A method of additive compensation of a composite forming mold profile

Abstract

This invention discloses an additive manufacturing method for composite material molding die surfaces, belonging to the field of composite material manufacturing. Using thermosetting resin-based prepreg as the additive material, the die surface before and after compensation is processed and analyzed using geometric methods to obtain the required number, size, and application area of ​​additive material sheets. The material is then hardened through a thermosetting reaction, thereby achieving the surface repair effect of the composite material die. The method of this invention for repairing composite material molds overcomes the shortcomings of traditional milling repair methods, such as excessively long repair cycles and thinning of the die plate due to multiple iterations. It also eliminates the risk of air leakage or even scrapping caused by over-milling during the repair process.

Description

Technical Field

[0001] This invention relates to the field of composite material manufacturing and curing deformation control, specifically to an additive compensation method for the surface of a composite material molding die. Background Technology

[0002] Composite materials are characterized by their light weight, high specific strength, high specific modulus, fatigue resistance, corrosion resistance, and high design flexibility, making them one of the main materials for aerospace structures. With the increasing use of composite materials in aircraft structures, their applications have expanded to include aircraft skin, doors, flaps, ailerons, spoilers, rudders, elevators, as well as vertical and horizontal stabilizer panels, engine nacelles, and fairings.

[0003] Composite material parts undergo a certain degree of curing deformation after molding in an autoclave. After demolding, these parts may exhibit springback deformation (U-shaped parts) or warping deformation (flat parts), resulting in a discrepancy between the actual and designed shapes. While some coreless laminated parts can be assembled under low stress provided they meet design standards and specifications, for some rigid cored composite parts, stress assembly can cause delamination or other non-destructive defects within the parts.

[0004] For these types of sandwich composite parts, the common approach is to first perform numerical analysis on the part's crimping or warping, then perform reverse compensation based on the deformation to obtain a new part profile. Finally, the forming metal mold is repaired and compensated based on this new profile, allowing the part to return to its designed shape after stress release. However, for some batch-produced parts with tight production cycles, prolonged tooling repair time can affect aircraft delivery schedules. Because the forming molds are often thin-plate frame structures, repeated iterative repairs (including milling and heat treatment) can lead to serious consequences such as thinning of the mold plate, air leakage, or even scrapping.

[0005] Therefore, a mold compensation method with a fast iteration cycle that does not pose a quality risk to the mold is of great significance for the cycle and quality control of aircraft development. Summary of the Invention

[0006] To address the aforementioned issues, this invention proposes an additive compensation method for the surface of composite material molding dies. This method replaces the original cutting compensation with additive compensation, thereby reducing the mold repair cycle and minimizing the risk of mold damage.

[0007] A method for additive compensation of the surface of a composite material molding die includes the following steps:

[0008] Step 1: Import the compensation and modification surfaces provided by the process model designer and the molding die model together into the CAD system;

[0009] Step 1: Translate the springback compensation surface upward along the normal direction of the center point of the surface so that all points on the surface are above the forming mold surface, and use it as the final mold compensation surface.

[0010] Step 2: Select the additive material. Offset the final mold compensation surface towards the forming mold surface to create a set of equidistant surfaces with a spacing equal to the thickness of the additive material sheet. The last surface of the equidistant surface set should be below the forming mold surface. Select the equidistant surfaces in the equidistant surface set that intersect with the forming mold surface, and arrange them sequentially from top to bottom to form a set of contour lines, named DG1, DG2, ... DG n ;

[0011] Step 3: Use contour lines (DG) i The value of i ranges from 1 to n. The mold surface is divided, and the middle area is retained to form a set of dividing surfaces.

[0012] Step 4: Unfold the segmented surfaces sequentially to form a set of unfolded surfaces. Extract the outer contour of each unfolded surface and cut the material according to its outer contour to obtain a set of additive sheets, named LP1, LP2, ... LP1 in sequence. n ;

[0013] Step 5: Project all contour lines onto the surface of the physical molding die;

[0014] Step 6: Lay the sheet metal LPn to LP1 sequentially onto the forming mold, with their boundaries aligned with DG. n Align with DG1;

[0015] Step 7: Prepare a vacuum bag and place it in an autoclave for curing to complete the hardening of the additive material.

[0016] Furthermore, the additive material is selected as a thermosetting resin-based composite material, which can be a unidirectional prepreg, a woven prepreg, or a combination of both.

[0017] Furthermore, if more than three layers of additive material need to be laid, vacuum bag pre-compaction is required every three layers.

[0018] Furthermore, when compacting every three layers, each compaction session lasts 15 minutes, with a pressure of not less than 0.9 atmospheres.

[0019] The beneficial effects of this application are as follows: The invention replaces the traditional tooling surface milling repair method with a method of repairing tooling surfaces by using thermosetting composite material additive manufacturing. At the same time, it proposes a method for calculating the number of layers and area to ensure the accuracy of surface repair. This overcomes the shortcomings of the traditional milling repair method, such as the excessively long repair cycle and the thinning of the mold plate due to multiple iterations of repair. It also eliminates the risk of air leakage or even scrapping of the mold after repair. Attached Figure Description

[0020] Figure 1 Schematic diagram of additive compensation for mold surface

[0021] Figure 2 Offset effect diagram

[0022] Figure 3 Contour map

[0023] The numbers in the diagram are explained as follows: 1. Final mold compensation surface; 2. Molding mold profile; 3. Carbon fiber cloth. Detailed Implementation

[0024] like Figure 1-3 As shown, a method for additive compensation of the surface of a composite material molding die includes the following steps:

[0025] Step 1: By performing a series of operations such as rotation and translation on the compensation surface in 3D software, the final mold compensation surface 1 is completely placed on the forming mold surface 2 to create an additive tiling environment. Simultaneously, the minimum distance between the final mold compensation surface 1 and the forming mold surface 2 should be greater than the thickness of a single layer of carbon fiber cloth 3 to ensure that at least one layer of carbon fiber cloth 3 covers any part of the original surface. In addition to meeting the above conditions, the final mold compensation surface 1 should also be as close as possible to the forming mold surface 2 to minimize the number of tiling layers.

[0026] Step 2: Analyze the maximum distance between the final mold compensation surface 1 and the forming mold surface 2 to determine the maximum number of layers. Offset the final mold compensation surface 1 at equal intervals, with the offset interval equal to the thickness of a single layer of carbon fiber cloth 3. In this case, a 0.24mm thick prepreg fabric is selected, and the offset number is 9 layers. After the equidistant surface group intersects with the forming mold surface 2, a set of contour lines (DG) is obtained. 1～ DG9. As will be discussed in subsequent steps, after the ply profile is determined, the ply sequence will be ordered from smallest to largest. After this ordering, during the laying process, the boundary of each ply will lie on the original profile surface. Therefore, the aforementioned contour line set should be used as the final projection position of the laser equipment.

[0027] Step 3: Use contour lines (DG) i The value of i is from 1 to 9. The mold surface is divided, the middle area is retained, and a set of dividing surfaces are formed.

[0028] Step 4: Unfold the segmented surfaces in sequence to form a set of unfolded surfaces, extract the outer contour of the unfolded surfaces, and cut the material according to the outer contour to obtain a set of additive material sheets, named LP1, LP2, ... LP9 in sequence;

[0029] Step 5: Adjust the sheet order according to the size of the ply area. The principle for adjusting the sheet order is: keep the boundaries of each ply unchanged, place the ply with the smaller area at the bottom, and the ply with the larger area at the top, to ensure the smoothness of the top layer surface as much as possible. In this case, the ply order from smallest to largest is LP.9、 LP 8、 LP 7、 LP 6、 LP 5、 LP 4、 LP 3、 LP 2、 LP1;

[0030] Step 6: Project the contour lines obtained in Step 2 onto the molding die surface 2 using a laser projection device, see... Figure 3 The projection device achieves accurate projection by identifying target points evenly distributed around the mold.

[0031] Step 7: Following the sorting method in Step 5, using the laser projection lines as boundaries, lay the carbon cloth from bottom to top, following the sorting method in Step 5. This case requires a total of 9 layers of carbon cloth. Vacuum bag pre-compacting is performed every 3 layers, with each compaction taking 15 minutes.

[0032] Step 7: Place the laid carbon cloth into a vacuum bag and the molding mold into an autoclave for curing. After removing the vacuum bag from the autoclave, apply a release cloth to the surface to manufacture composite parts.

Claims

1. A method for additive compensation of the surface of a composite material molding die, characterized in that... Includes the following steps: Step 1: Import the compensation and modification surfaces provided by the process model designer and the molding die model together into the CAD system; Step 1: Translate the springback compensation surface upward along the normal direction of the center point of the surface so that all points on the surface are above the forming mold surface, and use it as the final mold compensation surface. Step 2: Select the additive material. Offset the final mold compensation surface towards the forming mold surface to create a set of equidistant surfaces with a spacing equal to the thickness of the additive material sheet. The last surface of the equidistant surface set should be below the forming mold surface. Select the equidistant surfaces in the equidistant surface set that intersect with the forming mold surface, and arrange them sequentially from top to bottom to form a set of contour lines, named DG1, DG2, ... DG n ; Step 3: Use contour lines (DG) i The value of i ranges from 1 to n. The mold surface is divided, and the middle area is retained to form a set of dividing surfaces. Step 4: Unfold the segmented surfaces sequentially to form a set of unfolded surfaces. Extract the outer contour of each unfolded surface and cut the material according to its outer contour to obtain a set of additive sheets, named LP1, LP2, ... LP1 in sequence. n ; Step 5: Project all contour lines onto the surface of the physical molding die; Step 6: Lay the sheet metal LPn to LP1 sequentially onto the forming mold, with their boundaries aligned with DG. n Align with DG1; Step 7: Prepare a vacuum bag, place it in an autoclave for curing, and complete the hardening of the additive material; The additive material is a thermosetting resin-based composite material. The additive material is any one or two of unidirectional prepreg and woven prepreg. If more than 3 layers of additive material need to be laid, vacuum bag pre-compaction is required every three layers. When compacting every three layers, the compaction time is 15 minutes and the pressure is not less than 0.9 atmospheres.

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