Conference Agenda

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Program for LiM 2021
Macro: Joining 2
Wednesday, 23/June/2021:
1:30pm - 2:30pm

Session Chair: Artur Leis, University of Stuttgart, Germany
Location: Room 1
ICM Ground Floor 125

1:30pm - 1:45pm

Correlation between the spatial weld seam morphology and the spatial-temporal temperature profile in laser transmission welding of polypropylene

Thomas Stichel1, Edgar Mayer1, Stephan Roth1,3, Michael Schmidt1,2,3

1Bayerisches Laserzentrum GmbH (blz), Germany; 2University of Erlangen-Nürnberg, Institute of Photonic Technologies, Germany; 3Erlangen Graduate School in Advanced Optical Technologies (SAOT), Germany

Laser welding of thermoplastic polymers is a well-known joining technology that is particularly efficient for joining thermoplastic polymers. Although the process is already in industrial use, the basic process-structure-property relationships are not fully understood. The key to understand the correlations between process parameters and final weld properties are the mechanisms of origin of crystallinity and spherulitic structures. Understanding is made difficult by the fact that the laser welding process is a highly dynamic thermomechanical process and therefore very sensitive to experimental circumstances and parameters.

In this study, the spatial distribution of microstructural features inside the weld seam is investigated. For this purpose, the occurrence and size of spherulitic structures of polypropylene in the weld seam is examined by microscopy as well as differential scanning calorimetry is performed in order to measure the crystallinity. The results are correlated with the spatial-temporal temperature profile inside the weld seam which is derived by a thermal simulation model applied with COMSOL.

1:45pm - 2:00pm

Investigations on the transmissivity and scattering behavior of additively manufactured components for laser transmission welding applications

Julian Kuklik, Verena Wippo, Peter Jaeschke, Stefan Kaierle, Ludger Overmeyer

Laser Zentrum Hannover e.V., Germany

Additive manufacturing (AM) of thermoplastic parts is a common technique for prototypes, small batches and mass customization products. A widely used AM process is the fused deposition modeling (FDM), where a part has an inhomogeneous volume structure, because it is build up line by line, layer by layer.

An industrial established joining technology is the laser transmission welding (LTW), e.g. for joining injection molded parts in the automotive sector. For this technique, the transmissivity of one joining partner has a high influence on the resulting weld seam quality and the welding process itself. In order to use LTW for joining AM parts, the transmissivity and scattering behavior of AM parts were investigated. The optical properties were analyzed with spectroscopy and shear tensile tests were performed with welded samples to enhance the knowledge about the relationship between the FDM process, the optical behavior and the weld seam strength.

2:00pm - 2:15pm

Methodology for analyzing the influence of contact temperatures in laser beam brazing

Sven Müller, Peer Woizeschke

BIAS - Bremer Institut für angewandte Strahltechnik GmbH, Germany

In laser beam brazing, the contact temperature between the brazing material and the substrate as well as the wetting behavior play decisive roles. In order to analyze the process by model experiments, droplet tests or tests with pre-placed small amounts of brazing material on the base material have been carried out up to now. While in the first case a certain comparatively high overheating of the molten brazing material is required to allow droplet formation, in the second case it is not possible to determine the emerging contact brazing temperature in the interface with sufficient accuracy. This contribution presents a novel setup and its ability to characterize the influence of the contact temperature on the laser beam brazing process. The setup enables the investigation of process temperatures slightly above the liquidus temperature of the brazing material and the surface temperature measurement of the brazing material shortly before contact generation.

2:15pm - 2:30pm

Prediction of Cu-Al weld status using convolutional neural network

Karthik Mathivanan, Peter Plapper

University of Luxembourg, Luxembourg

Welding copper (Cu) and aluminum (Al) result in brittle intermetallic (IMC) phases, which reduces the performance. The key for a strong joint is to maintain an optimum amount of Al and Cu composition in the joint. To implement this without the destruction of the sample is a challenge. For this purpose, high-resolution images of the weld zone are utilized after welding. With the image processing technique, the presence of (Al/Cu) material melted is distinguished. Therefore the different weld type/status like insufficient melt, optimum melt, and excessive melt is detected from the images.

This paper analyses the weld images and applies the neural network technique to predict the weld type. The microstructural analysis of the fusion zone and mechanical strength of each weld types are correlated to the weld images.