Single cores as energy supply

Profile

• What was needed: chainflex cables CF270 "spindle cables", energy chains
• Requirements: Power of 84 kW and currents up to 252 A, hardly any installation space and good oil resistance
• Industry: Mechanical engineering, vertical processing machines
• Success for the customer: High saving of installation space with simultaneous cost reduction

The VMC 450-5 MT enables high-precision five-axis machining of heavy components in a compact space.

Problem

High-precision vertical machining in five axes in a compact space: with this concept EMAG achieved real success in the precision machining market three years ago. The VMC 450-5 MT presented at that time is suitable for the machining of heavy components with diameters of up to 700 mm, which may also have inclined holes and surfaces. This is made possible by extending the basic model VMC 450 MT by a swivel axis (B axis) with integrated turning/milling spindle and a Y axis with integrated main spindle. The advantage: Manufacturers of gearbox parts and housings for lorries or mobile machines, for example, need a maximum of two machines instead of four or six, as was previously the case, to process a complete component. This saves space, costs and shortens the process chain.
Another advantage that applies to all vertical processing machines is their flexibility. The axes, shafts and housings are usually produced in medium quantities and with great variance. Set-up time is thus a crucial issue. Loading and unloading can be done by robot or manually. Optionally, the user can order an integrated tool magazine with up to 80 tools.
In the course of the development of the VMC 450-5 MT, the electrical designers also had the difficult 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 cables and during the acceleration processes currents of up to 252 A are achieved.
In addition, on vertical lathes the spindle is located below the workpiece and tool. The moving cables must therefore be well protected against swarf and oil.
Finally, the spindle cable must also be exceptionally resilient and of high quality. For example, the failure of a motor cable means that a replacement has to take place, which would mean a whole day of downtime due to the very compact design.

Solution

Under these conditions it was a logical step to implement the energy supply to the spindle exclusively with single cores.  The logic of this decision becomes even clearer when the alternative - a four-core motor cable with a cross section of 4G10 mm² - is considered. Such a cable cannot be laid in the existing installation space, and its bend radius would also be too large.
However, there are reservations in electrical engineering about this type of energy supply, because the cores or cables can influence each other. The cables from the CF270 series of the chainflex range from igus were developed precisely for this application and for moving applications. They achieve extremely long service life, which is of great importance to 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, while also reducing costs.
The result: The chainflex CF270.UL.D with PUR jacket, which is now known as a "spindle cable" in the market. It is, among other things, oil-resistant and notch-resistant, which is a great advantage in the oily environment of a machine tool with its many metal edges. The UL approval for the world market is of course also available here and this cable type can also convince in terms of price.
In the VMC machines, EMAG uses the single-core cables of up to a cross-section of 50 mm², in special cases up to 70 mm². The choice of material also contributes to this. The outer jacket is made of high-quality PUR. TPE is used for the core insulation below the shielding. This enables us to increase the temperature resistance of the cable, which takes into account the permanent high load on highly dynamic spindles.

Multi-core cable (top) or single cores (bottom)? For EMAG there are good reasons to rely on single cores.

The non-moving cables of the USC machines are also designed as single cores.

View into the control cabinet. Clearly visible: the orange chainflex cables CF270.UL.D.

igus energy chains are used on several axes of the VMC lathe centres.