Page 40 - eBook_Proceedings of the International Conference on Digital Manufacturing V1

Proceedings of the International Conference on Digital Manufacturing –
Volume 1

Uniformity in particle size is a critical factor, influencing melting
homogeneity and, subsequently, the reproducibility of mechanical
properties. Standardising flake sizes helped achieve consistent
thermal processing conditions and reduced variability across
specimen batches.

Specimen Preparation for Mechanical Testing

A total of six (6) batches of specimens were prepared, each
comprises of standardised dog-bone-shaped test bars in
accordance with ASTM D-638 Type I specifications. The dog-
bone geometry was precisely selected as it facilitates uniform
stress distribution during tensile testing, thus ensuring reliable and
comparable results. Specimen preparation involved systematically
melting HDPE flakes at controlled temperatures, varying
incrementally at 5°C intervals (130°C, 135°C, 140°C, 145°C,
150°C, and 155°C). These incremental temperature variations
provided an in-depth exploration of the temperature's impact on
the mechanical properties of recycled HDPE, aiming to identify
an optimal temperature that maximises mechanical performance.

Each specimen batch was carefully controlled by maintaining
a constant mass of HDPE flakes (38.58 g), meticulously measured
using a high-precision digital scale. The flakes were then evenly
distributed within a custom steel mould measuring 18.5 cm × 16.5
cm. Before introducing the flakes, the internal surfaces of the
mould were lined with heat-resistant overhead projector (OHP)
film. This precaution prevented the adhesion of molten HDPE to
the mould surfaces, easing the removal and reducing surface
imperfections on specimens.

Compression Moulding Process

The moulding process employed a hydraulic hot press machine,
set at the specified temperatures and exerting a uniform
compressive force sufficient to achieve complete consolidation of
the polymer flakes. Each batch of specimens underwent a precise
melting period of 180 seconds. The compression pressure and
holding time were systematically maintained across all specimen

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