A Die Surface Compensation Method for Suppressing Springback Deformation of L-shaped Composite Parts

Abstract

The present invention discloses a die surface compensation method for suppressing springback deformation of L-shaped composite parts, which specifically includes the following steps: 1) determining the basic parameters of the material used for the part; 2) determining the temperature difference from the glass transition temperature of the material to the indoor temperature according to the curing characteristics of the material and the curing process parameters; 3) performing finite element simulation prediction of springback deformation; 4) calculating the springback deformation amount; 5) calculating the temperature difference required for the L-shaped part to deform from the theoretical surface to the tooling compensation surface; 6) adjusting the chemical shrinkage rate parameter; 7) completing the finite element simulation of the L-shaped part deforming from the theoretical surface to the tooling compensation surface; 8) exporting the node information of the film sticking surface and establishing the tooling compensation surface. The present invention can reduce the iteration times of tooling surface compensation, realize the rapid modeling of the tooling compensation surface, and has important engineering significance for improving the manufacturing efficiency of parts with curvature.

Description

Technical Field

[0001] This application relates to the field of composite material manufacturing and curing deformation control, and particularly to a die surface compensation method for suppressing the springback deformation of L-shaped composite parts. Technical Background

[0002] Due to the differences in in-plane and out-of-plane properties, composite materials will generate different degrees of strain in both the in-plane and out-of-plane directions during the curing process, which will in turn cause the "springback" phenomenon in the formed composite parts with an included angle, that is, the included angle of the cured part is smaller than its nominal included angle. In engineering manufacturing, the die surface compensation method is usually used to suppress the springback deformation of composite materials. The determination of the die surface mainly adopts two methods: the trial-and-error method and computer simulation iteration. The trial-and-error method means that by repeatedly iterating the tooling surface and through multiple trial productions, a part that meets the requirements can finally be obtained; computer simulation iteration is to simulate and analyze the springback deformation of composite parts through finite element software, determine the tooling compensation surface according to the simulation results, and perform simulation and iteration based on the obtained surface data to obtain the optimal tooling surface.

[0003] The methods for determining the tooling compensation surface by the trial-and-error method or simulation iteration method have the following disadvantages:

[0004] 1. The compensation for the springback deformation of composite materials is a non-linear problem. For example, for an L-shaped part with a springback of 2° (included angle 90°), the method of compensating the tooling surface by 2° will not produce a part with an included angle of 90°. Therefore, it usually takes multiple trial productions or simulation iterations to determine the final surface, resulting in waste of manpower, material resources and financial resources.

[0005] 2. The simulation of the curing deformation of composite materials often requires many parameters such as the curing kinetic equation of the resin, gel point, glass transition temperature, and time-varying model of the elastic modulus of the composite material as input conditions. At the same time, the calculation process of this method is relatively cumbersome and the simulation calculation takes a long time. Multiple iterative simulations may affect the manufacturing cycle of composite parts and cannot meet the requirements of rapid development of parts.

[0006] 3. For composite parts with relatively complex surfaces, it is difficult to accurately determine the corresponding relationship of feature points by the geometric surface modification method.

[0007] Therefore, establishing a rapid modeling method for the tooling compensation surface to achieve precise control of the springback deformation of composite materials has very important engineering significance for the manufacturing quality and efficiency of composite parts. Summary of the Invention

[0008] In view of the problems and deficiencies existing in the above-mentioned prior art, the present application provides a die surface compensation method for suppressing the springback deformation of L-shaped composite parts. By combining the basic theory of composite material springback deformation and finite element simulation technology, the tooling compensation surface of the composite part with curvature can be quickly determined, so as to control the springback deformation of the composite part with curvature, and improve the part manufacturing quality and efficiency.

[0009] To achieve the above object, the present invention provides the following technical solutions:

[0010] A die surface compensation method for suppressing the springback deformation of L-shaped composite parts, where the included angle between the two straight edges of the L-shaped composite part is θ, and the range of θ is 60° to 120°. The method for compensating the die surface to eliminate the springback deformation specifically includes the following steps:

[0011] Step 1: Measure the basic performance parameters of the L-shaped composite part through experiments or obtain them from the supplier, including the engineering elastic constants, thermal expansion coefficients, and chemical shrinkage rates of the materials used.

[0012] Step 2: According to the curing process curve of the L-shaped composite part, calculate the temperature difference ΔT = T 室温 -T glass between the temperature at which the composite material just reaches the glass state and the indoor temperature, where T 室温 is the indoor temperature, and T glass is the temperature at which the material reaches the glass state during the curing process.

[0013] Step 3: Conduct a finite element simulation on the springback deformation of the L-shaped composite part. The specific process is as follows:

[0014] 1. Establish a model in the finite element software according to the theoretical design shape of the L-shaped composite part.

[0015] 2. Assign the material properties and ply information obtained in Step 1 to the established model.

[0016] 3. Establish an analysis step after instantiation.

[0017] 4. Apply displacement boundary conditions according to the position relationship between the die and the composite material, and apply temperature field boundary conditions according to the temperature difference ΔT obtained in Step S2.

[0018] 5. Divide the model into a three-dimensional solid element mesh.

[0019] 6. Submit the simulation model for calculation to obtain the deformed model of the L-shaped composite part.

[0020] Step 4: Analyze the finite element simulation calculation results in Step 3 to obtain the springback deformation amount Δθ of the composite part.

[0021] Step 5: Select an appropriate number of iterations \(n\) and calculate the temperature difference \(\Delta T'\) required for the L-shaped composite part to deform from the designed surface to the tooling compensation surface according to the formula where \(n\) is a positive integer not less than 2, and \(\alpha\) and \(\beta\) respectively represent the difference between the equivalent thermal expansion coefficient and the equivalent chemical shrinkage rate of the L-shaped composite part along the circumferential and radial directions.

[0022] Step 6: Multiply the chemical shrinkage rate obtained in Step 1 by -1, and keep the other parameters unchanged.

[0023] Step 7: Based on the temperature difference \(\Delta T'\) obtained in Step 5 and the material parameters obtained in Step 6, perform a deformation simulation. The specific process is as follows:

[0024] 1. Establish a model in the finite element software according to the theoretical design shape of the L-shaped composite part;

[0025] 2. Assign the material properties and ply information obtained in Step 6 to the established model;

[0026] 3. Establish an analysis step after instantiation;

[0027] 4. Apply displacement boundary conditions according to the positional relationship between the mold and the composite material, and apply temperature field boundary conditions according to the temperature difference \(\Delta T'\) obtained in Step 5;

[0028] 5. Divide the model into a three-dimensional solid element mesh;

[0029] 6. Submit the simulation model for calculation to obtain the deformed model of the L-shaped composite part.

[0030] Step 8: Export the mesh node coordinates of the mold-contact surface of the deformed L-shaped composite part obtained in Step 7 and establish the compensation surface of the mold.

[0031] Furthermore, the chemical shrinkage rate can be obtained through experimental measurement or by back-calculating from the springback deformation results of typical test pieces.

[0032] Furthermore, this compensation method is applicable to the autoclave molding process of prepreg.

[0033] The beneficial effects of the present invention are as follows:

[0034] (1) The present invention makes full use of the springback deformation mechanism of composite materials and realizes rapid simulation calculation of the springback deformation and "reverse curing" process of parts with curvature by calculating different in-plane and out-of-plane strain values of the composite materials.

[0035] (2) The present invention fully considers the non-linear characteristics of the springback deformation compensation of composite materials. When in use, only an appropriate number of iterations needs to be selected according to the size of the springback angle, and the tooling compensation surface can be determined through a single simulation calculation, solving the problem of time-consuming and laborious repeated iteration required for modeling the tooling compensation surface.

[0036] (3) Based on the springback deformation mechanism of composite materials, the present invention uses the method of "inverse curing" process simulation to realize the rapid modeling of the tooling compensation surface for the springback deformation of composite materials, solves the problems such as the difficult determination of the part contour line of the tooling compensation surface and the difficult determination of the structural feature area, and shortens the modeling cycle of the tooling compensation surface.

[0037] The following further describes the present invention in detail with reference to the accompanying drawings and specific embodiments. Description of the Drawings

[0038] Figure 1 Schematic diagram of the modeling of the L-shaped composite part in Embodiment 2 of the present invention;

[0039] Figure 2 Springback deformation simulation result of the L-shaped composite part in Embodiment 2 of the present invention;

[0040] Figure 3 Springback deformation simulation result of the L-shaped composite part in Embodiment 2 of the present invention. Specific Embodiments

[0041] Embodiment 1

[0042] A method for compensating the die surface to suppress the springback deformation of L-shaped composite parts. This compensation method is applicable to the autoclave molding process of prepreg. The included angle between the two straight edges of the L-shaped composite part is θ, and the range of θ is 60° to 120°. The method for compensating the die surface to eliminate the springback deformation specifically includes the following steps:

[0043] Step 1: Measure the basic performance parameters of the L-shaped composite part through experiments or obtain them from the supplier, including the engineering elastic constants, thermal expansion coefficients, and chemical shrinkage rates of the materials used;

[0044] Step 2: According to the curing process curve of the L-shaped composite part, calculate the temperature difference ΔT = T 室温 -T glass between the temperature at which the composite material just reaches the glassy state and the indoor temperature, where T 室温 is the indoor temperature and T glass is the temperature at which the material reaches the glassy state during the curing process;

[0045] Step 3: Conduct a finite element simulation of the springback deformation of the L-shaped composite part. The specific process is as follows:

[0046] 1. Establish a model in the finite element software according to the theoretical design contour of the L-shaped composite part;

[0047] 2. Assign the material properties and ply information obtained in Step 1 to the established model;

[0048] 3 Establish an analysis step after instantiation;

[0049] 4 Apply displacement boundary conditions according to the positional relationship between the mold and the composite material, and apply temperature field boundary conditions according to the temperature difference ΔT obtained in step S2;

[0050] 5 Divide the model into a three-dimensional solid element mesh;

[0051] 6 Submit the simulation model for calculation to obtain the deformed model of the L-shaped composite part.

[0052] Step 4: Analyze the finite element simulation calculation results in step 3 to obtain the springback deformation amount Δθ of the composite part;

[0053] Step 5: Select an appropriate number of iterations n, and according to the formula Calculate the temperature difference ΔT′ required for the L-shaped composite part to deform from the designed surface to the tooling compensation surface. In the formula, n is a positive integer not less than 2, and α and β respectively represent the difference between the equivalent thermal expansion coefficient and the equivalent chemical shrinkage rate of the L-shaped composite part along the circumferential and radial directions.

[0054] Step 6: Multiply the chemical shrinkage rate obtained in step 1 by -1, and keep the other parameters unchanged.

[0055] Step 7: Based on the temperature difference ΔT′ obtained in step 5 and the material parameters obtained in step 6, perform deformation simulation. The specific process is as follows:

[0056] 1 Establish a model in the finite element software according to the theoretical design shape of the L-shaped composite part;

[0057] 2 Assign the material properties and ply information obtained in step 6 to the established model;

[0058] 3 Establish an analysis step after instantiation;

[0059] 4 Apply displacement boundary conditions according to the positional relationship between the mold and the composite material, and apply temperature field boundary conditions according to the temperature difference ΔT′ obtained in step 5;

[0060] 5 Divide the model into a three-dimensional solid element mesh;

[0061] 6 Submit the simulation model for calculation to obtain the deformed model of the L-shaped composite part.

[0062] Step 8: Export the mesh node coordinates of the mold-attached surface of the deformed L-shaped composite part obtained in step 7 to establish the compensation surface of the mold.

[0063] Among them, in step 5, the derivation process of the formula is as follows:

[0064] The differences in the in-plane and out-of-plane properties (thermal expansion coefficient and chemical shrinkage rate) of the composite material are the fundamental causes of the springback deformation of the L-shaped part. The curing springback angle Δθ of the L-shaped composite part can be expressed as:

[0065]

[0066] In the formula, α θ and α R respectively represent the thermal expansion coefficients along the circumferential and radial directions of the L-shaped composite part, and β θ and β R respectively represent the chemical shrinkage rates along the circumferential and radial directions of the L-shaped composite part. Since α R ΔT and β R are extremely small, formula (1) can be simplified to

[0067]

[0068] Δθ = (αΔT + β)θ (3)

[0069] In the formula, α = α θ -α R , β = β θ -β R . For an L-shaped part with an included angle of θ on both sides, its curing springback deformation amount is Δθ. Using Δθ for the first die surface compensation, its springback deformation can be calculated by the following formula:

[0070] (αΔT + β)(θ + Δθ) = Δθ + (αΔT + β)Δθ (4)

[0071] It can be seen from the above formula that compensating the die surface once through Δθ cannot completely eliminate the springback deformation amount. Therefore, on the basis of the first compensation, a secondary iterative compensation (αΔT + β)Δθ is also required. At this time, its springback deformation angle is:

[0072] (αΔT + β)(θ + Δθ + (αΔT + β)Δθ) = Δθ + (αΔT + β)Δθ + (αΔT + β) 2 Δθ (5)

[0073] Furthermore, the third iterative compensation amount (αΔT + β) 2 Δθ can be obtained.

[0074] Furthermore, the die surface modification compensation amount for the nth iteration is (αΔT + β) n-1 Δθ. Furthermore, the total die surface modification compensation amount for n iterations can be obtained as: That is, when n approaches infinity, the required tooling compensation surface can be obtained.

[0075] To meet the demand for computing efficiency in industrial manufacturing, and considering that the influence mechanisms of chemical shrinkage and thermal expansion / contraction on springback deformation are the same, the curing process of the part from the glass transition temperature to room temperature is simulated, and adding the chemical shrinkage rate can satisfy the prediction of the curing deformation of the L-shaped part. Similarly, multiplying the chemical shrinkage rate by -1 can also achieve the simulation of the reverse curing process of the part from room temperature to the glass transition temperature. Based on this, the temperature difference ΔT′ required for the L-shaped part to deform from the designed surface to the tooling compensation surface during the reverse curing process can be obtained:

[0076]

[0077] In this method, the chemical shrinkage rate can be obtained through experimental measurement or by back-calculating from the springback deformation results of typical test pieces.

[0078] Example 2

[0079] For Figure 1 the shown L-shaped composite part, with the lengths of its two sides being 45 mm and 20 mm respectively, and the included angle between the two straight sides being 90°, it is fabricated by laying up with T800 grade carbon fiber plain weave prepreg in the [0] 10 ply layup. The present invention provides a rapid modeling method for the tooling compensation surface to control the springback deformation of this component, and the specific steps are as follows:

[0080] 1 By referring to the material handbook, when the T800 grade carbon fiber plain weave prepreg cures according to its curing process curve, the temperature at which the material reaches the glass state is 180 °C, and its basic performance data is shown in Table 1.

[0081] Table 1 Material parameters of T800 grade carbon fiber plain weave prepreg

[0082]

[0083] 2 Establish the Figure 1 shown model in the finite element software ABAQUS, and assign the material parameters and the ply layup [0] 10 to the established model.

[0084] 3 Instantiate the model and establish a "Static, General" analysis step.

[0085] 4 Calculate the temperature difference ΔT = T 室温 - T glass = 20 °C - 180 °C = -160 °C, and assign this temperature reduction process to the established model in the form of a predefined temperature field.

[0086] 5 Apply boundary conditions, and divide the model into three-dimensional solid meshes, with the mesh type being C3D8R.

[0087] 6 Establish the analysis step and submit the calculation to obtain the springback deformation of the L-shaped composite part, as Figure 2 shown.

[0088] 7 Process the Figure 2 simulation results shown. Read the coordinates of two points on the two straight edges of the L-shaped composite part, which are (1.76296e+000, -1.54888e+002, 4.98542e+000), (1.21230e-001, -7.05934e+000, 5.00094e+000), (5.50000e+001, -4.72447e-002, 5.00168e+000), and (7.05568e+000, -4.72391e-002, 5.00168e+000) respectively. Calculate the included angle between the two straight edges by the vector dot product method to be 89.3637°, that is, the springback deformation amount is Δθ = 90° - 89.3637° = 0.6363°.

[0089] 8 For the [0] 10 ply, the equivalent thermal expansion coefficient fractions of the L-shaped composite part along the radial and circumferential directions are α R = 38.1×10 -6 / °C and α θ = 6×10 -6 / °C respectively, and the equivalent chemical shrinkage rates along the radial and circumferential directions are β r = -2.14×10 -3 and β θ = -2×10 -4 , that is, α = α θ - α R = -32.1×10 -6 / °C, β = β θ - β R = 1.94×10 -3 . Since the springback deformation amount of the L-shaped composite part is small, the number of iterations n is taken as 2 times. According to the formula we can get

[0090] 9 Re-establish the model as Figure 1 in ABAQUS.

[0091] 10 Multiply the chemical shrinkage rate by -1 to get β R = 2.14×10 -3 and β θ = 2×10 -4 . Keep the other parameters in Table 1 unchanged. Assign this material parameter and the ply [0] 10 to the model established in step 9.

[0092] Instantiate the model from the previous step and establish a "Static, General" analysis step. At the same time, assign the temperature difference ΔT′ = 161.37 °C to the established model in the form of a predefined temperature field.

[0093] Apply boundary conditions and divide the model into a three-dimensional solid mesh with the mesh type of C3D8R.

[0094] Establish an analysis step and submit the calculation to obtain the springback deformation of the L-shaped composite part, as Figure 3 shown.

[0095] Export Figure 3 the grid node coordinate information of the die contact surface of the deformed L-shaped composite part in

[0096] Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A die surface compensation method for suppressing springback deformation of L-shaped composite parts, where the included angle between the two straight edges of the L-shaped composite part is θ, characterized in that The method for compensating the die surface to eliminate springback deformation specifically includes the following steps: Step 1: Measure through experiments or obtain from the supplier the basic performance parameters of the L-shaped composite material part, including the engineering elastic constants, thermal expansion coefficient, and chemical shrinkage rate of the material used; Step 2: According to the curing process curve of the L-shaped composite part, calculate the temperature difference ΔT = T 室温 - T glass , where T 室温 is the indoor temperature, and T glass is the temperature when the material reaches the glassy state during the curing process; Step 3: Conduct a finite element simulation on the springback deformation of the L-shaped composite material part; Step 4: Analyze the finite element simulation calculation results in Step 3 to obtain the springback deformation amount Δθ of the composite material part; Step 5: Select an appropriate number of iterations n, and according to the formula calculate the temperature difference ΔT′ required for the L-shaped composite part to deform from the designed surface to the tooling compensation surface. In the formula, n is a positive integer not less than 2, and α and β respectively represent the difference between the equivalent thermal expansion coefficient and the equivalent chemical shrinkage rate of the L-shaped composite part along the circumferential and radial directions; Step 6: Multiply the chemical shrinkage rate obtained in Step 1 by -1, and keep the other parameters unchanged; Step 7: Based on the temperature difference ΔT′ obtained in Step 5 and the material parameters obtained in Step 6, conduct a deformation simulation; Step 8: Export the mesh node coordinates of the die-attached surface of the deformed L-shaped composite material part obtained in Step 7, and establish the compensation die surface.

2. The die surface compensation method for suppressing springback deformation of L-shaped composite parts according to claim 1, characterized in that The range of the included angle θ of the L-shaped composite material part is 60° to 120°.

3. The die surface compensation method for suppressing springback deformation of L-shaped composite parts according to claim 1, characterized in that In Step 1, the chemical shrinkage rate can be measured through experiments or inversely deduced from the springback deformation results of typical test pieces.

4. The die surface compensation method for suppressing springback deformation of L-shaped composite parts according to claim 1, characterized in that The specific process of the finite element simulation in Step 3 is as follows: 4-1 Establish a model in the finite element software according to the theoretical design shape of the L-shaped composite material part; 4-2 Assign the material properties and ply information obtained in Step 1 to the established model; 4-3 Establish an analysis step after instantiation; 4-4 Apply displacement boundary conditions according to the positional relationship between the die and the composite material, and apply temperature field boundary conditions according to the temperature difference ΔT obtained in Step 2; 4-5 Divide the model into a three-dimensional solid element mesh; 4-6 Submit the simulation model for calculation to obtain the deformed model of the L-shaped composite material part.

5. The die surface compensation method for suppressing springback deformation of L-shaped composite parts according to claim 1, characterized in that The specific process of the deformation simulation in Step 7 is as follows: 5-1 Establish a model in the finite element software according to the theoretical design shape of the L-shaped composite material part; 5-2 Assign the material properties and ply information obtained in Step 6 to the established model; 5-3 Establish an analysis step after instantiation; 5-4 Apply displacement boundary conditions according to the positional relationship between the die and the composite material, and apply temperature field boundary conditions according to the temperature difference ΔT′ obtained in Step 5; 5-5 Divide the model into a three-dimensional solid element mesh; 5-6 Submit the simulation model for calculation to obtain the deformed model of the L-shaped composite material part.

6. The die surface compensation method for suppressing springback deformation of L-shaped composite parts according to claim 1, characterized in that This compensation method is applicable to the autoclave molding process of prepreg.

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