WO2018067164A1

WO2018067164A1 - Injection molding with multiple gates

Info

Publication number: WO2018067164A1
Application number: PCT/US2016/055875
Authority: WO
Inventors: Chien-Chih Chiu; Ya-Ting Yeh; Ken Tsai; Guess WEI
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2016-10-07
Filing date: 2016-10-07
Publication date: 2018-04-12

Abstract

Example relating to an injection mold are described, in one example, the injection mold may include a mold cavity having a portion for accommodating a metal substrate. The injection mold may further include at least three injection gates formed in an upper surface of the mold cavity, to inject a moldable plastic material into the mold cavity to form a structure onto the metal substrate.

Description

INJECTION MOLDING WITH MULTIPLE GATES

BACKGROUND

[0001] Injection molding as a manufacturing process may be used for molding plastic structures on a metal substrate which then may be used in a wide variety of components such as electronic device enclosures, automobile instrument panels, household machines, industrial machines and the like. Injection molding, generally, involves injecting a mokJable plastic material over a metal substrate which may be placed in a mold cavity. As the plastic material cools, it hardens and assumes the configuration and shape of the mold cavity.

BRIEF DESCRIPTION OF DRAWINGS

[0002] The detailed description is provided with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference like features and components.

[0003] FIG. 1 illustrates an example injection mold having at least three injection gates;

[0004] FIG. 2 illustrates another example injection mold having multiple injection gates;

[0005] FIG. 3 illustrates yet another example injection mold having air vents on at least two opposite walls; and

[0006] FIG. 4 illustrates a method for injection molding process implemented on an example injection mold.

DETAILED DESCRIPTION

[0007] Nowadays, a wide variety of articles are made from the combination of different materials, say, plastic and metal. Such articles can be formed using polymer metal hybrid (PMH) based injection molding technologies.

[0008] PMH based injection molding techniques may include forming an article, or a part thereof, by bonding plastic to metal. For example, through PMH based injection molding technology plastic structures, such as mounting bosses, snap fits, reinforcement ribs, and the like, may be directly formed on a surface of the metal. In this way, an end product is a single article formed integrally constituting both plastic and metal.

[0009] An example of such PMH based injection molding technology is nanc-molding technology (NMT). NMT provides for bonding and molding a plastic structure onto a metal substrate. Generally, an NMT process involves multiple stages of pre -treatment of a bare metal substrate. The p re- treatment is carried out for removal of unwanted grease, oil, oxides, or other impurities, from the metal substrate. After the multi-stage pre-treatment, the metal substrate may be submerged into an anodizing agent to form irregularities, such as nano-pores, on exterior surface. Thereafter, the anodized metal substrate is rinsed in water. Finally, the metal substrate may be inserted into a mold cavity of a mold, wherein a moldable plastic material, such as material formed from molten plastic resin pellets, is injected to form a structure or shape directly on the exterior surface of the metal substrate. As would be understood the shape thus formed on the surface of the metal substrate would be corresponding to the shape as defined by the inner surface of the mold cavity.

[0010] Although NMT is suitable for many applications, NMT involves the usage of hazardous chemicals, such as acids, for pre-treatment and anodizing of the metal substrate. Such acids, if not removed properly, may create issues, such as formation of void gaps or air bubbles, between the moldable plastic material and the metal substrate. Such issues may affect the strength of plastic-to-metal bond, thereby limiting use of NMT to selected few applications.

[0011] Also, the mold may have only one point through which a moldable plastic material may be injected over the surface of the metal substrate. With such single point injection, the moldable plastic material when inserted may not uniformly advance within the mold cavity of the mold. With the resulting non-uniform distribution of the moldable plastic material there may be some areas on the surface of the metal substrate which may have adequate proportions of the plastic material whereas in other areas which are present farther away from the entry point, the proportion of the plastic material may be less. It may happen because pressure applied for injecting the moldable plastic material from a single entry may not be sufficient for the moldable plastic material to completely reach the furthermost spaces situated away from the single injection point. Such a non-uniform distribution results in improper gaps between the moldable plastic material and the metal substrate. With such improper gaps, the plastic-to-metal bond achieved by the NMT has a relatively short shelf-life with the adhesion strength diminishing after some time period.

[0012] Various examples of an injection mold and approaches for forming a structure on a metal substrate by an injection moulding process, are described herein. In one example, the injection mold may include a mold cavity. The mold cavity may enclose a volume which is larger than a volume required for accommodating a metal substrate during injection molding of a structure. In an example, the metal substrate may be a stamped sheet metal substrate having a nano-porous layer on its exterior surface.

[0013] The injection mold may further include at least three injection gates formed in an upper surface of the mold cavity. The three injection gates may be formed on the mold cavity at specific distances from each other. In an example, the number of injection gates is at least three, but may range between 4 and 6 in numbers. The number of injection gates may be selected based on length of the plastic structure that would be formed on the metal substrate.

[0014] Returning to the molding process, a moldable plastic material, which may be formed from molten plastic resin pellets, is injected through the injection gates on the injection mould. As would be understood, the injection gates are uniformly situated across the dimensions of the mold cavity. The moldable plastic material is injected through the three respective injection points into the mold cavity. As it is injected, the moldable plastic material occupies the vacant space between the inner walls of the mold cavity and the metal substrate, to form a structure onto the metal substrate. Owing to the moldable plastic material being injected through multiple gates distributed across the injection mold, the moldable plastic material uniformly advances within the mold cavity resulting into a uniform distribution of the moldable plastic material onto the entire surface of the metal substrate. Furthermore, since the moldable plastic material is injected through a larger number of injection gates, the moldable plastic material is able to reach the farthermost spaces and uniformly occupy the spacing between the inner walls of the mold cavity and the metal substrate. This reduces irregular gaps between the moldable plastic material and the metal substrate, and further enables formation of a strong mechanical bond between the moldable plastic material and the metal substrate.

[0015] The above described subject matter is further described with reference to FIGS. 1-4. It should be noted that that the description and the figures merely illustrate the principles of the present subject matter along with examples described herein, and should not be construed as a limitation to the present subject matter. K is, thus, understood that various arrangements may be devised that although not explicitly described or shown herein, embody the principles of the present subject matter. Moreover, all the statements herein reciting principles, aspects, and implementations of the present subject matter, as well as specific examples thereof, are intended to encompass equivalents thereof.

[0016] FIG. 1 illustrates an example of an injection mold 102. The injection mold 102 may include a body 104 having a mold cavity 106 formed therein. The mold cavity 106 defines a volume. The volume enclosed within the mold cavity 106 such that a portion of the volume is sufficient to accommodate a metal substrate (not shown in FIG. 1) during injection molding process. In one example, the metal substrate can be formed from materials including, but not limited to, aluminium, 5052 aluminium, aluminium alloy, titanium, titanium alloy, magnesium, and/or magnesium alloy.

[0017] The injection mold 102 further includes at least three injection gates 108-1, 2, 3 N, collectively referred to as gates 108. It should be noted that in the present description, a reference to injection gates 108 implies at least three injection gates 108. The injection gates 108 may be formed on an upper surface of the mold cavity 106, with one side opening into, and fluidly connected with an inner surface of the mold cavity 106. The other end of the injection gates 108 is in communication with channels (not shown in FIG. 1) for receiving and feeding a moldable plastic material. In an example, the moldable plastic material can be molten plastic resin pallets selected, without limitation, from the group consisting of polyamide, polycarbonate, acrylonitrile butadiene styrene copolymer, polypheny! sulfide, polypropylene, polybutylene terephthalate, and polyethylene terephthalate. In another example, the moldable plastic material can be a thermoplastic and/or an injection moldable thermosetting plastic.

[0018] During the injection molding process, the injection gates 108 may be opened or closed to control the flow of the moldable plastic material there through. Each of the injections gates 108 may be opened or closed either independently from each other, or in conjunction with each other during a single injection molding cycle. An injection molding cycle may be considered as a sequence of processes are performed for injection molding of a single structure on a metal substrate.

[0019] In one example, the injection gates 108 may be opened by a pressure applied by the moldable plastic material received from the channels. When opened, the injection gates 108 may permit the injection of the moldable plastic material at three respective injection points into the mold cavity 106. As would be understood the different injection gates 108 are distributed across the injection mold 102 to uniformly distribute the injected moldable plastic material over the entire surface of metal substrate. As a result, the moldable plastic material is able to reach the farthermost spaces from the injection gates 108. Since the moldable plastic material is uniformly distributed and formed over the entire surface of the metal substrate, the instances of irregular gaps forming between the moldable plastic material and the metal substrate are also less. Thereby, a strong mechanical bond between the moldable material and the metal substrate is formed.

[0020] FIG. 2 illustrates another example of the injection mold 102. In the example shown in FIG.2, the injection mold 102 may include a multipart body 202. The multi-part body 202 may include a fixed portion 204 and removable portion 206 with a mold cavity 106 formed there between. The mold cavity 106 encloses a volume, a portion of which is used for accommodating metal substrate 208. The inner surface of the mold cavity 106 further defines the shape corresponding to a portion of an outer surface to a structure that is to be formed, on the metal substrate 208, within the mold cavity 106.

[0021] In one example, the removable portion 206 may include runner system. The runner system may be considered as channels or openings for receiving the mokJable plastic material, at high pressure and temperature from an injection nozzle of an injection moulding machine (not shown in figures). The runner system may include a sprue 210 and channels or runners 212 connected to the sprue 210. The sprue 210 receives the moldable plastic material from the injection nozzle, which is then introduced into the runners 212. The runners 212 may include a series of locations and pathways which are in fluid communication with the sprue 210. In one example, the runners 212 form pathways through which the moldable plastic material flows towards the mold cavity 106. In an alternative example, the runner system may be formed on a metallic insert which is then placed above the injection mold 102 designed with single-part body.

[0022] In order to regulate the flow of the moldable plastic material, the replaceable portion 204 may further include a series of injection gates

108-1, 2, 3 N, collectively referred to as 108, formed within upper surface of the mold cavity 106. In one example, the injection gates 108 may be formed in such a way that the one side of the injection gates 108 communicates with the respective runners 212 and the other side of the injection gates 108 is in fluid communication with the inner surface of the mold cavity 106.

[0023] In one example, the injection gates 108 may be formed as gate valves. Each of the gate valves may include a valve housing having passageways therein for receiving the moldable plastic material from the respective runners 212. Further, each of gate valves may include a cylindrical gate of restricted dimensions adapted to communicate with an orifice formed on the upper surface of the mold cavity 106, for injecting a jet of the moldable plastic material under a predetermined pressure into the mold cavity 106. Such jet of the moldable plastic material may then advance over entire inner surface, including walls and comers, of the mold cavity 106, and flow around the mold cavity 106 to fill therein. Furthermore, in an example, to control the flow of the moldable plastic material, the dimensions of the cylindrical gate can be varied using a control system (not shown in FIG.2). In an example, the control system may include one of a mechanical control system and an electronic control system.

[0024] In one example, the number of injection gates 108 is at least three, but may range between 4 and 6 in numbers. The number of injection gates 108 may correspond to the length of the structure, say plastic structure, that would be formed on the metal substrate 208. Furthermore, the number of injection gates 108 may be also based on appearance, deformation, molding constringency rate, and strength of articles molded in the injection mold 102. For example, by having the series of the injection gates 108, the injection mold 102 described herein may be able to fill distant spaces, such as corners in the mold cavity 106 with the moldable plastic material in a minimum possible time. This, in turn, improves the molding stage yield rate of the injection molding process.

[0025] Furthermore, the series of the injection gates 108 may allow the injection of the moldable plastic material at different equidistant injection points into the mold cavity 106. With such injection, the moldable plastic material evenly flows into the entire mold cavity 106. As a result, the moldable plastic material is able to reach farthermost points over the metal substrate 208. Since the farthermost points are still close as compared to the instances when injection was carried out with one single gate, the irregular gaps between the moldable plastic material and the metal substrate 208 are reduced. This, in turn, enables formation of a strong mechanical bond between the moldable plastic material and the metal substrate 208.

[0026] In operation, the mold cavity 106 formed inside the injection mold 102 may be pre-processed before molding stage. For instance, the mold cavity 106 may be pre-processed with a smooth or textured finish in order to impart a smooth or textured finish on the metal substrate 208 during the molding stage. Furthermore, after the pre-processing, the mold cavity 106 receives the metal substrate 208 in a portion of its volume.

[0027] On completion of the molding stage, a pressure retention stage is initiated. The pressure retention stage involves maintaining a specified pressure applied to the injected moldable plastic material so as to compensate shrinkage of the plastic material injected, into the mold cavity 106 which may occure due to a natural fall in temperature. In an example as shown in FIG. 3, for pressure retention, the injection mold 102 may include a plurality of air vents 302-1, 2 N, collectively referred to as air vents 302. The air vents 302 may be provided on at least two opposite walls of the mold cavity 106 and with a prescribed width. In one example, the prescribed width is about 0.15 mm. With such configuration of the air vents 302 in the mold cavity 106, the specified pressure can be easily maintained on to the injected moldable plastic material.

[0028] Additionally, in another example, the air vents 302 included in the mold cavity 106, may be used for expulsion of residuals of the chemicals, such as acids, along with the air from the mold cavity 106. The air vents 302 thus facilitates removal of residuals of the acids, which otherwise may involve complex pre-treatment of the mold cavity 106. This, in turn, enhances the yield rate of the injection molding process, as the described air vents 302 can potentially lower the number of injection mold stages by eliminating the involvement of pre-treatment of the mold cavity 106 for acid related issues. This, in turn, reduces the issues, such as void gaps or air bubbles, between the metal substrate 208 and the structure formed on the metal substrate 208, as the acids are suitably removed from the mold cavity 106 before initiation of the molding stage. Furthermore, the reduction of the acid related issues may help to prevent partial filling of nano-pores formed on the external surface of the metal substrate 208 or the mold cavity 106, and prevent various other defects in a product that would be formed.

[0029] After the pressure retention stage, a cooling stage may be initiated in which the removable portion 206 of the injection mold 102 is separated from the fixed portion 204 after the mold cavity 106 is completed filled with the moldable plastic material and the moldable plastic material is allowed to cool. Furthermore, for cooling of the moldable plastic material, the injection mold 102 may include a plurality cooling channels (not shown in figures) formed in the fixed portion 204. The plurality cooling channels can allow a liquid coolant to flow through the fixed portion 204 to conduct heat away from the mold cavity 106. Once the surface of the moldable plastic material injected over the metal substrate 208 cools down in the mold cavity 106, the molded article is taken out of the mold cavity 106. Thereafter, the surface finish of the molded article can be refined or altered using plating and other similar post-processing techniques.

[0030] The molded article may include the metal substrate 208 and the structure formed on the metal substrate 208. In an example, the metal substrate 208 may be a thin-walled structure and the structure formed on the metal substrate 208 may be a stiffener operative to rigidity the thin walled structure.

[0031] FIG. 4 illustrates a method 400 for carrying out injection molding process, according to an example of the present subject matter. The method 400 is implemented in an injection molding device, such as the injection mold 102. The order in which the method 400 is described is not intended to be construed as a limitation, and any number of the described method blocks can be combined in any order to implement the method 400, or alternative method. Furthermore, the method 400 can be implemented in any suitable devices having applicability in the fields of PMH) injection molding technologies. [0032] At block 402, the method includes positioning a metal substrate 208 in the mold cavity 106 of the injection mold 102. In an example, the mold cavity 106 may include a volume having a portion for accommodating the metal substrate 208, during an injection molding of a structure, say, plastic structure, on the metal substrate 208. The volume of the mold cavity 106 is such that a portion of the volume is sufficient to accommodate the metal substrate. The metal substrate may be a stamped sheet metal substrate having a nano-porous layer on its exterior surface.

[0033] The injection mold 102 may further include channels or runners 212. The runners 212 may include a series of pathways through which the moldable plastic material flows within the mold cavity 106. In an example, the moldable plastic material can be molten plastic resin pallets selected, without limitation, from the group consisting of polyamide, polycarbonate, acrylonitrile butadiene styrene copolymer, polypheny! sulfide, polypropylene, polybutylene terephthalate, and polyethylene terephthalate. In another example, the moldable plastic material can be a thermoplastic and/or an injection moldable thermosetting plastic.

[0034] The injection mold may further include at least three injection gates 108 formed in an upper surface of the mold cavity 106. In one example, the injection gates 108 may be formed in such a way that one side of the injection gates 108 communicates with the respective runners 212 and the other side of the injection gates 108 is in fluid communication with the inner surface of the mold cavity 106.

[0035] At block 404, the method includes injecting a moldable plastic material through the at least three injection gates 108 into the mold cavity 106 to form the structure, say, plastic structure, on the exterior surfaces of the metal substrate 208. As another option, the injecting may be performed by over-molding the moldable plastic material with the at least three injection gates 108 over the nano-pores formed on the exterior surface of the metal substrate 208.

[0036] By injecting the moldable plastic material over the exterior surface of the metal substrate 208 using the at least three injection gates 108, the mokJable plastic material is injected at multiple injection points on the external surface of the metal substrate 208. With such multipoint injection, the mokJable plastic material is uniformly distributed on each of the nano-pores present on the exterior surface of the metal substrate 208. As a result, the mokJable plastic material is able to reach and penetrate all the nano-pores, which are even farthermost nano-pores from the at least three injection gates 108. Since all the nano-pores are filled by the at least three injection gates 108, the irregular gaps between the mokJable plastic material and metal substrate 208 are reduced. This, in turn, provides a strong mechanical bond between the mokJable plastic material and the metal substrate 208.

[0037] Although the examples of the present disclosure have been described in language specific to plastic structure formed on the metal substrate, it is to be understood that the present disclosure is not limited to the formation of the plastic structures as described. Rather, the structures from other specific materials can be formed using the structural features and approaches disclosed and explained in the context of a few examples in the present disclosure.

Claims

We Claim:

1. An injection mold, comprising:

a mold cavity, wherein the mold cavity enclosing a volume capable of accommodating a metal substrate; and

at least three injection gates, formed in an upper surface of the mold cavity, to inject a moldable plastic material into the mold cavity to form a structure onto the metal substrate.

2. The injection mold as claimed in claim 1 , wherein the number of the at least three injection gates is selected from a range of 4 to 6 injection gates.

3. The injection mold as claimed in claim 1, further comprising a plurality of air vents opposite walls of the mold cavity, wherein the plurality of air vents are to expel air from the mold cavity.

4. The injection mold as claimed in claim 3, wherein the width of each of the plurality of air vents is about 0.15 mm.

5. The injection mold as claimed in claim 1 , further comprising runners connected with each of the at least three injection gates for supplying the moldable plastic material to the at least three injection gates.

6. The injection mold as claimed in claim 1 , wherein the at least three injection gates are opened and closed in conjunction during a single injection molding cycle.

7. An injection mold, comprising:

a fixed portion; a removable portion comprising at least three injection gates and runners corresponding to each of the at least injection gates for supplying a moldable plastic material to the at least three injection gates; and

a mold cavity formed between the fixed portion and the removable portion, wherein the mold cavity is to receive the moldable plastic from the at least three injection gates to form a structure on a metal substrate accommodated in the mold cavity.

8. The injection mold as claimed in claim 7, wherein the number of the at least three injection gates is selected from a range of 4 to 6 injection gates.

9. The injection mold as claimed in claim 7, wherein the at least three gates are gate valves, and wherein each of gate valves comprises a cylindrical gate to communicate with an orifice formed in the upper surface of the mold cavity, for injecting the moldable plastic material into the mold cavity.

10. The injection mold as claimed in claim 7, wherein the at least three injection gates are opened and closed for multiple times within a single molding cycle.

11. The injection mold as claimed in claim 7, further comprising a plurality of air vents on at least two opposite walls of the mold cavity, wherein the plurality of air vents are to expel air from the mold cavity

12. A method for injection molding, comprising:

positioning a metal substrate in a mold cavity of an injection mold, wherein the injection mold comprises at least three injection gates formed in an upper surface of the mold cavity; and injecting a moWable plastic material, through the at least three injection gates, into the mold cavity to form a structure on the metal substrate.

13. The method as claimed in claim 12, further comprising expulsing air from the mold cavity through a plurality of air vents provided in the mold cavity.

14. The method as claimed in claim 13, wherein the plurality of air vents are provided on at least two opposite walls of the mold cavity.

15. The method as claimed in claim 13, wherein the width of each of the plurality of air vents is about 0.15 mm.