A method of continuous carbon fiber skeleton reinforced injection molding

Abstract

The application relates to a method for continuously reinforcing injection molding of a carbon fiber framework, which comprises the following steps: step 1: obtaining a carbon fiber framework area of a designed part; step 2: slicing the obtained carbon fiber framework area to generate G-code capable of being printed by a continuous carbon fiber printer, and obtaining a continuous carbon fiber framework of the part; step 3: placing the carbon fiber framework in an injection mold to pour thermoplastic, melt and combine with plastic outside the formed carbon fiber framework, and removing the mold after forming to obtain a finished product. Compared with the prior art, the application has the advantages of improving structural efficiency, being suitable for plastic products with complex shapes and large stress, increasing the strength and rigidity of the injection molded part without increasing the mass, improving the durability of the injection molded part, and the like.

Description

Technical Field

[0001] This invention relates to the field of injection molding technology, and in particular to a method for continuous carbon fiber skeleton reinforced injection molding. Background Technology

[0002] Composite materials produced by 3D printing are highly sensitive to many process parameters, such as nozzle temperature and filament wetting. FDM technology is the only technology for composite material 3D printing; however, the quality of composite materials produced by this method is inconsistent, and there are limitations on the mass fraction of continuous carbon fibers. Compared with products produced by injection molding, it still falls short in terms of surface quality and precision. Injection molding can create products with complex geometries and high precision in a single step, but injection-molded parts lack strength and may crack under stress or during use, thus affecting the product's function and lifespan.

[0003] Current injection molding processes enhance the strength of injection molded products by incorporating short fibers into the injection molding material; however, the strong anisotropy of carbon fibers is not fully utilized in short carbon fibers. Continuous carbon fibers possess high specific strength and specific stiffness. Precisely designed zone-oriented carbon fiber layup can fully leverage the anisotropic advantages of continuous carbon fibers.

[0004] In the prior art, Chinese patent 202110972007.X discloses a method for planning continuous fiber reinforcement paths in 3D printing based on principal stress trajectory lines. This method draws principal stress trajectory lines by mapping the principal stress directions of each node within the design domain of the part to be printed, and plans a continuous fiber reinforcement path based on these principal stress trajectory lines within the part. However, the density of the generated printing path is independent of the stress magnitude at that location, failing to allocate carbon fibers to areas where they are most needed. Therefore, the reinforcement path planned using this method is not optimal. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the prior art and provide a method for continuous carbon fiber skeleton reinforcement injection molding.

[0006] A method for continuous carbon fiber skeleton-reinforced injection molding, the method comprising the following steps:

[0007] Step 1: Obtain the carbon fiber skeleton area of ​​the designed part;

[0008] Step 2: Slice the obtained carbon fiber skeleton area to generate G-code that can be printed by a continuous carbon fiber printer, and obtain the continuous carbon fiber skeleton of the part.

[0009] Step 3: Place the carbon fiber skeleton in the injection mold and pour thermoplastic to melt and bond it with the plastic on the outside of the formed carbon fiber skeleton. After molding, remove the mold to obtain the finished product.

[0010] In step 1, the carbon fiber skeleton region is generated in various ways, including based on principal stress line form, force flow tube form, U* force flow form, and uniform two-dimensional and three-dimensional uniform mesh forms generated by uniform reinforcement of the part.

[0011] The generation method based on principal stress lines specifically includes the following steps:

[0012] Step 101: Perform finite element analysis on the designed parts under the corresponding working conditions;

[0013] Step 102: Post-process the results of the finite element analysis to obtain the principal stress lines of the part, and draw the principal stress lines of the part on the stress distribution diagram according to the stress information of the nodes under the corresponding working conditions.

[0014] Step 103: Extract the principal stress lines in the CAD software, organize and draw the principal stress lines to obtain the center line of the skeleton;

[0015] Step 104: Offset the drawn principal stress trajectory lines to both sides to obtain the carbon fiber skeleton region.

[0016] In step 101, the finite element analysis software used for the finite element analysis includes Ansys, Abaqus, and Comsol.

[0017] In step 102, the absolute density of the principal stress lines is controlled by the designed strength enhancement value and the distance of the streamlines, and the relative density of the principal stress lines in different areas of the same part is controlled according to the stress value of the part itself.

[0018] In step 104, the offset distance is determined based on the load level and size limitations of the part.

[0019] In step 104, a positioning structure is set on the carbon fiber skeleton area according to the characteristics of the part itself, so as to facilitate placement in the injection molding material and thus ensure the positional accuracy of the skeleton. The positioning structure includes hole positioning and boundary positioning.

[0020] In step 2, the process of obtaining the continuous carbon fiber skeleton of the part is specifically as follows:

[0021] Grasshopper is used to parameterize control variables, and Python programming is used for slicing to generate G-code for the carbon fiber skeleton. During the Python programming process, after each trajectory is printed, a carbon fiber cutting command is added to the G-code, and the cutting is performed by the cutting device built into the continuous carbon fiber printer. Path planning is performed in each layer to save time. The first principal stress line and the third principal stress line are set to be printed alternately. The generated G-code is printed out using a continuous carbon fiber printer to obtain the continuous carbon fiber skeleton of the part. The continuous carbon fiber printer includes a desktop continuous carbon fiber printer and a robotic arm-based continuous carbon fiber printer.

[0022] In step 3, the carbon fiber skeleton is impregnated with plastic before the thermoplastic is poured to obtain a stable and continuous carbon fiber skeleton.

[0023] In step 3, the plastic includes PLA and PA plastics.

[0024] The objective of this invention can be achieved through the following technical solutions:

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] This invention uses 3D printing to create a continuous carbon fiber skeleton for the designed part, which is then combined with injection molding to conform to the stress distribution, leverage the tensile properties of the fiber, and improve structural efficiency. It is suitable for plastic products with complex shapes and high stress, and can increase the strength and rigidity of injection molded parts without increasing their weight, thereby improving their durability. Attached Figure Description

[0027] Figure 1 This is a flowchart of the method of the present invention.

[0028] Figure 2 This is a diagram showing the dimensions of the perforated plate sample in the embodiment.

[0029] Figure 3 This is a schematic diagram of the stress condition of the perforated plate sample in the embodiment.

[0030] Figure 4 The diagram shows the finite element stress cloud diagram and principal stress line schematic of the perforated plate under stress conditions in the embodiment.

[0031] Figure 5 This is a schematic diagram of the second stress condition of the perforated plate specimen in the embodiment.

[0032] Figure 6 The diagram shows the finite element stress cloud and principal stress line of the perforated plate under stress condition two in the embodiment.

[0033] Figure 7 This is a schematic diagram of the stress condition three for the perforated plate specimen in the embodiment.

[0034] Figure 8 The diagram shows the finite element stress cloud and principal stress line of the perforated plate under stress condition three in the embodiment.

[0035] Figure 9 This is a schematic diagram of the centerline of the continuous carbon fiber skeleton drawn in CAD software based on the principal stress lines in the embodiment.

[0036] Figure 10 This is a schematic diagram of the continuous carbon fiber skeleton with perforated plate in the embodiment.

[0037] Figure 11 Figure 11a shows the stress distribution of the perforated plate in the embodiment. Figure 11b shows the stress distribution of the pure plastic perforated plate and the stress distribution of the injection-molded perforated plate reinforced with carbon fiber skeleton.

[0038] Figure 12 Figure 12a shows the stress density diagram of the perforated plate node in the embodiment. Figure 12b shows the stress density diagram of the perforated plate node made of pure plastic and the perforated plate node made of carbon fiber skeleton reinforced by injection molding. Detailed Implementation

[0039] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0040] like Figure 1 As shown, the present invention provides a method for continuous carbon fiber skeleton reinforcement injection molding. The method obtains stress information through the actual working conditions of the designed part, obtains principal stress lines through post-processing of finite element analysis, obtains the continuous carbon fiber placement area after flattening in CAD software, places the carbon fiber printed skeleton in the mold for injection molding, and finally obtains a lightweight, high dimensional accuracy and high performance injection molded product.

[0041] The method includes the following steps:

[0042] Step 1: Perform finite element analysis on the designed part under the corresponding working conditions. The stress results of the designed part will be different under different working conditions. Finite element analysis can be obtained in commonly used finite element analysis software, including Ansys, Abaqus and Comsol.

[0043] Step 2: Post-process the results of the finite element analysis in Step 1. Based on the stress information of the nodes under the corresponding working conditions, draw the first principal stress line and the third principal stress line of the part on the stress distribution diagram. Control the absolute density of the principal stress lines by the designed strength enhancement value and the distance of the streamlines. Control the relative density of the principal stress lines in different areas of the same part according to the stress value of the part itself.

[0044] The post-processing of finite element results to obtain principal stress is only one example of the method for generating printed skeletons. In addition to principal stress, other methods can be used to generate carbon fiber skeletons, including force flow tubes, force flow forms such as U*, and uniform two-dimensional and three-dimensional uniform meshes generated by uniform reinforcement of parts.

[0045] Step 3: The principal stress lines generated directly by the software are relatively discrete and have regions with small curvature. Since the continuous carbon fiber bundles are somewhat brittle, it is not easy to print a trajectory with small curvature. Therefore, it is necessary to extract the principal stress lines in the CAD software, organize and draw the principal stress lines to obtain the center line of the skeleton.

[0046] Step 4: Offset the drawn principal stress trajectory lines to both sides to obtain the carbon fiber skeleton area. The offset distance is determined by the load and size limitations of the part. Since the printed carbon fiber skeleton needs to be located in the correct area of ​​the injection mold, a positioning structure, including hole positioning and boundary positioning, is added according to the characteristics of the part itself to facilitate placement in the injection material and ensure the positional accuracy of the skeleton.

[0047] Step 5: Generate G-code for the continuous carbon fiber skeleton that can be printed by a continuous carbon fiber printer. The slicing process requires using Grasshopper to parametrically control variables and combining Python programming to generate the G-code of the carbon fiber skeleton. During the programming process, after each trajectory is printed, a carbon fiber cutting command is added to the G-code, and the cutting is performed by the cutting device built into the continuous carbon fiber printer. Since the cutting process is time-consuming, path planning is performed in each layer. During the programming process, the first principal stress line and the third principal stress line are set to be printed in an interleaved manner. The generated G-code is printed using a desktop continuous carbon fiber printer or a robotic arm-based continuous carbon fiber printer to obtain the continuous carbon fiber skeleton of the part.

[0048] Because continuous carbon fibers have a certain degree of resistance to melting, continuous carbon fiber filaments need to be impregnated with plastics such as PLA and PA before being printed using a fused deposition modeling printer in order to obtain a more stable continuous carbon fiber skeleton.

[0049] Step 6: Place the carbon fiber skeleton in the injection mold and pour thermoplastic to melt and bond it with the plastic on the outside of the formed carbon fiber skeleton, so that the continuous carbon fiber skeleton and the injection material are more firmly bonded. After molding, remove the mold to obtain the finished product.

[0050] like Figure 2 As shown, this embodiment uses a perforated plate as an example. Under different working conditions, the stress distribution of the perforated plate itself is different, such as... Figure 3 , Figure 5 and Figure 7 As shown, finite element analysis was performed on injection-molded parts under different working conditions, and stress cloud diagrams and principal stress directions were obtained, as shown below. Figure 4 , Figure 6 and Figure 8 As shown. However, the principal stress lines extracted by finite element software are not suitable for the printing process of continuous carbon fibers. It is necessary to integrate and draw the principal stress lines in CAD software to obtain the center line of the carbon fiber skeleton. The perforated plate uses the center circle of the carbon fiber as the positioning reference, which is easy to position in the injection mold. In this embodiment, taking the case of the perforated plate being stretched in the 45° direction as an example, the principal stress lines are redrawn according to the principal stress lines to obtain the center line of the carbon fiber trajectory skeleton, as shown. Figure 9 As shown, the skeleton lines are offset to both sides to obtain the carbon fiber skeleton. Then, path planning is performed, as follows... Figure 10 As shown.

[0051] Carbon fibers were embedded in plastic to obtain injection-molded parts. Finite element simulations were then performed again, ultimately showing that the maximum displacement of the designed carbon fiber-reinforced injection-molded material was 46.6% lower than that of pure injection-molded material. Figure 12 As shown, the addition of the carbon fiber skeleton increases the number of low-stress areas in the injection molded part, which is quantified in the stress distribution density diagram. This demonstrates that the stiffness of the injection molded part is improved while maintaining surface smoothness and precision.

[0052] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method of continuous carbon fiber skeleton reinforced injection molding, characterized by, The method comprises the following steps: Step 1: Obtain the carbon fiber skeleton region of the designed part; Step 2: Slice the obtained carbon fiber skeleton region to generate G-code that can be printed by a continuous carbon fiber printer, and obtain the continuous carbon fiber skeleton of the part; Step 3: Place the carbon fiber skeleton in an injection mold, pour thermoplastic, and melt and combine with the plastic outside the formed carbon fiber skeleton, then remove the mold to obtain the finished product; In step 1, the generation method of the carbon fiber skeleton region includes generating a uniform two-dimensional and three-dimensional grid form based on a principal stress line form, a force flow tube force flow form, a U* force flow form, and a part uniform reinforcement; The generation method based on the principal stress line form specifically comprises the following steps: Step 101: Perform finite element analysis on the designed part under the corresponding working condition; Step 102: Post-process the results of the finite element analysis to obtain the principal stress lines of the part, and draw the principal stress lines of the part in a stress distribution diagram according to the stress information of the nodes under the corresponding working condition; Step 103: Extract the principal stress lines in the CAD software, organize and draw the principal stress lines to obtain the center line of the carbon fiber skeleton; Step 104: Offset the drawn principal stress lines to both sides to obtain the carbon fiber skeleton region; In step 102, the absolute density of the principal stress lines is controlled by the designed strength reinforcement value and the distance of the set flow lines, and the relative density of the principal stress lines in different regions of the same part is controlled according to the stress value of the part itself; In step 104, a positioning structure is set on the carbon fiber skeleton region according to the characteristics of the part to facilitate placement in the injection material, thereby ensuring the position accuracy of the carbon fiber skeleton, and the positioning structure includes hole positioning and boundary positioning.

2. The method of claim 1, wherein the continuous carbon fiber skeleton reinforced injection molding is characterized by, In step 101, the finite element analysis software for finite element analysis includes Ansys, Abaqus, and Comsol.

3. The method of claim 1, wherein the continuous carbon fiber skeleton reinforced injection molding is characterized by, In step 104, the offset distance is determined according to the load degree and size limitation of the part.

4. The method of claim 1, wherein the continuous carbon fiber skeleton reinforced injection molding is characterized by, In step 2, the process of obtaining the continuous carbon fiber skeleton of the part is specifically as follows: Use Grasshopper parameterized control variables and combine python programming to slice and generate G-code of the carbon fiber skeleton, add carbon fiber cutting commands in the G-code after each track is printed in the python programming process, use the cutting device of the continuous carbon fiber printer to cut, plan the path in each layer to save time, set staggered printing for the first principal stress line and the third principal stress, use the continuous carbon fiber printer to print the generated G-code to obtain the continuous carbon fiber skeleton of the part, and the continuous carbon fiber printer includes a desktop continuous carbon fiber printer and a continuous carbon fiber printer based on a mechanical arm.

5. The method of claim 1, wherein the continuous carbon fiber skeleton reinforced injection molding is characterized by, In step 3, before pouring the thermoplastic, the carbon fiber skeleton is impregnated with plastic to obtain a stable continuous carbon fiber skeleton.

6. A method of continuous carbon fiber skeleton reinforced injection molding according to claim 5, wherein, In step 3, the plastic includes PLA and PA plastic.

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