Analysis of spindle bearing load with regard to the false brinelling effect caused by machine hammer peening

摘要

Machine hammer peening (MHP) is a high-frequency incremental forming process for surface treatment, which is used on milling machines. Because of the stationary motor spindle as a result of the pneumatic and electrical connections to the hammer head, point loads can occur and may initiate false brinelling wear on the spindle bearing rings. The aim of this work is an experimental and numerical analysis of the interdependencies between MHP reaction forces on the spindle adapter and bearings as well as the associated false brinelling wear of the spindle bearing rings during MHP. Firstly, MHP reaction force measurements on a servo-mechanical press with high stiffness with variation of frequency, electrical power, and time were conducted. Secondly, the spindle bearing wear during MHP was analyzed using fatigue tests and complementary simulations by means of numerical FE-software Abaqus 6.14 and software NewSpilad and WinLager. Thirdly, the effect of damaged spindle bearings on the milling operation was analyzed by means of an endurance test system for bearings. The results showed that false brinelling wear on spindle bearing rings occurs at frequencies around f (mhp) = 100 Hz and maximum reaction forces of F (compr.) = 3,450 N during MHP on milling machines. Furthermore, a significant raise in temperature of the damaged spindle bearing from T (initial) = 25 A degrees C to T (final) 80 A degrees C during fatigue test using 5.76 x 10(6) load cycles could be detected. Thus, a damaged spindle bearing is not suitable for application in permanent operation. However, at frequencies around f (mhp) = 200 Hz, no false brinelling wear could be detected and the temperature did not raise significantly during fatigue test. Therefore, this undamaged spindle bearing can be used without impairment for permanent operation.