NSK Develops Ball Screws for Next-Generation High-Accuracy Machine Tools

Reduced motion errors help improve machine tool productivity through higher quality surface finish

Eliminates or reduces time needed for burnishing/polishing

NSK has developed new ball screws that contribute to achieving higher surface finish quality for high-accuracy machine tools used in die and mold machining and other applications. The new product embodies ongoing NSK research and development into improving machining surface quality, thereby eliminating or reducing the time needed for burnishing/polishing work while also reducing the amount of drive torque.

NSK will continue to contribute to the elimination or reduction of surface finishing processes by improving the surface quality achieved in machining, and to achieving energy savings by reducing drive torque.

The new ball screws will be exhibited at “JIMTOF 2022 The 31st Japan International Machine Tool Fair” to be held from November 8-13, 2022.

NSK plans to start taking orders in select regions from April 2023, followed shortly by a global rollout. NSK aims to achieve sales of 100 million yen by 2024 of ball screws adopting this technology.

Background

In recent years, machine tools such as 5-axis milling machines have been demanding higher accuracy to produce higher quality die/mold surfaces, and the ball screws used in these machines must further improve their motion accuracy.

When a ball screw reverses direction, sudden fluctuations in friction cause "quadrant glitch" motion errors with two peaks, leaving streak marks on the machined surface and reducing surface quality. Numerous studies have been conducted on quadrant glitches, and the first peak can be corrected through numerical control (software-based servo controller compensation) of machine tools. However, it is more difficult to fully compensate for the second peak due to the combined effects of more factors compared to the first peak, and the machining industry is seeking a solution to this problem.

Features

Using NSK Real Digital Twin simulation and friction analysis, we have developed a new ball screw with an optimized internal design by understanding the underlying mechanism of the friction fluctuations in ball screws that causes quadrant glitches.

1. Stable drive torque during reversals eliminates a quality roadblock

Reduced friction fluctuations when the ball screw reverses direction of motion, thereby improving motion accuracy and reducing quadrant glitch motion errors to nearly eliminate the second peak.

2. Reduced friction fluctuations

Friction fluctuations have been reduced by up to 20% contributing to reducing the height of the first peak.

3. Compatible with existing mountings

Mountings are fully interchangeable with those of conventional products, allowing ball screws with quadrant glitch control to be used without costly equipment changes.

Relationship between motion error and frictional torque when reversing the direction of motion

Benefits

The combination of NSK's new product and software servo controller compensation can significantly improve the quality of the machined surface.

The elimination of the need to compensate for the second peak facilitates adjustments (parameters, etc.) of the machine tool.

The improved surface quality eliminates or reduces the need for the previously required burnishing/polishing processes, reducing lead times and energy consumption.

Reduced drive torque contributes to energy savings in machine tools.

Specifications

Shaft Diameter: 25-63mm

Lead: 5-30mm (Lead / Shaft Diameter ≤ 1/2)

Preload Type: Offset preload (Z preload), Double nut preload (D preload), Spring type double nut preload (J preload)