Monorails help raise precision grinding output 20%

When engineers at the Barden wanted to increase throughput and accuracy for a grinding operation, the result was an all-new machine using a pair of RUE 25 D FE monorail guidance systems.

When production engineers at the Barden Corp wanted to increase throughput and accuracy for a grinding operation on miniature ball bearings, the result was a completely new machine that uses a pair of RUE 25 D FE monorail guidance systems from the INA Bearing Company.

Thanks to these linear bearings and a Neff ballscrew, the new machine cuts 5-10s from the typical cycle time of 30s per part, holds tighter tolerances (around 25um) and the state-of-the-art machine is capable of grinding a wider range of bearing diameters.

Barden, which recently became part of the INA Bearing Company, uses the machine to grind the bore of the outer ring of deep groove and angular-contact ball bearings with an outer diameter of 4 to 16mm.

Such bearings are typically used for dental drills, instruments and similar miniature applications.

In most cases the grinding operation requires a feed in one axis only, but some products with a back shoulder require vector grinding, where movement is along two axes simultaneously.

Prior to the completion of the new machine, Barden was using equipment that was, in some cases, up to 35 years old.

Although several of these machines had been rebuilt at some point, it was recognised that a new design would enable throughout to be increased, accuracy to be improved, and for new user interfaces to be developed that would make the machines far easier to use.

Knowing that the linear slides would be critical to the success of the project, one of the first activities was to invite the local BSL representative to a meeting to discuss the requirements.

As soon as he had an inkling of what was required, the BSL representative decided to bring an INA engineer with him.

After agreeing the required weights, speeds and stiffness, the INA engineer specified the bearings that would meet the requirements.

A pair of RUE 25 D FE monorail guides was selected, 800mm long.

Each rail supports two carriages 70 x 90mm with a defined preload, and the carriages are fully sealed against the ingress of any cutting fluid or debris from the grinding operation (though the slides are also provided with covers).

With four rows of rollers in an X-arrangement, the RUE configuration gives outstanding stiffness and running accuracy, which is ideal for controlling the precision grinding operation.

In addition to the monorail guides, the INA engineer also specified a Neff ballscrew (INA is the UK main agent for Neff).

This is a KGTN 2005 unit with a 20mm diameter screw and 5mm lead; a preloaded double nut arrangement provides zero backlash.

As with the bearings, the ballscrew is a standard item that is available on short deliveries should a replacement ever be required.

David Cook, the BSL representative, explains: "Barden wanted a high-specification standard solution and, aware of the level of technical back-up available from INA, I was fully confident that they could specify exactly the right bearings for the application.

I therefore contacted INA immediately".

Chris Lait, INA Application Engineer, takes up the story: "Within 24 hours of being called, I was on site with David Cook, discussing Barden's requirements.

I specified the RUE monorails and the Neff ballscrew, then Mike Hughes, our Technical Support Engineer, ran the calculations and confirmed that these would do the job.

Less than four days after the initial inquiry, we were in receipt of a purchase order from Barden".

Barden's engineers designed the rest of the machine around the bearings and ballscrew, then went on to build and commission it.

No special operations were required to install either the monorails or the ballscrew, though care was taken to follow the comprehensive manuals supplied by INA.

Thanks to a special design feature of the RUE monorails, the rollers are retained when the carriages are removed from the rail.

Paul Young, Barden's Rebuild Team Leader, concludes: "We are extremely pleased with the outcome.

BSL and INA worked together to offer us the right solution and then deliver it as quickly as possible.

There is no denying that the monorails and ballscrew are an integral part of the machine that is now giving us an increase in throughput of some 20% - an achievement we are very proud of".

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