A mold and a molding method for NOL ring preparation

Abstract

This invention discloses a mold and molding method for preparing NOL rings. By designing clamps on the surface of the segmented cylindrical mandrel and adjusting the axial width of the sample, two different NOL ring preparation methods, namely single-ring winding and cylindrical ring cutting, can be used as needed. The mold design is compact, and after modifying the yarn comb of the winding machine, it can achieve simultaneous winding of 3 NOL rings in a single operation, increasing efficiency by 2 times. After winding, a vacuum bag can be made on the smooth mandrel surface after removing the clamps, so that some dry prepreg samples can be bag-pressed or autoclaved. Under external molding pressure, the interlaminar shear strength is increased by 70% compared with dry samples without external pressure.

Description

Technical Field

[0001] This invention belongs to the field of composite fiber winding molding, and in particular, a mold and molding method for preparing NOL rings. Background Technology

[0002] Fiber winding technology for composite materials has been widely used in civilian and defense fields due to its low cost and stable quality, becoming an ideal molding method for fiber-reinforced composite rotors, pressure vessels, and solid rocket motor casings. For the winding process, the tensile and shear properties of the NOL ring specimen are often used as evaluation criteria to verify the rationality of the process. The molding methods are divided into two categories: single-ring winding and cylindrical ring cutting. Currently, the single-ring winding method is more commonly used to ensure the fiber continuity of the specimen and avoid damage to the specimen's performance due to machining. The cylindrical ring cutting method ensures uniform winding of the material inside the NOL ring and avoids the influence of slippage on the sides of the winding process on the specimen's performance. The winding process for preparing NOL rings is divided into wet and dry processes. For some dry-wound prepreg NOL rings, external molding pressure is required during curing to ensure sufficient compaction between layers. However, most existing molds are single-ring molds for a single purpose, which cannot form NOL cylinders. The mold structure is complex, and only one NOL ring can be wound at a time. Furthermore, they do not have external pressure conditions and rely solely on the winding tension as the curing pressure, making it difficult to guarantee the interlayer quality of some dry NOL rings.

[0003] To prepare NOL ring specimens that meet the requirements, relevant units proposed a single-ring winding mold and forming fixture. The specimen diameter is guaranteed by the mold, the width is guaranteed by the left and right baffles or machining, and the outer diameter is guaranteed by the winding process control and thickness direction grinding. This scheme initially solved the problem of preparing NOL ring specimens by the single-ring winding method. However, in actual operation, the mold is not universal and can only prepare single-ring specimens. When the influence of the slip line has a significant impact on the uniformity of the internal material, it is impossible to prepare specimens by the cylindrical ring cutting method. When winding a single ring, only one NOL ring can be wound at a time, resulting in low forming efficiency. Some prepreg dry-wound specimens cannot provide effective external pressure during curing, resulting in low interlaminar shear performance.

[0004] Patent CN 204894497 U, entitled "A Winding Mold Assembly for Manufacturing Resin-Based Fiber Composite Material NOL Rings," designs a NOL ring winding mold assembly that can fit multiple single-ring winding molds onto a mandrel to achieve the winding and forming of multiple NOL rings. However, the segmented mold feature determines that this mold cannot produce NOL cylinders, can only wind one NOL ring at a time, and cannot apply external pressure during curing.

[0005] Patent CN 114074434 A, entitled "A Winding Device for Manufacturing Composite Material NOL Rings," developed a single-ring winding device that can conveniently and quickly prepare NOL rings while controlling process parameters such as winding speed, winding tension, adhesive content, and yarn width. However, it can only produce one NOL ring at a time and does not have the conditions for vacuum bag curing. Summary of the Invention

[0006] The purpose of this invention is to provide a mold and molding method for the preparation of NOL rings, so as to solve the problems of poor versatility, low molding efficiency and unsuitability for bag pressing and autoclave curing of existing NOL ring winding tooling.

[0007] The technical solution to achieve the purpose of this invention is as follows:

[0008] A mold for preparing NOL rings includes a mandrel, front and rear cover plates, a cylindrical mandrel, clamps, a yarn separating comb, and a pressure equalizing plate.

[0009] The mandrel has two symmetrically protruding discs for supporting the cylindrical mandrel on the mandrel, and the outer diameter of the discs is equal to the inner diameter of the cylindrical mandrel.

[0010] The cylindrical core mold adopts a multi-lobed structure;

[0011] The front and rear cover plates are respectively set on both sides of the cylindrical core mold, which on the one hand provide boundary constraints during the winding of the cylinder, and on the other hand restrict the circumferential and axial misalignment of the cylindrical core mold;

[0012] The front and rear cover plates extend inwards, and the inner wall of the extended section matches the outer diameter of the cylindrical core mold.

[0013] The clamp is tightened onto the surface of the cylindrical mandrel, and the inner diameter of the clamp is equal to the outer diameter of the cylindrical mandrel.

[0014] When winding a single ring, the assembly spacing between adjacent clamps is the width of the NOL ring sample; when winding a cylinder, the assembly spacing between adjacent clamps is the custom cylinder width.

[0015] The core mold is L in length and the disk is b in width. d The distance L between the two disks on the spindle d =L-2b d The length of the front and rear cover plates extending inward is l. p Satisfying L = 2l p +(n-1)b h +nb nol Where n is the number of single-ring specimens formed; b h b is the width of the clamp; nol This refers to the assembly spacing between adjacent clamps;

[0016] The yarn separating comb is equipped with multiple rubber rollers, with each pair of rubber rollers forming a group. The distance L between the axes of adjacent rubber rollers in each group is [missing information]. r1 =b c +D r The distance L between the axes of two adjacent rubber rollers in each group r2 =b r +D r ; where b c For yarn width, D r b is the diameter of the rubber roller; r This refers to the distance between two adjacent rubber rollers in different groups;

[0017] The equalizing plate is the same width as the sample and is used to fix the sample surface during dry prepreg winding to dry and cure the sample.

[0018] The significant advantages of this invention compared to existing technologies are:

[0019] 1) The clamp position is adjustable. Based on the test requirements, the NOL ring can be prepared by single ring winding method or cylindrical ring cutting method on the same set of molds. The number of tensile test specimens and the number of shear test specimens in a single molding can be selected independently, which increases the flexibility of test design.

[0020] 2) The mold design is highly compact. When winding a single ring, with the modified yarn separating comb, it can wind 3 NOL rings at the same time, which increases the forming efficiency by 2 times compared with other molds.

[0021] 3) After removing the clamps, the mold surface is smooth and flat. For some dry winding samples, bags can be made for bag pressing or autoclave curing. Under external pressure, the interlayer bonding strength is guaranteed, and the interlayer shear strength is increased by 70% compared with the sample without external pressure. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the NOL ring sample assembly mold.

[0023] Figure 2 This is a schematic diagram of the assembly of a three-lobed cylindrical core mold.

[0024] Figure 3 This is a schematic diagram of the dimensions of the NOL ring sample assembly mold.

[0025] Figure 4 This is a schematic diagram of single-ring synchronous winding.

[0026] Figure 5 This is a schematic diagram of a modified yarn separating comb.

[0027] Figure 6 This is a schematic diagram of the curing process for vacuum bags made using the dry NOL tube method. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0029] Combination Figures 1-3 The present invention provides a mold for preparing NOL rings, comprising a mandrel 11, front and rear cover plates 12, a three-lobed cylindrical mandrel 13, clamps 14, a pressure equalizing plate 15, and a yarn separating comb 21; after assembling the clamps 14 according to the sample width requirements, n single-ring samples (n being a multiple of 3) or n ’ A cylindrical sample. The mandrel 11 is of stepped design, with two symmetrically raised discs on it, each disc having a width of b. d This serves to support the three-lobed cylindrical core mold 13 and ensure circumferential fit accuracy; the distance L between the two disks on the core shaft 11 d =L-2b d The outer diameter of the disk is equal to the inner diameter d of the cylindrical core mold. c The front and rear cover plates 12 provide boundary constraints during cylindrical winding and, in addition, engage with the three-lobed cylindrical mandrel 13 via pins to limit circumferential and axial misalignment of the mandrel 13. Furthermore, when engaged with the mandrel 11, they restrict overall axial movement. The front and rear cover plates 12 are mounted on both sides of the cylindrical mandrel 13, each extending inward by 1... p The length of the extension section inner wall and the outer diameter D of the cylindrical core mold 13 c The fit is such that the assembly spacing is L-2l. p The actual winding range is represented by the combined outer diameter D of the cylindrical mandrel 13. c The inner diameter of the NOL ring sample is equal to the required inner diameter, i.e., 150 ± 0.2 mm. The mandrel 13 is divided into sections with a length of L and a wall thickness of t from the front end to the rear end. c The mold has three lobes. The arc lengths of the three lobes are not evenly divided: the smaller lobe, core mold 131, has a smaller outer arc length lc1, shorter on the outside and longer on the inside, and the normals of its two sides have a certain included angle θ (about 160°) to facilitate demolding; the other two lobes, core mold 132 and core mold 133, have the same outer arc length lc2, lc1 + 2lc2 = πD. c Clamp 14 has a two-lobed structure, and the inner diameter of clamp 14 is equal to the outer diameter D of the three-lobed cylindrical mandrel 13. c The circumference is slightly shorter than that of a complete circular ring by Δl (1-2mm), ensuring that the clamp 14 can be tightly clamped onto the surface of the cylindrical core mold 13 after connection. That is, the inner arc length l of a single clamp 14 is... h Satisfy πD c =2l h +Δl; Clamp 14 is bolted to the surface of the three-lobed cylindrical core mold 13. During single-ring winding, the assembly spacing between adjacent clamps 14 is b. nol That is, the width of the NOL ring sample is 6 ± 0.2 mm; when winding the cylinder, the assembly spacing between adjacent clamps 14 is the custom cylinder width b. cy ; clamp 14 width b hThe diameter should be ≤5mm, and should be as small as possible to make the mold axis as compact as possible while ensuring the required rigidity. The length L of the cylindrical core mold 13 should be designed in conjunction with this diameter to ensure L = 2l. p +(n-1)b h +nb nol .

[0030] Combination Figure 4 To achieve single-pass molding of multiple NOL single loops, the yarn separating comb 21 at the yarn box outlet and the end of the guide nozzle of the winding machine 2 was modified according to the mold design. Combined with... Figure 5 The yarn-splitting comb has a total of 6 rubber rollers 212. Each rubber roller 212, relying on the engagement of its bottom thread and nut, can move and be fixed axially along the opening slot on the mounting platform 211. Every two rubber rollers 212 form a group, and the distance L between the axes of adjacent rubber rollers 212 in each group... r1 =b c +D r The distance L between the axes of two adjacent rubber rollers 212 between groups r2 =b r +D r Among them, b c For yarn width, D r For the diameter of the rubber roller 212, b r >0 represents the spacing between two adjacent rubber rollers 212 in a group, satisfying 2D. r +b c +b r =b h +b nol For different yarn widths b c The spacing L of the rubber rollers 212 r1 With L r2 Fine adjustments can be made along the opening groove at the bottom of the mounting platform 211.

[0031] Combination Figure 6 For some dry prepreg winding samples, the clamps 14 need to be removed during curing, and a segmented (2-3 segments) metal plate is placed on the sample surface as a pressure equalizing plate 15. The pressure equalizing plate 15 is the same width as the sample and has a thickness of 1-2 mm.

[0032] The present invention also provides a molding method for preparing NOL ring specimens based on the aforementioned mold, comprising the following steps:

[0033] Step 1: After assembling the mandrel 11, front and rear cover plates 12 and the three-lobed cylindrical core mold 13 together, adjust the number and spacing of the clamps 14 according to the test requirements, and then tighten them.

[0034] Step 2: The sample thickness is controlled by the number of winding turns, which is defined on the winding machine. Wherein, h... t The thickness of the tensile specimen is 1.5 ± 0.1 mm; h sThe thickness of the shear test specimen is 3 ± 0.1 mm.

[0035] Winding single layer thickness t ply Calculated by the following formula:

[0036]

[0037] In the formula, Y is the linear density of the fiber bundle; V f ρ is the fiber volume fraction; f This refers to fiber density.

[0038] Number of turns of tensile specimen winding c t The number of turns of the shear sample winding c s Calculated by the following formula:

[0039]

[0040] Step 3: For the single-loop winding method, before preparation, replace the yarn separating comb 21 at the yarn box outlet and the end of the guide nozzle of the winding machine 2, according to the actual yarn width b. c Adjust the spacing L between the axes of two rubber rollers 212 in the same group and two adjacent rubber rollers 212 in different groups on the bottom opening groove of the mounting platform 211. r1 With L r2 The fibers are impregnated with resin or prepregs and wound circumferentially. A set (3) of NOL single rings can be formed simultaneously in one winding. Each winding is done in n / 3 times, with a spacing of b between n-1 rings. nol Between clamps 14, n are prepared according to requirements. t A thickness of h t Single-ring stretched sample 3 and n s A thickness of h s Single-ring layer shear sample 4, n t +n s =n. For the cylindrical circumferential method, n is the number of segments. ’ The segment is continuously wound circumferentially between the two cover plates 12n ’ Within a range of -1 adjacent clamps (14), n clamps can be prepared in a single batch as needed. t ’ A thickness of h t Cylindrical stretching samples 9 and n s ’ Each width is h s Cylindrical layer shearing sample 10, n t ’ +n s ’ =n ’ .

[0041] Step 4: After winding, wet-wound samples can be directly placed in an oven for curing. For some dry-wound prepreg samples, the clamps 14 need to be removed, and a segmented pressure plate 15 needs to be placed on the sample surface to obtain a smooth surface. Sealing strips 5 should be placed on both sides of the sample to prevent excessive resin overflow. Then, the release film 6 and breathable felt 7 should be placed in sequence. Vacuum bags 8 should be fixed at both ends of the mandrel 11 using sealing strips 5. Finally, the sample should be placed in an oven for vacuum bag pressing curing, or in an autoclave for curing. Under external pressure, the interlaminar bond strength is guaranteed, and the interlaminar shear strength is increased by 70% compared to samples without external pressure.

[0042] Step 5: After curing is complete, remove the auxiliary materials, mandrel 11 and front and rear cover plates 12. Gently tap the unwound area of ​​the smaller mandrel 131 in the three-lobed cylindrical mandrel 13 until the fit is loose. Then remove the three-lobed mandrel 13 to complete the demolding of all samples at once.

[0043] Step 6: Single-ring wound specimens do not require machining in the width direction; cylindrical wound specimens require machining to b. nol The width is then determined. After removing burrs and processing the shear test specimen, it is then tested.

Claims

1. A mold for preparing NOL rings, characterized in that, Includes mandrel, front and rear cover plates, cylindrical mandrel, clamps, yarn separating comb and equalizing plate; The mandrel has two symmetrically protruding discs for supporting the cylindrical mandrel on the mandrel, and the outer diameter of the discs is equal to the inner diameter of the cylindrical mandrel. The cylindrical core mold adopts a multi-lobed structure; The front and rear cover plates are respectively set on both sides of the cylindrical core mold, which on the one hand provide boundary constraints during the winding of the cylinder, and on the other hand restrict the circumferential and axial misalignment of the cylindrical core mold; The front and rear cover plates each extend inward, and the inner wall of the extended section matches the outer diameter of the cylindrical core mold. The clamp is fastened to the surface of the cylindrical core mold, and the inner diameter of the clamp is equal to the outer diameter of the cylindrical core mold; When winding a single ring, the assembly spacing between adjacent clamps is the width of the NOL ring sample; when winding a cylinder, the assembly spacing between adjacent clamps is the custom cylinder width. The core mold is L in length and the disk is b in width. d The distance L between the two disks on the spindle d =L-2b d The length of the front and rear cover plates extending inward is l. p Satisfying L=2l p +(n-1)b h +nb nol Where n is the number of single-ring specimens formed; b h b is the width of the clamp; nol This refers to the assembly spacing between adjacent clamps; the clamp position is adjustable. The yarn separating comb is equipped with multiple rubber rollers, the spacing between which is adjustable. Each pair of rubber rollers forms a group, and the distance L between the axes of adjacent rubber rollers in each group is [missing information]. r1 =b c +D r The distance L between the axes of two adjacent rubber rollers in each group r2 =b r +D r ; where b c For yarn width, D r b is the diameter of the rubber roller; r This refers to the distance between two adjacent rubber rollers in different groups; The equalizing plate is the same width as the sample and is used to fix the sample surface during dry prepreg winding to shape and solidify the sample.

2. The mold for preparing NOL rings according to claim 1, characterized in that, The spacing between adjacent rollers in each group should meet the 2D requirement. r +b c +b r =b h +b nol .

3. The mold for preparing NOL rings according to claim 1, characterized in that, The cylindrical core mold adopts a three-lobed structure.

4. The mold for preparing NOL rings according to claim 3, characterized in that, The arc lengths of the three segments of the cylindrical core mold are not evenly divided: the angle between the normals of the two sides of the smaller segment of the core mold is an obtuse angle.

5. The mold for preparing NOL rings according to claim 4, characterized in that, The outer arc length of the other two core lobes is lc2, satisfying lc1 + 2lc2 = πD. c lc1 is the outer arc length of the smaller mandrel, D c It is the outer diameter of the cylindrical core mold.

6. A molding method for preparing NOL ring specimens, characterized in that, The method of using the mold for preparing NOL rings as described in any one of claims 3-5 includes the following steps: Step 1: After assembling the mandrel, front and rear cover plates and the three-lobed cylindrical mandrel, adjust the number and spacing of the clamps and tighten them. Step 2: Write the processing program on the winding machine and define the sample thickness; Step 3: For the single-loop winding method, replace the yarn separating combs at the yarn box outlet and the end of the guide nozzle of the winding machine before preparation, according to the actual yarn width b. c Adjust the distance L between the axes of two rubber rollers in the same group and two adjacent rubber rollers in different groups. r1 With L r2 ; The fibers are impregnated with resin or wound circumferentially using prepreg, with n-1 intervals of b. nol Between the clamps, n are prepared according to requirements. t A thickness of h t Single-ring stretched sample and n s A thickness of h s Single-ring layer shearing, n t +n s =n; For the cylindrical circumferential method, divide into n ’ The segment is continuously wound circumferentially between the two cover plates. ’ Within a range of -1 adjacent clamps, n are prepared in a single process. t ’ A thickness of h t cylindrical stretching sample and n s ’ A thickness of h s Cylindrical layer shearing sample, n t ’ +n s ’ =n ’ ; Step 4: After the winding is completed, the wet-wound sample can be directly put into the oven for curing; some dry-wound prepreg samples need to have the clamps removed, and a segmented pressure plate placed on the sample surface to obtain a smooth part surface. Sealing strips are placed on both sides of the sample to prevent excessive resin overflow. Then, the release film and breathable felt are placed in sequence, and the vacuum bag is fixed at both ends of the mandrel with sealing strips. Finally, it is put into the oven for vacuum bag pressing and curing, or into the autoclave for curing. Step 5: After curing is complete, remove the auxiliary materials, mandrel and front and rear cover plates, and take out the cylindrical core mold. All samples can be demolded at once.

7. The molding method for preparing NOL ring specimens according to claim 6, characterized in that, The thickness of the sample is controlled by the number of winding turns, and the thickness of a single winding layer is t. ply Calculated by the following formula: ； In the formula, Y is the linear density of the fiber bundle; V f is the fiber volume fraction; is the fiber density; Number of turns of tensile specimen winding c t The number of turns of the shear sample winding c s Calculated by the following formula: ； In the formula, h t h is the thickness of the tensile specimen. s The thickness of the shear test specimen is given.

8. The molding method for preparing NOL ring specimens according to claim 7, characterized in that, For single-ring wound specimens, no machining is required in the width direction; for cylindrical wound specimens, the specimen needs to be machined to b. nol The width is then determined; after removing the burrs and processing the layered shear test specimen, it is tested.

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