Important - SMW Autoblok AN Manuel D'utilisation

Ø of
the chuck AN-AL-IN-IL BH
130 0.015 0.015
140
165 0.024 0.024
175
210 0.057 0.050
250 0.12 0.115
305
315 0.21 0.19
400 0.50 0.43
450 0.56
500 1.58 0.68
610 1.94
630 2.60 1.41
640 2.07
800 4.3 2.16
The values for m · r are the mass and baricentric radius of the jaws only
2 2
and can be easily calculated by the user (for standard hard top jaws, the
weight and the baricenter are indicated in the catalogues).
Example: For a type 210 BHD-3 jaw chuck, with standard soft top jaws
in the most external position but not outside of the external diameter, at
4000 r.p.m., the calculation is as follows:
Fct = M · R ·
m · r = 0.050 Kg · m (see schedule above)
1 1
m · r = 0.72 · 0.060 = 0.043 Kg · m
2 2
= –––– · n = –––––– · 4.000 = 419 rad/sec
30
therefore the theoretical centrifugal force is:
Fct = (0.050 + 0.043) · 3 · 419
Measuring the internal performance of the power chuck, the "effective
centrifugal force" (Fca), measured experimentally, is about 0,7 of the
theoretical one, therefore we have:
Fca ≅ Fct · 0.7
the "effective dynamic gripping force" is:
Fsa = Fso - Fca
Example: continuing the previous example, we have the "real centrifugal
force":
Fca ≅ Fct · 0.7 ≅ 50 · 0.7 = 35 kN
and the "Effective dynamic gripping force"
Fsa = Fso - Fca = 110-35 = 75 kN
this value is found in the diagram for a type 210 BHD-3 jaw chuck.
IMPORTANT: With standard jaws, NEVER exceed the maximum
allowed speed.
IMPORTANT: When using special jaws which are heavier than
standard jaws or in a more external position, it is necessary to calculate
the Fcs and Fsa and correspondingly reduce the speed.
IMPORTANT: We suggest using a dynamic gripping force measurement
system type GFT to measure the "Effective dynamic gripping force" in
order to confirm the safe gripping conditions at each speed.
3.4 Draw coupling
To explain the concept of "Effective draw
coupling (force)", we must begin with the
"Effective dynamic gripping force" explained at
point 3.3.
The gripping force acts radially on the workpiece,
to create a coupling. This must be changed into
"effective draw force" (Fra), which acts tangential-
ly on the piece, multiplying it by the coefficient of
friction "f".
We have shown below the average values of the coefficient of friction "f"
for the different types of jaws and surfaces of the workpiece.
Schedule 4 - Coefficient of friction "f"
GRIPPING CONDITIONS
Turned soft top jaws
Hard top jaws (square teeths)
Hard top jaws (scharp teeths)
Jaws with carbide inserts
The draw coupling is determined by multiplying the draw force by the
arm "b" (clamping radius) (see drawing 4).
18
INSTRUCTIONS AND SAFETY REGULATIONS
TYPES
BB BF/FC-HN/FC
0.016
-0.015
0.027
0.048 -0.05
0.11 -0.09
0.17 -0.19
-0.10
-0.20
-0.60
. r
2 = (m + m · r ) · z · 2
1 1 2 2
3.14
30
= 48.981 N ≅ 50 kN
2
drw.4
Fra = Fsa . f
Rough piece Worked piece
0.15
0.20
0.40
0.60
For machining on lathes, with a rotating piece, it is necessary to consider
the "effective dynamic draw coupling" (Tda) determined by multiplying
RCD-RCM
the "Effective draw force" (Fra) by the clamping radius (b).
0.021
where : Tda [N·m] = Effective dynamic draw coupling
0.049
Fra [N]
0.11
b
0.16
Example: clamping with a type 210 BHD-3 jaw chuck, speed 4.000
0.38
r.p.m. in a finishing operation with soft top jaws on machined piece
(f=0,1) with a clamping on diameter of 160 mm (b = 0,08 m).
0.65
Once the draw coupling has been calculated, it is necessary to determine
the "cutting coupling" (Tz), generated by the contact of the tools with the
workpiece. Verify that it is, at least, 2.5 times less than the Tda:
3.5 Maximum rotation speed
The maximum rotation speed in revolutions/minute (r.p.m.) is one of the
main technical features of each power chuck. It is specified in all catalo-
gues and is engraved on the front of each power chuck (N max - r.p.m.).
The system to calculate the max speed is specified in the EN 1550 regu-
lation according to the following formula:
where: n max [r.p.m.] = Maximum r.p.m.
Fsmax [N]
m
m
Z
THE MAXIMUM SPEED is the one at which the power chuck looses 2/3
of "maximum static clamping force" due to the "theoretical centrifugal
force" using standard hard top jaws in reversed position (high slot
outwards) in an external position but within the diameter of the power
chuck.
THE MAXIMUM SPEED is not an absolute value, but can be
reached only under the following conditions:
A)If the "maximum static gripping force " (Fsmax) acts on the workpiece.
B)If the standard hard top jaws (or soft top jaws with equivalent weight
moment) are positioned within the outside diameter of the chuck.
If the "Maximum draw pull" is not applied (Ftmax) and the
"Maximum static clamping force" (Fsmax) is not achieved, or if heavier
jaws are used in a more external position, it is necessary to reduce the
rotation speed according to the following formula:
Example: on a 210 BHD-3 jaw chuck, with Fso=Fsmax=105kN
(105000N) verified; with m
· r =0,043 (weight of 1 jaw by its baricentric radius), the maximum speed
2
(according to ISO and DIN standards) is the following:
2
n =
3 (m r +m r ) z
max i
1 1
i
4. CLAMPING JAWS AND T-NUTS.
The clamping jaws are among the most important components in the
Z
workpiece gripping operation. It is ESSENTIAL to know exactly how to
use them.
0.1
Any type of jaw used, must be positioned so that the clamping of
0.12
the workpiece is in the middle of the radial stroke of the master jaw.
0.25
-
CONCENTRICITY: Concentricity is the value of the difference from the
theoretical rotation axis of the external surface of a round workpiece
clamped between the jaws of a power chuck; usually it is measured with
Tda = Fra · b
= Effective draw force
[m] = Clamping radius
Fra = Fsa · f = 75 · 0.1 = 7.5 kN = 7500 N
Tda = Fra · b = 7500 · 0.08 = 600 Nm.
Tda ≥ 2.5 . Tz
2 Fs
n =
max
3 (m r +m r ) z
max
i i
1 1 2 2
i i i
= Max. static gripping force
· r [Kg·m] = Mass moment of 1 jaws,"T" nut and screws
1 1
· r [Kg·m] = Mass moment of 1 gripping jaws
2 2
= Number of chuck's jaws.
2 Fs
n =
max
3 (m r +m r ) z
max i i
1 1 2 2
i i i
· r =0.050 (see schedule at point 3.3); with m
1 1
Fs 30 2 105.000
=
max
3 (0,050 + 0,043) 3
i i
π
2 2
i i
30
π
30
π
2
30
= 4 8 8 00 rpm
i
π
i