JP4297277B2 - Injection molding method - Google Patents

Description

  The present invention relates to an injection molding method suitable for use in molding a thermosetting molding material or the like with an injection molding machine.

  In general, when thermosetting molding materials such as epoxy resin, polyester resin, phenol resin, etc. are molded with an injection molding machine, heating of the heating cylinder and injection nozzle to a certain temperature ensures resin fluidity during measurement. In addition to shortening the resin curing time in the metal mold, after the injection, the screw is set so that the resin remaining in the heating cylinder and the injection nozzle does not cure due to the heating of the heating cylinder and the injection nozzle. By moving forward as much as possible, the residual resin is reduced. However, if the screw moves forward too much, the tip of the screw comes into contact with the inside of the tip of the heating cylinder, and a so-called galling phenomenon occurs in which the screw and the heating cylinder are rubbed at the initial stage of measurement. Normally, a slight gap is secured between the tip of the screw and the inside of the tip of the heating cylinder to cause damage, but on the other hand, since there is little residual resin, friction heat due to screw rotation during measurement This causes a problem of accelerating the curing rate of the residual resin.

Therefore, an injection molding method for solving this problem is also known from JP-A-6-270214. In the thermosetting resin injection molding method disclosed in the publication, when the thermosetting resin is injected into the mold from the injection device, the screw that has advanced to the advance limit position at the time of the previous injection is once forcibly retracted, The screw rotation for the next weighing of the resin material is started.
JP-A-6-270214

  However, the conventional injection molding method described above has the following problems.

  First, the screw retraction avoids the generation of frictional heat due to screw rotation at the beginning of metering, but the screw simply retreats, so the residual resin in the injection nozzle cannot be effectively extracted, and eventually The risk that the residual resin in the injection nozzle hardens with heating of the injection nozzle or the like cannot be sufficiently avoided.

  Secondly, since the residual resin is simply extracted from the injection nozzle side, if the resin that has already been cured is mixed into the molten resin being measured, it will be injected as it is mixed into the molten resin. If a non-uniform molten resin is used, the quality of the molded product is deteriorated and defective molding occurs.

  An object of the present invention is to provide an injection molding method that solves the problems existing in the background art.

  In order to solve the above-described problems, the injection molding method according to the present invention measures the molding material by rotating the screw 2 built in the heating cylinder 3 having the injection nozzle 3n at the tip, and the measured molding material is used as the screw. When the screw 2 reaches the first preset condition when the screw 2 moves forward when the screw 2 is moved forward and injected into the mold 4 from the injection nozzle 3n, the screw 2 is moved in the direction of rotation (forward direction Rp). ) In the reverse direction Rn, and a negative negative pressure is generated in the interior of the injection nozzle 3n to move the residual resin in the injection nozzle 3n to the inside of the heating cylinder 3 that is behind. The resin pressure in the cavity is not injected until the second condition is reached after the first condition is reached after the first condition is reached at a slow speed of a predetermined speed Vs or less that can be extracted. The pressure is limited so that it does not exceed the preset injection pressure Ps, which is a magnitude that does not exceed the injection pressure at the time, and when the second condition is reached, the screw 2 is rotated in the forward direction Rp to perform measurement. It is characterized by that.

  In this case, according to a preferred embodiment of the invention, if the resin pressure in the cavity exceeds a predetermined pressure Ps after the screw 2 reaches the first condition and then reaches the second condition, the advancement of the screw 2 is stopped or The forward speed can be switched to a speed slower than the fine speed. The first condition can be set by the injection time Ts or the screw position, and the second condition can be set by the screw most advanced position Xb. On the other hand, if the screw 2 reaches the second condition, the screw 2 is rotated in the forward direction Rp with the back pressure applied to the screw 2 released, and retracted to the preset switching position Xc, and the screw 2 is moved to the switching position Xc. Can be measured by rotating the screw 2 in the forward direction Rp with a predetermined back pressure applied to the screw 2 and retracting it to a preset measuring end position Xd. As the molding material, a thermosetting molding material can be used.

  According to the injection molding method according to the present invention using such a technique, the following remarkable effects can be obtained.

  (1) If the screw 2 reaches the first condition, the screw 2 is rotated in the reverse direction Rn, and a negative pressure is generated backward in the interior of the injection nozzle 3n to cause residual resin in the injection nozzle 3n. Is moved forward to the inside of the heating cylinder 3 which is the rear and is advanced at a slow speed of a predetermined speed Vs or less that can be extracted, so that the residual resin in the injection nozzle 3n can be effectively extracted, It is possible to avoid the risk of curing by heating while the resin remains in the injection nozzle 3n.

  (2) If the screw 2 reaches the first condition, the screw 2 is rotated in the reverse direction Rn, and a negative pressure is generated backward in the interior of the injection nozzle 3n, thereby remaining resin in the injection nozzle 3n. Is moved to the rear of the heating cylinder 3 and can be extracted at a slow speed that is equal to or lower than a predetermined speed Vs set in advance, so that the residual resin extracted from the injection nozzle 3n becomes the molten resin being measured. When mixed, the product is uniformly stirred by the screw 2 rotating in the reverse direction Rn, so that the quality of the molded product and the yield can be improved.

  (3) After the screw 2 reaches the first condition, until the second condition is reached, the resin pressure in the cavity does not exceed a predetermined pressure Ps that is set in advance so as not to exceed the injection pressure at the end of injection. Therefore, the residual resin can be extracted smoothly and stably from the injection nozzle 3n.

  (4) According to a preferred embodiment, if the resin pressure when the screw 2 moves forward exceeds the predetermined pressure Ps, the forward pressure of the screw 2 is stopped or the forward speed is switched to a slower speed than the fine speed. The following pressure restrictions on the resin pressure can be easily and reliably performed.

  (5) According to a preferred embodiment, when the screw 2 reaches the second condition, the measurement is performed with the back pressure applied to the screw 2 released, that is, by rotating the screw 2 in the forward direction Rp, the screw 2 moves backward to the switching position Xc. By doing so, it is possible to reliably avoid the so-called galling phenomenon that the screw 2 and the heating tube 3 rub against each other at the initial stage of measurement, thereby preventing the screw 2 and the heating tube 3 from being damaged.

  Next, the best embodiment according to the present invention will be given and described in detail with reference to the drawings.

  First, the outline | summary of the injection molding machine M which can implement the injection molding method which concerns on this embodiment is demonstrated with reference to FIG.

  The injection molding machine M includes a machine base Mb, and an injection device Mi and a mold clamping device Mc installed on the machine base Mb. The injection device Mi includes a heating cylinder 3 shown in FIG. 3 (FIG. 2). The heating cylinder 3 has an injection nozzle 3 n at the tip, and a hopper 11 that supplies a molding material to the rear of the heating cylinder 3. . In addition, the heating cylinder 3 includes the screw 2, and the rear part of the heating cylinder 3 includes a rotation drive unit 12 and a screw 2 that rotate the screw 2 forward (forward direction Rp) or reversely (reverse direction Rn). An advance / retreat drive unit 13 for moving forward or backward is provided.

  In this case, the rotation drive unit 12 includes a servo motor 12m and a speed reduction mechanism (not shown) that decelerates the rotation of the servo motor 12m and transmits the rotation to the screw 2, and a rotary encoder 12e that detects the rotation speed of the servo motor 12m. Is provided. The advancing / retreating drive unit 13 further includes a servo motor 13m and a ball screw mechanism (not shown) that converts the rotation of the servo motor 13m and transmits the rotation to the screw 2, and a rotary encoder that detects the rotation speed of the servo motor 13m. 13e. The rotary encoder 13e also serves as a screw position detector that detects the advance / retreat position of the screw 2.

  The servo motor 12m and the rotary encoder 12e, and the servo motor 13m and the rotary encoder 13e are connected to the controller 15, respectively. The controller 15 performs various sequence controls according to a preset control program and performs various data processing based on computer functions. The controller 15 also includes a display 16, which also serves as a setting unit using a touch panel that can perform various settings. The display 16 is disposed on a side panel 17 raised on the machine base Mb.

  On the other hand, the mold clamping device Mc includes a mold 4 composed of a movable mold and a fixed mold. The mold 4 has a cavity that does not appear in the figure, and includes a pressure detector 18 that detects the resin pressure of the molten resin injected and filled in the cavity. The pressure detector 18 is connected to the controller 15.

  Next, the injection molding method according to the present embodiment will be described according to the flowchart shown in FIG. 1 with reference to FIGS.

  First, in the injection molding method according to the present embodiment, a thermosetting molding material such as a thermosetting resin (epoxy resin, polyester resin, phenol resin, etc.) or rubber having thermosetting characteristics is used as a molding material.

  In the injection molding method according to the present embodiment, necessary conditions are set in advance using the display (touch panel) 16. In particular, as conditions unique to the injection molding method according to the present embodiment, the first condition and the second condition for the forward movement of the screw 2 used in the injection process are set, and after reaching the first condition, the second condition The advance speed of the screw 2 and the resin pressure until reaching the value are set. In this case, the first condition can be set by the injection time Ts (or screw position), and the second condition can set the screw most advanced position Xb. The screw most advanced position Xb is slightly before the tip of the screw 2 comes into contact with the inside of the tip of the heating cylinder 3, preferably 0.1 [mm] or more. It is desirable to set the position where the resin is easily connected. On the other hand, the forward speed is set to a very low speed that is equal to or lower than the predetermined speed Vs, and the resin pressure is set to a predetermined pressure Ps that does not exceed the injection pressure at the end of injection, thereby limiting the pressure on the resin pressure. Do. Further, a switching position Xc for switching from the released state of the back pressure to the screw 2 used in the weighing process to the state of applying the back pressure is set. Each of these conditions can be experimentally determined according to the type of thermosetting molding material.

  Now, when the thermosetting molding material is put into the hopper 11 and the screw 2 is rotated in the forward direction Rp (forward rotation), the thermosetting molding material is plasticized and melted and measured as a molten resin in front of the screw 2. Accumulated. FIG. 3A shows a state in which the weighing process is finished and the screw 2 is at the injection start position Xa.

  Hereinafter, the injection molding procedure from this state will be described. First, an injection process is performed from this state (step S1). In the injection process, the screw 2 moves forward at a preset injection speed. The forward direction is indicated by arrow Ff. Then, when the preset injection time Ts is up, it is stopped (steps S2 and S3). This time-up point is indicated by Ts in FIG.

  On the other hand, if the screw 2 stops due to time-up, the screw 2 is immediately rotated in the reverse direction Rn with respect to the rotation direction (forward direction) Rp during measurement (step S4). At the same time, the resin pressure detected from the pressure detector 18 is monitored. If the resin pressure is equal to or lower than the predetermined pressure Ps, the screw 2 is advanced at a very low speed equal to or lower than a predetermined speed Vs (steps S5 and S6). . As a result, a backward negative pressure is generated inside the injection nozzle 3n, so that the molten resin (residual resin) in the injection nozzle 3n moves to the inside of the heating cylinder 3 as the rear.

  That is, since the screw 2 moves at a slow speed while rotating in the reverse direction, the residual resin in the injection nozzle 3n is pushed back backward, and the residual resin extracted from the injection nozzle 3n is effectively extracted from the injection nozzle 3n. When mixed into the molten resin being weighed, it is uniformly stirred by the screw 2 rotating in the reverse direction Rn. In the case of a normal thermosetting resin or rubber, since a certain amount of time is required for the gate sealing time, even if the screw 2 is moved forward at a slow speed while being reversely rotated, there is no problem in the molding cycle. Absent.

  At this time, the controller 15 monitors the resin pressure in the cavity detected from the pressure detector 18, and if the resin pressure exceeds the predetermined pressure Ps, the controller 2 stops the advancement of the screw 2 (steps S7 and S8). As a result, the resin pressure decreases with the reverse rotation of the screw 2. Therefore, when the resin pressure becomes equal to or lower than the predetermined pressure Ps, the screw 2 is again advanced at a slow speed (steps S9 and S6). By monitoring the resin pressure and stopping the advancement of the screw 2, the pressure can be limited so that the resin pressure is equal to or lower than the predetermined pressure Ps, and the removal of the residual resin from the injection nozzle 3n can be performed smoothly and stably. It is possible to perform the pressure restriction easily and reliably. If the resin pressure exceeds the predetermined pressure Ps, the forward speed can be switched to a speed slower than the fine speed without stopping the forward movement of the screw 2. Then, while performing such pressure restriction, when the screw 2 is advanced at a very low speed and reaches the screw most advanced position Xb, the reverse rotation and advance of the screw 2 are stopped (steps S10 and S11). The screw most advanced position Xb is shown in FIG.

  On the other hand, if the screw 2 has reached the screw most advanced position Xb, a measuring step of rotating the screw 2 in the forward direction Rp with the back pressure applied to the screw 2 released is performed (step S12). That is, the screw 2 is moved back to the switching position Xc with no back pressure, and measurement is performed (steps S12 and S13). In this case, since the screw 2 moves backward with the back pressure released, the so-called galling phenomenon that the screw 2 and the heating cylinder 3 are rubbed at the initial stage of measurement can be avoided to prevent the screw 2 and the heating cylinder 3 from being damaged. . Therefore, the switching position Xc can be set to a position where this phenomenon does not occur. The switching position Xc is indicated by an imaginary line in FIG. 3D, and the backward direction of the screw 2 is indicated by an arrow Fr.

  Then, when the screw 2 moves backward and reaches the switching position Xc, a predetermined back pressure is applied to the screw 2, and in this state, a normal measuring process for rotating the screw 2 in the forward direction Rp is performed (step S14). ). In this case, since the screw 2 moves backward in a state where a back pressure is applied, when the measurement end position Xd is set in advance, the screw 2 is stopped from rotating and the measurement process is ended (steps S15 and S16). . The measurement end position Xd coincides with the above-described injection start position Xa. This measurement end position Xd is indicated by a solid line in FIG.

  Therefore, according to such an injection molding method according to the present embodiment, when the screw 2 reaches the first condition, the screw 2 is moved forward in a reverse speed Rn and at a very low speed of the predetermined speed Vs or less. The residual resin in the injection nozzle 3n can be effectively extracted, and thus the risk of curing by heating while the resin remains in the injection nozzle 3n can be avoided. In addition, when the residual resin extracted from the injection nozzle 3n is mixed with the molten resin being measured, it is uniformly agitated by the screw 2 rotating in the reverse direction Rn, thereby improving the quality of the molded product and the yield. Can be planned.

  Although the best embodiment has been described in detail above, the present invention is not limited to such an embodiment, and the scope of the present invention does not depart from the gist of the present invention in the detailed configuration, technique, material, numerical value, and the like. You can change, add, or delete them arbitrarily.

  For example, although a thermosetting molding material has been exemplified as the molding material, it can be applied to various molding materials that are not desirably left in the injection nozzle 3n after the injection process. In addition, when the resin pressure exceeds the predetermined pressure Ps, the method of stopping the advancement of the screw 2 or switching the advancement speed to a speed slower than the fine speed is exemplified. However, the reverse rotation speed of the screw 2 is increased. It may be a method. Furthermore, the illustrated injection molding machine M is an electric injection molding machine equipped with servo motors 12m and 13m, but may be a hydraulic injection molding machine. When an electric injection molding machine is used, position control can be performed with high accuracy and rotation control can be easily performed. In addition, although the case where the screw 2 is rotated with the back pressure released from the second condition to the switching position Xc is shown, the case where the screw 2 is rotated with the back pressure applied from the second condition is excluded. Not what you want.

The flowchart which shows the process sequence of the injection molding method which concerns on the best embodiment of this invention, External view including the configuration of a control system of an injection molding machine that can implement the injection molding method, Action explanatory drawing which shows the position of the screw at the time of carrying out the injection molding method step by step,

Explanation of symbols

2 Screw 3 Heating cylinder 3n Injection nozzle 4 Mold Ts First condition (Injection time)
Xb 2nd condition (screw most advanced position)
Xc switching position Xd Weighing end position Rp Positive direction Rn Reverse direction

Claims (6)

  In the injection molding method, the screw contained in a heating cylinder having an injection nozzle at the tip is rotated to measure the molding material, and the measured molding material is advanced from the injection nozzle to the mold by moving the screw forward. When the screw reaches the first preset condition during the forward movement, the screw is rotated in the reverse direction with respect to the rotation direction (forward direction) at the time of metering and backward with respect to the inside of the injection nozzle. The negative pressure is generated, and the residual resin in the injection nozzle is moved to the inside of the heating cylinder at the rear to be extracted, and advanced at a very low speed below a predetermined speed set in advance, and the first condition is reached. After that, until the preset second condition is reached, the resin pressure in the cavity is equal to or lower than a preset predetermined pressure that does not exceed the injection pressure at the end of injection. Sea urchin and pressure limiting, the has been reached in the second condition, an injection molding method and performing a metered by rotating the screw in the forward direction.   If the resin pressure in the cavity exceeds the predetermined pressure by the time the second condition is reached after the screw reaches the first condition, the advance of the screw is stopped or the advance speed is made lower than the fine speed. The injection molding method according to claim 1, further comprising switching to a slower speed.   The injection molding method according to claim 1, wherein the first condition is set by a screw position or an injection time.   The injection molding method according to claim 1, wherein the second condition is set by a screw most advanced position.   When the screw reaches the second condition, the screw is rotated in the forward direction with the back pressure applied to the screw released, and retracted to a preset switching position, and the screw has reached the switching position. The injection molding according to claim 1, wherein the measurement is performed by rotating the screw in a forward direction in a state where a predetermined back pressure is applied to the screw and retracting the screw to a predetermined measurement end position. Method.   The injection molding method according to claim 1, wherein a thermosetting molding material is used as the molding material.

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