A novel approach to minimizing material loss for computer numerical control flank-regrinding of worn end mills

Abstract

Flanks of end mills are prone to wear in a long machining process. Regrinding is widely used in workshops to restore the flank to an original-like state. However, the traditional method involves material waste by trial and error and dramatically decreases the potential regrinding. Moreover, over-cut would happen to the flutes of worn cutters in the regrinding processes because of improper wheel path. This study presented a new approach to planning the wheel path for regrinding worn end mills to minimize material loss and recover the over-cut. In planning, a scaling method was developed to determine the maximum size of the new cutter according to the similarity of cutter shapes before and after regrinding. Then, the wheel path is first generated by envelope theory to regrind the worn area with a four-axis computer numerical control grinder according to the new size of cutters. Moreover, a second regrinding strategy is applied to recover the flute shape over-cut in the first grinding. Finally, the proposed method is verified by an experiment. Results showed that the proposed approach could save 25% of cutter material compared with the traditional method and ensure at least three regrinding times. This work effectively provides a general regrinding solution for the worn flank with maximum material-saving and regrinding period.

Key words： flank-regrinding; worn end mill; wheel position and orientation; material loss; over-cut

Nomenclature

Abbreviations
CNC	Computer numerical control
FEA	Finite element analysis
GA	Genetic algorithm
ID	Inner diameter
OD	Outer diameter
Variables
[dx, dy, dz]	Gradient of the ground reaction curve
d	Length of PrOT
fphase, frelief	Parametric equations of solving flank phase angle θf and relief angle α
G(h, θ)	Parametric representation of the wheel
hd	Drop distance
h^{\ast }\left({\theta }^{\ast }\right)	Solution of contact curve
Η	Saving rate of cutter materials
HGP	Length from point G to point GP
L	Length of the PAPC
Μ	Loss rate of the flute angle
n(h, θ)	Wheel surface normal
r1	Radius of arc PFPE
r2	Radius of arc PBPF
rt	New radius of the traditional method
rT	Original end mill radius
rT1	Radius solved by the scaling method
rT2	Radius solved by the traditional method
R	Radius of the grinding wheel
RZ(ω, t)	Helix motion’s kinematics matrix
t	Machining time
v	Translation velocity of wheel
v(h, θ, t)	Tangent vector of the contact curve
WT(h, θ, t)	Equation of the wheel path
[x(i), y(i)]	Points clouds in various section
[x_{P_0},y_{P_0}]	Position of the deepest point P0
α	Relief angle
α0	Original relief angle
β	Angle by which the grinding wheel is rotated counter-clockwise around the XT axis
ξ(HGP, β, rT2)	Error between the calculating parameter value and the original parameters
θ	Arc parameter in the equation of the wheel
θf	Flank phase angle
θf0	Original flank phase angle
θp	Checking phase angle
{\varphi }_1, {\varphi }_2	Arc parameters in the parametric equations of PFPE and PBPF
Φ	Original flute angle
γ	Rake angle
τ	Arc parameter in the equation of PEPD
\eta	Saving rate of cutter materials
\lambda	Helix angle
μ	Loss rate of the flute angle
μ0	Arc parameter in the equation of PAPC
μ1	Arc parameter in the equation of PCPB
Δ	Radial wear
ω	Velocity of cutter

Acknowledgements

This research was supported by the National Key R&D Program of China (Grant No. 2020YFB1711603), the Key Technology R&D Program of Shandong Province, China (Grant No. 2020CXGC010304), and the National Natural Science Foundation of China (Grant No. 52175473).

Conflict of Interest

The authors declare that they have no conflict of interest.

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