The cutting tool is
one of the most important elements necessary for realizing
the full potential of any metal cutting operation. Carefully
chosen grinding wheels are essential to enable the cutting
tools obtain sharp edges and accurate geometry.
The prominent cutting
tool materials that are being used today are High Speed
Steels (HSS), Carbides, Ceramics, Cubic Boron Nitride
(CBN) among these materials, HSS still dominates the
field because of their versatility and low cost. Table
I gives the approximate composition of commonly used
Molybdenum - based HSS.
TYPICAL ANALYSIS OF HIGH SPEED STEELS
STEEL TYPE
C%
Cr%
W%
Mo%
V%
Co%
M2
0.88
4.00
6.20
5.00
2.00
-
M7
1.00
4.00
1.80
8.75
2.00
-
M35
0.90
4.00
6.20
5.00
2.00
5.00
M42
1.10
3.75
1.50
9.50
1.15
8.00
Table 1
CUMI has over the years developed unique grinding
wheels to suit various applications in the manufacture of
cutting tools. The applications include Drill and Tap Fluting,
Point Grinding, Thread Grinding, Cylindrical, Centreless,
Surface and Tool Room Grinding. This write-up coveres Flute,
Point and Thread Grinding details of Drills, Taps and crushers.
Fluting and Point Grinding wheels:
Hot Press flute and Point
grinding wheels are extensively used in the manufacture of
straight and taper-shank twist drills and taps. These wheels
can be used on modern machines operating at peripheral speeds
ranging between 45 and 80 meters per second (8500 and 16000
SFPM), Drills and taps upto 1” diameter are fluted on high
speed grinding machines using hot pressed grinding wheels
in one or two passes. CUMI’s hot pressed wheels manufactured
using white Aluminium, Oxide abrasives, are capable of cooler
cutting and form-holding and are designed for use on hardened
and soft steels.
The starting recommendations
for CUMI’s wheel gradings are as follows:
Machine
Grading
Fluting
Normac, J&L
AA 1001 R 19 BHK (upto 80 mps)
Normac, J&L
AA 80 R19 BHK (upto 80 mps)
Hertlien
DA 120 R RB (upto 60 mps)
Hertien
A 120 R8 BN
Point Grinding
Normac
AA 100 S12 BHP (upto 80 mps)
Winslowmatic
A 80 06 BRT (upto 60 nps) AA 80 S12 BHP
Fluting wheels with notches on the sides can
be used for effective swarf - removal and cooler cutting.
Drill Flute relieving wheels are also available
in similar gradings in the required sizes.
Thread Grinding Wheels:
CUMI has in its product range,
Single-rib and Multi-rib Thread Grinding wheels that operate
at peripheral speeds ranging from 33 to 80 Metres Per Second
(6000 - 16000 SFPM). These wheels can be used on hardened
High Speed Steel taps.
CUMI’s thread grinding wheels
assure repeatability of parameters and excellent form-holding
characteristics resulting in reduced dressing frequencies.
Refer Table II for Popular machines and Wheel-gradings are
given at Table III.
Machines and Wheel
Sizes
MACHINES
WHEEL SIZE
NORMAC GT 77
450 x t x 228.6 mm (18” x t x 9”)
MATRIX
200 X T X 76.2 MM (8” X T X 3”)
REISHAUER.RAG
250 x t x 155mm (10” x t x 6.1”)
REISHAUER.RGM
400 x t x 203.2mm (16” x t x 8”)
REISHAUER.NRK
350 x t x 160mm (14” x t x 6.2”)
t = Wheel thickness)
Table II
Recommended starting Gradings for Thread
Grinding Wheels
