Page 557 - ISCAR(MILLINGCATALOG 38_2021)

INTRODUCTION

Balancing Elements

Balancing Definitions Balancing Coolent Chucks

Introduction TOOLING SYSTEMS
Balancing is the process of equalizing the mass m
distribution of a body so it rotates in its bearing
without unbalanced centrifugal forces.
Balancing causes reduced vibration, lower
spindle strain and improved machining qualities, r
and allows for higher cutting parameters.
The measuring equipment available today enables
unbalance to be reduced to low limits. However, it would
be uneconomical to exaggerate the quality requirements. Example 1
It has therefore become necessary to determine to what U=2 g x mm can be treated as an unbalance mass
extent the unbalance should be reduced and where of m=2 g in radial distance of r=1 mm or as a mass
the optimum economic and technical compromise of m=0.1 g in radial distance of r=20 mm, etc.
on balance quality requirements would be struck.
Example 2
Definition The residual unbalance is independent of the speed.
This value reflects the unbalance mass and its distance
G - Balance quality (mm/s) from the true center of mass. The residual unbalance
e - Specific unbalance (gxmm/Kg) value is measured on balancing machines.
Ω - Speed (rad/s)
U
N - Speed (rpm) U = m ∙ r = >m = = 4 = 0.2g
M - Mass of the body (kg) r 20
m - Mass of the unbalance (g) G value reflects the balancing quality of a
r - Radius of the unbalance (mm) toolholder according to its rotational speed (N)
U - Residual unbalance (gxmm)
U
e = M = > U = M ∙ e G = Ω ∙ e = π ∙ N ∙ U = U ∙ N ∙ π
M
30
M ∙ 30

G ∙ 30
Ω = 2πN = πN e = π ∙ N
60

30
Operation Example 3
Residual unbalance equals the tool’s mass (M) G value reflects the balancing quality of a toolholder
times its eccentricity (e). Eccentricity measures the according to its rotational speed (N).
extent to which the tool’s weight is off-center.
π
U
π
It is defined as the distance from the tool’s center of the G = ∙ N ∙ = ∙ 15, 000 ∙ 8 ≈ 6.3 (mm/s)
M
30

30
2,

000
rotation to its true center of mass.
If eccentricity is measured in microns and tool
8
mass is measured in kilograms, this unit yields e = U = e = = 4 (g ∙ mm/kg)
residual unbalance in gram-millimeters. M 2
Any two sets of mass and eccentricity that yield the The G value will change to G=2.5 mm/s when using the
same unbalance value will have the same effect on same toolholder at a rotational speed
the tools, so long as the residual unbalance is in the N=6, 000 rpm and to G=1.0 mm/s at
same plane perpendicular to the rotation axis. N=2, 500 rpm.
Balance quality grades for various
U = r ∙ m groups of representative rotors:
• General machine tool parts - G6.3
The residual unbalance is independent of the speed. • General toolholders and machine drivers - G2.5
This value reflects the unbalance mass and its distance • Grinding machine drivers - G1.0
from the true center of mass. The residual unbalance • Spindles of precision grinders - G0.4
value is measured on balancing machines.

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