RESEARCH PAPER

Vibration welding of components with angled areas in the directionof vibration

Sascha Vogtschmidt1 & Isabel Fiebig1& Volker Schoeppner1

Received: 8 December 2019 /Accepted: 15 July 2020# The Author(s) 2020

AbstractConventional manufacturing processes for plastic products, such as injection molding or extrusion, often limit the achievablecomponent geometries. Therefore, it is necessary to join components in order to generate highly complex geometries. Vibrationwelding is one way of joining components. This process is frequently used and is characterized by short cycle times, high energyefficiency, and the possibility of joining large components. In vibration welding, plastic components are heated by an oscillatingfriction movement of the joining surfaces, then plasticized and subsequently welded together. The joining of three-dimensionalseam geometries is therefore a challenge for vibration welding, as the components can be lifted off by the linear movement andthe surfaces do not plasticize sufficiently. Previous investigations have shown that angles of up to 20° can be welded in thedirection of vibration, but that the deviation from the plane considerably reduces the weld strength. In order to weld three-dimensional weld seam geometries with short cycle times and simultaneously achieve a high weld seam strength, a process isbeing developed which is intended to extend the design freedom in vibration welding.

Keywords Vibration welding . Infraredwelding . Polymer joining

1 Introduction

The welding of plastics is often one of the last process steps inthe production of plastic products and enables the realizationof geometries and functions that cannot be achieved by injec-tion molding and extrusion. The joining processes essentiallydefine the component design. In the often design-orientedproducts, these geometries partly represent a major limitation,especially when joining processes with short cycle times have

to be selected from an economic point of view. In the devel-opment of new products, it makes sense to use a joining pro-cess that is flexible and suitable for complex geometries. In thegroup of plastic welding processes, only hot plate welding andinfrared welding offer the necessary degrees of freedom [1, 2]for three-dimensional joining surfaces. In addition to the fea-sibility of the joining geometry, the cycle time is a decisivefactor. In this case, hot plate and IR welding have deficienciescompared with other methods such as ultrasonic and vibrationwelding.

2 Motivation

The requirements for complex weld seam arrangements andcycle times collide in currently available plastic welding pro-cesses. For example, fast welding processes such as ultrasonicor vibration welding is frequently used. A major disadvantageis the limited freedom of these welding processes with regardto the weld geometry. In ultrasonic welding, it is necessary toplace the joining surface perpendicular to the sonotrode axisand parallel to the sonotrode surface, because the position and

Recommended for publication by Commission XVI - Polymer Joiningand Adhesive Technology

* Sascha Vogtschmidtsascha.vogtschmidt@ktp.upb.de

Isabel Fiebigisabel.fiebig@ktp.upb.de

Volker Schoeppnervolker.schoeppner@ktp.upb.de

1 Kunststofftechnik Paderborn, Paderborn University,Paderborn, Germany

Welding in the Worldhttps://doi.org/10.1007/s40194-020-00964-6

design have a decisive influence on the weld seam quality.Vibration welding has the disadvantage of limited design free-dom with regard to three-dimensional seam structures, as therelative movement for the energy input during vibrationwelding occurs in one plane. Generally, the relative move-ment is parallel to the joining surface. In the case of deviationsfrom the flat joining surface, the energy input is not optimal,which limits the process to small partial inclinations [1, 2].

If the joining planes of the components do not lie in thedirection of the vibration movement during vibration welding,the shearingmovement is superimposed, which can lead to thejoining partners being lifted off. For this reason, processeswith longer cycle times are currently being selected for com-plex weld seam geometries.

Due to the energy supply via heat conduction, hot platewelding is a much slower joining process than ultrasonic orvibration welding, even if an attempt is made to shorten thecooling time by convection. In addition, a low-viscosity meltcan adhere to the heating element and reduce the quality of theweld seam, so that hot plate welding is only of limited use forlow-viscosity materials. [2–6].

The aim of these investigations was to develop a newwelding process that allows the welding of large deviationsfrom the joining plane for design-oriented products in shortcycle times. The idea was to develop an alternating expansionwelding process which dissipates energy into a thin moltenfilm which was plasticized by infrared radiation, and in thisway, a complete weld seam can be formed in a short cycletime. The plasticizing process continues due to a superpositionof shear and strain dissipation. The process is shown schemat-ically in Fig. 1. Due to the similarity of this process to vibra-tion welding, these processes can be combined in one processstep. As a result, the previous process limits of vibrationwelding are overcome and the design freedom of the designeris hardly restricted in the arrangement of the joining zone. Theresearch project aims to combine the process requirements ofhigh design freedom with process times.

2.1 Vibration welding

The scientific analysis of vibration welding started veryearly [7–11]. The welding process is based on plasticmelting by friction of the joining partners on each other,whereby the energy transformation is proportional to theaverage friction speed. The basic principle of vibrationwelding is the introduction of heat by shear dissipation.Linear vibration welding is the form of vibration weldingwith the most frequent application. In addition to linearoscillation, orbital oscillation is used in industrial practice.The mechanical properties and morphology of vibration-welded components are the subject of various publications[7–9, 12, 13] in addition to process comparisons. Linearand orbital vibration welding are theoretically understood;concepts for pressure-staged process control, process au-tomation, and quality assurance are available [14], where-by the work was published mainly in Germany (LKT,IKV, KTP) and in North America (Bates, Wu). TheGerman Welding Society (DVS) guidelines provide theuser with information on process design [15].

Previous investigations have shown that vibration weldingcan be used to produce high-quality welds. The quality of aweld seam is often described by the weld factor. This factorrelates the strength of the weld to the strength of the basematerial. This relationship is shown in the following equation:

fw ¼ σw

σm

The aim of every welding process is to generate the highestpossible welding factor so that the weld seam of the resultingcomponent is not a critical point. The welding factor of 1means that the weld has the same strength as the basematerial.Tests already carried out have shown that welding factors of 1could be determined for vibration welds made of polypropyl-ene and polyamide [10, 16] and welding factors of 0.85 forwelds made of PC-ABS [17]. Despite the high level of processunderstanding, the high weld strengths are often not achievedin industrial series production [18, 19]. Besides different wallthicknesses, component distortion, and different vibration di-rections, deviations of the joining zone from the vibrationplane are also responsible for this. In these areas, the energyinput via shear dissipation can only take place to a limitedextent and insufficient weld seams of low strength are theresult. According to relevant guidelines, only deviations <10° from the vibration plane can be successfully welded[15]. Furthermore, Bates et al. showed that with increasingangle of the deviations from the vibration plane, vibrationwelding could be performed, but decreasing weld strengthswere registered in these areas [18, 19]. For example, an in-crease in the joining angle from 0 to 20° for glass fiber–reinforced polyamide 6 resulted in a 50% reduction instrength.Fig. 1 Schematic illustration of the process

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2.2 Infrared welding

Infrared welding has significant advantages compared withother welding processes. For example, there is no contactbetween the component and the heat source and the radiatorcan be switched on and off in a process-controlled manner.Contactless preheating is used to prevent particle output dur-ing vibration welding in order to generate a melt film beforethe vibration starts [3, 4, 20–22]. In vibration welding withinfrared preheating, the heat is generated at the beginning ofthe process by pure radiant heating. Infrared welding can beused to create joints of high strength. Previous investigationshave shown that infrared welding factors above 0.9 can beachieved for most materials [23].

2.3 Dissipation heating

The physical dissipation energy used in these investigationsfor the rapid joining of three-dimensional geometries de-scribes the energy converted into heat. It leads to a furtherheating of the preplasticized melt, with the friction havingthe largest part. The heating takes place due to the shear flowcaused by the squeezing flow and the vibrating movement. Inthe case of high-molecular liquids such as plastic melt, a largeproportion of the energy used for the flow movement is con-verted into heat [24, 25].

3 Experimental setup

The investigations concerning vibration welding with angledareas in the direction of vibration are generally divided intotwo areas. The first area comprises the preliminary investiga-tions regarding the material data, while welding experimentsare carried out in the second area. Because the vibrationmove-ment stretches the melt by the amplitude length, it is importantfor a high-quality joint that no melt break occurs. For thisreason, the preliminary investigations on the one hand includeexperiments concerning the elongation ability of plastic melt,and on the other hand, the heat input via alternating elongationis examined. The preliminary investigations thus form the

prerequisite for the subsequent welding experiments with an-gled areas in the direction of vibration and are intended todemonstrate the feasibility of the process.

3.1 Preliminary investigations

For the preliminary investigations, a test bench was developedwhich enables the generation of a defined melt layer L0 andwith which both a static and a dynamic load can be introducedinto the melt. The basic structure is shown in Fig. 2 and com-prises a heating element for the plasticizing of the material anda fluidic muscle by which the static or dynamic load of themelt is applied. The fluidic muscle provides a dynamic load ofultrasonic type with frequencies up to 100 Hz.

To determine the maximummelt elongation, the two joiningpartners are plasticized until a defined melt layer thickness L0 isachieved. Then both components are repositioned and joined atlow pressure in order to minimize the squeezing flow of themelt into theweld bead. Subsequently, one component is pulledaway from the other component at high speed. Themelt tear-offLt is then detected with a high-speed camera (Fig. 3).

As shown in Fig. 4, vibration welding of plastic compo-nents with angled areas in the direction of vibration poses twochallenges. On the one hand, there is the danger that the ini-tially generated melt is displaced by the oscillating movementand that unmelted areas of the components collide. This col-lision must be avoided in order to prevent unacceptable load-ing of the drive unit.

The maximum selectable amplitude without collision ofunmelted material can be calculated using the trigonometricfunctions (see Fig. 5). As Fig. 5 shows, even small melt layerthicknesses of 0.25 mm can compensate angle-dependent am-plitudes of 0.25 mm (joining angle 90°) up to an amplitude of0.5 mm (joining angle 30°). On the other hand, the melt mustaccommodate the expansion due to the vibration movementwithout tearing off the melt film. The initial melt layer thick-ness L0 in combination with the determined elongation abilityof the plastic melt then limits the maximum adjustableamplitude.

To evaluate the heat input by alternating elongation, onejoining part is moved away from and towards the other joining

Fig. 2 Experimental setup of thepreliminary investigations

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part at different frequencies (cf. Fig. 3). Afterwards, the heatinput is checked by microscopic images of the heat-affectedzone and by analysis of the temperature development in theweld seam. For material data acquisition, semi-crystalline(polypropylene, polyamide 6), amorphous (acrylonitrile-butadiene-styrene-copolymer, polystyrene, polycarbonate)and fiber-reinforced thermoplastics (PP-LGF30, PP-

GF30, PA6-GF30) are investigated with regard to theelongation ability of polymer melt and heat input byalternating elongation. To determine the elongation abil-ity and the heat input, test specimens with the dimen-sions 40 × 30 × 2 mm3 were used, which were producedat the research institute by injection molding and thenmechanically processed.

Fig. 3 Schematic representationof the elongation analysis ofpolymer melt (left) and theinvestigations regarding heatinput via alternating elongation(right)

Fig. 4 Challenges of vibration welding with angled areas in vibration direction

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3.2 Welding experiments

A linear vibration welding machine with integrated IRpreheating unit is used for the welding experiments.Amplitudes of 0.35 to 1 mm (peak-to-peak 0.7 to 2 mm) atfrequencies up to 240 Hz (working frequency of approx.230 Hz for the investigations carried out) can be realized withthis machine. The emitters are 10 short-wave twin-tube infra-red emitters, which can be individually adjusted with regard to

emitter power and irradiation duration, allowing homoge-neous initial melt layer thicknesses to be set even for compo-nents with different distances to the emitters. Injection-moldedrectangular plates (130 × 70 × 4mm3) are used for the weldingexperiments, which are mechanically adapted to the corre-sponding joining zone geometry. The resulting test specimensconsist of a flat surface and an angled area. The angle betweenflat and angled area (joining angle) was successively increasedfrom a 30° joining angle to an angle of 45° during the course

Fig. 5 Maximum amplitude toavoid melt tear-off

Fig. 6 Schematic representation of alternating elongation welding (left: generation of the homogeneous, initial melt layer by IR preheating; middle: heatinput by vibration movement; right: specimen removal in the angled and flat areas)

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of the investigations. This gradually reduces the proportion ofheat input due to shear dissipation and increases the propor-tion of heat input due to elongation dissipation. Figure 6shows the principle sequence of alternating elongationwelding and the schematic representation of the specimengeometry. The welding experiments focus on amorphous(PC-ABS blend) and semi-crystalline materials (PP, PA6).

4 Results

Subsequently, the results of the elongation tests of polymermelt, the tests concerning the heat input via alternating elon-gation, and the welding tests on specimens with varying join-ing angles are presented.

4.1 Elongation ability of polymer melt

As already described, in order to determine the elongationability of the plastic melt, first, a melt layer L0 is producedby contact heating at the heating element and the plasticizedsurfaces are joined at low pressure (the resulting weld seamthen had the thickness of 2 × L0). The aim is to minimize thedisplacement of the melt into the weld bead. In the first step ofthe investigations, the change of the melt layer thickness withincreasing heating times is investigated (Lt: melt tear-off). Onthis basis, tests are carried out to determine the maximumelongation ability of molten plastic. The investigations showthat polymer melt has a high elongation ability, but that thisdepends strongly on the material and the fillers. The meltlayers of non-reinforced materials can be stretched by theirown thickness and beyond (cf. Figure 7). The melt layers offiber-reinforced thermoplastics, on the other hand, can bestretched to a lesser extent until the melt tears-off.Furthermore, the maximum melt elongation εt of non-reinforced materials increases with increasing melt film thick-ness L0. This effect does not occur with reinforced materials.

As already described, the resulting melt layer thicknesslimits the entire subsequent welding process. Therefore, afterIR preheating, the melt layer must be sufficiently large toavoid an impermissible lifting movement on the one handand to avoid the tearing off of the melt film on the other hand.The maximum amplitude then results from the equation inFig. 5 (maximum amplitude without collision of the compo-nents) and the following equation:

amax ¼ 0:5 � Lt

sin α

4.2 Heat input through alternating elongation

In order to investigate the heat input through alternating elon-gation at the mobile hot plate welding machine, the moltenboundary layer was dynamically loaded with different fre-quencies. The examined frequencies are 50 and 100 Hz (min-imum and maximum frequency of the pneumatic muscle). Inthe first step of the investigations, the heat-affected zones ofloaded and unloaded samples were analyzed microscopicallyin order to show the heat input by alternating elongation.Figure 8 shows schematically the determination of the widthof the heat-affected zone and the typical structure of a weldseam. The weld seams of loaded and unloaded seams do notdiffer in terms of structure, but only in the width of the heat-affected zone.

Subsequently, the surface temperature of loaded andunloaded samples is determined at different times with athermal imaging camera. Differences in the cooling be-havior of the specimen surfaces are determined and atemperature increase due to the dynamic load inside theweld seam can be inferred. As an example, the determi-nation of the cooling rates of loaded and unloaded weldsis shown in Fig. 9.

The microscopic examinations showed that the heat-affected zone of the loaded weld seams was wider comparedwith the width of the unloaded seams. In addition, the

Fig. 7 Elongation ability of polymer melt

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dynamically loaded weld seams cool down slower. This cor-relation can be observed for reinforced and non-reinforcedmaterials, but this effect occurs to a greater extent in non-reinforced plastics. This suggests that heat is introduced intothe materials via elongation dissipation. Figure 10 shows thetemperature difference between the weld seam surface at thebeginning of the joining process and after a time of 10 s, forunloaded and loaded components. Here, it can be seen that thedynamically loaded weld seams cool down more slowly. Thissuggests that heat is introduced into the materials via elonga-tion dissipation. This effect can be observed for reinforced andnon-reinforced materials but occurs to a greater extent in non-reinforced plastics, especially polypropylene.

4.3 Welding experiments

During the vibration welding experiments, specimens weretested with a flat surface and an angled area (cf. Figure 6).Initially, a joining angle of 30° was investigated, which wassuccessively increased to evaluate possible process limits. Theprocess parameters include the amplitude, the frequency withwhich the vibrating head is excited, the joining pressure, thewelding time, and the initial melt layer thickness resultingfrom the IR preheating. The working frequency is limited onthe machine side by the weight of the clamping tool. Due tothe fact that the investigations were carried out with a high-frequency machine and a tool with a low mass, the operating

Fig. 9 Determination of thecooling behavior of unloaded anddynamically loaded weld seams

Fig. 8 Schematic representationof a typical hot plate weld seamand determination of the heat-affected zone width

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frequency was above 200 Hz. In order to compensate theoscillating movement and therefore to avoid a collision ofnon-plasticized areas and to prevent a tearing off of the melt,the welding tests are carried out with low amplitudes. Thejoining pressure was adjusted according to the joining angleso that pressures between 0.5 and 5 MPa were achieved in theplane and in the angled areas. By varying the IR parameters,different initial melt thicknesses could be generated (0.3 mm ≤L0 ≤ 0.7 mm). The smallest initial melt layer was only so largethat there was no collision of the unmelted areas. After reachingthe third, stationary phase, the vibration was stopped and theprocess could be terminated. The welded joints in the flat and inthe angled areas were then characterized by mechanical andmicroscopic examinations. As already described, welding testswere carried out using various materials (PP, PC-ABS, PA6)with different melt viscosities in order to determine their influ-ence on the welding process. PP had the highest and PA6 thelowest melt viscosity of the materials under consideration. Themelt viscosity of PC-ABS can be classified between the viscos-ities of the other two materials [26].

During the welding tests, the main variables tested werejoining pressure and the initial melt layer thickness. For weldswith joining angles of 30° as well as for welds with a joiningangle of 45°, it was determined that the weld strength was lessinfluenced by the joining pressure than by the initial melt layerthickness due to IR preheating. Figure 11 shows the tensilestrength of welded 30° specimens as a function of the initialmelt layer thickness. The investigations regarding the weldstrength showed that for welds with an initial melt layer thick-ness L0 of 0.3 mm as well as for welds with a melt layerthickness L0 of 0.7 mm, cohesive joints could be generated.However, a significant difference in weld strength could beidentified between welds with different initial melt layers. Theincrease of the initial melt layer resulted in an improved bondstrength for PP with a comparatively high melt viscosity andfor the materials with a lower melt viscosity.

This correlation can be explained exemplarily by the mi-croscopic images of the PP specimens in Fig. 12. On the one

hand, the illustrations show weld seams with a low initial meltlayer thickness and, on the other hand, the weld seam with acomparatively high initial melt layer. In the welds with a lowmelt layer, material was forced into the bead by the joiningpressure and the vibration movement before additional mate-rial was plasticized through the alternating elongation. Theremaining melt film could not be sufficiently stretched andsheared. As a result, shear and elongation dissipation are re-duced. The vibration movement in combination with the smallmelt layer also creates vacuoles. These structures acted asdefects in the material and led to a lower weld strength. For30° welds with a larger initial melt layer, these defects couldno longer be identified respectively only to a very small ex-tent. In this case, the melt in the joining zone was large enoughto be heated by shearing and elongation for additionalplastification. Comparable results were also found in the mi-croscopic examinations of the two other materials.

As already described, the heat input in conventional vibra-tion welding takes place via shearing of the melt. In vibrationwelding of angled areas, the energy input occurs throughsuperimposed shear and strain dissipation. While the propor-tion of shear dissipation predominates for smaller joining an-gles, the proportion of elongation dissipation increases as thejoining angle rises (complete elongation dissipation withoutshear dissipation would occur at a joining angle of 90°). Forthis reason, the joining angle was successively increased to45°. In this context, Fig. 13 shows the weld seam strength ofthe angled areas in relation to the initial melt layer at a joiningangle of 45°. Similar to the results of the welding tests with anangle of 30°, an increased melt layer proved to be a moredecisive factor for a high weld quality than the applied joiningpressure was. Higher weld seam strengths could be obtainedfor all three investigated materials by previously generating alarger initial melt layer by IR preheating. This effect had astronger influence on materials with a low initial melt viscos-ity, due to the increased melt being pressed out of the joiningzone by the vibration and joining pressure. This means PP canbe welded at a joining angle of 45° with a tensile strength

010203040506070

0.3 0.7

tens

ile s

tren

gth

[MPa

]

initial melt layer thickness [mm]

PP PA6 PC-ABS

Fig. 11 Weld seam strength of the angled areas in relation to the initialmelt layer (joining angle 30°)

0

10

20

30

40

50

Cooling of unloadedsamples

Cooling of loadedsamples

∆(T

-T0)

PP Moplen HP 501L PP TechnoFiberPP Altech NXT PA6 Durethan B30SPA6 GF30 Durethan BKV ABS TerluranPC Makrolon

Fig. 10 Cooling behavior of dynamically loaded and unloaded weldseams

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comparable with the base material. For the thinner melt layerand the additional squeeze flow into the bead, the weldstrengths of PA6 and PC-ABS are below the base materialstrength level (welding factor < 1).

While the 45° weld seams of the PP specimens did notexhibit any visible anomalies, the welded joints of other ma-terials showed clear defects. The comparison between thewelds of PA6 at the angles of 30° and 45° showed significantdifferences. The microscopic examinations of the PA6 weldswith different initial melt thicknesses are shown in Fig. 14.Both the welds with a low initial melt layer and those with ahigher melt layer thickness exhibited conspicuous structuresin the joining zone. However, the weld seams with a lower

initial melt layer showed significantly fragmented structureswith significantly larger vacuoles. These defects caused thelower tensile strength compared with weld seams with highermelt layer thickness.

To evaluate welded joints, the so-called welding factoris often calculated. This indicates the ratio of the weldseam strength to the base material strength and should ide-ally be 1. In this case, the weld seam is not a weak part ofthe entire component. Table 1 shows the maximumwelding factors of the welded joints in the angled areasusing optimized welding parameters. For the comparisonbetween angled and flat areas, the welding factors of theflat area are also given. The welding tests showed thathigh-quality welds can be realized for the joining angleof 30°. The joints showed weld seam qualities which werecomparable with conventional vibration welding. For the45° joining angle, a different result could be determined.For the PP specimens, high welding factors could never-theless be achieved, while for the PA6- and PC-ABS-weldslower welding factors were obtained. This correlation canbe explained by the lower melt viscosity of the materials.The viscous melt of the PA6 and the PC-ABS was pressedout of the joining zone by the applied joining pressure andthe vibration movement. As a result of this process, shearand elongation dissipation had a reduced effect and lessheat energy was introduced into the material. At lowerjoining angles, this effect occurred to a lesser extent andaffected the weld quality less. Despite the comparatively

Fig. 12 Weld seam in the angledarea with different initial meltlayer thicknesses (joining angle30°)

0

10

20

30

40

50

0.3 0.7

tens

ile s

tren

gth

[MPa

]

initial melt layer thickness [mm]

PP PA6 PC-ABS

Fig. 13 Weld seam strength of the angled areas in relation to the initialmelt layer (joining angle 45°)

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low welding factors, the weld seams of the 45° componentsshow a cohesive material bonding and solid weld seamstrengths.

Consequently, the described process can compete with IRwelding in terms of weld strength in the three-dimensionalareas. In addition to the process-technical side, the investiga-tions also showed that the combined method of vibrationwelding with infrared preheating is also an alternative to IRwelding in terms of economy. While comparable componentscan be joined within 52 s using IR welding [27], welding withthe presented method takes 38 s. As a result, the method cancompete with IR welding in terms of both process technologyand economy, and industrial application can be economicallyviable.

5 Summary and conclusion

The welding of three-dimensional joining seams with shortcycle times has long been studied, and the investigations pre-sented here are intended to add to that literature. Vibrationwelding is known for short cycle times, but deviations fromthe flat joining zone are a challenge for the process. For angledareas in the direction of vibration, only a small amount of heatenergy is introduced into the joining zone, often resulting in apoor joint. During the investigations presented here, experi-ments were carried out to introduce additional heat into apreviously plasticized initial molten layer by introducing vi-bration movements. The heat is then introduced bysuperimposed shear and elongation dissipation. For this pur-pose, preliminary investigations were carried out with regardto the elongation ability of polymer melt and with regard to theheat input by elongation dissipation. The aim of the prelimi-nary investigations was to demonstrate the general feasibilityof the process and to enable further investigations. In order tointroduce as much heat as possible into the initial melt layer, itis essential that the melt does not tear off during elongation.The investigations carried out showed that polymer melt has ahigh elongation ability in principle, but that this is influencedby the material itself and by the additives contained in thematerial. Unreinforced melt, for example, can be stretchedby its ownwidth, while the fiber-reinforcedmelt only tolerates

Fig. 14 Weld seam in the angled area at different initial melt layer thicknesses (joining angle 45°)

Table 1 Welding factors of the different materials with varying joiningangles (joining angle 0° denotes the welding factor in the flat areas)

Welding factor weld strengthmaterial strengthÞ

�Material

PP PA6 PC-ABS

Joining angle 0° 1 0.9 0.7

30° 1 0.7 0.7

45° 0.9 0.5 0.5

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significantly lower elongations before the melt tears off. Theinvestigations concerning heat input into polymer melt byelongation dissipation showed that the elongation of the meltintroduced additional energy and thus enabled further weldingexperiments.

The subsequent welding experiments showed that both flatand angled areas can be welded using the method described.The bond strength in the angled areas depends strongly on thejoining angle, the amplitude, the initial melt layer thickness,and the material-specific melt viscosity. In small initial meltlayers, a large part of the melt is pressed into the bead by thevibration and the applied joining pressure. As a result, theamount of melt that can be further heated by shear and elon-gation dissipation is too low to generate a high-quality weld.This effect can be counteracted by increasing the initial meltlayer thickness after IR-preheating. For materials with com-paratively low viscosity melts, this effect is more pronouncedand has a negative effect on weld strength at higher joiningangles, despite the larger initial melt layers.

Acknowledgments Open Access funding provided by Projekt DEAL.The IGF P ro j e c t 19031N o f t h e r e s e a r ch a s s o c i a t i on“Forschungsvereinigung Schweißen und verwandte Verfahren e.V. desDVS. Aachener Straße 172. 40223 Düsseldorf” was, on the basis of aresolution of the German Bundestag, promoted by the German Ministryof Economic Affairs and Energy via AiF within the framework of theprogram for the promotion of joint industrial research and development(IGF).

Abbreviations L0, initial melt layer thickness after IR-preheating; Lt,melt tear-off; εt, maximum melt elongation; amax, maximum amplitude;α, joining angle; LF, low frequent machine; HF, high frequent machine;PP, polypropylene; PA6, polyamide 6; ABS, Acrylnitril-Butadien-Styrol-Copolymer; PC, polycarbonate; IR, infrared; fw, welding factor; σm, ma-terial strength; σw, weld strength

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