1. Mechanics of Cutting
Mahfudz Al Huda Magister Teknik Mesin Univ. Pancasila, 2010 1
cos
sin
,
1 sin
cos
Cutting ratio, tan
c
o
t
t
r
-r α
r α
45
2 2
45
tan
Shear angle predictions :
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
2. 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
3. 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.
