Preparation method and forming tool of a particle therapy device terminal membrane window

Abstract

This application provides a method for preparing a terminal membrane window of a particle therapy device, comprising: applying radial pretension to a Kevlar fiber liner to place the Kevlar fiber liner in a pre-tensioned state; sequentially positioning and stacking at least two layers of epoxy resin prepreg and polyimide film on the Kevlar fiber liner to construct a tooling unit; vacuum sealing the tooling unit to press and adhere the Kevlar fiber liner, at least two layers of prepreg, and polyimide film together; and performing heat curing on the sealed tooling unit to form an integral membrane window structure with a preset prestress, wherein the at least two layers of prepreg are cured to form a gradient stiffness layer with gradually decreasing thickness and smooth stiffness transition along the axial direction away from the Kevlar fiber liner. This application also provides a molding tooling for performing the above method.

Description

Technical Field

[0001] This disclosure relates to the field of precision instrument manufacturing technology, and more specifically, to a method for preparing a terminal membrane window of a particle therapy device and a molding tooling. Background Technology

[0002] In proton or heavy ion therapy devices, the high-energy beam generated by the accelerator needs to be introduced into the treatment chamber through a transmission line or rotating gantry. As the physical boundary between the vacuum system and the atmospheric environment, the vacuum window needs to withstand a pressure difference of approximately 0.1 MPa while minimizing beam scattering to ensure the energy accuracy of the Bragg peak.

[0003] Currently, the mainstream technology adopts a composite structure of "polyimide film + Kevlar fiber reinforcement layer + epoxy resin". However, in traditional manufacturing processes, the penetration behavior of liquid epoxy resin in Kevlar textile structures is difficult to control precisely. Uneven resin distribution is easily caused by capillary effect, resulting in increased brittleness in resin-rich areas and potential vacuum leakage in resin-deficient areas. At the same time, the abrupt change in performance between the rigid flange and the flexible film can create shear stress concentration under differential pressure loads, often leading to fatigue tearing from the sealing edge after hundreds of cyclic loading cycles.

[0004] Furthermore, the relaxed Kevlar liner lacks effective pre-tensioning, and its large deformation under pressure makes the equivalent medium thickness through which the beam passes unpredictable, affecting beam spot stability. Existing processes are highly dependent on manual operation, involving cumbersome procedures and long cycles. Environmental fluctuations further lead to poor product consistency, making it difficult to meet the quality control requirements of large-scale production. Summary of the Invention

[0005] In view of this, the present disclosure provides a method for preparing a terminal membrane window of a particle therapy device and a molding tooling.

[0006] One aspect of this disclosure provides a method for preparing a membrane window for a particle therapy device terminal, comprising: applying radial pretension to a Kevlar fiber liner to place the Kevlar fiber liner in a pre-tensioned state; sequentially positioning and stacking at least two layers of epoxy resin prepreg and a polyimide film on the Kevlar fiber liner to construct a tooling unit; vacuum sealing the tooling unit to press and adhere the Kevlar fiber liner, the at least two layers of epoxy resin prepreg, and the polyimide film together; and performing heat curing on the sealed tooling unit to form an integral membrane window structure with a preset prestress, wherein the at least two layers of epoxy resin prepreg are cured to form a gradient stiffness layer with a gradually thinning thickness and smooth stiffness transition along the axial direction away from the Kevlar fiber liner from the outside to the inside.

[0007] According to embodiments of this disclosure, the at least two epoxy resin prepreg sheets are annular sheets with the same outer diameter and an inner diameter that increases sequentially in the direction away from the Kevlar fiber liner.

[0008] According to embodiments of this disclosure, the step of vacuum sealing the tooling unit to press and bond the Kevlar fiber liner, the at least two epoxy resin prepreg sheets, and the polyimide film together includes: inserting the tooling unit entirely into a vacuum chamber for sealing and covering; activating the vacuum system to evacuate the vacuum chamber and remove air between the Kevlar fiber liner, the at least two epoxy resin prepreg sheets, and the polyimide film.

[0009] According to embodiments of this disclosure, the heat curing of the packaged tooling unit includes: maintaining a constant temperature below the resin gel point to soften the resin matrix in the epoxy resin prepreg and impregnate the Kevlar fiber liner and the polyimide film; heating to the curing temperature at a predetermined rate and applying external pressure to cause the resin matrix to undergo a crosslinking reaction and cure, thereby bonding the Kevlar fiber liner, the at least two epoxy resin prepreg layers, and the polyimide film in a pre-tensioned state together to form an integral membrane window structure with a preset prestress.

[0010] According to embodiments of this disclosure, before clamping the Kevlar fiber liner membrane to the pre-tightening assembly, the method further includes: subjecting the Kevlar fiber liner membrane to plasma surface activation treatment to form polar functional groups on its surface for enhancing chemical bonding with the resin matrix.

[0011] Another aspect of this disclosure provides a molding fixture for performing the preparation method as described in any of the preceding aspects, comprising: a positioning structure; at least one fixture unit, sequentially stacked along the axial direction of the positioning structure, the fixture unit comprising at least: a pre-tightening component for clamping a Kevlar fiber liner and applying radial pretension to the Kevlar fiber liner; at least two epoxy resin prepreg sheets, the at least two epoxy resin prepreg sheets being concentric ring sheets with the same outer diameter and an inner diameter that gradually increases in a direction away from the Kevlar fiber liner, stacked above the Kevlar liner; a polyimide film disposed above the at least two epoxy resin prepreg sheets; the fixture unit, after being vacuumed and heated for curing, forms an integral membrane window structure with a preset prestress, the at least two epoxy resin prepreg sheets being cured to form a gradient stiffness layer with a gradually thinning thickness and a smooth transition in stiffness along the axial direction away from the Kevlar fiber liner.

[0012] According to an embodiment of this disclosure, the pretensioning assembly includes: an outer ring, a mating ring, and a plurality of fastening bolts that cooperate with each other; when the outer ring and the mating ring are engaged, radial pretension is applied to the Kevlar liner membrane held between the outer ring and the mating ring; the plurality of fastening bolts are used to lock the outer ring and the mating ring.

[0013] According to an embodiment of this disclosure, the positioning structure includes: a base platform and at least two positioning guide posts vertically fixed on the base platform; the tooling unit is sleeved on the positioning guide posts.

[0014] According to an embodiment of this disclosure, the tooling unit further includes: a lower mold partition, sleeved on the positioning structure and located below the tooling unit, for supporting the tooling unit.

[0015] According to an embodiment of this disclosure, the tooling unit further includes: an upper molding plate, which is slidably sleeved on the positioning structure and located above the tooling unit, for transmitting molding pressure during the curing process.

[0016] This disclosure utilizes prepreg to replace manual casting, fundamentally solving the problem of brittleness or leakage caused by uneven resin penetration, and achieving a high degree of consistency in product thickness and performance. Through a gradient layup design, a smooth stiffness transition is created between the flange and the membrane, effectively eliminating edge stress concentration and significantly improving the fatigue life of the membrane window. Simultaneously, the introduction of the Kevlar membrane pre-tensioning process imparts initial structural stiffness to the membrane window, greatly reducing axial deformation under vacuum pressure differential and ensuring the stability of beam passage. Furthermore, the design of a multi-station stacked mold enables "one mold, multiple outputs," shortening the average manufacturing time of a single membrane window and upgrading the manufacturing process from a workshop-style operation to traceable, standardized industrial production. Attached Figure Description

[0017] The above and other objects, features and advantages of this disclosure will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0018] Figure 1 A flowchart illustrating a method for preparing a terminal membrane window of a particle therapy device according to an embodiment of the present disclosure is shown schematically.

[0019] Figure 2 A schematic diagram of the tooling unit according to an embodiment of the present disclosure is shown.

[0020] Figure 3 A schematic diagram of the structure of a molding tooling according to an embodiment of the present disclosure is shown.

[0021] Explanation of reference numerals in the attached figures:

[0022] 110 - Base platform; 120 - Positioning guide post; 210 - Pre-tightening component outer ring; 220 - Pre-tightening component mating ring; 230 - Fastening bolt; 240 - Lower mold partition plate; 250 - Upper mold pressure plate; 300 - Vacuum cavity; A - Kevlar fiber liner; B - Polyimide film; C1 - One layer of epoxy resin prepreg sheet; C2 - Another layer of epoxy resin prepreg sheet. Detailed Implementation

[0023] The embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the disclosure. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the present disclosure for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.

[0024] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0025] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0026] When using expressions such as "at least one of A, B and C", they should generally be interpreted in accordance with the meaning that is commonly understood by those skilled in the art (e.g., "a system having at least one of A, B and C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B and C, etc.).

[0027] Figure 1 A flowchart illustrating a method for preparing a terminal membrane window of a particle therapy device according to an embodiment of the present disclosure is shown.

[0028] like Figure 1 As shown, the preparation method of this embodiment is used to fabricate the membrane window of the terminal of a particle therapy device, including steps S110 to S140.

[0029] S110, apply radial pretension to the Kevlar fiber liner to put the Kevlar fiber liner in a pre-tensioned state.

[0030] In this embodiment, the Kevlar fiber liner is first subjected to plasma surface activation treatment to form polar functional groups on its surface that enhance chemical bonding with the resin matrix. Specifically, using plasma surface treatment technology, the Kevlar fiber liner is placed in a plasma treatment device, and process gases such as oxygen or argon are introduced under vacuum conditions. High-frequency power supply excitation generates high-energy active particles. These active particles effectively remove residual organic contaminants and weak boundary layers from the fiber manufacturing process through physical bombardment, while simultaneously introducing highly active polar functional groups, such as hydroxyl (-OH) and carboxyl (-COOH) groups, onto the chemically inert Kevlar surface through chemical reactions. This treatment significantly increases the surface free energy of the Kevlar fiber, laying the foundation for a strong chemical bond with the epoxy resin matrix and effectively preventing interfacial delamination.

[0031] Secondly, the liner is mechanically pre-tensioned to introduce initial stiffness. The activated Kevlar liner is placed in a dedicated metal pre-tensioning mechanism, placing it in a pre-tensioned state. This process not only flattens the flexible textile structure but, more importantly, ensures that the Kevlar liner possesses a preset initial tension, or prestress, before curing. This ensures that the finished membrane window has higher initial stiffness when subjected to vacuum loads, significantly reducing axial deformation during operation and guaranteeing controllable deformation of the polyimide film.

[0032] S120, at least two layers of epoxy resin prepreg and polyimide film are sequentially positioned and stacked on the Kevlar fiber liner to construct a tooling unit.

[0033] In this embodiment, aerospace-grade low-temperature curing epoxy resin prepreg with uniform thickness and precisely controllable resin content is selected as the adhesive carrier. Based on the simulation results of stress distribution of the membrane window under vacuum pressure difference, i.e., the distribution law of large edge shear stress and small center stress, CNC cutting technology is used to cut the prepreg into a series of concentric rings with the same inner diameter and increasing outer diameter. These prepreg rings with different apertures will form a gradient stiffness layer with gradually decreasing thickness and smooth stiffness transition from the edge of the metal flange to the central beam region away from the Kevlar fiber liner during subsequent laying, so as to eliminate the edge stress concentration effect.

[0034] In this embodiment, a Kevlar liner assembly in a pre-tensioned state is used as the skeleton layer; at least two layers of epoxy resin prepreg are stacked on the Kevlar liner, and an ultrathin polyimide film, i.e., the H-film, serving as the main airtight layer, is placed on the prepreg to construct the tooling unit. This specific layup method successfully creates a transition region with gradually decreasing stiffness between the rigid metal support and the flexible functional film, effectively avoiding stress singularities caused by abrupt changes in interface stiffness.

[0035] S130, vacuum sealing of the tooling unit to press and bond the Kevlar fiber liner, at least two layers of epoxy prepreg and polyimide film together.

[0036] In this embodiment, the tooling unit is installed in a vacuum chamber 300 or a vacuum bag film for sealing and covering; the vacuum system is activated to evacuate the vacuum chamber 300, removing air and volatiles between the Kevlar fiber liner, at least two layers of epoxy resin prepreg and polyimide film, and achieving initial tight bonding between the prepreg and the substrate under atmospheric pressure, thus eliminating internal pore defects.

[0037] S140, heat curing is performed on the packaged tooling unit to form an integral membrane window structure with preset prestress, wherein at least two layers of epoxy resin prepreg are cured to form a gradient stiffness layer with gradually thinning thickness and smooth stiffness transition along the axial direction away from the Kevlar fiber liner.

[0038] In this embodiment, the packaged tooling system is placed in an autoclave or cured using a vacuum chamber 300 with built-in heating and pressurization functions, strictly following a specific segmented temperature-pressure coupling curve. The first stage is a low-temperature leveling and wetting stage. A constant temperature is maintained for a period of time at a specific temperature below the resin's gel point, while maintaining a high vacuum. During this stage, the viscosity of the epoxy resin in the prepreg decreases, resulting in softening and leveling. Driven by the vacuum negative pressure, it fully impregnates the Kevlar fiber liner and polyimide film, while simultaneously continuously extracting trace amounts of volatile gases escaping from the resin.

[0039] The second stage is the high-temperature and high-pressure crosslinking stage. The temperature is increased to the final curing temperature at a predetermined rate, and external mechanical pressure or autoclave pressure is applied. During this stage, the resin undergoes a crosslinking reaction and finally cures and sets. This process bonds the pre-tensioned Kevlar fiber liner, at least two layers of epoxy resin prepreg, and the polyimide film together to form an integral membrane window structure with preset prestress. The gradient stiffness layer increases in outer diameter along the direction away from the Kevlar fiber liner, effectively avoiding stress singularities caused by abrupt changes in interface stiffness.

[0040] It should be noted that the epoxy resin prepreg used can be replaced with a polyimide resin system or a cyanate ester resin system prepreg, which have better radiation resistance, to adapt to higher dose beam environments. Furthermore, the adhesive layer can also be a thermoplastic polymer film, bonded via high-temperature melt bonding, instead of a thermosetting prepreg, achieving a similarly strong bond between layers.

[0041] Regarding the interface modification method, the plasma treatment used in the embodiments of this disclosure can be replaced by chemical etching treatment, such as acid washing activation to treat the surface of Kevlar fibers; or it can be replaced by coupling agent surface coating treatment, by coating the surface of Kevlar fibers with silane coupling agents, etc., which can achieve similar surface activation effects and enhance the interfacial bonding strength.

[0042] Regarding the curing process, for small-batch production scenarios, the autoclave process used in this embodiment can be replaced by a combination of a vacuum oven and a mechanical press. Specifically, the packaged laminated mold can be placed in a vacuum oven for heating and vacuuming, while an external mechanical press applies mechanical pressure to the mold, thereby replacing the gas isostatic pressure of the autoclave and achieving the same resin curing and molding.

[0043] This disclosure provides a molding tooling, including: a positioning structure and at least one tooling unit.

[0044] In this embodiment of the disclosure, the positioning structure includes: a base platform 110 and at least two positioning guide posts 120 vertically fixed on the base platform 110.

[0045] The tooling unit is fitted onto the positioning guide post 120 through corresponding guide holes, and the positioning guide post 120 ensures the coaxiality and positional accuracy of each tooling unit. At least one tooling unit is stacked sequentially along the axial direction of the positioning structure. This stacked design allows multiple membrane window components to be processed simultaneously within the same curing cycle, achieving a "one mold, multiple outputs" production efficiency improvement.

[0046] The tooling unit includes at least: a pre-tightening assembly, a polyimide film B, and at least two layers of epoxy resin prepreg sheets (C1 and C2).

[0047] A pretensioning assembly is used to clamp a Kevlar fiber liner A and apply radial pretension to the Kevlar fiber liner A.

[0048] Figure 2 and Figure 3 Schematic diagrams of tooling units and molding tooling according to embodiments of the present disclosure are shown respectively.

[0049] like Figure 2 and Figure 3As shown, the pretensioning assembly includes: an outer ring 210, a mating ring 220, and multiple fastening bolts 230 that cooperate with each other. When the outer ring 210 and the mating ring 220 are engaged, the outer ring 210 forces the Kevlar fiber liner A to undergo relative displacement, thereby applying radial pretension to the Kevlar fiber liner A sandwiched between the outer ring 210 and the mating ring 220. The multiple fastening bolts 230 are distributed circumferentially to lock the outer ring 210 and the mating ring 220, maintaining the tension of the Kevlar liner A. This ensures that the finished membrane window has higher initial stiffness when subjected to vacuum loads, significantly reduces axial deformation under working conditions, and ensures controllable deformation of the polyimide film B.

[0050] A polyimide film B is placed above the Kevlar liner A as the main airtight layer. This film uses ultrathin polyimide (H film) material, which has excellent airtightness and radiation resistance.

[0051] At least two epoxy resin prepreg sheets (C1 and C2) are stacked between the polyimide film B and the Kevlar liner A. These epoxy resin prepreg sheets (C1 and C2) are made of aerospace-grade low-temperature curing epoxy resin prepreg, which features uniform thickness and precise controllable resin content.

[0052] like Figure 2 As shown, at least two epoxy resin prepreg sheets (C1 and C2) with the same outer diameter and an inner diameter that increases sequentially away from the Kevlar fiber liner are stacked below the polyimide film B, forming a stepped arrangement. By laying ring sheets with different outer diameters, a gradient stiffness layer is constructed with a gradually thinning thickness and smooth stiffness transition from the edge of the metal flange to the central beam region in the radial direction, thereby eliminating the edge stress concentration effect and preventing interface delamination.

[0053] In this embodiment of the invention, the tooling unit further includes a lower mold partition 240 and an upper mold pressure plate 250.

[0054] A lower mold partition plate 240 is fitted onto the positioning structure, located below the tooling unit, to support the tooling unit. An upper mold plate 250 is slidably fitted onto the positioning structure, located above the tooling unit, to transmit molding pressure during the curing process.

[0055] When multiple tooling units are stacked vertically through positioning guide posts 120, adjacent tooling units are separated by lower mold partitions 240 to ensure that each membrane window assembly is formed independently.

[0056] This molding tooling can be used to achieve, for example... Figure 1 The preparation method shown.

[0057] The thickness deviation of the membrane window manufactured according to the preparation method and molding apparatus provided in this disclosure is controlled within ±0.02 mm. The membrane window can be held under pressure difference of 1.5 times for 24 hours without leakage. In the fatigue test of simulated alternating pressure difference load, the average cycle life of the membrane window reaches more than 100,000 cycles. In the axial deformation test, the maximum axial displacement of the membrane window under a pressure difference of 0.1 MPa is 0.5 mm, which verifies the significant effect of the pre-tensioning process on improving geometric stability.

[0058] In summary, this disclosure fundamentally solves the problems of uneven resin penetration, edge stress concentration, uncontrollable deformation, and low manufacturing efficiency in traditional manufacturing processes by using quantitative prepreg to replace manual casting, creating a unique gradient stiffness transition structure, introducing a dual enhancement process of interface activation and stress pre-setting, and developing a layered vacuum hot-press curing mode. It realizes the leap from "handmade art" to "industrial standardized product" for vacuum membrane windows, and has extremely high industrial application value.

[0059] The embodiments of this disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this disclosure, and all such substitutions and modifications should fall within the scope of this disclosure.

Claims

1. A method for preparing a terminal membrane window of a particle therapy device, characterized in that, include: Apply radial pretension to the Kevlar fiber liner to put the Kevlar fiber liner in a pre-tensioned state; At least two layers of epoxy resin prepreg and polyimide film are sequentially positioned and stacked on the Kevlar fiber liner to construct a tooling unit. The tooling unit is vacuum-sealed to press and bond the Kevlar fiber liner, the at least two layers of epoxy resin prepreg, and the polyimide film together. The packaged tooling unit is heated and cured to form an integral membrane window structure with a preset prestress, wherein the at least two layers of epoxy resin prepreg are cured to form a gradient stiffness layer with gradually thinning thickness and smooth stiffness transition along the axial direction away from the Kevlar fiber liner.

2. The preparation method according to claim 1, characterized in that, The at least two epoxy resin prepreg sheets are concentric ring sheets with the same outer diameter and an inner diameter that increases sequentially in the direction away from the Kevlar fiber liner.

3. The preparation method according to claim 1, characterized in that, The step of vacuum sealing the tooling unit to press and bond the Kevlar fiber liner, the at least two layers of epoxy resin prepreg, and the polyimide film together includes: The tooling unit is installed into a vacuum chamber and sealed. The vacuum system is activated to evacuate the vacuum chamber, removing the air between the Kevlar fiber liner, the at least two layers of epoxy resin prepreg, and the polyimide film.

4. The preparation method according to claim 1, characterized in that, The process of performing heat curing on the packaged tooling unit includes: Maintaining a constant temperature below the resin gel point softens the resin matrix in the epoxy resin prepreg sheet and impregnates the Kevlar fiber liner and the polyimide film. The temperature is increased to the curing temperature at a predetermined rate, and external pressure is applied to cause the resin matrix to undergo a cross-linking reaction and cure. This process bonds the Kevlar fiber liner, the at least two layers of epoxy resin prepreg, and the polyimide film in a pre-tensioned state together to form an integral membrane window structure with a preset prestress.

5. The preparation method according to claim 1, characterized in that, The method further includes: The Kevlar fiber liner is subjected to plasma surface activation treatment to form polar functional groups on its surface for enhancing chemical bonding with the resin matrix.

6. A molding fixture for performing the method for preparing the terminal membrane window of a particle therapy device as described in any one of claims 1 to 5, characterized in that, include: Positioning structure; At least one tooling unit is stacked sequentially along the axial direction of the positioning structure, and the tooling unit includes at least: A pretensioning assembly for clamping a Kevlar fiber liner and applying radial pretension to the Kevlar fiber liner; At least two layers of epoxy resin prepreg sheets are concentric ring sheets with the same outer diameter and an inner diameter that gradually increases in a direction away from the Kevlar fiber liner, and are stacked on top of the Kevlar fiber liner. A polyimide film is disposed above the at least two layers of epoxy resin prepreg sheets; After vacuuming and heating curing, the tooling unit forms an integral membrane window structure with a preset prestress. The at least two layers of epoxy resin prepreg sheets are cured to form a gradient stiffness layer with gradually thinning thickness and smooth stiffness transition along the axial direction away from the Kevlar fiber liner.

7. The molding tooling according to claim 6, characterized in that, The pretensioning component includes: A mutually cooperating outer ring, a mating ring, and multiple fastening bolts; When the outer ring engages with the mating ring, a radial pretension is applied to the Kevlar fiber liner membrane held between the outer ring and the mating ring; The plurality of fastening bolts are used to lock the outer ring and the mating ring.

8. The molding tooling according to claim 6, characterized in that, The positioning structure includes: A base platform and at least two positioning guide posts vertically fixed on the base platform; The tooling unit is fitted onto the positioning guide post.

9. The molding tooling according to claim 6, characterized in that, The tooling unit also includes: A lower mold partition is fitted onto the positioning structure and located below the tooling unit to support the tooling unit.

10. The molding tooling according to claim 6, characterized in that, The tooling unit also includes: An upper molding plate is slidably sleeved on the positioning structure and located above the tooling unit, used to transmit molding pressure during the curing process.

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