CN113878827A

CN113878827A - Injection mold, injection molding machine, and injection molding method

Info

Publication number: CN113878827A
Application number: CN202010617033.6A
Authority: CN
Inventors: 卢湘武; 杨光明; 侯体波; 樊泽平
Original assignee: Guangdong Oppo Mobile Telecommunications Corp Ltd
Current assignee: Guangdong Oppo Mobile Telecommunications Corp Ltd
Priority date: 2020-07-01
Filing date: 2020-07-01
Publication date: 2022-01-04

Abstract

The application provides an injection mold, an injection molding machine and an injection molding method. This injection mold includes: a conductive mold core; and the magnetic field generating assembly is used for providing an alternating magnetic field for the conductive mold core so as to heat the conductive mold core under the action of the alternating magnetic field. This injection mold can realize the moulding plastics of higher temperature to can control the temperature accurately, heating efficiency is high, and the homogeneity of heating is good, can not cause the waste of the energy, and the plastic products that injection moulding obtained is difficult for appearing "floating fine" phenomenon, and the internal stress is low, is difficult for appearing appearance defects such as weld mark, gas line, flow mark, and this injection mold simple structure, cost are lower, easily realize the industrialization.

Description

Injection mold, injection molding machine, and injection molding method

Technical Field

The application relates to the technical field of material processing, in particular to an injection mold, an injection molding machine and an injection molding method.

Background

In the related art, when manufacturing engineering plastics, glass fibers are usually added to the engineering plastics to increase the strength of the materials, and the addition of the glass fibers to the materials can also improve the elastic modulus and the heat resistance temperature of the plastic materials. However, the addition of glass fibers can also cause the phenomenon of fiber floating during the injection molding process of the material. The phenomenon of "fiber floating" is caused by the exposure of glass fibers: the white glass fiber is exposed on the outer surface in the flowing process of the plastic melt, and forms radial white marks on the surface of the plastic part after the plastic melt is condensed and formed, so that the difference of the colors is more obvious when the plastic part is black. The method for improving the phenomenon of fiber floating in the industry at present is mainly realized by a steam-assisted injection molding technology and an electric heating-assisted molding technology, however, the two technologies are expensive in equipment, high in cost, high in safety risk, capable of causing energy waste, incapable of realizing high heating temperature, and not ideal in heating uniformity and heating efficiency.

Thus, the related art of the existing injection molding still needs to be improved.

Disclosure of Invention

In one aspect of the present application, an injection mold is provided. This injection mold includes: a conductive mold core; and the magnetic field generating assembly is used for providing an alternating magnetic field for the conductive mold core so as to heat the conductive mold core under the action of the alternating magnetic field. This injection mold can realize the moulding plastics of higher temperature to can control the temperature accurately, heating efficiency is high, and the homogeneity of heating is good, can not cause the waste of the energy, and the plastic products that injection moulding obtained is difficult for appearing "floating fine" phenomenon, and the internal stress is low, is difficult for appearing appearance defects such as weld mark, gas line, flow mark, and this injection mold simple structure, cost are lower, easily realize the industrialization.

In another aspect of the present application, an injection molding machine is provided. The injection molding machine comprises the injection mold described above. This injection moulding machine can realize the moulding plastics of higher temperature to can control the temperature accurately, and heating efficiency is high, and the homogeneity of heating is good, can not cause the waste of the energy, and the plastic products that injection moulding obtained is difficult for appearing "floating fine" phenomenon, and the internal stress is low, is difficult for appearing appearance defects such as weld mark, gas line, flow mark, and has preceding all characteristics and the advantage of injection mold, no longer too much repeated here.

In yet another aspect of the present application, there is provided an injection molding method implemented using the aforementioned injection mold or the aforementioned injection molding machine. The injection molding method comprises the following steps: providing an alternating magnetic field for the conductive mold core by using a magnetic field generating assembly so as to heat the conductive mold core under the action of the alternating magnetic field; injecting a material to be injection molded into a mold cavity defined by the conductive mold core; and pressurizing the material to be subjected to injection molding. The injection molding method is simple and convenient to operate, easy to realize and easy for industrial production, and the plastic product obtained by injection molding is not easy to have the phenomenon of fiber floating, has low internal stress and is not easy to have appearance defects such as welding marks, air marks, flow marks and the like.

Drawings

FIG. 1 shows a schematic cross-sectional view of an injection mold according to the present application.

Fig. 2 shows a schematic cross-sectional structure of another injection mold of the present application.

Fig. 3 shows a schematic cross-sectional structure of yet another injection mold of the present application.

Fig. 4 shows a schematic sectional view of a further injection mold according to the present application.

FIG. 5 shows a schematic flow diagram of an injection molding method of the present application.

FIG. 6 shows a schematic flow diagram of another injection molding process of the present application.

FIG. 7 shows a graph of mold temperature versus time for the injection molding process of FIG. 6.

Reference numerals:

10: injection mold 100: the conductive mold core 110: 120 of the core insert: the cavity insert 200: magnetic field generating assembly 300: insulating layer 400: the cooling assembly 500: temperature sensor

Detailed Description

In one aspect of the present application, an injection mold is provided. With reference to fig. 1, it can be understood that the injection mold 10 includes: a conductive mold core 100; and the magnetic field generating assembly 200 is used for providing an alternating magnetic field for the conductive mold insert 100, so that the conductive mold insert 100 is heated under the action of the alternating magnetic field. The applicant surprisingly finds that as the injection mold 10 is heated through the magnetic field, the injection mold 10 can realize injection molding at a higher temperature, the temperature can be accurately controlled, the heating efficiency is high, the heating uniformity is good, energy waste is avoided, the plastic product obtained by injection molding is not easy to generate a fiber floating phenomenon, the internal stress is low, appearance defects such as welding marks, air marks, flow marks and the like are not easy to generate, and the injection mold 10 is simple in structure, lower in cost and easy to realize industrialization.

Specifically, the applicant has conducted a great deal of intensive investigation and experimental verification on the cause of the "fiber floating" phenomenon in the injection molding process of the related art before the injection mold 10 is heated by using the magnetic field: first, it can be understood that, during the injection molding process, when the plastic melt flows, the glass fiber and the plastic have a certain difference in flowability, and the mass and density of the glass fiber and the plastic are different, so that the glass fiber and the plastic have a tendency to separate from each other during the injection molding process, wherein the glass fiber with the lower density tends to float to the surface of the plastic melt, and the plastic with the higher density tends to move away from the surface of the plastic melt, thereby forming a so-called "fiber floating" phenomenon.

Secondly, it can be understood that, in the process of injection molding, the plastic melt is subjected to the action of frictional shear force of the injection molding screw, the nozzle, the runner and the gate in the flowing process, so that the local viscosity of the plastic melt is different, and the interface layer on the surface of the glass fiber is also damaged, the interface layer is damaged more seriously and the adhesive force between the glass fiber and the plastic is smaller as the viscosity of the plastic melt is smaller, and when the adhesive force is small to a certain degree, the glass fiber gradually breaks away from the constraint of the plastic melt and gradually accumulates on the surface of the plastic melt until the glass fiber is exposed.

Again, it will be appreciated that when the plastic melt is injected into the cavity, a "fountain" effect is created, i.e. the glass fibers flow from the inside to the outside and contact the surface of the cavity, and because the temperature of the surface of the cavity in contact with the glass fibers in the injection mold is low, the glass fibers, which are lighter in weight and faster in condensation rate, are frozen instantaneously, and if they do not contact the plastic melt at a higher temperature in time, they are exposed and form "floating fibers".

Based on the above research of the applicant, it can be understood that the most important means for solving the phenomenon of the "floating fiber" is to reduce the contact resistance between the glass fiber and the injection mold, so that the speed difference between the glass fiber and the plastic is as small as possible, and the injection mold 10 is heated by the magnetic field. Firstly, the flow length ratio of the plastic melt can be obviously increased, so that the fluidity of the plastic melt is very good, the thickness of a product obtained by injection molding is thin, appearance defects such as welding marks, air marks, flow marks and the like are not easy to appear, the internal stress of the injection molding product can be greatly reduced, and the injection molding product with high light is formed.

Secondly, it can be understood that the injection mold 10 is heated by the magnetic field, so that the simulation thermal analysis of the injection mold core is facilitated, the temperature deviation of each position of the surface of the mold core is accurately controlled within +/-1 ℃, further, the appearance defects such as welding marks, air marks or flow marks do not exist in the injection molded product, and the internal stress of the injection molded product is reduced.

Thirdly, it can be understood that, because the precision of heating the mold core through magnetic induction is high, the electric energy is converted into heat energy, the heating efficiency is obviously improved, in the application, compared with the heating mode of an injection mold in the related art, the energy can be saved by 50%, the period of the whole forming process is shortened, and the production efficiency is obviously improved.

In summary, after a great deal of research, the applicant finds that the injection mold 10 of the present application can mold plastic with glass fiber added in an amount of up to 50% by mass, and can better avoid the phenomenon of fiber floating after the injection molding process is completed.

Further, it can be understood that, when the conductive mold core 100 is located at the position where the magnetic field intensity in the alternating magnetic field is the maximum, since the magnetic field intensity at the position is the maximum, the temperature rising speed of the conductive mold core 100 under the action of the alternating magnetic field can be higher, and meanwhile, the temperature can be raised to a higher temperature, so that the heating efficiency is further improved, and the plastic product obtained by injection molding is further not prone to have a phenomenon of "floating fibers".

It can be understood that, specifically, the magnetic field generating assembly may be an electromagnetic induction coil, and further, the magnetic field generating assembly has a wide and easily available material source and a low cost, and can provide a better magnetic field, so that the heating efficiency is further improved.

In addition, it can be understood that when the magnetic field generating assembly described above is an electromagnetic induction coil, the setting position of the magnetic field generating assembly is also flexible and convenient, for example, in some examples of the present application, the electromagnetic induction coil may be set around the conductive mold insert 100, so that in the injection molding process, the magnetic flux of the magnetic force lines cut by the conductive mold insert 100 in the moving process reaches the highest, thereby providing higher magnetic induction intensity, and further improving the heating efficiency.

Specifically, it is understood that, when the electromagnetic induction coil is disposed around the conductive mold core 100, in conjunction with fig. 2, the injection mold 10 may further include: the insulating layer 300 is disposed around the conductive mold core 100, a plurality of annular pipes are disposed around the insulating layer 300, and the electromagnetic induction coil is disposed in the annular pipes. Therefore, the insulating layer 300 can prevent the electromagnetic induction coil from contacting the conductive mold core to influence the magnetic field, and can also play a role in fixing the electromagnetic induction coil, so that the structure is simple and convenient, and the industrial production is easy to realize.

It can be understood that the specific shape of the multi-turn annular heating pipeline can be set by those skilled in the art according to actual needs, and will not be described in detail herein.

Further, it is understood that the specific type of the electromagnetic induction coil is not particularly limited, and in a specific example of the present application, the electromagnetic induction coil may be a copper wire wrapped with glass fiber, which has a wide and easily available material source, a low cost, and a high strength, and can stably provide an alternating magnetic field for a long time, so as to make the heating effect of the injection mold 10 better and the service life longer.

In addition, it is understood that the material of the conductive mold core may specifically include metal, and specifically, the metal may specifically be iron. Therefore, the material source is wide and easy to obtain, the cost is low, and the temperature can be stably increased under the action of the alternating magnetic field provided by the magnetic field generating assembly.

In addition, it is understood that, in order to further control the temperature of the conductive mold core 100, with reference to fig. 3, the injection mold 10 may further include: and a cooling assembly 400, wherein the cooling assembly 400 is disposed at one side of the magnetic field generating assembly 200 and is used for cooling the conductive mold core. Thus, the temperature of the conductive mold core 100 can be more precisely controlled.

Specifically, referring to fig. 3, it can be understood that the conductive mold core may include a core insert 110 and a cavity insert 120 that are disposed opposite to each other, the cooling assembly 400 may be specifically a liquid cooling pipeline embedded in the conductive mold core, and the liquid cooling pipeline is located in at least one of a side of the core insert 110 close to the cavity insert 120 or a side of the cavity insert 120 close to the core insert 110. It should be noted that although fig. 3 shows the liquid cooling pipeline located on both the side of the core insert 110 close to the cavity insert 120 and the side of the cavity insert 120 close to the core insert 110, it is understood by those skilled in the art that the liquid cooling pipeline may be located on only one side. Therefore, the cooling effect is better.

It is understood that, with reference to fig. 4, the injection mold 10 may further include: a temperature sensor 500, wherein the temperature sensor 500 is disposed on at least one of a surface of the core insert 110 facing the cavity insert 120 or a surface of the cavity insert 120 facing the core insert 110. It should be noted that although fig. 4 shows that the temperature sensor 500 is only disposed on the surface of the core insert 110 facing the core insert 120, it is understood by those skilled in the art that the temperature sensor 500 may also be disposed on the surface of the core insert 120 facing the core insert 110, or disposed on both surfaces. Therefore, the temperature of the surface of the conductive mold core 100 can be controlled more precisely, and the heating effect is further improved.

Specifically, it can be understood that the aforementioned temperature sensor 500 may be a thermocouple, which has low cost and is convenient to use, and can also control the temperature of the surface of the conductive mold insert 100 more accurately, so as to further improve the heating effect.

In summary, it can be understood that, by using the injection mold 10 heated by the magnetic field in the present application, the temperature rising rate of the conductive mold core 100 can reach 20 ℃/s to 24 ℃/s, and specifically, in some examples of the present application, the temperature rising rate can be 20 ℃/s, 21 ℃/s, 22 ℃/s, 23 ℃/s, or 24 ℃/s, etc. From this, this injection mold 10 can realize the moulding plastics of higher temperature to can control the temperature accurately, and heating efficiency is high, and the homogeneity of heating is good, can not cause the waste of the energy, and the plastic products that injection moulding obtained is difficult for appearing "floating fine" phenomenon, and the internal stress is low, is difficult for appearing appearance defects such as weld mark, gas line, flow mark, and this injection mold 10 simple structure, cost are lower, easily realize the industrialization.

Specifically, in a specific example of the present application, when the injection mold 100 described herein is used to injection mold a PC (polycarbonate) electronic device cover plate, the mold temperature may be set to 160 ℃, the cooling temperature is 90 ℃, the whole molding cycle is shortened by 33% compared to the heating mode of the oil temperature machine in the related art for injection molding a PC cover plate, and the heating temperature may be as high as 1000%; in addition, the direct heating by magnetic induction and the non-heat conduction heating can obviously save energy, and the energy saved by the direct heating device is up to more than 40% of the energy required by the oil temperature machine in the related technology.

It is understood that, besides the injection mold described above, a person skilled in the art can understand that the injection molding machine may further include other structures and components of a conventional injection molding machine in the related art, and the connection relationship and the position relationship between the other structures and the components may be the same as those of the injection molding machine in the related art, and will not be described in detail herein.

In yet another aspect of the present application, there is provided an injection molding method implemented using the aforementioned injection mold or the aforementioned injection molding machine. With reference to fig. 5, the injection molding method may specifically include the following steps:

s10: and providing an alternating magnetic field for the conductive mold core by using the magnetic field generating assembly so as to heat the conductive mold core under the action of the alternating magnetic field.

S20: and injecting a material to be injection molded into a mold cavity defined by the conductive mold core.

S30: and pressurizing the material to be subjected to injection molding.

Further, with reference to fig. 6 and 7, it can be understood that the method may further include:

s100: and (3) closing the male die core and the female die core in the conductive die core (refer to the 1 st section of the curve in the attached figure 7).

It is understood that, in this step, the mold temperature is an initial temperature, which may be 60 ℃ to 100 ℃, specifically, 60 ℃, 70 ℃, 80 ℃, 90 ℃ or 100 ℃, and the like.

S200: the magnetic field generating assembly is activated to raise the conductive mold core to a predetermined temperature under the action of the alternating magnetic field (see section 2 of the curve in fig. 7).

It will be appreciated that in this step, the mould temperature is gradually raised from an initial temperature to a predetermined temperature, which may be 160 ℃ to 200 ℃. In some specific examples of the present application, the predetermined temperature may be specifically 160 ℃, 170 ℃, 180 ℃, 190 ℃, or 200 ℃, and the like. Thus, the predetermined temperature is appropriate, and the heating efficiency can be further improved.

S300: the conductive mold core is kept at the predetermined temperature for a first predetermined time, and the material to be injection molded is injected into the mold cavity (refer to the 3 rd and 4 th sections of the curve in fig. 7; in addition, in the description of the present application, it is to be noted that the terms "first" and "second" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features.

Further, it is understood that the first predetermined time may be 2s to 10 s. In some specific examples of the present application, the first predetermined time may be specifically 2s, 4s, 6s, 8s, 10s, or the like. Therefore, the first preset time is proper, the heating efficiency can be further improved, and the production efficiency is high.

S400: and carrying out the pressurization treatment on the material to be subjected to injection molding to a preset pressure.

Further, it is understood that the predetermined pressure may be 20 to 50 MPa. In some specific examples of the present application, the predetermined pressure may be specifically 20MPa, 30MPa, 40MPa, or 50MPa, or the like. Therefore, the preset pressure is proper, so that the difference between the plastic and the glass fiber is small in the injection molding process, and the phenomenon of fiber floating is further avoided.

S500: the material to be injection molded is held at the predetermined pressure for a second predetermined time (note that this step refers to the 4 th segment of the graph in fig. 7 together with the previously described step S400).

Further, it is understood that the second predetermined time may be 3s to 8 s. In some specific examples of the present application, the second predetermined time may be specifically 3s, 4s, 5s, 6s, 7s, 8s, or the like. Therefore, the second preset time is proper, so that the difference between the plastic and the glass fiber is small in the injection molding process, the phenomenon of fiber floating is further avoided, and the production efficiency is high.

S600: the magnetic field generating assembly is turned off and the material to be injection molded is subjected to a cooling process (see section 5 of the graph in fig. 7).

It can be understood that, since the magnetic field generating assembly is turned off and no heating source is provided, the cooling rate of the material to be injection molded is high, and the production efficiency is remarkably improved.

It is understood that, besides the aforementioned steps and parameters, the injection molding method may further include other conventional operation steps of the injection molding method, such as a demolding step (see section 6 of the curve in fig. 7), other specific step operations, and the aforementioned specific operation steps and parameters that are not mentioned above, which may be the same as those of the conventional injection molding method in the related art, and are not described in detail herein. Therefore, the method is simple and convenient to operate, easy to realize and easy for industrial production.

In the present specification, although the embodiments of the present application have been shown and described above, it is to be understood that the above embodiments are exemplary and not to be construed as limiting the present application, and that variations, modifications, substitutions and alterations may be made to the above embodiments by those of ordinary skill in the art within the scope of the present application.

Claims

1. An injection mold, comprising:

a conductive mold core; and

and the magnetic field generating assembly is used for providing an alternating magnetic field for the conductive mold core so as to heat the conductive mold core under the action of the alternating magnetic field.

2. The injection mold of claim 1, wherein the conductive mold core is located at a position where a magnetic field intensity in the alternating magnetic field is the largest.

3. An injection mold as claimed in claim 1, wherein the magnetic field generating assembly comprises an electromagnetic induction coil.

4. An injection mold according to claim 3, further comprising:

the insulating layer is arranged around the conductive mold core, a plurality of circles of annular pipelines are wound in the insulating layer, and the electromagnetic induction coil is arranged in the annular pipelines.

5. An injection mould according to claim 4, characterized in that the electromagnetic induction coil is a glass fibre wrapped copper wire.

6. The injection mold of claim 1, wherein the conductive core comprises a metal.

7. An injection mold according to any of claims 1-6, further comprising:

and the cooling component is arranged on one side of the magnetic field generating component and is used for cooling the conductive mold core.

8. The injection mold according to claim 7, wherein the conductive mold core comprises a male mold core and a female mold core which are disposed opposite to each other, the cooling assembly comprises a liquid cooling pipeline embedded in the conductive mold core, and the liquid cooling pipeline is located in at least one of a side of the male mold core close to the female mold core or a side of the female mold core close to the male mold core.

9. An injection mold as claimed in claim 8, further comprising:

the temperature sensor is arranged on at least one of the surface of the core insert facing the cavity insert or the surface of the cavity insert facing the core insert.

10. The injection mold of claim 1, wherein the temperature increase rate of the conductive core is 20 ℃/s to 24 ℃/s.

11. An injection molding machine comprising the injection mold according to any one of claims 1 to 10.

12. An injection molding method using the injection mold according to any one of claims 1 to 10 or the injection molding machine according to claim 11, comprising:

providing an alternating magnetic field for the conductive mold core by using a magnetic field generating assembly so as to heat the conductive mold core under the action of the alternating magnetic field;

injecting a material to be injection molded into a mold cavity defined by the conductive mold core;

and pressurizing the material to be subjected to injection molding.

13. The injection molding method of claim 12, further comprising:

closing the male mold core and the female mold core in the conductive mold core;

starting the magnetic field generating assembly to enable the conductive mold core to be heated to a preset temperature under the action of the alternating magnetic field;

at the preset temperature, the conductive mold core is kept at the first preset time, and the material to be injection molded is injected into the mold cavity;

performing the pressurization treatment on the material to be subjected to injection molding to a preset pressure;

keeping the pressure of the material to be subjected to injection molding for a second preset time under the preset pressure;

and closing the magnetic field generating assembly, and cooling the material to be subjected to injection molding.

14. An injection molding method according to claim 13, wherein at least one of the following conditions is satisfied:

the preset temperature is 160-200 ℃;

the first preset time is 2 s-10 s;

the preset pressure is 20MPa to 50 MPa;

the second predetermined time is 3s to 8 s.