No abstract

Purpose -This paper aims to explore the influence of the materials used in moulding blocks of hybrid moulds on the injection moulding setup and the properties of the mouldings. Design/methodology/approach -An instrumented (pressure and temperature) hybrid mould with exchangeable moulding blocks, produced by rapid prototyping and tooling techniques (RPT), was used to produce polypropylene tubular mouldings. The configuration of the mould was varied with combinations of moulding block materials, namely, an epoxy resin composite processed by vacuum casting and steel. The processing conditions were adjusted to obtained steady processing conditions. The mouldings were assessed in terms of the microstructure and the shrinkage. Findings -Due to the properties of the moulding block obtained by RPT being different from tool steel, the injection moulding processing conditions and the plastics parts properties are different when hybrid moulds are used. The cycle time depends on the moulding block properties and must be adjusted to the desired running temperature. The morphology of the mouldings is strongly affected by the thermal properties of the moulding block materials. When different materials are used in the core and the cavity asymmetric structures develop in the part. The shrinkage of the mouldings, when resin cores are used is also affected by the deformation of the core caused by the injection pressure. Originality/value -This paper makes a contribution to understanding the morphology of semi-crystalline mouldings obtained using hybrid moulds and enhances the importance of the core deformation on the shrinkage of the mouldings.

The increase in waste has motivated the adoption of the circular economy concept, which assumes particular relevance in the case of plastic materials. This has led to research of new possibilities for recycling plastics after their end-of-life. To achieve this goal, it is fundamental to understand how the materials’ properties change after recycling. This study aims to evaluate the thermal and mechanical properties of recycled plastics, namely polycarbonate (PC), polystyrene (PS), glass fibre-reinforced polyamide 6 (PA6-GF30), and polyethylene terephthalate (PET). With this purpose, injected samples were mechanically recycled twice and compared through thermal and mechanical tests, such as differential scanning calorimetry, hardness, tensile strength, and the melt flow rate. The results show that the amorphous materials used do not suffer significant changes in their properties but exhibit changes in their optical characteristics. The semicrystalline ones present some modifications. PET is the material that suffers the biggest changes, both in its flowability and mechanical properties. This work demonstrates that the mechanical recycling process may be an interesting possibility for recycling depending on the desired quality of final products, allowing for some materials to maintain comparable thermal and mechanical properties after going through the recycling process.

No abstract

Hybrid moulds are an increasingly considered alternative for prototype series or short production runs. This type of tools resorts on the use of Rapid Prototyping and Tooling (RPT) to produce the moulding elements (blocks or other inserts). This study was developed using a hybrid injection mould with exchangeable moulding elements that were produced by additive manufacturing (AM), namely vacuum epoxy casting, stereolithography and ProMetal. A full steel tool was also used as a reference. The processing conditions for the polypropylene moulded parts using the hybrid mould were monitored for pressure, temperature and ejection force. The hybrid mould performance was assessed in terms of pressure and temperature evolution during the injection cycle and the AM moulding elements for physical integrity. The data from the polypropylene moulded parts and the moulding inserts are compared with structural and rheological simulations using ANSYS Workbench and MOLDEX 3D. The results show that the hybrid mould performance and the structural integrity of the moulding elements depend on the properties of the materials used. The moulding shrinkage, when resin cores are used, is also affected by the core deformation caused by the injection pressure.