Aim: To measure the cutting force during milling operation using
Dynamometer
Theory: Milling is the process of cutting away material by feeding a workpiece past a
rotating multiple tooth cutter. The cutting action of the many teeth around the milling cutter
provides a fast method of machining. The machined surface may be flat, angular, or curved.
The surface may also be milled to any combination of shapes. The machine for holding the
workpiece, rotating the cutter, and feeding it is known as the milling machine. The
following two methods are commonly used for performing milling operations:
Up Milling: Up milling is also referred to as conventional milling. The direction of the
cutter rotation opposes the feed motion. For example, if the cutter rotates clockwise, the
workpiece is fed to the right in up milling.
Fig. 1 type of milling
Down Milling: Down milling is also referred to as climb milling. The direction of cutter
rotation is same as the feed motion. For example, if the cutter rotates counterclockwise, the
workpiece is fed to the right in down milling.
During machining, the cutter and the w/p material experience intense forces and
temperature at the chip formation zone. The nature and magnitude cutting forces depends
on the complex phenomena of metal deformation involving cutter and w/p material
characteristics, tool geometry, internal and external friction at interface and several other
physical and chemical factors. Estimation of cutting forces is essential for determination
of the power requirement of machine tools, design of machine tools and development of
new cutting tool materials.
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The forces experienced by a workpiece while milling can be resolved in three perpendicular
directions (Fx, Fy, Fz) and are shown in Fig 1. The workpiece is mounted on piezo-electric
dynamometer which is mounted on the table of the milling machine. The cutting forces are
picked by the charged amplifier that in turn digitize and display these forces. The
specifications dynamometer is given in Table 1.
Figure 1: Dynamometer
Table 1: Specifications of dynamometer
Measuring range
Force/ moment
Fx
Fy
Fz
Mz
Range
-5 – 5 kN
-5 – 5 kN
-5 – 20 kN
-200 – 200 N-m
fn (x,y)
fn (z)
fn (Mz)
Operation temperature
3.1 kHz
6.3 kHz
4.2 kHz
0 – 70 oC
Temperature coefficient of sensitivity
-0.02 %/ oC
4.2 kg
Natural frequency
Temperature
characteristics
weight
Procedure:
Apparatus required:
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a) Machine: HMT model FN2U Universal Milling machine (Horizontal
configuration)
b) Dynamometer: Kistler model 9272
c) Cutter: High Speed Steel (HSS) side & end milling dia 100mm & 24 teeth
d) Workpiece: Mild Steel
Figure 2 Side and end Milling cutter
The HSS side and end milling cutter is a cylinder made of tool steel with teeth on the
periphery, used to produce a flat surface is shown in Figure 2.
The following steps were followed during the experiment
1. The multi teeth cutter is mounted the arbor and the work piece is mounted on the
dynamometer as shown in Fig 3
2. The dynamometer is rigidly clamped on the table of the machine.
3. The cable is connected between dynamometer and charged amplifier as shown in
Fig 4.
4. The required rotational speed (10-30 m/min) and feed (0.1 – 0.5 mm/tooth) is
selected on machine. Cutting fluid flow is turned on.
5. Depth of cut 0.2 mm is given and the feed button is engaged.
6. The cutter revolves at a fairly high speed and the work fed slowly past the cutter.
7. The cutting forces are measured as shown in Fig. 5.
8. The experiment is repeated for required number of runs.
3
Figure 3 Dynamometer and work piece assembly
Figure 4 Connection of dynamometer
4
Figure 5 Display of charged amplifier
Precautions:
The following precautions are to be taken
1.
Handle the dynamometer very carefully
2.
Don’t change speed or feed in running condition of machine
3.
Keep safe distance from metal cutting zone.
Observations:
Run
Cutting
Feed
Depth of cut
Cutting
Thrust
velocity (mm/tooth)
(mm)
force Fz
force Fy
(m/min)
(N) ch2
(N) ch3
10
0.1
0.2
1
10
0.5
0.2
2
30
0.1
0.2
3
30
0.5
0.2
4
Note: The cutting forces are displayed on the screen as depicted in Fig 5
Feed force
Fx (N) ch4
Conclusion:
Two graphs are to be drawn between cutting forces (Fz and Fx) vrs feed/tooth for
various feed.
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