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Processing | electrical and electronics


thin-wall and micro-electronic parts may be moulded on standard machines using melt compression techniques to deliver precise high speed filling


electronics moulding may work best when put under pressure


the continuing miniaturisation of electronic devices is driving demand for plastics enclosures and components with ever thinner wall thicknesses and features that present tough challenges for injection moulders. the traditional solution is to use powerful injection systems capable of delivering the high injection pressures and accelerations required but, says Peter Pokorny, head of application technology at Austrian injection machinery maker engel, the company’s X-melt expansion injection moulding technology can provide a less costly and more energy efficient alternative for some applications. “X-melt technology can be used for small, thin-


walled components or micro parts with shot weights of less than one gram,” says Pokorny. normally, special machines are required for micro injection moulding and machines with injection speeds of 1,000 mm/s or more are needed for thin-walled components.” the X-melt injection moulding process – which is


patented by engel - exploits the natural compressibility of the polymer to power mould filling. it employs a standard injection and plasticising unit with the addition of a special needle valve nozzle. during the first phase of the process, the screw plasticises a defined amount


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of material and meters it into the space in front of the screw. in the second phase, the screw is used as a plunger to compress this volume of melt to pressures of up to 2,500bar. the pressurisation reduces the volume of the melt


by around 10%. when the needle valve nozzle is opened in the third phase of the moulding process, the compressed melt expands rapidly into the mould cavity to fill it in fractions of a second. expansion of the melt is the sole driving force in the X-melt process – the screw is maintained at its post pressurisation position during both filling and holding phases. the process was first developed around a decade ago on hydraulic moulding equipment. engel has continued to work on optimisation of the technique since then and now recommends using it only with the latest generation of servo-electric injection systems that offer much improved positional control. while the X-melt process may sound uncontrolled,


engel says that repeatability is actually high due to the very accurate positional control of the screw in the servo-electric drive system and the characteristics of the expansion process itself. Pokorny says while


April 2012 | injection world 31 Above:


Expansion injection


moulding can allow produc- tion of micro-


scale electronic parts on


conventional moulding


machines, says Engel


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