Special purpose machining becomes flexible

03/01/2007 - Oliver Hagenlocher

Flexible and highly efficient: SW presents the modular, scaleable BM 1250 Manufacturing System

The automotive industry and its 1st-tier suppliers still use transfer and special purpose machines to produce their large batches of crankshaft lines for motor units and their cylinder heads, con-rods and differential housings. Such machines are difficult or impossible to retool and therefore most inflexible. This puts their users to great expense, in particular in the prototype and phase-out stages of a batch run.

Manufacturing companies have been able to make great improvements in this area with the recently developed BM 1250 Manufacturing System from SW Schwäbische Werkzeugmaschinen GmbH, Waldmössingen. The machine's modular construction combines the advantages of the highly flexible machining centre with the excellent output rate of revolving transfer and transfer machines. The to a large extend standardised platform, consisting in the main of monobloc, positioning unit and workpiece loading/unloading station, carries horizontally mounted spindle units. Apart from the workholding fixtures, the only other machine components that need to be adapted to particular customer requirements are the spindle units. The 1000 mm wide and 1900 mm high tooling zone of the monobloc accommodates a number of multiple drilling and milling units of a total weight of max 6000 kg. The positioning unit, travelling in X-, Y- and Z-direction, employs the pick-up principle to convey the workpieces from the loading/unloading station to the drilling heads. Its mounting surface accommodates workpieces and holding fixtures to a weight of max 800 kg. Powerful axis drives and generously dimensioned ball screws produce feed forces of up to 15000 N, in Z-direction even short-term bursts as high as 28000 N. Optional swivel axes (A and C) are available to machine at any desired angle. Direct position feedback systems in all axes guarantee great positioning accuracy across the whole machining area. As there is no need for tool changes and the workpieces are conveyed to the spindle units, the machine offers chip-to-chip times of 1.0 to 1.5 s. The system is capable of working in parallel mode, using multi-spindle drilling heads, or in serial mode, using a number of vertically arranged machining units. This allows the BM 1250 to achieve the productivity levels of a revolving transfer or a transfer machine, but on a noticeably smaller footprint.

This excellent performance is also party due to the cycle-time concurrent loading and unloading of raw-parts and finish-machined components respectively, which can be done manually or automatically. Interlinking the BM 1250 Manufacturing System with other production machines is an equally uncomplicated procedure. During machining, the loading/unloading station is protected against the ingress of chips and coolant from the machining area by a door. The chips fall through an opening in the machining area into the chip conveyor below. The horizontal arrangement of the spindles is again of great advantage. When worn tools need replacing, the positioning unit travels to the loading/unloading station, where a work platform swings in to allow the operator access to the spindle units. The changeover of heavier tools can be accomplished using a swivelling tool changing aid available as an option.
The investment of the BM 1250 Manufacturing System user is considerably better protected than that of companies using conventional special purpose machines, as only drilling heads and fixtures are project-specific on the SW machine, where it takes only a few days to reset the machine to a completely different workpiece. As standardised, process-capable manufacturing systems the machines are also subject to considerably shorter delivery times than comparable special purpose machines. They can be adjusted to required output rates, e.g. for prototype and phase out series. Furthermore, the capital outlay is less than for classical special purpose machines


Oliver Hagenlocher

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