Page 839 - Iscar

INTRODUCTION

Balancing Definitions

Balancing Elements

Introduction TOOLING SYSTEMS
Balancing is the process of equalizing the mass The measuring equipment available today enables
distribution of a body so it rotates in its bearing unbalance to be reduced to low limits. However, it would
without unbalanced centrifugal forces. be uneconomical to exaggerate the quality requirements.
It has therefore become necessary to determine to what
Balancing causes reduced vibration, lower extent the unbalance should be reduced and where
spindle strain, improved machining qualities the optimum economic and technical compromise
and allows for higher cutting parameters. on balance quality requirements would be struck.

Definition
G - Balance quality (mm/s) M - Mass of the body (kg)
e - Specific unbalance (gxmm/Kg) m - Mass of the unbalance (g)
Ω - Speed (rad/s) r - Radius of the unbalance (mm)
N - Speed (rpm) U - Residual unbalance (gxmm)

U
e = M =>U=M x e Ω = 2πN = πN
60 30
Operation
Residual unbalance equals the tool’s mass (M) Any two sets of mass and eccentricity that yield
times its eccentricity (e). the same unbalance value will have the same effect
Eccentricity measures the extent to which the on the tools, so long as the residual unbalance is in
tool’s weight is off-center. the same plane perpendicular to the rotation axis.
It is defined as the distance from the tool’s center U=r x m
of the rotation to its true center of mass. The residual unbalance is independent of the speed. This
If eccentricity is measured in microns and tool mass value reflects the unbalance mass and its distance from
is measured in kilograms, this unit yield the true center of mass.
residual unbalance in gram-millimeters. The residual unbalance value is measured
on balancing machines.

Balanceable Collet Chucks

Balancing Elements
m
Example 1
U=2 g x mm can be treated as an unbalance mass
of m=2 g in radial distance of r=1 mm or as a mass
of m=0.1 g in radial distance of r=20 mm, etc.
r
Example 2
The residual unbalance is independent of the speed.
This value reflects the unbalance mass and its
distance from the true center of mass. The residual
unbalance value is measured on balancing machines. π U π 8
G = xNx = x15,000x ≈ 6.3 (mm/s)
30 M 30 2,000
U 4
U = m x r = >m = = = 0.2g
r 20 U 8
e = = e = = 4 (gxmm/kg)
M 2
G value reflects the balancing quality of a
toolholder according to its rotational speed (N) The G value will change to G=2.5 mm/s when using
the same toolholder at a rotational speed
π x N U U x N x π N=6,000 rpm and to G=1.0 mm/s at
G = Ω x e = x = N=2,500 rpm.
30 M M x 30
Balance quality grades for various groups of
G x 30 representative rotors:
e =
π x N
• General machine tool parts - G6.3
Example 3 • General toolholders and machine drivers - G2.5
G value reflects the balancing quality of a toolholder • Grinding machine drivers - G1.0
according to its rotational speed (N). • Spindles of precision grinders - G0.4

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