MICRO MOULDING | ARTICLE


In addition, mould filling in micro injection moulding can be quite tricky due to the frozen layer appearing near the mould surface, and in many cases injection moulding processes involve high temperatures, long heating times and mechanical stresses that can contribute to polymer degradation.


Micro injection moulding machines are often extremely costly, and in addition they exhibit high and continuous energy consumption in the area of 1.7 kilowatts per hour. In an increasingly competitive and taxing manufacturing environment, there are understandable restrictions on capital outlay, and also a high level of scrutiny on running costs.


Ultrasonic Micro Moulding


While technology and material advances are able to confront many of the problems inherent in micro injection moulding, they all focus on the re-iteration of the existing injection moulding process. However, today, a new and cost-effective technology has been commercialised that completely re-spins the process of micro moulding, using ultrasonic waves to fabricate micro parts from thermoplastic polymers.


The process — developed by Ultrasion SL in conjunction with technology Centre ASCAMM, both based in Barcelona, Spain — is simple, and harnesses the ability of ultrasound to heat and melt materials cyclically at ultrasonic frequencies, providing a highly energy-efficient solution to micro part fabrication. Only the shot size necessary for each shot is fed into the mould using standard pellets at room temperature. Melt occurs in milliseconds through the use of ultrasonics, which increases fluidity characteristics when compared with alternative technologies due to various physical factors. Vibration disturbs the convergent melt flow in the entry region while reducing elastic tensile strains. In addition, the ultrasonic energy reduces molecular chain entanglement and facilitates molten polymer flow.


Moulding can take place using low pressures while at the same time being highly replicable, and there is minimised waste as the parts are ejected. The low-pressure characteristic of the technology is important as it means that standard moulds can be used, 50% savings in mould cost being achievable as they do not need to be made to withstand high pressure typical in micro injection moulding.


The machine that has been developed that encapsulates this ultrasonic technology is called the Sonorus 1G, which is especially well suited to the production of long, thin and flat precision parts, as it is able to induce extremely low viscosity in the melted plastic. 15 mm long parts with 0.075 mm thick walls are easily produced. In addition, as there are no heaters and no residence time as is the case with micro injection moulding technologies, there is no material degradation. In addition, the machine never needs purging, which can lead to substantial raw material savings, especially important, for example, when using high-cost medical grade polymers.


“The low pressure characteristic of the technology is important as it means that standard moulds can be used, 50% savings in mould cost being achievable as they do not need to be made to withstand high pressure typical in micro injection moulding.”


For the first time in a long time, Ultrasion’s technology approaches the process of precision injection moulding from a brand new and innovative angle. There has been a lot of work and research brought to bear on the Sonorus machine over a period of about seven years, the machine now being used commercially in the United States and Europe for the first time.


The Core of the Technology


The key to the success of the Sonorus machine has been the harnessing of the potential of inherently clean and highly efficient ultrasound energy. Sound is always caused by vibration, and


<< Figure 2: Close up of parts produced by ultrasonic technology on the Sonorus 1G machine. >>


10 | commercial micro manufacturing international Vol 7 No.1


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