe heat transfer in the joining zone ensures an indirectplasticizing of the laser transparent partner [24]

3 Influences on the Laser TransmissionWelding Process

There is a series of factors (eg the laser wave lengths) whichhave a major influence on the laser transmission weldingprocess The material properties have the major effect on theprocess based on the optical properties like the innerstructure (amorphous or semicrystalline) and the amountof additives and pigments In order to achieve a high andreproducible weld seam quality also the geometric boundaryconditions like the design of the joint area the thickness ofthe laser transparent joining partner or the componentsrsquotolerances have to be considered [25 26] In addition thewelding parameters are of particular importance for thequality of the joint In this regard the following parametershave to be mentioned especially [9 27]

(i) Laser power

(ii) Energy density or energy input per unit length

(iii) Joining pressure

(iv) Power densitylaser intensity distribution

(v) Process variant

The optical properties are of decisive importance for the laserwelding process as the radiationrsquos intensity is reduced due tointeractionswith thematerial when the radiation penetrates amedium [28ndash31]

Journal of Polymers 3

Laser beam

Laser absorbingcomponent

Laser transparentcomponent

4mm

2mm

2mm

115mm

30mm

Figure 2 Specimen

4 Researched Materials and AppliedExperimental Setup

Since the influences of scattering semicrystalline thermo-plastics on the laser transmission welding process are notnegligible experiments are performed with the followingsemicrystalline polymers polyamide 66 (PA 66 UltramidA3W BASF SE LudwigshafenGermany) polypropylene (PPHD120MO Borealis AG ViennaAustria) and polybuty-lene terephthalate (PBT Ultradur B4520 BASF SE Lud-wigshafenGermany)

The specimens are injectionmolded step blocks (Figure 2)with four different thicknesses (1 2 3 and 4mm) The stepwhich is irradiated is 2mm thick

During the experiments the process variant simultaneouswelding is performedwhere a rectangular focused laser beam(15 times 27mm2) irradiates the material In the course of theexperiments the laser power119875119871 and the irradiation time 119905119871 arevaried as welding parameters

Six parts are welded for each parameter combinationThetwo laser systems LDF 400-90 (119875119871max = 90W) and LDM400-40 (119875119871max = 400W) are high-power diode lasers supplied byLaserline GmbH Mulheim-Karlich Germany Both devicesemit laser radiation at a wavelength of 120582 = 940 nm

The joining tests are evaluated using a tensile-shear-testaccording to DIN ISO 527 [13] and microscopy images Themicroscopy images should illustrate the welding zonebetween the joining partners and the dimensions of theHAZ

5 Determining the Shape of the EnergyDensity Distribution after Passing the LaserTransparent Part

For the modelling of the laser transmission welding processthe intensity profile of the laser spot when hitting theabsorbable layer is crucial The exact determination of theshape of the transmitted intensity distribution is of highimportance Different approaches to determine the intensityprofile can be found in [32ndash37] Becker and Potente describemeasurements of the power flux distribution at the weld

interface after passing through a 5mm thick sample of unre-inforced polypropylene A near Gaussian radial power fluxis obtained and the incoming beam diameter is significantlyspread [34] Zak et al present a technique for measuring thescattering of the laser beam caused by the laser transparentpart An easy way to determine the intensity profile forcontour welding is presented [37] The exact determinationof the intensity profile is decisive for the quality of the simu-lation results For these reasons two systems (FocusMonitorSpiricon Camera) for the determination of the intensityprofile of line focus optics are presented and compared in thispaper

The FocusMonitor (Primes GmbH Pfungstadt Ger-many) measures the intensity profile with a rotating measur-ing tip which scans the laser spot line-by-line At the measur-ing tip is a small point like opening where the radiation isforwarded to the detector inside the device using a mirrorsystem (Figure 3) During the measurement the prevalentintensity in dependence of the angle and line is recordedUsing these data the device calculates an overall picture ofthe laser spot whereas the pixels can have relative intensityvalues from 0 to 4096 During this ldquostaticrdquo measurementthe measuring range of the FocusMonitor has a size of 24 times12mm2 with a resolution of 256 times 256 pixels There is thepossibility of a ldquodynamicrdquo measurement for increasing themeasuring range In this setup the measuring tip rotates inone line while the lasermoves over itThe resulting recordingcan be converted into a 2D-picture using the rotational speedof the measuring tip and the traverse speed of the laser

In both measuring procedures the sample is positionedon top of the case of the FocusMonitor while equivalent tothe welding process the laser is focused on the bottomof the sample In this process the distance 119867 = 4mmshown in Figure 3(b) exists between the measuring layer andthe sample Depending on the scattering behavior of thesample an expansion of the transversal intensity profileoccurs which results in a distortion of the measurementThe necessity of dynamic measuring of the linear spot isanother disadvantage caused by the small range of the deviceThe dynamic measurement results in additional work and


y

z

(a)

Case

Laser beam

MirrorRotating measuring tip

with point like opening

Detector

Sample

H

[NN13]

(b)

Figure 3 Design of the FocusMonitor for the measurement of the intensity profile of the laser spot [42]

adds further uncertainties regarding the rotational speedof the measuring top and the transversal speed of thelaser

The Spiricon SP620U (Ophir Optronics Solutions LtdJerusalem Israel) is a USB camera based on a CCD-sensorThe CCD-sensor is equipped with 1600 times 1200 pixels onan active area of 71 times 54mm2 and reacts to light between190 nm and 1100 nm In combination with the CCTV-lens-kit the SP620U functions like a conventional camera andallows the filming of a picture layer Intensity values from0 to 4096 are assigned to each pixel which correlate linearwith the real intensity values The objective is equipped witha dimming function and a manual focus facility which serveas a fine adjustment The schematic setup is established withneutral density filters and spacers between the objective andthe sensor Thus the choice of the combination of neutraldensity filters and spacers determines themagnification ratiothe object distance and the exposure of the sensor [38]

With the described configuration the intensity profilecannot be captured directly but merely the radiation emittedover a diffuse spreading area Ideally this area complies withthe bottom of the laser transparent sample while the laser isfocused on this layer equivalent to the welding process How-ever the diffuse spreading behavior of the semicrystallinesamples does not satisfy the requirements of the cameraFor this purpose an opal glass is set up beneath the samplewhich is equippedwith a diffuse spreading areaThe resultingmeasuring setup is schematically shown in Figure 4 Thecamera ismounted vertically beneath the sample and focusedon the coated area of the opal glass The focusing takes placeusing a halogen spotlight which illuminates a paper which ispositioned on the opal glass for this purpose A writing oranother sharp structure on the paper serves as a referencewhen setting up the objective The camera is connected via

USB to a Windows computer which controls the camerawith the software BeamMic The recordings of the cameraare subjected to the so-called natural edge lighting effectThiseffect results in a reduction of the measured intensity on theedge of the recording and requires a mathematical correctionof the results

The comparison of both measurement methods wouldlead to the conclusion that the measuring setup using theSP620U is much more suitable for the determination of theintensity profile needed for the simulation The larger mea-suring area and the identical measuring layer in the weldingprocess can be stated out as decisive advantages To keep theworkload low the comparison is reduced to the parameterswidth 119882 and the boundary range 119861 of the intensity profile(Figure 5)

For the comparison the cross sections of the intensityprofile of ten experiments are replicated centered over thespot The results are contrasted in Figure 6 showing themedian and the range It appears from the diagram thatthe results of the FocusMonitor are generally and specif-ically with highly spreading samples such as PA66 andPBT afflicted with a higher measurement uncertainty Theseresults strengthen the choice of the SP620U for themodellingof the welding process Furthermore the records partiallyindicate significant material dependent differences which donot follow a consistent trend Using the FocusMonitor theexpected beam expansion resulting from the distance of themeasuring layers can only be confirmed for PA66 but notfor PP When measuring PA66 the widths of the linear spotdiffer by approx 40which is why a significant higher powerdensity in the welding area in the optimized model can beexpected In particular the influence of the used opal glasshas to be mentioned which has not been examined yet andshould be analyzed in further studies


Laser spot

AA

Focusing lens

Tripod

SP620U

Filter amp spacer

Objective

Sample

Halogen spotlight

Opal glass

Sample

Diffuse layer

Figure 4 Measuring setup of the Spiricon for the determination of the intensity profile of the laser spot

B = 15

B = 500

1

e2middot IN max

IN max

W

minus3 minus2 minus1minus4 1 2 3 40Coordinate x (mm)

minus02

0

02

04

06

08

1

12

Nor

mal

ized

inte

nsity

I N(1

mm

2)

Figure 5 Width 119882 of the intensity profile and influence of theboundary range 119861 on the intensity profile

PP PA66 PBT

FocusMonitorSP620U

W W W BB B00102030405060708090

Wid

th W

(mm

)

00

05

10

15

20

25

Boun

dary

rang

eB(mdash

)

Figure 6 Comparison of the measuring results of FocusMonitorand Spiricon

6 Modelling the Heat Transfer Process duringLaser Transmission Welding

After several steps of experimental quantification of scatter-ing on the laser beam caustic and intensity distribution afinite element model was implemented for the purpose ofthermal process simulation [20 23 30 31] The thermalcalculations are carried out using the FE simulation programAbaqus by Dassault Systemes Simulia Corp Rhode IslandUSA The elaborated two-part simulation model consists ofone upper and one lower joining partner During simul-taneous welding there is no relative movement betweenthe processing optics and the joining member This meansthat it is not necessary to implement any movement ofthe laser beam in the calculation model either Within theimplemented model the temporal and spatial fluctuatingtemperature fields are calculated on the basis of the generaldifferential equation of thermal conduction according toFourier

120588 (119879) sdot 119888119901 (119879) sdot (120597119879120597119905 sdot (nablaV) 119879) = Δ (120582 sdot 119879) + 101584010158401015840 (1)

Within (1) 119879 is the temperature which has to be calculateddepending on the time 119905 and the spatial coordinates 119909 119910 and119911 while 120588 119888119901 and 120582 are material properties The materialproperties of the transparent material are assigned to theupper joining partner and those of the absorbing material tothe lower joining partner The properties to be allocated arematerial-specific and temperature-dependent and must bedetermined for the utilized materials The following materialproperties are required density 120588 specific heat capacity 119888119901and thermal conductivity 120582 Apart from this the absorptioncoefficient 120572 of the laser transparent and laser-absorbingpartner and also the heat transfer coefficient ℎ must bedetermined


PA66

PP

PBT

500120583m

500120583m

200120583m

P = 100W

P = 50 W

P = 200W

tB = 015 s

tB = 05 s

tB = 05 s

300320340360380400

300320340360380400

TLiq

TLiq

TLiq

300320340360380400

T (∘

C)T

(∘C)

T (∘

C)

Figure 7 Validation of the simulation model based on the optical appearance of the HAZ

Neglecting heat transfer in 119911-direction (depth) because ofa rectangular focused beam the direction of the incident laserbeam (1) can be simplified as follows

120588 (119879) sdot 119888119901 (119879) sdot 120597119879120597119905 = nabla (120582 sdot nabla119879) + 101584010158401015840 (2)

The volume heat source 101584010158401015840 representing the laser beamand some of the regarded aspects of the laser beam matterinteraction within (2) can be described as shown by (3) whileit is assumed on basis of determined values

101584010158401015840 = 119860 (119910) sdot 120591119866 sdot (1 minus 120588abs) sdot 119890minus120576119905 sdot119889 sdot 119875 sdot amp sdot 119890minus2|119909119903|119861 (3)

with 119860(119910) = 120572 sdot 119890minus120572sdot(119910minus119889)Within (3) 101584010158401015840(119909 119910) is the intensity distribution of

the laser beam in Cartesian coordinates which is fittedto the above discussed experimental data 119860(119910) is a func-tion which depends on the absorption coefficient 120572 of thetreated material The absorption coefficient 120572 depends onthe coordinate 119910 (thickness) the material thickness 119889 andthe materialrsquos local as well as temporal changing temperature119879 The transmittance of the laser transparent component isconsidered with 120591119866 and 120588abs includes the surface reflection ofthe material 120576119905 is the extinction coefficient which describesthe attenuating radiation behavior of the material The laserpower is considered with 119875 and the amplitude of the intensitydistribution with amp Furthermore 119861 is the boundary rangeand 119903 is the radius of the boundary range According to theseequations the volume heat source 101584010158401015840 is implemented usingFORTRAN code

After its implementation themodel is used to calculate theweld seam width 119882 its height 119867 depending on the processparameters radiation time 119905119861 and laser power 119875

The calculations for simultaneous welding were carriedout with a two-dimensional model in order to reduce thecalculation duration without losing relevant informationabout the dimension of the HAZ In order to validate thecalculations the heat affected zone heights119867 andwidths119882ofwelded test specimens are determined using thin sections andwere correlated with calculated isotherms of themelting tem-perature at the end of the radiation exposure duration sincethe isotherms correspond to the completely molten regionOne effect which arises with semicrystalline materials is theinhomogeneity or random arrangement of the crystalsThusthe formation of the HAZ is afflicted with a deviation withregard to the dimensions because of the different trans-mittance factors from component to component Since thedimensions of the heat affected zone serve to validate thesimulation results it is necessary to determine the standarddeviation of these values for statistical substantiationThus itis necessary to consider a tolerance window for assessing thereal welds in comparison to the simulation

In Figure 7 only the completely molten region is por-trayed in color All the regions which are below the meltingtemperature (119879119878 = 265∘C) are portrayed in grey The dashedline represents the joining plane The temperature distribu-tions portray the condition at the end of the radiation expo-sure duration Long radiation exposure durations and highpowers lead to large energy input into the material As arule the heat affected zone therefore becomes larger with anincreasing radiation exposure duration or power that ismorematerial is melted completely The qualitative comparison of


010 010 010 015 015 015 025 025 050 075 10080 100 120 60 80 100 40 60 30 20 20P

Measured

005010015020025030035040

tB (s)

Hei

ght-w

idth

ratio

HW

(mdash)

Calculation

Figure 8 Comparison of calculated HAZ with measured welddimensions in the simultaneous welding process for PP

the experimentally measured and the calculated HAZ provesthe validity of the elaborated model for laser beam trans-mission welding Figure 7 portrays this optical comparisonfor the HAZ for various materials and different laser weldingparameters

The comparison shows that the results of the simulationregarding the optical appearance of the HAZ for PP PA66and PBTmdashparticularly with regard to the elliptical shapemdashare close to reality

For a detailed analysis a quantitative comparison of theHAZ regarding the sizes of the HAZ is performed Thecomparison of the height-width ratio of the HAZ is shownin Figure 8 In general there is a good match between thecalculated and the measured dimensions The match for PPis significantly better than for PA66 [20] This indicates thatthere is a potential for improvement when modelling highlyscattering materials such as PA66

7 Measuring the Maximum Temperature inthe Heat Affected Zone

For the validation of the calculated results the real HAZ aremeasured and their sizes and shapes are compared Howeverin the simulation temperatures higher than the decomposi-tion temperature are calculated during the welding processThe capture of the absolute temperature distribution duringthe laser transmission welding process is of major interest

In laser transmission welding process the heating of thepolymer takes place in the range of milliseconds The max-imum temperatures are not maintained for long since theHAZ is very small and the heat is taken away rapidly Inprevious studies [39] thermal cameras or infrared radiationmeasuring instruments were used for the determination ofthe temperature distribution in the weld seam although inmany cases only the surface temperature of the transparentcomponent is used to draw conclusions about the realtemperature distribution inside the weld seam

The experimental setup (Figure 9) shows the used mea-surement technology for the determination of the maximumtemperature in the weld seam During the experiment the

objective of the thermal camera is positioned in a distance of10 cm from the surface of the sample The emissivity of thePA66 sample is approximated as 120576 = 095 Since themeasurement is performed without the laser transparentcomponent the adjusted laser power is reduced by thereduction of the transmission For this purpose the nominallaser output of the welding system is set to the power whichhas been calculated in the simulation after the penetrationof transparent component based on the optical properties ofthe material Possible beam expansions which lead to dis-tortion of the laser beam when penetrating the transparentcomponent are neglected in this experimental setup Thethermal camera type A655 of Flir Systems WilsonvilleOregon USA has a recording rate of 50Hz and the thermalresolution exceeds 30mK To provide a statistical reliabilityof the results each measurement is replicated three times

The average standard deviation between the calculatedand measured temperatures is 2643 In average temper-atures higher than 485∘C are measured in the weld seamAccording to the safety data sheet the thermal decompositionof the polymer starts at 320∘C [40] Inmicroscopy one cannotdetermine thermal decomposition in the weld seam for mostof the samples although the decomposition temperature isexceeded The phenomenon that polymers can shortly beheated above the decomposition temperature has alreadybeen discussed in earlier studies Russek explains the hightemperatures in the weld seamwith the Arrhenius law whichdeals with the temperature dependence of the speed of a reac-tion [9] Although polymers start to decompose with hightemperatures this effect does not directly occur when exceed-ing the decomposition temperature Only after a determinedretention time above the decomposition temperature didirreversible decompositions occur Thus the retention timeof a polymer temperature decreases exponentially with thetemperature above the decomposition while the degradationrate increases equally [41]The absence of oxygen in the weld-ing zone due to the welding pressure additionally supports alonger retention time

As shown in Table 1 the measured temperatures inmost cases are higher than the simulated temperatures Themeasurement of higher temperatures on the surface of theabsorbing component in comparison to the simulation canbe explained by the fact that the transparent component isabsent The power that impacts the absorbing componentis adjusted by the transmission and reflection factor of thetransparent part However the beam expansion of the laserfocus due to the penetration of the upper component isnot considered in the measurement Additionally there is arisk that the frame rate of 50Hz is not able to capture themaximum temperature Measurements with short weldingtimes at high power show a low reproducibilityThe accuracyof this measuring method increases with the welding timeThe development of the temperature along the length of theHAZ of the three measurements (at 119905119861 = 01 s) is shown inFigure 8

Overall the approach of measuring the temperature usinga thermal camera on the absorbing component is a suitablemethod for obtaining at least an indication of the resultingtemperatures in the HAZ To achieve even better results and


Table 1 Comparison of the measured temperatures in the ldquoheat affected zonerdquo and the maximum temperature in the simulation

Time 119905119871 [s]power 119875119871 [W] Measured temperature [∘C] Standard deviation [] Simulated temperature [∘C]01160 41953 4708 3208602570 41742 1057 2863402590 47189 2632 36200025120 50342 2154 476000550 48571 2696 303390570 52275 813 418050590 50009 144 5329807550 49880 598 3677607570 49855 334 5109510050 53788 411 41945

Thermal camera

Focusing lens

Absorbingcomponent

ldquoHeat affected zonerdquo

(a)

T(∘

C)

510

499 25

600

400

200

0

22

50 100 1500

(∘C)

(∘C)

Pixel (mdash)

(b)

Figure 9 Measuring setup for the determination of the temperature (a) and the comparison of the calculated and measured values (b)

to increase the reproducibility with short welding times andhigh laser intensities the performedmeasurements should berepeated with a high speed thermal camera

8 Conclusions and Perspective

A successful implementation of the spatial temperature dis-tribution between the welding partners has been performed

and added to the simulationmodelWith the reliable thermalsimulation model for the visualization of the heating of thejoining areas one is able to predict the required laser powerand the achievable process times for the process variantsimultaneouswelding For the transfer to additionalmaterialsit is necessary to determine the material properties as well asthe distribution of the laser output density In further studiesthe developed model has to be specified whereby a high


priority should be assigned to the determination of theprovided energy density

Competing Interests

The authors certify that they have no affiliations with orinvolvement in any organization or entity with any financialinterest (such as honoraria educational grants participationin speakersrsquo bureaus membership employment consultan-cies stock ownership or other equity interest and experttestimony or patent-licensing arrangements) or nonfinancialinterest (such as personal or professional relationships affilia-tions knowledge or beliefs) in the subjectmatter ormaterialsdiscussed in this manuscript

Acknowledgments

The research Project 17509N of the ForschungsvereinigungKunststoffverarbeitung was sponsored as part of the ldquoIndus-trielle Gemeinschaftsforschung und Entwicklung (IGF)rdquo bythe German Bundesministerium fur Wirtschaft und Energie(BMWi) due to an enactment of the German Bundestagthrough the AiF The authors would like to extend theirthanks to all organizations mentioned The authors are verygrateful to BASF SE Ludwigshafen Germany and BorealisAG Vienna Austria who supported the research with testmaterials and technical support Furthermore they wouldlike to thank Firma Primes GmbH Pfungstadt Germanyand Ophir Optronics Solutions Ltd Jerusalem Israel fortechnical support for the measurement systems

References

[1] J Klein and A Kraus ldquoIst das Laserstrahlschweiszligenwirtschaftlichrdquo Kunststoffe vol 94 no 7 pp 49ndash51 2004

[2] K Lenfert S Hierl and F Brunnecker ldquoSchritt fur Schritt oderalles zugleichrdquo Plastverarbeiter vol 53 no 5 pp 34ndash35 2002

[3] B Geiszligelmann S Hierl and K Lenfert ldquoPerfekt verschlossenrdquoPlastverarbeiter vol 55 no 11 pp 74ndash75 2004

[4] J Korte Laserschweiszligen vonThermoplasten [Dissertation] Uni-versitat-GH Paderborn 1998

[5] H Klein Laserschweiszligen von Kunststoffen in der Mikrotechnik[Dissertation] RWTH Aachen 2001

[6] Y C Kennish H R Shercliff and G C McGrath ldquoHeat flowmodel for laser welding of polymersrdquo in Proceedings of the 60thAnnual Technical Conference of the Society of Plastics Engineers(ANTEC rsquo02) pp 1132ndash1136 San Francisco Calif USA 2002

[7] J Schulz Werkstoff- Prozess- und Bauteiluntersuchungen zumLaserdurchstrahlschweiszligen von Kunststoffen [Dissertation]RWTH Aachen University Aachen Germany 2002

[8] Y C Kennish Development and modelling of a new laserwelding process for polymers [thesis] University of CambridgeCambridge UK 2003

[9] U A Russek Prozesstechnische Aspekte desLaserdurchstrahlschweiszligens von Thermoplasten [Dissertation]RWTH Aachen University Aachen Germany 2006

[10] F Becker Einsatz des Laserdurchstrahlschweiszligens zum Fugenvon Thermoplasten [thesis] Universitat-GH Paderborn Pader-born Germany 2003

[11] G Fiegler Ein Beitrag zum Prozessverstandnis desLaserdurchstrahlschweiszligens von Kunststoffen anhand derVerfahrensvarianten Quasi-Simultan- und Simultanschweiszligen[Dissertation] Universitat Paderborn Paderborn Germany2007

[12] T Frick Untersuchung der prozessbestimmenden Strahl-Stoff-Wechselwirkungen beim Laserstrahlschweiszligen von Kunststoffen[thesis] Friedrich-Alexander-Universitat Erlangen-NurnbergErlangen Germany 2007

[13] M Fargas L Wilke O Meier and H Potente ldquoAnalysis of weldseam quality for laser transmission welding of thermoplasticsbased on fluid dynamical processesrdquo in Proceedings of the 65thAnnual Technical Conference of the Society of Plastics Engineers(ANTEC rsquo07) Cincinatti Ohio USA May 2007

[14] L S Mayboudi A M Birk G Zak and P J Bates ldquoLasertransmission welding of a lap-joint thermal imaging observa-tions and three-dimensional finite element modelingrdquo Journalof Heat Transfer vol 129 no 9 pp 1177ndash1186 2007

[15] M Ilie J-C Kneip S Matteı A Nichici C Roze and TGirasole ldquoThrough-transmission laser welding of polymersmdashtemperature fieldmodeling and infrared investigationrdquo InfraredPhysics amp Technology vol 51 no 1 pp 73ndash79 2007

[16] D Grewell and A Benatar ldquoSemiempirical squeeze flow andLntermolecular diffusion model II Model verification usinglaser microweldingrdquo Polymer Engineering amp Science vol 48 no8 pp 1542ndash1549 2008

[17] L S Mayboudi A M Birk G Zak and P J Bates ldquoInfraredobservations and finite element modeling of a laser transmis-sion welding processrdquo Journal of Laser Applications vol 21 no3 pp 111ndash118 2009

[18] T Zoubeir andG Elhem ldquoNumerical study of laser diode trans-mission welding of a polypropylene mini-tank temperaturefield and residual stresses distributionrdquo Polymer Testing vol 30no 1 pp 23ndash34 2011

[19] B Acherjee A S Kuar S Mitra and D Misra ldquoModelingof laser transmission contour welding process using FEA andDoErdquo Optics amp Laser Technology vol 44 no 5 pp 1281ndash12892012

[20] S Sooriyapiragasam and C Hopmann ldquoModeling of the heat-ing process during the laser transmission welding of thermo-plastics and calculation of the resulting stress distributionrdquoWelding in the World vol 60 no 4 pp 777ndash791 2016

[21] G W Ehrenstein Handbuch Kunststoff-VerbindungstechnikCarl Hanser Munchen Germany 2004

[22] H Potente Fugen von Kunststoffen-Grundlagen VerfahrenAnwendungen Carl Hanser Munchen Germany 2004

[23] J Hopmann and S Sooriyapiragasam ldquoProzessmodellierungdes Erwarmvorgangs beim Laserdurchstrahlschweiszligen vonKunststoffenrdquo Joining Plastics vol 8 no 3-4 pp 170ndash177 2014

[24] H Jundt ldquoSchweiszligen in allen Formenrdquo Plastverarbeiter vol 57no 4 pp 88ndash89 2006

[25] M Aden A Rosner and A Olowinsky ldquoOptical character-ization of polycarbonate influence of additives on opticalpropertiesrdquo Journal of Polymer SciencemdashPart B Polymer Physicsvol 48 no 4 pp 451ndash455 2010

[26] X F Xu P J Bates and G Zak ldquoEffect of glass fiber andcrystallinity on light transmission during laser transmissionwelding of thermoplasticsrdquo Optics amp Laser Technology vol 69pp 133ndash139 2015

[27] R Lutzeler Laserdurchstrahlschweiszligen von teilkristallinenTher-moplasten [Dissertation] RWTH Aachen University AachenGermany 2005


[28] M Devrient X Da T Frick and M Schmidt ldquoExperimentaland simulative investigation of laser transmission weldingunder consideration of scatteringrdquo Physics Procedia vol 39 pp117ndash127 2012

[29] M Hohmann M Devrient F Klampfl S Roth and MSchmidt ldquoSimulation of light propagation within glass fiberfilled thermoplastics for laser transmission weldingrdquo PhysicsProcedia vol 56 pp 1198ndash1207 2014

[30] C Hopmann and S Sooriyapiragasam ldquoSimulation of the heatprocess in laser transmission weldingrdquo in Proceedings of theInternational Institute of Welding (IIW rsquo13) Essen Germany2013

[31] S Sooriyapiragasam and C Hopmann ldquoModelling of theheating process during the laser transmission welding of ther-moplastics and calculation of the resulting stress distributionrdquoin Proceedings of the International Institute of Welding (IIW rsquo15)Helsinki Finland 2015

[32] W Plass R Maestle K Wittig A Voss and A Giesen ldquoHigh-resolution knife-edge laser beam profilingrdquoOptics Communica-tions vol 134 no 1ndash6 pp 21ndash24 1997

[33] J F Ready K Nagarathnam and JMazumder LIAHandbook ofLaser Materials Processing Laser Institute of America OrlandoFla USA 2001

[34] F Becker and H Potente ldquoA step towards understanding theheating phase of laser transmission welding in polymersrdquoPolymer Engineering and Science vol 42 no 2 pp 365ndash3742002

[35] E Haberstroh J Schulz and R Lutzeler ldquoThermographic char-acterisation of polymers for the laser transmission weldingrdquo inProceedings of the 59th Annual Technical Conference (ANTECrsquo01) San Francisco Calif USA 2001

[36] H Haferkamp A von Busse M Hustedt J Bunte E Haber-stroh and R Lutzeler ldquoUtilisation of a thermographic processin order to determine the laser weldability of plastics at differentwavelengthsrdquoWelding and Cutting vol 1 no 3 pp 43ndash49 2004

[37] G Zak L Mayboudi M Chen P J Bates and M BirkldquoWeld line transverse energy density distribution measurementin laser transmission welding of thermoplasticsrdquo Journal ofMaterials Processing Technology vol 210 no 1 pp 24ndash31 2010

[38] Datenblatt der Spiricon Sp620U Technische Beschreibung OphirOptronics Solutions Ophir Optronics Solutions JerusalemIsrael 2015

[39] L S Mayboudi Heat transfer modelling and thermail imagingexperiments in laser transmission welding of thermoplastics[Dissertation] Queenrsquos University Kingston Canada 2008

[40] Sicherheitsdatenblatt BASF SE Ludwigshafen Germany 2015[41] G Menges E Haberstro W Michaeli and E Schmachtenberg

Werkstoffkunde Kunststoffe Carl Hanser Munchen Germany2002

[42] Original Betriebsanleitung Focus-MonitorBeamMonitor Tech-nische Beschreibung Primes Pfungstadt Germany 2013

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


Reflectedlaser radiation

Transmittedlaser radiationTransmitting

component

Absorbingcomponent

Heat affected zone Heat transfer Q

Q

Q

Figure 1 Principle of radiation fluxes during laser transmission welding

In [20] the thermal simulation model for the calculationof the temperature distribution in the weld seam duringthe laser transmission welding process of thermoplastics ispresentedOne focus of this paper is the topic of ldquodeterminingthe energy input in the welding zone during weldingrdquoThereforemeasurements with a spectrometer were comparedto measurements with an integrating sphere For the mea-surements with the integrating sphere a new measurementsetup is presented Furthermore the topic ldquooptical interfacesrdquois considered for portraying the simplifications which havebeen made in the simulation Finally a first attempt for athermomechanical simulation has been presented Based onthe calculated temperature distribution thermally inducedresidual stresses have been calculated

Today still most of the model simplifications are maderegarding the input parameters in the simulation As a resultbased on the thermal model in [20] here temperature-dependentmaterial properties and the influence of the degreeof crystallinity on the optical properties are considered in theheating simulation In addition significant effort was spentto determine these material properties experimentally Inorder to determine the shape of the intensity distribution ofthe laser beam after passing the laser transparent part twomeasurement systems are introducedMoreover ameasuringsystem to determine the maximum temperature in the weldline is presented

2 Principle of the Laser Transmission Welding

In laser transmission welding the heating of two plastics partsand the joining operation of the two partners occur in a singlestep [21ndash23] For this reason the welding technique of lasertransmission welding requires joining partners with differentoptical properties One joining partner is required to have ahigh transmittance for the laser radiation whereas the otherone needs to have a high absorbance at the wavelength of thelaser In Figure 1 the process is shown schematically

The laser radiation irradiates the laser transparent joiningpartner and is absorbed and converted into thermal energynear the surface of the laser-absorbing partner This resultsin heating up the material above the melting temperatureThe heat transfer in the joining zone ensures an indirectplasticizing of the laser transparent partner [24]

3 Influences on the Laser TransmissionWelding Process

There is a series of factors (eg the laser wave lengths) whichhave a major influence on the laser transmission weldingprocess The material properties have the major effect on theprocess based on the optical properties like the innerstructure (amorphous or semicrystalline) and the amountof additives and pigments In order to achieve a high andreproducible weld seam quality also the geometric boundaryconditions like the design of the joint area the thickness ofthe laser transparent joining partner or the componentsrsquotolerances have to be considered [25 26] In addition thewelding parameters are of particular importance for thequality of the joint In this regard the following parametershave to be mentioned especially [9 27]

(i) Laser power

(ii) Energy density or energy input per unit length

(iii) Joining pressure

(iv) Power densitylaser intensity distribution

(v) Process variant

The optical properties are of decisive importance for the laserwelding process as the radiationrsquos intensity is reduced due tointeractionswith thematerial when the radiation penetrates amedium [28ndash31]


Laser beam



4mm

2mm

2mm

115mm

30mm

Figure 2 Specimen













y

z

(a)

Case

Laser beam



Detector

Sample

H

[NN13]

(b)









Laser spot

AA

Focusing lens

Tripod

SP620U

Filter amp spacer

Objective

Sample

Halogen spotlight

Opal glass

Sample

Diffuse layer


B = 15

B = 500

1

e2middot IN max

IN max

W


minus02

0

02

04

06

08

1

12

Nor

mal

ized

inte

nsity

I N(1

mm

2)


PP PA66 PBT

FocusMonitorSP620U

W W W BB B00102030405060708090

Wid

th W

(mm

)

00

05

10

15

20

25

Boun

dary

rang

eB(mdash

)







PA66

PP

PBT

500120583m

500120583m

200120583m

P = 100W

P = 50 W

P = 200W

tB = 015 s

tB = 05 s

tB = 05 s

300320340360380400

300320340360380400

TLiq

TLiq

TLiq

300320340360380400

T (∘

C)T

(∘C)

T (∘

C)












010 010 010 015 015 015 025 025 050 075 10080 100 120 60 80 100 40 60 30 20 20P

Measured

005010015020025030035040

tB (s)

Hei

ght-w

idth

ratio

HW

(mdash)

Calculation
















Thermal camera

Focusing lens

Absorbingcomponent


(a)

T(∘

C)

510

499 25

600

400

200

0

22

50 100 1500

(∘C)

(∘C)

Pixel (mdash)

(b)








Competing Interests


Acknowledgments


References



















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Laser beam



4mm

2mm

2mm

115mm

30mm

Figure 2 Specimen













y

z

(a)

Case

Laser beam



Detector

Sample

H

[NN13]

(b)









Laser spot

AA

Focusing lens

Tripod

SP620U

Filter amp spacer

Objective

Sample

Halogen spotlight

Opal glass

Sample

Diffuse layer


B = 15

B = 500

1

e2middot IN max

IN max

W


minus02

0

02

04

06

08

1

12

Nor

mal

ized

inte

nsity

I N(1

mm

2)


PP PA66 PBT

FocusMonitorSP620U

W W W BB B00102030405060708090

Wid

th W

(mm

)

00

05

10

15

20

25

Boun

dary

rang

eB(mdash

)







PA66

PP

PBT

500120583m

500120583m

200120583m

P = 100W

P = 50 W

P = 200W

tB = 015 s

tB = 05 s

tB = 05 s

300320340360380400

300320340360380400

TLiq

TLiq

TLiq

300320340360380400

T (∘

C)T

(∘C)

T (∘

C)












010 010 010 015 015 015 025 025 050 075 10080 100 120 60 80 100 40 60 30 20 20P

Measured

005010015020025030035040

tB (s)

Hei

ght-w

idth

ratio

HW

(mdash)

Calculation
















Thermal camera

Focusing lens

Absorbingcomponent


(a)

T(∘

C)

510

499 25

600

400

200

0

22

50 100 1500

(∘C)

(∘C)

Pixel (mdash)

(b)








Competing Interests


Acknowledgments


References



















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




y

z

(a)

Case

Laser beam



Detector

Sample

H

[NN13]

(b)









Laser spot

AA

Focusing lens

Tripod

SP620U

Filter amp spacer

Objective

Sample

Halogen spotlight

Opal glass

Sample

Diffuse layer


B = 15

B = 500

1

e2middot IN max

IN max

W


minus02

0

02

04

06

08

1

12

Nor

mal

ized

inte

nsity

I N(1

mm

2)


PP PA66 PBT

FocusMonitorSP620U

W W W BB B00102030405060708090

Wid

th W

(mm

)

00

05

10

15

20

25

Boun

dary

rang

eB(mdash

)







PA66

PP

PBT

500120583m

500120583m

200120583m

P = 100W

P = 50 W

P = 200W

tB = 015 s

tB = 05 s

tB = 05 s

300320340360380400

300320340360380400

TLiq

TLiq

TLiq

300320340360380400

T (∘

C)T

(∘C)

T (∘

C)












010 010 010 015 015 015 025 025 050 075 10080 100 120 60 80 100 40 60 30 20 20P

Measured

005010015020025030035040

tB (s)

Hei

ght-w

idth

ratio

HW

(mdash)

Calculation
















Thermal camera

Focusing lens

Absorbingcomponent


(a)

T(∘

C)

510

499 25

600

400

200

0

22

50 100 1500

(∘C)

(∘C)

Pixel (mdash)

(b)








Competing Interests


Acknowledgments


References



















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Laser spot

AA

Focusing lens

Tripod

SP620U

Filter amp spacer

Objective

Sample

Halogen spotlight

Opal glass

Sample

Diffuse layer


B = 15

B = 500

1

e2middot IN max

IN max

W


minus02

0

02

04

06

08

1

12

Nor

mal

ized

inte

nsity

I N(1

mm

2)


PP PA66 PBT

FocusMonitorSP620U

W W W BB B00102030405060708090

Wid

th W

(mm

)

00

05

10

15

20

25

Boun

dary

rang

eB(mdash

)







PA66

PP

PBT

500120583m

500120583m

200120583m

P = 100W

P = 50 W

P = 200W

tB = 015 s

tB = 05 s

tB = 05 s

300320340360380400

300320340360380400

TLiq

TLiq

TLiq

300320340360380400

T (∘

C)T

(∘C)

T (∘

C)












010 010 010 015 015 015 025 025 050 075 10080 100 120 60 80 100 40 60 30 20 20P

Measured

005010015020025030035040

tB (s)

Hei

ght-w

idth

ratio

HW

(mdash)

Calculation
















Thermal camera

Focusing lens

Absorbingcomponent


(a)

T(∘

C)

510

499 25

600

400

200

0

22

50 100 1500

(∘C)

(∘C)

Pixel (mdash)

(b)








Competing Interests


Acknowledgments


References



















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




PA66

PP

PBT

500120583m

500120583m

200120583m

P = 100W

P = 50 W

P = 200W

tB = 015 s

tB = 05 s

tB = 05 s

300320340360380400

300320340360380400

TLiq

TLiq

TLiq

300320340360380400

T (∘

C)T

(∘C)

T (∘

C)












010 010 010 015 015 015 025 025 050 075 10080 100 120 60 80 100 40 60 30 20 20P

Measured

005010015020025030035040

tB (s)

Hei

ght-w

idth

ratio

HW

(mdash)

Calculation
















Thermal camera

Focusing lens

Absorbingcomponent


(a)

T(∘

C)

510

499 25

600

400

200

0

22

50 100 1500

(∘C)

(∘C)

Pixel (mdash)

(b)








Competing Interests


Acknowledgments


References



















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




010 010 010 015 015 015 025 025 050 075 10080 100 120 60 80 100 40 60 30 20 20P

Measured

005010015020025030035040

tB (s)

Hei

ght-w

idth

ratio

HW

(mdash)

Calculation
















Thermal camera

Focusing lens

Absorbingcomponent


(a)

T(∘

C)

510

499 25

600

400

200

0

22

50 100 1500

(∘C)

(∘C)

Pixel (mdash)

(b)








Competing Interests


Acknowledgments


References



















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






Thermal camera

Focusing lens

Absorbingcomponent


(a)

T(∘

C)

510

499 25

600

400

200

0

22

50 100 1500

(∘C)

(∘C)

Pixel (mdash)

(b)








Competing Interests


Acknowledgments


References



















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





Competing Interests


Acknowledgments


References



















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials


























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



Documents

Research Article Modelling the Heating Process in ...downloads.hindawi.com/archive/2016/3824065.pdfResearch Article Modelling the Heating Process in Simultaneous Laser Transmission