Dynamic Simulation of Boring Process

B. Moetakef-Imani , N.Z.Yussefian 10 July 2009

Aaron BoydOctober 28, 2009

FUNCTIONTo simulated the dynamic response in boring

processesTo predict vibrations in the operation

Why Important?Tool vibrations result in reduced tool life,

poor surface finish and may also introduce chatter.

Predicting these vibrations allow the operator to know under what conditions the operation will be most efficient.

References

Boring ProcessProcess of enlarging a previously drilled holeHigh Precision and good surface finish

Vibrations3 types

Free/Transient: most common, caused by initial engagement between tool and part, will vibrate naturally until damped

Forced: applied to tool structure, commonly caused by multi-insert tools and run-out of the tool tip; also caused by other machinery; if it hits natural frequency, resonance can occur

Self-Excited: caused when tool cuts, chatter occurs when parameters (DOC, feed rate, etc.) are incorrect; can cause part deflection

Chatter Loop

Equations of MotionEuler-Bernoulli Beam Differential Equation

Natural Frequency

Beam Deflection

Kinematics of Chip-Load FormationCutting Edge Equations

B-Spline Parametric Curves

Instantaneous Chip Load

Cutting Edge Contact Length

Dynamic Simulation

Tests

Test A: • Undergoes transient vibrations, but stabilizes• Chatter free• Vibrates at constant amplitude

Test B: • Process that doesn’t stabilize• Chatter present

Results (test A)

Simulated peak frequency is 672 Hz compared to a measured value of 594 Hz – 12.94% error.

Deviation stems from overestimation by the Euler-Bernoulli beam equation

For x, y and z measurements – 9%, 2%, and 12% error respectively

Results (test B)• simulation shows chatter• chattering freq. at 573 Hz• random oscillation• variation increases• tool plunges into workpiece• makes prediction almost impossible• However, still useful to predict chatter

ConclusionsMore accurate than previous modelsPrevious models only predicted stability

region, while this model predicts dynamic region – very useful

In chatter-free operation, the simulation predicts within +/- 15% of the actual measured value

It is a valid simulation for both smoothing and roughing

Predicts chatter so operators can avoid it completely

Uses all influential parameters

Impacted IndustriesAutomotive IndustryFirearmsPretty much any industry that involves

drilling holes

Useful?There seemed to be a lack of some vital

information, but this information could be found by referring to the references (the refer to them often).

However, the results will allow operators to know what to expect from their operations. They will be able to know what frequencies to expect and will be able to prevent chatter.

Overall, it’s a rather useful paper.