Linear motors used in machine tools

In many types of production machine tools, linear motor drives have replaced ballscrews to power and position machining tables or machining heads writes Mike Page.

It is no news that linear motor drives have come a long way from when it was, at one time, reckoned you needed a small power station to keep a linear motor cool.

You only have to think back ten or 12 years ago when the idea of putting linear motor drives in machine tools was considered 'whacky' - and expensive.

Keeping the units cool, finding space for them, that they could burn out and stopping them from magnetising ferrous workpieces were among the arguments against.

Yet now, in 2007, go to a machine tool event - or materials handling show - and you will find linear motors everywhere.

Even transfer lines have linear motored machining units and transfer devices.

And why? Because the production guys love them! You don't have to plan for ballscrew replacements after some few thousand hours of use.

The transfer line users also say that the linear motor drive is a positive performer and always repeats its position within a few microns.

Ballscrew makers say that they can equal linear motor performances up to a point.

Indeed, the rapid development of linear motors to power machine tool axis travels has spurred the new development of very fast acting ballscrew drives.

And yes, these too appear on new machine tools.

Ask a machine tool builder ten years ago whether there had been any linear motor 'burn-outs', and the spokesman would have changed the subject.

Today, no one is unsure about linear motor reliability.

One company said that of all the thousands of linear motor machine tools now working in factories, none have experienced a 'burn-out'.

One could draw a parallel in production manager/engineer attitudes towards linear motors with the old one of hydraulics versus mechanics.

Some engineers would not have a piece of hydraulic equipment on the shopfloor.

I well remember a group of directors invited to see a new wheel rim-rolling machine to be showered with hydraulic oil when a faulty seal suddenly gave up! That would put any one off! I guess the same could have been said about any production manager who had sanctioned a linear motor machine tool, only see it 'burn out' halfway through a shift.

The first machine tool builders to put linear motor powered axes on their machines were the builders of CNC laser profilers.

To double the positioning and drive speed of a powerful laser cutting thin steel or aluminium sheet was a great boon.

The linear motor gave these laser machine guys the very high acceleration/deceleration rates they craved for.

Ask the likes of Amada, Finn Power, Prima, Trumpf and Yamazaki, they will tell you.

One of the earliest production machining centres I saw fitted with linear motor powered axes was from MCM in Italy.

Perhaps Gildemeister (DMG Group) was one of the first to fit a linear motor to a lathe turret X-axis.

Later, linear motors moved into CNC automatic lathes, such as those built by Citizen, Index, Star and Tornos.

Linear motors are also used in larger machine tools, such as those by DMG, Mazak or Mori Seiki.

As more machine tool, automation systems and transfer line builders used linear motors, so the price of linear motors came down.

The German machine tool group, DMG (Deckel Maho Gildemeister) professes to have shipped the most machine tools - now over 6000 installed - equipped with linear motors.

It will be interesting to see how many will be offered with linear motor drives at the forthcoming EMO 2007 (September 17-22) in Hannover, Germany.

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