JP2640716B2 - Injection molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding method for measuring a material resin, injecting the resin into a cavity in a mold by advancing a screw in an injection heating cylinder, and molding the resin into a required molded product.

[0002]

2. Description of the Related Art In an injection molding by an injection device having an injection screw in an injection heating cylinder, a measuring process of rotating the screw while applying a back pressure to accumulate plasticized resin in the tip of the injection heating cylinder. After completing the above, the process is shifted to an injection step of filling the cavity in the mold with the measured resin by advancing the screw.

[0003] The injection step usually comprises a step of filling the cavity with a resin by a primary pressure and a pressure-holding step performed continuously by a secondary pressure. Generally, the filling step is performed under control of speed. The pressure-holding step is performed by pressure control. This is because immediately after removing the filling pressure and shifting to cooling, the molten resin flows backward from the gate until the gate cools and solidifies, so preventing this and shrinking when the resin solidifies, This is to compensate for the contraction.

[0004] Therefore, since the holding pressure is not necessary after the gate resin is solidified, the holding pressure time is set for the time until the gate is solidified. Therefore, the holding pressure time depends on the design dimensions of the molded product. On the other hand, in the case of a thick molded product in which the runner and the gate are designed to be thick, the pressure holding time is inevitably set to be long. After the elapse of the dwell time, the process shifts to resin measurement.

The back pressure at the time of this weighing is applied to the screw by hydraulic pressure as a resistance to the screw retreat due to the forward movement of the molten material. If the back pressure is high, the screw retreat speed becomes slow and the plasticization occurs. Usually, it is set lower than the holding pressure because the capacity decreases.

[0006] The cooling process of the cavity is measured from the completion of the pressure holding, and when the set time is up, the process is completed and the process shifts to the process of opening the cavity and taking out the molded product. The cooling time varies depending on the thickness and shape of the molded product, but is generally longer than the measuring time in many cases. However, some of them may be short, but excessive cooling does not have any particular effect on the molded product. In some cases, cooling is performed until the measurement is completed before the next step.

[0007]

If the resin is measured in accordance with the conventional molding method and the pressure is immediately shifted to the holding pressure after the injection and filling, the molded product may be partially warped or sinked. Although this phenomenon can be prevented to some extent by the shape of the molded product and the design of the cavity gate, there has been no means to prevent this in the case of a molded product that is limited by the shape and the design of the gate.

Therefore, as a solution to the above-mentioned problem, the present inventors set the injection pressure at the time when the resin is filled in the cavity to zero value, depressurize the resin in the cavity, and then maintain the pressure. The molding method was found earlier. This new molding method has the advantage of preventing the occurrence of partial warpage or the like of the molded product without drastically changing the molding process. There is a new problem that it takes a long time.

The present invention has been made in view of the above circumstances, and an object of the present invention is to reduce the time required from the start of injection to the completion of metering and start timing of cooling time by combining the pressure-holding step and the metering step. to enable the forward feed of the time, thereby even molding method requiring depressurization time to the injection process, it is to provide an injection molding method can shorten the molding time.

[0010]

According to the present invention, the resin is injected and filled into the cavity by advancing the screw, and when the pressure is maintained after the filling is completed, the injection pressure at the time when the resin is filled into the cavity is reduced to zero. To release the pressure of the resin in the cavity, and then rotate the screw to start the measurement of the resin and hold the pressure by the back pressure at the time of measurement. Do it.

The setting time of the injection pressure 0 value is in the range of 0.1 to 10 seconds, and the range time is set in consideration of the shape and thickness distribution of the molded product, gate design, cavity volume, and the like. The holding pressure is performed by controlling the back pressure in a plurality of stages.

[0012]

In the above molding method, the energy in the cavity is temporarily removed before the holding pressure is set by setting the injection pressure to 0 or at the beginning of the holding pressure, and the cooling of the previously filled downstream portion is promoted. As a result, the flowable region of the resin in the cavity is narrowed.

In the pressure holding in such a state, the resin in the flow region solidifies under a predetermined pressure, and the energy at that time is smaller than that in the case of the solidification by the pressure holding in a state where the flowable region is wide. be small Te, energy overall balance to warpage or shrinkage occurs in the molded article hardly occurs.

[0014] Further, by combining the holding pressure and the measurement, the resin is measured by the rotation of the screw even while the back pressure acts as the holding pressure. Since the back pressure as the holding pressure is set higher than the normal back pressure, the plasticizing ability is smaller than the normal case during the holding pressure, so the weighing time is longer, but overall The time is shorter than when weighing is started after the dwell.

Also, by starting the measurement of the cooling time at the same time as the start of the measurement, the three steps of the pressure-holding step, the measuring step, and the cooling step are started at the same time. The timing is completed before the normal case where the timing is started, and the timing is completed earlier by the time of the advance, thereby shortening the time of the molding process.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail by taking as an example the injection molding of a molded article (box-shaped connector) having the shape shown in FIG. In injection molding, there are cases where the process immediately shifts from the filling process to the pressure-holding process, and cases where the process proceeds in the order of the filling process, the compression process and the pressure-holding process. However, since the compression step is included as a part of the pressure holding step, all the steps will be described as pressure holding.

When the molded article 1 is molded by a conventional injection molding method, warpage occurs in a portion shown by oblique lines. This portion is a thin side plate portion 4 formed on the side of the cavity gates 3 and 3 branched from the runner 2, and is difficult to remove by conventional injection molding means.

Also in this embodiment, resin injection is performed with the side plate portion 4 serving as the gate side. FIG. 2 is a waveform data diagram depicting the operating state of the molding machine at the time of actual molding in this embodiment on the time axis starting from the start of injection, and the injection speed, injection pressure, in-mold pressure, and back pressure corresponding to each process. FIG.

First, injection filling of resin by speed control is started (see FIG. 1). The resin fills the cavity with injection filling, and the pressure in the mold rises as shown in FIG.
After c, the pressure in the mold reaches its peak. In the cavity,
As shown in FIG. 3 (A), the solidification of the resin at the flow front (downstream side) is progressing, and the other portions are in a flowable state except for the contact portion with the cavity surface, and the energy in the cavity is The upstream side where the gate is located is higher than the downstream side.

[0020] immediately migrate the time in such a state holding pressure as the filling completion, the resin will be solidified to remain upstream side of the energy balance, also as the energy that warpage level significantly exceeded Therefore, the molded product is likely to be warped. In the case where the molded article 1 is a box-shaped connector having a shape as shown in FIG. This portion is a thin side plate portion 4 formed on the side of the cavity gates 3, 3 branched from the runner 2.

However, in this embodiment, the injection pressure is preset so that the injection pressure becomes zero when the in-mold pressure reaches a peak, and thereafter, the injection pressure does not act on the resin in the cavity. Therefore, the pressure in the mold is 0
Value. When this state is maintained for about 3.3 seconds, the pressure in the mold is equalized during that time, and as shown in FIG. Solidification is also promoted and the flowable area is further narrowed.

Next, the injection step is completed with the lapse of the above time, and the screw is rotated to shift to a resin measuring process. In this measuring step, as shown in FIG. 1, first, the back pressure is set high as the back pressure primary pressure, and the back pressure is used as the holding pressure to perform the measurement and the holding pressure of the resin at the same time. After the elapse of the dwell time, the pressure is reduced to the back pressure secondary pressure, and the measurement is continued until the set time. At the same time as the start of the measurement, the measurement of the cooling time is started.

It takes 1.5 seconds to increase the holding pressure due to the back pressure.
After about ec, the pressure in the mold increases. Energy in this holding pressure is applied only to the flow region which is narrowed, even if its energy by warpage level Redirecting a listen, it is as shown in FIG. 3 (C), very small area as seen from the entire Becomes

[0024] Thus, compared to the case of solidification due to the holding pressure of the flowable region is a wide state, only a small energy in the cavity, the energy is totally balanced to warpage or shrinkage occurs resulting in a molded article It becomes difficult. In the box-type connector 1, the result of the analysis, I prevention coupled with the distortion due to low-pressure injection, appears markedly greater modulation of pressure distribution, shear stress, the etc. volumetric shrinkage, the final value of the volume accommodating rate Even at the same, the shear stress is small and the warpage is hardly recognized. In addition, the conventional method of shifting to the measuring process after the completion of the pressure holding process
Is shortened compared to the case of

FIG. 5 shows molding under the set conditions of the conventional method.
FIG. 4 is a comparison diagram showing an overall time difference when performing according to the present invention. According to this, the weighing time of the embodiment is 1.74 sec longer than that of the conventional method. This is because the back pressure was set to 300 kg / cm ² for holding pressure, and the metering time was inevitably lengthened by the decrease in the plasticizing ability. However, in comparison with the time from the pressure holding step in the conventional method, the time is reduced by 1.56 sec. In addition, the cooling time is the same for both, but the example is completed earlier by about 3.3 seconds (previous feed) due to the difference in the measurement start time.

Therefore, when the point of completion of the measurement is determined to be the completion of the molding step and the process is shifted to the mold opening step, the molding time is 1.5
When the cooling is completed, the molding time is 3.3 seconds.
Will be shortened. As a result, even if time is required for depressurization, the time can be offset.

[0027]

As described above, according to the present invention, when the resin is filled in the cavity, the resin in the cavity is depressurized to prevent the molded product from warping or sinking by injection molding. Molding can be performed without warping etc. even for molded products subject to design restrictions,
Further, there is an advantage that it can be adopted in a conventional injection molding machine without setting any other special means just by setting and setting the pressure to a zero value when the resin fills the cavity.

Further, since the holding pressure is performed by the back pressure and the holding pressure step and the measuring step are combined, the depressurizing time can be cancelled, and the cooling time is also advanced. In the case where the molding step is completed, the time is shortened in both cases where the cooling completion is regarded as the completion of the molding step.

Furthermore, the molding time can be shortened by combining the pressure-holding step and the measuring step, and by only advancing the cooling time start point, and does not require any special equipment or complicated molding operation. It has advantages such as being economical.

[Brief description of the drawings]

FIG. 1 is a process explanatory view of an injection molding method according to the present invention.

FIG. 2 is a waveform data diagram illustrating an operation state of a molding machine according to the present invention.

FIG. 3 is an explanatory diagram showing a state of energy with respect to a resin in a cavity.

FIG. 4 is a perspective view of a molded product and a runner in which a warped portion in a conventional method is indicated by oblique lines.

FIG. 5 is a comparison diagram of an embodiment of the present invention and time reduction by injection molding according to a conventional method.

[Explanation of symbols]

 Reference Signs List 1 Molded product 2 Runner 3 Cavity gate 4 Side plate

Claims (1)

(57) [Claims] 1. Injecting and filling a resin into a cavity by advancing a screw, and performing pressure holding after filling is completed, setting the injection pressure at the time when the resin is filled into the cavity to a zero value to release the resin in the cavity. An injection molding method characterized in that the screw is rotated to start the measurement of the resin, and then the pressure is held by the back pressure at the time of the measurement, and the measurement of the cooling time is started simultaneously with the start of the measurement.