Chatter in Metal Cutting

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Chatter in Metal Cutting

• Kristen Hayes
• Dr. Scott Smith
• Bethany Woody
• July 31, 2004

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Agenda

• Purpose
• Why is chatter a problem?
• Background
• What is chatter?
• What affects chatter?
• Project
• Conclusions
• SFS Participation
• Questions

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What is Chatter?

• Chatter is a self-excited vibration that occurs
  during metal cutting
• Vibration between tool and workpiece causes
  regeneration of waviness
• Cutting force becomes variable, machined surface
  becomes undulated

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Why is Chatter a Problem?

• Can leave bad surface finish
• Can cause tool or machine to break
• Chip width and Metal Removal Rate
  (MRR(cm3)a(mm)fr(mm)v(m/min)) must be kept
  below the limit at which chatter occurs.

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What affects Chatter?

• Axial depth of cut
• Radial depth of cut
• Spindle speed
• Chatter frequency is directly related to natural
  frequency (fn), depth of cut, and spindle speed.

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Regeneration of Waviness
kristen
kristen

• Vibration between tool and workpiece causes
  waviness
• Next pass of tooth encounters surface and
  produces chip with variable thickness
• Regeneration of waviness is remedied when tooth
  passing frequency chatter frequency

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Frequency Response Equations
www.mmsonline.com
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Project

• Detecting Chatter
• Discovered how different tools and tuning could
  affect chatter
• Found several ways to detect and correct chatter
  using commercially available software

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Tools

• The dynamics of the tool can affect chatter
  greatly
• Changing or buying new tools to avoid chatter
  expensive and time consuming

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Harmonizer

• Helps user to find maximum depth of cut and
  corresponding spindle speed
• Uses microphone to listen to and process milling
  operation to determine chatter
• Matches chatter frequency to natural frequency by
  changing spindle speed
• Chatter frequency spindle speed(rpm) number
  of teeth
• Regulates user to another spindle speed where a
  greater depth of cut is possible

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TXF

• Calculates frequency response function and plots
  the Real and Imaginary parts of FRF
• Makes stability lobe diagrams which show doc vs.
  spindle speed and where chatter occurs

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Stability lobe diagram

• Displays stable depth of cut (mm) vs. spindle
  speed
• Above the line chatter below the line - stable

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Conclusions

• This project is part of a larger project which is
  ongoing

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SFS Participation

• Gave me a chance to study something I probably
  wouldnt have seen as an undergrad
• Gave me the opportunity to see what research is
  like
• Before was considering grad school, now I
  definitely would like to go

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Questions?