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Research Papers

Analysis of the Weld Seam Morphology of Polypropylene in Laser Transmission Welding

[+] Author and Article Information
Bastian Geißler

Bayerisches Laserzentrum GmbH,
Konrad-Zuse-Str. 2-6,
Erlangen 91052, Germany
e-mail: b.geissler@blz.org

Tobias Laumer

Bayerisches Laserzentrum GmbH,
Konrad-Zuse-Str. 2-6,
Erlangen 91052, Germany;
Erlangen Graduate School in Advanced
Optical Technologies (SAOT),
Erlangen 91052, Germany

Andrea Wübbeke, Volker Schöppner

Polymer Engineering,
University of Paderborn,
Paderborn 33098, Germany

Thomas Frick

Bayerisches Laserzentrum GmbH,
Konrad-Zuse-Str. 2-6,
Erlangen 91052, Germany

Michael Schmidt

Bayerisches Laserzentrum GmbH,
Konrad-Zuse-Str. 2-6,
Erlangen 91052, Germany;
Erlangen Graduate School in Advanced
Optical Technologies (SAOT),
Erlangen 91052, Germany;
Friedrich-Alexander-Universität
Erlangen-Nürnberg (FAU),
Institute of Photonic Technologies,
Erlangen 91052, Germany

Manuscript received May 7, 2018; final manuscript received July 12, 2018; published online September 7, 2018. Assoc. Editor: Martine Dubé.

J. Manuf. Sci. Eng 140(11), 111017 (Sep 07, 2018) (7 pages) Paper No: MANU-18-1310; doi: 10.1115/1.4040876 History: Received May 07, 2018; Revised July 12, 2018

Laser transmission welding is a well-known joining technology for welding thermoplastics. Although the process is already used industrially, fundamental process-structure-property relationships are not fully understood and are therefore the subject of current research. One aspect of these mentioned process-structure-property relationships is the interaction between the temperature field during the welding process, the weld seam morphology of semi-crystalline thermoplastics, and the weld seam strength. In this study, the influence of the line energy on the weld seam morphology of polypropylenes is analyzed. For this purpose, the size of spherulites in the weld seam is investigated, as well as different occurring phases of polypropylene (α- and β-phase). It is shown that both the spherulite size of the α-phase and the amount of β-phase increase with increasing line energy. For the explanation and discussion of the results, a temperature-dependent thermal simulation model is used to derive characteristic attributes of the temperature field (maximum temperatures, cooling rates, temperature gradients).

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Figures

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Fig. 1

Principle of laser transmission welding

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Fig. 2

Absorbing and transparent joining partner

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Fig. 3

Experimental setup

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Fig. 4

Schematic of polarization microscopy with an exemplary thin section of the weld seam and the measurement area

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Fig. 5

DSC measurement curve of iPP with 0.2 wt % c.b.

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Fig. 6

Analysis of the weld seam morphology (parameter no. 3) by determining the size of α-spherulites and the number of β-spherulites

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Fig. 7

Comparison of the spherulite diameter (α-phase) of the base material with the weld seam in the investigated parameter range

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Fig. 8

Dependence of the spherulite size (α-phase) on the line energy

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Fig. 9

Temperature curves for different line energies and corresponding cooling rates in the crystallization range

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Fig. 10

Dependence of the cooling rate on the line energy

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Fig. 11

Comparison of spherulite size dependent on cooling rate with study from Piccarolo et al. [33]

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Fig. 12

Dependence of the amount of β-spherulites per mm2 on the line energy

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Fig. 13

Temperature distribution laterally to the weld seam for different line energies

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Fig. 14

Dependence of lateral temperature gradient and maximum temperature on the line energy

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