Filling multi-cavity moulds

For over 20 years a little-known, standard option on ARBURG hydraulic machines has been a very useful advantage for moulders suffering from unbalanced multi-cavity moulds – although not all customers know the feature. As well as the standard feature, there is now an advanced app on arburgXworld, “Control PressurePilot”, that smooths the pressure change even better, virtually eliminating mould underfilling.

Pressure switchover solution is standard

A common quality issue with multiple cavities in a single mould is the uneven filling of each cavity. This can lead to flash formation, or edge burr formation, as well as under-filling and higher scrap rates. It can be a persistent issue for multi-cavity moulds for some machines. ARBURG has not one but two solutions, which both address the core engineering problem: the sharp pressure change when switching from injection pressure to holding pressure in the mould. This pressure curve has a direct effect on uniform, even mould filling. The first is the control feature “Switchover via ramps”, standard on all ALLROUNDERS for many years, that ensures an even pressure transition. Many ARBURG owners are unaware of this standard feature, while alternative IMM brands can charge high amounts to offer this as an optional feature. And now in addition, “Control PressurePilot”, available for free on the arburgXworld platform, provides even more control, smoothing the pressure curve further to eliminate under underfilling in multi-cavities. The PressurePilot function is a nonlinear, bionically optimized pressure control system that increases the process window for a robust and reproducible injection moulding process. What is “bionically optimized”? It means that the curve progression, when switching from injection pressure to holding pressure, is based on natural processes. The pressure at first falls sharply and then ever more slowly, like discharging hydraulic accumulators, for example. A more visual example: like releasing air from a balloon.

Graph Pressure Pilot

At the start of the transition from injection pressure, a relatively dynamic and rapid pressure reduction is important to avoid internal pressure peaks in the cavities that can cause overfilling and flash formation on the components (see graph, area A). In this zone, the curves of the two functions, the ALLROUNDER’s standard “switchover via ramps” (blue) and PressurePilot (green), are basically identical. The advantages of the “PressurePilot” function become clear in the last third of the curve (area B).

No pressure drops

“PressurePilot” ensures a much smoother transition to the holding pressure. “The blue line is the older ramp time which, during the transition from the filling to the packing stage, drops below the actual set hold pressure. However with the new PressurePilot it never drops below the set hold pressure,” says Derek Cheetham, Applications & Digital Services Engineer, ARBURG Ltd. “The smoother transition also means there are no pressure drops in the distributor / hot runner manifold system or cavities that could lead to shutdowns at the melt front, caused by hesitations during pressure regulation at the switchover.” The bionically-optimized profile is automatically created by the control system. “All that is required is to enter the time of the transition. The cycle time is not extended because the transition is part of the holding pressure and can be correspondingly shorter,” adds Derek.

“The result is constant mould filling and improved balancing – a huge benefit for producing multi-cavity moulds, we know from these customers,” says managing director ARBURG Ltd, Colin Tirel. “Some IMMs are now charging for this feature, while in fact the standard pressure smoothing feature has been included on ALLROUNDERS since 1997 – and now there is an enhanced tool on arburgXworld, which is getting noticed by UK and Ireland customers who want zero waste.”

In summary, advantages of “PressurePilot” – free for users of the arburgXworld platform – are:

  • An enlarged process window for robust and reproducible injection moulding cycles.
  • Avoids edge burr formation and under filling, common issues with multi-cavity moulds.
  • Ensures a super-smooth pressure transition without undershooting the target replacement.