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Numerical and experimental study of end-milling process of titanium alloy with a cryogenic internal coolant supply

  • Do Young Kim
  • Dong Min Kim
  • Hyung Wook ParkEmail author
ORIGINAL ARTICLE
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Abstract

Cryogenic machining is an environmentally friendly process; liquid nitrogen (LN2) is sprayed onto cutting tool to reduce cutting temperature, increasing tool life. Cutting temperature and force were numerically predicted during cryogenic assisted milling with an internal coolant-assisted tool holder (internal cryogenic milling) for Ti-6Al-4V alloy. The influence of LN2 on the material temperature throughout the machining was estimated; a numerical model to simulate the initial temperature of work material was discussed by consideration of LN2 injective mechanism. A modified Johnson-Cook model including the cryogenic temperature range was adopted to model material plasticity. The predictive models were validated based on side-milling test. The predicted values captured the trend of experimental result; the minimum and maximum temperature errors were 0.1% and 8.6%, and those for the cutting force were 0.2% and 34.4%. Moreover, comprehensive experimental studies for the cutting temperature, cutting force, chip morphology, and chip composition were performed to understand the effect of cryogenic cooling condition. In internal cryogenic milling, the cutting temperature and force tended to be lower than dry machining. Based on the morphological analysis of the generated chip, the coefficient of sliding friction at tool-chip interface under the internal cooling was reduced by 21.4% as compared to the dry condition.

Keywords

Cryogenic machining Titanium alloy Internal coolant supply Milling 

Nomenclature

σ

flow stress (MPa)

A

material model parameter, yield stress (MPa)

B

material model parameter, strain hardening coefficient

n

material model parameter, strain hardening exponent

C

material model parameter, strain rate coefficient

λ, m

material model parameter, thermal coefficient

ε

plastic strain

\( {\dot{\varepsilon}}^{\ast } \)

dimensionless strain rate

T

temperature variable (°C)

Tr

room temperature (°C)

Tm

melting temperature (°C)

ΔTSZ

elevated temperature at shear zone by plastic deformation (°C)

ΔTWork

heat conducted into work material (°C)

β

proportion value of heat transferred to work material

ρ

density of work material (kg/m3)

S

specific heat of work material (J/kg-°C)

t1

cutting depth (m)

w

machining width (m)

FS

shear force (N)

Φ

shear angle (rad)

αn

rake angle of cutting tool (rad)

VC

cutting speed (m/s)

KWork

thermal conductivity of work material (W/m-°C)

ΔTC

average temperature rise in chip (°C)

θ

angle in slip-line field (rad)

λf

frictional angle (rad)

φ

rotating angle of cutting tool (rad)

f

feed (m/rev/tooth)

dR

radial depth (m)

DTool

Diameter of cutting tool (m)

h

convective coefficient of LN2 (W/m2-°C)

KLN2

thermal conductivity of LN2 (W/m-°C)

Pr

Prandtl number of LN2

Re

Renold number of LN2

D

diameter of injective nozzle (m)

ANozzle

correlation coefficient of injective nozzle

L

characteristic distance for LN2 injection (m)

Tmp

temperature of work material at position and time of m and p (°C)

T

temperature of LN2 (°C)

Fo

Fourier number

Bi

Biot number

αWork

thermal diffusivity of work material (m2/s)

Δt

time for step simulation (s)

Δx

distance between adjacent points for step simulation (m)

RPM

Number of revolutions per minute of cutting tool

ΔTCryo

temperature change due to cryogenic heat source (°C)

qCryo

cryogenic heat source (W/m2)

VChip

cutting speed of chip (m/s)

K0

modified Bessel function with second order of zero

R, R ' , R ' '

distance from cryogenic heat source (m)

TChip

temperature of chip surface (°C)

TLN2

temperature of LN2 (°C)

X, x, Z

Cartesian coordinate representing location of simulated temperature

tch

deformed chip thickness (m)

TWork, Machined

work material temperature at machined surface (°C)

TMaterial

temperature of raw material (°C)

ν, δ, Ψ

temperature factors

ΔTInitial

temperature change caused by initial temperature reduction (°C)

ΔTCryogenic − Shear

temperature change caused by cryogenic heat source at shear zone (°C)

ΔTCryogenic − Chip

temperature change caused by cryogenic heat source at tool-chip interface (°C)

ΔTM

maximum temperature rise in chip (°C)

lContact

tool-chip contact length

P1, P2, P3

cutting forces in cutting, tangential, radial directions (N)

Cs

side cutting angle (rad)

FC, FT, FR

cutting force components (N)

kAB

shear flow stress at shear zone (Pa)

kChip

shear flow stress at tool-chip interface (Pa)

σAB

normal flow stress at shear zone (Pa)

σChip

normal flow stress at tool-chip interface (Pa)

i

inclination angle (rad)

η

chip flow angle (rad)

FX, FY, FZ

cutting forces in x, y, z directions (N)

rf

cutting ratio

PC

distance between teeth of serrated chip (mm)

P

height of serrated chip (mm)

μ

frictional coefficient at interface of tool and chip

r

nose radius (m)

d

cutting depth (m)

Q

amount of heat transferred (W-s)

ΔtC

time for heat transfer (s)

AC

area for heat transfer (m2)

TM

temperature of work material at machined surface (°C)

Tn

temperature of thermocouple at position of n (°C)

dn

distance between machined surface and thermocouple position of n (m)

Notes

Funding information

This research was supported by the technology innovation program (10053248, Development of Manufacturing System for CFRP (Carbon Fiber Reinforced Plastics) Machining) funded by the Ministry of Trade, industry & Energy (MOTIE) of Korea and the Mid-career Researcher Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT of Korea (No. 2018R1A2B3007806).

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Copyright information

© Springer-Verlag London Ltd., part of Springer Nature 2019

Authors and Affiliations

  • Do Young Kim
    • 1
  • Dong Min Kim
    • 2
  • Hyung Wook Park
    • 1
    Email author
  1. 1.Department of Mechanical EngineeringUlsan National Institute of Science and Technology, UNIST-gil 50UlsanRepublic of Korea
  2. 2.Dongnam Regional DivisionKorea Institute of Industrial TechnologyJinju-siRepublic of Korea

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