A standard injection moulding machine has at least five axes of motion: the movements mould, ejector, dosage, injection and nozzle. In hydraulically powered machines, these axes of motion are all supplied by a central hydraulic drive with electric motor and regulating pump. Electric machines, on the other hand, are equipped with mutually independent electro-mechanical direct drives, with an electric motor for each axis of motion.
The independent nature of the drives enables movements to be executed simultaneously, making it possible to cut cycle times. However, in order to provide a power reserve, the outputs of the individual loads have to be totalled, which inevitably results in electric machines having higher installed power. This in turn influences the electrical bay installation in terms of fuses and supply cables.

Installed power has nothing to do with a machine’s energy consumption, but rather is a measure of its capacity. The defining element of energy consumption is the actual power input, which depends upon the ON time, utilisation and efficiency of the switched on loads. These factors are, in turn, influenced by the injection moulding cycle.
As a result of fluctuating energy requirements in the individual phases of an injection moulding cycle, an energy-efficient
drive must be capable of providing the energy required at any one time in a demand-oriented manner. Electro-mechanical direct drives have advantages in this respect, as they are only switched on during use and consume considerably less power in power-down mode. In the cooling phase, above all, energy is saved due to lower no-load losses. In the end, the efficiency of electro-mechanical direct drives also contributes to lower energy consumption. This becomes particularly clear when we look at the example of the rotating dosage movement, the efficiency of which is 60 % higher than its hydraulic alternative. Moreover, since losses in efficiency are usually dissipated in the form of heat, this also reduces the expenditure on the cooling of electric machines.
If we only examine the energy consumption of injection moulding machines, various process settings and sequences are not taken into consideration. Therefore, it often makes more sense to employ specific energy consumption as a comparative quantity. This quantity incorporates the shot weight and cycle time, enabling us to ascertain energy savings in direct relation to the application. In terms of the energy efficiency of injection moulding machines, specific energy consumption permits a realistic comparison.

Basically, with the same material throughput, electric machines work in a significantly more energy-efficient manner than hydraulic machines. Potential energy savings amount to 25 to 50 %, and even up to 75 % in individual cases. Furthermore, the diagram illustrates that low utilisation of the machine results in higher specific energy consumption. Low utilisation occurs when comparatively small injected parts are produced with a long cycle time on a large machine. Thus, the design of an injection moulding machine is a decisive factor in the efficient use of energy. This wide-ranging subject will be examined in depth in the next issue of “today”, along with a description of the advantages of modular machine technology.