Precise hole forming process method for large-size carbon fiber composite material wall plate

Abstract

The invention discloses a large-size carbon fiber composite material wallboard precise hole making process method, and relates to the field of aviation composite material wallboard hole making, and the method comprises the steps that a chip containing space extending in the axial direction is machined in a preset hole position of a composite material wallboard forming mold, and the chip containing space is of a blind hole structure; the chip containing space is filled with a sacrificial layer material matched with thermal expansion, and the difference value between the thermal expansion coefficient of the sacrificial layer material and the forming mold and the composite material is smaller than a preset threshold value; the composite material wallboard is kept in a non-demolding state after being cured, and the wallboard and the forming mold are integrally positioned to machining equipment; establishing a processing coordinate system based on the reference features of the forming die; and a multi-cutting-edge tool is adopted for drilling the wall plate with the mold, so that the tool penetrates through the composite laminated plate and cuts the sacrificial layer material, and the tail end of the tool does not make contact with a forming mold body. According to the scheme, the precision of the connecting hole site of the composite material wallboard can be ensured, and the demolding deformation error, the outlet layering damage and the secondary clamping cost are synchronously eliminated.

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 release of demolding stress has a nonlinear characteristic, the traditional orthopedic technology cannot completely eliminate the residual strain, causing the coordinate reference of hole making 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 generated in the reference conversion process 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 shear stress concentration between carbon fiber layers, leading to splitting, delamination and other damages; when using co-curing process, the longer truss is embedded in the mold profile to form mechanical interlocking, and forced demolding may cause structural damage, while retaining the longer truss for hole making requires a complex flexible tooling system, significantly increasing 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] OBJECTIVE 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 can avoid the coordinate reference drift caused by profile mismatch from the root, simultaneously realize the position precision control and outlet quality optimization of hole making, and reduce the dependence on auxiliary tooling, solve the systematic defects such as profile distortion caused by demolding stress release, secondary positioning reference conversion error and outlet delamination damage in the traditional hole making process.

[0005] TECHNICAL SCHEME In order to achieve the above-mentioned purpose, the present application provides a large-size carbon fiber composite material wallboard precision drilling 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 larger 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 drilling, the path error is dynamically compensated, and the hole machining precision is ensured.

[0006] In the first aspect, the present application provides a large-size carbon fiber composite material wallboard precision drilling process method, comprising: Processing an axial extension chip space in a preset hole position of a composite material wallboard forming die, the chip space is a blind hole structure; Filling a thermal expansion matched sacrificial layer material in the chip space, 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; Keeping the composite material wallboard in an undemoulded state after curing, and positioning the wallboard and the forming die as a whole to a machining equipment; Establishing a machining coordinate system based on the reference features of the forming die; Using a multi-blade tool to drill 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.

[0007] 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 larger than the design hole diameter of the wallboard to form an annular chip area, providing axial support and buffer to avoid damage to the layered structure at the outlet.

[0008] Further, the sacrificial layer material has a powder form of machining chip, which synchronously inhibits carbon fiber splitting and die damage.

[0009] Filling a sacrificial material with a thermal expansion coefficient matched with the composite material and the die 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 drilling 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.

[0010] Further, the wallboard is fixed to the forming die through a detachable mechanical restraint or a magnetic attraction structure, and the clamping force direction is perpendicular to the profile of the contact area of the wallboard.

[0011] Further, the establishment of the machining coordinate system comprises: defining a first coordinate axis with the center line of the reference hole at both ends of the forming die, and defining a second coordinate axis with the normal direction of the reference plane.

[0012] A positioning system is constructed with the forming die body as the machining reference, and the composite material wall plate remains in the undemoulded state after curing, and the reference plane and the reference hole of the die are reused to establish the machining coordinate system. The distortion of the surface caused by the demoulding stress release and the reference conversion error caused by the secondary clamping in the traditional process are eliminated, the position drift problem of the hole making is fundamentally solved, and the stable control of the aviation level assembly precision is realized.

[0013] Further, the cutting edges of the multi-blade cutter are asymmetrically distributed, and the parameter combination of high-speed rotation and low-speed feeding is adopted during machining, so as to reduce the interlaminar shear stress of the laminated plate.

[0014] Further, when the hole making depth exceeds the preset critical value, a segmented feeding strategy is adopted to control the axial cutting force.

[0015] Further, the spatial pose data of the cutter is obtained in real time through an online detection system before hole making, the cutter path is dynamically compensated based on the vector deviation of the design hole position, and the surface normal deviation is automatically corrected.

[0016] In the second aspect, the application further provides a precision hole making system for a large-size carbon fiber composite material wall plate, which comprises the method according to the first aspect. The forming die is provided with a positioning reference feature on the surface and has a chip space; The sacrificial layer module is filled in the chip space and has a thermal expansion coefficient matched with the adjacent material; The cooperative clamping mechanism is configured to constrain the displacement of the wall plate under the condition of maintaining the air tightness of the die; The pose closed-loop control module comprises an online detection unit and a path compensation unit.

[0017] 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, so as to realize the whole-process unmanned precision hole making.

[0018] 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.

[0019] 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.

[0020] Advantages 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: (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.

[0021] (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.

[0022] (3) The integrated online detection system acquires the spatial coordinates and normal vector of the tool in real time, generates path compensation instructions dynamically based on the vector deviation between the theoretical value of the designed hole and the actual value, and drives the tool to adjust the normal posture along the theoretical profile of the wallboard. This method breaks through the adaptability limitations of traditional static positioning to composite material curved surface deformation, automatically corrects the normal deviation of the profile without demolding, ensures that the hole axis perpendicularity meets the assembly requirements of high locking force fasteners, and the compensation process does not interrupt the processing flow.

[0023] (4) The mold constraint clamping is realized by the wallboard edge ear structure combined with the U-shaped clamp, and the interface residual stress generated in the solidification stage is released during the hole making process. This method solves the demolding difficulty problem of large-size co-cured wallboard caused by long string embedding, significantly reduces the external force required for demolding, avoids the fiber breakage and matrix cracking caused by forced demolding, and prolongs the service life of the mold. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to make the above-mentioned large-size carbon fiber composite material wallboard precision drilling process method of the present application more obvious and easy to understand, the drawings needed in the specific embodiment of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained from these drawings without creative labor for those skilled in the art.

[0025] Figure 1 The method flowchart of the present application is shown; Figure 2 The schematic diagram of the online detection system is shown; Figure 3 The schematic diagram of the A surface of the carbon fiber wallboard is shown; Figure 4 The schematic diagram of the B surface of the carbon fiber wallboard is shown; Figure 5 The schematic diagram of the carbon fiber wallboard machining is shown; Reference signs: 1-composite wallboard; 2-wallboard stringer; 3-wallboard skin; 4-molding mold; 5-wallboard ear; 6-fixture reference hole; 7-wallboard hole position. DETAILED DESCRIPTION

[0026] Example 1: A large-size carbon fiber composite material wallboard precision drilling process method is provided, and the method flowchart is shown as Figure 1 The method includes the following steps: Step one, after the curing of the composite wallboard, keep the wallboard and the forming mold integrated body in the unmolded state, and transfer the integrated body to the workbench of the five-axis machining center; adjust the workbench to meet the accuracy requirements through the machining reference plane of the forming mold, 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 end 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, and extend the Z-axis vertically to the reference plane, and determine the direction of the Y-axis according to the right-hand rule.

[0027] Step two, select a three-point drill as the hole making tool; set the machining parameter range as 4000-8000 rpm for the rotation speed and 30-80 mm / min for the feed speed, and consider the segmented pecking drill process when the hole depth is greater than 5 mm.

[0028] Step three, drive the spindle of the machining equipment to move to the designed hole coordinate, obtain the actual space coordinates of the tool tip point and the axial normal vector of the tool in real time through the online detection system, analyze the deviation between the measured tool tip coordinates and the normal vector and the designed hole, and execute the fixed-axis hole making along the theoretical normal direction after confirming that the deviation meets the assembly accuracy requirements. The online detection system is shown in Figure 2 .

[0029] The method and tooling design are as follows.

[0030] Avoidance hole structure: In the preset hole position area of the carbon fiber composite material wallboard forming mold, an axially extending blind hole type chip space is processed, which corresponds to Figure 5 the projection position of the wallboard connecting hole of sequence number 7.

[0031] The avoidance hole meets the requirement that the depth is 1 / 2 of the thickness of the forming mold, and maintains the integrity of the mold structure; the diameter is greater than the designed hole diameter of the wallboard, and forms an annular cutting accommodation area.

[0032] The blind hole structure guarantees the airtightness of the mold during the curing stage, Figure 3 the A-surface skin of the wallboard needs to be vacuum sealed, and the axis is coaxial with the designed hole position of the wallboard.

[0033] Sacrificial layer material composite structure: Before the composite material is laid, a thermally coupled sacrificial material is filled into the avoidance hole; the difference between the thermal expansion coefficients is less than 10%.

[0034] The machining process generates powder-shaped chips, eliminates the risk of fiber splitting and delamination, reduces the damage risk to the composite product, and increases the tool life; the sacrificial layer material can withstand high temperature and high pressure without plastic deformation during the curing stage, and avoids indentation defects of the laminated board.

[0035] Wallboard clamping system: The unmolded wallboard is fixed through the double mechanisms of mechanical constraint and profile interlocking, as shown in Figure 5 sequence number 3.

[0036] Wallboard edge integrated ear structure, such as Figure 5 No. 5, the thickness is the same as the wallboard, and the width is greater than or equal to 50 mm; the U-shaped clamp clamps the ear in the radial direction, and the clamping direction is perpendicular to the ear profile direction.

[0037] Wallboard B face stringer, such as Figure 4 No. 2, embedded in the mold profile groove, forming a distributed mechanical interlocking.

[0038] The clamping interface avoids the mold reference plane and the vacuum pipe interface.

[0039] Positioning reference system: the forming mold integrates high-precision geometric reference features, such as Figure 5 No. 6.

[0040] The reference plane surface roughness Ra is less than or equal to 0.8 microns, and the flatness is less than or equal to 0.05 mm / m², which is used for workpiece leveling and Z-axis tool setting.

[0041] The reference hole group is distributed at both ends of the mold length direction, and the coaxiality is less than or equal to 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+.

[0042] 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.

[0043] Example 2: On the basis of the foregoing embodiment, the large-size composite wallboard with mold hole process method is further described.

[0044] A blind hole type avoidance hole is processed in the preset hole position of the forming mold, the depth is 1 / 2 of the mold thickness, and the diameter Φ8mm is greater than the design hole diameter. Then, the composite sacrificial material is vacuum filled into the avoidance hole, and the thermal expansion coefficient is less than 10% of the carbon fiber composite material and the mold The difference is less than 10%, and the filling layer formed after curing is flush with the mold, and the machining chips are in a powder state.

[0045] The carbon fiber wallboard remains in the demolding state after curing, and the wallboard and mold integrated body is transported to the five-axis machining center. The Z-axis tool setting is completed by leveling the workbench through the mold reference plane, 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 center line of the two holes is the positive direction of X axis, and the normal direction of the reference plane is the positive direction of Z axis, and the right-hand coordinate system is constructed.

[0046] 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.

[0047] 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.

[0048] 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 precision hole-making process for large-size carbon fiber composite wall panels, characterized in that, include: A chip-receiving space extending axially is machined at a preset hole position in the composite material wall panel molding die, and the chip-receiving space is a blind hole structure. The chip space is filled with a sacrificial layer material that matches thermal expansion, and the difference between its coefficient of thermal expansion and that of the molding die and the composite material is less than a preset threshold. Keep the composite wall panel in a state of being cured and not demolded, and position the wall panel and molding die together in the processing equipment; A machining coordinate system is established based on the reference features of the molding die; A multi-bladed tool is used to make holes in the molded wall panel, allowing the tool to penetrate the composite laminate and cut the sacrificial layer material, while the tip of the tool does not contact the forming mold body.

2. The method according to claim 1, characterized in that: The depth of the chip-containing space is 1 / 3 to 2 / 3 of the thickness of the forming mold, and its diameter is larger than the design aperture of the wall panel to form an annular chip-containing area.

3. The method according to claim 1, characterized in that: The machining chips of the sacrificial layer material are in powder form.

4. The method according to claim 1, characterized in that: The wall panel is fixed to the forming mold by a detachable mechanical constraint or magnetic structure at the edge, and the clamping force is perpendicular to the surface of the contact area of ​​the wall panel.

5. The method according to claim 1, characterized in that: The establishment of the machining coordinate system includes: defining the first coordinate axis by connecting the centers of the reference holes at both ends of the forming mold, and defining the second coordinate axis by the normal direction of the reference plane.

6. The method according to claim 1, characterized in that: The cutting edges of the multi-bladed tool are asymmetrically distributed, and a combination of high-speed rotation and low-speed feed is used during machining.

7. The method according to claim 6, characterized in that: When the hole depth exceeds the preset critical value, a segmented feed strategy is adopted to control the axial cutting force.

8. The method according to claim 1, characterized in that: Before drilling, the spatial pose data of the tool is acquired in real time through an online detection system, and the tool path is dynamically compensated based on the vector deviation between this data and the designed hole position.

9. A precision drilling system for large-size carbon fiber composite wall panels, characterized in that: The system executes the method according to any one of claims 1-8 during operation, including: A molding die with a chip space has positioning reference features on its surface; The sacrificial layer module is filled within the chip space and its coefficient of thermal expansion matches that of the adjacent material. The collaborative clamping mechanism is configured to constrain the displacement of the wall plate while maintaining the airtightness of the mold; The pose closed-loop control module includes an online detection unit and a path compensation unit.

10. The system according to claim 9, characterized in that: The pose closed-loop control module generates tool path correction commands by comparing the deviation between the actual tool pose and the theoretical normal vector of the designed hole position in real time.

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