Vibration Analysis in High Speed Rough and Finish Milling Hardened Steel Presented By: Peter Cannon October 27, 2004 Author: C.K. Toh Published: Journal of Sound and Vibration (accepted 29 September 2003)

Agenda

Function Characterize chatter vibration effects in high speed milling (HSM) Compare chatter effects for –Different cutter path orientations –Different cutter conditions –Different milling directions (up and down) –Different milling processes (rough and finish)

Importance Chatter and vibration affect –Dimensional accuracy –Surface finish –Tool Life –Spindle Life Chatter creates waste Suggestions needed for optimal cutter orientation in HSM

References

Class Relevance The paper investigates relationship between terms introduced in class –Chatter –Down Milling –Up Milling –Profiling Paper recommends guidelines for High Speed Milling to improve tool life and operation efficiency

Design Definition Cutter experiences dynamic forces in 3 dimensions (x, y, z) Dynamic force signatures for each dimension are collected, and a fast Fourier transform is performed to create a frequency spectrum Frequency patterns can indicate presence of chatter

Parameters Down Milling – cutting speed in same direction as part feed (Thick to thin chips) Up Milling – cutting speed in opposite direction of part feed (Thin to thick chips) Rough Milling –10,000 RPM –Fpt =.0667 mm/tooth –Axial Depth = 20, 25, 10 mm –Radial Depth =.5 mm Finish Milling –3,250 RPM –Fpt =.1 mm/tooth –Axial Depth =.5 mm –Radial Depth =.5 mm New Cutter – Flank wear land width <.05 mm Worn Cutter – Flank wear land width ≥.3 mm

Design Principle The design principle here is procedural Results will not affect cutter, spindle, or machine design Results will affect design of milling operation, order and aggressiveness of cut, and orientation of cutter

Experimental Equipment Material –Hardened AISI H13 hot worked steel (HRC 52) –HRC 52 –Face milled and ground as prep Cutters –Tungsten Carbide –6-Flute –10 mm Diameter –45° helix angle –-14° radial rake angle –(Al,Ti)N monolayer coating 2.5 µm thick –Runout < 10 µm Vertical prismatic high speed mill Three-component piezoelectric platform dynamometer Four channel O-scope

Experimental Procedure Rough Milling Fy component analyzed for chatter effects

Experimental Setup Finish Milling

Results Rough Milling (New Cutter) Known Frequencies Tooth Passing Frequency 1000 Hz Harmonics 2000, 3000 Hz Spindle Frequency Hz Chatter should show between 2000 and 5000 Hz

Results Rough Milling (Worn Cutter) Known Frequencies Tooth Passing Frequency 1000 Hz Harmonics 2000, 3000 Hz Spindle Frequency Hz Observations Virtually all amplitudes are increased Up milling appears to have little or no vibrations compared to down

Results Down Finish Milling (New Cutter) Known Frequencies Tooth ≈ 325 Hz Harmonics Observations Upward has higher amplitudes No significant chatter Harmonics with significant amplitudes (Fig. D) indicate cutter deflections (possibly from runout) create low tool life

Results Down Finish Milling (Worn Cutter) Known Frequencies Tooth ≈ 325 Hz Harmonics Observations Figure A and B show chatter between 2000 and 3000 Hz

Results Up Finish Milling (New Cutter) Known Frequencies Tooth ≈ 325 Hz Harmonics Observations Chatter between 2000 and 3000 Hz in Figure C This beating effect could cause chipping on clearance face of cutter

Results Up Finish Milling (Worn Cutter) Known Frequencies Tooth ≈ 325 Hz Harmonics Observations Figures A and B high amplitudes on harmonics No significant chatter

Conclusions For Rough Milling –Lower amplitudes and less chatter when up milling Finish Milling –Upward cutter path orientation increased tendency for chipping –Downward cutter path promoted longer tool life Chatter most predominant when down milling with a vertical downward orientation and a worn cutter Vertical upward (up or down milling) showed no chatter even with worn cutter

Practical Industrial Use Knowing orientations and conditions that lead to chatter can help machinists plan around it Reducing the amount of chatter will help extend tool life and create more dimensionally accurate parts with better surface finish

Technical Advancement Questionable – The interpretation of the frequency signatures is highly subjective Some statements made in the explanation of the frequency charts do not match the charts Asking an experienced machinist would likely produce at least as much information regarding when chatter occurs and how to avoid it

Industries Impacted High Speed Milling industry Mould and die making

Questions