Ingenieria

micro moulding

ARTICLE

Effects of Glass Fibres on the Properties of Micro Moulded Plastic Parts
A. Islam, H. N. Hansen, S. Gasparin, Department of Mechanical Engineering, Technical University of Denmark and M. Bondo, Sonion A/S Introduction
In the current state of injection moulding technologies micro injection moulding is an immensely important process for industries and the technologyis growing at a rapid speed. The need for micro parts in the industries is on the rise and the demand for tailor made materials with specific parameters becomes larger. One effective and economic way of mass production for micro parts is injection moulding and the used materials for the process are mostly plastics because of their suitability for injection moulding, good replication quality andcost. Nevertheless, plastic materials lack stiffness and mechanical strength. The most common way to improve the mechanical properties of a plastic material is to add glass fibres. Glass fibres improve the >

Figure 1: Picture of glass fibees (left picture), magnified view of one single glass fibre (right picture).

click to view advertiser’s page opens in new window structural properties likestrength, stiffness and reduce the shrinkage of the part [1]. Glass fibres used in plastic materials are distinguished as short glass fibres and long glass fibres. Typical lengths of short glass fibres are 0.2 to 0.5 mm and for long glass fibres, 10 to 15 mm. Short fibre reinforced thermoplastics are most commonly used for injection moulding [2]. Although all thermoplastics can be reinforced withfibres, Polyamide, Polypropylene, Polystyrene, ABS and SAN are the most widely used fibre reinforced materials in the plastic industries [2]. Figure 1 shows the short glass fibres used with thermoplastic materials. The right picture of the figure 1 shows the cross sections of an individual glass fibre. The pictures were taken by Scanning Electron Microscope during the experiment of currentinvestigation. Mechanical properties of glass fibre reinforced plastics can vary depending on the fibre distribution, fibre orientation, fibre size, fibre fraction, fibre-plastic adhesion etc [2]. Glass fibres are used as reinforcing materials in many sectors like automotive and naval industries, sport equipments, airplane industries and in many other plastic industries. Glass fibres improve themechanical properties of plastic materials; on the other hand, they also impart some unwanted conditions and properties in the process and in the product, especially for micro moulding and for micro products, for example poor replication and surface finish, filling problems and so on. The investigation carried out in this paper reveals the effect of glass fibres on the replication quality and surfaceproperties of the micro moulded plastic parts.

Name

Glass

Manufacturer

Moulding condition Tmo Tme 235°C 235°C Vin 102 mm/s 102 mm/s

PS 158K PS 158KGf30

0% 30%

BASF BASF

60°C 60°C

Experiments

Table 1: List of plastic materials.

The aim of the current study is to investigate the effects of glass fibres on the replication quality of thin polymeric ribs. The geometricalsize effect on the amount of glass fibre in the moulded plastic parts was also investigated in the experiments.

Test geometry
The test specimen used for this experiment (shown in figure 2) was 2.5 dimensional having long ribs with different aspect ratio. Different rib thickness of this geometry will simulate the different filling behaviour of the glass-filled material. The section of the partshown with the red circle is termed as the critical section of the part as it has sharp corners and the thinnest cross section with an aspect ratio of nine. >

Figure 2: Part geometry used in the experiment (critical section of the part is shown with the red circle).

click to view advertiser’s page opens in new window

Figure 3: Injection moulding machine used for moulding of the plastic...