Deep dive into machine drives

Which moulding drives offer the greatest flexibility and energy efficiency? Knowing that highly dynamic movements can help to shorten the cycle time and increase component quality, Nigel Flowers, Managing Director of Sumitomo (SHI) Demag UK examines the drive options and their respective performance, operational flexibility, environmental credentials and machinery longevity.

Powering the moulding process, every year the gap between hydraulically driven machines and all-electric ones closes that little bit more. Traditionally, most machines on production floors were pure hydraulics. Although they remain a common sight in UK mould shops, the last two decades has seen a shift. This has really ramped up in the last five years, with eIMM now accounting for almost 30 percent of all new machine installed in the UK & Ireland in 2021.

That said, there remains a prolific volume of hydraulic machines installed in the UK and Ireland - of the 12,000 machine imports in the last 20 years, only 2,000 were all-electric. Yet, over this duration there have been incremental improvements, with newer drive technologies and variants of these emerging all the time. Including hybrid drives, variable frequency, electric servos, electric belt drives, direct drives and more. Some are inherently more energy hungry than others.

Powering progress: New drive technologies

A machine drive works much like any gearbox, in that it provides the force transmission. Although the science behind this transmission is always the same – it transforms the rotational speed into linear movement – not all drives are equal. As the infographic opposite illustrates, their relative efficiency now means that all-electric drives now tend to hold the upper processing hand. Until recently, matching the motion force of hydraulics in larger tonnage machines was regarded as inconceivable. However, indicative of the innovation in drive technology, ‘servo’ variants fusing all- electric direct drives with high-speed servo pumps is now catering to the medium and high clamping force range and further enhancing energy-efficiency. 

The PAC-E packaging machine launch at K 2022 is testament.  Other fields of applications include medium clamp force packages for multi-component moulding, LSR and physical foaming MuCell. Offering higher processing speeds, greater processing repeatability and reliability, plus improved energy efficiency, these new machines build upon existing technologies by integrating all-electric drive technologies.

One of the key processing advantages of electric drives is the ability to control the linear axis with velocities in excess of 500mm/s. These are typically controlled by a closed loop control system located in either the machine controller (software) or the servo drive itself (hardware). The hardware solution offers a key performance advantage as the position control calculations are performed in real-time in the servo drive hardware. Resulting in the maximum performance. Drive design synergy is another critical difference. The requirements for sector and processing applications need to factor in so many varying aspects – including holding patterns, rapid changes in acceleration and deceleration, cooling times and component removal. The only constant is injection moulding is high speed with very fast acceleration and braking.

These aren’t off the shelf drives. Designed by our Japanese parent company and built purely for the injection moulding process by experts truly dedicated to motion control, our high torque drive is more reactive and reduces the risk of inertia. In certain conditions, moulders can achieve energy savings exceeding 70 percent and even faster cycle times in comparison to conventional moulding.

Optimising all production conditions 

Compared to hydraulic machines, electric direct drives only consume electricity when operational.  In  addition, kinetic braking energy can be recovered by means of recuperation technology. This increased efficiency gained from direct drives means that they use considerably less energy than hydraulic machines – in the case of the IntElect between 40% and 85% less than conventional solutions.

Heat transference is another consideration. A portion of this electrical power is used to directly heat the barrel to melt resin. Another to run the machine drive, inverters and motors, which in turn also generates heat. All of the heat generated must be dispersed either via thermal convection or – in most cases – an active cooling system.

Thermal imaging of the direct drive provides a good indicator of any inefficiencies and heat emissions. On the IntElect machines, the active air cooling (fan) is not activated until the motor reaches 55°C. If no heat emission on the drive, no additional energy is consumed. As this graphic illustrates, the IntElect direct drive shows no hotspots.

Furthermore, active cooling systems provide another advantage. one consideration of drive size selection is the duty cycle, how much the motor is working compared to recovering. Active cooling allows the recovery period to be reduced, often allowing a smaller motor to be selected. Electric drives also reduce maintenance costs and breakdown callouts. A result of fewer mechanical components and fewer process steps, wear and tear is significantly lower. Because neither oil nor hydraulic hoses have to be changed, maintenance costs can be up to 50% lower. Mean Time Between Failure (MTBF) is another valuable KPI metric. As well as providing an accurate machine availability benchmark, this data can highlight when machines are not performing at the optimal cycle speed or quality.

With fewer moving parts, the time lapse between one failure to the next is significantly less for machines with electric drives. A recent study on machines under warranty revealed that the IntElect2 had an average MTBF of 4.2 years – double that of an equivalent hydraulic machine.Emergency call outs and time dedicated to servicing is also proven to be lower. A separate in-housestudy on a 130-ton hydraulic machine needed 30 hours of service work, compared to just six hoursfor an equivalent-sized all-electric model.

Finally, replacing a drive system can be costly. Many moulding machine suppliers source their all- electric drives from external OEMs. This can make it much more challenging to exchange or source replacement components or access service support. This is another benefit of having our own R&D centre dedicated to drive development purely for injection moulding. Having a modular drive design means users can replace a power module rather than spend thousands on a complete drive replacement.

As this Drives 101 feature clearly illustrates, electric drives not only hold their own in the efficiency, energy and sustainability stakes, but can now deliver the upper hand when processing heavier loads previously handled by conventional hydraulic workhorses.