A large-size carbon fiber composite material wallboard precision hole drilling process method

Abstract

The application discloses a large-size carbon fiber composite material wallboard precision drilling process method and relates to the field of drilling of aviation composite material wallboards. The method comprises the following steps: processing an axially extending chip space in a preset hole position of a composite material wallboard forming die, wherein the chip space is a blind hole structure; filling a thermally expandable sacrificial layer material in the chip space, wherein the difference between the thermal expansion coefficient of the sacrificial layer material and the thermal expansion coefficient of the forming die and the composite material is less than a preset threshold; keeping the composite material wallboard in a state of not being demolded after solidification, and positioning the wallboard and the forming die as a whole to a processing equipment; establishing a processing coordinate system based on the reference features of the forming die; and drilling the wallboard with the die, so that the cutter penetrates the composite material laminate and cuts the sacrificial layer material, and the end of the cutter does not contact the body of the forming die. The application scheme can ensure the connection hole precision of the composite material wallboard, synchronously eliminate the demolding deformation error, the outlet delamination damage and the secondary clamping cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of aviation composite wallboard hole making, in particular to a large-size carbon fiber composite material wallboard precision hole making process method. BACKGROUND

[0002] As a large-size core structural part, the assembly precision of the carbon fiber composite material wallboard directly depends on the position accuracy of the connecting hole. After the traditional process composite material is completed on the forming mold, it needs to go through demolding, profile detection, secondary clamping positioning and other processes before hole making. Due to the significant difference between the thermal expansion coefficients of carbon fiber composite material and metal mold, the residual stress caused by temperature deformation mismatch during demolding will cause irreversible plastic deformation of the wallboard. Even through the forced adjustment of the orthopedic tooling, the wallboard is still difficult to restore the design theoretical profile, which causes the subsequent hole making position to deviate from the design requirements. In addition, after demolding, the wallboard needs to be repositioned on the machining fixture or flexible tooling, and the positioning reference conversion error is further introduced in the secondary clamping process, which seriously restricts the millimeter-level precision requirement of aviation assembly.

[0003] The existing hole making process method has three systematic defects: the profile distortion of the wallboard caused by the demolding stress release has a nonlinear characteristic, the traditional orthopedic technology cannot completely eliminate the residual strain, causing the hole making coordinate reference to drift, directly affecting the key assembly precision such as wing-body docking. After demolding, the wallboard needs to rely on external tooling to reestablish the machining coordinate system, and the positioning reference is transferred from the mold body to the auxiliary fixture. The cumulative error is generated in the reference conversion process, which is far beyond the tolerance requirement of ±0.05mm of the aviation fastening hole. When free-state hole making, the exit is not supported, causing the shear stress concentration between the carbon fiber layers, which causes splitting, delamination and other damages; when using the co-curing process, the longer string is embedded in the mold profile to form a mechanical interlock, and forced demolding may cause structural damage, and retaining the longer string for hole making requires a complex flexible tooling system, which significantly increases the manufacturing cost. Therefore, based on the above problems, the present application provides a large-size carbon fiber composite material wallboard precision hole making process method. SUMMARY

[0004] PURPOSE OF THE INVENTION

[0005] In order to solve the above problems, the purpose of the present application is to provide a large-size carbon fiber composite material wallboard precision hole making process method, which avoids the coordinate reference drift caused by the profile mismatch from the root, simultaneously realizes the hole making position precision control and the exit quality optimization, and reduces the dependence on auxiliary tooling, solves the systematic defects such as profile distortion caused by demolding stress release, secondary positioning reference conversion error and exit delamination damage in the traditional hole making process.

[0006] TECHNICAL SCHEME

[0007] In order to achieve the above object, the present application provides a large-size carbon fiber composite material wallboard precision hole making process method, which processes an axial blind hole type chip space in a preset hole position of a forming die, the diameter of the chip space is greater than the design hole diameter to form an annular chip area; a sacrificial material with a thermal expansion coefficient matched with the die and the composite material is filled in the chip space, and the machining chip is in a powder state to avoid fiber splitting; the wallboard is kept in an undemoulded state after curing, and a machining coordinate system is established through the die reference plane and the two end reference holes; an asymmetric multi-blade tool is used for high-speed low-feed machining, and a segmented feed strategy is used when the depth is above a critical value; the tool space pose and normal vector are obtained in real time through online detection before hole making, the path error is dynamically compensated, and the hole machining precision is ensured.

[0008] In the first aspect, the present application provides a large-size carbon fiber composite material wallboard precision hole making process method, comprising:

[0009] An axial extension chip space is processed in a preset hole position of a composite material wallboard forming die, and the chip space is a blind hole structure;

[0010] A sacrificial layer material with a thermal expansion matching coefficient is filled in the chip space, and the difference between the thermal expansion coefficient of the sacrificial layer material and the forming die and the composite material is less than a preset threshold value;

[0011] The composite material wallboard is kept in an undemoulded state after curing, and the wallboard and the forming die are positioned as a whole to a machining equipment;

[0012] A machining coordinate system is established based on the reference features of the forming die;

[0013] A multi-blade tool is used for hole making on the wallboard with the die, so that the tool penetrates the composite material laminate and cuts the sacrificial layer material, and the end of the tool does not contact the body of the forming die.

[0014] Further, the depth of the chip space is 1 / 3 to 2 / 3 of the thickness of the forming die, and the diameter of the chip space is greater than the design hole diameter of the wallboard to form an annular chip area, providing axial support and buffer to avoid damage at the outlet.

[0015] Further, the sacrificial layer material has a powder state of machining chip, which synchronously inhibits carbon fiber splitting and die damage.

[0016] A sacrificial material with a thermal expansion coefficient matched with the composite material and the die is filled in the pre-processed chip space of the die, the hardness of the sacrificial material is between the hardness of the composite material and the die, and the machining chip is in a powder state, forming an axial thermal deformation buffer and an outlet support composite structure. Synchronously realize the expansion stress equalization transmission in the thermal curing stage and the outlet damage inhibition in the hole making process, reduce the machining damage rate to below the critical threshold value, and avoid the damage of the equipment caused by the contact between the tool and the die body.

[0017] Further, the wallboard is fixed with the forming mold through detachable mechanical constraint or magnetic structure at the edge, and the clamping force direction is perpendicular to the profile of the contact area of the wallboard.

[0018] Further, the establishment of the machining coordinate system comprises: defining the first coordinate axis with the center line of the reference hole at both ends of the forming mold, and defining the second coordinate axis with the normal direction of the reference plane.

[0019] The positioning system is constructed with the forming mold body as the machining reference, the reference plane and the reference hole of the mold are reused to establish the machining coordinate system after the composite material wallboard is cured and remains in the unmolded state. The profile distortion caused by the demolding stress release and the reference conversion error caused by the secondary clamping are eliminated, the hole position drift problem is fundamentally solved, and the stable control of the aviation assembly precision is realized.

[0020] Further, the cutting edges of the multi-edge cutter are asymmetrically distributed, and the parameter combination of high-speed rotation and low-speed feeding is adopted during machining to reduce the interlaminar shear stress of the laminated plate.

[0021] Further, when the hole depth exceeds the preset critical value, a segmented feeding strategy is adopted to control the axial cutting force.

[0022] Further, the spatial pose data of the cutter is obtained in real time by an online detection system before the hole is made, the cutter path is dynamically compensated based on the vector deviation of the design hole position, and the curved surface normal deviation is automatically corrected.

[0023] In the second aspect, the application further provides a precision hole making system for large-size carbon fiber composite material wallboard, which comprises:

[0024] The forming mold with a chip space is provided with positioning reference features on the surface;

[0025] The sacrificial layer module is filled in the chip space and has a thermal expansion coefficient matched with the adjacent material;

[0026] The cooperative clamping mechanism is configured to constrain the displacement of the wallboard while maintaining the airtightness of the mold;

[0027] The pose closed-loop control module comprises an online detection unit and a path compensation unit.

[0028] Further, the pose closed-loop control module generates a cutter path correction instruction by comparing the deviation amount of the actual pose of the cutter and the theoretical normal vector of the design hole position in real time, and realizes the whole-process unmanned precision hole making.

[0029] The present application processes a blind hole type chip space in a preset hole position of a forming die, the depth is 1 / 2 of the thickness of the die, and the diameter is greater than the designed hole diameter of the wall plate; a sacrificial material with a thermal expansion coefficient matched with the composite material and the die is filled in the chip space, the machining chip is in a powder state and the hardness is between the composite material and the die; the wall plate remains in an unmolded state after curing, and a machining coordinate system is established through the reference plane and the two end reference holes of the forming die; high-speed low-feed machining is performed by using a three-point drill, and segmented feed is used when the depth exceeds the threshold value; the tool space pose and normal vector are obtained in real time through online detection before hole making, the path deviation is dynamically compensated, and it is ensured that the tool only cuts the sacrificial layer after penetrating the composite material and the end does not contact the die body.

[0030] The scheme directly reuses the reference features of the forming die, eliminates the demolding stress deformation and secondary positioning error, stabilizes the hole making position accuracy to meet the ±0.05mm tolerance requirement of the aviation fastening hole, provides axial support by the sacrificial layer and generates powder-like chips, completely solves the carbon fiber splitting and delamination defects at the outlet, omits the demolding, surface detection, secondary clamping and other processes and special machining equipment, shortens the process flow by more than 30%, and significantly reduces the manufacturing cost; the sacrificial layer material is cut during the hole making process, and the interface residual stress generated in the curing stage is actively released, so that the demolding external force is reduced by more than 70%, and the fiber breakage and die damage caused by forced demolding are avoided.

[0031] Advantages

[0032] By implementing the large-size carbon fiber composite material wall plate precision hole making process method provided by the present application, the following technical effects are achieved:

[0033] (1) The sacrificial material with a thermal expansion coefficient matched with the composite material and the die is filled in the machining chip space of the die, the hardness is between the two, and the machining chip is in a powder state, forming an axial thermal deformation buffer and outlet support composite structure. Synchronously realize the expansion stress equalization transmission in the thermal curing stage and the outlet damage inhibition in the hole making process, reduce the machining damage rate to below the critical threshold value, and avoid the equipment loss caused by the tool contacting the die body.

[0034] (2) A positioning system taking the forming die body as the machining reference is constructed, the composite material wall plate remains in an unmolded state after curing, and the machining coordinate system is established by directly reusing the reference plane and the reference hole of the die. The surface distortion caused by the demolding stress release in the traditional process and the reference conversion error caused by the secondary clamping are eliminated, the hole making position degree drift problem is fundamentally solved, and the stable control of the aviation assembly precision is realized.

[0035] (3) An integrated online detection system acquires the tool's spatial coordinates and normal vector in real time. Based on the vector deviation between these coordinates and the theoretical values ​​of the designed hole positions, a path compensation command is dynamically generated to drive the tool to adjust its posture along the normal of the theoretical surface of the panel. This breaks through the limitations of traditional static positioning in adapting to the deformation of composite material surfaces. It automatically corrects the deviation of the surface normal without demolding, ensuring that the perpendicularity of the hole axis meets the assembly requirements of high-clamping-force fasteners, and the compensation process does not interrupt the machining process.

[0036] (4) The mold is constrained and clamped by using the edge lug structure of the wall panel combined with the U-shaped clamp, and the residual stress at the interface generated during the curing stage is released during the hole making process. This solves the problem of difficult demolding caused by the long stringer locking of large-size co-cured wall panels, significantly reduces the external force required for demolding, avoids fiber breakage and matrix cracking caused by forced demolding, and extends the service life of the mold. Attached Figure Description

[0037] To make the above-described precision hole-making process for large-size carbon fiber composite wall panels of the present invention more obvious and understandable, the accompanying drawings used in the specific embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0038] Figure 1 This is a flowchart illustrating the method described in this application;

[0039] Figure 2 This is a schematic diagram of an online detection system;

[0040] Figure 3 This is a schematic diagram of side A of the carbon fiber panel.

[0041] Figure 4 This is a schematic diagram of side B of the carbon fiber panel.

[0042] Figure 5 This diagram illustrates the machining process for carbon fiber wall panels.

[0043] Figure reference numerals: 1-Composite wall panel; 2-Wall panel stringer; 3-Wall panel skin; 4-Forming mold; 5-Wall panel ear piece; 6-Tooling reference hole; 7-Wall panel hole position. Detailed Implementation

[0044] Example 1:

[0045] A method for precision drilling of large-size carbon fiber composite wall panels is provided, the process flow is as follows: Figure 1 As shown, it includes the following steps:

[0046] Step 1: After the composite material wall panel has cured, keep it in the un-demolded state and transfer the wall panel and molding die assembly as a whole to the worktable of the five-axis machining center; level the worktable using the machining reference plane of the molding die to meet the accuracy requirements and complete the Z-axis tool setting; take the reference holes at both ends of the mold length direction as the geometric reference: select the center of one reference hole as the origin of the workpiece coordinate system, define the direction of the line connecting the centers of the two reference holes as the positive direction of the X-axis, extend the Z-axis perpendicular to the reference plane upwards, and determine the Y-axis direction according to the right-hand rule.

[0047] Step 2: Select a three-pointed drill as the hole-making tool; set the machining parameters as follows: rotation speed 4000-8000 rpm, feed rate 30-80 mm / min. When the hole depth is >5 mm, consider the segmented pecking drilling process.

[0048] Step 3: Drive the machining equipment spindle to the designed hole position coordinates. The actual spatial coordinates of the tool tip and the tool axial normal vector are acquired in real time through an online detection system. The deviations between the measured tool tip coordinates and normal vector and the designed hole position are analyzed. After confirming that the deviations meet the assembly accuracy requirements, fixed-axis hole drilling is performed along the theoretical normal direction. The online detection system is as follows: Figure 2 As shown.

[0049] The tooling design is as follows.

[0050] Clearance hole structure:

[0051] In the pre-set hole area of ​​the carbon fiber composite panel molding die, an axially extending blind hole-type chip-receiving space is machined, corresponding to... Figure 5 Projected position of the wall panel connection hole of serial number 7.

[0052] The clearance hole has a depth of 1 / 2 of the forming mold thickness to maintain the integrity of the mold structure; its diameter is larger than the design aperture of the wall plate to form an annular cutting and accommodating area.

[0053] Its blind hole structure ensures airtightness during the mold curing stage. Figure 3 The skin on side A of the wall panel needs to be vacuum sealed, and the axis should be coaxial with the designed holes in the wall panel.

[0054] Sacrificial layer material composite structure:

[0055] Before laying the composite material, fill the clearance holes with a thermocoupled sacrificial material; the difference in their coefficients of thermal expansion is <10%.

[0056] The machining process generates powdery chips, eliminating the risk of fiber splitting and delamination, reducing the risk of damage to composite products, and increasing tool life; the curing stage can withstand high temperature and high pressure without plastic deformation, avoiding indentation defects in laminates.

[0057] Panel clamping system:

[0058] The unmolded wallboard is fixed by the double mechanism of mechanical constraint and profile interlocking, such as Figure 5 as shown in No. 3.

[0059] The wallboard edge is integrated with an ear structure, such as Figure 5 as shown in No. 5, with the same thickness as the wallboard and a width of ≥50 mm; the U-shaped clamp clamps the ear in the radial direction, and the clamping direction is perpendicular to the ear profile direction.

[0060] The wallboard B face stringer, such as Figure 4 as shown in No. 2, is embedded in the mold profile groove to form a distributed mechanical interlocking.

[0061] The clamping interface avoids the mold reference plane and the vacuum pipe interface.

[0062] Positioning reference system: the forming mold is integrated with high-precision geometric reference features, such as Figure 5 as shown in No. 6.

[0063] The reference plane surface roughness Ra≤0.8 μm, and the flatness is ≤0.05 mm / m², which is used for workpiece leveling and Z-axis tool setting.

[0064] The reference hole group is distributed at both ends of the mold length direction, and the coaxiality is ≤0.02 mm; the center line of the circle defines the processing coordinate system X axis, and the reference hole A is the origin, and the reference hole B points to X+.

[0065] The coordinate system Z axis is perpendicular to the reference plane upward, and the Y axis is determined according to the right-hand Cartesian rule.

[0066] Example 2:

[0067] On the basis of the foregoing examples, the process method of large-size composite wallboard with mold holes is further described.

[0068] Blind holes are processed in the preset hole position of the forming mold, with a depth of 1 / 2 of the mold thickness, and a diameter Φ8 mm greater than the design hole diameter. Then, the composite sacrificial material is vacuum injected into the avoidance hole, and the thermal expansion coefficient is less than 10% different from that of the carbon fiber composite material and the mold The difference is less than 10%, and the filling layer is flush with the mold after curing, and the machining chips are in a powder state.

[0069] After the carbon fiber wallboard is cured and kept in the unmolded state, the wallboard and mold integrated body are transported to the five-axis machining center. The workbench is leveled through the mold reference plane to complete the Z-axis tool setting, and the length direction two ends Φ10H7 reference holes are used as geometric reference: the left reference hole center is taken as the workpiece origin, the two hole center lines are taken as the X axis positive direction, the reference plane normal is taken as the Z axis positive direction, and the right-hand coordinate system is constructed.

[0070] The wallboard edge ear structure cooperates with multiple U-shaped clamps to be radially clamped, the clamping force of a single U-shaped clamp is 600N, and the wallboard B face stringer is embedded into the mold surface groove to form passive constraint. An asymmetric three-point drill is selected, the rotating speed is set to 4000-8000 rpm, and the feeding speed is 50 mm / min: continuous feeding when the hole depth is less than or equal to 5 mm; when the hole depth is greater than 5 mm, peck drilling is divided into three sections, and the feeding and chip removal are 0.5 s after each section; before drilling, the coordinates and normal vector of the drill tip are obtained in real time by a laser tracker, the tool pose is automatically corrected when the normal deviation is detected, the drilling is ensured along the theoretical normal direction, the tool only cuts the sacrificial layer after penetrating the composite material, and the depth is less than the thickness of the cutting layer.

[0071] After the drilling is completed, the wallboard is ejected. According to three-coordinate measurement, the maximum deviation of 120-hole position degree is 0.04 mm; the industrial CT shows that the hole wall has no delamination, and the outlet has no split wire.

[0072] By filling the sacrificial layer of thermal expansion matching through the reserved escape hole of the mold, the coordinate system is established by reusing the datum plane and the datum hole of the mold in the state that the wallboard is not demolded, combined with dynamic drilling of the three-point drill and online detection of the pose compensation, finally, the drilling position accuracy of ±0.04 mm can be realized, the solidification stress can be released synchronously, the demolding force can be reduced, and 25% cost can be saved by eliminating the secondary clamping process under the premise of considering the additional cost.

Claims

1. A large size carbon fiber composite material wallboard precision drilling process method, characterized in that, Comprising: Processing an axial extension of the chip space in the pre-set hole position of the composite panel forming die, the chip space is a blind hole structure, and the axis of the chip space is coaxial with the panel design hole position; Filling the sacrificial layer material in the chip space, the thermal expansion coefficient of the sacrificial layer material is less than the preset threshold value compared with the forming die and the composite material; the hardness of the sacrificial layer material is between the composite material and the forming die, and the machining chip shape of the sacrificial layer material is powder; Keeping the composite panel in the undemoulded state after curing, and positioning the panel and the forming die as a whole to the processing equipment; Establishing a machining coordinate system based on the reference features of the forming die; Using a multi-edge cutter to make holes in the die with the panel, so that the cutter penetrates the composite laminate and cuts the sacrificial layer material, and the cutter end does not contact the forming die body; Before drilling, the spatial pose data of the cutter is obtained in real time through the online detection system, and the deviation between the data and the theoretical normal vector of the design hole position is compensated dynamically based on the deviation.

2. The method of claim 1, wherein: The depth of the chip space is 1 / 3 to 2 / 3 of the thickness of the forming die, and its diameter is greater than the design hole diameter of the panel to form an annular chip area.

3. The method of claim 1, wherein: The panel is fixed with the forming die through detachable mechanical restraint or magnetic structure, and the clamping force direction is perpendicular to the panel contact area profile.

4. The method of claim 1, wherein: The establishment of the machining coordinate system includes defining the first coordinate axis with the center line of the reference hole at both ends of the forming die, and defining the second coordinate axis with the normal direction of the reference plane.

5. The method of claim 1, wherein: The cutting edges of the multi-edge cutter are asymmetrically distributed, and the parameter combination of high-speed rotation and low-speed feeding is used in processing.

6. The method of claim 5, wherein: When the drilling depth exceeds the preset critical value, a segmented feeding strategy is used to control the axial cutting force.

7. A large scale carbon fiber composite panel precision hole making system characterized by: The system executes the method of any one of claims 1-6 when running, comprising: A forming die with a chip space, the surface of which is provided with positioning reference features; A sacrificial layer module filled in the chip space and having a thermal expansion coefficient matched with the adjacent material; A cooperative clamping mechanism configured to constrain the displacement of the panel while maintaining the airtightness of the die; A pose closed-loop control module including an online detection unit and a path compensation unit.

8. The system of claim 7, wherein: The pose closed-loop control module generates cutter path correction instructions by comparing the deviation between the actual pose of the cutter and the theoretical normal vector of the design hole position in real time.

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