A plastic part in-mold forming and metal insert composite process

Abstract

The application provides a plastic part in-mold forming and metal insert composite process, and belongs to the technical field of notebook structure part manufacturing, and comprises the following steps: constructing a three-level interlocking structure from macro to nanometer scale in the connecting area of a metal frame skeleton; depositing a functional gradient interface layer containing a chemical bonding promotion layer on the surface of the interlocking structure; attaching a pre-formed decorative functional film and a pre-composite foamable sheet to a mold; multi-stage injection molding to make the melt fill the multi-level interlocking structure step by step and activate the chemical bonding, while forming a lightweight core in situ by foaming; and cooling by partition temperature control to eliminate residual stress. The application realizes the integration of metal-plastic five-level anchoring combination, structure skeleton forming, surface decoration and foaming weight reduction in one in-mold process, solves the problems of low interface strength, process dispersion and insufficient lightweight of the existing insert injection molding process, and is especially suitable for high-quality manufacturing of light and thin notebook computer frames.

Description

Technical Field

[0001] This invention belongs to the field of notebook structural component manufacturing technology, specifically relating to a composite process of in-mold forming of plastic parts and metal inserts. Background Technology

[0002] Laptops are increasingly moving towards thinner, lighter, more rigid designs and unibody aesthetics. While traditional all-metal frames offer excellent strength, they suffer from drawbacks such as heavy weight, high cost, antenna signal shielding, and difficulties in molding complex structures (like clips and ribs). Traditional all-plastic frames, on the other hand, are lightweight and inexpensive, but lack rigidity and a premium feel. Therefore, composite structures of metal and plastic are gradually becoming the mainstream solution in the industry.

[0003] Currently, the main technological approaches used in the manufacturing of metal-plastic composite notebook frames include the following categories: (1) Insert Molding Process: A pre-processed metal insert is placed into an injection mold, and the injection-molded plastic forms a mechanical or physical bond with the metal insert. For example, a groove and a thin wall are machined on the metal shell, and then plastic is injected and molded before the thin wall is removed. This method has problems such as insufficient interfacial bonding strength and shrinkage of the plastic after injection, which leads to a decrease in dimensional accuracy. The metal insert and the plastic are also prone to displacement due to asynchronous ejection.

[0004] (2) Nano Molding Technology (NMT): This process involves treating the aluminum alloy surface with alkaline etching, acid etching, and T-agent etching to create micropores at the 20-40 nm level. This allows the plastic to penetrate the nanopores during the injection molding process and achieve anchoring bonding. Although this process provides better bonding than traditional methods, the T-treatment involves multiple chemical reagents, resulting in a narrow process window, high waste liquid treatment costs, and its applicability is limited to specific grades of aluminum alloys.

[0005] (3) In-film decoration (IMR / IMD) process: By embedding a pre-printed film into an injection mold, the decorative layer and the substrate are integrated and compositely formed during the resin injection stage. However, this process is mainly used to achieve the surface decoration function and does not contribute to the structural strength.

[0006] (4) Adhesive bonding process: The metal shell and the plastic part are bonded together with adhesive. This method has problems such as glue aging, poor reliability, the need for additional glue application process, and inconsistent deformation at high and low temperatures. Summary of the Invention

[0007] The purpose of this invention is to provide a composite process for in-mold forming of plastic parts and metal inserts, which aims to solve the problems of insufficient interfacial bonding strength and stress concentration in existing insert injection molding processes.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A composite process for in-mold forming of plastic parts and metal inserts includes the following steps: S1. Provide a metal sheet and process it to form a metal frame skeleton. On the metal frame skeleton, the connection area that needs to be combined with plastic is constructed with at least three levels of interlocking structure from macro to nano scale by laser or electrochemical processing to form a multi-level gradient interlocking interface. S2. Using physical vapor deposition, cold spraying or electrophoretic deposition, a gradient interface layer is sequentially deposited on the surface of the gradient interlocking structure in the connection area, wherein the gradient interface layer includes at least a chemical bonding promoting layer that can be activated under subsequent high temperature injection molding conditions and covalently bonded or strongly hydrogen bonded with polar groups in the plastic. S3. Prepare a multilayer decorative functional film and preform it into a three-dimensional shape that matches the shape of the metal frame skeleton by hot pressing; optionally, pre-composite a foamable thermoplastic resin sheet on the back of the preformed decorative functional film, wherein the foamable thermoplastic resin sheet contains thermally expanding microcapsule foaming agent. S4. The pre-formed decorative functional film is attached to the mold cavity surface, and the metal frame skeleton treated with gradient interface layer is positioned on the moving mold side of the mold. After the mold is closed, thermoplastic resin melt is injected into the cavity through at least one injection unit. During the injection molding process, a) the melt fills the multi-level gradient interlocking interface step by step and forms mechanical interlocking, b) the chemical bonding promotion layer is activated and the interface chemical bonding is achieved, c) the decorative functional film is integrated with the injection molding substrate, and d) the foamable sheet is foamed in situ at the melt temperature to form a lightweight core structure. S5. After injection molding, a zoned temperature control cooling strategy is adopted to cool the area where the metal frame skeleton is located at a higher temperature than the plastic matrix area in stages.

[0009] As a preferred embodiment of the present invention, the multi-level gradient interlocking interface in step S1 includes: a first-level macroscopic interlocking structure with a trapezoidal or T-shaped dovetail groove or bottom-cut hole array, the groove width is 0.5-3mm and the groove depth is 1-5mm, and the bottoms of adjacent dovetail grooves are connected by a single connecting through hole; a second-level mesoscopic interlocking structure is formed on the inner wall surface of the first-level structure by laser or electrochemical etching of a micron-level trench array, the trench width is 5-50m and the depth is 5-30m; and a third-level microscopic interlocking structure is formed by plasma treatment or short-pulse laser surface modification of a nanoscale oxide rough structure with Ra of 0.05-5m.

[0010] In a preferred embodiment of the present invention, the gradient interface layer in step S2 comprises a bottom layer, an intermediate layer, and a top layer: the bottom layer is a stress buffer layer with a thermal expansion coefficient between that of metal and plastic, and a thickness of 0.1-5 μm, made of Cr, Ti, CrN, or TiN; the intermediate layer is a chemical bonding promoting layer containing active functional groups, with a thickness of 0.05-2 μm, and the active functional groups are - Or -OH groups; the top layer is a gradient molecular chain density nanolayer formed by molecular self-assembly, with a thickness of 10-200nm.

[0011] As a preferred embodiment of the present invention, the multilayer decorative functional film in step S3 includes, from the mold cavity side to the back side, a transparent protective layer, a decorative pattern layer and an adhesive underlayer, wherein the transparent protective layer has a nano-indentation hardness of 10-200 N / mm at 30°C and 100 N / mm at 150°C.

[0012] As a preferred embodiment of the present invention, the foaming initiation temperature of the thermally expanding microcapsule foaming agent dispersed in the foamable thermoplastic resin sheet in step S3 is 120-180℃, the expansion ratio is 10-50 times, and the thickness of the foamable sheet is 0.1-0.5mm.

[0013] As a preferred embodiment of the present invention, the injection molding in step S4 adopts a multi-stage injection method: in the first stage, an unreinforced or low-reinforced thermoplastic resin melt is injected at an injection pressure of 80-120MPa, and the melt front linear velocity is 0.1-0.5m / s, so that the melt can fully penetrate into each scale layer of the multi-level interlocking structure; in the second stage, after an interval of 0.5-3s, a second thermoplastic resin melt containing 5-30% by mass of short-cut fiber reinforcement is injected into the locally reinforced area of ​​the frame at an injection pressure of 1.2-1.5 times that of the first stage.

[0014] As a preferred embodiment of the present invention, the zoned temperature control cooling strategy in step S5 is as follows: the temperature of the area where the metal frame skeleton is located is 20-50°C higher than that of the plastic matrix area, the temperature of the foaming area is independently controlled at 120-180°C, and after cooling, it is annealed at 50-80°C for 2-8 hours.

[0015] In a preferred embodiment of the present invention, the metal frame skeleton is made of magnesium alloy, aluminum alloy or titanium alloy, and the thermoplastic resin is polycarbonate (PC), polyamide (PA), polyphenylene sulfide (PPS) or its fiber-reinforced composite material.

[0016] Compared with the prior art, the beneficial effects of the present invention are: By constructing a multi-level gradient interlocked interface consisting of millimeter-level dovetail groove interlocking, micron-level groove guidance, nano-level rough wetting, interfacial chemical bonding, and molecular chain segment interpenetration, and employing an in-mold integrated composite molding process, the structural skeleton forming, surface decorative functional layer bonding, and in-situ foaming for lightweighting in designated areas are simultaneously achieved in a single injection molding process. This significantly improves the bonding strength between the metal insert and the plastic, achieving an interfacial shear strength of 25–50 MPa and a peel strength of 5–12 N / mm, which are 2–5 times and 3–6 times higher than traditional insert injection molding processes, respectively. At the same time, the stress buffer layer in the functional gradient interface layer works synergistically with the zoned temperature control cooling strategy to effectively absorb the thermal shrinkage difference between the metal and the plastic, controlling the product warpage to within 0.1 mm, increasing the yield to over 95%, and eliminating interfacial gaps and overflow defects. Attached Figure Description

[0017] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1 Please see Figure 1 The present invention provides the following technical solutions: A composite process for in-mold forming of plastic parts and metal inserts includes the following steps: Step 1: Fabrication of magnesium alloy frame skeleton and processing of multi-level interlocking structure The metal skeleton of the laptop's C-side frame is formed by stamping and CNC precision machining using 1.2mm thick AZ31B magnesium alloy sheet. Its main body extends along the outer contour of the frame and has a width of 8-15mm. In the areas where the skeleton and plastic meet (the continuous areas on the inner sides of the four sides of the frame and the corner joints), multi-scale processing is performed using ultraviolet pulsed laser (wavelength 355nm, pulse width 15ns).

[0020] The first-level dovetail grooves are processed using laser layer scanning. The groove opening width is 1.2mm, the groove bottom width is 2.0mm, the groove depth is 3mm, and the groove spacing is 8mm. They are evenly distributed along the contour direction in the connection area of ​​the skeleton. Between the bottom of every two adjacent dovetail grooves, a primary connection through hole with a diameter of 0.5mm is processed by laser drilling. The axis of the through hole is parallel to the thickness direction of the metal skeleton.

[0021] The second-level micro-groove array uses a coaxial laser to scan and etch the inner wall of the dovetail groove at a pulse frequency of 50kHz. The groove width is 15m, the depth is 10m, the groove spacing is 30m, and the groove extension direction forms a 45° angle with the length direction of the dovetail groove. The two sets of 45° grooves are interwoven to form a diamond woven texture.

[0022] The third-level micro-interlocking structure is achieved through... Low-temperature plasma treatment with mixed gas (volume ratio 1:1), power 200W, treatment time 120s, in situ generation of MgO nano-rough layer in micron-grooves and inter-grooves region, the arithmetic mean roughness Ra was measured to be 1.2m.

[0023] Step 2: Construction of the Functional Gradient Interface Layer Using a multi-arc ion plating apparatus, the following deposition processes are sequentially performed on the surface of the metal skeleton connection area: Bottom layer (stress buffer layer): Cr layer, 1.5m thick, deposition parameters: arc current 80A, bias voltage -100V, nitrogen partial pressure 0.5Pa.

[0024] Intermediate layer (chemical bonding enhancement layer): Plasma-enhanced chemical vapor deposition (PECVD) was used to deposit a layer containing - on the Cr layer using aminosilane (APTES) as a precursor. Plasma-polymerized film of functional groups, 0.3 μm thick.

[0025] Top layer (interface wetting control layer): Using self-assembly technology (SAM), the Cr-silane surface is immersed in solutions of mercapto-olefin functionalized molecules of different concentrations. The molecular chain density gradient is achieved by controlling the pulling speed and solution concentration. The self-assembly layer is about 50 nm thick.

[0026] Step 3: Preparation of decorative functional film, preforming and lamination of foam layer Preparation of multi-layer decorative functional film: 100 μm thick optical grade polycarbonate (PC) is selected as transparent protective layer. On its inner side, a pattern layer and a UV-curable protective varnish are printed sequentially by gravure printing (1200 dpi precision). Then, a 15 μm thick PC hot melt adhesive underlayer is laminated on the pattern layer.

[0027] The aforementioned film is heated to above the glass transition temperature of PC (approximately 160°C) using infrared heating, and then hot-pressed in a preforming mold into a three-dimensional shape matching the magnesium alloy skeleton. Subsequently, on the back of the preformed film, corresponding to the non-load-bearing areas of the C-side wrist rest and keyboard perimeter, a 0.3mm thick foamable PC / ABS blend sheet is hot-laminated, containing 3% by mass of EXPANCEL 950DU120 thermally expandable microcapsules (AkzoNobel, foaming initiation temperature approximately 135°C, maximum expansion temperature 190-210°C).

[0028] Step 4: In-mold integrated injection molding An injection mold with two independent injection units is used. A pre-formed decorative functional film (decorative side facing outwards) is attached to the cavity surface of the fixed mold using vacuum adsorption. The moving mold is equipped with locating pins to precisely position the magnesium alloy skeleton. After mold closing, a cavity to be filled is formed between the skeleton and the decorative film.

[0029] The first stage injection molding used a 200-ton clamping force injection molding machine with an injection unit diameter of 40mm. PC+10%GF (glass fiber reinforced polycarbonate) thermoplastic melt was injected at a melt temperature of 280℃, an injection pressure of 105MPa, and an injection speed controlled at a melt front flow rate of 0.3m / s. As the melt front flowed through the multi-level interlocking interface region of the skeleton, it progressively filled the third-level nano-roughened layer, the second-level micro-grooves, the first-level dovetail grooves, and the connecting through-hole network. The high-temperature melt triggered the chemical bonding reaction of the amino functional groups on the skeleton surface. Simultaneously, the pre-placed foamable sheets underwent thermal expansion under the high temperature of the melt, causing the microcapsules to expand and form a closed-cell foam core layer in situ in the designated area.

[0030] 1.5 seconds after the first injection, the second injection unit injects PC resin reinforced melt containing 20% ​​short-cut carbon fibers (200m in length) at 130MPa pressure at the four corners of the frame and the hinge mounting position. The local fiber orientation is arranged along the principal stress direction.

[0031] Step 5: Controlled Cooling and Post-processing A zoned temperature control system with built-in electromagnetic induction heating / water cooling is used in the mold. The mold temperature for the magnesium alloy skeleton area is set to 120℃, the plastic substrate area is cooled to 80℃, and the foaming area is controlled at 140℃ to facilitate foaming. The cooling time is 30 seconds, and after mold opening and part removal, the part is annealed in a 65℃ oven for 4 hours.

[0032] Example 2 The difference between this embodiment and Embodiment 1 lies in the metal substrate and some parameter adjustments: 6061 aluminum alloy sheet with a thickness of 1.0 mm is used. In the three-stage interlocking structure processing, electrochemical etching is used instead of laser etching in the second stage, and the third stage uses a short-pulse femtosecond laser (pulse width 800 fs) to generate an aluminum oxide nanofiber structure on the aluminum surface, with Ra of 0.8 μm. The bottom layer of the gradient interface layer is TiN with a thickness of 2 μm. The decorative protective layer is PMMA. The injection molding resin is PA66 + 30% GF. The remaining steps are the same as in Embodiment 1.

[0033] Example 3 The difference between this embodiment and Embodiment 1 is that: the first-stage interlocking structure uses a T-shaped groove instead of a dovetail groove; the extension direction of the second-stage microgroove forms a 60° angle with the length direction of the dovetail groove (unidirectional layout); the mass fraction of the microcapsule foaming agent in the foamed sheet is 5%; and no annealing treatment is performed after zoned temperature-controlled cooling. The remaining steps are the same as in Embodiment 1.

[0034] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite process for in-mold forming of plastic parts and metal inserts, characterized in that, Includes the following steps: S1. Provide a metal sheet and process it to form a metal frame skeleton. On the metal frame skeleton, the connection area that needs to be combined with plastic is constructed with at least three levels of interlocking structure from macro to nano scale by laser or electrochemical processing to form a multi-level gradient interlocking interface. S2. Using physical vapor deposition, cold spraying or electrophoretic deposition, a gradient interface layer is sequentially deposited on the surface of the gradient interlocking structure in the connection area, wherein the gradient interface layer includes at least a chemical bonding promoting layer that can be activated under subsequent high temperature injection molding conditions and covalently bonded or strongly hydrogen bonded with polar groups in the plastic. S3. Prepare a multilayer decorative functional film and preform it into a three-dimensional shape that matches the shape of the metal frame skeleton by hot pressing; optionally, pre-composite a foamable thermoplastic resin sheet on the back of the preformed decorative functional film, wherein the foamable thermoplastic resin sheet contains thermally expanding microcapsule foaming agent. S4. The pre-formed decorative functional film is attached to the mold cavity surface, and the metal frame skeleton treated with gradient interface layer is positioned on the moving mold side of the mold. After the mold is closed, thermoplastic resin melt is injected into the cavity through at least one injection unit. During the injection molding process, a) the melt fills the multi-level gradient interlocking interface step by step and forms mechanical interlocking, b) the chemical bonding promotion layer is activated and the interface chemical bonding is achieved, c) the decorative functional film is integrated with the injection molding substrate, and d) the foamable sheet is foamed in situ at the melt temperature to form a lightweight core structure. S5. After injection molding, a zoned temperature control cooling strategy is adopted to cool the area where the metal frame skeleton is located at a higher temperature than the plastic matrix area in stages.

2. The in-mold forming and metal insert composite process for plastic parts according to claim 1, characterized in that, The multi-level gradient interlocking interface mentioned in step S1 includes: a first-level macroscopic interlocking structure with a trapezoidal or T-shaped dovetail groove or bottom-cut hole array, with a groove width of 0.5-3mm and a groove depth of 1-5mm, and the bottoms of adjacent dovetail grooves are connected by a single connecting through hole; a second-level mesoscopic interlocking structure is formed on the inner wall surface of the first-level structure by laser or electrochemical etching of a micron-scale trench array, with a trench width of 5-50m and a depth of 5-30m; and a third-level microscopic interlocking structure is formed by plasma treatment or short-pulse laser surface modification of a nanoscale oxide rough structure with Ra of 0.05-5m.

3. The in-mold forming and metal insert composite process for plastic parts according to claim 2, characterized in that: The gradient interface layer described in step S2 includes a bottom layer, an intermediate layer, and a top layer: the bottom layer is a stress buffer layer with a thermal expansion coefficient between that of metal and plastic, 0.1-5 μm thick, and the material is Cr, Ti, CrN, or TiN; the intermediate layer is a chemical bonding promoting layer containing active functional groups, 0.05-2 μm thick, and the active functional groups are - Or -OH groups; the top layer is a gradient molecular chain density nanolayer formed by molecular self-assembly, with a thickness of 10-200nm.

4. The in-mold forming and metal insert composite process for plastic parts according to claim 3, characterized in that: The multilayer decorative functional film in step S3 includes, from the mold cavity side to the back side, a transparent protective layer, a decorative pattern layer, and an adhesive underlayer. The transparent protective layer has a nano-indentation hardness of 10-200 N / mm at 30°C and 100 N / mm at 150°C.

5. The in-mold forming and metal insert composite process for plastic parts according to claim 4, characterized in that: The foaming initiation temperature of the thermally expanding microcapsule foaming agent dispersed in the foamable thermoplastic resin sheet in step S3 is 120-180℃, the expansion ratio is 10-50 times, and the thickness of the foamable sheet is 0.1-0.5mm.

6. The in-mold forming and metal insert composite process for plastic parts according to claim 5, characterized in that: In step S4, injection molding adopts a multi-stage injection method: in the first stage, unreinforced or low-reinforced thermoplastic resin melt is injected at an injection pressure of 80-120MPa, and the melt front linear velocity is 0.1-0.5m / s, so that the melt can fully penetrate into each scale layer of the multi-level interlocking structure; in the second stage, after an interval of 0.5-3s, a second thermoplastic resin melt containing 5-30% by mass of short-cut fiber reinforcement is injected into the local reinforcement area of ​​the frame at an injection pressure of 1.2-1.5 times that of the first stage.

7. The in-mold forming and metal insert composite process for plastic parts according to claim 6, characterized in that: The zoned temperature control cooling strategy in step S5 is as follows: the temperature of the area where the metal frame skeleton is located is 20-50℃ higher than that of the plastic matrix area, the temperature of the foaming area is independently controlled at 120-180℃, and after cooling, it is annealed at 50-80℃ for 2-8 hours.

8. The in-mold forming and metal insert composite process for plastic parts according to claim 7, characterized in that: The metal frame skeleton is made of magnesium alloy, aluminum alloy or titanium alloy, and the thermoplastic resin is polycarbonate (PC), polyamide (PA), polyphenylene sulfide (PPS) or its fiber-reinforced composite material.

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