Milling
Indexable Milling Tools Technical information
Common problems and solutions for milling Main points of solution and Selection inspection of tool material
Improper geometry shape of cutting edge
Improper geometry shape of cutting edge
Improper geometry shape of cutting edge
Cutting condition Improper technology
Improper cutting condition
Improper geometry shape of cutting edge
Power, gap
Other
Chippings are twisting and jamming
Overhang of tool
Great vibration
Clamping system of workpiece
Improper cutting condition
Worse planeness Improper geometry shape of cutting edge and parallelism
Improve the rigidity of tool
Improper geometry shape of cutting edge
Improper cutting condition
Check the run-out of end face
Side collapse
Improper cutting condition
Improper cutting condition
Wiper
Machining precision
Causing burr
Examine the geometry shape of Minor cutting edge.
shape of cutting edge
Abrasion of tool Great vibration of milling tool
Increase the width of chip pocket
Improper cutting
Coarse surface
Fracture condition of cutting Improper geometry edge
Thermal cracking
Number of teeth
Improper geometry shape of cutting edge
Strength of cutting edge
Improper cutting condition
Approach angle
Severe abrasion of rake face
Improper geometry shape of cutting edge
Rake angle
Fracture of tool nose
Technical information
Improper cutting condition
Machine clamping system
Tool shape Cutting liquid
Indexable milling tools
Severe abrasion of clearance face
Change the diameter and width of milling tools
Cutting depth
Feed rate
Cutting speed
Fault content
Build-up edge
B 164
Material with perfect toughness
Material with higher hardness
B
Cutting condition
Milling
Indexable Milling Tools Technical information
Difference and selection between down milling and up milling
B
Vf
Vf
Up milling
Technical information
magnified X
Indexable milling tools
Y
X
magnified Y Dowm milling
Climb milling (also called down milling): the feed direction of workpiece is the same as that of the milling rotation at the connecting position. Conventional milling (also called up milling): the feed direction of workpiece is opposite to that of the milling rotation at the connecting position. In down milling, the major force of cutting edge borne is compressive stress; in up milling, cutting edge bears the tensile stress. The compressive strength of cemented carbide material is larger than its tensile strength. In down milling, chip becomes thin from thick gradually , cutting edge and workpiece press each other. The friction between edge and workpiece is small, thus can reduce the abrasion of edge , the hardening of workpiece surface and the surface roughness (Ra). In up milling, chip becomes thick from thin gradually. When insert cutting into the workpiece, it generates strong friction and more heat than down milling, and make workpiece surface harden. In up milling, because horizontal direction of cutting force that milling cutter conducting on workpiece is opposite to the feed direction of workpiece, therefore the lead screw of worktable joints closely with one side of screw nut. In down milling, the direction of cutting force is same as the feed direction. When edge’s radial force on workpiece is big enough to some extend , the worktable will bounce left and right, thus make the gap fall behind. The gap will return to front side along with the continuing rotation of lead screw. At this moment the worktable stops motion, however it will bounce left and right again when the radial cutting force is big enough to some extend again. The periodical bounce of worktable will cause poor surface quality of workpiece and tool breakage. When use end mills for down milling, every time the edges begin the cutting at workpiece surface, therefore end mills are not suitable for machining the workpiece with hardened surface. Up milling is recommended for milling the thin-wall components or square milling with the demand of high precision.
B 165
Milling
Indexable Milling Tools Technical information
Pitch selection Pitch is the distance between one point on one cutting edge and the same point on the next edge. Milling cutters are mainly classified into coarse, close and extra close pitches, Operational stability
L
M
(Low)
Coarse pitch
H
(High)
(Medium)
Close pitch
Differential pitch
Extra close pitch
Indexable milling tools
B Technical information
When the milling width equal to diameter of cutter, the machining system is stable and main power of machine is sufficient, selecting coarse pitch can achieve high productive efficiency.
General milling function and multiple mixed productions
When the milling width is less than diameter of cutter, cutting by maximum edges can achieve high productive efficiency.
Selection of approach angle
The approach angle is composed by insert and tool body, Chip thickness, cutting forces and tool-life are affected especially by the approach angle. Decreasing the approach angle reduces chip thickness and spreads the cutting area between cutting edge and workpiece for a given feed rate. A smaller approach angle also guarantee that it is stable entrying into or exiting workpiece, to protect the cutting edge and extend tool life. However this will increase higher axial cutting
Approach angle
Feed rate per tooth
Real maximum cutting depth
90°
fz
hex=fz×sinkr
75°
fz
hex=0.96×fz
60°
fz
hex=0.86×fz
45°
fz
hex=0.707×fz
Round insert
fz
forces on the workpiece, thus is not suitable for machining thin workpiece such as thin plate.
B 166
hex=
i C 2× ( i C - 2 a p) 2 iC
×fz
Indexable Milling Tools Technical information
Milling
General formula Vc ：cutting speed(m/min) Dc ：nominal diameter of milling tool(mm) n ：spindle speed(rev/min) zn ：number of teeth Q ：metal removal rate(cm3/min) ●
Cutting speed
Vc=
B
(m/min)
1000
Spindle speed
n=
1000× V c
(rev/min)
π×Dc
Technical information
●
π × D c× n
Indexable milling tools
●
Vf ：feed rate of worktable ( feed speed)(mm/min) fz ：feed rate per tooth(mm/z) π ：circumference ratio≈3.14 Tc ：machining time(min) fz ：feed rate per revolution (mm/rev)
Feed rate of worktable ( feed speed)
Vf = fz× n × z n (mm/min)
●
Feed rate per tooth
f z=
●
(mm/z)
Vf n
(mm/rev)
Feed direction
Minor angle
Tooth shape
Feed rate per tooth(fz)
Machining time
Tc=
●
n×Zn
Feed rate per revolution
f n=
●
Vf
1000×Vc π×Dc
(min)
Metal removal rate
Q=
a p× a e× V f 1000
(cm3/min)
B 167
Milling
Indexable Milling Tools Technical information
Function of each part in face milling Axial rake angle rf Approach angle
Kr
Indexable milling tools
B
λs Inclined angle of
Rake angle R
Main angles of face mills
cutting edge
Radial rake angle rp
Main angles of face mills Designation
Technical information
Function
Effect
Determining the chip direction
negative angle, excellent capability of chip removal
Determining whether the cutting is light and fast or not
Positive angle, good cutting performance
Approach angle Kr
Determining the chip thickness
Kr↑，chip thickness↑；Kr↓，chip thickness↓；
Rake angle R
Determining whether the cutting is light and fast or not
Axial rake angle
rf
Radial rake angle
rp
Inclined angle of cutting edge Determining the chip flow
λs
direction
Poor cutting performance， high strength of cutting edge Poor cutting performance， high strength of cutting edge
(－)←0→(+)
(－)←0→(+)
Good cutting performance， low strength of cutting edge Good cutting performance， low strength of cutting edge
Characteristics of different rake angles combined Double positive
Negative rake angle
Double negative
One positive, one negative
rf (+)
rf (-)
rf (+)
rp (+)
rp (-)
rp (-)
0o
0° rake angle
+
Positive rake angle Axial rake angle
rf
﹢
－
﹢
rp
﹢
－
－
Radial rake angle
Applicable material machined
B 168
P
√
√
M
√
√
K
√
N
√
S
√
√ √
Indexable Milling Tools Technical information
Milling
Cutting performances of different approach angles Approach angle
Schematic diagram
Instruction Axial force is largest. It will bend when machining thin-wall workpiece, and reduces the precision of
45°
workpiece. It is benefit to avoid fringe breakage of workpiece when machining cast iron
B
The main purpose is to resolve the radial cutting
75°
force, it is often used for general face milling.
Indexable milling tools
The axial force is zero in theory, suitable for
90°
milling thin plate workpiece.
Technical information
Wiper insert
It has axial and radial run out because of tools and inserts exist manufacturing tolerance. The axial runout lead to poor
fn Rz
fz
surface roughness.
Solution Aassembling wiper inserts
usage
The wiper insert must protrude below the other
Wiper insert
Common insert
inserts by 0.03-0.10 mm at axial direction, only that the wiping function can take into effect. Generally speaking, a cutter can just assemble only one wiper insert. If the diameter of cutter is much bigger or cutter's feed rate per revolution is bigger than the length of wiper edge, 2 to 3 wiper inserts can be assembled.
B 169
Milling
Indexable Milling Tools Technical information
Selection of cutting width and tool cutting diameter in face milling
Generally speaking, the relation between cutting width and tool cutting diameter is Dc=(1.2—1.5) ae. In the machining practice,
Indexable milling tools
B
it need to avoid coincidence of tool center and workpiece center as much as possible.
(1.2 - 1.5)ae
Dc=ae
Technical information
Dc：Tool cutting diameter ae：Cutting width
B 170