The Evaluation of Cutting-Force Coefficients Using Surface Error Measurements

Journal of Materials Processing Technology 196 (2008) 42-51

Mariana Dotcheva, Huw Millward, Alan Lewis

Presenter: Andrew Gerla

07 October 2009

Purpose

To provide a new approach for the determination of cutting forces.

References

Cutting Force Affects...Required machine power rating

Tool wear

Tolerances

Surface finish

Required lubrication and cooling

Economy of prototyping and small batches

Old MethodsUse mechanistic models with empirical

coefficients

Require expensive instrumentation to gather empirical data

Require skilled technicians to record and process data

Applicable only to the conditions under which test was performed

Not easily implemented for prototyping or small batch work

The Proposed Method• Cutting force is proportional to tool

deflection

• Tool deflection is related to surface finish

• Empirical relationship may apply to operations with different cutting conditions

Find equations like these:

• Tangential force KT(tc) = Ct1(tc)−kt1

• Radial force KR(tc) = Ct2(tc)−kt2

Method

Method

Discretize cutting tool by:

• Flute

• Angle of rotation

• Discs normal to axis of rotation

Analytical Models

Cutting Forces:

FX(θ(i, k, j)) = KT(EX1 + KREX2)

FZ(θ(i, k, j)) = KT(EZ1 + KREZ2)

FY(θ(i, k, j)) = KT(EY1 + KREY2)

Analytical Models

Tool Deflection:

δ(h) = δs + θs(h) + δt(h)

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Experimental Procedure

Experimental Procedure

Cutting Test• Cut two strips with the same cutting

conditions

• Vary axial depth by ∆a

• Calculate difference in surface finish

• Difference in surface finish mainly due to additional forces from elemental disc ∆a

• 12 different feed rates

Experimental Procedure

Cutting Test• End milling operation

• HSS 3-flute 16mm cutter

• Aluminum alloy 6082

• Down-milling (climb-milling)

• Radial depth 3 mm, axial depths 8 and 9mm

• ∆a = 1mm

Experimental Procedure

Data Acquisition• CNC operated profilometer

• Maximum error 3.2%

• Straight measuring tool paths, 0.1mm increment

Analysis

Results

MATLAB curve fit:

Conclusions

• Analytical model accurately predicts experimental data in similar cutting conditions

• Uncut chip thickness can be calculated

• Study needs more verification of accuracy for different cutting conditions

• Different materials require different coefficients