At the Spanish factory, some 117 ballscrews facilitate linear motion and tool table/changer positioning in a large number of CNC machining centres. However, because of stringent requirements and tough environmental conditions, the ballscrews have an average service life of only six months. As a consequence, unscheduled downtime were causing considerable additional costs to be incurred.
The supplier asked NSK for its expert advice to help to reduce the downtime frequency. A team of company specialists investigated the raceways and lubrication conditions in three faulty linear drives in order to determine failure causes. The result: a combination of high loads, penetrating cutting fluids and high ambient temperatures was responsible for the short lifespan.
To counter these issues, NSK recommended using ballscrews that have been specially developed for high speeds and loads. This product range features a customer-specific nut that is tailored exactly to the application and provides greater axial stiffness, not just of the ballscrew, but the entire powertrain, thus increasing machine precision. Moreover, as preload is spread over several balls, service life is increased considerably.
As recommended by NSK, the ballscrews were equipped with the company´s proprietary X1 high-performance seals. These seals prevent any cutting fluid from penetrating the linear system and stop the ballscrew lubricant from contaminating the machining centre's cutting fluid or coolant. The X1 seal also has excellent grease-retention capabilities.
Optimal lubrication of the ballscrew in tough operating conditions is assured by using the K1 lubrication unit, which enables the lubricant's useful life to be prolonged, again contributing to lower maintenance costs.
On a trial basis, two of the new NSK ballscrews were fitted to the machining centres. The results were successful: ballscrew lifespan increased by a factor of six and, furthermore, since installation, there have been no more failures.
The automotive supplier can now benefit from lower spare part costs and, above all, from significantly less production downtime: total yearly cost savings of approximately €266,000 have been achieved.
