JPS63176124A - Injection molding method and equipment - Google Patents

Abstract

PURPOSE:To reduce residual stress by preventing formation of a skin layer, by a method wherein temperature control of a movable core is performed at least at the preset softening temperature of resin, a mold is cooled always, and in a cooling process the movable core is cooled suddenly through heat conductivity by bringing the movable core into contact with the mold by moving the movable core. CONSTITUTION:Hydraulic oil from a hydraulic mechanism 35 is fed into each of hydraulic oil chambers 19a, 19b through a command of a sequencer 36 and rams 17a, 17b are shifted. Then a gap delta is generated between mold bodies 10a, 10b corresponding to each of movable cores 11a, 11b, and heat insulation of the mold bodies 10a, 10b and movable cores 11a, 11b, which are cooled always, is performed. A temperature rise of each of the movable cores 11a, 11b is performed by operating a mold temperature control instrument 31. Heating equipments 13a, 13b are controlled by a control instrument 34 based on a deflection (e) among each of temperatures detected by each of temperature detecting instruments 12a, 12b and a preset temperature Tset of at least the preset softening temperature. Injection is started and a process is entered into a filling process. Heat insulation control is performed during the injection also through a mold temperature control instrument 31. When resin pressure on the inside of the cavity 15 is raised by completing the filling process, the hydraulic oil is discharged and the movable cores 11a, 11b come into contact with the mold bodies 10a, 11b.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides an injection molding method and an injection molding method that make it possible to maintain the inside of a cavity at a uniform high temperature in the filling process and rapidly cool it in the cooling process. This invention relates to injection molding equipment.

(Prior Art) In an injection molding method in which molten resin is injected into a mold cavity, when the molten resin flows in the cavity, the part in contact with the mold is cooled by the mold and becomes highly viscous. A layer with extremely poor fluidity (called a skin layer) is formed. As a result, transferability from the cavity surface deteriorates, and molding defects such as flow marks or weld lines are likely to occur.

As a countermeasure against this problem, a method has been proposed, for example, in Japanese Patent Publication No. 58-40504, in which injection molding is performed after high-frequency induction heating of the cavity surface to a temperature higher than the softening temperature of the resin.

To briefly explain its configuration, FIG. 4 shows a mold part for carrying out the method, and a high-frequency induction heating coil is placed between the fixed side 1a and the movable side 1b of the mold 1 by an industrial robot (not shown). will be moved and installed. The coil 2 is made by molding a steel pipe with a diameter of 3 cm into a dish shape in a spiral pattern at 5-diameter intervals, then casting it with epoxy resin to a thickness of 3 am, and solidifying it into a flat plate. It was formed.

During injection molding, when the mold is in an open state after the previous molded product has been taken out, the coil 2 is lowered by an industrial robot (not shown) and is placed between the fixed side 1a and the movable side 1b of the mold l. After insertion, the mold 1 is closed, the coil 2 is sandwiched between the fixed side 1a and the movable side 1b of the mold 1, and in this state, high frequency current is applied to heat the IC on the cavity surface.

At this time, cooling water is not flowing through the mold 1.

FIG. 5 shows an example of measuring mold temperature by this high-frequency induction heating. Points A, B, C, and D in the figure indicate points corresponding to A, B, C, and D in FIG. 4. As is clear from Figure 5, the temperatures at points A and B on the mold surface rise rapidly in a short period of time, and at points 0 and D inside the mold, there is almost no temperature rise due to high-frequency induction heating. I understand.

Now, after confirming the temperature rise on the mold surface by the above operation,
The mold 1 is once opened, the coil 2 is extracted from between the fixed side 1a and the movable side 1b of the mold 1, the mold 1 is closed again, and the injection process consists of a filling process and a pressure holding process similar to normal injection molding. , a cooling process is performed in which cooling water is passed through the mold 1 to cool it.

According to this injection molding method, since injection is performed after the cavity surface is heated above the softening temperature of the resin, a skin layer is less likely to form on the cavity surface, and transferability is significantly improved, resulting in flow marks, weld lines, etc. The occurrence of molding defects can be prevented.

(Problems to be Solved by the Invention) By the way, heating the mold surface using the above-mentioned coil has the following problems.

(1) When the shape of the cavity becomes complex, it becomes difficult to create a coil that perfectly copies the shape, and in this case, the coil does not completely adhere to the entire surface of the cavity, resulting in differences in the degree of heating of the cavity surface. As a result, molding defects such as flow marks and weld lines cannot be resolved.

(2) Since the cavity is heated only when the coil is inserted into the mold, the molding cycle is extended by the operating time required to take the coil in and out and insert it into the mold. .

(3) If the room temperature, mold opening time, or molded product removal time changes, the cooling rate of the cavity will change accordingly, so even if the heating time is the same, the cavity temperature will fluctuate, and therefore the molding quality will not be stable.

(4) Particularly in the case of thin-walled molded products, the formation rate of the skin layer during the injection process is fast, which creates a pressure gradient in the flow direction of the molten resin, causing excessive pressure to be applied near the gate, causing the skin layer and gate to Shear stress occurs between the resin and the supplied resin. This abrasion stress causes residual stress, resulting in deformation and cracking.

Poor dimensional accuracy occurs, especially with optical discs.

In the base of a compact disc, a fatal molding defect occurs due to worsening of birefringence.

(5) As a countermeasure for the previous item, the resin temperature is raised higher than usual during molding, but the heating temperature setting for the cavity before injection starts must be determined based on the experience and intuition of the operator. It is something.

The present invention was developed to solve these problems all at once. It automatically and uniformly heats the cavity surface to a predetermined temperature before entering the injection process, and enables rapid cooling during the cooling process to achieve high temperatures. It is an object of the present invention to provide an injection molding method and apparatus that make it possible to obtain high-quality molded products.

(Means and effects for solving the problem) Therefore, the present invention provides an injection molding method with a double structure consisting of a movable core forming a cavity and a mold body surrounding the movable core which is constantly cooled. The mold is used, and the mold body and the moving core are kept in a non-contact state from before the start of injection until during the filling process, thereby insulating the space between them and raising the temperature of the moving core to a temperature higher than the softening temperature of the resin. In the subsequent cooling process, the moving core is brought into contact with the mold body by the pressure inside the cavity (holding pressure), and the heating of the moving core is stopped, allowing rapid cooling in the next cooling process. A device for carrying out this method includes a moving core that forms a cavity, a mold body that surrounds it, a drive mechanism that drives the moving core within the mold body, and A mold having a heating device disposed inside the core and a temperature detector, and a mold temperature controller configured to control the temperature of the moving core to a set temperature in response to a signal from the temperature detector. These configurations are intended to solve the above-mentioned problems.

That is, in the present invention, (11) the mold has a double structure in which the part forming the cavity is used as a moving core and the mold body surrounding it can be in contact or non-contact.

(2) The temperature of this moving core is controlled to be higher than a preset softening temperature of the resin, and the mold body is constantly cooled.

(3) Before starting injection and during the injection process, the moving core and the mold body are kept in a non-contact state. Therefore, the space between the moving core and the mold body is insulated, and the temperature of the cavity surface is maintained at a predetermined temperature in conjunction with the temperature control described above, which prevents the formation of a skin layer during the injection process. prevent and reduce residual stress. As a result, no molding defects occur.

(4) When the cooling process begins, the moving core is moved and brought into contact with the mold body, increasing the heat transfer rate from the mold body to the moving core, and rapidly cooling the moving core. In this way, the mold body is constantly cooled, and the molding cycle can be shortened to the extent that only the moving core needs to be cooled in the cooling process.

(5) On the other hand, since the movable core can be processed into any shape by ordinary machining, it can be easily applied to complex molded products.

(Example) Hereinafter, an example of the present invention will be described in detail based on the drawings. 1st
The figure shows a side cross section of a mold consisting of a moving core and a mold body for carrying out the method of the invention.

In the figure, 10 is a mold, and the mold 1o is composed of a fixed side mold and a movable side mold as in the conventional case, and each mold has a movable core 11a and a movable core llb.

The mold body 1 is formed so as to surround each of the mold bodies 11b.
The basic configuration consists of 0a and 10b.

The cavity 15 is formed by the movable core 11 on the fixed side and the movable core 11b on the movable side. That is, the mold 10 according to the present invention has a fixed side and a movable side, all of which are paired, and in the drawings, the fixed side is denoted by a and the movable side is denoted by b. Therefore, in explaining the structure, the movable side will be mainly explained, but the fixed side has a similar structure.

The moving core 11b is formed to be as thin as possible to reduce its mass relative to its surface area, and is made of a material with high thermal conductivity such as aluminum. Inside the moving core 11b,
A temperature detector 12b using a thermocouple or the like to detect the surface temperature on the cavity side of the moving core 11b, that is, a cavity surface temperature T, and a heating device 13b using a heater or the like are installed. The outer periphery of the moving core 11b is made of nylon.

Synthetic resin such as Bakelite, or zirconia (ZrO□
) A liner 14b made of a heat insulating material made of a material with low thermal conductivity such as ceramics is fixed. The liner 14b has a minimum size that can prevent leakage of the molten resin and withstand the resin pressure within the cavity 15.

Mold body 1 on the side opposite to the cavity (rear end) of the moving core 11b
A ram 17b is held by a bush 16b made of an oil-impregnated bearing or the like, and a seal 18b made of a lip seal or the like is fitted to the outer periphery of the ram 17b, which is driven forward and backward by pressure oil in an oil chamber 19b formed between the mold body 10b. is installed, and the tip of the ram 17b is covered with a heat insulating material 2 similar to the liner 14b.
It is connected to the rear end of the movable core 11b via 0b.

21b is the end of the oil hole communicating with the oil chamber 19b, which is a connection port for a high-pressure rubber hose, and 22b is a cooling water passage for cooling the mold body 10b. 23 is a sprue bushing attached to the stationary mold body 10a. The moving cores 11a and llb on the fixed side and the movable side are connected to each corresponding ram 17a.
, 17b for each mold body 10a.

10b by the gap δ. The value of δ is 0.3 to 1
, 0** is preferable.

These moving cores 11a and llb are each mold body 11a,
When moving forward in llb by δ, the same moving core 11a
.

11b is a cavity 15, a corresponding liner 14a,
14b - Thermal insulation 20a, 20b and each moving core 11a
, llb are insulated from the mold bodies 10a and 10b by the spaces A and A formed by the movement of the mold bodies 10a and 10b.

FIG. 2 shows a control block diagram of the cavity surface temperature.

The mold temperature controller 31 includes a setting device 32 that outputs a set value Tset of the cavity surface temperature that is higher than a preset softening temperature of the resin, and a temperature detector 1 that detects the cavity surface temperature.
A comparator 33 that subtracts the output T of 2a and 12b from the set value Tset and outputs the deviation e (= Tset - T), and a comparator 33 that outputs the deviation e (= Tset - T), and a comparator 33 that outputs the deviation e (= Tset - T), and a
...integral, D-i minute).
Heating device 1 whose calorific value changes according to the output of the controller 34
It is configured as a closed loop control system consisting of 3a and 13b.

This mold temperature controller 31 and a pair of high pressure rubber hose connection ports 2
A sequencer 36 is provided which sequentially controls a hydraulic mechanism 35 that supplies pressure oil to each oil chamber 19a, 19b through 1a, 21b or discharges pressure oil from each oil chamber 19a, 19b.

Although Fig. 2 shows a single closed loop system, if the fixed mold body 10a and the movable mold body 10b have different heat capacities, it is more efficient to perform closed loop control for each independently. .

FIG. 3 shows an example of an injection molding process to which the present invention is applied. The process will be explained below with reference to FIGS. 1 and 2.

(11 First, the mold is opened and the product is taken out, and then the mold is closed. Then, according to a command from the sequencer 36, pressure oil from the hydraulic mechanism 35 is supplied to each oil chamber 19a, 19b, and the ram 1
7a, 17b to each moving core 11a, ll
A mold body 10a corresponding to b.

The mold bodies 10a, 10b and the moving core 11a are constantly cooled by creating a gap δ between them and the moving core 11a.

11b. This moving operation of the moving core may be performed simultaneously with the mold closing operation or during the mold closing operation.

(2) The mold temperature controller 31 is activated by the command from the sequencer 36.
operates to raise the temperature of each moving core 11a, llb.

Each moving core 11a is controlled by each temperature detector 12a, 12b.
, llb on the side closer to the cavity 15 is detected, and the heating device 13a is controlled by the controller 34 based on the deviation e between the output from the detectors 12a and 12b and a preset temperature Tset that is higher than the softening temperature of the resin. , 13b to maintain the deviation e at zero, that is, the set temperature Tset.

(3) When the temperature of the moving cores 11a and llb reaches the set temperature Tset, a signal is received from the mold temperature controller 31, and injection is started according to a command from the sequencer 36, and the filling process begins. Even during injection, the mold temperature controller 31 maintains the temperature at the set temperature.

(4) When the filling process is completed and the resin pressure inside the cavity 15 rises, each oil chamber 19a,
The pressure oil 19b is discharged, and the moving cores 11a, llb
contact the mold bodies 10a, 10b.

Generally, this switching state is the screw position.

Detection is possible using injection oil pressure, resin pressure inside the cavity, etc. At this time, the injection control is switched to pressure holding control to enter the pressure holding process, and at the same time, the heating devices 13a and 13b stop heating according to a command from the sequencer 36.

(5) In the pressure holding process and the next cooling process,
The mold bodies 10a, 10b have cooling water passages 22a, 2.
The moving cores 11a, llb and the mold bodies 10a, 10b come into contact with each other, thereby creating a gap between the moving cores 11a, llb and the mold bodies 10a, 10b. heat transfer is promoted and the molten resin in the cavity 15 is rapidly cooled.

The shape and dimensions of the molded product are set so as to have the cavity shape and dimensions when the movable core 118° 11b and the mold bodies 10a, 10b are in contact with each other.

(6) Here, when the preset cooling time has elapsed, mold opening is started according to a command from the sequencer 3'6.

(7) Return to (1) above and repeat the same operation thereafter.

Moving cores 11a, llb and mold bodies 10a, 10b
The shape and dimensions of the portions facing the rams 17a, 17b are determined by the strength of the liners 14a, 14b disposed at the portions where they come into contact with each other, and the heat insulating materials 20a, 20b located at the joints between the moving cores 11a, llb and the rams 17a, 17b. The surface shape and dimensions are such that the movable cores 11a and Ilb come into contact with each other when they retreat.

Furthermore, as described above, the moving cores 11a, llb have a small thickness, have a small mass relative to the surface area, and are made of a material with high thermal conductivity.
1lbO heating time is shortened, and at the same time the moving core 11a
, llb and the mold bodies 10a, 10b promote heat transfer.

In addition, although the explanation was avoided in the above embodiment, the mold body 10a
, 10b and the moving cores 11a, Ilb, the gap δ may be evacuated to create a vacuum by removing air from the gap δ. In this way, the time required to raise the temperature of the moving cores 11a and Llb can be further shortened.

(Effects of the Invention) As described above in detail, according to the present invention, the mold is divided into a portion forming a cavity and a mold body, so that the following effects can be achieved.

(1) Since the moving core can be heated without contacting the mold body, only the cavity surface can be heated efficiently, and at the same time, the time required to insert a heating coil as in the conventional method is unnecessary. This can significantly shorten the cycle.

(2) Since the surface temperature of the cavity is controlled in a closed loop using a moving core that is insulated from the mold body, a predetermined temperature is maintained during control, making the quality of the molded product more stable.

(3) During the injection process, by separating the cavity from the mold body, which is constantly cooled, and insulating it, it becomes easier to maintain the cavity surface temperature above the softening temperature of the resin, preventing the formation of a skin layer that remains. Reduced stress and deformation.

Molding defects such as cracks and deterioration of birefringence are resolved.

In addition to the above-mentioned effects, since the moving core can be easily processed by ordinary machining, it also has the effect that even molds with complicated shapes and dimensions can be easily obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a mold showing an embodiment of the present invention, FIG. 2 is a block diagram for temperature control of the cavity surface according to the present invention, and FIG. 3 is a process explanatory diagram of an injection molding process according to the present invention. FIG. 4 is a side view showing the concept of heating a mold by conventional high-frequency induction heating, and FIG. 5 is an explanatory diagram showing an example of the temperature distribution of the mold by the same heating. Description of main parts of the figure 10 - Mold 10a, 10b - Mold body 11a, 1lb - Moving core 12a, 12b - Temperature detector 13a, 13b - Heating device 14a, 1
4b-liner 15--cavity 4 17a, 1
7b--Ram 19a, 19b-1 Oil chamber 20a, 20b-=-Insulating material 22a, 22b--Cooling water passage 30-Mold temperature controller Fig. 1 Fig. 4 Fig. 8 )

Claims (2)

[Claims] (1) A mold with a double structure consisting of a movable core that forms a cavity and a mold body that surrounds it and is in a constantly cooled state is used, and from before the start of injection to during the filling process, the mold body and the mold body are moving. The moving core is kept in a non-contact state by keeping it in a non-contact state, and the temperature of the moving core is raised and maintained above the softening temperature of the resin.In the subsequent pressure holding process, the moving core is heated by the pressure inside the cavity (holding pressure). An injection molding method characterized in that rapid cooling is performed in the next cooling step by bringing the moving core into contact with the mold body and stopping heating of the moving core. (2) A moving core that forms a cavity, a mold body surrounding it, a drive mechanism that drives the moving core within the mold body, and a heating device and temperature disposed inside the moving core. What is claimed is: 1. An injection molding apparatus, comprising: a mold having a detector; and a mold temperature regulator that receives a signal from the temperature detector and controls the temperature of the moving core to a set temperature.