PSI - Issue 28

Shayan Eslami et al. / Procedia Structural Integrity 28 (2020) 659–666 Shayan Eslami/ Structural Integrity Procedia 00 (2019) 000–000

661

3

2. Materials and Methods 2.1. Materials

Polyamides are synthetic polymers that contain multiple amide -CONH- groups as a recurring part of the chain, commercially known as Nylons. The most used polyamides are the semi-crystalline ones, accounting for 90% of global usage (Wiley-VCH, 2016). In this study the base material to be welded is 4mm thick composite plates of polyamide 6 (PA6) reinforced with 30% short glass fibers (Durethan BKV 30 H2.0 901510) supplied by Lanxess, with properties as presented in Table 1. The plates were cut and machined to guarantee the perfect surface alignment for butt-joint welding.

Table 1. Mechanical properties of 30% GF PA6.

Density [kg/m 3 ]

Tensile Modulus [MPa]

Tensile stress at break [MPa]

Melting temperature [ºC]

1360

9500

150

222

2.2. Methods In this study, a modified 3-axis milling machine was used for the welding operations. This section is dedicated to the design and development of the developed welding system to study composite’s behavior under different welding conditions. The main focus was to study all the influential factors during the welding process with the aim of improving the tool design, as well as selecting the most suitable welding parameters. Sensitized clamping device FSW process can be divided in three main phases: heating, deforming and forging. When the welding tool advances, frictional heat between the tool and the parent materials is generated, which leads to plastic deformation of the materials, and forges the soft material into the weld bead under the axial force. The applied axial force plays an important role to obtain strong welds with high mechanical properties. The importance of measuring the forces arises from the fact that the generated frictional heat is proportional to the applied force during welding (Su et al., 2013). For this purpose, a customized clamping system equipped with load cells was used to measure the active forces during welding, as well as to clamp the weld plates rigidly during the welding procedure (Eslami et al., 2018). Welding temperature In any welding technique, the generated heat is a crucial factor, and measuring the welding temperature can help to optimize the welding process and its parameters. Due to this fact, a temperature measurement device was used to measure the welding temperature. The tool’s temperature was recorded using a K-type thermocouple, which uses a Maxim Integrated MAX31855 cold junction compensated thermocouple-to-digital converter. During the butt-joint welding process, the welding temperature was monitored inside the welding tool and its relation to the welding parameters and weld strengths were studied. Different tool designs As the FSW tool plays a fundamental role in this process, depending on the parent material’s characteristics and joint configuration, tool design modifications are required to adopt to the new conditions. From the previous experiences obtained from FSW of polymeric materials (Eslami, 2019), different tools were designed in order to investigate the possibility of welding thermoplastic composites. A conventional FSW tool, a stationary shoulder, and a new tool design which is combination of rotating shoulder and static shoulder were tested. From the initial results, the most appropriate tool was selected to optimize the parameters.