Introduction to Machining Dynamics

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The science of Machining Dynamics is the vibration or frequency of the tool point self-generated during machining often resulting in chatter. Understanding Machining Dynamics will have the SINGLE GREATEST IMPACT on your milling operations.

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Introduction to Machining Dynamics

  1. 1. ©Copyright 2010 BlueSwarf LLC<br />Introduction toMACHINING DYNAMICS<br />BlueSwarf® Technical Series<br />
  2. 2. The science of Machining Dynamics is the vibration or frequency of the tool point self-generated during machining often resulting in chatter. Understanding Machining Dynamics will have the SINGLE GREATEST IMPACT on your milling operations<br />
  3. 3. 4/18/2010<br />To begin to understand machining dynamics, you must recognize that the cutting tool is part of an entire cutting system<br />
  4. 4. 4/18/2010<br />The cutting tool is gripped in a toolholder<br />1<br />
  5. 5. 4/18/2010<br />2<br />The toolholder is pulled into a spindle<br />
  6. 6. 4/18/2010<br />3<br />The spindle is rotating on bearings and is mounted into a the headstock<br />
  7. 7. 4/18/2010<br />4<br />The headstock slides up and down on guide ways<br />
  8. 8. 4/18/2010<br />3<br />2<br />4<br />Each of these connections creates a flexible joint<br />1<br />
  9. 9. Force is applied when a tooth of the tool makes contact with the workpiece<br />
  10. 10. The flexibility of the system allows it to deflect. The amount of the deflection, or the amplitude, is determined by the force applied which is in proportion to the depth of cut<br />
  11. 11. When the tooth releases the tool then rebounds, or responds, back in the opposite direction, past the center line. Think of Newton’s third law of motion, “For every action there is an equal and opposite reaction”<br />
  12. 12. Then the tool continues to vibrate back and forth until it is fully dissipated. The rate and duration of the vibration is the tool point’s natural frequency<br />
  13. 13. An example of natural frequency is to hang a ruler over the edge of a table and flick the end with your finger. The ruler will vibrate at its natural frequency<br />
  14. 14. The vibration is not allowed to fully dissipate. The next tooth impacts the workpiece and the process starts all over again. For example a four flute tool, running at 15,000 RPM, will have 1000 impacts per second<br />
  15. 15. There is an up and back vibration and the tool is also rotating. If not perfectly in sync each tooth will impact the workpiece at different points within the up and back cycle.<br />If the rotating tool tooth passing frequency is not perfectly in sync with the back and forth natural frequency, each tooth will impact the part at a different depth, changing the force applied<br />
  16. 16. Here is the programmed chip thickness that is provided by the cutting tool manufacturer for maximum tool life<br />4/18/2010<br />
  17. 17. 4/18/2010<br />If the tool rotation is not in sync one tooth will have a much smaller “instantaneous “ chip thickness<br />
  18. 18. 4/18/2010<br />Another tooth will have a much larger instantaneous chip thickness<br />
  19. 19. 4/18/2010<br />Tool Life<br />This excessive instantaneous chip thickness will cause premature tool failure<br />
  20. 20. 4/18/2010<br />Energy Use<br />The excessive instantaneous chip thickness will also increase spindle load and energy consumption<br />
  21. 21. One revolution of the cutter looks something like this. These rapid frequency change caused by the chip thickness variation results in audible chatter or feedback like a microphone<br />
  22. 22. 4/18/2010<br />Because the unequal cuts leave a wavy surface, each subsequent pass creates even greater chip thickness variations and the chatter gets much, much worse. We call this regenerative chatter<br />
  23. 23. 4/18/2010<br />The BlueSwarf® Tool Dashboard™ enables users to determine the maximum stable speeds, cutting depths and feed rates for any milling tool in any material<br />We do this by measuring the tool point and synchronizing the tooth passing frequency (RPM) with the cutting system’s natural frequency<br />
  24. 24. Results<br />Up to 5X increase in metal removal rate<br />DOUBLE tool life<br />Reduce energy consumption by up to 75%<br />Plus<br />Improved Surface Finishes<br />Reduced Maintenance Costs<br />Lower Scrap Rates<br />
  25. 25. 4/18/2010<br />Any change to any component of the cutting system will change the tool point frequency and its performance<br />Factors Include:<br /><ul><li>Cutter Length
  26. 26. Cutter Diameter
  27. 27. Cutter Projection
  28. 28. Number of Teeth
  29. 29. Spacing of Teeth
  30. 30. Tool Coating
  31. 31. Workpiece Material
  32. 32. Gripping Force of Toolholder
  33. 33. Weight of Toolholder
  34. 34. Run-out
  35. 35. Imbalance
  36. 36. Drawbar Force
  37. 37. Bearing Preload</li></ul>…and many more<br />
  38. 38. No paper speed and feed chart can accurately predict the performance of every different cutting system combination and its unique tool point frequency<br />
  39. 39. For more information:<br />www.BlueSwarf.com<br />

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