Single cores as energy supply

High-precision vertical machining in five axes in a compact space: Three years ago, EMAG landed a real success in the precision machining market with this concept. The VMC 450-5 MT presented at that time is suitable for machining heavy components with diameters of up to 700 mm, which can also have angled holes and surfaces. This is made possible by the addition of a swivelling axis (B-axis) with an integrated turning/milling spindle and a Y-axis with an integrated main spindle to the basic VMC 450 MT model. The advantage: Manufacturers of transmission parts and housings for lorries or mobile machinery, for example, only need a maximum of two machines to machine a complete component instead of four or six, as was previously the case. This saves space, costs and shortens the process chain.
Another advantage of vertical machining centres is their flexibility. The axles, shafts and housings are generally manufactured in medium quantities and with a high degree of variance. The set-up time is therefore a crucial issue. Loading and unloading can be carried out by robot or manually. As an option, the user can order an integrated tool magazine with up to 80 tools.
In the course of developing the VMC 450-5 MT, the electrical designers also had to solve the not-so-easy task of supplying the high-performance spindle developed in-house with power and signals. The spindle motor has an output of 84 kW, there is hardly any space for the cable and currents of up to 252 A are achieved during acceleration processes.
In addition, the spindle on vertical turning machines is located underneath the workpiece and tool. The moving cables must therefore be well protected against swarf and oil.
Finally, the spindle cable must also be particularly resilient and of high quality. The failure of a motor cable means that a car has to be replaced, which would mean a whole day of downtime due to the very compact design.

Under these conditions, it made sense to realise the power supply to the spindle exclusively with single wires. The logic of this decision becomes all the clearer when you consider the alternative - a four-core motor cable with a cross section of 4G10 mm2. Such a cable cannot be laid in the available installation space, and its bend radius would also be too large.
However, there are reservations in electrical engineering about this type of power supply because the core and cable can influence each other. However, the cables from the CF270 series of the chainflex® programme from igus® have been developed precisely for this application and for moving applications. They achieve extremely long service lives, which is of great importance for EMAG and the users of EMAG machines. Since costs always play a role in machine tool construction, igus® has adopted the principle of single-core cables from crane construction, but at the same time reduced the costs.
The result: the chainflex® CF270.UL.D with PUR-jacket, which is now known on the market as the "spindle cable". Among other things, it is oil-resistant and notch-resistant, which is a great advantage in the oily environment of a machine tool with its many metal edges. UL approval for the global market is of course also available here and this cable type is also convincing in terms of price.
In the VMC-series machines, EMAG uses single-core cables up to a cross section of 50 mm2, in special cases up to 70 mm2. The choice of materials also contributes to this. The outer jacket is made of high-quality PUR. TPE is used for the core insulation underneath the shielding. This increases the temperature resistance of the cable, which takes into account the permanent high load of highly dynamic spindle.