Net-shape undercut finocyl grain casting mandrel and a method thereof
The mandrel assembly for solid rocket propellants addresses the limitations of conventional methods by enabling net-shape manufacturing of undercut finocyl grains with a core and fins, ensuring safety and efficiency in grain formation without propellant machining or squeeze casting.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- DIRECTOR GENERAL DEFENCE RES & DEV ORG
- Filing Date
- 2025-12-23
- Publication Date
- 2026-07-09
AI Technical Summary
Conventional mandrel assemblies for manufacturing undercut finocyl grains in solid rocket propellants face issues with non-rigid mandrels' inconsistency, safety, stability, scalability, and reusability, and require propellant machining to achieve the final shape, which is unsafe and slow.
A mandrel assembly comprising a core and forward swept fins, securely fastened to the rocket case, allows for net-shape manufacturing by assembling the mandrel parts inside the case, inverting for propellant casting, and decoring without squeeze casting or propellant machining, using a core and fins to form the final grain shape directly.
Enables safe, efficient, and automated manufacturing of undercut finocyl grains with reduced part count, minimizing manual intervention and safety risks, suitable for high viscosity propellant slurries, and achieving precise grain features without additional machining.
Smart Images
Figure IN2025052128_09072026_PF_FP_ABST
Abstract
Description
[0001] TECHNICAL FIELD
[0002] Present disclosure relates to the field of casting mandrels, particularly but not exclusively, the invention describes a rigid, disassemblable, casting mandrel assembly and a method for net-shape manufacturing of undercut finocyl grains of solid propellant rockets, without employing squeeze casting or propellant machining methods, towards generating typical high performance booster thrust profiles.
[0003] BACKGROUND OF THE DISCLOSURE
[0004] Solid rockets are self-contained jet propulsion devices. A typical solid rocket generates thrust force by burning solid chemical reactants called a propellant grain and expelling the resulting hot gases through a supersonic nozzle. The propellant grain is contained inside an internally insulated, thin walled, high-pressure vessel called a rocket case. The typical rocket case is cylindrical shaped with a fore-end dome and an aft-end dome. The fore-end dome has a central aperture for attaching an igniter. The aft-and dome has a central aperture for attaching a nozzle. The igniter starts the combustion process. Once ignited, the grain burns on all its exposed surfaces in parallel layers. Different types of burning patterns and thus thrust profiles can be preprogrammed in a solid rocket by shaping its grain geometry accordingly.
[0005] A common method of manufacturing solid rocket propellant grains is by filling propellant slurry around a monolithic casting mandrel placed inside the rocket case (casting), followed by heating the total assembly till the propellant slurry solidifies into propellant grain (curing), and lastly removing the mandrel (decoring).
[0006] Large solid rockets are mainly used as space launch vehicle boosters. To maximize payload capability for a given orbit and to minimize size and mass of the space launch vehicle, typical advanced space solid rocket boosters use monolithic, light-weight, filament-wound, composite cases with small apertures in their end domes. Optimal launch vehicle booster thrust profile shapes are ‘M-type’ for first stages and neutral or regressive for upper stages. To produce the high and sustained initial thrust force, the propellant grain configurations need large burning surface area. The propellant grains are also required to have maximum volumetric loading to keep the boosters compact. Finocyl is one versatile grain configuration that meets all the above criteria. In a finocylgrain, a circular array of local longitudinal cavities or fin slots are disposed around a central cylindrical cavity. The fin slots extend radially almost up to the grain boundary in typical high performance boosters. But the composite rocket case apertures are usually less than half of the case diameter. As the cross sectional dimensions of the grain cavities are larger than the case apertures, the conventional monolithic casting mandrels are not suitable for manufacturing the undercut finocyl grains.
[0007] Early methods of making undercut finocyl grains involved the use of non-rigid casting mandrels made of wax or Eutectic alloy that melted at slightly elevated temperatures (US 3983780). Later, water-soluble mandrels were used in some large segmented rockets (AIAA 93-2057). Mandrels that could be deflated (JP 2013040588A), consumed (US 3570364) or collapsed (US 6101948) were also developed. But the non-rigid mandrels performed poorly in terms of either consistency, cleanliness, safety, stability, scalability or reusability.
[0008] To overcome said limitations, rigid undercut mandrels that could be disassembled into smaller parts were developed. In them, individual mandrel parts are temporarily connected to each other using some type of mechanism. The parts are sequentially assembled inside the empty rocket case prior to propellant casting and removed in reverse order after propellant curing.
[0009] In the conventional casting process, propellant slurry is filled into the rocket case through annular gap between the case aft-end aperture and the casting mandrel. Along with the insides of the case, the annular gap remains filled with propellant as the slurry solidifies. After mandrel extraction, the unwanted propellant in the aft-end aperture is removed by carefully scrapping or machining the cured grain. In a rocket using submerged nozzle, a matching counterbore is also created in the grain using special cutting tools. But propellant machining is both unsafe and slow. Therefore, it is desirable to directly realize the final grain shape without propellant machining but by using minimum number of mandrel parts and assembly steps.
[0010] A European Patent Application EPl 522711 A2 teaches a rigid type mandrel for net-shape casting of undercut finocyl grains with aft-end counterbore. The mandrel employs a central locating body releasably joined to a number of fins by means of a hydraulic or mechanical cam actuated device housed within the locating body. Annular sectorial gaps formed between case aft-end aperture, fins and locating body are used for filling the propellant slurry inside the rocket case. Once theslurry is filled up to the brim, ‘n’ number of annular plugs are sunk or pushed into the propellant slurry between ‘n’ number of fin mandrels. Each plug is outwardly shaped as a sector of a counterbore. As the plugs are hollow and have entry holes at bottom, excess propellant slurry enters the plugs and solidifies. During decoring, the annular plugs filled with cured propellant are removed first followed by the locating body and the fins. However, said squeeze casting method is not suitable when propellant slurry viscosity levels are high. Also, for smooth assembly, sufficient gaps are maintained all around the assembled plugs. Slurry solidifying in those gaps as thin slices or chips of the combustible material can pose a safety risk. With high total part count, the prior art employs complex mechanisms that need adjusting during field assembly. All these shortcomings with the prior art call for better and safer techniques.
[0011] Another prior art (IN479665) discloses a mandrel assembly for net-shape casting of undercut finocyl grains with forward swept fins and aft-end counterbore. The counterbore is formed by a base mandrel. Major part of the central cavity is formed by a core mandrel coaxially inserted into the base mandrel. In this prior art, fins are suspended inside the case from the case fore-end aperture and the setup is lowered onto the base mandrel. The fins are then manually assembled to core mandrel from inside the case. It does not teach about secure sealing at interfaces of fins and core. The method involves manual assembly inside the rocket case and therefore is slow and less safe.
[0012] The present disclosure is directed to overcome one or more limitations stated above or any other limitations associated with the prior arts.
[0013] SUMMARY OF THE DISCLOSURE
[0014] One or more shortcomings of conventional mandrel assemblies have been overcome by a mandrel assembly and assembly method as claimed and additional advantages are provided through constructional aspects and assembly methods of the mandrel assembly as claimed in the present disclosure.
[0015] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined together to form a further embodiment of the disclosure.Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.
[0016] Accordingly, the present disclosure relates to a novel net-shape casting mandrel assembly for making undercut finocyl grains in advanced solid rocket cases with small end-dome apertures. The mandrel assembly has minimum part count. The mandrel assembly comprises of a core and a plurality of forward swept fins in circular pattern around the core. The core is a hollow axisymmetric structure, removably and securely fastened to aft-end aperture of the case. The core comprises of a wide aft-end section capable of forming a counterbore in grain, a long mid-section capable of forming a cylindrical cavity in grain and a thin fore-end section with a conical end capable of distributing propellant slurry inside the case. The core has a plurality of core-wedges for removably connecting to a plurality of fins. The fins have a plurality of fin-wedges, fin studs and nuts for removably connecting to the core. A rubber seal fills the gap between each fin and the core. Each fin is capable of forming a longitudinal cavity in the grain.
[0017] Further, the present disclosure relates to a method of manufacturing the net-shape undercut finocyl grain using the mandrel assembly by assembling the mandrel parts inside the rocket case in the following sequence. With their aft-ends up, all the fins are suspended from the core in a circular pattern using a fin hanger and a plurality of long flexible cables. The total mandrel setup is hoisted above the case aft-end aperture and lowered into the case, fins first, followed by the core. Mating of fin and core wedges and fastening of the fin studs and nuts follow. After the core aft-end is fastened to the case aft-end aperture, for propellant casting, the total setup is inverted. Through a hopper in the case fore-end aperture, propellant slurry is cast. After curing, the total setup is inverted back for decoring. After unfastening from the case and the fins, the core is removed. A fin decoring tool is used for removing one fin at a time. This net-shape manufacturing process does not need propellant machining or squeeze casting. All final grain features including the counterbore are directly formed by the core and the fins themselves.
[0018] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined together to form a further embodiment of the disclosure.The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
[0019] BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0020] The novel features and characteristic of the disclosure are set forth in the appended claims. The disclosure itself, however, as well as a preferred mode of use, further objectives, and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures. One or more embodiments are now described, by way of example only, with reference to the accompanying figures wherein like reference numerals represent like elements and in which:
[0021] Figure 1 shows sectional view of a mandrel assembly ready for insertion into a rocket case in accordance with an embodiment of the present disclosure
[0022] Figure 2 shows sectional and detailed views of core in accordance with an embodiment of the present disclosure
[0023] Figure 3 shows sectional and detailed views of fin in accordance with an embodiment of the present disclosure
[0024] Figure 4 shows sectional view of mandrel assembly partially inserted into the rocket case in accordance with an embodiment of the present disclosure
[0025] Figure 5 shows sectional view of mandrel assembly fully inserted into the rocket case in accordance with an embodiment of the present disclosure
[0026] Figure 6 shows inverted rocket case with mandrel assembly ready for propellant casting in accordance with an embodiment of the present disclosure
[0027] Figure 7 shows fin being removed from the cured propellant grain in accordance with an embodiment of the present disclosure
[0028] Figure 8 shows net-shape cast and decored undercut finocyl grain with aft-end counterbore in accordance with an embodiment of the present disclosureThe figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the apparatus and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
[0029] DETAILED DESCRIPTION
[0030] While the embodiments in the disclosure are subject to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the figures and will be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.
[0031] It is to be noted that a person skilled in the art would be motivated from the present disclosure and modify construction of the mandrel assembly along with a method for manufacturing a solid propellant grain using the mandrel assembly. However, such modifications should be construed within the scope of the disclosure. Accordingly, the drawings show only those specific details that are pertinent to understand the embodiments of the present disclosure, so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.
[0032] The terms “comprises”, “comprising”, or any other variations thereof used in the disclosure, are intended to cover a non-exclusive inclusions, such that a device and a method that comprises a list of components does not include only those components but may include other components not expressly listed or inherent to such device and the system. In other words, one or more elements in the device or the system proceeded by “comprises... a” does not, without more constraints, preclude the existence of other elements or additional elements in the device or the system.
[0033] The present disclosure describes a casting mandrel assembly (100) and a method for net-shape manufacturing of undercut finocyl shaped propellant grains (133) with aft-end counterbore (140) in typical advanced monolith composite solid rocket cases with small end apertures (103, 104). An innovative approach is used for making provision for filling propellant slurry inside the rocket case (101) and at the same time obtain the final shape in one-step without the need for propellantmachining or squeeze casting. The basic mandrel assembly (100) comprises of a central hollow core (105) and a plurality of forward swept fins (106) circular patterned about the core (105). The core (105) at its aft-end is removably connected to the case (101) aft-end, effectively closing the case aft-end aperture (104). In the grain, the core (105) forms a central cylindrical cavity with an aft-end counterbore (140). Fore-end of the core (105) may project out of the case fore-end aperture (103), radially unsupported, forming an annular gap for propellant slurry casting. On its outer surfaces, the core (105) has a plurality of core-wedges (115) for removably connecting to the plurality of fins (106). Two different embodiments of wedges (115, 116) are shown in the disclosure. The core (105) also has a plurality of axial elongated through holes (118) for passing a plurality of fin cables (108) of a fin hanger (107). The fin (106) is a thin longitudinal structure with a root (119), tip (120) and forward-swept leading and trailing edges (121). Fin root (119) conformally interfaces with the core (105) while maintaining a uniform gap for a sandwiched rubber seal. Each fin (106) has fin-wedges (124, 125) to mate with core-wedges (115, 116). When a mating wedge pair is brought together axially, the core (105)-wedge pushes the fin (106)-wedge radially towards the core (105), thus compressing the rubber seal. Each fin (106) also has tapped holes for two axial studs (127) to connect to fin cables (108) and also removably fasten to the core (105) with nuts. The fins (106) form forward swept fin cavities (139) in the grain that can support mass of the fins (106) before decoring.
[0034] The mandrel (100) parts are assembled inside the rocket case (101) using a novel method. The plurality of fins (106) is hung from the core (105) using a fin hanger (107) with a plurality of long and flexible fin cables (108). The mandrel assembly (100) is hoisted above the case aft-end aperture (104) and lowered inside the rocket case (101). The suspended fins (106) are bundled for insertion into the case (101). Once inside, the fins (106) are let free to be disposed in a circular pattern around the core (105). When near their final location, further downward movement of the fins (106) is stopped. The core (105) is further lowered, even as the fin cables (108) by themselves align the core-wedges (115) to enter into respective fin slots (123) so as to engage core-wedges (115, 116) and fin-wedges (124, 125). Once fully lowered, fin studs (127) projecting inside the core (105) are fastened with nuts, and in the process, compressing the sandwiched seals and securing the fins (106) to the core (105). Core aft-end flange (114) is fastened to case (101). Fin hanger (107) and cables (108) are removed. The setup is inverted for propellant casting through case fore-end aperture (103). After propellant curing, once again the setup is inverted for decoring.Core (105) is removed first. A novel fin decoring tool (134) is used for smoothly removing the fin (106) out of the undercut (139) it formed.
[0035] Figure 1 shows all major parts of the disclosed mandrel assembly (100) ready for insertion into a typical rocket case (101). The typical rocket case (101) is an axisymmetric, hollow, monolithic, filament- wound composite structure with a case axis (102) and end domes with a fore-end aperture (103) and an aft-end aperture (104). In one embodiment, the fore-end aperture (103) may be smaller than the aft-end aperture (104). For mandrel assembly (100) activities, the case (101) is mounted with its aft-end aperture (104) facing up.
[0036] The mandrel assembly (100) basically consists of a core (105) and a plurality of fins (106) suspended from the core (105) using a fin-hanger (107) and a plurality of flexible fin-cables (108) disposed in a circular pattern about core (105) axis which also aligns with the case axis (102) as shown in Figure 1.
[0037] Details of the core (105) are shown in Figure 2. The core (105) helps form the central cavities in the cast propellant grain (133). The core (105) is an axisymmetric hollow body with three sections - a core aft-end section (109), a core mid-section (110), and an optional core fore-end section (111). The core aft-end section (109) is a short and wide cylindrical structure that forms the aft-end counterbore (140) in the propellant grain (133). The core mid-section (110) is almost as long as the grain itself and it forms the main central cylindrical cavity (138) in the propellant grain (133). The core fore-end section (111), if present, may be a short and slender section with a conical end which will act as propellant slurry distributer during casting activity. All external surfaces of the core (105) are slightly tapered to ease and ensure its safe removal from cured propellant grain (133) at the end.
[0038] As shown in Figure 2, adjacent cylindrical sections of the core (109, 110, 111) with different diameters are connected by conical frustums (112, 113) or flat sections (not shown) with liberal fillet radii. Aft-end conical frustum (112) connects core sections (109) and (110). Fore-end conical frustum (113) connects core sections (110) and (111). The core aft-end section (109) has an aft-end flange (114) with a plurality of equispaced holes for fastening the mandrel assembly (100) to the rocket case (101) at its aft-end aperture (104).For removably connecting each fin (106) to core (105), at least two wedge-pairs are needed. The wedge-pairs may be flat wedges or conical wedges. The wedge-pairs may be similar or dissimilar. In the shown embodiment, the core mid-section (110) on its outer surface has a plurality of flat fore-end core-wedges (115) circular patterned about the core (105) axis. Each of the flat fore-end core- wedge (115) has a dovetail feature to enable engagement with linear motion (LM) guides in fin slots (123) later. Inside the core aft-end frustum (112) is housed a conical aft-end core-wedge (116), coaxial with core (105). Alternatively, in another embodiment (not shown), the conical wedge axis can be within the wedge itself. Conical wedges have some advantages. During assembling, the conical wedges are self-aligning. When fully assembled, the conical wedges by themselves can completely constrain the radial and lateral degrees of freedom of the fin (106) to core (105) assembly. The core-wedges (115, 116) may be integral, welded or removably fastened to the core (105).
[0039] In the aft-end frustum (112) shown in Figure 2, in-line with the circular patterned fore-end corewedges (115), are an equal number of axial rectangular holes (117) opening towards the aft-end core- wedge (116). The rectangular holes (117) will later allow fin wedges (125) to pass through and mate with the aft-end core-wedge (116) when assembling the mandrel (100) parts. Additionally, in the same radial direction as each rectangular hole (117), are two elongated holes (118), to accommodate fin cables (108) and fin studs (127) described later. In the shown embodiment, one of the elongated holes (118) is located in the aft-end frustum (112) and the other is in the aft-end core- wedge (116),
[0040] The fin (106) is shown in Figure 3. A plurality of fins (106) forms the undercut fin cavities (139) in the propellant grain (133). Their exact shape and numbers depend on design requirements. The basic fin (106) structure of this disclosure has the following regions: fin root (119), fin tip (120), fin leading edge (121) and fin trailing edge (122). Fin root (119) conformally interfaces with mid and aft-end sections of the core (105) with a uniform gap between them. For ease of extraction after propellant curing, fin (106) thickness decreases from root (119) to tip (120) and trailing edge (122) to leading edge (121). Fin (106) leading and trailing edges (121, 122) are forward swept, and the acute angle the fin leading edge (121) makes with case axis (102) on fore-end side is greater than that made by the trailing edge (122).As shown in Figure 3, the fin (106) at its root (119) has a stepped longitudinal slot (123) housing a flat fore-end fin-wedge (124) and a conical aft-end fin-wedge (125), matching with the flat foreend core-wedge (115) and the conical aft-end core-wedge (116) respectively. The fin slot (123) has linear motion guides (126) in the form of an opposing pair of longitudinal undercuts to engage the dove-tailed fore-end core-wedge (115) during assembly. The fin (106) wedges may be integral, welded or removably fastened to the fin (106). The fin (106) has two axial studs (127) to suspend from fin hanger (107) using fin cables (108) and to fasten to the core (105). On its exposed end, each stud (127) has a blind tapped hole to attach to a fin cable (108). In one embodiment, one of the studs (127) is screwed into the aft-end fin-wedge (125) and the other is screwed directly into the fin root (119) as shown in Figure 3. Radial locations of the fin studs (127) in the fin (106) are chosen such that center of gravity of the fin (106) lies between and beneath the two studs (127) when assembling the mandrel (100). Verticality of the fin (106) when suspended in fin hanger (107) may be achieved by adjusting relative lengths of fin cables (108).
[0041] A fin seal groove (128) runs all along inside the edges of the fin root (119). The closed-circuit groove (128) has undercuts to snap-fit a fin seal (129) with necessary protrusions. In one embodiment, the fin seal (129) is made of moulded rubber. Seal thickness should allow for sufficient compression (typically, 10% to 30%) when sandwiched between the core (105) and the fin (106) during mandrel assembly (100).
[0042] After the plurality of fins ( 106) are suspended from the core (105) and hoisted above the case (101) coaxially as shown in Figure 1, the total mandrel assembly (100) is partially lowered into the case (101) through its aft-end aperture (104) as shown in Figure 4. The length of the flexible fin cables (108) allows the fins (106) to be bundled and first let into the case aperture (104), even as the core (105) stays just outside the case aperture (104), as shown in Figure 4. When location of the fins (106) is just below its final assembly position inside the case (101), fin hanger (107) is stopped from moving further down. The core (105) is continued to be lowered in to the case (101). The twin cables (108) will align entry of the fore-end core-wedges (115) into respective fin slot guides (126). The core (105) is fully lowered till its aft-end flange (114) rests on the case aft-end apertureAt this point, fore-end wedge pairs (115, 124) and aft-end wedge pairs (116, 125) of the core (105) and the fins (106) would have started mating. The fin studs (127) would have projected into the elongated holes (118) in the core aft-end section (109). Fin-core nuts (130) previously threaded in the fin cables (108) above the elongated holes (118) are assembled to the fin studs (127). As the fin-core nuts (130) are tightened, mating wedge pairs (115-124 and 116-125) will bring the fins (106) closer to the core (105), axially as well as radially and thereby compressing the sandwiched fin-seals (129). Next, core-case screws (131) between the core aft-end flange (114) and the case aft-end aperture (104) are fastened to firmly but releasably join the mandrel assembly (100) to the case (101). Finally, the fin hanger (107) along with the cables (108) are removed from the fin studs (127) as shown in Figure 5.
[0043] For propellant casting activity, the total assembly is inverted with the case fore-end aperture (103) made to face up as shown in Figure 6. A hopper (132) is mounted on the fore-end aperture (103) for filling propellant slurry into the rocket case (101) using standard method. After propellant casting, the hopper (132) is removed and the total setup in the same orientation is heated as per specification to cure the propellant grain (133).
[0044] Once the grain is ready for decoring (removal of mandrel (100) parts), the total assembly is once again inverted to make its aft-end aperture (104) face up. The core-case screws (131) and the fin-core nuts (130) are removed. The core (105) is pulled out first. The fins (106) are still embedded inside the undercuts (139) in the grain.
[0045] For removing fins (106), one at a time, a fin decoring tool (134) is assembled to the case aft-end aperture (104) as shown in Figure 7. The tool (134) consists of three major parts - an opposing pair of guideways (135) in the shape of the trajectory the fin (106) is to take on its way out of the grain, an axle with wheels (136) that moves inside the guideways (135) and a fin lifting bracket (137) attached to the axle (136) at its top and the fin studs (127) at its bottom. Using an overhead crane, the fin lifting bracket (137) is gently pulled vertically up to securely bring the attached fin (106) out of the undercut (139) along the guideways (135). The steps are repeated till all fins (106) are extracted.
[0046] The decored grain shown in Figure 8 has a central cylindrical cavity (138), a plurality of undercut fin cavities (139) circular patterned about case axis (102) and an aft-end counterbore (140).The disclosed mandrel assembly (100) and method have many advantages over the prior art. The disclosure allows net-shape manufacturing of undercut (139) finocyl grains without squeeze casting or propellant machining. It is suitable for casting high viscosity propellant slurries and those propellant compositions with high friction sensitivity. When compared to prior art, it has significantly reduced part-count with minimal number of joints and crevices. The grain counterbore is fully formed by a monolithic core (105). As the fin (106) is handled by the fin hanger (107) and cables (108) attached to the core (105), there is no need for separate fin (106) handling tools. All assembly activities are carried out from outside the rocket case (101). There are no loose parts, especially fasteners, that may accidentally fall inside the empty rocket case (101) during the assembly process. Since the core (105) and the fins (106) are inserted together inside the rocket case (101), assembly duration is minimized. Manual intervention is not needed when the core wedges (115) enter into respective fin slots (123) to mate with fin wedges (124) as the flexible cables (108), dovetails and linear motion guides (126) ensure self-alignment. There is no need for a mandrel (100) centering device, as the mandrel assembly (100) locates itself with reference to aft-end aperture (104) of the case (101). There is no need for a separate propellant slurry distributer, as the core fore-end section (111) acts as one. As the mandrel assembly (100) is firmly fastened to the rocket case (101), there is no risk of displacement due to mandrel (100) buoyancy when submerged in propellant slurry. The fin decoring tool (134) is configured to guide each fin (106) out of its undercut (139) without touching the grain surfaces. The mandrel assembly (100) and decoring methods are configured for remote operations and automation.
[0047] EQUIVALENTS
[0048] With respect to the use of substantially any plural and / or singular terms herein, those having skill in the art can translate from the plural to the singular and / or from the singular to the plural as is appropriate to the context and / or application. The various singular / plural permutations may be expressly set forth herein for sake of clarity.
[0049] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as“includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and / or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations.
[0050] In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and / or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and / or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and / or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.” While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodimentsdisclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.
[0051] REFERENCE NUMERALS
[0052]
[0053]
Claims
Claims:
1. A mandrel assembly (100) for net-shape casting of an undercut finocyl grain (133) with an aft-end counterbore (140), in a solid propellant rocket case (101) with a case axis (102), a case fore-end aperture (103) and a case aft-end aperture (104); the mandrel assembly (100) comprising:a core (105), removably connectable at aft-end of the core (105) to the case aft-end aperture (104), removably connectable on a circumferential surface of the core (105) to a plurality of fins (106) using a plurality of core-wedges (115, 116) and capable of forming central cylindrical cavities in the undercut finocyl grain (133)the plurality of fins (106), removably connectable to the core (105) using a plurality of fin-wedges (124, 125), a plurality of fin-studs (127), a plurality of fin-core nuts (130) and a plurality of snap-fit fin seals (129), and capable of forming a plurality of forward- swept undercut fin cavities (139) circular patterned about the case axis ( 102) in the undercut finocyl grain (133),a fin-hanger (107) with a plurality of flexible fin-cables (108) passing through the core (105) and connecting to the plurality of fin studs (127), capable of carrying, aligning and assembling the plurality of fins (106) to the core (105) inside the rocket case (101); anda fin decoring tool (134) with a fin lifting bracket (137) attached to an axle with a pair of wheels (136) moving inside a pair of opposing and parallel guideways (135), capable of assisting with interference-free removal of the plurality of fins (106) from the undercut fin cavities (139).
2. The mandrel assembly (100) as claimed in claim 1, wherein the core (105) is a multisectional, axi-symmetric, hollow structure, opening towards its aft-end, the core (105) comprising:an aft-end flange (114) for fastening the core (105) to the case aft-end aperture (104);a core aft-end section (109) capable of forming the aft-end counterbore (140) in the gram;a mid-section (110) adjoining the core aft-end section (109) capable of forming an axial cylindrical cavity (138) in the undercut finocyl grain (133) and having a diameter lesser than a diameter of the core aft-end section (109);a fore-end section (111) adjoining the core mid-section (110) and capable of providing an annular gap with the case fore-end aperture (103) for propellant slurry casting, the fore-end section (111) having a diameter lesser than the diameter of the core aft-end section (109) and the core mid-section (110); andconical frustums (112, 113) or flat sections connecting adjacent core sections (109, 110, 111).
3. The mandrel assembly (100) as claimed in claim 2, wherein the core aft-end section (109) being configured to completely close the case aft-end aperture (104).
4. The mandrel assembly (100) as claimed in as claimed in claim 2, wherein the mid-section (110) of the core (105) comprises a plurality of protruding and circular patterned flat foreend core- wedges (115) with dovetails.
5. The mandrel assembly (100) as claimed in claim 2, wherein the aft-end frustum (112) of the core (105) comprises a conical aft-end core- wedge (116) defining an axis of revolution in line with the case axis (102).
6. The mandrel assembly (100) as claimed in claims 4 and 5, wherein the core-wedges (115, 116) define a conical geometric configuration with axes of revolution lying within the conical geometry.
7. The mandrel assembly (100) as claimed in claim 2, wherein the core aft-end frustum (112) comprises a plurality of axial rectangular holes (117) in-line with fore-end core- wedges (115) of claim 4.
8. The mandrel assembly (100) as claimed in claim 2, wherein the core aft-end frustum (112) comprises a plurality of twin axial elongated holes (118) disposed radially to accommodate the plurality of fin cables (108) and fin studs (127).
9. The mandrel assembly (100) as claimed in claim 8, wherein one of the axial elongated holes (118) passes through the conical aft-end core-wedge (116).
10. The mandrel assembly (100) as claimed in claim 1, wherein each fin in the plurality of fins (106) is a thin longitudinal structure, comprising:a fin root (119) conformally offset from the outer surfaces of the core (105); the fin root (119) radially tapering down to a fin tip (120); andforward-swept leading and trailing edges (121, 122) allowing extraction of the plurality of fins (106) from the undercut fin cavities (139).
11. The mandrel assembly (100) as claimed in claim 10, wherein the fin root (119) comprises a longitudinal fin slot (123) to house a flat fore-end fin-wedge (124) and a conical aft-end fin-wedge (125) to mate with respective core-wedges (115, 116) during assembling of the mandrel assembly (100).
12. The mandrel assembly (100) as claimed in claim 11, wherein the fin slot (123) opens towards its aft-end and has opposing undercut linear motion guides (126) to engage the dove-tailed fore-end core-wedge (115) of claim 4, during assembling of the mandrel assembly (100).
13. The mandrel assembly (100) as claimed in claim 10, wherein the fin root (119) comprises a closed circuit fin seal groove (128) with undercuts running all along inside the edges of the fin root (119) to partially house the snap-fit fin seal (129).
14. The mandrel assembly (100) as claimed in claim 10, wherein each fin in the plurality of fins (106) comprises two axial fin studs (127) facing the aft-end.
15. The mandrel assembly (100) as claimed in claim 14, wherein one stud of the two fin studs (127) is screwed into fin root (119) and another stud is screwed into aft-end fin-wedge (125).
16. The mandrel assembly (100) as claimed in claim 14, wherein the two studs are located such that center of gravity of the fins (106) lies between and beneath them during assembling of the mandrel assembly (100).
17. The mandrel assembly (100) as claimed in claim 14, wherein each assembled stud has a tapped hole on its exposed aft-end.
18. The mandrel assembly (100) as claimed in claim 1, wherein lengths of the plurality of fin cables (108) in the fin hanger (107) exceed the length of the core (105).
19. The mandrel assembly (100) as claimed in claim 1, wherein a plurality of fin-core nuts (130) is threaded to the plurality of fin cables (108) inside the core aft-end section (109).
20. The mandrel assembly (100) as claimed in claim 1, wherein the plurality of fin cables (108) has threaded ends that can fasten them to tapped holes in the fin studs (127) of claim 17.
21. A method of net-shape casting of an undercut finocyl grain (133) with an aft-end counterbore (140) in a solid propellant rocket case (101) using the mandrel assembly (100) as claimed in claim 1, the method comprising acts of:mounting the rocket case (101) with a case aft-end aperture (104) of the rocket case (101) facing up;mounting the core (105) with its aft-end flange (114) facing up and passing the plurality of fin cables (108) of the fin hanger (107) first through the plurality of fin-core nuts (130) and then through the elongated holes (118) in the core aft-end frustum (112);fastening free end of the plurality of fin cables (108) to the fin studs (127) of the plurality of fins (106);hoisting the core (105) along with the plurality of fins (106) over the case aft-end aperture (104) and aligning the core (105) to the case axis (102);bundling the plurality of fins (106) and coaxially lowering the mandrel assembly (100) inside the case aft-end aperture (104);once inside the rocket case (101), freeing the plurality of fins (106) and letting the plurality of fins (106) be disposed in a circular pattern about the core (105);continuing the lowering of the plurality of fins (106) and when location of the plurality of fins (106) is just below its final assembly position inside the rocket case (101), stopping the fin hanger (107) from moving further down, and lowering the core (105) further into the case, as the plurality of fin cables (108) self-align the entry of fore-end core-wedges (115) into their respective fin slot guides (126);assembling of the fin-core nuts (130) on fin studs (127) that protrude inside the core aft-end section (109);assembling of the core-case screws (131) thereby fastening the mandrel assembly (100) to the rocket case (101) followed by removing the fin hanger (107) along with the plurality of fin cables (108) from fin studs (127);rotating the rocket case (101) along with the mandrel assembly (100) to make the case fore-end aperture (103) face up for propellant casting;assembling of a hopper (132) to the case fore-end aperture (103), casting of propellant slurry through the case fore-end aperture (103), and curing of the propellant;rotating the total assembly back to make the case aft-end aperture (104) face up for mandrel removal;removing of the core-case screws (131) and the fin-core nuts (130) followed by axially removing the core (105);assembling of the fin decoring tool (134) to the case aft-end aperture (104) after aligning the tool (134) with any one of the plurality of fins (106) to be removed, fastening the fin studs (127) to fin lifting bracket (137), pulling the fin lifting bracket (127) vertically up using a crane to bring that one fin of the plurality of fins (106) out of its undercut fin cavity (139) and the rocket case (101), and repeating the process till all the plurality of fins (106) are extracted.
22. A solid propellant rocket with net-shape cast undercut finocyl grain (133) is manufactured by the mandrel assembly (100) as claimed in claim 1, wherein squeeze casting or propellant machining has not been employed.