The cause and prevent machine crawling phenomenon

Machine tools crawl phenomenon reason and prevent 2019 - 03 - 18 ( Shen a lathe factory) What is the crawling machine? In brief, the speed of the machine tool feed moving parts has obvious cyclical changes, even appear alternately instantaneous pause and impulse phenomenon, called the crawl. Due to a crawl irregular intermittent movement, not only destroyed the required operation rule, and shock and vibration of the great harm of precision of feed. Imagine coolie school when I was a sophomore in Turner practice, in order to achieve high accuracy, very low very low, adjust feeding results processing of parts size accuracy and roughness are unqualified, want to come that is the fault of the crawling phenomenon of. Crawl phenomenon causes and influencing factors: if anyone has an impression of college physics, should be able to remember a lot of times the kinetic friction factor and static friction factor is not equal. Crawling main reason is that the relative sliding between the surface of the friction factor and the difference between the static friction factor exist, as well as the friction factor with the increase of the relative sliding velocity fell sharply, and sliding friction in the process of dynamic negative damping. It in addition to related to the friction characteristics, but also with the system natural frequency, changes in stiffness, friction drive system, the system damping. By measuring found that the crawling phenomenon exists' critical velocity, when driving at a faster rate than the critical speed, the moving parts to drive speed to do uniform motion in a straight line; When driving speed is less than the critical speed, the moving parts of sliding speed will be equal to zero at a certain moment, appear the crawling phenomenon. When driving speed is equal to the critical speed, critical state is somewhere in between. In calculating the critical speed formula is as follows: type: vc critical speed & Delta; The difference between the static and dynamic friction force F & delta; Damping coefficient K of vibration system stiffness of transmission system, N / m) The weight of the moving parts (m. kg） Damping coefficient can choose according to the following table: crawl phenomenon is harmful to machining, that how to eliminate the crawling? And the way to listen to me slowly. Eliminate crawling measures: in general, eliminate crawling need in the process of machine tool design, manufacture, use take action, in general, there are 6 kinds of methods can eliminate crawl: 1) Use rolling friction, fluid friction instead of sliding friction, such as using ball screw, static pressure nut, rolling guideway and hydrostatic guideway, change the friction surface friction properties, to eliminate creep; 2) The use of special lubricants ( The guide rail oil or prevent climbing oil) , can greatly reduce the friction surface of the difference of the static and dynamic friction, reduce the critical speed, eliminate creep; 3) Select the appropriate friction pair material, reduce the friction factor; 4) Improve the quality of rail manufacturing, at the same time should also guarantee the quality of heat treatment of castings, otherwise guide will use for a period of time after deformation, can also cause creep; 5) Shorten the transmission chain, reduce the amount of transmission parts; 6) Appropriate to improve the stiffness of the transmission job components, narrow the span of each transmission shaft, reasonable decorate the position of the shaft parts. We according to the above crawling prevention measures, for our new CAK numerical control lathe made comprehensive optimization improvement, the product by the laser inspection qualified rear can leave the factory, the masses of users, please rest assured to use.