3D printing child chair forming method based on ergonomics and finite element simulation

Abstract

The present application relates to the technical field of children's seat, and particularly relates to a 3D printing children's seat forming method based on ergonomics and finite element simulation, which adopts PETG material and has continuous contour and zero filling structure. Compared with the prior art, the present application establishes a children's seat collaborative design system integrating space optimization, function adaptation and FDM printing, and through data analysis, determines the optimal ergonomic parameter combination of the seat designed for preschool children, and realizes FDM forming and preparation of the preschool children's seat.

Description

Technical Field

[0001] This invention relates to the field of children's chair technology, and in particular to a 3D printing method for children's chairs based on ergonomics and finite element simulation. Background Technology

[0002] With the acceleration of urbanization, small apartments (<90 m²) have become the main form of urban housing, making efficient space utilization a core requirement of modern furniture design. The essence of space-optimized furniture design lies in minimizing space occupation through integrated and functionally consistent design schemes, while ensuring structural safety and usability. In such living environments, children's furniture must not only meet the physiological comfort and safety needs of young users but also adapt to the inherent space constraints of small apartments.

[0003] However, traditional child car seats suffer from limitations such as limited functionality, poor customizability, and insufficient precision in matching ergonomic parameters. The concept of space optimization design is underutilized in children's furniture research, and a quantitative relationship between spatial needs and functional adaptation has not yet been established. Furthermore, ergonomic parameter optimization for preschool children is inadequate, the finite element method is rarely used in children's furniture research, and there is a lack of research on structural optimization pathways for FDM-manufactured child car seats.

[0004] It can be seen that existing research lacks an integrated framework for space-optimized child seats, and fails to address the synergistic requirements of space efficiency, ergonomic precision, structural safety, and FDM-PETG process compatibility, thus hindering the development of innovative child seats for small apartments.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] To address the shortcomings of the existing technology, this invention provides a 3D printing method for children's chairs based on ergonomics and finite element simulation. This method constructs an integrated collaborative design system of space optimization, structural optimization, and FDM process, enabling the integrated manufacturing of lightweight, multifunctional children's chairs.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for molding a 3D-printed children's chair based on ergonomics and finite element simulation includes the following steps: S100. Based on the raw data of percentile height of children aged 3-6 years and 9 months, a weighted model was performed to determine the dimensional data of the standardized ergonomic shape of the chair. The dimensional data includes seat width, seat height, backrest height, effective seat depth, seat tilt angle, and backrest tilt angle; S200. Based on the stated dimensional parameters, construct multiple sets of integrated seat parametric 3D models with no internal filling and only closed multi-layered outer walls for support. Each set of 3D models has a different number of outer wall rings and wall thickness. S300 performs finite element static load simulation on each group of three-dimensional models and outputs the simulation indicators of the maximum displacement, maximum equivalent stress, and overall safety factor of each group of three-dimensional models. S400: Using PETG consumables, solid samples of each group of three-dimensional models are printed out using FDM equipment, and the weight of PETG consumables and molding time of each group of solid samples are recorded at the same time. S500. Conduct static load tests on the entire machine for each group of physical samples to obtain the fitted stiffness of the entire machine. S600: Real-person sitting pressure distribution test was conducted on children aged 3 to 6 years and 9 months to obtain the uniformity of seat pressure. S700, based on the simulation indicators of maximum displacement, overall safety factor, PETG material weight, molding time, overall fitting stiffness, and seat pressure uniformity, obtains the optimal outer wall thickness and number of outer wall rings, and finally completes the mass production of integrated children's chairs.

[0008] In step S100: The specific dimensions are as follows: seat width 320mm, effective seat depth 260mm, seat height 260mm, effective backrest height 230mm, seat angle 5°, backrest angle 15°, and overall outer dimensions of the seat are 444mm×320mm×479mm.

[0009] In step S200: The number of outer wall rings and wall thickness of each group of 3D models are as follows: 0.8mm wall thickness corresponds to 3 outer wall printing paths, 6.4mm wall thickness corresponds to 4 outer wall printing paths, and 8.0mm wall thickness corresponds to 5 outer wall printing paths.

[0010] In step S300: The assigned parameters for PETG material are: density 1290 kg / m³, elastic modulus 1695 MPa, Poisson's ratio 0.35, and yield strength of printed parts 36 MPa.

[0011] In step S400: The molding process parameters for the FDM equipment are: nozzle constant temperature 240℃, molding base plate constant temperature 75℃, layer thickness 0.8mm, and outer wall printing speed 60mm / s.

[0012] In step S500: The specific method for static load testing of the whole machine is as follows: the displacement control loading rate is 5mm / min, the loading range is 20~1300N, the load is held for 30s after reaching 1300N, the contact interference data below 50N are eliminated, and the fitting stiffness of the whole machine is calculated by fitting the load and displacement curves with linear equations. The linear equation is: ; The overall fitting stiffness is: ; In the above formula: F is the applied load, δ is the corresponding displacement, a is the fitting slope, b is the intercept, and k fit This is the overall fitting stiffness of the machine.

[0013] In step S600: Before the real-person seating pressure distribution test, unqualified physical samples were rejected. The criteria for rejection were: simulation index of overall safety factor <1.1 or maximum displacement of seat surface under static load of 1300N >25mm.

[0014] Compared with existing technologies, the 3D printing method for children's chairs based on ergonomics and finite element simulation provided by this invention has the following technical advantages: 1. Based on national standard anthropometric data, this invention establishes a quantitative method for ergonomic parameters of preschool children's seats, realizing the transformation of children's physiological data into core functional parameters of seat design.

[0015] 2. This invention proposes a hyperboloid structure optimization strategy and verifies its effectiveness in improving load dispersion and stress uniformity through finite element simulation.

[0016] 3. This invention constructs an integrated collaborative design system of space optimization, structural optimization, and FDM process, realizing the integrated manufacturing of lightweight and multifunctional child seats.

[0017] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described in detail below. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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] This invention provides a method for molding a 3D-printed children's chair based on ergonomics and finite element simulation, comprising the following steps: S100. Based on the raw data of percentile height of children aged 3-6 years and 9 months, a weighted model was performed to determine the dimensional data of the standardized ergonomic shape of the chair. Specifically, using the height data of preschool children (3–6 years and 9 months) from WS / T 423–2022 "Reference Standards for Growth and Development of Children Under 7 Years Old", the weighted average height of preschool boys and girls was calculated. The calculation process is as follows: For children of age A, whose height is lower than the median percentile for that age, where A takes values ​​of 1, 2, 3, 4, 5, 6, and 7, the weighted average height of children of age A is calculated as follows:

[0020] For example, if a 6-year-9-month-old preschool girl's height is below the 3rd percentile, she is denoted as P3. If her height is below the 10th percentile, she is denoted as P. 10 (Table 1).

[0021] Table 1. Percentile values ​​of height / length in children aged 6 years and 9 months

[0022] The weighted average length / height of a 6-year-9-month-old girl is:

[0023] The average height of boys and girls aged 3 to 6 years and 9 months was calculated using a weighted average method to obtain the target height range. The weighted average heights of boys and girls aged 3 to 6 years and 9 months were 117.56 cm and 115.93 cm, respectively, with a combined average height of 116.75 cm.

[0024] Using height measurement data, and aiming for optimal fit and comfort, the core parameters of the chair were determined after literature review, referencing GB / T 3976-2014 "Functional Dimensions and Technical Requirements for School Desks and Chairs". These parameters are seat width (b), seat height (h1), height from the top edge of the backrest to the seat (h2), effective seat depth (t), seat tilt angle (α), and backrest tilt angle (β). The optimal combination is b = 320 mm, h1 = 260 mm, h2 = 230 mm, t = 260 mm, β = 15°, and α = 5°.

[0025] S200. Based on the stated dimensional parameters, construct multiple sets of integrated seat parametric 3D models with no internal filling and only closed multi-layered outer walls for support. Each set of 3D models has a different number of outer wall rings and wall thickness. In the steps described above, the parametric modeling of the child car seat was completed using Rhino software. During the modeling process, ergonomic parameters were used as core constraints to ensure that the seat dimensions matched the physiological characteristics of preschool children. A series of quality checks and verifications were conducted to ensure the morphological accuracy of the integrated structure. After modeling was completed, the model was exported in STL format, which can be directly used for subsequent structural mechanics optimization analysis and is compatible with FDM processes. This achieves efficient integration between design, simulation, and manufacturing.

[0026] In terms of structural design, FDM manufacturing employs a continuous profile, zero-fill strategy, with the outer wall thickness directly providing the structural load-bearing capacity. Wall thickness was selected as the sole design variable, with three levels set: 4.8 mm, 6.4 mm, and 8.0 mm, corresponding to 3, 4, and 5 profile paths (i.e., the number of outer wall rings), respectively.

[0027] Based on the above parameters, a 3D model of the chair was created, with overall dimensions of 444 mm x 320 mm x 479 mm (length x width x height). All models differed only in wall thickness, while other geometric parameters remained consistent to ensure comparability in subsequent simulations and experiments. The completed model was exported in STEP (.stp) format for finite element analysis and 3D printing.

[0028] S300 performs finite element static load simulation on each group of three-dimensional models and outputs the simulation indicators of the maximum displacement, maximum equivalent stress, and overall safety factor of each group of three-dimensional models. In the above steps, the 3D model of the preschool chair is imported into the Static Structure Analysis module of SolidWorks Simulation in STEP (.stp) format. To ensure a balance between computational accuracy and efficiency, an adaptive mesh generation strategy based on geometric curvature is used to discretize the model.

[0029] The maximum element size was set to 10 mm, and automatic local mesh refinement was performed in high curvature regions to improve the accuracy of stress and deformation prediction in critical load-bearing areas. Mesh convergence studies were conducted to ensure that the results were independent of mesh density.

[0030] The maximum element size was set to 10 mm, and automatic local mesh refinement was performed in high curvature regions to improve the accuracy of stress and deformation prediction in critical load-bearing areas. Mesh convergence studies were conducted to ensure that the results were independent of mesh density.

[0031] Boundary conditions: The bottom support surface of the chair is defined as a fixed constraint to simulate stable contact between the chair and a rigid ground, thereby eliminating rigid body motion during the simulation. To simulate realistic loading conditions, a uniformly distributed vertical load of 1300 N is applied to the seat surface. The load magnitude is determined according to the requirements of GB / T 10357.3-2013 "Mechanical Properties of Furniture - Part 3: Strength and Durability of Chairs and Stools" and GB / T 32487-2016 "General Technical Conditions for Plastic Furniture".

[0032] Material properties: The material is assumed to be homogeneous and isotropic, exhibiting linear elastic behavior. The mechanical properties of PETG are defined in SolidWorks Simulation as follows: density 1290 kg / m3, elastic modulus 1695 MPa, Poisson's ratio 0.35.

[0033] In finite element analysis, wall thickness is considered the only variable. Static structural simulations were performed on chair models with different wall thicknesses to evaluate their seat load-bearing capacity. The simulation output includes displacement contour plots, von Mises stress distribution, and structural stiffness.

[0034] Based on the above results, key areas such as stress concentration zones, locations of maximum displacement, and stiffness distribution patterns were identified. The influence of wall thickness on the overall structural stiffness and load-bearing capacity of the chair was systematically analyzed.

[0035] In addition, the numerical results obtained from finite element simulation were compared with experimental data to assess the consistency of deformation and stiffness trends and to reveal the mechanism by which wall thickness affects structural performance.

[0036] Table 2 Comparison of Finite Element Analysis Results of Preschool Children's Chairs with Different Wall Thicknesses

[0037] S400: Using PETG consumables, solid samples of each group of three-dimensional models are printed out using FDM equipment, and the weight of PETG consumables and molding time of each group of solid samples are recorded at the same time. To ensure the repeatability and reliability of the experimental data, two specimens were manufactured for each wall thickness (4.8 mm, 6.4 mm, and 8.0 mm). Each specimen was tested three times, for a total of 18 tests. During the manufacturing and testing process, the system recorded key data, including printing time and material consumption, as shown in Table 3. Table 3. Statistics of 3D printing parameters for different wall thicknesses

[0038] S500. Conduct static load tests on the entire machine for each group of physical samples to obtain the fitted stiffness of the entire machine. In the above steps, the static load performance of the chair was evaluated according to standard GB / T 10357.3-2013, Mechanical Properties of Furniture Part 3: Strength and Durability of Chairs and Stools. A vertical static load was applied to the seat surface under the following conditions: Loading Procedure: The specimen was securely fixed on the testing platform of the STM S6.200 universal testing machine to ensure stability during the test. Displacement-controlled loading was used, starting at 20 N and increasing to 1300 N at a constant rate of 5 mm / min. The load was maintained for 30 s to ensure sufficient stress development, and then unloaded to 0 N at the same rate.

[0039] Evaluation criteria: After testing, the specimen shall be inspected according to the six criteria specified in the standard: (a) component fracture, (b) permanent loosening, (c) displacement change, (d) visible deformation, (e) mechanical damage, and (f) abnormal noise. If any of the above criteria are violated, the specimen shall be deemed unqualified.

[0040] Meanwhile, TestMaster V6.1 software was used to continuously record load-displacement data throughout the loading process.

[0041] To ensure the reliability of the load-displacement data, the original curves were preprocessed before calculating the stiffness. Data with loads below 50 N were excluded to minimize initial contact artifacts caused by incomplete contact between the loading head and the chair surface. The effective loading range of 50–1300 N was retained for subsequent analysis, as this range better represents the structural response of the chair under static load.

[0042] Two independent specimens were fabricated for each wall thickness, and each specimen was tested three times. Descriptive statistics were calculated from repeated measures to assess repeatability. For inferential statistical analysis, the specimen mean was used as the independent statistical unit to avoid spurious replication.

[0043] The statistical results of the static load tests are summarized in Table 4, including peak load, maximum displacement, fitted stiffness, and repeatability index. The effective load-displacement data were fitted using the following linear model: δ=aF+b Where F is the applied load, δ is the corresponding displacement, a is the fitted slope, and b is the intercept. The fitted stiffness is calculated as the reciprocal of the fitted slope.

[0044]

[0045] k fit A higher value indicates stronger resistance to deformation under static load. The coefficient of determination is used to evaluate the goodness of fit of the load-displacement regression; the closer the value is to 1, the more linear the structural response. The root mean square error (RMSE) is used to quantify the residual deviation between the measured displacement data and the fitted curve; a lower RMSE indicates a smaller fitting error.

[0046] The processed experimental results were further compared with finite element simulation results to assess the consistency of deformation and stiffness trends across different wall thicknesses. Considering the difference between the global deformation predicted by the finite element model and the local seat displacement measured experimentally, the simulation results were primarily used for trend-level verification rather than direct quantitative prediction of absolute displacement.

[0047] Table 4. Static properties of child car seats with three wall thicknesses

[0048] S600, a real-life sitting pressure distribution test was conducted on children aged 3 to 6 years and 9 months to obtain the uniformity of seat pressure.

[0049] In the above steps, a total of six preschool children were recruited as volunteers, including three boys and three girls. The target participants were aged 3 to 6 years and 9 months. All participants were generally in good health, able to sit independently, and willing to cooperate with the testing procedures. Children with spinal deformities, lower limb dysfunction, hip soft tissue injuries, recent musculoskeletal discomfort, or any other condition that might affect their normal sitting posture were excluded.

[0050] Inclusion criteria are as follows: preschool children aged 3 to 6 years and 9 months who are in good general health, can sit independently, and are willing to cooperate with the testing procedure. Children with spinal deformities, lower limb dysfunction, hip soft tissue injury, recent musculoskeletal discomfort, or any condition that may affect normal sitting posture are excluded.

[0051] During the test, participants were instructed to maintain a standardized sitting posture: feet flat on the ground, hands resting naturally on their thighs, torso upright, and back in contact with the backrest. Data collection began after participants maintained this stable posture for 10 seconds. Each participant was allowed to stop the test at any time. The collected data was anonymized and used only for academic analysis and paper writing. Human-chair interface pressure was measured using the TekScan human pressure measurement system. Six preschool children were recruited as participants, including three boys and three girls. All participants were in good health and had no spinal deformities, lower limb dysfunction, or hip soft tissue injuries.

[0052] During the test, participants were instructed to maintain a standardized sitting posture: feet flat on the ground, hands resting naturally on their thighs, torso upright, and back in contact with the backrest. Data collection began after maintaining this stable posture for 10 seconds.

[0053] Seat pressure distribution measurements were performed on chairs with wall thicknesses of 6.4 mm and 8.0 mm. Evaluation parameters included effective contact area, peak pressure, average pressure, and pressure distribution uniformity. Each condition was tested three times. Outliers were excluded—defined as sudden peak fluctuations, distorted pressure distribution, discontinuous contact areas, or values ​​significantly deviating from the normal range. Remaining data are expressed as mean + / - standard deviation.

[0054] Seat pressure is a key indicator for evaluating the ergonomic performance of a seating system. This study uses four main indicators for comprehensive evaluation: effective contact area, peak contact pressure, average contact pressure, and pressure distribution uniformity.

[0055] Considering that the skeletal and muscular structures of preschool children are relatively underdeveloped and their soft tissues are thinner, making them more sensitive to concentrated local pressure, the following comfort thresholds are adopted: average pressure <35 kPa and peak pressure <60 kPa.

[0056] Raw pressure data were extracted using CONFORMat Research 7.60 software to obtain quantitative parameters such as average pressure, peak pressure, and contact area. Furthermore, qualitative analysis of the pressure distribution map was performed to assess the location, distribution pattern, and symmetry of high-pressure areas, thereby identifying potential localized pressure concentrations.

[0057] To ensure data reliability, the relative deviation of repeated measurements is calculated as follows:

[0058] Where x i This is a single measurement value. This represents the average value. Lower deviation indicates higher repeatability and data consistency.

[0059] S700, based on the simulation indicators of maximum displacement, overall safety factor, PETG material weight, molding time, overall fitting stiffness, and seat pressure uniformity, obtains the optimal outer wall thickness and number of outer wall rings, and finally completes the mass production of integrated children's chairs.

[0060] The final mass production of the integrated children's chair, based on the above steps, is determined by the following: 1. Finite element prediction of deformation and stress response Finite element analysis was performed on seat models with wall thicknesses of 4.8 mm, 6.4 mm, and 8.0 mm under a standard static load of 1300 N to evaluate their mechanical response. All structures exhibited typical bending deformation modes, characterized by downward deflection of the seat surface followed by coordinated forward rotation of the backrest through the connection area. The maximum displacement occurred at the upper free end of the backrest, while the displacement in the bottom constrained area was negligible, indicating that the load was mainly transmitted along the seat-backrest load path.

[0061] As the wall thickness increases, the structural deformation decreases significantly. The model with a wall thickness of 4.8 mm exhibits a maximum displacement of 202.90 mm, with the seat displacement ranging from 81.17 to 121.8 mm. When the wall thickness increases to 6.4 mm, the maximum displacement decreases to 82.22 mm, and the seat displacement range shrinks to 32.89–49.33 mm. Further increasing the wall thickness to 8.0 mm reduces the maximum displacement to 37.10 mm, with the seat displacement limited to 14.84–22.26 mm. This monotonically decreasing displacement with increasing wall thickness indicates a significant increase in bending stiffness, which can be attributed to the increase in the moment of inertia of the cross section.

[0062] The strain distribution results show that the high strain areas are concentrated at the front edge of the seat and in the transition area where the seat connects to the backrest. The maximum strain decreases from 1.66% to 1.28%, and further to 0.67%, showing a clear downward trend. Meanwhile, the strain concentration range decreases with increasing wall thickness, and the strain gradient becomes smoother, indicating that local deformation has been effectively mitigated.

[0063] Similarly, stress is mainly concentrated in the seat-back transition area. The maximum stresses for the 4.8 mm, 6.4 mm, and 8.0 mm models are 37.64 MPa, 31.82 MPa, and 26.55 MPa, respectively. Assuming the yield strength of 3D-printed PETG is 36.00 MPa, the corresponding safety factors are 0.96, 1.13, and 1.36, indicating that the structural safety margin increases significantly with increasing wall thickness. Therefore, the 4.8 mm model has a risk of local yielding, while the 6.4 mm and 8.0 mm models remain within a safer stress range.

[0064] Overall, the results indicate that wall thickness plays a crucial role in determining the structural mechanical response of the seating structure. Increasing wall thickness improves structural stiffness while significantly reducing deformation and stress levels, demonstrating a shift from potential local yield risk to a safer structural response under applied static loads. In continuous profile, zero-fill configurations, wall thickness is a key parameter controlling load-bearing capacity and structural stability.

[0065] 2. Static load response and wall thickness-dependent deformation behavior Static load results reveal a significant dependence of mechanical properties on wall thickness. As the wall thickness increases from 4.8 mm to 8.0 mm, the average fitted stiffness increases from 20.13 N / mm to 99.89 N / mm, an increase of 396.3%. Simultaneously, the maximum displacement decreases from 54.68 mm to 13.09 mm, a reduction of 76.1%. These results indicate that increasing the wall thickness significantly improves the resistance to deformation under static load.

[0066] Each wall thickness group comprised two independent specimens, each tested three times. The 4.8 mm specimen exhibited the largest displacement and a significant nonlinear response at high load levels. In contrast, the 6.4 mm and 8.0 mm specimens showed significantly reduced displacement and more stable quasi-linear responses. The two independent specimens in the 6.4 mm group exhibited two distinct deformation levels, suggesting inter-specimen variability. A single repeated test of the 8.0 mm group showed a large displacement, which may be related to contact instability, fixture positioning effects, or manufacturing variability.

[0067] One-way ANOVA showed that wall thickness had a statistically significant effect on both stiffness and displacement (p<0.05), confirming its dominant role as a key structural parameter controlling the static performance of the seat.

[0068] To quantitatively describe the relationship between wall thickness and mechanical response, linear regression analysis was performed on the experimental data. The results show a clear decreasing trend between wall thickness and maximum displacement.

[0069] And the strong positive correlation between wall thickness and stiffness:

[0070] Where x is the wall thickness (mm), δ max For the maximum displacement (mm), k fit The fitted stiffness (N / mm) is given. These results show that the fitted stiffness increases almost linearly with wall thickness, while the displacement response exhibits a clear but not strictly linear decreasing trend.

[0071] 3. Seat pressure distribution and functional suitability Seat comfort was evaluated using a TekScan CONFORMat 32 x 32 pressure mapping system combined with CONFORMatResearch 7.60 software to quantitatively measure the contact pressure at the human-chair interface. Evaluation metrics included average contact pressure, peak contact pressure, effective contact area, and pressure distribution uniformity. Key system parameters were as follows: 32 x 32 sensor matrix, 1.4732 cm sensor spacing, 2.17032 cm² effective sensing area per sensor, 3 RAW noise threshold, and S-17 sensitivity level. Raw pressure data were calibrated and converted to kPa for subsequent statistical analysis.

[0072] The 4.8 mm wall thickness configuration was excluded from the comfort assessment because it failed to meet the structural strength requirements specified in GB / T 32487-2016 (exhibiting insufficient stiffness and excessive deformation in static load tests). Therefore, the comfort analysis was only conducted for the 6.4 mm and 8.0 mm configurations that met the mechanical performance standards.

[0073] The results showed that the average and peak contact pressures of both configurations were below the preset comfort thresholds (average pressure <35 kPa, peak pressure <60 kPa), indicating that they meet the basic seat comfort requirements for preschool children. The relative deviation of repeated tests was less than 5%, indicating that the measurements had good repeatability and reliability.

[0074] In terms of pressure distribution characteristics, the 6.4 mm configuration exhibits a more uniform distribution and a smoother pressure gradient. The high-pressure area is mainly located at the ischial tuberosity, corresponding to the physiological load-bearing area, with no obvious stress concentration. In contrast, the 8.0 mm configuration, due to its higher structural stiffness and reduced surface compliance, results in a smaller contact area, restricted pressure diffusion, and an increased pressure gradient, thereby increasing local pressure concentration.

[0075] These findings indicate that structural stiffness plays a crucial role in determining the uniformity of pressure distribution. Although no significant differences were observed in the overall pressure levels (p>0.05), the 6.4 mm group showed a trend toward a more uniform pressure distribution. Therefore, the 6.4 mm wall thickness achieves an optimal balance between structural support and uniform pressure distribution, providing more desirable seating comfort.

[0076] In summary, this invention evaluated the impact of wall thickness on the static load-bearing capacity and seat comfort of a parametrically designed FDM-PETG preschool chair manufactured using a continuous profile, zero-fill strategy. The results confirm that wall thickness is a key structural parameter affecting deformation, stiffness, and safety performance.

[0077] Based on the corrected load-displacement fitting results, the average fitted stiffness increased from 20.13 N / mm for 4.8 mm to 99.89 N / mm for 8.0 mm, an increase of 396.3%. Linear regression showed that within the test range, there was an almost linear relationship between wall thickness and fitted stiffness (R²). 2 =0.9980). Meanwhile, the maximum displacement decreased from 54.68 mm to 13.09 mm, a reduction of 76.1%. FEA results also show that increasing the wall thickness can reduce stress concentration and improve the structural safety margin.

[0078] The FEA model captures the overall deformation trend with increasing wall thickness, but there is a significant discrepancy between the simulated and experimental displacement values. Therefore, the simulation results should be understood as trend-level support rather than a direct quantitative prediction of absolute displacement.

[0079] The 4.8 mm configuration exhibited excessive deformation and potential local yielding risk under a static load of 1300 N, indicating serviceability failure despite the absence of macroscopic fracture. The 8.0 mm configuration offered the highest stiffness and safety margin but required greater material consumption and a longer molding time. In contrast, the 6.4 mm configuration achieved a better balance between deformation control, structural safety, manufacturing efficiency, material consumption, and seat pressure distribution.

[0080] The results demonstrate the feasibility of using FDM-PETG integrated manufacturing to create load-bearing preschool chair structures. Under the current manufacturing strategy, a wall thickness of 6.4 mm is the preferred configuration.

[0081] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for molding a 3D-printed children's chair based on ergonomics and finite element simulation, characterized in that, Includes the following steps: S100. Based on the raw data of percentile height of children aged 3-6 years and 9 months, a weighted model was performed to determine the dimensional data of the standardized ergonomic shape of the chair. The dimensional data includes seat width, seat height, backrest height, effective seat depth, seat tilt angle, and backrest tilt angle; S200. Based on the stated dimensional parameters, construct multiple sets of parametric 3D models of an integrated seat with no internal filling and only closed multi-layered outer walls for support. Each set of 3D models has a different number of outer wall rings and wall thickness. S300 performs finite element static load simulation on each group of three-dimensional models and outputs the simulation indicators of the maximum displacement, maximum equivalent stress, and overall safety factor of each group of three-dimensional models. S400: Using PETG consumables, solid samples of each group of three-dimensional models are printed out using FDM equipment, and the weight of PETG consumables and molding time of each group of solid samples are recorded at the same time. S500. Conduct static load tests on the entire machine for each group of physical samples to obtain the fitted stiffness of the entire machine. S600: Real-person sitting pressure distribution test was conducted on children aged 3 to 6 years and 9 months to obtain the uniformity of seat pressure. S700, based on the simulation indicators of maximum displacement, overall safety factor, PETG material weight, molding time, overall fitting stiffness, and seat pressure uniformity, obtains the optimal outer wall thickness and number of outer wall rings, and finally completes the mass production of integrated children's chairs.

2. The method for molding a 3D-printed children's chair based on ergonomics and finite element simulation according to claim 1, characterized in that, In step S100: The specific dimensions are as follows: seat width 320mm, effective seat depth 260mm, seat height 260mm, effective backrest height 230mm, seat angle 5°, backrest angle 15°, and overall outer dimensions of the seat are 444mm×320mm×479mm.

3. The method for molding a 3D-printed children's chair based on ergonomics and finite element simulation according to claim 2, characterized in that, In step S200: The number of outer wall rings and wall thickness of each group of 3D models are as follows: 0.8mm wall thickness corresponds to 3 outer wall printing paths, 6.4mm wall thickness corresponds to 4 outer wall printing paths, and 8.0mm wall thickness corresponds to 5 outer wall printing paths.

4. The method for molding a 3D-printed children's chair based on ergonomics and finite element simulation according to claim 3, characterized in that, In step S300: The assigned parameters for PETG material are: density 1290 kg / m³, elastic modulus 1695 MPa, Poisson's ratio 0.35, and yield strength of printed parts 36 MPa.

5. The method for molding a 3D-printed children's chair based on ergonomics and finite element simulation according to claim 4, characterized in that, In step S400: The molding process parameters for the FDM equipment are: nozzle constant temperature 240℃, molding base plate constant temperature 75℃, layer thickness 0.8mm, and outer wall printing speed 60mm / s.

6. The method for molding a 3D-printed children's chair based on ergonomics and finite element simulation according to claim 5, characterized in that, In step S500: The specific method for static load testing of the whole machine is as follows: the displacement control loading rate is 5mm / min, the loading range is 20~1300N, the load is held for 30s after reaching 1300N, the contact interference data below 50N are eliminated, and the fitting stiffness of the whole machine is calculated by fitting the load and displacement curves with linear equations. The linear equation is: ; The overall fitting stiffness is: ; In the above formula: F is the applied load, δ is the corresponding displacement, a is the fitting slope, b is the intercept, and k fit This is the overall fitting stiffness of the machine.

7. The method for molding a 3D-printed children's chair based on ergonomics and finite element simulation according to claim 6, characterized in that, In step S600: Before the real-person seating pressure distribution test, unqualified physical samples were rejected. The criteria for rejection were: simulation index of overall safety factor <1.1 or maximum displacement of seat surface under static load of 1300N >25mm.

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