Production Technology

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  • Topic: Lathe, Milling machine, Cutting
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  • Published : May 21, 2013
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-VW VW Ao
A1
O Z

-VW
V= VW+VT

N Workpiece

Chip

VT
Cutting tool

X Y

Ao

b=f

N

VT
Absolut velocity

a

VW = f (x, y, z)

VT = f (x, y, z)

Basic condition of cutting

Forces in the material of workpiece and tool makes strain that makes elastic and plastic deformation.

(σ1 ) W ≥ (R m ) W (σ1 )T ≤ (σm )T
HVT ≈ ( 3 ÷ 5 ) ⋅ HVW Main parameters of cutting procedure

V V

Vc=Vy
Chip

Vc=Vy

O Z

VZ
X Y

N N

VX VX
Cutting tool

Workpiece

VZ

N

VW , = VW − VW = 0 VT , = VT − VW = V
V ≅ VC
Calculation of the main cutting velocity 1. By broschure Manufacturer’s brosschure contains cutting parameters (cutting velocity, feed, depht of cut, material workpiece ect.,) In this case the tool life is T=60min. 2. Empiric approaches Kronenberg-method T= 60 min, r

=45° for HSS tool

 m  CV V60,  =ε  min  V A 

A=Ao [mm2] .. normal crossection of chip in starting phase

CV [m/perc]….cutting velocity (1.1. table)

εV, ………..experimental data (1.1.table)

1.1. table
TOOL WORKPIECE BRASS BRONZ HSS

εV
1,65 2,23 2,75 500 N/mm2 Rm=500600 N/mm2 Rm=600800 N/mm2

CV
112 80 28,7 50 35 20

ALLOY STEEL Rm=300-

STEEL

2,4

CAST IRON-MILD CAST IRON-MIDDLE
CAST IRON-HARD

3,6

42 26 15

 m  , V60   = V60 ⋅ ξk ⋅ ξ m  min 

ξκ modification factort of setting angle of main edge of tool (1.2. table) ξW modification factor that depend of material of cutting edge and workpiece (1.3. table) 1.2. table
Setting angle of main edge of tool modification factor

κ

20

30

40

50

60

70

80

90

κ 1,27 1,17 1,05 0,95 0,86 0,79 0,75 0,74

1.3. table
Material of workpiece STEEL CAST IRON

Carbon tool steel HSS
0,25 0,3 1 1

Carbid cut
4…8 5 and more

Walich-method T= 60 min,
r

=45° for HSS tool

This equation regarding the HSS tool. This method is more accurate than KRONENBERGmethod. Because this respect not only the normal cross-section of chips but the surface distibution of chips as well. The (CV, a, b) depends on the material of workpiece and tool (1.4. table).

C '  m  V60  = x Vy  min  a ⋅ b 

a [mm] ………... depht of cut b [mm] ……...… wide of chip CV [m/min]…..... cutting velocity x, y……………… experimental data (1.4. table) ∆V................... ... correction factor of the cutting velocity (1.5. table)

1.4. table
HSS ROUGHING Cv x y 55,6 0,26 0,66 36,1 0,26 0,66 28,6 0,26 0,66 160 26 0,16 0,38 66 0,4 0,6 0,6 80 - 100 182 0,4 HB

WORKPIECE

Rm (N/mm2) 450 600 700 30 - 40

STEEL

FINISHING Cv x y 85,9 0,18 0,26 55,8 0,18 0,26 44,3 0,18 0,26 85,1 235 0,4 0,4 0,4 0,4

GREY CAST IRON
BRONZ ALUMINIUM

Correction of the velocity of cutting If the material of the tool is not HSS We can make a correction of the (V60’) value as followes:  m  , V60   = V60 ⋅ ∆V  min 

As (∆V) the correction factor of the cutting velocity 1.5. table Δ – correction factor of cutting velocity
Material of tool

WORKPIECE STEEL CAST IRON Cu, Cu ALLOY Al ALLOY

HSS 1 0.7 1.8 4

CARBIDE 6 4.2 10 24

CERAMIC 14 9.8 25 56

Calculation of the main cutting force

FT
N

FZ=Ff

FX=Fp
Cutting tool
O

Z

N
Workpiece Chip Cutting tool CY FF=

X Y

F

FW The properties of materials of workpiece determine the cutting force value. FS = F
F = F x + Fy + Fz = F c + Fy + Fz

(

)

F c : F p : F f ≈ 5 : 2 :1
Fp = 0,4 ⋅ Fc F f = 0,2 ⋅ Fc

Fc [N ] = kC ⋅ A
A=Ao [mm2]….Normal cross section of chip kC [N/mm2]… Specific cutting force The (kC) specific cutting can be determinated by various way:

kC ≈ c ⋅ Rm
c=4 - 6
kC = kc1⋅1 ⋅ h − z ⋅ Kγ ⋅ KV ⋅ K k ⋅ K s ⋅ K a

WORKPIECE

h

A
CHIP

κ

a
CUTTING TOOL

h=f sinκ

b=f

kC 1·1 [N/mm2]…… (a=1 mm b=1 mm) specific cutting force (1.8. table)

κ.[o]........................ setting angle of main edge of tool h [mm]……………thickness of chip (1.4.picture) a [mm]……………depth of cut b=f [mm]…………wide of chip - feed

Effect...
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