Quadruple drive boosts impeller production

Waldmössingen, 16 September 2014 – Within a few years the number of diesel and gasoline engines equipped with turbo-charger has increased significantly. The Schwäbische Werkzeugmaschinen GmbH (SW) presents at the AMB the four-spindle processing centre BA 341, which is currently the most powerful solution for the impeller machining of medium and large-scale series. As compared to a single-spindle machine the BA 341 offers fourfold productivity - at significantly reduced investment costs and space requirements. 

In motor engineering new turbo-charger solutions are currently setting the pace of further progress. Speeds of up to 300,000 min-1 improve the response behaviour of motors, but also lead to permanently growing demands on manufacturing tolerances. At the same time, turbo-chargers have to cope with higher temperatures, which is associated with an increased use of titanium alloys. "In addition, a growing number of manufacturers is opting for the combination of two turbo-chargers per motor“, Reiner Fries, Head of Marketing at SW, explains the current development. "This has led to another significant rise in lot sizes and model variants.“

Positive experience with two-spindle machining 
With the new machining centre BA 341 users meet the requirements for reproducible accuracy at very low unit costs. The new machine simultaneously uses four spindles and four direct-drive rotational axes for the 5-axis machining of four impellers. "The two-spindle high-speed machines of SW have demonstrated for years that the specified tolerances are reproducibly achieved even in simultaneous machining“, Reiner Fries explains. "On the basis of that experience users had expressed an active interest in a four-spindle version.“

Position accuracy of 8 microns 
The BA 341 is equipped with four parallel main spindles arranged at a distance of 150 mm. A torque of up to 80 Nm at the main spindles and optional spindle speeds of up to 40.000 rpm also permit the processing of new materials such as titanium alloys. For thermal reasons these alloys are increasingly used for compressor wheels. The position accuracy of the feed axes meets the 0,008mm requirement of VDI/DGQ 3441. The direct-drive rotational axes, purpose-made for impeller production, add further dynamics and precision.

Reduction of non-productive times: pallet change in less than three seconds 
At highly dynamic accelerations of 10 to 15 m/s² the high-speed machining centre achieves feed and rapid traverse rates of up to 75 m/min. "On top of high-speed chipping requirements we have addressed the most important adjusting lever for productivity - the minimisation of non-productive times“, says Wolfgang Armleder, Head of Development at SW. The chip-to-chip time is as brief as 2.5 seconds.

In the single-position machine the "pallet change" via the double swivel bracket takes less than 3 seconds. This increases the lot sizes in large-scale series, in addition to permitting simultaneous machining. "Operators using a zero-point clamping system can change the tooling within a few minutes", says Reiner Fries. "This is an important requirement for the flexible production of medium-sized series.“

The BA 341 builds on SW's proven and tested concept of a rigid mono-block with suspended traverse member and horizontal main spindles. This guarantees optimal chip fall. At the same time, the BAZ controls the process forces in simultaneous machining, which is the design precondition for high precision.