A method for accurately controlling the temperature rise of autoclave curing

Abstract

The present invention provides a method for accurately controlling the temperature rise of autoclave curing, and belongs to the field of autoclave molding manufacturing technology of aviation composite material manufacturing technology. The method of the present invention adopts a solution combining a precisely movable tooling platform with simulation and emulation, based on the autoclave temperature rise requirements, ensures the accuracy of part temperature rise, increases the accuracy of autoclave temperature control, and greatly reduces the internal defects and shape rebound of parts.

Description

Technical Field

[0001] The invention belongs to the technical field of aviation composite material manufacturing technology and autoclave molding manufacturing technology, and relates to a method for accurately controlling the curing temperature rise of an autoclave. Background Art

[0002] There are temperature-sensitive prepregs in the manufacturing of aviation composite materials, and high requirements are placed on precise temperature control during the curing and heating process. The traditional method is usually used for heat distribution testing, that is, the leading thermocouple is usually placed at the corner of the part or the thinner margin area and the adjacent tooling area, and the lagging thermocouple is usually placed in the center of the plane, the thickest part, and a replacement thermocouple is found. The traditional method has the advantage of simple operation, but its limitation is that it is difficult to find a replacement thermocouple line for the lagging thermocouple, and the thermocouple line placed at the characteristic position often cannot represent the leading point and the lagging point of the actual heating of the part. When the part structure is an unconventional structure, the temperature distribution of the part during the autoclave curing process is related to the position of the autoclave, the interference of other parts in the tank, the placement of the part itself, and the shape of the part. Therefore, the leading and lagging thermocouples tested by the conventional method may not represent the highest and lowest points of the actual temperature of the part, and the leading and lagging thermocouple curves are prone to cross, which leads to deviations in the autoclave temperature control system based on the temperature control of the thermocouple, which leads to uneven temperature distribution of the part, internal defects or excessive deformation rebound. Summary of the invention

[0003] Traditional heat distribution test methods cannot find the leading and lagging pair line positions for complex structural parts, and traditional heat distribution tests do not determine the position of the tooling in the autoclave, and do not consider the influence of airflow at different positions of the autoclave on the heat distribution and the influence of other parts in the autoclave on the heat distribution test; therefore, the present invention proposes a method for accurately controlling the curing temperature rise of the autoclave, which adopts a solution combining a precisely movable tooling platform with simulation, based on the autoclave heating requirements, to ensure the accuracy of the part heating, increase the accuracy of the autoclave temperature control, and reduce internal defects and appearance rebound.

[0004] The technical solution of the present invention is:

[0005] A method for accurately controlling the temperature rise of autoclave curing, comprising the following steps:

[0006] 1. Design a hot-press tank positioning device based on thermal distribution deformation

[0007] The autoclave positioning device includes a first tooling platform plate 1, a first positioning slide rail 2, a first slide rail 5, a second slide rail 8, a guide pin 11, a tooling platform 12, a threaded control system 13, a threaded lifting column 14, a reinforcing rib 15, a second positioning slide rail 16, a third slide rail 19 and a fourth slide rail 24.

[0008] The two ends of the first positioning slide rail 2 are respectively welded and fixed on the first tooling platform plate 1 by the first fixing device 3 and the second fixing device 4; the length direction of the first positioning slide rail 2 is the X direction, and the direction perpendicular to the X direction is the Y direction. The first slide rail 5 is constrained on the track of the first positioning slide rail 2 by the sliding protrusion, and can slide along the first positioning slide rail 2. At the same time, the first fixing device 3 and the second fixing device 4 limit the movement limit of the first slide rail 5 in the X movement direction; the first slide rail 5 is constrained in all movement directions except the X movement direction. The first positioning slide rail 2 is provided with a scale line between the first fixing device 3 and the second fixing device 4 to determine the position of the first slide rail 5; after the position of the first slide rail 5 is determined, the relative position relationship between the first slide rail 5 and the first positioning slide rail 2 is fixed by the first slide rail positioning device A6 and the first slide rail positioning device B7.

[0009] The second slide rail 8 can move along the Y direction, and is constrained in all directions except the Y direction; the guide pin 11 is arranged in the slideways of the first slide rail 5 and the second slide rail 8, and is used for the relative movement of the first slide rail 5 and the second slide rail 8. The second slide rail positioning device A9 and the second slide rail positioning device B10 are respectively arranged at both ends of the first slide rail 5, and are used to fix the relative position relationship between the first slide rail 5 and the second slide rail 8; the first slide rail 5 is engraved with scale lines for positioning the second slide rail 8.

[0010] The thread control system 13 is used to control the thread lifting system; a plurality of thread lifting columns 14 are connected to the bottom of the tooling platform 12, and the thread lifting columns 14 are controlled by the thread lifting system 13 to achieve height adjustment. The tooling platform 12 and the thread lifting columns 14 are fixed in four directions by reinforcing ribs 15.

[0011] The two ends of the second positioning rail 16 are welded and fixed to the tooling platform 12 along the X direction by the third fixing device 17 and the fourth fixing device 18 respectively. The third rail 19 is installed on the track of the second positioning rail 16 and can slide along the second positioning rail 16. The third rail 19 is constrained in all movement directions except the X movement direction. The second positioning rail 16 has a scale line between the third fixing device 17 and the fourth fixing device 18 to determine the position of the third rail 19. After the position of the third rail 19 is determined, the relative position relationship between the third rail 19 and the second positioning rail 16 is fixed by the third rail positioning device A20 and the third rail positioning device B21.

[0012] The fourth slide rail 24 can move along the Y direction, and is constrained in all directions except the Y direction. The fourth slide rail positioning device A22 and the fourth slide rail positioning device B23 are respectively arranged at both ends of the third slide rail 19, and are used to determine the position of the fourth slide rail 24. The third slide rail 19 is engraved with scale lines for positioning the fourth slide rail 24.

[0013] All slide rail positioning devices are realized by using a thread control system in conjunction with a push rod.

[0014] 2. Simulation method of thermal distribution deformation based on autoclave positioning device

[0015] (1) A gas flow meter 25 is installed on the first tooling platform plate 1, and the gas flow meter 25 is used to accurately measure the flow velocity of the tail of the autoclave.

[0016] (2) Based on the given non-uniform temperature field, the thermal chemical simulation is used to obtain the thermal distribution and springback results of the parts, and determine the fastest and slowest points of temperature rise and fall. The solution equation used is as follows:

[0017] 1) The computational fluid dynamics equations involved are:

[0018] NS (Navier-Stokes equations)

[0019]

[0020]

[0021]

[0022] Among them, ρ is the fluid density; u, v, w are the velocity components of the fluid at the point (x, y, z) at time t; P is the pressure. f is the external force per unit volume of fluid. If only gravity is considered, f = ρg; constant μ is the dynamic viscosity.

[0023] The gas physics parameters around the part, that is, the boundary conditions of the part, are calculated through this equation.

[0024] 2) The equation involved in the curing process is:

[0025] Calculation method of curing degree:

[0026] α=(H 0 -H R ) / H 0

[0027] Among them, α is the degree of curing, H 0 is the total reaction heat, H R is the residual reaction heat.

[0028] Heat conduction equation:

[0029]

[0030] Among them, ρ c is the density of the composite material, C c For hot melt composite materials, K x , K y , Kz are the thermal conductivity of the composite material in the x, y, and z directions, T is temperature, t is time, and ρ r is the resin density, V r is the resin volume fraction, and H is the exothermic rate of the curing reaction.

[0031] Under the condition of known gas environment around the part, the solidification degree and heat distribution of the part can be calculated by the above equation.

[0032] 3) The equation involving springback deformation is

[0033] F=KX

[0034] Wherein, K is the thermal expansion coefficient or chemical shrinkage, and X is the deformation.

[0035] When the degree of curing and heat distribution of the part are known, the deformation springback of the part can be calculated.

[0036] (3) The simulation results are combined with traditional methods to conduct thermal distribution tests, that is, characteristic position points and the optimal points obtained by simulation are selected for testing to obtain the actual highest and lowest even line positions.

[0037] (4) Change the tooling position, perform the above operations, and compile a program to verify the optimal tooling position and optimal results.

[0038] Beneficial effects of the present invention: The method of the present invention improves the accuracy of the heat distribution test, accurately controls the curing temperature rise, and greatly reduces the internal defects and shape rebound of parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a top view of the tooling platform.

[0040] Figure 2 This is a three-dimensional diagram of the tooling platform.

[0041] Figure 3 Schematic diagram of the reinforcement rib.

[0042] Figure 4 This is a schematic diagram of the guide pin installation position.

[0043] In the figure: 1 first tooling platform plate; 2 first positioning slide rail; 3 first fixing device; 4 second fixing device; 5 first slide rail; 6 first slide rail positioning device A; 7 first slide rail positioning device B; 8 second slide rail; 9 second slide rail positioning device A; 10 second slide rail positioning device B; 11 guide pin; 12 tooling platform; 13 threaded control system; 14 threaded lifting column; 15 reinforcing rib; 16 second positioning slide rail; 17 third fixing device; 18 fourth fixing device; 19 third slide rail; 20 third slide rail positioning device A; 21 third slide rail positioning device B; 22 fourth slide rail positioning device A; 23 fourth slide rail positioning device B; 24 fourth slide rail; 25 gas flow meter. DETAILED DESCRIPTION

[0044] The specific implementation of the present invention is further explained below in conjunction with the examples and drawings, but is not intended to limit the present invention.

[0045] A method for accurately controlling the temperature rise of autoclave curing, the specific implementation steps are as follows:

[0046] (1) Modeling is performed based on the actual autoclave area, where the tooling parts and control platform are set as solid domains and the rest of the area is set as fluid domains.

[0047] (2) The fluid field in the autoclave is calculated based on the Navier-Stokes equations. The wall boundary condition is set to a no-slip wall, and the wall friction is set to smooth-friction. The tooling parts, the control platform surface, and the inner wall of the autoclave are set as flow surfaces. The inlet flow setting area is the fluid inlet at the tail of the autoclave, and the boundary conditions are input according to the measurement results. The boundary condition fluid temperature setting is consistent with the autoclave temperature setting. The outlet flow setting area is the fluid outlet at the tail of the autoclave. The temperature field around the part is obtained by simulation calculation.

[0048] (3) Using the temperature field solved by the Navier-Stokes equation as the boundary condition and the heat conduction equation as the basis, simulate the curing of the part. Set the contact between the part and the tooling surface to full contact and set the initial working temperature. Set the convection fluid temperature to the imported fluid field simulation result.

[0049] (4) Using the springback deformation equation, import the curing analysis results as the basic data for deformation springback analysis. Establish temperature loads and import the temperature field generated by fluid field simulation. Fix the tooling, set the surface contact parameters, set the friction coefficient of tangential behavior, and set the change of time friction coefficient with time by creating a new field. Set fixed displacement constraints and divide all nodes into three categories: corner node 1, corner node 2, corner node 3, and other nodes. All nodes are fixed before demolding. After demolding, node 1 continues to constrain the XYZ directions, node 2 continues to constrain the XY direction, and node 3 continues to constrain the Z direction.

[0050] (5) Change the modeling method to place the tooling in different positions and perform simulations according to the above method. The actual position of the tooling is (X1+X2, Y1+Y2, Z), and its position is divided into five equal parts according to different coordinate systems.

[0051] X-axis coordinate Y-axis coordinate Z-axis coordinate X1(1)+X2(1) Y1(1)+Y2(1) Z1 X1(2)+X2(2) Y1(2)+Y2(2) Z2 X1(3)+X2(3) Y1(3)+Y2(3) Z3 X1(4)+X2(4) Y1(4)+Y2(4) Z4 X1(5)+X2(5) Y1(5)+Y2(5) Z5

[0052] Use the orthogonal test principle to set different coordinate values:

[0053] X1(1)+X2(1) Y1(1)+Y2(1) Z1

[0054] X1(1)+X2(1) Y1(2)+Y2(2) Z3

[0055] X1(1)+X2(1) Y1(3)+Y2(3) Z5

[0056] X1(1)+X2(1) Y1(4)+Y2(4) Z2

[0057] X1(1)+X2(1) Y1(5)+Y2(5) Z4

[0058] X1(2)+X2(2) Y1(1)+Y2(1) Z5

[0059] X1(2)+X2(2) Y1(2)+Y2(2) Z2

[0060] X1(2)+X2(2) Y1(3)+Y2(3) Z4

[0061] X1(2)+X2(2) Y1(4)+Y2(4) Z1

[0062] X1(2)+X2(2) Y1(5)+Y2(5) Z3

[0063] X1(3)+X2(3) Y1(1)+Y2(1) Z4

[0064] X1(3)+X2(3) Y1(2)+Y2(2) Z1

[0065] X1(3)+X2(3) Y1(3)+Y2(3) Z3

[0066] X1(3)+X2(3) Y1(4)+Y2(4) Z5

[0067] X1(3)+X2(3) Y1(5)+Y2(5) Z2

[0068] X1(4)+X2(4) Y1(1)+Y2(1) Z3

[0069] X1(4)+X2(4) Y1(2)+Y2(2) Z5

[0070] X1(4)+X2(4) Y1(3)+Y2(3) Z2

[0071] X1(4)+X2(4) Y1(4)+Y2(4) Z4

[0072] X1(4)+X2(4) Y1(5)+Y2(5) Z1

[0073] X1(5)+X2(5) Y1(1)+Y2(1) Z2

[0074] X1(5)+X2(5) Y1(2)+Y2(2) Z4

[0075] X1(5)+X2(5) Y1(3)+Y2(3) Z1

[0076] X1(5)+X2(5) Y1(4)+Y2(4) Z3

[0077] Measure the distance between the part edge of the simulated springback result and the theoretical part edge:

[0078] 1) Measure the trim length of the part as L;

[0079] 2) The measuring distance is 300mm;

[0080] 3) The number of measurement points is N = L / 300 (rounding off decimal places);

[0081] 4) Measure the distance D between the edge of the corresponding point and the theoretical position through simulation results N ;

[0082] 5) Calculate the deformation characterization parameter ΔTn=D1 2 +D2 2 +....DN 2 (n=1-25);

[0083] 6) Find the n value corresponding to the minimum deformation characteristic parameter, and the coordinate value corresponding to the minimum n value is X1(Nmin)+X2(Nmin)Y1(Nmin)+Y2(Nmin)ZNmin

[0084] (6) Start the tooling control platform

[0085] 1) Move the first slide rail 5, align the edge of the first slide rail 5 with the scale line X1 (Nmin) on the first positioning slide rail 2, and lock the first slide rail positioning device A6 and the second slide rail positioning device B7.

[0086] 2) Move the second slide rail 8, align the edge of the second slide rail 8 with the position of the scale line Y1 (Nmin) on the first slide rail 5, and lock the second slide rail positioning device A9 and the second slide rail positioning device B10.

[0087] 3) Start the thread control system 13 and raise the thread lifting column 14 to ZNmin.

[0088] 4) Move the third slide rail 19, align the edge of the third slide rail 19 with the scale line X2 (Nmin) on the second positioning slide rail 16, and lock the third slide rail positioning device A20 and the third slide rail positioning device B21.

[0089] 5) Move the fourth slide rail 24, align the edge of the fourth slide rail 24 with the position of the scale line Y2 (Nmin) on the third slide rail 19, and lock the fourth slide rail positioning device A22 and the fourth slide rail positioning device B23.

[0090] 6) According to the simulation results of the X1(Nmin)+X2(Nmin), Y1(Nmin)+Y2(Nmin), and Z(Nmin) positions, find the point where the temperature rises fastest and slowest, and arrange thermocouples at the actual positions.

[0091] 7) According to the traditional method, thermocouples are arranged based on the simulation results. The leading thermocouple is placed in the corner area or thinner layer area of ​​the part, and the couple line is located between the two layers of prepreg closest to the vacuum bag. The lagging thermocouple is placed in the center of the part plane, the center of the thickest section plane area, the center of the thickest core material area, and the center of the film and honeycomb core. The lagging thermocouple of the laminate part is placed in the middle of the ply and between the first and second layers of prepreg near the tooling side.

[0092] 8) The optimal point obtained by comprehensive simulation and the traditional method are used to determine the thermocouple placement position.

Claims

1. A method for accurately controlling the temperature rise of autoclave curing, characterized in that: The following steps are involved: Step 1: Design a hot-press tank positioning device based on thermal distribution deformation The autoclave positioning device comprises a first tooling platform plate (1), a first positioning slide rail (2), a first slide rail (5), a second slide rail (8), a guide pin (11), a tooling platform (12), a threaded control system (13), a threaded lifting column (14), a second positioning slide rail (16), a third slide rail (19) and a fourth slide rail (24); The two ends of the first positioning slide rail (2) are fixed on the first tooling platform plate (1) by a first fixing device (3) and a second fixing device (4) respectively; the length direction of the first positioning slide rail (2) is the X direction, and the direction perpendicular to the X direction is the Y direction; the first slide rail (5) is installed on the track of the first positioning slide rail (2) and can slide along the first positioning slide rail (2), and at the same time, the first fixing device (3) and the second fixing device (4) limit the movement limit of the first positioning slide rail (5) in the X movement direction; the first positioning slide rail (2) is provided with a scale line between the first fixing device (3) and the second fixing device (4) for determining the position of the first slide rail (5); after the position of the first slide rail (5) is determined, the relative position relationship between the first slide rail (5) and the first positioning slide rail (2) is fixed by the first slide rail positioning device A (6) and the first slide rail positioning device B (7); The second slide rail (8) can move along the Y direction, and is constrained in all directions except the Y direction; the guide pin (11) is arranged in the slideways of the first slide rail (5) and the second slide rail (8), and is used for the relative movement of the first slide rail (5) and the second slide rail (8); a scale line is engraved on the first slide rail (5) for positioning the second slide rail (8); the second slide rail positioning device A (9) and the second slide rail positioning device B (10) are respectively arranged at both ends of the first slide rail (5), and are used to fix the relative position relationship between the first slide rail (5) and the second slide rail (8); The bottom of the tooling platform (12) is connected to a plurality of threaded lifting columns (14), and the threaded lifting columns (14) are controlled by a threaded control system (13) to achieve height adjustment; The two ends of the second positioning slide rail (16) are respectively welded and fixed on the tooling platform (12) along the X direction through a third fixing device (17) and a fourth fixing device (18); the third slide rail (19) is installed on the track of the second positioning slide rail (16) and can slide along the second positioning slide rail (16); the second positioning slide rail (16) is provided with a scale line between the third fixing device (17) and the fourth fixing device (18) for determining the position of the third slide rail (19); after the position of the third slide rail (19) is determined, the relative position relationship between the third slide rail (19) and the second positioning slide rail (16) is fixed by a third slide rail positioning device A (20) and a third slide rail positioning device B (21); The fourth slide rail (24) can move along the Y direction, and is constrained in all directions except the Y direction; scale lines are engraved on the third slide rail (19) for positioning the fourth slide rail (24); a fourth slide rail positioning device A (22) and a fourth slide rail positioning device B (23) are respectively arranged at two ends of the third slide rail (19) for determining the position of the fourth slide rail (24); Step 2: Simulation method based on thermal distribution deformation of autoclave positioning device (1) installing a gas flow meter (25) on the first tooling platform plate (1), and using the gas flow meter (25) to accurately measure the flow rate at the tail of the autoclave; (2) Based on a given non-uniform temperature field, thermochemical simulation is used to obtain the thermal distribution and springback results of the parts, and to determine the fastest and slowest points of temperature rise and fall; (3) Select characteristic position points and the optimal point obtained by simulation to conduct experiments and obtain the actual highest and lowest even line positions; (4) Change the tooling position, perform the above operations, and compile a program to verify the optimal tooling position and optimal results.

2. The method for accurately controlling the temperature rise of autoclave curing according to claim 1, characterized in that: The solution equation used in step (2) is as follows: 1) The computational fluid dynamics equations involved are: Navier-Stokes equations: Where ρ is the fluid density; u, v, w are the velocity components of the fluid at point (x, y, z) at time t; P is the pressure; f is the external force per unit volume of fluid. If only gravity is considered, f = ρg; The constant μ is the dynamic viscosity; The physical parameters of the gas around the part, i.e. the boundary conditions of the part, are calculated through this equation; 2) The equation involved in the curing process is: Calculation method of curing degree: α=(H0-H R ) / H0 Among them, α is the degree of curing, H0 is the total reaction heat, H R is the residual reaction heat; Heat conduction equation: Among them, ρ c is the density of the composite material, C c For hot melt composite materials, K x , K y , K z are the thermal conductivity of the composite material in the x, y, and z directions, T is temperature, t is time, and ρ r is the resin density, V r is the resin volume fraction, H is the exothermic rate of curing reaction; Under the condition of known gas environment around the part, the solidification degree and heat distribution of the part can be calculated by the above equation; 3) The equation involving springback deformation is F=KX Where K is the thermal expansion coefficient or chemical shrinkage, and X is the deformation; When the degree of curing and heat distribution of the part are known, the deformation springback of the part can be calculated.

3. A method for accurately controlling the temperature rise of autoclave curing according to claim 1 or 2, characterized in that: The first slide rail positioning device A (6), the first slide rail positioning device B (7), the second slide rail positioning device A (9), the second slide rail positioning device B (10), the third slide rail positioning device A (20), the third slide rail positioning device B (21), the fourth slide rail positioning device A (22) and the fourth slide rail positioning device B (23) are all implemented by using a thread control system in cooperation with a push rod.

4. A method for accurately controlling the temperature rise of autoclave curing according to claim 1 or 2, characterized in that: The tooling platform (12) and the threaded lifting column (14) are fixed in four directions via reinforcing ribs (15).

5. The method for accurately controlling the temperature rise of autoclave curing according to claim 3, characterized in that: The tooling platform (12) and the threaded lifting column (14) are fixed in four directions via reinforcing ribs (15).

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