In the transmission world, the ball screw assembly is an indispensable key mechanical component. It is the most commonly used transmission element on tool machinery and precision machinery. Its main function is to convert rotational motion into linear motion. Due to its small friction resistance, ball screws are widely used in various industrial equipment and precision instruments.
CNC Ball Screw Assembly
The CNC ball screw assembly consists of a screw and a nut, each with matching spiral grooves, between which the balls roll, providing the only contact between the nut and the screw.
When the screw or nut rotates, the balls are deflected by the deflector into the ball return system of the nut, and they pass through the return system in a continuous path to the opposite end of the ball nut. The balls then exit from the return system into the ball screw and nut thread raceway to recirculate in a closed loop.
The ball nut determines the load and life of the ball screw assembly. The ratio of the number of threads in the ball nut loop to the number of threads on the ball screw determines the extent to which the ball nut will reach fatigue failure (wear) faster than the ball screw.
Load Calculation of Ball Screw Assembly
Even if the ball screw is not used frequently and the speed is low, its maximum load must be much smaller than the basic static rated load of the ball screw assembly.
Basic Static Rated Load Co
When a certain axial static load causes the sum of the permanent deformation of the contact point between the raceway and the steel ball (including the nut and the nut shaft) that bears the maximum stress of this load and the permanent deformation of the steel ball itself to reach 0.01% of the steel ball diameter, this load is the basic static load.
Calculation of Maximum Allowable Load
Fₘₐₓ=Cₒ/fₛ
Here
fs: static allowable load factor
Normal operation: 1.2~2
Operation with vibration: 1.5-3
Life of Ball Screw Assembly
Fatigue life: life when the screw is eroded
The fatigue life of the ball screw can be calculated by the basic dynamic rated load, just like the rolling bearing.
L₁₀=(C/F)³x1000
( L_{10} ): Expected life of 90% of the ball screw under rated load (in hours).
( C ): Rated dynamic load of the ball screw.
( F ): Actual working load.
Summary
Calculating the load capacity of CNC ball screw assembly is a key step to ensure the stability and reliability of the mechanical system. Through reasonable calculation and design, the stable operation of the mechanical system can be ensured.
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