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Application of Ball Screw on High Speed CNC Machine Tool

Views:32     Author:Site Editor     Publish Time: 2020-10-20      Origin:Site

High-speed machining is a high-tech in the 21st century. Its basic characteristics are high efficiency, high precision and high surface quality. It has been widely used in aerospace, automotive industry, mold manufacturing, optoelectronic engineering, instrumentation and other industries, and it has achieved significant technical and economic benefits. It is an important part of contemporary fine manufacturing technology. In order to achieve high-speed machining, first of all must have high-speed CNC machine tools. High-speed CNC machine tools need to have both a high-speed spindle system and a high-speed feed system in order to realize the high-speed material cutting process. In order to achieve high-speed feed, relevant domestic and foreign manufacturers continue to take measures to increase the high-speed performance of ball screws. The main measures are:

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1.Properly increase the speed, lead and number of threads of ball screw. At present, the matchings of the nominal diameter and the lead of the commonly large-lead ball screw are: 40mm×20mm, 50mm×25mm, 50mm×30mm, etc., and the feed speed can reach 60m/min or more. In order to improve the rigidity and load-carrying capacity of ball screws, large-lead ball screws generally use double-threaded threads to increase the effective number of bearing turns of the steel ball.


2. Improve the structure to enhance the smoothness of ball movement. Improve the ball circulation reversal device, optimize the curve parameters of the ball return groove, and adopt the three-dimensional shape of the ball guide tube and the ball return device to truly introduce the balls into the nut body along the lead angle of the internal thread. Make the direction of ball movement tangent to the raceway instead of intersecting.


3. Using "hollow strong cooling" technology. High-speed ball screw generates high temperature due to friction during operation, which causes thermal deformation of the screw, and directly affects the machining precision of high-speed machine tools. Adopting the "hollow forced cooling" technology is to pass the constant temperature cutting fluid into the hole of the hollow screw to force the ball screw to keep the temperature constant. This measure is an effective way to improve the high-speed performance and working precision of medium and large ball screws.


4. For large-stroke high-speed feed systems, adopt fixed screw and rotating nut transmission method. At this time, the nut rotates while moving axially along the fixed screw. Because the screw does not move, it can avoid being restricted by the critical speed and avoid all kinds of problems that occur when the slender ball screw running at high speed. The nut has small inertia, flexible movement and high achievable speed.


5. Further improve the manufacturing quality of ball screws. After adopting the above-mentioned measures, some problems existing in traditional ball screws can be overcome. Japan and Switzerland have been leading the world in terms of high-speed ball screws. The maximum rapid movement speed can reach 60m/min, and in some cases it can even reach 90m/min, and the acceleration can reach 15m/s2. Because the ball screw has a long history, mature technology, wide range of applications, and reduced costs, it is most widely used on general high-speed machining centers and other economical types with medium deviations, feed speed requirements are not too high, and stroke ranges are not too large (less than 4~5m).

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The complete ball screw design and selection, in addition to considering the transmission stroke (indirectly affects other performance parameters), lead (selected in conjunction with the design speed and motor speed), use status (affects the force condition), rated load (especially dynamic load will affect life time), component stiffness (affect positioning precision and repeat positioning precision), installation form (force system composition and mechanical model), load pulsation (determine safety with static load), shape characteristics (affect manufacturability and installation ) And other factors, it is also necessary to check the repeat positioning precision, positioning precision, stability, limit speed, peak static load and limit speed (Dn value) of the circulatory system of the selected specifications. Only after making corrections can the fully applicable specifications be obtained, and then the characteristic parameters of related parts such as motors and bearings can be determined.


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