Mechanics of Cutting

Mahfudz Al Huda Magister Teknik Mesin Univ. Pancasila, 2010 1

cos

sin ,

sin1

costan ratio, Cutting

c

o

t

tr

α-r

αr

45

2245

tan

:sprediction angleShear

Velocities, Vc V sin

cos

r = cutting ratio

t0 = depth of cut, mm

tc = the chip thickness, mm

= shear angle,

= rake angle,

= coefficient of friction

= friction angle,

V = cutting speed, m/min

Vc = the velocity of the chip, m/min

Cutting Mechanisms

Mahfudz Al Huda Magister Teknik Mesin Univ. Pancasila, 2010 2

Asumsi-2 dlm membahas cutting mechanism:

•Proses pemotongan adl orthogonal cutting.

•Tool Speed, VT = 0

•Workpiece Speed = Cutting Speed = V

•Benda kerja terpotong krn terjadi deformasi plastis berupa slip

pd bidang geser (shear plane) akibat tekanan geser (shear stress).

•Slip terjadi secara teratur pd lapisan tipis geram dg tebal X dan

bergeser sejauh S, maka regangan geser (shear strain):

dimana : shear angle, : rake angle.

•Chip speed VC, dan Shear speed VS:

•Shear strain speed:

•Cutting ratio:

t1 & t2: tebal geram sebelum dan sesudah dipotong

•Cutting force R:

FH & FV: gaya potong horizontal & vertical, dpt diperoleh dg

mengukur gaya tsb menggunakan strain gauge atau tool

dynamometer.

Tool

Tool

Workpiece

Workpiece

Cutting Mechanisms

Mahfudz Al Huda Magister Teknik Mesin Univ. Pancasila, 2010 3

•Koefisien gesek (friction coefficient) pd rake face:

: friction angle, F& N: gaya gesek & gaya normal pd rake face.

•Gaya-gaya pd bidang geser (shear plane):

FS & FN: gaya geser (shear force) & normal pd shear plane.

•Sudut geser (shear angle) :

shg sudut geser dpt dihitung dg mengukur tebal geram sebelum dan sesudah pemotongan dan rake angle.

•Gaya-gaya pada rake face:

•Tegangan geser (shear strain) pd shear plane:

dimana AS: luas bidang geser, b: cutting width, S & S: tegangan geser (shear stress) & tegangan normal

(normal stress) pd bidang geser.