JPH02131909A - Injection molding method and its device - Google Patents

Abstract

PURPOSE:To obtain the molded object with very small dimensional shrinkage by a method in which not only ultrasonic wave vibration is applied to a mold, but also the mold is resonated, thereby improving the fluidity of material, and further the stress effect of ultrasonic wave in which the molding material brought into contact with the resonator of ultrasonic wave in drawn to the node, is used. CONSTITUTION:The nozzle 4 of a molding machine is brought in pressure- contact with the sprue 3a of the mold of stationary side, and while molding is achieved by injecting molding material into a cavity 2a through the sprue 3a, the mold 1 is resonated in (n)-wavelength by generating a vibrator 10 ultrasonic wave vibration by an ultrasonic wave generator 12. In order to act very effectively ultrasonic wave on the material in molding, the frequency of 10 kHz-100kHz is used. In the resonance in (n)-wavelengths, (n) is m/2 (m is positive integer), but in order to cause the node of resonance to coincide with the contact part of the stationary mold or the nozzle, the number of the node is as small as possible, and (n) is preferably less than three. Further even in the case of n<3, the mold is resonated so that the loop of resonance coincides with the cavity 2a and the vibration effect of ultrasonic wave is used most effectively.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for injection molding of molding materials such as polymeric materials.
The present invention relates to an injection molding method and apparatus that can mold a molded product with high physical properties and good appearance.

[Conventional technology] Conventionally, injection molding has the great advantage of high productivity and has been widely used for molding products made of thermoplastic resins or materials whose main composition is thermoplastic resins. By the way, in recent years, with the progress of research on the physical properties of Netomachi plastic resin, the rigidity, heat resistance, and chemical resistance of molded products have been improved depending on the material (
It has become known that the molecular weight of the thermoplastic resin influences its performance.

However, the molecular weight of thermoplastic resins that can be molded using conventional injection molding methods is not so large, and the molecular weight is generally smaller than that of those commercialized as film crates. As a result, problems may arise in that the physical properties of the molded product, such as rigidity, heat resistance, and chemical resistance, are poor.

Therefore, from the perspective of improving physical properties, a method of molding that attempts to increase the molecular weight of the resin that makes up the molded product by improving the fluidity of the resin during injection molding has begun to be considered.
Several proposals have been made so far. For example, the method of applying ultrasonic vibration to the gate part of a mold proposed in Japanese Patent Publication No. 57-2088, or the method proposed in Japanese Patent Publication No. 61-4
There is a method of inductively heating the mold surface using high frequency waves, as proposed in No. 4616.

On the other hand, when a polymeric material is used for injection molding, the polymeric material is filled into a mold in a heated state.

For this reason, 81li1 is stretched during heating and shrinks when cooled in the mold, so that only a molded product smaller than the cavity size of the mold can be obtained.

Therefore, from the viewpoint of improving the dimensional accuracy of molded products, several proposals have been made to reduce the shrinkage of the material filled in the mold. For example, a method of molding by lowering the temperature of the material by significantly increasing the injection pressure and similarly increasing the mold clamping force, or
A method, as proposed in No. 134722, in which the cavity is configured with a horn for ultrasonic vibration, and the material is injected into the cavity and the non-uniformity of the material temperature during the cooling process is significantly reduced. etc. [Problems to be solved] However, the conventional forming method described above had the following problems. Namely, Japanese Patent Publication No. 57-2088, Japanese Patent Publication No. 58-13
The technology proposed in No. 4722 has the problem that the structural force of the mold is very complicated, the sonic vibrations have a negative impact on the mold itself and other parts of the equipment, and the material and horn are Since the structure is such that there is direct contact, a large load is placed on the horn and vibration-generating parts, which poses the problem of not being able to apply sufficient sonic vibration to the material. Further, as a result of experiments, it has been revealed that the fluidity of the resin does not improve as expected even when the surface of the mold is heated in the technique proposed in JP-A No. 61-44616.

Furthermore, the method of molding at a low clamping temperature of the material by significantly increasing the injection pressure and the mold clamping force also creates distortion in the molded product, causing it to deform when used as a product. There was a problem with how easy it was. The present invention [month] was made in consideration of the above problems, and the first development [y1] is simply the application of TFL sonic vibration to the mold.
The aim is to provide an injection molding method that dramatically improves the fluidity of the material by making the mold resonate, and furthermore, the molding material that comes into contact with the ultrasonic resonator is attracted to the foreground. The stress effect of ultrasonic waves (parts of resonance)
The purpose of the present invention is to provide an injection molding method that makes it possible to obtain a molded product with extremely small dimensional shrinkage compared to when a molding material is press-fitted into a cavity using only injection pressure.

A further object of the second invention is to provide an injection molding device that allows the above-mentioned method to be carried out smoothly and has a reasonable construction. [Means for solving the problem] In order to achieve the above object, the injection molding method of the first invention comprises:
In a method of injection molding a molding material, there is a method in which molding is performed while causing a mold to resonate at n wavelengths (n=m72m+positive integer) using ultrasonic waves. In a preferred embodiment, in order to most efficiently reduce the contact resistance between the injected material and the mold wall surface using the vibration effect of ultra-11 waves, the position of the cavity of the mold or the abdomen of resonance caused by the ultrasonic wave is In order to resonate in unison and/or to prevent ultrasonic vibrations from being transmitted to the outside of the mold, the nodes of resonance due to ultrasonic waves or the positions of the fixed mold holder and the movable mold holder should be adjusted. There is a method to make them resonate so that they match. In addition, as another preferred embodiment, the stress effect of ultrasonic waves (
In order to suppress the dimensional shrinkage of the molded product and improve the dimensional accuracy at the resonance nodes), the ultrasonic resonance points are caused to resonate in a manner that matches the position of the mold cavity, and/or the ultrasonic waves are In order to prevent vibrations from being transmitted to the outside of the mold, there is a method of causing resonance so that the positions of the fixed mold holder and movable mold holder match the points of resonance caused by ultrasonic waves. Furthermore, the injection molding apparatus of the second invention supplies the molding material from the molding machine to the cavity of the mold through the sprue of the fixed side mold, and in the apparatus for performing injection molding, the fixed side mold and the movable side mold are is held by a fixing jig, and an ultrasonic vibrator is coupled to the mold surface opposite to the cavity side of the movable die. Preferably, the fixed die and the movable die are held by a fixing jig. The mold is held using a holding structure using line contact.

[Example] An example of the above solution will be described below.

First, an example of an injection molding apparatus will be explained based on FIG. 1.

In the figure, l indicates a mold, which is divided into a movable mold 2 and a fixed mold 3. A cavity 2a is provided on the contact surface of the movable mold 2 with the fixed mold 3, and a sprue 33 is provided at a position on the fixed mold 3 corresponding to the cavity 2a. The mold l contains metals, ceramics.
Graphite or the like can be used, or it is preferable to use a material that has low ultrasonic transmission loss and is less fatigued even when the amplitude of ultrasonic vibration is increased, such as titanium alloy or duralumin. Further, the surface of the mold l may be subjected to treatments such as plating or graining. Furthermore, is it possible to divide the mold l into three or more parts? In this case, the dividing surface should be located as close to the abdomen of ultrasound resonance as possible in order to improve the transmission of ultrasonic vibrations. It is preferable to do so. In addition, mold temperature control. For details on how to eject molded products,
A known method may be used, but the joint attached to the mold for introducing or discharging the mold temperature regulating medium is preferably installed near the joint. In addition, when an ejector pin is provided in the mold, it is preferable to set the clearance between the ejector pin and the hole through which it passes to the minimum value at the position of the joint in the state before ejection.4 is a molding machine (not shown) There is a nozzle, sprue 33
The molding material is injected and supplied to the cavity 2a through the. The contact surface of the sprue 3a with the nozzle 4 is located at approximately the location (described later) of the ultrasonic vibration (displacement waveform) in the stationary mold 3. Reference numeral 5 denotes a first holding member (mold clamping member), which is supported by a cylinder q so as to be movable forward and backward, and a fixing plate 7 serving as a fixing jig is attached to the tip thereof. This fixed plate 7 holds the outer periphery of the movable mold 2 at approximately the center. The movable mold 2 is held by the fixed plate 7 by grooves 2b on the outer periphery of the movable mold 2.
This is accomplished by providing a groove 2b and bringing the tapered tip 7a of the fixing plate 7 into contact with the groove 2b. Therefore, in this case, the movable mold 2 is held by the fixed plate 7 through line contact, and the contact area between the movable mold 2 and the fixed plate 7 becomes extremely small.

This makes it possible to minimize the external leakage of mold vibrations. A second holding member 8 is fixed to the outside of the cylinder 6, and a fixing plate 9 serving as a fixing jig is attached to the tip thereof. This fixed plate 9 holds the outer periphery of the fixed side mold 3 at approximately the center, and the holding in this case is the same as the holding of the movable side mold 2, and the fixed side mold y! In order to suppress the vibrations of the fixed mold 3 from flowing out to the outside, the groove 3b of the fixed mold 3 and the tapered tip 9a of the fixed plate 9 are held in a line contact state.

As a method of holding the mold 1, it is preferable to use a holding member with a small contact area to hold the nodes of resonance caused by ultrasonic waves, as in this embodiment.

10 is the vibrator, and the movable side metal! ! The tip of the li2 is brought into contact with the mold surface on the opposite side from the cavity 2a, and is connected by a mounting member 1l such as a screw. l2 is a-ff
Using the wave oscillation base, ultrasonic vibration is generated in the vibrator 1o, and the mold l (movable mold 1!!2, fixed mold 3) is excited and resonated. This resonant frequency is designed and manufactured in advance to a frequency that allows the tracking of the ultrasonic oscillator.
When supplying power to the cavity 2a via the power source, the system constantly tracks changes in the resonant frequency due to momentary load fluctuations, and also adjusts the required amount of power (
It is set to supply a maximum output (below the maximum output). Next, a specific example of the first invention of the injection molding method performed using the above injection molding apparatus will be described.

The nozzle 4 of a molding machine (not shown) is pressed against the sprue 33 of the stationary mold 3, and the cavity 2 is inserted through the sprue 3a.
Injection molding is performed with a molding material on a, and at the same time, the ultrasonic oscillator 12 generates ultrasonic vibrations in the vibrator 10, thereby causing the mold 1 to resonate at n wavelengths. The timing for generating ultrasonic vibrations can be selected depending on the desired effect.

The vibration frequency at this time is set to IKI1, to IOMII,l, and in order to make the ultrasonic waves act extremely effectively on the material during molding. l OKIII〜100KHIl
Let it be the JFil wave e. It is preferable to set the amplitude of the ultrasonic vibration to be large enough to fully demonstrate its effect, or to match the fatigue level of the material of the mold l. Also, n in n-wavelength resonance is m/2 (m is positive! I
(Figure 2), in order to match the resonance part (the intersection of the displacement waveforms, the point where there is no vibration) with the mold fixing part and the contact part of the nozzle, it is necessary to place the nodal part as much as possible. It is preferable to set n<3, which is a small number. Furthermore, even in the case of n<3, the resonance belly (the farthest part of the displacement waveform is the point that vibrates most strongly),
It coincides with the cavity 2a, and resonates so that the vibration effect of the ultrasonic wave can be utilized to the maximum extent possible. This will improve the flow of the molding material.

Next, a specific example of the injection molding method according to claim 3 will be explained.

This injection molding method differs from the injection molding method described above in that the cavity 2 is aligned with the node of resonance caused by ultrasonic waves. In this way, the dimensional shrinkage of the molded product is significantly reduced due to the stress effect of the ultrasonic waves.

Molding materials that can be molded by the above injection molding method and apparatus include organic materials such as plastics, inorganic polymers, ceramics, metals, inorganic materials such as glass, and other foods. Examples include materials that have some fluidity during molding, such as adhesive tapes and mixed materials thereof. Furthermore, the injection molding method in the present invention is a multicolor molding method. All molding methods, including injection compression molding methods, in which a fluid or rubber-like molding material is press-fitted into a mold, shaped into a predetermined shape, and then the molded product is taken out. This includes:

[Experimental Examples] Hereinafter, the results of experiments conducted using the injection molding method and apparatus of the present invention will be explained while comparing them with comparative examples.

Experimental Example 1 Injection molding apparatus: The apparatus shown in Figure 1 Injection molding was performed under the above conditions while the mold was made to resonate, and the flow length at that time was determined. Flow length is wall thickness 0.51
The length of the resin flowing into the groove-shaped cavity was measured and evaluated based on the average value of 10 times.

The results are shown in Table 1. Comparative Example 1 An experiment was conducted under the same conditions as Experimental Example 1, except that the mold was not caused to resonate by ultrasonic waves. Comparative Example 2 An experiment was conducted under the same conditions as Comparative Example 1, using a far-infrared heater to heat the mold temperature to 200'C. This example is considered to be equivalent to the conventional example in which molding is performed by raising the mold surface temperature using a high-frequency induction heating device. Comparative Example 3 An experiment was conducted under the same conditions as Experimental Example 1, except that the vibrator 10 was positioned at the contact area between the movable mold 2 and the fixed mold 3, as shown in FIG. At this time, the mold was not in a resonant state.

The results of Comparative Examples 1 to 3 are shown in Table 1. Table 1 ■) The standard deviation in parentheses is a.As a result, according to the present invention, it is much better than when ultrasonic waves are not applied, or when ultrasonic waves are simply applied, or when the metal is heated. It was found that the fluidity of the molding material improved. Experimental Example 2 Injection molding apparatus W1: Same as ii shown in FIG. 1 except that the fixed side mold and the movable side mold are slightly longer. The experiment was conducted under the same conditions as Experimental Example 2, except that the mold was not caused to resonate by ultrasonic waves. leather! A1 The experiment was conducted under the same conditions as Experimental Example 2, except that the vibrator IO was positioned at the contact area between the movable mold 2 and the fixed mold 3 (see Figure 6). Table 2 shows the results of Comparative Example 4.5. Table 2 Injection molding was performed under the above conditions while making the mold resonate, and the diameter of the molded product at that time was measured.

Evaluation was performed using the average value of 10 molded products.

The results are shown in Table 2. Comparative Example 4 As a result, according to the present invention, not only when ultrasonic waves are not applied, but also compared to when only a-sonic waves are applied.
It was found that it was possible to obtain a molded product with small dimensional shrinkage.

The load current of the super-wave oscillator was measured when the molds were held in contact with each other and the molding of Experimental Example 1 was carried out. The results are shown in Table 3.

Comparative Example 6 An experiment was conducted under the same conditions as Experimental Example 3, except that the mold was held using a fixed plate having the same shape and dimensions as the grooves of the movable mold and the fixed mold. I did this.
In this case, the fixing plate is in surface contact with the mold.

The results are shown in Table 3. Table 3 In Comparative Example 6 (surface contact) where the load current was high, it was clearly found that the vibration was flowing through the fixed plate. As a result, it was found that holding the mold by line contact is very effective.

[Effects of the Invention] As described below, according to the injection molding method of the first invention, vibrations can be efficiently transmitted by causing the mold to resonate with ultrasonic vibrations. Furthermore, by maximizing the vibration effect of ultrasonic waves, it is possible to improve the fluidity of molding materials, making it possible to mold composite materials containing large amounts of high molecular weight plastics and fillers, which was difficult with conventional molding techniques. It becomes easier.

Furthermore, by making the mold resonate with ultrasonic vibrations, the vibrations can be transmitted efficiently and the stress effect of ultrasonic waves can be utilized, so the dimensional shrinkage of the molded product is greater than when simply applying ultrasonic waves to the mold. can be significantly reduced. According to the injection molding apparatus of the second invention, it is possible to improve the fluidity of the molding material, to mold products with excellent physical properties and dimensional accuracy, and to minimize the outflow of mold vibrations. This has the effect of not having a negative impact on other parts of the device.

[Brief explanation of drawings]

Fig. 1 is a cutaway side view of essential parts of a specific example of the injection molding apparatus of the present invention, Figs. 2 and 3 are explanatory diagrams of displacement waveforms and wavelengths at the time of mold resonance in the first invention, and Fig. 4 is an explanatory diagram of the wavelength of the mold according to the first invention. An explanatory diagram of the cavity used in the molding experiment, Figure 5 is Experimental Example 1
Fig. 6 is a schematic diagram of an example of a device other than the present invention using an ultrasonic vibrator, Fig. 7 is an explanatory diagram of the cavity used in the molding experiment of Experimental Example 2, Fig. 8 is an explanatory diagram of the resonance conditions in the molding experiment of
The figure shows an explanatory diagram of resonance conditions in the molding experiment of Experimental Example 2. 1 Mold 2: Movable side mold 3/fixed side mold 2a: Cavity 2b/3b/groove 3a: Sprue 7, 9 Fixing jig IO: Vibrator 2nd figure n PLX section 3rd figure n

Claims (6)

[Claims] (1) An injection molding method for injection molding a molding material, characterized in that molding is performed while causing a mold to resonate at n wavelengths (n=m/2m; positive integer) using ultrasonic waves. (2) The injection molding method according to claim 1, characterized in that the molding is performed while resonating so that the resonance region of the ultrasonic waves coincides with the position of the cavity of the mold. (3) The injection molding method according to claim 1, characterized in that the molding is performed while resonating so that the node of resonance caused by the ultrasonic waves coincides with the position of the cavity of the mold. (4) The first aspect of the present invention is characterized in that molding is performed while resonating so that the nodes of resonance caused by ultrasonic waves coincide with the positions of the stationary mold holder and the movable mold holder.
The injection molding method according to item 2 or 3. (5) In a device that performs injection molding by supplying molding material from a molding machine to a mold cavity through a sprue of a fixed mold, the fixed mold and movable mold are held by a fixing jig. An injection molding apparatus characterized in that an ultrasonic vibrator is coupled to the mold surface of the movable mold on the side opposite to the cavity side. (6) The injection molding apparatus according to claim 5, wherein the fixed mold and the movable mold are held by the fixing jig through line contact.