JP3896461B2 - Precision mold - Google Patents

Description

  The present invention relates to a mold used for molding using a mold such as plastic injection molding, casting, forging, and press molding, and more particularly to a precision molding mold for obtaining a precise product.

In a molding method using a mold such as casting of metal or injection molding of plastic, the mold is filled with a molten material, cooled and solidified, and released into a product.
In the process of pouring molten metal or plastic into the mold, the temperature of the molten material decreases due to heat transfer to the mold, eventually solidification occurs and the fluidity deteriorates so that the voids in the mold cannot be filled. There is. Even in plastic injection molding, in the process where high-temperature molten resin is injected from the nozzle and flows into the runner, gate, and cavity, heat is removed from the relatively low-temperature metal components, and the temperature is reduced. There is a case where a so-called short shot is generated in which a predetermined shape cannot be obtained without decreasing and increasing the viscosity and increasing the flow resistance and further solidifying to reach every corner of the mold. Further, when the cooling state is locally biased, warping or sinking may occur.

Temperature drop and flow stoppage during hot water flow are handled empirically with reference to various experimental results. The distance that flows until the flow stops, that is, the flow length, is affected by the composition of use, the degree of superheat that is the difference between the temperature of the molten material and the liquidus temperature, the shape of the gate head, the physical properties of the mold, the temperature, the atmosphere, and the like.
Further, the molded product shrinks unevenly in the mold. This is because the cooling rate and temperature of each part of the molded product are different and the mold prevents free shrinkage. Cracks occur when tensile force acts on the part where the mold is constrained and solidification is delayed, and even if cracks do not occur, if non-uniform shrinkage occurs, residual stress is generated, and deformation may occur after unpacking. is there.

Thus, in the molding process using a mold, the fluidity of the molten material becomes a problem, and the temperature of the material and the mold greatly affects the quality of the molded product.
There is a cartridge heater embedded in a mold for the purpose of preventing the above problems. In this method, the die temperature is increased by the Joule heat of the heater, the temperature difference between the resin and the resin is reduced, the heat escaping from the resin is reduced, the temperature of the resin is prevented from decreasing, and fluidity is ensured.
There is also a method of heating the mold by providing a heater outside the mold, connecting it with a heat transfer pipe provided inside the mold, and circulating a heat transport fluid such as water or oil. .

  In the heating method using a heater embedded in a mold or the heating method using a heat transport fluid, the temperature of the entire mold is raised from around the heater due to heat conduction, and the molded product in the mold is predetermined in the subsequent cooling process. It took a lot of time to lower the temperature. In addition, in the method using a heat medium, a heat transfer tube having a complicated structure is arranged near the resin flow part, so that the smaller the molded product, the more difficult the mounting becomes, and the higher the fluid transport and heat exchange. The device becomes large for control. In addition, since the heat transport fluid is supplied to the mold at a high temperature and heat exchange with the mold, the temperature decreases, so there is a temperature difference between the upstream and downstream of the heat transfer tube, and the molded product part can be heated strictly uniformly Have difficulty.

  Patent Document 1 discloses a plastic molding die in which a heat pipe is embedded in a block sandwiching a die. Since heat pipes use a phase change between the gas phase and the liquid phase for the heat transfer mechanism, the heat transfer rate is much faster than solid heat conduction or convective heat transfer. The effective heat conductivity of the heat pipe is extremely large, which is several tens of times that of copper or aluminum. Since the disclosed mold uses a heat pipe to release heat to an external cooling source, the cooling rate can be easily controlled while cooling the mold uniformly and quickly. The cooling rate can be controlled by adjusting the refrigerant flow rate of the cooling source.

  However, the disclosed mold is one in which a heat pipe is inserted in parallel to the cavity, and the temperature of the entire mold can be changed uniformly, but it cannot be adjusted to a locally different temperature. In addition, although patent document 1 also describes what inserted the heat pipe into metal mold | die itself, this is also what adjusts the temperature of the whole metal mold | die with a heat pipe, and does not perform local temperature control. . Therefore, it is impossible to prevent local defects from occurring in the product by defining the local temperature in an optimum state corresponding to the shape of the mold.

  Furthermore, in recent years, it has become possible to accurately perform simulations to achieve high-quality machining by numerically analyzing the heat state in the mold and calculating the ideal temperature distribution or heat flow state. ing. For example, by changing the temperature according to the plan for each part of the mold during the molding process, uneven distribution of materials due to solidification and crystallization, abnormalities due to inhomogeneous shrinkage, and residual stress can be prevented, resulting in precise molded products. Obtainable. In order to enable precision molding using the simulation result, a specific method for bringing an actual mold to an ideal temperature state is desired.

For example, if local temperature control is to be performed by a conventional heating / cooling method using heat transfer tubes, it is necessary to arrange a number of independent heat transfer tubes near the cavity surface and control the heat transfer amount for each one. is there. In order to achieve such control, a complicated structure and a large-scale control device must be provided.
As described above, in the conventional mold, as described above, there has been provided a method of embedding the heating / cooling pipe in a direction parallel to the cavity surface to rapidly bring the entire mold to a uniform temperature. There was no method for controlling the temperature distribution of the mold or the molded product in the mold by adjusting the local temperature state.
JP-A-5-337997

  Therefore, the problem to be solved by the present invention is to provide a mold capable of quickly heating and cooling the molded product without arranging a complicated structure near the molded product in the mold. In addition, another object is to provide a mold capable of appropriately performing necessary heating and cooling for each part in each part of the mold.

In order to solve the above problems, the precision molding die of the present invention has a large number of heat transfer columns with the front end face close to the surface in contact with the molten material of the mold, and the temperature at the rear end of these heat transfer columns. An adjustable heat source is arranged.
There are many heat transfer points on the mold surface in contact with the molten material, and these heat transfer points are connected to a temperature-controllable heat source, and the temperature can be controlled, so the temperature of the molten material filled in the mold The distribution can be adjusted.
Therefore, when the mold of the present invention is used, a highly accurate molded product having no defects can be obtained.

The front end surface of the heat transfer column can be arranged in the mold cavity, gate, and runner portion, and the temperature can be adjusted for each minute range of these portions.
It should be noted that the end face of the heat transfer column may be disposed over substantially the entire surface of one cavity of the split mold. Since such a mold is provided with a temperature adjustment point on the entire cavity surface, the desired molded product can be obtained with almost the desired result regardless of the desired temperature distribution obtained by the simulation. Even if there is no temperature adjustment point on the other part of the split mold, if the molded product is thin enough, the temperature can be controlled almost as desired. What is necessary is just to provide a pillar.

The heat transfer column is formed of a material having a higher thermal conductivity than the material constituting the mold. For example, it may be a high thermal conductivity metal such as copper, aluminum, copper alloy, or SiC ceramic.
The heat transfer column is preferably a heat pipe. The heat pipe can perform heat transport with efficiency several tens of times that of metals by using evaporation and condensation of a working liquid confined together with a wig in a closed container such as a circular pipe, that is, phase change.
The heat source provided at the rear end opposite to the front end surface close to the mold surface of the heat transfer column adjusts the temperature at the end of each heat transfer column and has a small heat transfer mechanism. It is preferable.

  In particular, it is preferable to adjust the temperature by induction heating by applying a material having high dielectric loss to the rear end face of the heat conducting column and applying a high frequency current from a high frequency oscillation source thereto. The high dielectric loss material can be formed small enough to be attached to each heat conduction column, and if power supply wiring is provided from a high frequency oscillation source, heat generation can be easily controlled by voltage adjustment. It is suitable for the purpose. In addition, since the tip surface of the heat conduction column installed on the mold surface is small and the heat source and the control device can be placed at a position sufficiently away from the molten material, the device can be configured relatively freely. This is particularly effective when a mold for producing a fine and precise molded product is required.

Furthermore, it is preferable to provide a heat source with a cooling source so that heating and cooling can be performed quickly. A cooling pipe can be used as a cooling source, and a heating source such as a high dielectric loss material can be cooled through cooling water.
In addition, the front end surface of the heat transfer column such as a heat pipe that is close to the surface in contact with the molten material may be directly exposed to the surface in contact with the molten material and become a part of the surface. Since heat is directly added to or melted from the molten material, more direct temperature adjustment can be performed. In addition, since the end surface of the heat transfer column has sufficient smoothness and flatness, there is no problem as a mold surface.

Hereinafter, a precision mold according to the present invention will be described in detail with reference to the drawings.
FIG. 1 is a sectional view of a precision molding die in one embodiment of the present invention, and FIG. 2 is a plan view thereof.

As conceptually shown in the cross-sectional view of FIG. 1 and the plan view of FIG. 2, the precision molding die 1 of this embodiment has a cavity 4 that forms the final shape of the molded product with two split dies 2 and 3. Is formed. In one split mold 2, an appropriate number of holes penetrating from the cavity surface 21 to the back surface 22 are formed, and a heat pipe 6 whose outer periphery is covered with a heat insulating material 5 is embedded in the hole.
The front end surface 61 of the heat pipe 6 forms the same surface as the cavity surface 21 and constitutes a part of the cavity surface.
A thin high dielectric loss body 7 is tightly bonded to the rear end face of the heat pipe 6, and a high frequency heater 8 is provided on the outside thereof. A high frequency current is supplied to the high frequency heater 8 from an external high frequency power supply device 9.

When a high frequency current is supplied to the high frequency heater 8 and an AC electric field is applied, the high dielectric loss body 7 generates heat. Since the periphery of the high dielectric loss body 7 is covered with the heat insulating material 5, the heat generated in the high dielectric loss body 7 flows to the heat pipe 6 and the high frequency heater 8. Since it has conductivity, most of the heat escapes to the heat pipe 6, the temperature of the front end face 61 constituting a part of the cavity surface 21 rises, and the temperature of the part of the molded product that the front end face 61 contacts decreases. Can be prevented.
After the molded product is faithfully formed in a predetermined shape by this heat retention effect, the mold is cooled and the molded product is taken out. If the cooling time is long, the next charge cannot be made, so the length of the cooling time is an important factor affecting the productivity.

Since the high dielectric loss body 7 of this embodiment has a very small heat capacity as compared with the mold 1 as a whole, it is cooled instantly by simply applying forced convection air to the outer surface, and the temperature is lowered. Due to the transport efficiency, the molded product is quickly cooled.
Although not shown in the drawing, if a cooling pipe is attached to the high-frequency heater 8 so that a cooling fluid such as water or oil is allowed to pass through, cooling after molding can be performed very quickly.
In addition, although the said description was performed about the case where molten material is heated and cooled about the cavity part of a metal mold | die, as long as it is a surface where molten materials, such as a runner and a gate, contact, it can say that the same effect can be acquired by the same structure. Nor. Further, although a heat pipe is used as the heat transfer body, an effect similar to this can be obtained even when a metal material having a higher thermal conductivity than the mold material is used.

  According to the precision molding die of the present embodiment, a large number of spots with high thermal conductivity can be formed on the surface of the mold where the molten material contacts, and the temperature can be controlled for each spot. A precise molded product can be manufactured efficiently by matching the shape well. In addition, when the front end surface of a heat pipe having an extremely high heat transport capability is applied to the spot, the temperature of the spot is managed very quickly, and the cooling after molding is quick. Furthermore, it is only necessary to place small and simple components near the cavity surface, and to place heaters and control equipment at positions away from the cavity surface. Therefore, the mold can be configured easily.

In addition, since the direction of the heat transfer in the heat pipe is automatically switched according to the sign of the temperature difference between both ends of the heat pipe, it is not necessary to use a special switching device and the control is simple.
Further, since high frequency induction heat generation is used as a heat source, the heat generation density is high and the heat efficiency is high. Moreover, since the structure in the mold is simple and the elements can be miniaturized, it is suitable for precision molding.
Furthermore, because heat transfer can be performed quickly on each part of the mold surface, it is a technology that is very suitable for numerical control with the advantage of high speed and precision, and as a processing technology that makes full use of information technology It can be used for heat transfer control of molds.

  As described above in detail, according to the precision molding die of the present invention, heating and cooling required in each part of the die can be appropriately performed with a simple structure, and thus a precision molded product having no defects can be obtained. Can do. Further, since the temperature distribution on the surface in contact with the molten material can be controlled, it can be used as an element for realizing high-speed and precise numerical control and processing using advanced information technology.

It is sectional drawing explaining the concept of the precision molding die in one Example of this invention. It is a top view of the split mold of the metal mold | die of FIG.

Explanation of symbols

1 Precision molding mold 20 Split mold 21 Cavity surface 22 Back surface 30 Split mold 4 Cavity (molten material or molded product)
5 Insulation 6 Heat pipe (heat transfer column)
61 Front end face 7 High dielectric loss body 8 High frequency heater 9 High frequency power supply

Claims (5)

In the precision molding mold in which the front end face is brought close to the surface in contact with the molten material of the mold, a large number of heat transfer columns with the outer periphery insulated are arranged, and a heat source capable of adjusting the temperature is arranged at the other end of the heat transfer column , A precision molding die, wherein a front end surface of a heat transfer column that is close to a surface in contact with a molten material is directly exposed to a surface in contact with the molten material and becomes a part of the surface .   2. The precision according to claim 1, wherein the mold is a split mold, and the front end surface of the heat transfer column is arranged over the entire surface of the cavity in one of the split molds. Molding mold.   3. The precision molding die according to claim 1, wherein the heat transfer column is a heat pipe.   The heat source is a high dielectric loss material disposed at a rear end portion of the heat transfer column, and the high dielectric loss material generates heat from a high frequency oscillation source. Described precision mold.   The precision molding die according to claim 4, wherein the heat source further includes a cooling pipe and cools the cooling water by passing water.

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