Injection-molded part, method for producing same, and method for evaluating internal stress of same

Abstract

The application relates to an injection molded part and a production method and an internal stress evaluation method thereof, and relates to the technical field of automobile parts.The application comprises the following steps: determining a three-dimensional model of the injection molded part; performing mold flow analysis on the three-dimensional model of the injection molded part to determine at least one key factor of the internal stress of the injection molded part; performing test design analysis on the at least one key factor to obtain the internal stress of the injection molded part, and establishing a response relationship between the at least one key factor and the internal stress; based on the response relationship, performing conditional constraint on the key factor to obtain an optimal value range of the key factor; and evaluating the three-dimensional model of the injection molded part by using the optimal value range of the key factor to obtain an evaluation result of the internal stress of the injection molded part.In the mold flow analysis process, the key factor is matched with the internal stress to accurately predict stress mark defects, so that the surface stress mark defects of the injection molded part can be avoided in advance, and the purpose of canceling the surface defect covering post-processing process of the injection molded part is achieved.

Description

Technical Field

[0001] This application relates to the field of automotive parts technology, specifically to an injection molded part, its production method, and its internal stress assessment method. Background Technology

[0002] Against the backdrop of current changes in the global macroeconomic and industrial environment, enterprises generally face challenges such as increased pressure on profitability, intensified market competition, and rising supply chain uncertainty. Effective low-cost technologies are the key to maintaining competitiveness. Many companies have begun to restructure their product design and manufacturing processes, with the elimination of unnecessary processing steps, such as the post-processing step of masking surface defects on injection molded parts, being a key area of ​​review. However, eliminating the post-processing step of masking surface defects will expose the original surface defects of injection molded parts, the most obvious being stress mark defects, which are the most common type of defects on the surface of injection molded parts. Summary of the Invention

[0003] One objective of this application is to provide a method for evaluating the internal stress of injection molded parts, so as to solve the problem in the prior art that the most common stress mark defects on the surface of injection molded parts will be exposed without any trace after the post-processing step of covering surface defects is eliminated; the second objective is to provide a method for producing injection molded parts.

[0004] To achieve the above objectives, the technical solution adopted in this application is as follows: a method for evaluating the internal stress of an injection molded part, comprising: determining a three-dimensional model of the injection molded part; performing mold flow analysis on the three-dimensional model of the injection molded part to determine at least one key factor for the internal stress of the injection molded part; performing experimental design analysis on the at least one key factor to obtain the internal stress of the injection molded part, and establishing a response relationship between the at least one key factor and the internal stress; based on the response relationship, imposing conditional constraints on the key factor to obtain the optimal value range of the key factor; and evaluating the three-dimensional model of the injection molded part using the optimal value range of the key factor to obtain the evaluation result of the internal stress of the injection molded part.

[0005] Based on the above technical means, key factors such as volume shrinkage rate, temperature gradient, freezing time difference, and residual stress are introduced into the mold flow analysis process. These factors are combined with internal stress to establish the response relationship between key factors and internal stress, accurately predicting stress trace defects. This aims to avoid stress trace defects on the surface of injection molded parts in advance, thereby eliminating the need for post-processing steps to cover surface defects.

[0006] Furthermore, the step of performing mold flow analysis on the three-dimensional model of the injection molded part to determine at least one key factor affecting the internal stress of the injection molded part includes: performing mold flow analysis on the three-dimensional model of the injection molded part to obtain at least one candidate factor affecting the internal stress of the injection molded part, wherein the candidate factor is a result parameter of the injection molded part responding to the process parameters of the injection molded part in the mold flow analysis; and determining at least one key factor affecting the internal stress of the injection molded part from the at least one candidate factor.

[0007] Based on the above technical means, by adjusting the process parameters of the injection molded part, the injection molded part can exhibit result parameters. Key factors are obtained from the result parameters, and these key factors are used to correlate with the internal stress of the injection molded part. Thus, the internal stress of the injection molded part can be evaluated based solely on the result parameters.

[0008] Further, determining at least one key factor for the internal stress of the injection molded part from the at least one candidate factor includes: determining a quality score for each candidate factor; the quality score characterizing the importance of the candidate factor relative to the internal stress of the injection molded part; and determining at least one key factor for the internal stress of the injection molded part from the at least one candidate factor based on the quality score corresponding to each of the at least one candidate factor.

[0009] Based on the above technical means, each candidate factor can be comprehensively evaluated based on the quality score. The evaluation method is relatively objective and can better present the relationship between key factors and the internal stress of injection molded parts, which is more helpful for subsequent evaluation of the internal stress of injection molded parts.

[0010] Furthermore, the step of conducting experimental design analysis on the at least one key factor to obtain the internal stress of the injection molded part and establishing the response relationship between the at least one key factor and the internal stress includes: using the at least one key factor as an experimental factor to conduct experimental design analysis, using the internal stress of the injection molded part as a response variable to obtain experimental design results; and based on the experimental design results, performing regression analysis and accuracy verification based on the experimental factor and the response variable to obtain the regression equation between the response variable and the experimental factor.

[0011] Based on the above technical means, the accuracy of regression analysis can be improved through experimental design analysis, thereby further improving the accuracy of the evaluation results of the internal stress of injection molded parts.

[0012] Furthermore, the step of performing regression analysis and accuracy verification based on the experimental factors and the response variable, and obtaining the regression equation between the response variable and the experimental factors, according to the experimental design results, includes: performing factor regression analysis on the response variable and the experimental factors to obtain the factor regression analysis results; determining the fitting model and the significance relationship of each coefficient based on the factor regression analysis results; eliminating one factor term at a time for factor terms with a p-value greater than 0.05, and then performing factor regression analysis again until there are no factor terms with a p-value greater than 0.05, thereby obtaining the regression equation between the response variable and the experimental factors.

[0013] Based on the above technical means, the accuracy of regression analysis can be improved by eliminating factor terms with P-values ​​greater than 0.05, thereby further improving the accuracy of the assessment results of internal stress in injection molded parts.

[0014] Furthermore, the step of applying conditional constraints to the key factors based on the response relationship to obtain the optimal value range of the key factors includes: obtaining the optimal solution for each key factor based on the expected value of the internal stress of the injection molded part and the response relationship.

[0015] Based on the above technical means, the key factors can be optimized, and the injection molded parts can be evaluated based on the optimal solution of each key factor, which simplifies the evaluation method and replaces the method of directly using the internal stress of the injection molded parts as the evaluation basis.

[0016] Furthermore, the step of evaluating the three-dimensional model of the injection molded part using the optimal value range of the key factors to obtain the evaluation result of the internal stress of the injection molded part includes: for each key factor, obtaining the optimal value range of the targeted key factor and its value in the mold flow analysis; determining the factor internal stress evaluation result based on the optimal value range and value of the targeted key factor; and obtaining the evaluation result of the internal stress of the injection molded part based on the factor internal stress evaluation result of each of the at least one key factor.

[0017] Based on the above technical means, key factors are used as evaluation factors. When the key factors of the injection molded part meet the requirements, it can be considered that the internal stress of the injection molded part meets the requirements. In this way, it is possible to quickly determine whether the internal stress of the injection molded part meets the requirements, and thus accurately predict stress mark defects. This is intended to avoid stress mark defects on the surface of the injection molded part in advance, thereby achieving the goal of eliminating the post-processing step of covering surface defects of the injection molded part.

[0018] The second objective of this application is to provide a method for producing an injection molded part, comprising: determining a three-dimensional model of the injection molded part; evaluating the internal stress of the injection molded part based on the three-dimensional model of the injection molded part, and obtaining an evaluation result of the internal stress of the injection molded part; the evaluation result of the internal stress of the injection molded part is determined based on at least one key factor for the injection molded part and its corresponding optimal value range, wherein the key factor is determined by performing mold flow analysis on the three-dimensional model of the injection molded part, and the optimal value range is determined by the response relationship between the key factor and the internal stress of the injection molded part; and, if the evaluation result of the internal stress of the injection molded part indicates that the internal stress of the injection molded part meets the requirements, performing injection molding of the injection molded part according to the three-dimensional model of the injection molded part.

[0019] Based on the above-mentioned technical means, stress mark defects can be accurately predicted during the injection molding process based on the response relationship between key factors and internal stress. This aims to avoid stress mark defects on the surface of injection molded parts before injection molding, thereby eliminating the need for post-treatment processes to cover surface defects.

[0020] Furthermore, the production method further includes: when the evaluation result of the internal stress of the injection molded part indicates that the internal stress of the injection molded part does not meet the requirements, updating the three-dimensional model of the injection molded part to obtain an updated three-dimensional model, and returning to the step of evaluating the internal stress of the injection molded part based on the three-dimensional model of the injection molded part to obtain the evaluation result of the internal stress of the injection molded part, until the evaluation result of the internal stress of the injection molded part indicates that the internal stress of the injection molded part meets the requirements.

[0021] Based on the above-mentioned technical means, the internal stress of injection molded parts can be assessed during the design of injection molded parts, thereby initially eliminating some defects and ensuring the quality of injection molded parts.

[0022] Furthermore, the production method also includes: designing a mold, the mold having an exhaust system, an ejection system and a cooling system.

[0023] Based on the aforementioned technical means, the mold is designed to further reduce the internal stress of the injection molded parts.

[0024] Furthermore, the mold includes a core-pulling structure and an insert, wherein the core-pulling structure and the insert are evenly distributed with venting grooves and are designed with venting channels.

[0025] Based on the above technical means, venting grooves and venting channels are set on the mold to further reduce the internal stress of the injection molded parts through venting design.

[0026] Furthermore, the mold has a parting surface, and the ejection system includes an ejector block arranged circumferentially along the outer contour of the parting surface, and ejector pins arranged within the outer contour of the parting surface.

[0027] Based on the above technical means, ejector blocks and ejector pins are used for ejection to further reduce the internal stress of the injection molded parts.

[0028] Furthermore, the step of injection molding the injection molded part according to the three-dimensional model of the injection molded part includes: injection molding process debugging; injection molding the injection molded part based on the process parameters in the injection molding process; evaluating the injection molded part; if the evaluation shows that the injection molded part is unqualified, then return to the step: injection molding process debugging; if the evaluation shows that the injection molded part is qualified, then solidify the process parameters in the injection molding process, or continue to injection mold the injection molded part based on the process parameters in the injection molding process.

[0029] Based on the above technical means, the internal stress of injection molded parts can be further reduced by adjusting the injection molding process.

[0030] Furthermore, the injection molding process debugging includes: injection pressure debugging, using low-pressure injection, with a debugging range of 60-80 bar, controlled in four stages; injection speed debugging, using high-speed injection, with a debugging range of 70%-90%, controlled in four stages; V / P conversion point debugging, low holding pressure requires the conversion point to be later, with filling reaching over 98%; and injection temperature debugging, with material temperature and mold temperature controlled within the recommended range for the material, and debugging from low to high.

[0031] Based on the above technical means, the internal stress of injection molded parts can be further reduced by adjusting the injection pressure, injection speed, V / P conversion point, and injection temperature. At the same time, it also helps to solidify the process parameters in the injection molding process, which is convenient for the subsequent mass production of injection molded parts. Attached Figure Description

[0032] Figure 1 This is a flowchart outlining the injection molding production method in some embodiments of this application; Figure 2 This is a schematic diagram of the structure of the dashboard trim cover in some embodiments of this application; Figure 3 for Figure 2 Isometric view of the dashboard trim cover in the illustrated embodiment; Figure 4 This is a flowchart illustrating the framework for obtaining a 3D model of an injection molded part in some embodiments of this application. Figure 5 This is a comparison table of the physical properties of PC+ABS and PC+ASA materials in some embodiments of this application; Figure 6This is a flowchart illustrating the framework of the evaluation method in some embodiments of this application; Figure 7 This is a schematic diagram of the gating scheme in some embodiments of this application; Figure 8 This is a table identifying key factors in some embodiments of this application; Figure 9 This is a schematic diagram illustrating the relationship between key factors and internal stress of injection molded parts in some embodiments of this application; Figure 10 It shows the high and low levels of key factors; Figure 11 This is a data table used in some embodiments of this application during the DOE simulation model grouping design process; Figure 12 These are illustrations of simulations performed using Moldflow software in some embodiments of this application; Figure 13 This is a data table collected during the grouping design of DOE simulation models in some embodiments of this application; Figure 14 This is a diagram illustrating the significance relationship between the fitted model and the coefficients in some embodiments of this application; Figure 15 This is a diagram illustrating the significance relationship between the fitted model and the coefficients in some embodiments of this application; Figure 16 This is a schematic diagram of the mold venting structure in some embodiments of this application; Figure 17 These are schematic diagrams of mold ejection in some embodiments of this application; Figure 18 This is a schematic diagram of the mold water channel in some embodiments of this application; Figure 19 This is a flowchart illustrating the framework of injection molding of injection-molded parts in some embodiments of this application. Figure 20 This is a table showing the fixed process parameters in some embodiments of this application. Detailed Implementation

[0033] The embodiments of this application will be described below with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. This application can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be understood that the preferred embodiments are only for illustrating this application and are not intended to limit the scope of protection of this application.

[0034] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this application. Therefore, the drawings only show the components related to this application and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0035] This application describes a method for producing injection molded parts that eliminates the need for surface defect masking and maintains a good appearance. Consequently, this method can effectively reduce the production cost of injection molded parts. Of course, it does not limit the use of surface defect masking.

[0036] In some scenarios, this production method can effectively avoid stress mark defects on the surface of injection molded parts without the need for surface defect masking. In other words, it can circumvent the stress mark defect problem caused by the elimination of surface treatment masking.

[0037] Please see Figure 1 , Figure 1 This is a framework flowchart of an injection molded part production method according to some embodiments of this application. The production method may include: Step S101: Determine the three-dimensional model of the injection molded part.

[0038] The 3D model of the injection molded part can be data obtained from a known or self-built database, publicly available data obtained from network devices, data obtained from others, or even a 3D model of the injection molded part designed independently based on the styling intention and structural spatial arrangement. In some embodiments, modeling software can be used to design the 3D model of the injection molded part.

[0039] In some embodiments, the injection-molded part may be a dashboard trim cover for an automobile.

[0040] Please see Figure 2 and Figure 3 , Figure 2 This is a schematic diagram of the structure of the dashboard trim cover in some embodiments of this application. Figure 3 for Figure 2 The illustrated embodiment shows an isometric view of the dashboard trim cover. The dashboard trim cover may have mounting clips 1.

[0041] In some embodiments, please refer to Figure 4 , Figure 4 This is a flowchart outlining the process of obtaining a 3D model of an injection-molded part in some embodiments of this application. Step S101 may include: Step S1011: Design the three-dimensional model of the injection molded part.

[0042] A 3D model of an injection-molded part can be independently designed based on the intended shape and structural space layout. Taking a dashboard trim cover as an example, a design can be created such as... Figure 2 and Figure 3 The image shows a 3D model of the dashboard trim cover.

[0043] Of course, when producing injection molded parts based on existing 3D models of injection molded parts, step S1011 can be omitted. For example, when the 3D model of the injection molded part is data obtained from a known or self-built database, publicly available data obtained from a network device, or data obtained from others, step S1011 can be omitted.

[0044] In step S1011, material selection can be performed to meet the relevant performance and requirements of the injection molded part. Specifically, based on the performance requirements of the injection molded part, a preliminary range of materials can be determined, and material adjustments can be made during the production process.

[0045] For example, based on Figure 2 and Figure 3 The dashboard trim cover shown can be made of materials such as PC (polycarbonate) + ABS (acrylonitrile-butadiene-styrene copolymer) or PC + ASA (acrylonitrile-styrene-acrylate terpolymer) based on heat resistance and weather resistance requirements. For example, while meeting the general performance requirements of injection molded parts, materials can be selected based on requirements to increase flowability, i.e., melt flow index (MFI / MFR).

[0046] In some embodiments, please refer to Figure 5 , Figure 5 This table compares the physical properties of PC+ABS and PC+ASA materials in some embodiments of this application. Since PC+ABS generally has poor weather resistance, this can be addressed by masking surface defects, thus enhancing overall weather resistance. However, based on the production method, stress mark defects on the injection molded part surface can be effectively avoided without surface defect masking. Therefore, due to the limitation of not performing surface defect masking, the PC+ASA material with excellent weather resistance can be selected.

[0047] In step S1011, the structure of the injection molded part can be designed, such as setting the wall thickness, size, and shape. In some embodiments, the wall thickness can be designed to be 2.5-3.0 mm; additionally, from a cost perspective, the wall thickness design tends to be thinner. In some scenarios, based on... Figure 2 and Figure 3The dashboard trim cover shown can be designed with different wall thicknesses; for example, for cost considerations, the main wall thickness of the dashboard trim cover can be designed to be 2.5 mm.

[0048] In step S1011, the spacing between mounting points can be designed. The more mounting points there are, the more complex the structure of the injection molded part will be, and the more obvious the corresponding surface defects will be. For example, stress mark defects will become more obvious with the increase of mounting points.

[0049] While ensuring the reliability of injection molded parts assembly, design the spacing as large as possible to reduce mounting points. For example, it can be designed... Figure 2 and Figure 3 The spacing between mounting points (e.g., mounting clip 1) on the dashboard trim cover. For example, the mounting point spacing may not exceed 220 mm.

[0050] In step S1011, reinforcing ribs can be designed. The more and / or taller the reinforcing ribs, the more noticeable the surface defects of the injection molded part. For example, stress mark defects become more pronounced with more and / or taller reinforcing ribs.

[0051] For example Figure 2 and Figure 3 Reinforcing ribs can be designed at the mounting points (such as mounting clip 1) on the instrument panel trim cover. Of course, reinforcing ribs can also be designed in other areas as needed, or they can be omitted.

[0052] Step S1012: Perform computer-aided engineering topology optimization on the 3D model of the injection molded part.

[0053] Computer-aided engineering (CAE) topology optimization can meet design requirements and manufacturing feasibility requirements, especially under the premise of meeting performance constraints, to achieve efficient and lightweight structures and improve performance.

[0054] Internal stress in injection molded parts can exist in certain structures such as reinforcing ribs. Therefore, computer-aided engineering topology optimization can effectively avoid internal stress in injection molded parts and minimize it as much as possible. Please combine this with... Figure 2 and Figure 3 The dashboard trim cover may have a mounting clip 1, at which a reinforcing rib may be present. Step S1012 can be performed to optimize the profile and structure. For example, the reinforcing rib may be optimized, replacing it as much as possible to reduce internal stress.

[0055] Step S1013: Perform performance analysis and evaluation on the optimized 3D model of the injection molded part.

[0056] In step S1013, the stiffness, strength, and thermal deformation of the three-dimensional model of the injection molded part can be analyzed and evaluated to determine whether the performance of the injection molded part meets the standards. Injection molded parts that meet the performance standards have higher quality.

[0057] Understandably, if the optimized 3D model of the injection molded part fails the performance analysis evaluation after the evaluation, that is, the performance of the injection molded part does not meet the standards, then step S1011 can be continued to redesign or change the 3D model of the injection molded part.

[0058] Of course, based on the optimized 3D model of the injection molded part, the results of performance analysis and evaluation show that the performance of the injection molded part meets the standards, and then subsequent steps such as step S102 can be performed.

[0059] The execution of step S1013 allows for performance analysis and evaluation during the design of injection molded parts, thereby initially eliminating some defects and ensuring the quality of injection molded parts.

[0060] Step S102: Based on the three-dimensional model of the injection molded part, evaluate the internal stress of the injection molded part and obtain the evaluation result of the internal stress of the injection molded part.

[0061] The evaluation method for assessing the internal stress of the injection molded part in step S102 can form an internal stress assessment method for injection molded parts. It aims to assess the internal stress of the injection molded part, measure the internal stress of the injection molded part through the evaluation method, and provide a basis for further improving the three-dimensional model of the injection molded part, so as to avoid the problem of stress mark defects in the injection molded part caused by the removal of surface treatment masking.

[0062] In some embodiments, please refer to Figure 6 , Figure 6 This is a flowchart illustrating the framework of the evaluation method in some embodiments of this application. The evaluation method may include: Step S1021: Determine the three-dimensional model of the injection molded part.

[0063] For details, please refer to step S101, which will not be repeated here. In addition, in some embodiments, since step S101 exists, step S1021 can be omitted.

[0064] Step S1022: Perform mold flow (MF) analysis on the three-dimensional model of the injection molded part to determine at least one key factor for the internal stress of the injection molded part.

[0065] In step S1022, the position and number of gates can be set. For example, based on... Figure 2 and Figure 3The dashboard trim cover shown is 1050mm long and 100mm wide. Based on the material flow length of the dashboard trim cover, a multi-point sequence valve can be designed. This means that in the injection molding process, the sequence valve controls the injection timing of multiple independent gates to precisely control the multi-gate hot runner mold and ensure consistent molding quality of the injection molded parts. Please refer to [link / reference]. Figure 7 , Figure 7 This is a schematic diagram of the gating scheme in some embodiments of this application. The diagram shows that there are 5 gating gates 2, which can be designed as a five-point sequence valve corresponding to each of the 5 gating gates 2. In other embodiments, the specific location and number of multi-point sequence valves are determined based on the structural characteristics of the injection molded part, and are not limited to the embodiments listed herein.

[0066] In mold flow analysis, Moldflow software can be used to simulate the injection molding process, or other simulation software that can perform mold flow analysis can be used.

[0067] In step S1022, process parameters can be adjusted using software such as Moldflow, or result parameters corresponding to the process parameters can be obtained. Process parameters include melt temperature, mold temperature, injection time, injection pressure, holding pressure, holding time, cooling time, etc., and may also include material selection and material parameters. Result parameters may include volume shrinkage rate, temperature gradient, freezing time difference, residual stress, shear rate, V / P conversion pressure, shrinkage factor, internal stress, etc., and may also include others.

[0068] In some embodiments, step S1022 may include: Step S10221: Perform mold flow analysis on the three-dimensional model of the injection molded part to obtain at least one candidate factor affecting the internal stress of the injection molded part.

[0069] In some embodiments, candidate factors are the result parameters of the injection molded part's response to the injection molded part's process parameters in mold flow analysis.

[0070] Step S10222: Determine at least one key factor for the internal stress of the injection molded part from at least one candidate factor.

[0071] In some embodiments, key factors may include volume shrinkage rate V, temperature gradient T, freezing time difference S, residual stress δ, and of course, others.

[0072] In some embodiments, step S10222 may include: Step S10223: For each candidate factor, determine the quality score of the candidate factor; the quality score is used to characterize the importance of the candidate factor relative to the internal stress of the injection molded part.

[0073] Step S10224: Based on the quality score corresponding to each of the at least one candidate factor, determine at least one key factor for the internal stress of the injection molded part from the at least one candidate factor.

[0074] In some embodiments, step S10222 may identify key factors affecting the internal stress of the injection molded part through a Quality Function Deployment (QFD) analysis system.

[0075] In some embodiments, in step S10222, the injection molded part is analyzed using a QFD analysis system, and process parameters or result parameters are used as candidate factors. Key factors affecting the internal stress of the injection molded part are then identified from these candidate factors. Specifically, each candidate factor is scored using a house of quality to determine its significance level.

[0076] Furthermore, based on the data reflected in the House of Quality, several factors with high proportions were selected as key factors.

[0077] Please see Figure 8 , Figure 8 This is a table identifying key factors in some embodiments of this application. Figure 8 In this process, using the outcome parameters as candidate factors for identification can identify key factors. Figure 8 For example, based on the data reflected in the House of Quality, the top four candidate factors with the highest proportions are selected as key factors. Key factors may include volume shrinkage rate V, temperature gradient T, freezing time difference S, and residual stress δ.

[0078] Step S1023: Perform experimental design analysis on at least one key factor to obtain the internal stress of the injection molded part, and establish the response relationship between at least one key factor and internal stress.

[0079] In step S1023, key factors can be used as experimental factors to conduct Design of Experiment (DOE) analysis, and the internal stress of the injection molded part can be used as a response variable to establish the response relationship between the experimental factors and the response variable.

[0080] In some embodiments, step S1023 may include: Step S10231: Using the at least one key factor as an experimental factor, conduct experimental design analysis, and use the internal stress of the injection molded part as a response variable to obtain the experimental design results.

[0081] Please see Figure 9 , Figure 9 This diagram illustrates the relationship between key factors and internal stress in injection-molded parts in some embodiments of this application. Figure 9In injection molding, key factors such as volume shrinkage rate V, temperature gradient T, freezing time difference S, and residual stress δ can affect internal stress P. Therefore, in order to adjust internal stress P and overcome stress mark defects in injection molded parts, this can be achieved by adjusting key factors such as volume shrinkage rate V, temperature gradient T, freezing time difference S, and residual stress δ.

[0082] In step S10231, the high and low levels of key factors can be defined. In some embodiments, see [reference needed]. Figure 10 , Figure 10 It shows the high and low levels of key factors. Figure 9 In this model, the key factors are V (1, 6), T (0, 20), S (0, 10), and δ (1, 40), which allows for the adjustment of internal stress P within the range of key factors, thus overcoming stress mark defects in injection molded parts.

[0083] In step S10231, the DOE simulation model can be designed in groups. For example, the system can be designed using Minitab (e.g., Minitab Statistical Software), or other software can be used.

[0084] In step S10231, a factorial design is created: at least one key factor is selected as an experimental factor, and the level of each experimental factor is determined to design the experiment. (See also...) Figure 11 , Figure 11 This is a data table for the DOE simulation model grouping design process in some embodiments of this application.

[0085] Furthermore, simulations were performed using Moldflow software to generate 17 combinations of key factors, resulting in different experimental data; then the data were collected. Please refer to [link / reference needed]. Figure 12 and Figure 13 , Figure 12 These are illustrations of simulations performed using Moldflow software in some embodiments of this application. Figure 13 This is a data table collected during the grouping design process of DOE simulation models in some embodiments of this application. In some embodiments, key factors calculated by Moldflow and internal stress P values ​​can be input into Minitab.

[0086] Step S10232: Based on the experimental design results, regression analysis and accuracy verification are performed on the experimental factors and the response variables to obtain the regression equation between the response variables and the experimental factors.

[0087] In step S10232, based on the factor regression analysis results, the significance relationship between the fitted model and each coefficient can be obtained. For factor terms with a P value greater than 0.05, one factor term is eliminated at a time, and the factor regression analysis is repeated until there are no factor terms with a P value greater than 0.05, thus obtaining the regression equation between the response variable and the experimental factor.

[0088] Please see Figure 14 and Figure 15 , Figure 14 This is a diagram illustrating the significance relationship between the fitted model and the coefficients in some embodiments of this application. Figure 15 This is a diagram illustrating the significance relationship between the fitted model and the coefficients in some embodiments of this application. Figure 14 The data shown contains factor terms with p-values ​​greater than 0.05. After removing factor terms with p-values ​​greater than 0.05, we can obtain... Figure 15 The data shown. Among them, based on Figure 15 The data can be fitted to obtain the regression equation P=-10.41+3.525V+2.449T+3.447S+1.680δ+2.243T*S+3.455S*δ+1.655T*S*δ.

[0089] In some embodiments, factor regression analysis results can be performed based on Minitab to obtain the regression equation.

[0090] Step S1024: Based on the response relationship, apply conditional constraints to the key factors to obtain the optimal range of values ​​for the key factors.

[0091] By applying conditional constraints to key factors based on response relationships, the optimal value range for each key factor can be obtained. Specifically, the optimal solution for each key factor can be obtained based on the expected value of the internal stress of the injection molded part and its response relationship.

[0092] In some embodiments, factors can be region-constrained in Minitab, and the results (i.e., stress values ​​obtained from response relationships) can be analyzed to ultimately derive evaluation criteria (i.e., the optimal range of values ​​for key factors). The optimal range of values ​​for key factors is determined based on the requirements of the internal stress of the injection molded part, and more importantly, to avoid stress mark defects in the injection molded part caused by the removal of surface treatment masking.

[0093] In some embodiments, the optimal range of values ​​for the key factors is: V(1,4), T(0,9), S(0,5), δ(1,25).

[0094] Step S1025: Evaluate the three-dimensional model of the injection molded part using the optimal value range of the key factors to obtain the evaluation results of the internal stress of the injection molded part.

[0095] During the evaluation process, the values ​​of key factors in the mold flow analysis process can be compared with the optimal range of key factors to ensure that the values ​​of key factors are within the optimal range of key factors, thereby adjusting the internal stress P to effectively overcome the stress mark defects of injection molded parts.

[0096] Furthermore, step S1025 may include: Step S10251: For each key factor, obtain the optimal value range and its numerical value in the model flow analysis; based on the optimal value range and numerical value of the key factor, determine the internal stress evaluation result of the factor. Step S10252: Based on the factor internal stress evaluation results of at least one key factor, obtain the evaluation results of the internal stress of the injection molded part. In step S1025, the values ​​of key factors can be obtained in the model flow analysis. For details, please refer to step S1022, which will not be elaborated here.

[0097] In step S1025, the three-dimensional model of the injection molded part can be evaluated using the optimal value ranges of four key factors: volume shrinkage rate V, temperature gradient T, freezing time difference S, and residual stress δ, to obtain an injection molded part with internal stress meeting the requirements. The optimal value ranges of the four key factors are set based on the internal stress requirements of the injection molded part.

[0098] Step S103: If the evaluation result of the internal stress of the injection molded part indicates that the internal stress of the injection molded part meets the requirements, the injection molded part is injection molded according to the three-dimensional model of the injection molded part.

[0099] When the internal stress of the injection molded part meets the requirements, the stress mark defect caused by the removal of surface treatment masking can be avoided after injection molding. If the internal stress does not meet the requirements, step S101 can be performed to adjust the three-dimensional model of the injection molded part. That is, the production method may also include: Step S104: If the evaluation result of the internal stress of the injection molded part indicates that the internal stress of the injection molded part does not meet the requirements, the three-dimensional model of the injection molded part is updated to obtain the updated three-dimensional model, and the internal stress of the injection molded part is evaluated based on the three-dimensional model of the injection molded part to obtain the evaluation result of the internal stress of the injection molded part (i.e., step S102), until the evaluation result of the internal stress of the injection molded part indicates that the internal stress of the injection molded part meets the requirements.

[0100] Based on the above-mentioned technical means, stress mark defects can be accurately predicted during the injection molding process based on the regression equation between key factors and internal stress. This aims to avoid stress mark defects on the surface of injection molded parts before injection molding, thereby eliminating the need for post-processing steps to cover surface defects.

[0101] In some embodiments, the production method may further include: Step S105: Design the mold, which has an exhaust system, an ejection system and a cooling system.

[0102] The mold is designed in step S105 to further reduce the internal stress of the injection molded part.

[0103] In some embodiments, step S105 may be performed before step S103. In some embodiments, step S105 may be performed after step S102.

[0104] In some embodiments, the exhaust system design: see [link / reference] Figure 16 , Figure 16 This is a schematic diagram of the mold venting structure in some embodiments of this application. The mold may include a core-pulling structure and an insert 4. The core-pulling structure and the insert 4 have evenly distributed venting grooves 5 and are designed with venting channels 6 to allow gas to be drawn out from the cavity. In some embodiments, the size of the venting grooves 5 is 0.05mm * 5mm. In some embodiments, the size of the venting channel 6 is 1mm * 5mm. Further, Figure 16 The sloping top 3 (i.e., the core-pulling structure) is also shown.

[0105] In some embodiments, each doghouse structure (i.e., the connection and fixing structure of plastic parts and sheet metal) is provided with an exhaust channel 6.

[0106] In some embodiments, the ejection system design is described in the following reference: Figure 17 , Figure 17 These are schematic diagrams of mold ejection in some embodiments of this application. Figure 17 In this mold, the mold has a parting surface, and the ejection system includes ejector blocks 7 arranged circumferentially along the outer contour of the parting surface, and ejector pins 8 arranged within the corresponding outer contour of the parting surface. The cooperation of the ejector blocks 7 and ejector pins 8 can achieve ejection balance and reduce internal stress in the injection molded part. In some embodiments, the distance between the two ejector blocks 7 is less than or equal to 100 mm. In some embodiments, the diameter of the ejector pins 8 is 8 mm. In some embodiments, the distance between the ejector pins 8 and the injection molded part is less than or equal to 5 mm.

[0107] In some embodiments, cooling system design: see [link / reference] Figure 18 , Figure 18 This is a schematic diagram of the mold water channel in some embodiments of this application. The diameter of the water channel can be 12mm. The water channel can be designed according to the shape of the injection molded part, and the water channel can be designed in segments along the length direction of the injection molded part. The distance between the water channel and the surface of the injection molded part is 12-20mm, and the spacing between the water channels is 48-58mm. The water channel is designed in groups along the length direction, which can make the cooling as uniform as possible and reduce the internal stress of the injection molded part.

[0108] In some embodiments, please refer to Figure 19 , Figure 19 This is a flowchart illustrating the basic process of injection molding of parts in some embodiments of this application. Step S103 may include: Step S106: Injection molding process debugging.

[0109] In some embodiments, step S106 may include adjusting injection pressure, adjusting injection speed, adjusting V / P conversion point, and adjusting injection temperature, etc. Of course, it may also include other process adjustments, which will not be elaborated here.

[0110] In some embodiments, injection pressure adjustment can be performed using low-pressure injection, with an adjustment range of 60-80 bar, controlled in four segments. In some embodiments, the adjustment range can be divided into multiple segments, using a "low-high-low" setting, with the specific value adjusted according to actual conditions. In some embodiments, the adjustment range can be divided into four segments: the first segment is 60-70 bar, the second segment is 70-75 bar, the third segment is 75-80 bar, and the fourth segment is 65-70 bar.

[0111] In some embodiments, injection speed adjustment can be implemented using high-speed injection, with an adjustment range of 70%-90%, controlled in four segments. In some embodiments, the adjustment range can be divided into multiple segments, using a "low-high-low" setting, with specific values ​​adjusted according to actual conditions. In some embodiments, the adjustment range can be divided into four segments: the first segment is 70%, the second segment is 70-80%, the third segment is 80-90%, and the fourth segment is 70%. The percentages within the adjustment range represent the proportion of the current system flow rate of the injection molding machine to the maximum rated flow rate.

[0112] In some embodiments, V / P switching point adjustment: the low holding voltage requires the switching point to be later, and the filling reaches more than 98%; In some embodiments, the injection temperature is adjusted by controlling the material temperature and mold temperature within the recommended range for the material, gradually increasing the temperature.

[0113] In some embodiments, the adjustment range can be divided into multiple segments, adjusted from low to high. In some embodiments, the first to sixth segments of the injection molding machine screw temperature are set to 250°C, 245°C, 245°C, 240°C, 230°C, and 220°C, respectively; the hot runner temperature is set to 250°C; and the mold temperature is set to 80°C.

[0114] The execution of step S106 can further reduce the internal stress of the injection molded parts based on the adjustment of injection pressure, injection speed, V / P conversion point, and injection temperature. It also helps to solidify the process parameters in the injection molding process, which is convenient for the subsequent mass production of injection molded parts.

[0115] Step S107: Inject the part into the injection mold based on the process parameters in the injection molding process (i.e., the process parameters determined in step S106).

[0116] Step S108: Evaluating the injection molded part obtained by injection molding.

[0117] Quality assessment of the injection molded part can be performed based on assessment methods well known to those skilled in the art, and in particular, assessment of the internal stress of the injection molded part is required.

[0118] Step S109: If the injection molded part is assessed as qualified, curing the process parameters in the injection molding process. Please refer to Figure 20 , Figure 20 is a display diagram of a process parameter fixing table in some embodiments of the present application. In addition, the state of the injection molded part can also be locked, and a sealed sample part is signed.

[0119] Of course, in step S109, injection molding of injection molded parts can also be continued based on the process parameters in the injection molding process.

[0120] In addition, if the injection molded part is assessed as unqualified, return to step S106: re-commission the injection molding process. That is, step S103 may include: if the injection molded part is assessed as unqualified, re-commission the injection molding process, and then perform step S107.

[0121] In the present application, after the post-processing masking process is canceled for injection molded parts, systematic design is carried out to avoid stress mark defects. Through scientific analysis of the whole process from material performance adjustment, product structure CAE topology optimization, MF analysis and scheme design, mold structure and molding process, especially in the MF analysis process, an interactive evaluation model of volume shrinkage, temperature gradient, freezing time difference and residual stress is introduced to accurately predict stress mark defects.

[0122] The above embodiments are merely preferred embodiments for fully illustrating the present application, and the protection scope of the present application is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art on the basis of the present application all fall within the protection scope of the present application.

Claims

1. A method for evaluating the internal stress of injection molded parts, characterized in that, include: Determine the 3D model of the injection molded part; Mold flow analysis is performed on the three-dimensional model of the injection molded part to determine at least one key factor for the internal stress of the injection molded part. Experimental design analysis is performed on at least one key factor to obtain the internal stress of the injection molded part, and the response relationship between the at least one key factor and the internal stress is established. Based on the response relationship, conditional constraints are applied to the key factors to obtain the optimal value range of the key factors; The three-dimensional model of the injection molded part is evaluated using the optimal value range of the key factors to obtain the evaluation results of the internal stress of the injection molded part.

2. The evaluation method according to claim 1, characterized in that, The process of performing mold flow analysis on the three-dimensional model of the injection molded part to determine at least one key factor affecting the internal stress of the injection molded part includes: Mold flow analysis is performed on the three-dimensional model of the injection molded part to obtain at least one candidate factor affecting the internal stress of the injection molded part. The candidate factor is the result parameter of the injection molded part responding to the process parameters of the injection molded part in the mold flow analysis. At least one key factor for the internal stress of the injection molded part is determined from the at least one candidate factor.

3. The evaluation method according to claim 2, characterized in that, Determining at least one key factor for the internal stress of the injection molded part from the at least one candidate factor includes: For each of the candidate factors, a quality score is determined for that candidate factor; the quality score is used to characterize the importance of the candidate factor relative to the internal stress of the injection molded part. Based on the quality scores corresponding to each of the at least one candidate factor, at least one key factor for the internal stress of the injection molded part is determined from the at least one candidate factor.

4. The evaluation method according to claim 1, characterized in that, The experimental design analysis of the at least one key factor to obtain the internal stress of the injection molded part, and the establishment of the response relationship between the at least one key factor and the internal stress, includes: The at least one key factor is used as an experimental factor for experimental design analysis, and the internal stress of the injection molded part is used as a response variable to obtain the experimental design results. Based on the experimental design results, regression analysis and accuracy verification were performed using the experimental factors and the response variables to obtain the regression equations between the response variables and the experimental factors.

5. The evaluation method according to claim 4, characterized in that, Based on the experimental design results, regression analysis and accuracy verification are performed using the experimental factors and the response variable to obtain the regression equation between the response variable and the experimental factors, including: Factor regression analysis was performed on the response variable and the experimental factor to obtain the factor regression analysis results; Based on the factor regression analysis results, the significance relationship between the fitted model and each coefficient is obtained. For factor terms with a P-value greater than 0.05, one factor term is eliminated at a time, and the factor regression analysis is repeated until there are no factor terms with a P-value greater than 0.05, thus obtaining the regression equation between the response variable and the experimental factor.

6. The evaluation method according to claim 1, characterized in that, The process of applying conditional constraints to the key factors based on the response relationship to obtain the optimal value range of the key factors includes: Based on the expected value of the internal stress of the injection molded part and the response relationship, the optimal solution for each of the key factors is obtained.

7. The evaluation method according to claim 1, characterized in that, The evaluation of the three-dimensional model of the injection molded part using the optimal value range of the key factors to obtain the evaluation result of the internal stress of the injection molded part includes: For each of the key factors, obtain the optimal value range and the numerical value of the key factor in the model flow analysis; based on the optimal value range and numerical value of the key factor, determine the stress evaluation result of the factor. The internal stress assessment result of the injection molded part is obtained based on the factor internal stress assessment results of each of the at least one key factor.

8. A method for producing injection molded parts, characterized in that, include: Determine the 3D model of the injection molded part; Based on the three-dimensional model of the injection molded part, the internal stress of the injection molded part is evaluated, and the evaluation result of the internal stress of the injection molded part is obtained. The evaluation result of the internal stress of the injection molded part is obtained based on at least one key factor for the injection molded part and the corresponding optimal value range. The key factor is determined by performing mold flow analysis on the three-dimensional model of the injection molded part, and the optimal value range is determined by the response relationship between the key factor and the internal stress of the injection molded part. If the evaluation result of the internal stress of the injection molded part indicates that the internal stress of the injection molded part meets the requirements, the injection molded part is injection molded according to the three-dimensional model of the injection molded part.

9. The production method according to claim 8, characterized in that, The production method further includes: If the evaluation result of the internal stress of the injection molded part indicates that the internal stress of the injection molded part does not meet the requirements, the three-dimensional model of the injection molded part is updated to obtain an updated three-dimensional model, and the process of evaluating the internal stress of the injection molded part based on the three-dimensional model of the injection molded part and obtaining the evaluation result of the internal stress of the injection molded part is repeated until the evaluation result of the internal stress of the injection molded part indicates that the internal stress of the injection molded part meets the requirements.

10. The production method according to claim 8, characterized in that, The production method further includes: The mold is designed to include an exhaust system, an ejection system, and a cooling system. The mold includes a core-pulling structure and inserts. The core-pulling structure and inserts are evenly distributed with venting grooves and are designed with venting channels. The mold has a parting surface. The ejection system includes top blocks arranged circumferentially along the outer contour of the parting surface and ejector pins arranged within the outer contour of the parting surface.

11. The production method according to claim 8, characterized in that, The injection molding of the injection molded part according to the three-dimensional model of the injection molded part includes: Injection molding process debugging; The injection molded part is injection molded based on the process parameters in the injection molding process. The injection-molded part is evaluated; If the injection molded part is deemed unqualified, return to step: Injection molding process debugging; If the injection molded part is deemed qualified, the process parameters in the injection molding process are solidified, or the injection molding of the part continues based on the process parameters in the injection molding process.

12. The production method according to claim 11, characterized in that, The injection molding process debugging includes: Injection pressure adjustment uses low-pressure injection, with an adjustment range of 60-80 bar, and is controlled in four stages. Injection speed adjustment: High-speed injection is adopted, and the adjustment range is 70%-90%, controlled in four stages. For V / P conversion point adjustment, the low holding pressure requires the conversion point to be further back, and the filling should reach more than 98%; Injection molding temperature adjustment involves controlling the material temperature and mold temperature within the recommended range for the material, adjusting gradually from low to high.

13. An injection molded part, characterized in that, The injection molded part is configured to be evaluated using the internal stress evaluation method for injection molded parts as described in any one of claims 1-7, and is obtained when the evaluation result of the internal stress of the injection molded part indicates that the internal stress of the injection molded part meets the requirements; or, the injection molded part is configured to be produced using the production method as described in claims 8-12.

Images