PSI - Issue 53

João Soeiro et al. / Procedia Structural Integrity 53 (2024) 367–375 Soeiro et al. / Structural Integrity Procedia 00 (2023) 000–000

369

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2. Materials and methods

Figure 1 presents the two di ff erent geometrical configuration of parts that were subjected to this study. The overmolded and insert-molded parts are presented in figures 1a and 1b, respectively. As regards the polymer polymer adhesion, the addition of a compatibilizer (HPDE-g-MAH) has been tested and the adhesion strength of the manufactured sampels was assessed through pull-out testing. In polymer-metal adhesion, insert surface treatment and its pre-heating were varied. The interface at the metallic pins and polymer (signalled in figure 1b) was analysed on SEM microscopy.

Fig. 1. Overmolded (a) and insert-molded (b) parts submitted to adhesion enhancement strategies.

2.1. Polymer-polymer samples preparation and testing

A compatibilizer weight percentage of 5% of the overmold has been tested (contrasting to 0%). For that a trial production run was performed, ensuring 30 parts with and without the compatibilizer. The overmolding machine Hercule 150 / 470-200 was used. Prior to the production runs of the sample parts, a thorough cleaning of the injection units was carried out to avoid any contamination from previous materials. With regards to the processing conditions, the same operational parameters were used for the production of the samples with and without compatibilizer, as summarized in table 1.

Table 1. Processing conditions of the overmolding process with and without HDPE-g-MAH compatibilizer. Parameter PA6-GF30

HPDE ( + HDPE-g-MAH)

Melt temperature ( ◦ C) Injection speed (mm / s) Injection pressure (bar) Holding pressure (bar) Holding pressure time (s)

295

245 150

90

2100

1700

450

350 3.2

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Given the intricate geometry of the bi-material sample part, a custom pull-out test apparatus was developed for the assessment of the interface adhesion strength. A fixation plate was designed to allow for the separation of the two polymeric constituents of the tested geometry. The design of the fixation plate included two holes which allowed the HDPE tip of the part to slip through. Figure 2a and 2b illustrate the designed plate and the full apparatus (figure 3c) that was mounted on an INSTRON 5900R testing machine equipped with a 1kN load cell. A cross-head speed of 0.5 mm / min has been selected.

2.2. Polymer-metal samples preparation and testing

In order to inspect the adhesion improvement in polymer-metal adhesion, two di ff erent strategies were employed: (i) surface treatment on the insert surface and (ii) pre-injection heating of the metallic insert. An Engel Insert 200H / 80