polymer processing

C.A. Griffiths, S.S. Dimov, E.B. Brousseau
Manufacturing Engineering Centre, Cardiff University, CF24 3AA, UK

Abstract

To increase productivity and thus reduce the unit cost, often micro moulding tools incorporate multiple cavities. For this a runner design must be selected, the main function of the runner system is to facilitate the flow of molten material from the injection nozzle into the mould cavity. Therefore, the micro injection filling process depends on the optimum design of runner systems. In this context, the paper reports an experimental study that investigates the flow behaviour of the polymer melts in micro cavities with a particular focus on the relationship between the filling of micro parts and the size of the runner system. In particular, the runner size effects on the micro injection moulding process were investigated. The filling performance of spiral-like micro cavities was studied as a function of runner size in combination with melt temperature, mould temperature, injection speed and holding pressure time employing the design of experiment approach. In addition, the results were analysed further to identify the effects of the runner

A. Frick (a), C. Stern (a), U. Berger (b)
a Polymer Sciences and Processing, Aalen University of Applied Sciences AAUAS, Aalen 73430, Germany
b Department of Mechatronics, Aalen University of Applied Sciences AAUAS, Aalen 73430, Germany

Abstract

A larger number of polymeric prototypes with special material properties are often demanded for research and development. Thereby, it is most essential that the prototypes are made from the target material and the related processing technique. A sophisticated and fast possibility to obtain a mold for replicating parts (prototypes) by injection molding is making inserts for hybrid molds, using a rapid prototyping (RP) technique. RP technique (e.g. stereolithography) allows shaping complex mold cavity geometries as well as curved cooling conducts, what is not possible by conventional manufacturing.

The manufacturing of high quality micro parts by injection molding requires a plasticizing unit with small screw channel volume to reduce the residence time of the polymeric melt. Nowadays, the minimal commercially available screw diameter is 14 mm. A newly developed plasticizing unit with a screw diameter of 12mm, which was done at AAUAS in collaboration with ARBURG, permits a gentle processing of polymers, spending only half of the residence time. This is an advantage when micro prototypes are manufactured in a single-cavity mold.

The present work points out, how the combination of the benefits of stereolithography and micro injection molding can be successfully used for producing micro prototypes. By means of some examples, it is shown that the performance of small plastic products (part mass in the milligram range) can be optimized by choosing the right material and processing technique. Thus the spectrum of application of micro parts can be extended.

H. Schucka, Th. Veltena, T. Anhuta, D. Sauera, R. Le Harzicb, K. Königa
a Fraunhofer-Institute for Biomedical Engineering, D-66386 St. Ingbert, Germany
b JenLab GmbH, D-07745 Jena, Germany

Abstract

Sub-micrometer structuring has been performed on polymers, metal films and semiconductors using near 3
infrared, 90 MHz femtosecond laser pulses at <3 nJ pulse energy. A compact (65x62x48 cm ) multiport laser scanning microscope FemtoCut (JenLab GmbH) has been employed. A tuneable turn-key, one-box Chameleon (tunable from 720 - 930 nm) has been used as laser source.

Pulse energies in the sub-3 nJ range are sufficient to induce multiphoton ionisation when using a high NA 2
objective (e.g. NA = 1.3) in order to obtain transient TW/cm laser intensities. By exploiting this multiphoton effect, we were able to perform patterning of several types of material with sub-micron resolution. Depending on the pulse energy, cut widths of 350 nm and 900 nm have been achieved in 30 nm thin gold films. In polyimide Pyralin PI2611 (HD microsystems) we reached cut widths of 570 nm. Direct laser processing of silicon wafers resulted in cut widths of about 500 nm. Interestingly, besides the 500 nm cut we found two types of additional nanostructures. A first superficial layer contained non-homogenously distributed laser-induced nanocones which represent non-coherent structures. After removing this layer by etching with ammonium fluoride, a second highly coherent “ripple” structure became obvious. Most interestingly, these symmetric features possessed a wavelength (distance) of 50 – 70 nm. A clear dependence of the ripple structures on the polarization was proven.