FEATURE MICRO MOULDING MICRO MOULDING: Eliminating Material Degradation
Enric Sirera at Ultrasion investigates how degradation issues in micro moulding are being overcome by the latest ultrasonic moulding techniques, delivering compelling results
M
aterial degradation in moulding (and especially micro moulding)
applications is a common problem. Over the last couple of decades there has been numerous challenges related to material degradation, with great efforts being made to address these issues. However there is now a solution to degradation issues that provides a whole new range of possibilities in the area of product integrity. It can also stimulate innovation in
design and manufacture of micro products or components. The solution is provided by the use of ultrasonics in micro moulding, and the ability to dose only the plastic needed per shot direct to the mould. It is encapsulated in the Sonorus 1G machine supplied by Ultrasion SL. For some years now plastic injection
moulding has utilised the same technology for melting and processing polymers, the screw, barrel, and heater band configuration. Apart from the expanding group of OEMs that have now embraced ultrasonic moulding, everyone will be used to this screw, barrel, and heater band technology, and will also be aware of the fact that the big problem with this technology is residence time. Put simply, dosing raw material to the screw and barrel where is it is heated pre- injection means that it resides in melted form for a long time in advance of being injected into the mould. This residence time is the cause of material degradation. Degradation issues become more and
more of a problem as part size is reduced. Therefore, it is in the area of micro moulding that the demand for a solution is greatest. Traditional injection moulding machine suppliers have approached the micro manufacturing niche by reducing “macro” solutions to cater for micro applications. As such, without exception, they all still use variations on the theme of screws, barrels and heater bands, and therefore have done little to address the residence time and degradation problem. In the injection moulding arena, because the technologies are scaled down macro solutions, they not only use the problematic screw, barrel and heater band configuration, but they are also often hugely over-engineered and large footprint machines, using clamping and moulding pressures far in excess of what is actually needed on the micro level.
18 WINTER 2015 | MICROMATTERS
In a nutshell, they place the plastic being processed under huge and largely unnecessary stresses, and in so doing have inherent in them not just the traditional issues related to material degradation, but also issues associated with high and potentially damaging shear stresses. Ultrasonic micro moulding as provided in
the Sonorus 1G machine from Ultrasion is a technology built from the ground up to overcome the issue of residence time, eliminate degradation, but also to provide a technology engineered in a way that is sympathetic to the requirements of micro product manufacture.
PRECISION DOSAGE The screws, barrels and heater bands that are the cause of residence time are eliminated, and instead the technology has been designed to dose as near as possible the precise amount of material needed per shot direct to the mould right by the gate. It is here that the material is melted and
injected in-situ in the mould, minimising material waste, energy use, but also overcoming material degradation due to residence time. In this technology there is
Figure 1:
This new micro moulding process is based on the use of ultrasonics as the agent of polymer melting, and is designed specifically for manufacturers of small and precise plastic parts
no residence time. Material required per shot is processed and injected immediately through ultrasonic melting via an ultrasonic horn which melts the material and acts as the plunger. With this technology, there is no purging. The machine can be turned off in-between shots if you like, and restarted with no negative effects and no material waste. Also, ultrasonics (which has been found to process all materials except rubber and silicone) induces much reduced viscosity in melted polymer, allowing better flow through the mould, meaning longer thinner, flatter parts than previously possible. Also, of huge importance, as the viscosity
is lower, the required moulding pressures are substantially lower than those used in traditional micro injection moulding technologies. In fact they are typically 80% lower than used in traditional micro injection moulding technologies, and this means that shear stresses are dramatically reduced, and the technology can be used with intricate core pins or in over-moulding applications impossible in other technologies. The technology has been commercially
Figure 2:
Ultrasonic moulding was successfully used in the production of PEEK spinal cages
available for over three years now and numerous OEMs in the United States, Europe, and more recently the Far East are using it in exacting industrial applications. One medical device OEM in the United States was recently asked about the technology. The initial attraction for this OEM was the ability to make thin walled long hollow tubes, which play to the strengths of the technology, making high aspect ratio parts. In this instance, the technology was used to make 0.2mm hollow tubes with 0.075mm wall thicknesses and 25mm in length. The OEM reported that it was able (using
the Ultrasion technology) to make thin walled long capillary tube type parts that were impossible to manufacture in traditional micro injection moulding technologies. It also reported considerable savings in expensive implantable PEEK wastage, because only the material needed per injection cycle was processed, as well as significant energy savings as energy was only imparted to melt polymer per shot, not continuously as was the case in traditional injection moulding technologies.
Ultrasion
www.ultrasion.eu E:
cyoung@ultrasion.com
/ MICROMATTERS
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