GEAR MANUFACTURING
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Table 13.4.9
General Recommendations for Milling Operations
General-purpose starting
conditions
Range of conditions
Feed,
Speed,
Feed,
Speed,
mm/tooth
m/min
mm/tooth
m/min
Workpiece material
Cutting tool
(in/tooth)
(ft/min)
(in/tooth)
(ft/min)
Low-C and free-machining
Uncoated carbide, coated
0.13–0.20
120–180
0.085–0.38
90–425
steels
carbide, cermets
(0.005–0.008)
(400–600)
(0.003–0.015)
(300–1,400)
Alloy steels
Soft
Uncoated, coated, cermets
0.10–0.18
90–170
0.08–0.30
60–370
(0.004–0.007)
(300–550)
(0.003–0.012)
(200–1,200)
Hard
Cermets, PcBN
0.10–0.15
180–210
0.08–0.25
75–460
(0.004–0.006)
(600–700)
(0.003–0.010)
(250–1,500)
Cast iron, gray
Soft
Uncoated, coated,
0.10–0.20
120–760
0.08–0.38
90–1,370
cermets, SiN
(0.004–0.008)
(400–2,500)
(0.003–0.015)
(300–4,500)
Hard
Cermets, SiN, PcBN
0.10–0.20
120–210
0.08–0.38
90–460
(0.004–0.008)
(400–700)
(0.003–0.015)
(300–1,500)
Stainless steel, austenitic
Uncoated, coated, cermets
0.13–0.18
120–370
0.08–0.38
90–500
(0.005–0.007)
(400–1,200)
(0.003–0.015)
(300–1,800)
High-temperature alloys,
Uncoated, coated, cermets,
0.10–0.18
30–370
0.08–0.38
30–550
nickel base
SiN, PcBN
(0.004–0.007)
(100–1,200)
(0.003–0.015)
(90–1,800)
Titanium alloys
Uncoated, coated, cermets
0.13–0.15
50–60
0.08–0.38
40–140
(0.005–0.006)
(175–200)
(0.003–0.015)
(125–450)
Aluminum alloys
Free-machining
Uncoated, coated, PCD
0.13–0.23
610–900
0.08–0.46
300–3,000
(0.005–0.009)
(2,000–3,000)
(0.003–0.018)
(1,000–10,000)
High-silicon
PCD
0.13
610
0.08–0.38
370–910
(0.005)
(2,000)
(0.003–0.015)
(1,200–3,000)
Copper alloys
Uncoated, coated, PCD
0.13–0.23
300–760
0.08–0.46
90–1,070
(0.005–0.009)
(1,000–2,500)
(0.003–0.018)
(300–3,500)
Thermoplastics and
Uncoated, coated, PCD
0.13–0.23
270–460
0.08–0.46
90–1,370
thermosets
(0.005–0.009)
(900–1,500)
(0.003–0.018)
(300–4,500)
N
OTE
: Depths of cut,
d,
usually are in the range of 1–8 mm (0.04–0.3 in). PcBN: polycrystalline cubic boron nitride; PCD: polycrystalline diamond.
S
OURCE
: Based on data from Kennametal Inc.
Table 13.4.10
General Troubleshooting Guide
for Milling Operations
Problem
Probable causes
Tool breakage
Tool
material lacks toughness; improper
tool angles; cutting parameters too high
Tool wear excessive
Cutting parameters too high; improper tool
material; improper tool angles; improper
cutting fluid
Rough surface finish
Feed too high; spindle speed too low; too
few
teeth on cutter; tool chipped or worn;
built-up edge; vibration and chatter
Tolerances too broad
Lack of spindle stiffness; excessive temper-
ature rise; dull tool; chips clogging cutter
Workpiece surface burnished
Dull tool; depth of cut too low; radial relief
angle
too small
Back striking
Dull cutting tools; cutter spindle tilt; nega-
tive tool angles
Chatter marks
Insufficient stiffness of system; external
vibrations; feed, depth, and width of cut
too large
Burr formation
Dull cutting edges or too much honing;
incorrect angle of entry or exit;
feed and
depth of cut too high; incorrect insert
geometry
Breakout
Lead angle too low; incorrect cutting edge
geometry; incorrect angle of entry or exit;
feed and depth of cut too high
given in Table 13.4.9. A general
troubleshooting guide
for milling oper-
ations is given in Table 13.4.10.
GEAR MANUFACTURING
(See also Sec. 8.)
Gear Cutting
Most gear-cutting processes can be classified as
either
forming or generating.
In
a forming process, the shape of the tool
is reproduced on the workpiece; in a generating process, the shape pro-
duced on the workpiece depends on both the shape of the tool and the
relative motion between the tool and the workpiece during the cutting
operation. In general, a generating process is more accurate than a
forming process.
In the
form cutting
of gears, the tool has the shape of the space
between the teeth. For this reason, form
cutting will produce precise
tooth profiles only when the cutter is accurately made and the tooth
space is of constant width, such as on spur and helical gears. A form cut-
ter may cut or finish one of or all the spaces in one pass. Single-space
cutters may be disk-type or end-mill-type milling cutters. In all single-
space operations, the gear blank must be retracted and indexed, i.e.,
rotated one tooth space, between each pass.
Single-space form milling with disk-type cutters is particularly suit-
able for gears with large teeth, because, as
far as metal removal is con-
cerned, the cutting action of a milling cutter is more efficient than that
of the tools used for generating. Form milling of spur gears is done on
machines that retract and index the gear blank automatically.
For the same tooth size (pitch), the shape (profile) of the teeth on an
involute gear depends on the number of teeth on the gear. Most gears
have active profiles that are wholly, partially, or approximately involute,
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