Ball screws replace hydraulics in powder presses

Metal-cutting tools such as carbide inserts are typically produced using powder press technology. This entails filling a metal powder alloy into a die and pressing into the desired shape before final sintering. At the end of the process, tool manufacturers require inserts that are as close as possible to the final profile, as additional finishing is both expensive and challenging; the sintered inserts are extremely hard.

Focused on providing customer solutions that overcome issues such as these is Osterwalder, which is based in Lyss, around 15km from the Swiss capital, Berne. To help deliver extra precision into the powder pressing process, the company recently took the decision to introduce new drive systems: the CA SP Electric and CA HM Electric series. This ´Direct Drive Technology´ (DDT) with servo-electric motors and NSK ball screws, replaces the former hydraulic drives, which are now only used in presses requiring exceptionally high forces.

Using DDT, pressing is performed with far greater accuracy, as Michael Sollberger, Development Engineer at Osterwalder, confirmed: “We can position these systems to within 1µm and achieve very high repeatability levels.”

Heavy-duty ball screws from NSK´s HTF (High Trust Force) series are responsible for the linear motion of Osterwalder presses. Precise synchronisation of movement is important as any interruptions or irregularities in the process can lead to dimensional errors, or even cracked inserts during sintering.

HTF ball screws also permit very high traverse rates, thus helping to minimise cycle times. Furthermore, extremely high axial force can be delivered, with patented geometry ensuring equal load distribution over all of the balls in operation. In combination with special ball separator technology, this prevents premature wear and assures very high reliability.

Along with high precision and good controllability, users of Osterwalder powder presses featuring the new drive systems can also achieve energy savings of around 80%. A powder press with a hydraulic drive and pressing force of 160kN has an energy consumption of up to 15kW.

In contrast, a servo-electric system requires only 2.5-3.5kW. Since Osterwalder customers typically operate between 10-70 powder presses, the potential cost savings are vast.

A further advantage of adopting the ball screw drive solution is that the presses now take up much less space. In addition, servicing can be reduced because there are no hydraulic control valves or other high-maintenance components, while working temperatures are more constant as no heat is being produced by the hydraulic system.

Noise reduction is another benefit, as Sollberger explained: “Our hydraulic systems operate at just below the 75dB limit, whereas the servo-electric systems are very quiet, only 58-60dB.”

Various NSK ball screws are used in the CA SP Electric and CA HM Electric series, moving the upper and lower die together simultaneously. Osterwalder first introduced servo-electric drives on its 160kN presses, then its 320kN models.

In total, more than 100 such presses are now operating successfully in the field. Looking ahead, this trend could continue as NSK states that pressing forces of up to 4000 or even 5000kN can be sensibly transmitted with the HTF series.

HTF ball screws are available in a variety of diameter, recirculation systems, lead and seal options, and can be complemented by heavy-duty NSK ball screw support bearings (TAC series) and linear guides (RA series).

As well as carbide pressed parts, the technology is equally applicable to components made from iron powder, ceramic and magnetic materials. HTF series ball screws have also been adopted widely by manufacturers of plastic injection moulding machines.