Linear drives take on tools

by Dave Wilson, Editor

Two companies took the linear drive plunge this month incorporating the relatively new technology into both a high speed machining centre and an EDM machine.

While some manufacturers are still debating the merits of linear drive technology versus the more conventional ball-screw approach, EX-CELL-O has developed a machining centre, the XCH 241, that uses a powerful main spindle in conjunction with the latest linear motors from Indramat (Mannesmann Rexroth).

Using the technology, EX-CELL-O claims that floor space requirements have been reduced by 60%. Now, they say, 40,000 automobile gearboxes can be produced in one year on a total area of just 6m by 1.75m. What is more, the consumption of cooling lubricant can be reduced by 50% compared with the previous XHC model.

For its part, Sodick, a manufacturer of EDM machines, has designed and developed its own range of linear drives for incorporation within its AM35L, claimed to be the world’s first EDM machine to make use of linear drives. Linear driven incremental steps of 0.0001mm with servo speeds of up to 36m/min to all three axes have been achieved as a result. What is more, Sodick claims that the design eliminates the problems of backlash associated with a ballscrew design.

In classic sinking operations, as the depth of a cavity increases, the flushing efficiency declines, requiring continual retraction of the electrode to clear debris from the eroded cavity. The retraction and return of the electrode is time consuming, but linear drives have helped speed the process up, according to Sodick.

For example, when machining a cavity 25mm deep with an electrode with a cross section of 2mm by 5mm, eroding times with a conventional sinker with AC drives running with the same generator setting and surface finish limits is 4hrs. With the new linear drive technology, the same cavity can be produced in less than two.

Finally, it seems linear drive technology is coming out of the labs and into the machine design arena. We’ll be following up the progress of these beasts with a special report in the August issue of Design Engineering.