Page 1

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


166_B-Milling  

description

Advertisement
Read more
Read more
Similar to
Popular now
Just for you