JP2012035441A - Expansion molding method and toggle type mold clamping device - Google Patents

Abstract

An expansion molding method for obtaining a foam molded product with high dimensional accuracy without being affected by thermal expansion and contraction due to temperature change of an apparatus.
In a toggle type mold clamping device (1), a mold clamping force sensor (29) is provided on a tie bar (6), and the mold clamping force is monitored in a mold clamping process. Since the mold clamping force is detected when the molds (15, 16) are touched, the position of the movable platen (8) at this time is set as the reference mold platen position. After injecting molten resin with a foaming agent added to the cavity (C) in the molds (15, 16), the movable platen (8) is driven by a relative movement amount from the reference die plate position. The mold is opened by a predetermined mold opening amount. Bubbles are foamed in the molten resin to obtain a foam molded product.
[Selection] Figure 1

Description

  The present invention injects molten resin added with a foaming agent into a cavity in a clamped mold, opens the mold by a predetermined amount and expands the cavity, thereby forming fine bubbles in the resin. The present invention relates to an expansion molding method for obtaining a foam molded product having a desired size by foaming and a toggle type mold clamping device.

  Foam-molded articles containing a large amount of fine bubbles inside are not only lightweight but also have an excellent characteristic that they have sufficient strength depending on the foaming agent and the foaming rate, and thus are used in various fields. For example, in automobiles, interior parts such as dashboards are molded from such foam-molded products, which are indispensable for reducing vehicle weight and material costs for the purpose of improving fuel efficiency. Such a foam molded product can be molded by various molding methods, and the core back molding method, that is, the expansion molding method is also well known. Specifically, it is molded as follows. A molten resin to which a foaming agent is added, for example, a molten resin to which an inert gas in a supercritical state is added, is injected and filled into a cavity in a mold clamped mold. When the skin layer is formed on the surface of the molten resin in contact with the mold in the cavity, the mold is opened by a predetermined amount to expand the cavity. If it does so, the volume of a cavity will increase, a fine bubble will foam in molten resin, and the volume of a molded article will also increase. The mold is opened after cooling and solidification to obtain a foam-molded product. Since the bubbles are foamed in the resin after the skin layer is formed, scratches due to the bubbles are hardly formed on the surface, and an excellent molded product can be obtained. In the extended molding method, the shape of the product is determined with the mold opened, but it is difficult to accurately control the amount of mold opening. Conventionally, foam molded products have been required to have a relatively moderate dimensional accuracy. Has been applied. However, since foamed molded products can achieve weight reduction and cost reduction while having sufficient strength, application is also required for products that require high dimensional accuracy.

JP-A-2005-254607

  In Patent Document 1, in consideration of the influence of deviation of the opening amount of the mold platen caused by so-called rattling in the toggle mechanism of the toggle type mold clamping device, the mold platen is accurately controlled to have a desired mold opening amount, An expansion molding method for obtaining a foam molded product with high dimensional accuracy is described. Patent Document 1 describes as follows. In other words, the link that makes up the toggle mechanism is connected to the clevis of the platen via a pin, but the inner diameter of the pin hole opened in the link is slightly larger than the outer diameter of the pin. Therefore, there is a slight gap between the pin hole and the pin. Therefore, when the mold is opened in order to foam bubbles in the resin after injecting the molten resin into the mold that has been clamped in the expansion molding method, the mold plate opens more than the intended mold opening amount due to this gap. become. Therefore, in the expansion molding method described in Patent Document 1, the mold opening amount is controlled in consideration of this gap. Accordingly, it is possible to obtain a foam molded product having a relatively high dimensional accuracy. In the expansion method described in Patent Document 1, it is necessary to accurately know the crosshead position where the mold clamping force when the mold is opened from the mold clamped state is zero. This is because the crosshead is accurately controlled on the basis of this crosshead position. This reference crosshead position is measured only once at the beginning when the mold is mounted on the mold clamping device, and is detected by a mold clamping force sensor after the mold is clamped and the mold plate is slowly opened. The crosshead position when the mold clamping force becomes zero is read. The crosshead position is stored in a memory of a control device that controls the injection molding machine, and is used in subsequent expansion molding.

  Also by the expansion molding method described in Patent Document 1, the mold opening is opened in consideration of the backlash of the toggle mechanism, so that the mold opening amount can be controlled relatively accurately without being affected by the backlash. Therefore, it is possible to obtain a foam molded product having a relatively high dimensional accuracy. However, the expansion molding method described in Patent Document 1 also has a point to be improved. Specifically, since the reference crosshead position is measured only once when the mold is attached to the mold clamping device, thermal expansion will occur if the temperature of the mold or the mold clamping device changes during injection molding. Or the heat shrinks and the crosshead position shifts. If it does so, the amount of mold opening cannot be controlled correctly at the time of expansion molding, and the dimensional accuracy of a molded product will not become high enough. If the crosshead position serving as a reference is frequently measured, problems due to thermal expansion and contraction are likely to be solved, but there is another problem. That is, in order to frequently measure the crosshead position as a reference, it is necessary to measure even during expansion molding, but the molten resin injected into the cavity of the mold expands by foaming bubbles inside. Since the mold is pressed with a predetermined force, it is impossible to accurately detect the crosshead position where the mold clamping force is zero. Further, depending on the molding method, there is a case where the injection is continued slightly after the mold is opened. In this case, it is impossible to measure the crosshead position where the mold clamping force is zero. That is, when the method described in Patent Document 1 is adopted, the reference crosshead position cannot be frequently measured. If it does so, the problem of the fall of the dimensional accuracy by the thermal expansion by the change of the temperature of a metal mold | die or a mold clamping device and a thermal contraction cannot be avoided.

  An object of the present invention is to provide an expansion molding method and a mold clamping device that solve the above-described problems, and specifically, thermal expansion and contraction due to temperature changes in a mold and a platen machine. An expansion molding method that can accurately control the amount of mold opening without being influenced by the above, and thereby obtain a foam molded product with high dimensional accuracy, and implementing such an expansion molding method An object of the present invention is to provide a platen device that can be used.

  In order to achieve the above object, the present invention injects a molten resin to which a foaming agent has been added into a cavity in a mold that has been clamped to open the mold by a predetermined mold opening amount. In a toggle type mold clamping device that performs a so-called expansion molding method that expands and thereby foams bubbles in the molten resin to obtain a foam molded product, every time the fixed mold and the movable mold are clamped The mold clamping force is monitored by a mold clamping force sensor provided on the tie bar, and the timing when the mold touches is detected. Then, the position of the movable plate at this time is set as the reference mold plate position. In the expansion process of opening the mold by a predetermined amount after injection, the movable platen is driven by a relative movement amount from the reference die plate position, thereby making the die opening amount constant.

Thus, in order to achieve the above object, the invention according to claim 1 is attached to the stationary mold and the movable platen that are driven by the toggle type clamping device and are attached to the stationary platen of the toggle type clamping device. A mold clamping step of clamping the movable mold that is placed, and injecting a molten resin in which a foaming agent is added into a cavity formed by the clamped fixed mold and the movable mold A molding method for obtaining a foamed molded product from an injection step of filling, and an expansion step of expanding the cavity by opening the movable side mold by a predetermined mold opening amount and foaming in a resin, In the mold clamping step, the mold clamping force is monitored by a mold clamping force sensor provided on a tie bar of a component member of the toggle type mold clamping device, and the movable mold touches the fixed mold. The timing at which mold clamping force is generated is detected and There is also included a reference mold platen position detecting step in which the position of the platen is set as a reference mold platen position, and the expansion step is configured to drive the movable platen from the reference platen position by a relative movement amount. .
According to a second aspect of the present invention, in the method according to the first aspect, the movable platen position is provided in association with the movable platen, and the position of the movable platen can be detected. Configured to measure by.

According to a third aspect of the present invention, there is provided a fixed platen to which the fixed side mold is attached, a movable platen to which the movable side die is attached, a mold clamping housing, and the fixed platen and the mold clamping through the movable platen. A plurality of tie bars connecting the housing, and a toggle mechanism provided between the movable platen and the mold clamping housing, the toggle mechanism is driven by a command from a predetermined controller, A toggle type mold clamping device for an injection molding machine adapted to mold and open a mold, wherein the tie bar is provided with a mold clamping force sensor for detecting a mold clamping force, Clamping force is monitored each time the movable mold is clamped, and the timing at which the fixed mold and the movable mold touch is detected, and the position of the movable platen at that time is the reference mold Save to the controller as the panel position It has become way is, when the movable platen is by mold opening predetermined mold opening amount, configured so that the movable platen is driven by relative movement amount from the reference mold platen position.
Further, the invention according to claim 4 is the toggle type mold clamping device according to claim 3, wherein a mold platen position sensor is provided on the bed on which the toggle type mold clamping device is installed in relation to the movable platen. And the position of the movable platen is detected.

  As described above, according to the present invention, the molten resin to which the foaming agent is added is injected into the cavity in the clamped mold, and the mold is opened by a predetermined amount to expand the cavity. In the expansion molding method to obtain foamed molded products of desired dimensions by foaming fine bubbles in the resin, the mold clamping process is performed by a mold clamping force sensor provided on the tie bar in the mold clamping process of clamping the mold. , And the timing when the mold is touched and the mold clamping force is generated is detected. And since the reference | standard mold board position detection process which uses the movable board position at that time as a reference | standard mold board position is also included, a reference | standard mold board position is detected each time. The expansion process of opening the mold by a predetermined amount is configured to drive the movable plate by a relative amount of movement from the reference platen position. The amount of mold opening is kept constant even if it changes to cause thermal expansion or contraction. That is, a foam molded product with high dimensional accuracy can be obtained. And in patent document 1, although the play of the toggle mechanism became a problem, in the first place, bubbles are foamed in the molten resin and the movable mold is always pushed in the mold opening direction. Even when the method is carried out and the movable platen is opened by a predetermined amount from the reference mold platen position, the movable platen does not shift toward the fixed platen due to backlash. That is, there is no shift of the movable platen due to backlash, so that the mold opening amount can be made constant with high accuracy. According to another invention, the movable platen position is configured to be measured by a mold platen position sensor provided in association with the movable platen and capable of detecting the position of the movable platen. It is guaranteed that the position of can be measured easily and accurately. That is, it is possible to easily form a foam molded product with high dimensional accuracy.

It is a front view which shows the injection molding machine provided with the toggle type | mold clamping apparatus which concerns on embodiment of this invention. 5 is a graph showing a relationship between a movable platen position and a mold clamping force in the toggle type mold clamping apparatus according to the embodiment of the present invention. Each position of the movable plate of the toggle type clamping device and the screw of the injection device that operate in association with each other when the expansion molding is performed by the injection molding machine including the toggle type clamping device according to the present embodiment. It is a graph which shows the change of. It is a flowchart which shows each process of expansion molding in the injection molding machine provided with the toggle type | mold mold clamping apparatus which concerns on this Embodiment.

  Embodiments of the present invention will be described below. The injection molding machine SM according to the present embodiment is composed of a toggle type mold clamping device 1 and an injection device 3 as shown in FIG. The toggle type mold clamping device 1 according to the present embodiment is also configured in substantially the same manner as a conventional toggle type mold clamping device, and has a fixed platen 4 fixedly provided on the bed 2 and a shaft on the bed 2. The mold clamping housing 5 provided so as to be movable in the direction, four tie bars 6, 6,... Provided between the stationary platen 4 and the mold clamping housing 5, and these tie bars 6, 6,. A movable platen 8 that is movable in the axial direction, a toggle mechanism 10 provided between the mold clamping housing 5 and the movable platen 8, and driving the toggle mechanism 10, for example, a servo motor 11, a pulley 12, and a ball screw 13. And the like. A fixed mold 15 is attached to the fixed platen 4 thus configured, and a movable mold 16 is attached to the movable platen 8.

  The toggle mechanism 10 includes short links 18 and 18, long links 19 and 19, cross links 20 and 20, a cross head 21 and the like. One end of the short links 18, 18 is connected to the clevis 23, 23 provided in the mold clamping housing 5 by pins 24, 24, and one end of the long links 19, 19 is connected to the movable plate 8 by pins 26, 26. Are pivotally attached to clevises 27, 27 provided on the body, respectively. The other ends of the short links 18 and 18 and the other ends of the long links 19 and 19 are rotatably connected by pins 28 and 28. The cross head 21 is provided with a ball nut and screwed into the ball screw 13. The cross head 21 and the short links 18, 18 are rotatably connected to the cross links 20, 20 by predetermined pins. . Accordingly, when the mold opening / closing actuator, that is, the servo motor 11 is driven and the ball screw 13 is rotated via the pulley 12, the cross head 21 is driven in the left-right direction in FIG. 1 and the toggle mechanism 10 is driven. Then, the movable platen 8 is driven in the direction of the fixed platen 4, and the fixed side die 15 and the movable side die 16 are clamped. Alternatively, the movable platen 8 is driven in a direction away from the fixed platen 4, and the fixed mold 15 and the movable mold 16 are opened.

  In the toggle type mold clamping apparatus 1 according to the present embodiment, one tie bar 6 is provided with a mold clamping force sensor 29 for detecting a mold clamping force, and the mold clamping force sensor 29 is connected to a controller via a signal line 31. 32. Specifically, the mold clamping force sensor 29 is a strain sensor, and distortion of the tie bar 6 that occurs during mold clamping is detected as a change in resistance, and is converted into a mold clamping force by the controller 32.

  The bed 2 is provided with a mold platen position sensor 34 including a fixed guide 35 and a slider 36 that slides the guide 35, and the slider 36 is fixed to the movable platen 8. The position of the slider 36 on the guide 35 is detected. Therefore, the position of the movable platen 8 can be detected by detecting the position of the slider 36. The position of the slider 36 can be detected with high accuracy by a known encoder such as an absolute encoder or an incremental encoder. The platen position sensor 34 is also connected to the controller 32 via a signal line 38. The controller 32 can transmit a signal to the servo motor 11 via the signal line 39, and the servo motor 11 is controlled by the controller 32.

  Although the injection device 3 is well known and will not be described in detail, the cylinder 41, a screw provided in the cylinder 41 so as to be driven in the axial direction and the rotation direction, an injection nozzle 42 provided in front of the cylinder 41, and the like It is composed of A heater for heating the cylinder 41 is wound around the outer peripheral surface of the cylinder 41. FIG. 1 does not show the heater and the screw. The fixed platen 4 has an injection nozzle insertion hole 44, the injection device 3 is inserted from the back of the fixed platen 4, and the nozzle 42 touches the sprue of the fixed side mold 15. The injection device 3 is also connected to the controller 32 by a signal line 45 and is controlled by a command from the controller 32.

A method for obtaining a foam molded product by expansion molding using the injection molding machine SM according to the present embodiment will be described with reference to FIGS. 2, 3, and 4.
The metering process is performed in the injection device 3 as follows. The resin material is supplied to the cylinder 41 while heating the cylinder 41 with a heater and rotating the screw. Then, the resin material is melted and kneaded by the heat generated by the heater and the frictional heat generated by the rotation of the screw and sent to the front of the cylinder 41, and the screw moves backward. When a predetermined amount of molten resin is measured in front of the cylinder 41, the screw is rotated at a low speed. A foaming agent made of carbon dioxide in a supercritical state is injected into the cylinder 41 and kneaded with the molten resin. Finish the weighing process. Note that the flow chart of FIG. 4 does not show the first measurement step performed.

  In the toggle type mold clamping device 1, the mold clamping process is performed as follows. The servo motor 11 is driven by a command from the controller 32. Then, the cross head 21 is driven via the pulley 12 and the ball screw 13. The movable platen 8 is driven rightward in FIG. Since the mold clamping force is not generated until the fixed mold 15 and the movable mold 16 are touched, the mold clamping force detected by the mold clamping sensor 29 is substantially zero. The mold clamping force is detected at the moment when 16 is touched. The position of the movable platen 8 at the timing when the molds 15 and 16 are touched is detected by the platen position sensor 34, and this is input to the controller 32 as the reference platen position. Actually, since noise is applied to the mold clamping force detected by the mold clamping force sensor 29, a minute mold clamping force is detected even when the molds 15 and 16 are not touched. Therefore, when the mold clamping force reaches a predetermined threshold value which is a small mold clamping force, it is considered that the molds 15 and 16 are touched. The graph of FIG. 2 shows the relationship between the position of the movable platen 8 and the mold clamping force detected by the mold clamping force sensor. The position of the movable platen 8 at the timing when the mold clamping force reaches the threshold value is shown. It is shown that it is set as a reference mold platen position. Even after the molds 15 and 16 are touched, the movable platen 8 is driven until the mold clamping force reaches the set mold clamping force. The graph of FIG. 3 shows a state where the movable platen 8 is driven to the mold clamping completion position beyond the reference mold platen position 47. The servo motor 11 is stopped to complete the mold clamping process.

  After completion of the mold clamping process, after waiting for injection for a predetermined time, an injection pressure holding process is started in the injection device 3. The screw of the injection device 3 is driven in the axial direction. If it does so, the molten resin to which the foaming agent was added will be inject | emitted, and the molten resin will be filled into the cavity C comprised by the fixed side metal mold | die 15 and the movable side metal mold | die 16. FIG. At this time, the surface of the molten resin in contact with the molds 15 and 16 is cooled and solidified to form a skin layer.

  When the controller 32 detects that the screw has reached the predetermined position, the expansion process is started in the toggle type mold clamping apparatus 1 as follows. The servo motor 11 is driven by a command from the controller 32 to drive the movable platen 8 by a predetermined amount in the left direction in FIG. 1, and the fixed mold 15 and the movable mold 16 are set in the controller 32 in advance. Open only the set amount that is set. Specifically, the movable platen 8 is driven by a set die opening amount relative to the reference platen position. Then, since the mold is opened based on the reference mold platen position determined in the mold clamping process, it is not affected by the thermal expansion or contraction due to the temperature change of the toggle type mold clamping device 1 or the molds 15 and 16. The mold opening amount is guaranteed to be constant. The servo motor 11 is stopped at the position where the mold is opened by the set mold opening amount, and the extended holding process is started. When the molds 15 and 16 are opened, the capacity of the cavity C increases and the foaming agent foams in the molten resin.

  Even after the transition to the extended holding process in the toggle type mold clamping apparatus 1, the screw is driven to the pressure holding completion position in the injection apparatus 3 as shown in the graph of FIG. After passing the measurement standby for maintaining the screw position for a predetermined time, the injection device 3 performs the measurement process as described above to prepare for the next molding cycle. That is, the resin material is supplied to the cylinder 41 while heating the cylinder 41 with a heater and rotating the screw. Then, the resin material is melted and kneaded by the heat generated by the heater and the frictional heat generated by the rotation of the screw and sent to the front of the cylinder 41, and the screw moves back to the measurement completion position. When a predetermined amount of molten resin is measured in front of the cylinder 41, the screw is rotated at a low speed. A foaming agent made of carbon dioxide in a supercritical state is injected into the cylinder 41 and kneaded with the molten resin. Finish the weighing process.

  In the toggle mold clamping apparatus 1, the second half of the expansion holding process is also a cooling process in which the molten resin injected into the cavity is cooled and solidified. When the molten resin is cooled and solidified, the servo motor 11 is driven by a command from the controller 32 to drive the movable platen 8 to the mold opening completion position. After the mold is opened, although not shown in FIG. 1, the molded product is ejected by an ejector pin, and the molded product is taken out. Thereafter, molding is performed in the same manner.

  The injection molding machine SM according to the present embodiment can be variously modified. For example, although it has been described that the position of the movable platen 8 is directly detected by the platen position sensor 34, a position sensor is provided in association with the crosshead 21, and the position of the crosshead 21 is detected, You may make it detect the position of the movable board 8 indirectly. Alternatively, the rotation angle of the servo motor 11 may be detected to indirectly detect the position of the movable platen 8. Further, although the foaming agent added to the molten resin is described as being supercritical carbon dioxide, it may be nitrogen or other inert gas, and may further be a chemical foaming agent. In the description of the present embodiment, the toggle type mold clamping device 1 is described as an injection molding machine of the type laid on the bed 2, but the same applies to a vertical injection molding machine. can do. Further, the molding method can be modified. For example, in the above description, it is described that the screw is driven in the injection device 3 even after the expansion process is started, and a predetermined amount of molten resin is injected even after the predetermined mold opening amount is opened. However, the expansion process may be started after the injection is completed. Further, although the mold opening is performed only once in the expansion process, the cavity capacity may be increased little by little by gradually opening the mold over a plurality of times.

SM injection molding machine 1 toggle type clamping device 2 bed 3 injection device 4 fixed plate 5 mold clamping housing 6 tie bar 8 movable plate 10 toggle mechanism 11 servo motor 15 fixed side die 16 movable side die 29 mold clamping force sensor 32 controller 34 Platen position sensor C Cavity

Claims (4)

A mold clamping step of driving a toggle mold clamping device to clamp a fixed mold attached to the fixed plate of the toggle mold clamping device and a movable mold attached to the movable plate; An injection step of injecting and filling molten resin in which a foaming agent is added to a cavity constituted by the clamped fixed mold and the movable mold, and the movable mold is opened by a predetermined mold opening amount. An expansion step of expanding the cavity by opening the mold and foaming in the resin, and a molding method for obtaining a foamed molded product from the expansion step,
In the mold clamping step, the mold clamping force is monitored by a mold clamping force sensor provided on a tie bar of a component member of the toggle type mold clamping device, and the movable mold touches the fixed mold. It also includes a reference mold platen position detection process that detects the timing at which mold clamping force is generated and sets the position of the movable platen at that time as the reference mold platen position.
In the expansion step, the movable platen is driven by a relative movement amount from the reference platen position. 2. The method according to claim 1, wherein the movable platen position is measured by a platen position sensor provided in association with the movable platen and capable of detecting the position of the movable platen. Molding method. A fixed plate to which the fixed mold is attached, a movable plate to which the movable mold is attached, a mold clamping housing, and a plurality of plates that pass through the movable plate and connect the fixed plate and the mold clamping housing. And a toggle mechanism provided between the movable platen and the mold clamping housing, and the toggle mechanism is driven by a command from a predetermined controller so that the mold is clamped and opened. A toggle type clamping device for an injection molding machine,
The tie bar is provided with a mold clamping force sensor for detecting a mold clamping force, and the mold clamping force is monitored every time the fixed side mold and the movable side mold are clamped, and the fixed side mold The timing of touching the movable mold is detected, and the position of the movable plate at that time is stored in the controller as a reference mold plate position,
A toggle type mold clamping device, wherein when the movable platen is opened by a predetermined die opening amount, the movable platen is driven by a relative movement amount from the reference die platen position. 4. The toggle mold clamping device according to claim 3, wherein a mold platen position sensor is provided on the bed on which the toggle mold clamping device is installed in relation to the movable platen, and the position of the movable platen is detected. Toggle type mold clamping device characterized by being configured.

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