JP2008037068A - Injection molding method for resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a molding of a high accuracy by controlling a filling balance in a cavity with a simple constitution. <P>SOLUTION: An injection molding apparatus 1 is switched so that a pressure becomes constant after the speed of a screw is controlled to become constant first when the screw of an injection device is moved to inject while a resin material is injected while the resin material is being melted. The viscosity of the melt of the resin material is obtained from the moving time, etc. of the screw in the state that the pressure is constant, compared with a predetermined allowing range, and whether the present viscosity of the resin material is the viscosity suitable to mold accurately is judged. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for injection molding a resin material.

When injection molding a resin material, a movable mold is clamped to a fixed mold to form a molding cavity, and a thermosetting resin material pressurized by a cylinder is passed through a sprue and a runner of the fixed mold. It is known to be injected into a mold cavity and cured. Here, the conventional injection molding equipment incorporates pressure sensors in each of the runner, sprue, and molding cavity, grasps the resin material filling balance in the molding cavity, determines the quality of the molded product, and meets the molding conditions. Some are configured to provide feedback (see, for example, Patent Document 1).
JP-A-11-320642

However, since the melt viscosity of the resin material injected from the nozzle also changes depending on the material temperature and time of the hopper that supplies the resin material to the cylinder, it is difficult to keep the filling balance in the molding cavity constant. It was. For this reason, the quality of the molded product is likely to vary, and it has been difficult to manufacture a highly accurate molded product. In particular, such a problem appears remarkably in the case of a thermosetting plastic to which a curing reaction is applied.
Moreover, in the injection molding apparatus as disclosed in Patent Document 1, it is necessary to provide a plurality of pressure sensors in the mold, which increases the number of processing steps and the number of parts of the injection molding apparatus.
The present invention has been made in view of such circumstances, and it is a main object of the present invention to make it possible to predict the filling balance in the cavity with a simple configuration and to obtain a highly accurate molded product.

The invention according to claim 1 of the present invention for solving the above-mentioned problems is a process of melting a resin material in an injection device, and a pressing member provided in the injection device is moved to mold the molten resin material into a mold Injecting a molten resin material in a resin material injection molding method comprising: a step of injecting into a molding cavity through a resin reservoir and a resin supply path formed in a step; and a step of pressurizing a molten resin material And a step of controlling the movement of the pressing member so that the injection pressure of the resin material becomes constant and measuring the viscosity of the molten resin material from the moving amount or moving time of the pressing member. A material injection molding method was adopted.
In this resin material injection molding method, the pressing member is controlled so that the injection pressure is constant, and the viscosity of the resin material is measured from the behavior of the pressing member at this time. Using this measurement result, it is possible to determine whether or not the resin material has a viscosity suitable for molding.

According to a second aspect of the present invention, in the resin material injection molding method according to the first aspect, an allowable range of the amount of movement of the pressing member corresponding to a range of viscosity permitted as a resin material suitable for molding, and an actual range The movement amount of the pressing member is compared with an allowable range of the moving time of the pressing member corresponding to a range of viscosity allowed as a resin material suitable for molding, and an actual moving time of the pressing member. In comparison, when the actual movement amount or movement time of the pressing member exceeds an allowable range, the resin material is discarded.
In this resin material injection molding method, an allowable range is determined in advance, and a comparison with the allowable range is performed to determine whether the resin material has a viscosity suitable for molding.

The invention according to claim 3 is the resin material injection molding method according to claim 2, wherein when the molten resin material is injected, the movement of the pressing member is controlled so that the injection speed of the resin material is constant. After performing, the movement control of the pressing member is performed so that the pressure becomes constant, and then the movement control of the pressing member is performed again so that the injection speed of the resin material becomes constant.
This injection molding method of the resin material ensures the stability of the injection filling while measuring the viscosity of the resin material by controlling the pressure of only a part of the steps when the resin material is injected and filled.

According to a fourth aspect of the present invention, in the resin material injection molding method according to any one of the first to third aspects, the resin in the resin reservoir is formed by a pressure member provided in the mold. It has the process of pressing toward the said cavity, It is characterized by the above-mentioned.
In this resin material injection molding method, by operating the pressure member near the molding cavity, the controllability of the pressure when the resin material is pressurized or depressurized is increased, and high-precision molding is possible. become.

The invention according to claim 5 is the injection molding method according to any one of claims 1 to 4, wherein a thermosetting resin is used as the resin material.
This resin material injection molding method enables high-precision molding even when the viscosity changes with temperature and time.

  According to the present invention, since the viscosity of the resin material can be measured by controlling the pressing member so that the injection pressure is constant when the resin material is injection molded, the resin material is suitable for molding. It is possible to determine at the time of injection whether the viscosity is high. Since it is not necessary to provide a pressure sensor in the mold apparatus, the structure of the injection molding apparatus can be simplified, manufacturing becomes easy, and cost can be reduced.

The best mode for carrying out the invention will be described in detail with reference to the drawings.
As shown in FIG. 1, the injection molding apparatus 1 includes a mold apparatus 2, an injection apparatus (resin supply apparatus) 3 that injects a resin material into the mold apparatus 2, and a control apparatus 4.
The mold apparatus 2 includes a fixed mold 11 fixed to a fixed plate (not shown), and a movable mold 12 provided so as to be movable with respect to the fixed mold 11 by a mold clamping device (not shown).

  Inside the mold body 13, a sprue 21 (resin supply path) communicating with the injection device 3 is formed. The movable mold 12 is formed with a runner 22 communicating with the resin reservoir K and a passage 24 through which a pusher 23 (pressure member) is inserted. The passage 24 has a diameter that allows the pusher 23 to slidably pass except for the end 24A connected to the resin reservoir K, and does not leak the resin material to the outside. The end 24 </ b> A connected to the resin reservoir K has a larger diameter than the pusher 23.

As shown in FIG. 1, the injection device 3 has a heating cylinder 42 in which a nozzle 41 communicating with the sprue 21 of the fixed mold 11 is formed at one end, and a screw 43 (pressing member) is provided in the heating cylinder 42. It is inserted freely. A hopper 44 for supplying a resin material is fixed to the other end of the heating cylinder 42. An electric heater 45 is attached to the outer periphery of the heating cylinder 42 to control the temperature. The rotation of the screw 43 is controlled by a servo motor 46, and a pressure applied to the screw 43 can be detected as a resin pressure (injection pressure) by a sensor 47 such as a load cell.
The control device 51 is configured to perform temperature control of the heating cylinder 42 by the electric heater 45, control of the servo motor 46, and temperature control of the fixed mold 11 and the movable mold 12. Further, the control of the injection pressure which will be described later is performed in response to the input of the sensor 47.

Next, the molding process by the injection molding apparatus 1 will be described.
First, a thermosetting resin material (plastic) is supplied to the hopper 44 by a loader (not shown). The resin material flows from the hopper 44 into the inlet of the heating cylinder 42 and is fed into the heating cylinder 42 by the rotation of the screw 43. The resin material is melted by the temperature control of the heating cylinder 42 by the electric heater 45, the rotation of the screw 43, and the frictional heat of the resin material sheared by the rotation.
While maintaining the molten state of the resin, the screw 43 is rotated, and the molten resin is supplied to the sprue 21 formed in a state in which the fixed mold 11 and the movable mold 12 are combined and the cavity L to be a molded product. Further, the movable mold 12 is moved and the mold is clamped to apply pressure to the molten resin.

The resin material filled in the molding cavity L is heated to a curing temperature (for example, 170 ° C.) given to the movable mold 12 and cured to become a product.
When the resin filled in the molding cavity L is cured and a product is molded, the movable mold 12 is moved away from the fixed mold 11 to open the mold. At this time, the product is taken out of the mold by a separate pin or the like (not shown) while the sprue 21 is integrated, and the product and the sprue 21 are separated later. In the present invention, the mold configuration includes the fixed mold 11 and the movable mold 12. However, by interposing the intermediate mold between the fixed mold and the movable mold, the product and the sprue 21 simultaneously with the mold opening. Can also be separated.

Here, FIG. 2 shows a control example of the screw position when the resin material is injected. In FIG. 2, the horizontal axis indicates the screw position, and the vertical axis indicates the injection pressure and the injection speed. Line L1 shows the relationship of screw position-injection pressure. Line L2 shows the relationship between screw position and injection speed. The position of the screw closest to the mold apparatus 2 is 0 mm.
In the injection process, when the screw position is started from about 10 mm, the control device 51 controls the speed of the screw 43 so that the injection speed becomes constant at about 30 mm / sec, as indicated by a line L2. Further, the control device 51 switches from speed control to pressure control when the screw 43 has passed 15 mm. The control device 51 detects the injection pressure with the sensor 47 and controls the forward speed of the screw 43 so that the injection pressure becomes substantially constant as indicated by a line L1. In the present invention, since it is only necessary to determine a part of the moving range of the screw by pressure control using the melt viscosity, the range in which the pressure control can be performed is anywhere as long as the screw 43 can be moved.

  At this time, the control device 51 checks the melt viscosity of the resin material in the pressure control step. The melt viscosity can be obtained as the time required for the resin material to pass through the nozzle 41 at a constant pressure. Therefore, if the forward speed (moving speed) of the screw 43 is measured, the diameter and length of the nozzle 41, the cylinder capacity Is known so that the melt viscosity is known. In the control device 51, the advance speed range of the screw 43 corresponding to the melt viscosity range in which high-precision molding is possible is registered in the memory in advance as an allowable range. Therefore, the forward speed of the screw 43 obtained from the measurement result of the sensor 47 is compared with an allowable range, and if the forward speed of the screw 43 is within the allowable range, a non-defective product is determined and injection molding is continued. To do.

  Thereafter, for example, when the position of the screw 43 is closer to 30 mm, the control device 51 switches from pressure control to speed control again. Then, the remaining resin material is injected while changing the speed in two stages. By maintaining the melt viscosity of the resin material in an appropriate range, the filling balance in each molding cavity L becomes good. Furthermore, by performing additional pressure adjustment with the pusher 23, the filling balance is further improved. When the resin material is cured, a molded product having a predetermined shape is manufactured. On the other hand, as a result of comparing the forward speed of the screw 43 and the allowable range, when the forward speed of the screw 43 is larger than the allowable range, the melt viscosity is too small. When the holding pressure on the resin material is controlled so as to increase the viscosity, and the advance speed of the screw 43 is smaller than the allowable range, the melt viscosity is too large. By incorporating the holding pressure on the resin material as feedback control, it is possible to suppress defects in the molded product.

  Further, as a result of comparing the forward speed of the screw 43 and the allowable range, if the forward speed of the screw 43 is larger than the allowable range, the melt viscosity is too small and it is determined as defective. Further, when the forward speed of the screw 43 is smaller than the allowable range, the melt viscosity is too large, and it is determined as defective. If a failure is determined, the resin material in the injection device 3 and the mold device 2 may be discarded at that time.

  Furthermore, instead of the forward speed of the screw 43, the forward movement amount (movement amount) of the screw 43 may be measured as an index indicating the melt viscosity. The advance amount is calculated from the rotation amount of the servo motor 46 as the distance that the screw 43 moves during a predetermined time in the pressure control step in FIG. In this case, in the control device 51, a range (allowable range) of the advance amount of the screw 43 corresponding to a range of melt viscosity capable of high-precision molding is registered in advance. If it is within the allowable range, it is determined as a non-defective product and the molding process is continued. On the other hand, when the advance amount is smaller than the allowable range, it is determined that the melt viscosity is too large to be defective. Further, when the advance amount is larger than the allowable range, it is determined that the melt viscosity is too small to be defective. If it is determined to be defective, the resin material may be discarded.

According to this embodiment, since the melt viscosity is measured by controlling the pressure of the screw 43 in a partial region in the injection process that has been conventionally speed controlled, the resin material is used when performing injection molding. It becomes possible to check the actual melt viscosity. Further, the pressure loss in the molding cavity L can be reduced without providing the mold device 2 with a pressure sensor. Therefore, it becomes possible to manufacture a highly accurate molded product. Such an injection molding method is effective when high dimensional accuracy is required, such as a molded product for a commutator used for power supply of a brush motor. Even if the resin material is a thermosetting resin material (plastic) that easily changes with time due to a curing reaction, high-precision molding is possible.
Since the moving speed or moving amount of the screw 43 is used as an index for checking the melt viscosity of the resin material, the behavior of the resin material can be grasped with a simple configuration.
When determining the melt viscosity, the pressure control process is not performed in all steps except the pressure holding process, but pressure control is performed only in a certain section during speed control to prevent the quality of the molded product from deteriorating. it can.

  By using the cushion molding in which the pusher 23 is provided in the mold apparatus 2 to pressurize the resin material, a molded product with higher accuracy can be obtained. In such cushion molding, since there is a pressure generation source near the molding cavity L, it is excellent in controllability of pressure when the resin material is pressurized or depressurized, so the residual stress of the molded product can be reduced, This is because warping and twisting can be greatly reduced.

The present invention can be widely applied without being limited to the above-described embodiments.
The injection molding apparatus 1 is not limited to a cushion molding apparatus having the pusher 23.
The resin material is not limited to a thermosetting resin. It may be a plastic molding material whose melt viscosity depends on temperature.
When the resin material can be stably filled into the molding cavity L, the entire injection process may be performed by pressure control.
The screw 43 may be moved not only by the servo motor 46 but also by a hydraulic motor.

It is sectional drawing which shows schematic structure of the injection molding apparatus which concerns on embodiment of this invention. It is a figure explaining the process of injecting a resin material.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Injection molding apparatus 2 Mold apparatus 3 Injection apparatus 21 Sprue (resin supply path)
23 Pusher (Pressure member)
43 Screw (pressing member)
K Resin pool L Molding cavity

Claims (5)

A step of melting the resin material in the injection device;
A step of moving a pressing member provided in the injection device and injecting a molten resin material into a molding cavity through a resin reservoir and a resin supply path formed in the mold device;
A step of pressurizing a molten resin material;
In a resin material injection molding method having
When injecting the molten resin material into the mold apparatus, the pressing member is controlled so that the injection pressure of the resin material becomes constant, and the viscosity of the molten resin material is determined from the moving amount or moving time of the pressing member. A resin material injection molding method characterized by comprising a measuring step.   Compare the allowable range of movement of the pressing member corresponding to the range of viscosity allowed as a resin material suitable for molding with the actual amount of movement of the pressing member, or allow as a resin material suitable for molding. When the allowable range of the movement time of the pressing member corresponding to the range of viscosity is compared with the actual movement time of the pressing member, and the actual movement amount or movement time of the pressing member exceeds the allowable range The resin material injection molding method according to claim 1, further comprising a step of discarding the resin material.   When injecting the molten resin material, after performing the movement control of the pressing member so that the injection speed of the resin material is constant, the movement control of the pressing member is performed so that the pressure is constant, and thereafter 3. The resin material injection molding method according to claim 2, wherein the movement control of the pressing member is performed again so that the injection speed of the resin material becomes constant.   4. The resin material according to claim 1, further comprising a step of pressing the resin in the resin reservoir toward the cavity with a pressure member provided in the mold. 5. Injection molding method. The injection molding method according to any one of claims 1 to 4, wherein a thermosetting resin is used as the resin material.

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