Vibration Analysis in High Speed Rough and Finish Milling Hardened Steel

Presented By: Peter CannonOctober 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

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 166.67 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 166.67 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