Page 14 - Stanochny park

METALWORKING EQUIPMENT
AND TOOLS
In
Investigation of the stiffness and bearing vestigation of the stiffness and bearing
capacity of an HSK joint bythe method of y of an HSK joint bythe method of
capacit
The cutting process creates a
complex spatial picture of the loading
of the HSK joint by cutting forces and
mandrel fixing. As a rule, the axial
component of the cutting force provides
clamping of the mandrel to the spindle
and does not interfere with the operation
of the connection; therefore, the radial
component and the moment created
by it are of the greatest interest for
assessing the operational capabilities
of HSK.
The failure of the HSK tool joint
occurs when the maximum permissible
load is exceeded and is accompanied by
unacceptable movement of the mandrel
relative to the spindle, a significant
decrease in the joint rigidity during
cutting, and the occurrence of residual
deformations. Signs of a starting failure
may include:
● radial movement of the mandrel
flange relative to the spindle end
surface in contact with the shear load
at the joint [1];
a b
● axial movement of the flange relative
to the end surface of the spindle in
contact with the force pulling the
mandrel from the spindle [2].
It was proposed in [1] to evaluate
the maximum permissible load on the
tool joint with a statically indeterminate
basing system by the occurrence of
residual deformations in the joints
between the mating parts. However,
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simulation modelling
simulation modelling
its author considered the possibility
of residual radial deformations only
in a flat joint, between the flanges of
the mating parts, and the occurrence
of axial displacements caused by the
action of pulling loads was not taken
into account.
Given the results obtained in [2],
this approach should be considered
one-sided. To understand the physical phenomena
that lead to failure of the joint and the nature of the
faults, it is necessary to study the behavior of the joint
at different radial loads applied at different distances
from the flat ring joint.
Due to the fact that experimental observation
of the effects listed above is difficult, the study was
conducted in the environment of finite element
modeling Simulation, integrated into the CAD system
SolidWorks. The following describes the methodology
for constructing mathematical models and processing
results for the HSK-A40, HSK-A63 and HSK-A100
systems.
Fig. 1. The design model of the connection ‘‘spindle - tool holder‘‘..
When choosing a design scheme (see Fig. 1, a),
the following features of the functioning of structural
elements were taken into account:
● the ability to open the joints of the spindle 1
and mandrel 2 under load;
● the nature of the contact interaction at the
joints formed by the mandrel and the spindle depends
on a combination of their sizes within the tolerance
fields;
METALWORKING EQUIPMENT
AND TOOLS
the spindle before termination 3 was
● the length of the front end of
chosen minimally sufficient to maintain
unchanged the stress-strain state of the
system, the pattern of deformations at the
joints of the spindle and mandrel caused
by external loading and the action of the
clamping mechanism;
● the magnitude and direction
of the force (Fзаж) acting from the
clamping mechanism to the inner flange
of the mandrel 4, correspond to the force
developed by the clamping mechanism
in accordance with the recommendations
of ISO 12164-1: 2001 and ISO 12164-2: Taking into account the symmetry of the
2001; stress-strain state of the structure allows you to build
● the coefficient of friction at the an adequate mathematical model, while reducing
joints of the mandrel and spindle is taken its dimension by half. Accordingly, the magnitude
equal to 0.2 (contact of steel surfaces in of external forces should be reduced by half, and
the absence of lubrication); when analyzing the results, a reverse transition to
● the stress-strain state of the the full structure was performed. The critical load
structure is symmetrical with respect to (Fкр), which determines the moment of loss of
the plane of application of the external performance, depends on both external factors (F
radial load. and L), and from a combination of tolerances on the
When constructing the finite element geometric dimensions of the connecting surfaces of
model, the following simulation features the mandrel and spindle. The initial data for assessing
were used: the influence of the accuracy of manufacturing the
● to construct the mesh, finite mandrel and spindle on the value of Fкр connections
elements were used — tetrahedra with a were taken from GOST R 51547-2000 and GOST
second-order form function; R 51726-2001. Depending on the combination of
● joints were described by special tolerances of the connecting surfaces of the spindle
finite elements, taking into account the and mandrel, two extreme cases are possible:
possibility of mating surfaces coming out ● the conical part of the seat in the spindle
of contact and friction between them; is made along the lower boundary of the tolerance
● the sequence of application of field, the mandrel cone - along the upper boundary
forces - tightening the mandrel into the (hereinafter this combination is called a ‘‘tight‘‘fit);
spindle and the subsequent application ● the conical part of the seat in the spindle is
of radial load - is implemented using the made along the upper boundary of the tolerance
boundary condition ‘‘hot landing‘‘; field, the mandrel cone - along the lower
● geometric non-linearity of the boundary (hereinafter this combination is called a
model, arising due to the redistribution ‘‘weakened‘‘landing).
of contact pressures at the joints under The connecting surfaces of real joints have
the influence of radial force, is taken into shape deviations and roughness that affect the
account by the applied algorithm of ‘‘large distribution of loads in the structure and its rigidity.
displacements‘‘; In mathematical models, the shape is perfect,
● the symmetric nature of the solution and the surfaces are absolutely smooth, and the
is taken into account by the appointment influence of errors can be taken into account due to
of the corresponding boundary conditions the appropriate combination of tolerances.
in the section coinciding with the plane of In accordance with the recommendations of
load application; the standards ISO 12164-1: 2001 and ISO 12164-
● reduction of the radial load (F) 2: 2001, the flat ring joint should absorb at least
applied through the shoulder (L) to the 75% of the force from the clamping mechanism.
end of the mandrel is carried out by the Calculations carried out for cones 40, 63 and 100 of
boundary condition ‘‘distance loads‘‘- the the HSK-A joint showed that with a ‘‘tight‘‘fit, only
assignment of the corresponding forces 49%, 42% and 62%, respectively, perceive a ring
and moments in the grid nodes at the joint, and 84%, 89% and 83% of Fzag respectively
front end of the mandrel. (equal to 6.8 kN, 18 kN and 45 kN, respectively).
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