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Factors influencing the fiber orientation in welding of fiber-reinforced thermoplastics

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Abstract

In welding of fiber-reinforced thermoplastics, the welding pressure initiates squeeze flow of melt into the weld bead. This leads to reorientation of fibers into the flow direction. Therefore, the fibers in the weld are mainly oriented perpendicular to the joining direction. Since this is mostly identical to the load direction, the reinforcing effect of fibers is not effective in the weld because fibers only have a reinforcing effect on the polymer when they are aligned along the load direction. Current investigations at the Kunststofftechnik Paderborn (KTP) aim at reaching an effective reinforcing effect of fibers in the weld of fiber-reinforced thermoplastics. The experiments are carried out on polypropylene and polyamide. Three different grades of PP are used: unreinforced, short glass fiber-reinforced, and long glass fiber-reinforced PP with 30% fiber content each. The used grades of PA differ in viscosity and shear thinning behavior. Experiments are being conducted on influences on the weld strength and the fiber orientation in the weld for hot plate welding. Common welding parameters are varied. One aim of the investigations is to find a correlation between the flow velocity during squeeze flow and weld strength or fiber orientation.

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Abbreviations

a, b, c:

position of ROI’s in CT analysis

a xx, a yy, a zz :

component of orientation tensor

b :

width

CT:

computed tomography

d :

thickness

DP:

design point

DVS:

German Welding Association

\( \frac{dp}{dx} \) :

pressure gradient in x-direction

F :

joining force

f z :

welding factor

GF:

glass fiber-reinforced

h :

melt layer height

h 0 :

melt layer height at beginning of joining phase

HP:

hot plate (welding)

h residual :

melt layer height at end of joining phase

K :

flow consistency index

L 0 :

melt layer thickness after heating

n :

flow behavior index

P :

unit vector

PA:

polyamide

p F :

welding pressure

PP:

polypropylene

p x, p y, p z :

component of the unit vector P

ROI:

region of interest

s J :

joining displacement

T HP :

hot plate temperature

T M :

crystalline melt temperature

v J :

joining velocity

v x :

flow velocity in x-direction

v y :

joining velocity

x a, x b, x c :

position for calculation of flow velocity in squeeze flow

\( \dot{\gamma} \) :

shear rate

σW :

weld strength

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Acknowledgements

The IGF Project 18702N of the research association “Forschungsvereinigung Schweißen und verwandte Verfahren e. V. des DVS. Aachener Straße 172. 40223 Düsseldorf” was, on the basis of a resolution of the German Bundestag, promoted by the German Ministry of Economic Affairs and Energy via AiF within the framework of the program for the promotion of joint industrial research and development (IGF).

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  1. Kunststofftechnik Paderborn, Paderborn University, Paderborn, Germany

    Isabel Fiebig & Volker Schoeppner

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  1. Isabel Fiebig
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  2. Volker Schoeppner
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Correspondence to Isabel Fiebig.

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Recommended for publication by Commission XVI - Polymer Joining and Adhesive Technology

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Fiebig, I., Schoeppner, V. Factors influencing the fiber orientation in welding of fiber-reinforced thermoplastics. Weld World 62, 997–1012 (2018). https://doi.org/10.1007/s40194-018-0628-0

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