Ball screws, also known as linear ball screws, are mechanical actuators designed to convert rotational motion into linear motion and translate torque into thrust, resulting in the ultimate goal of moving devices and parts along a single axis. The former is performed by a ball screw nut, which runs up and down the helical grooves of a screw on ball bearings. To work, the threading of the nut and the threading of the screw must match one another. Together, the nut and threaded screw are known as a ball screw assembly; their movement powers torque and thrust.
In more detail, this movement begins with ball bearings rolling in the grooves of the threads, which simultaneously provides a smooth motion and a rolling friction. Next, the ball bearings encounter a deflector, stationed inside the nut’s ball return system, which reroute them to the opposite end of the nut. Thus, the balls continuously recirculate.
Ball screws are used for a wide variety of applications. These include: in steppers for semiconductor manufacturing, in robots, in precision assembly equipment, in machine tools, in automobile power steering motors, and in missiles and aircraft to move control surfaces, particularly electric fly by wire (FBW) systems. They serve these applications with levels of efficiency up to approximately 90%, all the while maintaining low levels of energy consumption. They also offer close tolerances, an ability to both withstand high thrust loads and low levels of friction. Read More…
To meet the various requirements of their applications, ball screws are available in multiple configurations, such as miniature, rolled, ground, and precision.
Miniature ball screws are popular for use in lasers, gauge measurement devices, semiconductors, medical instruments, and other small devices that require smooth and precise linear motion.
Rolled ball screws are named as such because, beginning as blank metal workpieces, they are formed through cold rolling. These ball screws offer the advantage of a positional precision of several thousandths of an inch per foot.
Ground ball screws, which boast extremely high levels of precision, are made in three steps: machining to gross shape, case hardening, and grinding. This grinding takes place on rapidly spinning machines that are coated with abrasive materials. This treatment bestows upon the finished ground screws the ability to withstand temperatures that would normally distort their shape and mar their efficiency. Ground ball screws are best for applications that require not only high precision, but high stiffness.
Finally, precision ball screws are simply a wider category of ball screws that carry exceptionally high levels of accuracy, or precision.
In addition to these standard configurations, buyers may request ball screws made with custom configurations. Custom ball screws offer the customer the assurance that they will encounter no problems in terms of productivity or compatibility. Common customizations include the conversion to the metric system (mostly for use outside of the United States), single or double nuts, customized screw ends, and customized nut designs.
Also, buyers may request lead screws, which, while not technically ball screws, are occasionally categorized as such, because they do convert rotational motion into linear motion. Lead screws are made up of a threaded shaft and a nut that generate friction via sliding, rather than through the rolling that is the practice of ball screws. Because they must rely on sliding action only, lead screws have a relatively low level of efficiency that sits anywhere between 25% and 75%. Commonly, lead screws are made with an acme screw design, which has a distinct threading pattern and shape.
Other choices customers may make about their ball screws or ball screw assemblies are whether the nuts are made from a plastic or a metal and whether they would like the shape of their nut ends to be rounded, flanged, or something else. Note that the shaft of the ball screw is always machined from steel. Quite commonly ball screws join other linear motion parts, such as carriages, drive units, linear slides, and linear actuators, to create a smooth, precise, and complete movement system.
No matter its configuration or whether it is identified with American or metric standards, ball screws are a great asset to manufacturers and engineers in the aerospace, automotive, computer, and electronics industries alike.
What’s more, as technology has advanced, ball screw designers have been able to produce increasingly precise devices. With the help of precision screw forming (PSF) processes, they have reduced the production of inferior products, such as lopsided or off-center ball screws.
With the help of automated equipment, computer programs, and special sensors, they can more easily find the center of a steel rod meant to be machined or rolled into a screw. With this same technology, they can also cut and grind material better, leading the more accurate and consistent ball screw threading. The better the threads and grooves, the smoother and faster ball bearings can work.
Also, with the help of computer and/or operator supervision, an assembly’s nut and carriage can be much more tightly controlled, resulting in fewer glitches, more concise movements and quieter operations.
A well-maintained ball screw that is properly lubricated and kept free of interferences like dust, will prove itself to be an integral component of many operations.