| Abstract [eng] |
The aim of this research is to evaluate the real world application and advantages of vibration-assisted aluminium machining process in comparison to conventional machining process by comparing surface roughness in unstable cutting conditions. In order to accomplish this goal, four task were set: 1) to analyze scientific research; 2) to do a numerical simulation of the machining process; 3) to verify the results of the simulation by experiments; 4) to compare conventional machining process to vibration assisted machining process economically. After the analysis of scientific literature, there was a clear tendency of improved machining results in all areas – tool wear reduction, surface quality improvement, cutting force reduction, etc. However, all of the experimentation was done in stable conditions. Therefore, potential analysis of high frequency excitation effect on surface roughness seemed relevant. Afterwards, numerical simulation of tool excitation frequency and workpiece frequency response was carried out. After simulation the excitation frequency was selected and potential reduction in vibration amplitudes was evaluated. Experimental session consists of 4 endmill tests with various levels of deterioration – from new endmill to severely damaged. Each endmill made two cuts – conventional cut and vibration assisted. Afterwards, surface roughness was measured and results compared. These conclusion were made: 1. After analyzing scientific literature and previously done experimentation the conclusioncan be made that vibration assisted machining currently is very relevant as many different processes are investigated with a lot of potential results (surface finish improvement, tool life extension, etc.). However, all analysis is based on stable cutting conditions. 2. After carrying out the numerical simulation of tool resonant frequency and two step workpiece frequency response analysis, two conclusions can be made: the excitation frequency of the tool should be ~23 kHz (minor adjustments may occur because the tool stickout might variate in small way). Potentialy, the vibration amplitudes at different points can be reduced 0,3 – 50,8 times. This great variation shows that improvement of vibration amplitudes very strongly depend on cutting conditions. 3. After experimentation session, the results show that in all cases the high frequency excitation improved the surface roughness compared to conventional milling. The improvement level depends on the severity of the tool wear. When the tool is new, the surface quality improvement was 13%, but when the tool is blunt and has some slight chipping at the cutting edge, the surface roughness improvement reaches only 10 – 11%. Finally, severely damaged tool showed only 7 % improvement in surface roughness. 4. On average, the improvement was 10 % therefore the tool life could be extended up to 10 %. This would save companies ~4,5 €/endmill used. Finally, potentionally other unstable cutting conditions could be improved by high frequency excitation of the tool. |
