In order to select the right precision ball screw for ensuring a long life of the product, it really helps to have a clear understanding of the necessary key characteristics for manufacturing it. Some external factors may also provide valuable clues about a precision ball screw’s quality. In most instances, poor quality is only discovered after a premature component failure.
According to experienced manufacturer Dynatect, it is possible to select the right precision ball screw confidently by understanding certain manufacturing details and asking the right questions to the manufacturer.
The Manufacturing Process:
The selection of the right kind of steel is the first step in manufacturing high-quality precision ball screws. The formation of microscopic inclusions in the material during the processing of steel is a common threat. This results in the propagation of surface fatigues such as cracks and compromises the life cycle of the ball screws. With advances in steel production technology, it is now possible to significantly reduce the size and number of inclusions. However, the higher quality steels such as vacuum-degassed purified alloy steel are much more expensive.
In order to strengthen the material, the components of a ball screw undergo heat treatment at some stage of the manufacturing process. However, the life of the ball screws may get reduced significantly, if the heat treatment is too shallow. This takes place primarily due to hardness differences between the shafts and the balls, producing microscopic indentations as the balls are compressed within the ball groove. Though this is not an obvious problem, it is advisable to ask the manufacturer upfront about the heat treatment process.
Ideally, the heat treatment of the ball screw shaft should be even, covering the entire length of the thread. If the heat treatment falls short of the necessary threaded length, it is possible that the untreated area may wear prematurely. This area will be softer compared to the rest of the ball groove. Therefore, please ask the manufacturer how quality and consistency are handled during the manufacturing process.
Strict process controls measures are essential throughout the processes of machining and grinding to ensure that the manufacturing is consistent. This is particularly true for grinding bearing journals that require a few microns of tolerances. As reliable accuracy and long product life demand extremely high precision, it is important to have strict temperature controls while grinding the ball screw components.
Deflectors or tubes are used for ball recirculation in most of the proven ball screw designs. Internal ball recirculation is the latest approach that involves no tubes or deflectors. Compared to the conventional recirculation methods, this delivers greater operating speeds and reduced levels of noise because the balls run faster and quieter.
While looking at the product specifications, it helps to have a clear understanding of the ball screw’s application and its operating environment. In order to make the best possible selection, tell the manufacturer about your particular application as well as the environmental factors. Always opt for a manufacturer that clearly understands your applications and has a wealth of experience.
When it comes to selecting precision ball screws, there are many different standards related to everything from mathematical tolerances to materials. Some of the most common standards include ISO 3408, DIN 69051, ANSI-B5.48, and JIS B1191.
Lead accuracy and lead error are the most important specifications for ball screws. Lead error may be defined as the difference between the lead screw nut’s actual travel distance and a specified distance. This parameter is key to determining a ball screw’s accuracy rating. The lead accuracy of a ball screw conforms to four characteristics as described in the JIS Standards, and includes ep, vu, v300, and v2π.