Clamping apparatus for injection molding machine

Disclosed herein is a five-joint clamping apparatus for an injection molding machine. The clamping apparatus according to the present invention keeps advantages of a conventional five-joint clamping apparatus, specifically, high mold opening or closing speed and control precision, has an increased stroke distance in link mechanism, and has a structure capable of pressing a central portion of a mold.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to clamping apparatuses for injection molding machines and, more particularly, to a five-joint clamping apparatus for an injection molding machine which retains the advantages of a conventional five-joint clamping apparatus, specifically, high mold opening or closing speed and control precision, has an increased stroke distance in link mechanism, and has a structure capable of pressing a central portion of a mold.

2. Description of the Related Art

Injection molding machines are apparatuses for forming products of synthetic resin material or the like. Generally, injection molding machines form products in such a way as to melt chips or powder and put it into a mold having a predetermined shape. There are various kinds of injection molding machines, from small sized machines to large sized machines. Polyester, vinyl acetate, different kinds of plastics, nylon, etc. can be used as material for forming products using the injection molding machines.

Such injection molding machines are classified into hydraulic injection molding machines and electric injection molding machines. In conventional techniques, hydraulic injection molding machines have been widely used.

Among hydraulic injection molding machines, a direct pressure type injection molding machine, in particular, has an advantage of a simple structure, being configured such that a mold is opened or closed by a cylinder.

However, the hydraulic injection molding machine requires consumption of a large amount of working fluid, inducing disadvantages of causing environment pollution and being difficult to maintain and repair.

As the above disadvantages of the hydraulic injection molding machine are magnified, electric injection molding machines, which are configured such that operation thereof including mold closing or opening operation is enabled by a servo-motor, are being more widely used.

Among the electric injection molding machines, toggle type injection molding machines are mainly used.

The electric injection molding machines require, in terms of maintenance, only the lubrication of toggle links, are able to reduce energy consumption by up to 80%, and markedly reduce the possibility of environment pollution because working oil is not used.

The injection molding machines are apparatuses which conduct injection molding operation after mold closing force has been applied to a mold between a movable plate and a stationary plate using tie bars.

As stated above, toggle type injection molding machines are mainly used as the electric injection molding machines and are operated in such a way that, while a mold is interposed between a movable plate and a stationary plate, as links are stretched, pushing force applied to the mold is increased, thus generating the mold closing force and increasing it.

For this, the injection molding machines include a clamping apparatus. Clamping apparatuses of the toggle type injection molding machines are classified into a single toggle type clamping apparatus including a pair of toggle links, and a double toggle type clamping apparatus including two pairs of toggle links.

The single toggle type clamping apparatus is suitable for a small injection molding machine. The double toggle type clamping apparatus is suitable for an injection molding machine that requires comparatively mold closing force.

Double toggle type clamping apparatuses are classified into a four-joint type and a five-joint type according to a structure of connecting a toggle link to a crosshead link.

The four-joint clamping apparatus is configured such that a crosshead link, a long link and a short link are connected together by a single joint.

The four-joint clamping apparatus is advantageous in that comparatively large mold closing force can be generated using relatively small input force, because mechanical advantage is large.

However, in the four-joint clamping apparatus, a displacement of the crosshead is comparatively large during a mold opening or closing stroke. Therefore, a mold opening speed is low, and the size of the clamping apparatus is increased.

To overcome the problems of the four-joint clamping apparatus, the five-joint clamping apparatus was proposed.

The five-joint clamping apparatus is configured such that a joint of connecting a crosshead link to a short link is provided separately from a joint of connecting a long link to the short link.

In the five-joint clamping apparatus, the crosshead link112is connected to the short link108at a joint E1which forms a smaller radius of rotation based on a joint B1than does a joint A1. Compared to the four-joint clamping apparatus in which the crosshead link112is connected to the joint A1, the speed of a mold opening or closing stroke is increased, and the length of the clamping apparatus can be reduced because of reduced displacement of the crosshead111.

Furthermore, the conventional five-joint clamping apparatus has an inward-folding and inner-joint type toggle link structure in which a toggle link is folded inwards and a link coupling part is fixed to an inner joint (refer toFIG. 2). Such an inward-folding and inner-joint type toggle link structure is advantageous in that it is suitable for a typical toggle link structure that is operated at high speed.

However, in the inward-folding and inner-joint type toggle link structure, the maximum stroke distance of the movable plate is 540 mm, and it is very difficult to further increase the stroke distance.

Meanwhile, to improve the conventional inward-folding and inner-joint type toggle link structure, an improved toggle link structure was proposed in U.S. Pat. No. 5,843,496 (hereinafter, referred to as conventional technique 1) in which a link coupling part is fixed to an outer joint.

Conventional technique 1 provides an inward-folding and outer-joint type toggle link structure, in which the area the links take in the injection molding machine is reduced and efficiency of mold clamping force generation is enhanced, compared to the inward-folding and inner-joint type toggle link structure.

The inward-folding and outer-joint type toggle link structure according to conventional technique 1 has advantages of improved efficiency in generating mold clamping force and being capable of more smoothly applying mold clamping force to a mold. However, it still has problems of difficulty in achieving a long stroke distance, that is, increasing the stroke distance, and difficulty in embodying high-speed operation.

Typically, in the case of the electric injection molding machines, toggle type injection molding machines are mainly used. In such a toggle type, links are connected to a perimeter of a movable plate rather than to a central portion thereof.

Therefore, during a mold closing operation, the links press the perimeter of the movable plate, thus markedly increasing the possibility of the mold being deformed compared to that of the direct pressure type injection molding machine. Furthermore, it is very difficult for the toggle type injection molding machines to realize a center pressing structure such that force is applied to central portion of the movable plate.

PRIOR ART DOCUMENT

Patent Document

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a clamping apparatus for injection molding machines which can achieve purposes of high-speed mold opening or closing operation and an increase in a stroke distance and is capable of embodying a center pressing structure of the same level as that of the direct pressure type injection molding machine.

In order to accomplish the above object, the present invention provides a clamping apparatus for injection molding machines, including: a motor; a ball screw operated by the motor, the ball screw being oriented in a horizontal direction; a crosshead coupled to the ball screw so that, when the ball screw rotates, the crosshead moves forwards or backwards; a stationary plate and a rear plate connected to a tie bar; and a movable plate disposed between the stationary plate and the rear plate, the movable plate being moved forwards or backwards by links,

wherein the links comprise: a first link having a first end forming a B-joint along with a first-side extension of the rear plate, the first link being oriented leftward and downwards based on the B-joint when the movable plate is moved backwards; a second link having a first end forming a G-joint along with a portion that protrudes outwards from a side surface of the first link, and a second end forming a D-joint along with the crosshead, the second link being oriented leftward and upwards based on the G-joint while connecting the G-joint to the D-joint; and a third link having a first end forming an A-joint along with a second end of the first link, and a second end forming a C-joint along with a second-side extension of the movable plate, the third link being oriented rightward and upwards based on the A-joint, wherein

when the movable plate is moved forwards, the first link the first end of which forms the B-joint along with the first-side extension of the rear plate is horizontally oriented rightward based on the B-joint, the first end of the second link forms the G-joint along with the portion that protrudes outwards from the side surface of the first link, the second end of the second link forms the D-joint along with the crosshead, and the second link is oriented upwards based on the G-joint while connecting the G-joint to the D-joint, and the first end of the third link forms the A-joint along with the second end of the first link, the third link is oriented rightward based on the A-joint, and the second end of the third link forms the C-joint along with the second-side extension of the movable plate.

A clamping apparatus for injection molding machines according to the present invention has the following advantages.

(1) a toggle link structure is operated in such a way as to extend outwards, thus making it possible to increase a stroke distance.

(2) because the toggle link structure is operated in such a way as to extend outwards, mold opening or closing operation can be conducted at very high speed compared to that of the conventional five-joint toggle link structure.

(3) since a link that is connected to a movable plate is connected to a center or central portion of the movable plate, pressure of the same level as that of the direct pressing mold clamping apparatus can be applied to a mold, during a mold closing operation.

(4) the toggle link structure is operated in such a way as to extend outwards, and a crosshead and the movable plate correspond to each other in speed distribution. Therefore, shock is not generated even during high-speed operation, so that low-vibration and high-speed mold opening or closing operation can be realized.

(5) force required to accelerate or decelerate the movable plate is comparatively low, thus making low-vibration operation and high-cycle operation possible.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a clamping apparatus for an injection molding machine according to a preferred embodiment of the present invention will be described in detail with reference toFIGS. 3 and 4.

The clamping apparatus of the injection molding machine according to the present invention includes a motor F, a ball screw15which is operated by the motor F and is horizontally disposed, a crosshead18which is coupled to the ball screw15and is moved forwards or backwards by rotation of the ball screw15, a stationary plate4and a rear plate6which are coupled to tie bars5, and a movable plate7which is disposed between the stationary plate4and the rear plate6and is moved forwards or backwards by links.

The motor F is disposed on a second side6bof the rear plate6. Preferably, a servo-motor is used as the motor F.

The motor F functions to operate the crosshead18for opening or closing a mold.

Furthermore, the motor F is connected to the crosshead18by the ball screw3.

The crosshead18moves forwards or backwards along the ball screw3connected to the motor F.

Crosshead links E are provided on the crosshead18. When viewed from a side view of the clamping apparatus1of the injection molding machine, the crosshead links E are oriented in the vertical direction.

D-joints80are provided on central portions of the respective crosshead links E.

In detail, each D-joint80is formed on an outer protrusion18aprovided on an outer surface of the corresponding crosshead link E. The outer protrusion18aof each crosshead link E is preferably formed at a point corresponding to about ⅔ of the length of the crosshead link E based on the ball screw3.

When viewed from the clamping apparatus1of the injection molding machine of the present invention, the outer protrusion18aof the crosshead link E that is disposed below the ball screw3is inclined rightward and upwards.

When viewed from the clamping apparatus1of the injection molding machine of the present invention, the outer protrusion18aof the crosshead link E that is disposed above the ball screw3is inclined rightward and downwards.

The tie bars are connected to the stationary plate6.

In detail, first ends5aof the tie bars are connected to a first side4aof the stationary plate6.

Second ends5bof the tie bars are connected to a first side6aof the rear plate6.

As such, the stationary plate4and the rear plate6are disposed on the front and rear ends of the tie bars5.

The movable plate7is disposed between the stationary plate4and the rear plate6.

The rear plate7is moved by the links, which will be explained later herein, forward or rearwards under guidance of the tie bars5.

Hereinafter, the links, which are operated such that, when the movable plate7is moved forwards or backwards by the operation of the motor F under guidance of the tie bars5, mold clamping force is applied to a mold (not shown) that is mounted between the movable plate7and the stationary plate4, will be explained in detail with reference to the drawings.

In the clamping apparatus1of the injection molding machine according to the present invention, when the movable plate7along with the crosshead18is moved backwards by the operation of the motor F, the mold opens, in other words, enters an open mold state.

In the open mold state, the position and shape of the links of the clamping apparatus1according to the present invention are as follows.

The links are configured to have a five-joint structure that depends on a connection structure of the crosshead link E.

Each first link14is connected to a first-side extension6cof the rear plate.

When viewed from the side view of the clamping apparatus1of the injection molding machine according to the present invention, the shape of the first-side extension6cof the rear plate will be explained below.

The first-side extension6cof the rear plate includes a first part6dand a second part6ewhich is connected to the first part6d.

The first part6dof the first-side extension of the rear plate is thicker than the second part6eof the first-side extension.

A B-joint60, which will be explained later herein, is formed on the second part6eof the first-side extension of the rear plate and is connected to the first link14.

A first end14aof the first link14forms the B-joint60between it and the first-side extension6cof the rear plate6, in detail, the second part6eof the first-side extension6c.

Thereby, the first link14is provided so as to be rotatable around the B-joint60.

When viewed from the side view of the clamping apparatus1according to the present invention, the first link14that is disposed below the ball screw3extends leftward and downwards based on the B-joint60and is longer and thicker than a second link16which will be explained later herein.

Furthermore, when viewed from the side view of the clamping apparatus1according to the present invention, the first link14that is disposed above the ball screw3extends leftward and upwards based on the B-joint60and is also longer and thicker than the second link16.

A second end14bof the first link14is connected to a third link19, which will be explained later herein, with an A-joint50formed between the second end14band the third link19. The connection of the second end14bof the first link14to the third link19will also be explained later.

A G-joint90is formed on a portion that protrudes outwards from a side surface of each first link14, that is, on a protrusion14cof the first link14.

The position at which the G-joint90is disposed is a point corresponding to about ⅔ of the length of the first link14below the B-joint60.

Each G-joint90is connected to the corresponding second link16.

A first end16aof each second link16forms the G-joint90between it and the portion that protrudes outwards from the side surface of the corresponding first link14, that is, the protrusion14cof the first link14.

A second end16bof each second link16forms the D-joint between it and the outer protrusion18aof the corresponding crosshead link E.

When viewed from the side view of the clamping apparatus1of the present invention, the second link16that is disposed below the ball screw3extends leftward and upwards based on the G-joint90.

Each second link16connects the corresponding G-joint90to the associated D-joint80.

When viewed from the side view of the clamping apparatus1of the present invention, the second link16that is disposed above the ball screw3extends leftward and downwards based on the G-joint90.

The outer protrusions18aof the crosshead links E are configured such that, when viewed from the clamping apparatus1of the injection molding machine, one of the outer protrusions18athat is disposed below the ball screw3is inclined rightward and upwards, and the other outer protrusion18athat is disposed above the ball screw3is inclined rightward and downwards.

The second link16is shorter than the first link14. When viewed from the sectional view of the clamping apparatus1of the present invention, the second link16is disposed between the first link14and the third link19which will be explained later herein.

In the clamping apparatus1according to this embodiment of the present invention, the two second links16are respectively disposed above and below the ball screw3.

Each third link19is connected at a first end19athereof to the second end14bof the corresponding first link, thus forming the A-joint50.

That is, each first link14is connected to the corresponding third link19, thus forming the A-joint50. When the movable plate7that has been moved forwards by the motor F to conduct a mold closing operation is moved backwards again to conduct a mold opening operation, the first links14and the third links19which are connected to the corresponding A-joints50are moved outwards.

Consequentially, the first links14and the third links19move towards the corresponding tie bars5.

As shown inFIG. 2, in the conventional five-joint clamping apparatus (refer to conventional technique 1), when the movable plate107is moved backwards, the links108and109move inwards, that is, towards the ball screw, based on the A1-joints.

Because the links108and109move inwards towards the ball screw, if the lengths of the links108and109are increased to increase a stroke distance, interference between the ball screw and the links108and109is inevitable. Therefore, there is a limitation in increasing the stroke distance.

However, in the clamping apparatus1of the injection molding machine according to the present invention, the first links14and the third links19which are connected to the A-joints50are moved outwards. Here, because open space is defined between the tie bars5of the injection molding machine, the first links14and the third links19enter the open space when moving outwards. Therefore, it becomes possible to increase the stroke distance (refer toFIG. 3).

Furthermore, because the first links14and the third links19which are connected to the A-joints50are moved outwards, force required to move the links is smaller than that of the conventional five-joint clamping apparatus (referring to conventional technique 1).

Therefore, force required to accelerate or decelerate the movable plate7is small, thus making it possible to conduct the mold opening or closing operation with low vibration. Since force required to conduct the mold opening or closing operation is reduced, high-cycle operation of the injection molding machine also becomes possible.

FIGS. 7A through 8Bare speed-weight analysis graphs of the clamping apparatus1of the injection molding machine according to the present invention and speed-weight analysis graphs of conventional five-joint clamping apparatus.

As shown inFIG. 7A, in the clamping apparatus1of the injection molding machine according to the present invention, the crosshead18and the movable plate7correspond to each other in speed distribution. Therefore, low-vibration and high-speed mold opening or closing operation becomes possible.

Furthermore, as shown inFIG. 7B, because force required when accelerating or decelerating the movable plate7to conduct the mold opening or closing operation is comparatively small, the present invention is suitable for realizing low-vibration and high-cycle operation of the injection molding machine.

According to speed analysis of the conventional five-joint clamping apparatus, there is a moment at which the crosshead and the movable plate do not correspond to each other in speed distribution. Hence, when the five-joint clamping apparatus is operated at high speed, shock is generated. Furthermore, because force required to accelerate or decelerate the movable plate is comparatively large, it is difficult to realize the low-vibration and high-cycle operation of the injection molding machine (refer toFIGS. 8A and 8B).

Meanwhile, when viewed from the side view of the clamping apparatus1of the injection molding machine according to the present invention, the third link19that is disposed below the ball screw3extends rightward and upwards based on the A-joint50.

Furthermore, when viewed from the side view of the clamping apparatus1according to the present invention, the third link19that is disposed above the ball screw3extends rightward and downwards based on the A-joint50.

A second end19bof each third link19is connected to a second-side extension7bof the movable plate with a C-joint70formed therebetween.

The joints50,60,70,80and90function to make it possible to rotate the links14,16and19, the crosshead links18and the second-side extensions7bof the movable plate which are connected to each other by the joints50,60,70,80and90.

Relative positions of the joints50,60,70,80and90are as follows.

These relative positions will be explained based on the B-joint60.

First, each C-joint70is at the right of the corresponding B-joint60. The C-joint70that is disposed below the ball screw3is below the corresponding B-joint60.

On the other hand, the C-joint70that is disposed above the ball screw3is above the corresponding B-joint60.

Each G-joint90is disposed between the corresponding B-joint60and the associated C-joint70at a position closer to the B-joint60than the C-joint70.

The G-joint90that is disposed below the ball screw3is positioned below the corresponding B-joint60and the associated C-joint70and above the corresponding A-joint50which will be explained later herein.

The G-joint90that is disposed above the ball screw3is positioned above the corresponding B-joint60and the associated C-joint70and below the corresponding A-joint50.

Each A-joint50is disposed between the corresponding G-joint90and the associated D-joint80at the left of the corresponding B-joint60. The A-joint50that is disposed below the ball screw3is positioned below the other joints60,70,80and90, in other words, at the lowermost position among the joints.

The A-joint50that is disposed above the ball screw3is positioned above the other joints60,70,80and90, in other words, at the uppermost position among the joints.

Each D-joint80is disposed at the left of the corresponding B-joint60, that is, at the leftmost position among the joints, and is connected to the crosshead link E.

The D-joint80that is disposed below the ball screw3is positioned below the corresponding B-joint60and above the associated G-joint90, in other words, between the G-joint90and the B-joint60.

The D-joint80that is disposed above the ball screw3is positioned above the corresponding B-joint60and below the associated G-joint90, in other words, between the G-joint90and the B-joint60.

In the clamping apparatus1of the injection molding machine according to the present invention, when the movable plate7is moved forwards by the operation of the motor F, the mold is closed, that is, enters a mold closed state.

In the mold closed state, the positions and shapes of the links of the clamping apparatus1of the injection molding machine according to the present invention are as follows.

Each first-side extension6cof the rear plate, in more detail, the second part6eof each first-side extension6cof the rear plate, along with the corresponding first link14, forms the B-joint60.

In the mold closed state, the first link14is oriented to the right towards the movable plate7.

As stated above, each G-joint90is formed on the protrusion14cof the corresponding first link14.

Each second link16is connected to the corresponding G-joint90.

That is, the first end16aof the second link16is connected to the first link14by the G-joint90.

The second end16bof each second link16is connected to the outer protrusion18aof the corresponding crosshead link by the associated D-joint80.

In this mold closed state, when viewed from the side view of the clamping apparatus1of the present invention, the second link16that is disposed above the ball screw3extends upwards based on the corresponding G-joint90.

On the other hand, when viewed from the side view of the clamping apparatus1of the present invention, in this mold closed state, the second link16that is disposed below the ball screw3extends downwards based on the corresponding G-joint90.

The second link16is disposed between the B-joint60and the A-joint50.

In the mold closed state, the positions and shapes of the third links19will be explained below.

The first end19aof each third link19is connected to the second end14bof the corresponding first link, thus forming the A-joint50.

Furthermore, the second end19bof each third link19, along with the corresponding second-side extension7bof the movable plate, forms the C-joint70.

The second-side extensions7bof the movable plate are disposed around a central portion of the movable plate7.

As stated above, each second-side extension7bof the movable plate is connected to the second end19bof the corresponding third link by the associated C-joint70.

In the mold closing operation, as the third links19move towards the movable plate7, the second-side extensions7bof the movable plate that are connected to the third links19push the movable plate7forwards.

Here, because the second-side extensions7bof the movable plate are disposed around the central portion of the movable plate7, mold closing force is applied to a central portion of the mold (not shown) that is disposed between the movable plate7and the stationary plate4.

Therefore, in the clamping apparatus1of the present invention, the intensity of the mold closing force that is applied to the mold during the mold closing operation can become almost the same level as that of a direct pressure type mold clamping apparatus

Each third link19is disposed at the right of the corresponding A-joint50and oriented towards the associated second-side extension7bof the movable plate.

In other words, the third link19is positioned between the second link16and the second-side extension7bof the movable plate.

In this embodiment of the clamping apparatus1of the injection molding machine according to the present invention, two pairs of first links14and two pairs of third links19, that is, four firs links14and four third links19, are provided. When viewed from the side view, a pair of first links14and a pair of third links19are disposed below the ball screw3.

In addition, a pair of first links14and a pair of third links19are disposed above the ball screw3.

As stated above, the joints50,60,70,80and90function to make it possible to rotate the links14,16and19, the crosshead links18and the second-side extensions7bof the movable plate which are connected to each other by the joints50,60,70,80and90.

The relative positions of the joints50,60,70,80and90, when in the mold closed state, are as follows.

Based on the B-joint60, the relative positions of the other joints will be explained below.

Each A-joint50is disposed at the right of the corresponding B-joint60and at the left of the associated C-joint70. In other words, the A-joint60is positioned between the B-joint60and the C-joint70.

The A-joint50that is disposed above the ball screw3is positioned slightly above the B-joint60and between the corresponding D-joint80and the corresponding G-joint90.

The A-joint50that is disposed below the ball screw3is positioned slightly below the B-joint60and also disposed between the corresponding D-joint80and the corresponding G-joint90.

Each C-joint70is disposed at the right of the corresponding B-joint60and even the corresponding A-joint50.

That is, the C-joint70is disposed at the rightmost position of the other joints.

The C-joint70that is disposed above the ball screw3is positioned slightly above not only the B-joint60but also the A-joint50.

However, the C-joint70is disposed between the D-joint80and the G-joint90.

The C-joint70that is disposed below the ball screw3is positioned slightly below not only the B-joint60but also the A-joint50.

Furthermore, the C-joint70that is disposed below the ball screw3is positioned between the D-joint80and the G-joint90in the same manner as that of the C-joint70that is disposed above the ball screw3.

Each D-joint80is disposed at the right of the corresponding B-joint60and at the left of the corresponding A-joint50. In other words, the D-joint80is positioned between the B-joint60and the A-joint50.

The D-joint80that is disposed above the ball screw3is positioned above the B-joint60, the A-joint50, the C-joint70and the G-joint90.

The D-joint80that is disposed below the ball screw3is positioned below the B-joint60, the A-joint50, the C-joint70and the G-joint90.

Each G-joint90is disposed at the right of the corresponding B-joint60and at the left of the corresponding A-joint50. In other words, the G-joint90is positioned between the B-joint60and the A-joint50.

The G-joint90that is disposed above the ball screw3is positioned below the B-joint60, the A-joint50, the C-joint70and the D-joint90. Therefore, in the mold closed state, among these joints, the G-joint90that is disposed above the ball screw3is disposed at the lowermost position.

On the other hand, the G-joint90that is disposed below the ball screw3is positioned above the B-joint60, the A-joint50, the C-joint70and the D-joint90. Thus, in the mold closed state, among these joints, the G-joint90that is disposed below the ball screw3is disposed at the uppermost position.

Based on the B-joint60, because the G-joint90is disposed at a position spaced slightly farther from the B-joint60than is the D-joint80, the G-joint90and the D-joint80are not placed on the same vertical line.

Unlike the conventional five-joint clamping apparatus, the clamping apparatus of the injection molding machine according to the present invention has a structure capable of center pressing, as shown in the schematic view (see,FIG. 9) illustrating mechanism of the links and the joints.

As described above, a clamping apparatus for an injection molding machine according to the present invention can realize a high-cycle and long-stroke distance structure, while keeping advantages of the conventional five-joint clamping apparatus, that is, the advantages of high mold opening or closing speed and control precision.