The present invention relates to a securing/clamping system and method
according to the first part of claims 1 and 7. Especially the present invention
relates to a clamp for an injection molding machine which uses an electric screw
drive for clamp stroke motions and at least one column engaging a hydraulic clamp
piston to provide clamp force. The present invention also includes a self adjusting
mechanism connected to the column so that dimensional changes caused by clamp
deflections do not damage the drive means.
The prior art includes many injection molding machines which use
tiebar clamping units for positioning a platen for the application of clamp-up
forces. Control systems using hydraulic fluid, pressurized air and electric motors
in combination with numerous switches and typically a controller unit are used
to control both the positioning of the platens and the application and removal
of clamp-up force for acquiring mold clamp-up and mold break.
JP-A-61261-017 discloses a clamping mechanism for injection molding
machines. The purpose of the control system therein is to maintain a parallel parting
line between the molds by sensing the distance traveled by each clamping cylinder
of each tiebar and maintaining the distances substantially equal. Accordingly,
parallelism of the parting line between the molds can be maintained when the injection
pressure of molten resin is uneven within the mold.
US-A-4,832,884 discloses a method for measuring and controlling the
closing force of a plastic injection molding machine. Accordingly, for an injection
molding machine, a closing force is measured for a predetermined number of operation
cycles. A mean value is calculated from the measurements and if the mean value
is within a predetermined tolerance, no control intervention takes place. However,
if the mean value is outside the tolerance but within a zone limited by alarm units,
control intervention takes place by stepwise changing the installed height of
the mold until the actual value measured for closing force after each operating
cycle is within the tolerance given. In this method and system, a toggle joint
system serves to generate the closing force on the first and second mold parts.
In this case, the force is measured and if the force is within a tolerance zone,
the spacing between the first and second mold parts is altered to less than or
no increase relative the old force.
US-A-4,966,738 discloses a method for mold clamping force adjustment.
Accordingly, in this method, a mold touch position is detected, at which the mold
halves of a mold contact each other. The mold temperature is detected by means
of thermocouple attached to the mold halves. The mold thickness is obtained based
on the position where a movable platen and a stationary platen of the injection
molding machine contact each other. After a molding operation is started, the mold
temperature is detected and the amount of change in mold thickness during a period
between a preceding cycle and a current cycle is calculated based on the change
of mold temperature, the mold thickness, and the thermal expansion coefficient
of the mold. A mold touch position for a current cycle is obtained based on the
calculated value. Accordingly, when the mold is clamped in the current cycle, the
movable platen is moved from the mold touch position toward the stationary platen
by a predetermined amount to produce a predetermined mold clamping force. For this
method, the measurements and adjustments are directed primarily to the mold position
and not to the position of the clamping units. A clamping unit is a singular one
which functions to force the movable platen against the stationary platen. That
is, no tiebar clamping units are used internal to any of the platens for producing
the clamp-up force.
US-A-5,147,661 discloses a mold aligning device for a compression
molding machine. The mold aligning device includes a plurality of mold position
adjusting cylinder actuators disposed on a bed wherein position detectors are
associated with the mold positioning adjusting cylinder actuators to detect the
strokes thereof. The hydraulic source for driving the mold position adjusting
cylinder actuators and control unit for controlling the strokes of the piston rods
of the actuators with reference to zero points of the piston rods of the actuators,
is determined beforehand. The zero points are decided by placing the upper mold
in close contact with the lower mold and extending the piston rods of the actuators
so that the piston rods are pressed against the lower surface of a slide block.
The strokes of the piston rods are controlled during a compression-molding operation
so that the upper mold is maintained precisely in parallel with the lower mold.
This device is directed to pressure molding. The cylinder actuators are not positioned
within a movable molten platen, and the actuators do not clamp onto tiebars The
main purpose of the machine is to maintain parallelism between the upper and lower
molds by the actuators placing direct pressure on the upper mold supporting surface
for maintaining the same parallel to the lower mold.
US-A-5,338,171 discloses a die-clamping apparatus with an aligning
device. The apparatus includes a stationary die plate for holding a stationary
die, a movable die plate for holding a movable die, a hydraulic cylinder for moving
the movable die plate forwardly and rearwardly with respect to the stationary
die plate, and a tiebar for clamping by a fastening device located in the movable
die plate. One or more alignment devices are provided so as to join the movable
die and the stationary die in such a manner that primary alignment can be performed.
The molding apparatus can be provided with a guide pin for secondarily aligning
the movable die with respect to the stationary die when the stationary die and,
the movable die have been placed at predetermined positions. Four die clamping
cylinders are provided at the corners of the stationary die plate so as to apply
a clamping force to the stationary and movable dies after the fastening device
has fastened to the tiebar. For this device, the tiebar fastener and clamping units,
while being located on the tiebars one adjacent the movable platen and one adjacent
the stationary platen, are separate devices adding to the complexity of the machine.
US-A-5,370,518 discloses an apparatus for injection and compression
molding. The apparatus includes an injection device and a compression molding device
wherein the compression molding device includes a stationary die plate for holding
a stationary die, a movable die plate for holding a movable die, means for rapidly
extending and retracting the movable die plate relative to the stationary die
plate and means for locking the movable die plate to the tiebars at a position
where the movable die plate approaches the stationary die plate. Means for fastening
the dies after the movable die plate is locked to the tiebars is also provided.
An injection device for feeding a molten plastic material into a mold cavity between
the stationary die and the movable die initiates feeding of the molten plastic
material into the mold cavity when the stationary die and movable die are parted
from each other by a predetermined distance. The plastic material is compressed
and drawn while the movable die is moved towards the stationary die after a predetermined
quantity of molten plastic material has been fed into the mold cavity. The apparatus
includes a device in a movable die plate for clamping onto the tiebars. However,
the device does not include a combined means for providing the clamping force
between the platens and fastening to the tiebars as the clamp force is provided
by separate die fastening cylinders which are positioned on the tiebars but separate
from the fasteners.
US-A-5,133,655 shows a clamp mechanism for an injection molding machine
in which four columns attached to the moving platen are individually gripped by
fluid actuated cylinders which also act as clamp force pistons. While this design
is effective, it requires very close tolerances to be maintained between the columns
and the inner bores of the cylinders since the amount of deflection of the cylinder
walls to achieve sufficient gripping on the columns is small. Thus, manufacturing
this clamp is expensive and in operation maintaining these small clearances imposes
costly maintenance procedures.
US-A-5,620,723, 5,624,695 and 5,645,875 show a novel lock nut arrangement
for engaging the tiebars of a two platen injection molding machine clamp, for example.
The locking nuts also act as clamp force pistons acting on the tiebars to clamp
the mold between the platens.
A further securing/clamping system is shown in the JP-A-09 029802.
A threaded shaft is engaged with the bore threaded part of a threader shaft disposed
coaxially with the shaft and engraved on a screw on the outer periphery. The end
of the shaft is fixed to a moving die plate. On the other hand, a nut engraved
with threads in the bore is engaged with the shaft via the general purpose threads
and the general purpose threads of the shaft. In this case, the nut is controlled
in its axial movement. A sleeve is controlled in the rotating motion by a spline
at the end of the mold clamping cylinder and coaxially disposed axially movable
at a predetermined gap from the profile of the shaft.
The combination of a screw driven clamp stroke and hydraulic clamping
are shown in US-A-3,191,235, JP-A-04332616, JP-A-2-252518 and EP-A-0 508 277. In
the '235 and '277 references, a single clamp piston is carried inside a cylinder
in the moving platen. The rod of the clamp piston is directly connected to a single
column which is threaded along most of its length such that a nut can engage the
thread and either the column or nut are rotated to cause the column, clamp piston
and moving platen to move. Once the screw drive has closed the mold, high pressure
hydraulic oil is supplied to the non-rod side of the clamp piston to cause the
moving platen to exert a clamping pressure against the mold.
The JP-A-2-252518 teaches a similar threaded column for mold closing
in combination with a variety of means for exerting clamp force against the mold.
Figures 1-3 illustrate the invention, which is a column blocking method. Center
column 46 is attached to the moving platen 5, which in turn is moved by nuts 32
engaging threaded columns 31 to cause stroke motion. When the moving platen has
moved to the mold closed position (see Figures 1 and 2), shutter 49 is moved by
cylinder 50 between the end of the column 46 and sleeve 39 blocking column movement.
Sleeve 39 is threaded into shutheight adjustment nut 38 carried in the clamp block
30. By rotating the nut 38, the end of the sleeve 39 that engages the shutter can
be moved with respect to the block 30, thereby adjusting the distance between
the closed platens 5 and 3 to provide for molds having different shutheights. Clamping
force is generated by hydraulic cylinders 35 acting on the ends of tiebars 4 and
mounted in the clamp block 35.
US-A-4,645,443 shows a hydraulic clamp having both stroke and clamp
functions performed by hydraulic cylinders acting through a single column. The
shutheight adjustment is made using a threaded connection between the column end
and the moving platen. Thus, clamping forces are transmitted via the column through
the threaded connection to the moving platen.
WO 98-19850 shows a means for applying a clamping force to a movable
platen. At least one column is affixed to the movable platen. A plurality of circumferentially
spaced teeth is provided on the end of the column spaced from the movable platen,
and a clamp piston and lock means engaging the clamp piston are provided operative
to engage and disengage the teeth.
A securing/clamping system as mentioned above is shown in the US-A-5,261,810
and the DE 30 06 609 A1. In both cases that means for reciprocatingly moving also
includes a threaded rod operatively engaging a threaded member, that threaded
member operatively engaging that at least one column.
It is highly desirable to provide a means for accommodating the variations
in column length that can occur due to the forces generated by the clamping piston
acting on the column. This is particularly important when the column transmits
the clamping and the opposed mold break forces to the moving platen, as described
in the WO 98-19850.
Accordingly, it is the object of the present invention to provide
a fast acting and energy efficient injection molding machine clamp assembly and
clamping method with low construction cost, low maintenance and good reliability,
which occupies less floor space than conventional designs and which accommodates
variations in column length that can occur due to the forces generated by the clamping
piston acting on the piston.
Further advantages of the present invention will appear hereinbelow.
SUMMARY OF THE INVENTION
In accordance with the present invention, it has now been found that
the foregoing objects and advantages are readily obtained by a securing/clamping
system according to the second part of claim 1. By this way the threaded member
engages said column and rod in a manner to accommodate variations in the positions
of said column and rod without inducing stress. Desirably, the movable platen
travels along a plurality of tiebars. Also, the column preferably includes an internal
channel, with the threaded rod and threaded member located at least in part in
the internal channel. In preferred embodiments, the threaded member is splined
within the column and floats axially with respect to the column.
The present invention also provides a securing/clamping method, which
comprises: providing a stationary platen having a first mold half affixed thereto,
and a movable platen having a second mold half affixed thereto; reciprocatingly
moving said movable platen between a mold open and a mold closed position; applying
a clamping force to said movable platen in the mold closed position, and applying
a mold break force to said movable platen in the mold closed position; and wherein
said reciprocatively moving step includes affixing a first end of at least one
column to the movable platen and spacing a second end of said at least one column
from the movable platen, operatively engaging a threaded member and said at least
one column, operatively engaging a threaded rod with said threaded member, characterised
by positioning said threaded member so that said threaded member floats axially
with respect to the column in a manner to accommodate variations in the positions
of the column and rod without inducing stress.
Particular embodiments of the invention are the subject of the respective
Further features of the present invention and advantages thereof
will appear from the following specification.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be more readily understood from a consideration
of the following illustrative drawings, wherein:
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
- FIG. 1 is a partial section view of a clamp mechanism of the present invention;
- FIG. 2 is a detailed section view of the clamp mechanism.
The present invention utilizes a clamping unit including at least
one column having circumferentially spaced teeth and at least one axial groove
circumferentially spaced between the teeth. Rotation of the column is operative
to engage and disengage the teeth with corresponding teeth on a clamp piston. This
type of clamping unit is shown in the aforementioned PCT '507 publication.
Referring to FIG. 1, stationary platen 10 is connected by tiebars
12 to clamp block 14. Moving platen 16 slides on the base or on the tiebars to
open or close mold 18 (shown in the mold open position in FIG. 1). Mold 18 includes
a first mold half 20 affixed to stationary platen 10 and a second mold half 22
affixed to movable mold half 16. Only one mold is shown in FIG. 1 for simplicity,
but naturally a plurality of the molds can readily be provided. Tiebars 12 connect
the stationary platen 10 and clamp block 14 while supporting the movable platen
16 which is free to slide along the tiebars. Generally four or more of the tiebars
are used with only two being shown in FIG. 1. Moving platen 16 is moved from a
mold open position as shown in FIG. 1 to a mold closed position by means which
will be described hereinbelow.
Column 24 is fixed to the back side of movable platen 16, i.e., the
movable platen side opposed to mold 18. At least one of said columns are provided
and two or more of same may readily be used. Column 24 has a first end 26 affixed
to the movable platen and a second end 28 spaced from the movable platen. Second
end 28 of column 24 passes through annular clamp piston 30 which in turn is housed
in clamp cylinder 42 in clamp block 14. Clamp piston 30 has teeth 34 that engage
corresponding teeth 36 on column 24. Rotation of clamp piston 30 may be accomplished
by any desired means, as by cylinder 38 (FIG. 2), or by servo drive means 40 (FIG.
1). Rotation of the clamp piston serves to engage or disengage clamp piston teeth
34 from column teeth 36. Alternatively or in addition, one may provide at least
one axial groove circumferentially spaced between column teeth 36 and rotate the
column to engage and disengage the clamp piston teeth and column teeth.
When the teeth are engaged, as shown in FIG. 2, hydraulic oil pressure
in cylinder 42 acting on clamp piston 30 causes column 24 to transmit a closing
or clamping force against moving platen 16 and hence against mold 18. When hydraulic
pressure is supplied to cylinder 44 and acts on the opposed "mold break" side of
piston 30, an opening force is transmitted via column 24 to moving platen 16 and
hence to mold 18. These opposed forces act through the engaged teeth 34, 36 of
the clamp piston 30 and column 24, respectively.
When cylinder 38 or servo drive 40 are activated, they cause piston
30 to rotate and disengage clamp piston teeth 34 from the corresponding column
teeth 36. Thus disengaged, column 24 and moving platen 16 are free to move with
respect to clamp piston 30 and clamp block 14. This motion is caused by rotating
threaded rod 46 and engaging threaded member or nut 48, which is splined by spline
means 50 inside internal channel 52 of column 24. Rotation of rod 46 can be by
any desired means, as by direct servo motor 54 or via a gearbox or belt, or any
other rotary drive means. Thus, as rod 46 is rotated, column 24 and movable platen
16 are moved. Reversing the rotation of the drive means 54 causes column 24 and
movable platen 16 to move in the opposite direction. Thus, the mold 18 can be opened
or closed using this drive means.
However, a drive means acting on a column through which clamp forces
are generated causes problems. Thus, absent any means for adjusting the relative
linear position between rod 46 and column 24 during actuation of clamp piston 30
in either direction (clamping or mold breaking), a binding force is created at
the threaded engagement of rod 46 and threaded member 48 which over time can cause
severe wear and even seizing. The present invention solves this problem.
Thus, in accordance with the present invention, threaded member 48
is splined by connection with spline means 50 and allowed to float axially with
respect to rod 46 and column 24 such that variations in their respective positions
can be accommodated without inducing stress. Threaded member 48 is provided with
means to limit the stroke thereof. Thus, the threaded member is trapped between
two collars 56, 58 which are themselves located by respective lock rings 60, 62
to limit their stroke. The end faces of collars 56, 58 are acted on by springs,
respectively 64, 66, to centralize the position of the threaded member 48 between
lock rings 60, 62. The springs act against stop means. Thus, spring 66 acts against
end wall 68, and spring 64 acts against stop plate 70 which in turn is fastened
to the end of column 24 by screws 72.
The strength of springs 64, 66 are selected to provide forces larger
than the mold opening or closing forces so as to limit the relative movement between
the threaded member 48 and column 24, during these motions. Other clamp ratings
would have correspondingly different spring ratings.
The springs 64, 66 allow column 24 to move with respect to rod 46
while maintaining a force on both ends of the threaded member 48 to insure that
its position remains centralized within the stroke permitted by lock rings 60,
62. Thus, the force exerted by the threaded member to cause the moving platen
to move passes through the springs.
Another option for smaller sized units is to rely on the screw drive
of the stroke motion to provide the mold break force prior to clamp opening. In
this configuration, the spring 64 can be eliminated and collar 56 can act directly
against stop plate 70 during mold break and clamp opening operations.
Thus, in operation, in the mold open position, motor 54 turns screw
drive or threaded rod 46 that engages threaded member or nut 48 to cause platens
10 and 16 to close. Next cylinder 38 rotates clamp piston 30 so that clamp piston
teeth 34 engage column teeth 36. Oil acts in cylinder 42 to clamp mold 18. After
cooling, the mold break cylinder 44 is activated to cause the mold 18 to open slightly.
The teeth 34, 36 are still engaged at this point. Then cylinder 38 causes piston
30 to rotate to disengage teeth 34, 36. The screw drive or rod 46 then rotates
in the opposite direction to open mold 18.
It is to be understood that the invention is not limited to the illustrations
described and shown herein, which are deemed to be merely illustrative of the best
modes of carrying out the invention, and which are susceptible of modification
of form, size, arrangement of parts and details of operation. The invention rather
is intended to encompass all such modifications which are within its scope as
defined by the claims.