Med-Tech Innovation Micro moulding
moulding process. It benefi ts from the fact that it was designed and developed specifically for the micro moulding sector, and from its inception it addressed many of the drawbacks inherent in existing micro injection moulding technologies.
Ultrasion was conceived after many years of research and development of the ultrasonic micro moulding technology by industrial research group, ASCAMM, also based in Barcelona. The results of this research can be seen in the Sonorus 1G ultrasonic micro moulding machine, which can accommodate shot weights from 0.05 g to 2 g
What is most obvious when looking at this technology is that there is no barrel and screw. Ultrasonic waves are used to melt plastic granules that are fed direct to the mould, and are melted in milliseconds once contacted by an ultrasonic horn, or “sonotrode”. Figure 1 shows the basic elements of the ultrasonic moulding process. The machine has a dosage system that delivers the correct quantity of standard pellets for every shot. The production cycle begins with the mould already closed and dosed with raw polymer at room temperature. The material is then contacted by the sonotrode, which is lowered, and as well as melting the polymer it forces the material to fl ow into the mould cavities. The sonotrode then returns to its original position, and the cycle begins again. Energy usage is minimal compared with traditional
micro injection moulding machines, the heater bands in the latter machines are replaced by the ultrasonic horn that only uses energy when contacting the raw material in the mould to induce melt (which occurs in milliseconds). This also means there is no material residence time and no material degradation, a common problem with micro injection moulding technologies. It is estimated that the Sonorus 1G uses 90% less energy than a traditional micro injection moulding machine. Reduced material waste is a product of the fact that only the material required per cycle is dosed and melted, therefore, there is no runner wastage and little in the way of sprue wastage.
Savings in tooling costs are achieved as a result of the unique characteristics induced in the plastic raw material when it is melted using ultrasonics, as opposed to electrical heating. Only low moulding pressures are required to produce highly accurate and replicable part characteristics. The characteristics of plastic when melted using ultrasonics also open up new areas for product innovation.
A spur to product innovation
It has been found that ultrasonic melting (coupled with a new sprue concept used in the Sonorus 1G) signifi cantly reduces the viscosity of the melted polymer. This means that manufacturers can achieve longer, fl atter and thinner- walled micro parts than previously possible. The sprue concept used in this ultrasonic technology acts as an energy director as well as part of the ejection system. The energy director orientates the waves in the fl ow direction so that the molten polymer and waves travel together towards the cavities in the mould, thereby reducing the viscosity of the material.
www.med-techinnovation.com
Figure 2: The part, with a membrane overmoulding, weighs 0.02 g, with a 0.5 mm wall thickness, an outside diameter of 4.4 mm and an internal diameter of 2.9 mm produced using the ultrasonic moulding process
The application of a high intensity mechanical vibration that transmits energy directly into the polymer’s molecular structure results in extremely rapid and effi cient melting “inside out” rather than “outside in”, which is typically how polymer is melted using heater bands in micro injection moulding machines.
Case studies The reduced viscosity and increased fl ow characteristics inherent in the ultrasonic moulding technology means that 15 mm long parts with wall thicknesses of 0.075 mm are easily attained, with tolerances as tight as 0.01 mm achievable. In a project for a tissue management medical device using coloured polypropylene (PP), a particularly diffi cult to manufacture tip was required. By using the ultrasonic technology, the company managed to produce a tip that was 43 mm long, weighed 0.22 g, with wall thicknesses of 0.075 mm, and with an outside diameter (OD) of 0.35 mm and an internal diameter (ID) of 0.2 mm. In another application for the manufacture of a cap with a filter for an ear protection device made from raw polyamide 12, the ultrasonic moulding process successfully manufactured a part weighing 0.02 g, with a 0.5 mm wall thickness, and OD of 4.4 mm and ID of 2.9 mm. In this product (Figure 2), the part with a membrane overmoulding was achieved in one operation. This had proved impossible to achieve using a conventional micro injection moulding process, which involved moulding the part in one process and then gluing the membrane in a secondary process. The manufacturer reported a 300% increase in productivity using the new technology. Finally, ultrasonic moulding was successfully used in the production of an eye retina surgery tip (Figure 3)
September/October 2014 ¦ 17
Figure 1: The ultrasonic micro moulding process
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48