JP5000213B2 - Mold clamping force setting method - Google Patents

Description

  The present invention relates to a mold clamping force setting method, and more particularly to a mold clamping force setting method for setting a mold clamping force generated by a mold clamping device of an injection molding machine.

  In an injection molding machine, with a mold clamping force applied to a mold by a mold clamping device, molten resin is injected into the mold, and the molten resin is solidified in the mold to obtain a molded product. The reason why the mold clamping force is applied to the mold is to prevent the mold from opening due to the resin pressure of the molten resin.

  Usually, the mold clamping force is set by the operator of the molding machine. If the mold clamping force is insufficient, the mold opens during molding and burrs are generated in the molded product. Therefore, the mold clamping force is often set to be strong. The required clamping force varies depending on the mold, but in many cases, the maximum clamping force that can be generated by the clamping device is added for safety.

  However, the life of the mold depends on the clamping force, and the lifetime of the mold is shortened as the larger clamping force is applied. Therefore, if an excessive mold clamping force is set, the life of the mold is unnecessarily shortened. Therefore, in order to set an appropriate mold clamping force, a method has been proposed in which the position of the movable mold relative to the fixed mold when the resin is filled is detected, and an appropriate mold clamping force is set based on the detected value. (For example, see Patent Document 1 and Patent Document 2).

In this mold clamping force setting method, a mold position sensor is attached between the movable mold and the fixed mold or between the movable platen and the fixed platen, the position of the mold during molding is detected, and based on the detected position, Determine appropriate clamping force.
JP-A-6-64010 JP-A-10-113963

  In the mold clamping force setting methods disclosed in Patent Document 1 and Patent Document 2 described above, it is necessary to detect the position of the mold by attaching a mold position sensor to the mold or the mold clamping device. As the mold position sensor, for example, an optical linear encoder, a magnet scale, or the like can be used.

  In order to obtain an appropriate mold clamping force, it is necessary to accurately measure the degree of mold opening with a mold position sensor. For example, it is necessary to detect the mold opening in units of microns. When using a mold position sensor, it is necessary to attach it to a movable part of a mold or a mold clamping device, which may cause a problem that it is difficult to ensure accuracy in micron units. Further, there may be a problem that it is difficult to attach the mold position sensor to the mold or the mold clamping device. Furthermore, the mold position sensor is a relatively expensive sensor, and there is a problem that the cost of the molding machine increases by the amount of the mold position sensor.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a mold clamping force setting method capable of accurately setting an appropriate mold clamping force without using a mold position sensor.

  In order to achieve the above object, according to the present invention, there is provided a mold clamping force setting method for setting a mold clamping force applied to a mold by a mold clamping device, wherein the mold clamping device has a predetermined magnitude. A mold clamping force is applied to the mold, a change in the detected value of the mold clamping force by the mold clamping force sensor is detected while filling the mold with resin, and the mold should be applied to the mold based on the detected change. A mold clamping force setting method is provided, wherein a mold clamping force value is set.

  In the mold clamping force setting method according to the present invention, the value of the mold clamping force of the predetermined magnitude is the maximum value of the mold clamping force that can be generated by the mold clamping device, and no change in the value of the mold clamping force is detected. In this case, it is preferable to detect the change in the value of the mold clamping force repeatedly while gradually decreasing the value of the mold clamping force of the predetermined magnitude. The mold clamping force sensor is preferably a tie bar sensor that detects the mold clamping force by measuring the extension of the tie bar of the mold clamping device.

  According to the present invention, a change in the detection value of the mold clamping force sensor is detected as compared with the conventional operation of determining the optimum value of the mold clamping force while measuring the actual mold opening amount by attaching the position sensor. Thus, the optimum value of the clamping force can be easily obtained, and the clamping force can be easily set with high accuracy.

  An embodiment of the present invention will be described with reference to the drawings.

  First, an example of a mold clamping device capable of setting a mold clamping force using the mold clamping force setting method according to the present invention will be described with reference to FIG. FIG. 1 is a side view of a mold clamping device capable of setting a mold clamping force using the mold clamping force setting method according to the present invention.

  In FIG. 1, the mold clamping device 10 of the injection molding machine is movable with respect to the frame 17 with a predetermined distance between the frame 17, the fixed platen 12 fixed to the frame 17, and the fixed platen 12. And a toggle support 15 disposed. The toggle support 15 functions as a toggle type mold clamping device support device. A plurality of (for example, four) tie bars 16 as guide means extend between the fixed platen 12 and the toggle support 15.

  The movable platen 13 is disposed so as to face the fixed platen 12 and functions as a movable mold support device disposed so as to be capable of moving back and forth (moving in the horizontal direction in the drawing) along the tie bar 16. The mold apparatus 11 includes a fixed mold 11a and a movable mold 11b. The fixed mold 11 a is attached to a mold mounting surface of the fixed platen 12 that faces the movable platen 13. On the other hand, the movable mold 11 b is attached to a mold attachment surface of the movable platen 13 that faces the fixed platen 12.

  A drive device for moving an ejector pin (not shown) may be attached to the rear end (left end in the figure) of the movable platen 13.

  A toggle mechanism 20 as a toggle type mold clamping device is attached between the movable platen 13 and the toggle support 15. A mold clamping motor 26 as a mold clamping drive source for operating the toggle mechanism 20 is disposed at the rear end of the toggle support 15. The mold clamping motor 26 includes a motion direction conversion device (not shown) composed of a ball screw mechanism or the like that converts rotational motion into reciprocating motion, and the toggle mechanism 20 is moved forward and backward (moved in the horizontal direction in the figure) by moving the drive shaft 25 forward and backward. Can be operated. The mold clamping motor 26 is preferably a servo motor, and includes a mold opening / closing position sensor 27 as an encoder for detecting the number of rotations.

  The toggle mechanism 20 described above includes a cross head 24 attached to the drive shaft 25, a second toggle lever 23 attached to the cross head 24 so as to be swingable, and a first toggle lever attached to the toggle support 15 so as to be swingable. 21 and a toggle arm 22 that is swingably attached to the movable platen 13. Between the first toggle lever 21 and the second toggle lever 23 and between the first toggle lever 21 and the toggle arm 22 are linked. The toggle mechanism 20 is a so-called inner volume five-node double toggle mechanism, and has a vertically symmetrical configuration.

  The toggle mechanism 20 can be operated by driving the mold clamping motor 26 and moving the cross head 24 back and forth. In this case, when the cross head 24 is moved forward (moved in the right direction in the figure), the movable platen 13 is moved forward to perform mold closing. Then, a mold clamping force obtained by multiplying the propulsive force of the mold clamping motor 26 by the toggle magnification is generated, and the mold clamping is performed by the mold clamping force.

  In order to adjust the position of the toggle support 15 with respect to the fixed platen 12, a mold clamping position adjusting device 35 is disposed at the rear end (left end in the figure) of the toggle support 15. The toggle support 15 is formed with a plurality of, for example, four tie bar insertion holes (not shown), and the left end of the tie bar 16 in the figure is inserted into each tie bar insertion hole. The right end of the tie bar 16 is fixed to the fixed platen 12 by a fixing nut 16a.

  The tie bar 16 has a screw portion 36 formed with a screw on the outer periphery at the left end in the figure, and an adjustment nut 37 is screwed to the screw portion 36 of each tie bar 16. The adjustment nut 37 is attached to the rear end of the toggle support 15 so as to be rotatable and immovable in the axial direction of the tie bar 16. A driven gear 37 a is attached to the outer periphery of the adjustment nut 37.

  A mold thickness motor 31 as a mold clamping position adjusting drive source is disposed at an upper portion of the rear end of the toggle support 15. A driving gear 33 is attached to the rotation shaft of the mold thickness motor 31. Around the driven gear 37a and the driving gear 33 of the adjustment nut 37, a driving linear body 34 such as a chain or a toothed belt is wound around. Therefore, when the mold thickness motor 31 is driven and the driving gear 33 is rotated, the adjustment nuts 37 screwed into the screw portions 36 of the tie bars 16 are rotated in synchronization. Thereby, the mold thickness motor 31 can be rotated by a predetermined number of rotations in a predetermined direction, and the toggle support 15 can be advanced and retracted by a predetermined distance. The mold thickness motor 31 is preferably a servo motor, and includes a mold clamping position sensor 32 as an encoder that detects the number of rotations.

  The means for transmitting the rotation of the mold thickness motor 31 to the adjusting nut 37 may be any means as long as the adjusting nut 37 screwed into the screw portion 36 of each tie bar 16 can be rotated synchronously. Good. For example, instead of the driving linear body 34, a large-diameter gear that meshes with all of the driving gear 33 and the driving gear 33 is rotatably disposed at the rear end of the toggle support 15. Also good.

  In the present embodiment, a mold clamping force sensor 18 is disposed on one of the tie bars 16. The mold clamping force sensor 18 is a sensor that detects distortion (mainly elongation) of the tie bar 16. The tie bar 16 is applied with a tensile force corresponding to the mold clamping force during mold clamping, and extends slightly in proportion to the mold clamping force. Therefore, the mold clamping force actually applied to the mold apparatus 11 can be known by detecting the extension amount of the tie bar 16 by the mold clamping force sensor 18.

  The above-described mold clamping force sensor 18, mold opening / closing position sensor 27, mold clamping motor 26 and mold thickness motor 31 are connected to the control device 19, and the detection signals output from the mold clamping force sensor 18 and the mold opening / closing position sensor 27 are controlled. Sent to device 19. The control device 19 controls the operations of the mold clamping motor 26 and the mold thickness motor 31 based on the detection signal.

  Here, an operation during normal molding will be described. When the mold clamping motor 26 is driven in the forward direction, the ball screw shaft 25 is rotated in the forward direction, and the ball screw shaft 25 is moved forward (moved in the right direction in FIG. 1) as shown in FIG. Accordingly, when the cross head 24 is advanced and the toggle mechanism 20 is operated, the movable platen 13 is advanced.

  When the movable mold 11b attached to the movable platen 13 comes into contact with the fixed mold 11a (mold closed state), the mold clamping process is started. In the mold clamping process, the mold clamping force is generated in the mold 11 by the toggle mechanism 20 by further driving the mold clamping motor 26 in the forward direction.

  And the injection drive part provided in the injection apparatus which is not shown in figure is driven, and a screw advances, The molten resin is filled in the cavity space formed in the metal mold | die 11. FIG. When opening the mold, when the mold clamping motor 26 is driven in the reverse direction, the ball screw shaft 25 is rotated in the reverse direction. Accordingly, when the cross head 24 is retracted and the toggle mechanism 20 is operated, the movable platen 13 is retracted.

  When the mold opening process is completed, an ejector driving unit (not shown) is driven, and the ejector device attached to the movable platen is operated. Thereby, an ejector pin protrudes and the molded article in the movable mold 11b protrudes from the movable mold 11b. Simultaneously with the driving of the ejector driving unit, a molded product take-out machine as a gripping means (not shown) is driven, and the arm of the molded product take-out machine enters between the fixed mold 11a and the movable mold 11b, and takes out the molded product. Stop at position. And the molded product protruded from the movable mold 11b by the advance of the ejector pin is gripped and taken out by the arm of the molded product take-out machine, and is conveyed to a conveyor device provided outside the injection molding machine.

  By the way, the mold clamping force generated by the toggle mechanism 20 is the spring constant of the entire mold clamping device 10 including the fixed platen 12, the toggle support 15 and the tie bar 16, that is, as in the mold clamping device using a general toggle mechanism. The mold clamping rigidity changes as a proportional constant. In the mold clamping device 10, since the rigidity of the tie bar 16 is lower than that of other members, it can be considered that the mold clamping rigidity is equal to the rigidity of the tie bar 16. Therefore, the mold clamping force generated by the toggle mechanism 20 uses the spring constant as the stiffness of the tie bar 16 as a proportional constant, and the toggle support 15 moves relative to the fixed platen 12 from the mold closing of the mold apparatus 10 to the completion of the mold clamping. It can be said that it changes in proportion to the amount to be done. That is, since the rigidity of the members such as the fixed platen 12 and the toggle support 15 is sufficiently high, the mold clamping force generated by the mold clamping device 10 is substantially generated by elastically deforming and extending the four tie bars 16. It can be said that it is proportional to the amount of elongation of the tie bar 16.

  Next, the mold clamping force setting method according to the present embodiment will be described.

  In the present embodiment, a mold clamping force sensor 18 (also referred to as a tie bar sensor) attached to the tie bar 16 is used in order to detect an appropriate mold clamping force. The mold clamping force sensor 18 is a sensor provided for detecting the mold clamping force during molding. In the present embodiment, an appropriate value of the mold clamping force is based on the detection value of the mold clamping force sensor 18 provided originally. Determine and set.

  The appropriate value of the clamping force is a value that is strong enough not to cause burrs in the molded product and is not too strong as necessary. Obtaining such an appropriate value of the mold clamping force is important in order to prevent the mold life from being unnecessarily shortened by suppressing the mold clamping force to the minimum necessary level.

  Assume that a mold having a minimum required clamping force of 50 tons is used. In this case, if molding is performed by applying a mold clamping force of 50 tons to the mold, it is possible to mold a molded product that does not cause burrs, which becomes a problem, and if the mold clamping force is less than 50 tons, The outbreak begins to stand out. That is, a defective product is formed. Applying a clamping force of 50 tons or more, for example 60 tons, to the mold means applying a mold clamping force more than necessary. If only the minimum required clamping force is generated, resin pressure is added to the reaction force of the clamping force if the resin is filled with the clamping force applied, that is, with the toggle extended. Thus, the toggle support 15 is retracted while the toggle is still extended, and the tie bar is further pulled. Therefore, by detecting the elongation of the tie bar at this time, the degree of opening of the mold can be known. However, in the above-mentioned case, for example, when 70 tons is applied as an excessive mold clamping force, the tie bar is already pulled by the reaction force of the mold clamping force more than necessary when the mold clamping force is applied. No. 15 is retracted, and the tie bar does not extend any further even when resin pressure is applied.

  FIG. 2 is a graph showing the change in the detected value of the mold clamping force sensor 18 when the mold clamping force sensor 18 detects the mold clamping force generated by the mold clamping device. FIG. 3 shows the detected value of the mold clamping force sensor (tie bar sensor) 18 and the amount of opening of the mold during filling and holding (die opening amount) when the mold clamping force applied to the mold is changed. ).

  First, when the mold clamping device is set so that a mold clamping force of 100 tons is applied to the mold, and the mold clamping force is set to 100 tons, as shown in FIG. The detected value of the mold clamping force by the tie bar sensor) 18 remains constant at 100 tons during resin filling and pressure holding. This indicates that even when a resin is filled in the mold and a resin filling pressure is applied, the mold clamping force is strong, so that the mold does not open without losing the resin filling pressure. Since the mold clamping force sensor 18 detects the elongation of the tie bar 16 and converts the elongation value into the mold clamping force, the elongation amount of the tie bar 16 is constant when the mold clamping force of 100 tons is applied. Yes, indicating no change. The extension amount of the tie bar 16 at this time is 0.6 mm as shown in the column of 100 tons in FIG. 3, and the mold opening amount is 0 μm because the mold is not opened.

  Here, when molding is performed with the set value of the mold clamping force gradually reduced from 100 tons by 10 tons, the mold opening amount is 0 μm up to 70 tons as shown in FIG. Therefore, as shown in FIG. 2, when the set value of the mold clamping force is up to 70 tons, the detected value of the mold clamping force is constant during the filling and holding of the resin. That is, since the mold clamping force is strong, the mold does not open without losing the resin filling pressure. As shown in FIG. 3, when the set value of the mold clamping force is decreased by 10 tons, the detected value of the tie bar sensor is proportionally decreased by 0.060 mm.

  When molding is performed with the set value of the mold clamping force set to 60 tons, as shown in FIG. 2, the detected value of the mold clamping force slightly increases during the filling and holding of the resin. An increase in the detection value of the mold clamping force indicates that the amount of extension of the tie bar 16 has increased, and accordingly, the mold has slightly opened. In FIG. 3, the detection value of the tie bar sensor at 60 tons is 0.361 mm, and when the mold does not open, it should be constant at 0.360 mm, whereas the mold opens by 0.001 mm. It will be. Note that the detection value of the tie bar sensor in FIG. 3 is the maximum value of the detection value during filling / holding pressure. As shown in FIG. 2, when the mold clamping force is set to 60 tons, the mold clamping force is substantially constant, but the detected value slightly increases near the start of pressure holding. The increase in the detected value corresponds to the mold opening amount 1 μm (0.001 mm described above) in FIG. In FIG. 2, the resin filling pressure from the start of filling to the completion of holding pressure is indicated by a one-dot chain line. The increase in the detected value of the mold clamping force indicates that the resin filling pressure is maximized in the vicinity of the start of holding pressure, and the mold is opened with the mold clamping force lost to the resin filling pressure.

  Here, when the relationship between the mold opening amount and the generation of burrs was examined, there was almost no burring up to a certain value of the mold opening amount, for example, 5 μm, and there is no practical problem even if the mold is opened to this extent. I understood. Therefore, it can be said that the mold opening amount of 1 μm when the set value of the mold clamping force is 60 tons is a mold opening amount that causes no practical problem. The allowable mold opening value, that is, the value of the mold opening when burr is not practically problematic, is not limited to 5 μm, and the size and type of the mold to be used, or the mold is used for molding. It varies depending on various conditions such as the shape of the molded product and the resin material. Therefore, it is preferable to check the allowable mold opening amount with an actual machine in advance. The allowable mold opening value of the mold used in this embodiment is 5 μm.

  If the set value of the mold clamping force is set to 60 tons and then further reduced by 10 tons to 50 tons, the increase in the detection value of the tie bar sensor becomes large as shown in FIG. The detection value of the tie bar sensor at this time is 0.305 mm as shown in FIG. 3, and the mold opening amount is 5 μm. Thus, it can be seen that the mold opening amount when the set value of the mold clamping force is 50 tons is an allowable mold opening amount of 5 μm. Therefore, if a good product is obtained in this state, it can be estimated that the optimum value of the mold clamping force for the above-mentioned mold is 50 tons, and the mold clamping force generated by the mold clamping device in the subsequent actual molding. It can be seen that it may be set to 50 tons.

  As described above, in the mold clamping force setting method according to the present embodiment, an allowable mold opening amount is set in advance, and the mold clamping force is increased from a large value (for example, the maximum value of the mold clamping force generated by the mold clamping device). Molding is performed while gradually decreasing, and the setting value of the mold clamping force when the mold opening amount obtained from the detected value of the mold clamping force is the above-described allowable mold opening amount is set as the optimum value of the mold clamping force. .

  That is, a clamping force of a predetermined magnitude (for example, 100 tons, 90 tons, 80 tons,...) Is applied to the mold by the mold clamping device, and the mold clamping force sensor is used to clamp the mold while filling the mold with resin. A change in the detection value of the force is detected, and a value of the clamping force to be applied to the mold is set based on the change in the detection value. The mold clamping force of a predetermined magnitude is desirably sufficiently larger than the optimum value of the mold clamping force, and a change in the mold clamping force can be detected while gradually decreasing from a sufficiently large mold clamping force. The sufficiently large mold clamping force may be started from the maximum value (maximum mold clamping force) of the mold clamping force that can be generated by the mold clamping device. This makes it easy to detect changes in the detection value of the tie bar sensor compared to the conventional method of determining the optimum value of the mold clamping force while measuring the actual mold opening by attaching a position sensor. The optimum value of the mold clamping force can be obtained, and the mold clamping force can be easily set.

It is a side view of the mold clamping device which can set a mold clamping force using the mold clamping force setting method by this invention. It is a graph which shows the change of the detection value of a mold clamping force sensor when the mold clamping force which generate | occur | produces with a mold clamping apparatus is detected with a mold clamping force sensor. It is a figure which shows the detection value of a tie bar sensor when the mold clamping force is changed, and the mold opening amount during filling and holding pressure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Clamping device 11 Mold device 12 Fixed platen 13 Movable platen 15 Toggle support 16 Tie bar 18 Clamping force sensor 19 Control device 20 Toggle mechanism 26 Clamping motor 27 Mold opening / closing position sensor 31 Mold thickness motor 32 Mold clamping position sensor

Claims (3)

A mold clamping force setting method for setting a mold clamping force applied to a mold by a mold clamping device,
A clamping force of a predetermined size is applied to the mold by the clamping device,
Detecting a change in the detected value of the clamping force by the clamping force sensor while filling the mold with resin,
A mold clamping force setting method, comprising: setting a value of a mold clamping force to be applied to the mold based on the detected change. The mold clamping force setting method according to claim 1,
The value of the predetermined mold clamping force is the maximum value of the mold clamping force that can be generated by the mold clamping device,
When no change in the value of the mold clamping force is detected, a change in the value of the mold clamping force is repeatedly detected while gradually reducing the value of the mold clamping force of the predetermined magnitude. Force setting method. The mold clamping force setting method according to claim 1,
The mold clamping force setting method, wherein the mold clamping force sensor is a tie bar sensor for measuring a mold clamping force by measuring an extension of a tie bar of the mold clamping device.

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