FR2843631A1 - Method and system for manufacturing propulsive sabot utilizes segmented winding mandrel with external thread to make sabot in several parts - Google Patents

Abstract

The method for making a propulsive sabot in several parts for an under sized projectile in a fiber reinforced structure utilizes a segmented winding mandrel (A) provided with an external thread. Threaded segments (F) of the mandrel are widened on one side by the insertion of a widening body. The mandrel is fitted over its length with several layers of fabric saturated with a synthetic resin. The rough part of the sabot is hardened in a hollow mold.

Description

For the acceleration of inertial ammunition under-calibrated in the barrel of

  the weapon, one uses complementary bodies which fill the volume between the body of ammunition and the caliber of the barrel. The pressure of the gases 5 driving the projectile cannot thus escape towards the outside. Complementary bodies are known as

  the name hoof or propellant plate.

  On the propellant shoes used for the acceleration of high performance sub-calibrated projectiles, the requirement is imposed to transform the existing gas pressure with the lowest possible overall mass of the propellant-penetrating shoe system into kinetic energy and thus to accelerate the penetrator as the actual payload at the highest possible speed. The connection between the propellant shoe and the penetrator can be done here in two different ways, one by complementarity of forms by means of threads, groove3, or the like, or by adhesion by means of friction. The present invention mainly relates to the complementarity bonding of 20 forms used in general. The solution of the invention is

  valid, however, also with friction connections.

  The main functions of a propellant shoe therefore include transporting the sub-calibrated projectile in the acceleration phase, ensuring gas tightness 25 and releasing the projectile in flight after the acceleration has taken place. The last requirement mentioned requires that, after the exit from the acceleration cannon, one must have the propulsion shoe detachment from the penetrator. This problem is generally solved in construction so that the propellant does not comprise a single construction element, but practically several segments.

  identical to each other (for example three parts arranged at 120 from each other; four parts at 90; etc.).

  For the safe transport of the projectile in the barrel, it is important that the gas tightness is maintained despite the segmentation of the propellant shoe into several individual construction elements. This can be achieved by introducing additional sealing elements; construction measures, such as mechanical interlocking elements in the contact surfaces (for example transverse teeth),

  are also possible and advantageous.

  As standard materials for propellants, very resistant aluminum alloys are generally used with a density of between 2.7 and 2.9 g / cm3. It can then be assumed that modern materials and methods of treatment can also be used advantageously in the manufacture of propellants. Some of these fairly new materials include fiber-reinforced materials. Given their excellent relationship between mechanical properties (rigidity and high strength) and specific weight, fiber-reinforced materials are very suitable for light construction. In the construction of the propulsion shoes, a significant reduction in dead weight can be obtained by correct and targeted use of these materials. EP 0 176 688 B1 describes a process for the efficient production of a conical, disc-shaped, one-piece building element based on fiber-reinforced material (for use as a spring disc valve) with a central bore. Around a conical mandrel, several layers of fabric, respectively provided or not with a circular cutout (depending on the diameter of the central bore), are fixed by "plugging"

  on a central conical mandrel. The use of layers of fabric with crossed weft and warp threads is very suitable for this application.

  With the use of fabric layers without bore, an individual fabric layer [00/90] is fixed axially on a mandrel. The fibers originally arranged at right angles to each other on the fabric layer (warp and weft) undergo due to the mandrel a local repression. In the present case, these fiber bundles are placed in the shape of a semicircle around the threaded bar. If we use several layers of fabric 15 arranged one behind the other, we arrive due

  upsets near the threaded bar to flares (accumulation of bundles of driven fibers3).

  This flaring has only slight consequences on the first layer of fabric, the fibers are almost all still arranged in a plane perpendicular to the mandrel. It is only by aligning many layers of fabric one behind the other that the angle of incidence of the layers relative to the mandrel is changed. If the orientation of the fibers of the layers of fabric one behind the other is not identical, but rotated relative to one another, one arrives at the formation of a "homogeneous" winding of the mandrel . If fabric layers with bore are used, the diameter of the bore in the fabric layers determines whether or not flares will form (bore diameter <mandrel diameter) or not (bore diameter 2 diameter of the mandrel), therefore the development of an angle of incidence. The angle of incidence of the tissue layers can also be influenced by means of a

  mold which predefines a defined angle of incidence.

  The fibers are arranged along the opening substantially in the peripheral direction and thus absorb the elongation stress along the opening periphery. On the other hand, the fibers are arranged approximately radially on the outer edge. By the flares and therefore by the variable angle of incidence of the layers of fabric relative to the threaded bar and the angle of incidence of the first layer of fabric, the course of the fiber can be adapted to the curve of strength. A force applied axially on the threaded bar causes in the fibers arranged in the peripheral direction around the mandrel an elongation, therefore a tensile load (the direction of stress corresponds to the orientation of the fiber). The fibers are used here in an ideal way and with a

ideal direction.

  After the arrangement in accordance with the stress of the individual layers, the blank is compressed on the central mandrel 20 either only in the axial direction or in both an axial and a radial plane and is then

hardened in the autoclave.

  Unfortunately, the known method is not suitable for the manufacture of propellants. If a propellant shoe is to be made around a threaded bar, for example by winding or simply aligning behind each other many individual layers of fabric or with a similar process from the start of a single coherent building element , it is formed during the consecutive segmentation due to the division (width of saw blade) and due to the transverse toothing to be introduced possibly (transverse toothing height) a "loss

  of material "which prevents a gas-tight connection of the construction elements formed on the threaded bar.

  The gas-tight assembly of the shoe construction elements on the threaded bar can only be obtained again by finishing or remanufacturing by removing chips from the internal thread.

  Considering the stresses which appear in the propellant-penetrator shoe system during the acceleration phase, very high thrust voltages possibly appear on the interfaces between the penetrator.

  and the shoe when converting the applied gas pressure into kinetic energy. It appears on the propellant itself both normal tensions (pressure forces, traction forces) as tangential tensions (thrust tensions).

  The most stressed area is the interface between the shoe and the indenter, which must be designed during the construction of the system so that an acceleration

  certain of the penetrator is guaranteed.

  If we consider this load distribution, it is the area with the highest load, i.e. the thread, which must be subjected to finishing by chip removal if the propellant is manufactured in the same way. which has just been described. This finishing has serious drawbacks, seen locally, on the properties of fiber reinforcement, because chip removal processes cause microcrack treatment surfaces.

in the fiber-matrix system.

  On the other hand, there are formed during the screwing or racking in of the numerous individual layers of fibers arranged one behind the other (process: stacking of layers of fabric) local air vents (corresponding to a disturbance in the orientation fibers in the immediate vicinity of the threaded bar). The resulting thread pitches, which are not ideally filled with fibers, but with too large a matrix fraction, alone already cause local deterioration of the mechanical properties of the fiber reinforcement. By re-machining the thread, the original thread pitches, aerated and filled with too large a quantity of matrix material are removed, but the use of chip removal methods causes other disadvantages due to

  micro lesions in the fiber matrix assembly.

  The necessary rework prevents, from the start, the use of the known method, to obtain locally at the point of connection between the shoe segment and the indenter, more favorable mechanical properties of the fiber assembly (ideal fiber concentration, elimination of local microcracks) by its use at

this place.

  The basic objective of the invention is to replace the metallic materials hitherto used for the construction of propellants, such as aluminum (for example in different alloys) with materials

reinforced with fibers.

  This problem is solved according to the invention by a process for the manufacture of propulsion shoes based on building materials reinforced with fibers, for example fibers of

  glass, and a device for applying the method.

  The advantages of the invention lie in the fact that there is now an efficient manufacturing process for a one-piece propellant shoe (which is ultimately dismantled into several individual elements) based on fiber-reinforced material with a fiber path defined precisely and adapted to the force curve and a fiber concentration in the internal thread pitches. Examples of embodiment of the invention are described in more detail below with the aid of the drawings. In the present case, the following figures show the following elements as a rough sketch: Figure 1 a threaded mandrel A subdivided into four threaded segments F with housing for a cross key D or E, Figure 2 a threaded mandrel A in the spread apart by means of an inflatable flexible hose B, FIG. 3 the outline of the pressing mold C, FIG. 4 a key made of: roix D without teeth, FIG. 5 a threaded mandrel A in the withdrawn state, spread with a cross key D without teeth, FIG. 6 a cross key E with teeth,

  Figure 7 a threaded mandrel A in the separated state, separated 20 with a key in a toothed cross.

  The manufacturing process for hooves has the following characteristics: The starting point is a winding mandrel segmented into n elements. This mandrel is provided with a thread which corresponds exactly to the zone of mechanical closure.

  projectile / propellant shoe. Instead of a thread, any other mechanical closure can be used.

  These segments of the threaded mandrel A represent the shape

  negative of the mechanical closure to be manufactured.

  Enlargement of the threaded mandrel A by an appropriate device, so that the individual elements 5 have a certain controlled spacing with respect to each other. This makes it possible to make available the central element for the manufacture of a rough part of substantially cylindrical propulsion shoe and of a

single piece.

  * Manufacture of a rough part of substantially cylindrical propellant shoe in a part, the interface for the payload, therefore the force transmission zone designed as a mechanical closure and / or a friction closure being generated in the final form without the need to perform a

rework in this area.

  * Manufacture of propellant shoe segments by division

of the blank in n elements.

  * Compensation for loss of material due to division.

  * Compensation for the loss of material which forms in

  due to the possible machining on the separating joints of the propellant elements (for example additional sealing measures, transverse teeth, etc.).

  As already mentioned, a threaded bar must be used instead of a conical mandrel (see above), so that a "conical" bore becomes a "cylindrical bore". For the stress of the shoe element, this has no significant effect, since a thread can be considered as a series alignment of several cone elements, but with a "cone angle"

bigger.

  Several layers of fabric are applied one above the other and at different angle orientations on the threaded mandrel A: the layers of fabric can be impregnated with a synthetic resin. These layers of fabric may have a bore if necessary. The size of the bore diameter controls the importance of the axial flaring as well as the adaptation of the fibers to

bottom of thread.

  Compared to the known method (with a conical mandrel), there is no variation in the load capacity of the molded body formed as a result of the measures and variations described hitherto and in accordance with the invention. Constraints

  maximum that can be supported with respect to the blank in one piece are then lower only due to the subsequent division in the manufacturing process in the autoclave and therefore to the peripheral forces which cannot be used completely.

  The device for the application of the method comprises a winding mandrel which has segmented elements, which can be disassembled by an amount chosen by the intercalation of an extensible body, and of a surrounding negative shape.

  The surrounding negative form may also have a segmented structure composed of individual elements, so that its lateral envelope can be extended in certain places of parts which can be determined.

  For practical use of the process, three variants are shown below.

  Variant A of the process according to the invention Unlike the known process, the different layers of fabric cannot be skewered, but must be "screwed" and thus be fixed on the basis of the present thread. The threaded mandrel A therefore no longer comprises a single construction element. In the initial state, it is already composed of 10 several individual thread segments F. The number of

  thread segments F corresponds to the number of shoe segments to be manufactured. For practical reasons, the number of thread segments F is between 2 and 8. The following explanations relate to a propellant shoe with four segments.

  FIG. 1 represents the threaded mandrel A divided into four segments with a housing for a cross key D or E. The raw part of the propellant shoe is not produced with the threaded mandrel A as an internal form, but the different segments of the threaded mandrel A are arranged offset towards the outside in the radial direction, and this in a precise manner so that the slots forming between the elements (in the peripheral direction) are of the same size and dimensioned sufficiently so that one has enough material for the application of a shear cut, and if

  necessary, other shapes to be made by chip removal. Due to the enlargement, the undivided blank therefore obtains a section which is not circularly symmetrical near the thread, but which approaches the square (due to the division into four).

  After the separation of the blank between the different segments and the machining, if necessary, formed again after the assembly of the individual elements, the bore of exactly cylindrical shape and provided with the

internal thread.

  A radial enlargement of the threaded mandrel A can be obtained by introducing an axial bore for example in the assembled threaded mandrel A. In this bore, one can insert for example an elastic hose B. After the application of the different layers of individual fibers (as described above), this flexible hose B must be enlarged with, for example, compressed air or a pressurized fluid, so that the threaded parts of the mandrel F can move under

  the effect of pressure radially outward.

  To illustrate, the threaded mandrel A is shown in Figure 2 in cross section in the separated state. The radial widening of the thread segments F is obtained by the introduction of an inflatable hose B into an appropriate bore of the threaded mandrel A. The individual layers of prepreg, which can expand radially in a small proportion , 20 follow the movement of the thread segments F. Thus, the slot which is formed by the radial displacement of the segments of the threaded mandrel F thus serves as excess material, because it fills both fibers and matrix due to displacement, without taking other special measures. This space formed by

  enlargement compensates for the "loss of material", which is used for the separation by removal of shavings from the segments, which must be carried out later (a saw blade width is lost during the division, as is the tooth height with transverse teeth).

  In other words: an exact impression of the mandrel thread, shifted only in the radial direction, is retained even after the displacement of the segments of the threaded mandrel F. The material in the partition planes is decisive for the loss of material which form due to consecutive division and eventual introduction

transverse teeth.

  An important advantage of this process is that both the fibers and the matrix are compressed in a radial plane in the thread of the blank due to the radial displacement of the thread segments F. Thus, an ideal reproduction of the threading with an ideal concentration of fiber matrix, because the local aeration of the composite, resulting from screwing or plugging in, is compensated in this way. As a result, the mechanical properties of the "assembly" into penetrating shoe segments are decisively improved compared to the individual layers arranged one behind the other, aerated on a radial plane, and only screwed or plugged in. After hardening, the shoes are separated into segments by trimming with a saw, for example. Subsequently, the propellant segments can be separated from the thread segments F of the threaded mandrel A. In another working step, sufficient material is removed from all the segment side surfaces so that, after the introduction of the axial mechanical closure 25 (for example transverse teeth), the

  propellant shoe segments can be assembled precisely. The "assembled" thread thus formed of the propellant shoe segments exactly coincides with the thread of the unenlarged threaded mandrel and therefore with that of the indenter.

  The production of a cylindrical outer shape as the final shape of the functional propulsion shoe must be carried out according to the version of the pressing mold C by a

overvoltage of the outer contour.

  This disadvantage can be largely or completely compensated for by appropriately designing the shape which must apply the radial pressure in the autoclave. First, account must be taken of the widening of the threaded mandrel A by an appropriate overcut when dimensioning the pressing mold C, so that the blank has an outside diameter greater than the gauge. On the other hand, one can proceed in two different ways with regard to the geometry and therefore the external contour of the

blank.

  As shown in Figure 3, the internal geometry of the pressing mold C is designed in a cylindrical fashion. In this case, the propellant shoe which is reassembled after the separation of the molded part into segments must be reworked on its non-cylindrical outer contour at the

  level of cylindricity and final dimension.

  If the final cylindrical shape of the propellant shoe must be obtained directly, therefore without special retouching, the internal geometry of the pressing mold C must be adapted accordingly, which means that it is formed, so to speak, by enlarging the external contour of the section of the threaded mandrel. In this way, one arrives at a manufacture close to the final form as regards the form.

  inner and outer shape of the hoof proper.

  After hardening in the autoclave, the shape responsible for the radial pressure is first removed. Then, the trimming of the building element is carried out with an axial saw at the locations where the excess material is found. In this case, there are then four individual pieces with raw thread pieces. After the separation of the raw thread parts and the possible integration of a transverse toothing or measures to guarantee gas tightness, the four segments obtained can be reassembled ideally to form a

  reference thread (identical thread or indenter).

  Variant B of the process according to the invention The process presented now resembles the variant presented first, with the only difference that the radial widening of the segments of the threaded mandrel F is not obtained with a flexible hose B, but with a tool 10 cross-shaped enlargement shown in Figure 4 or a cross key D. In this case, the front side of the tool is designed as a key, so that it can be better and easier to introduce into the threaded mandrel A. As shown in FIG. 5, the outside diameter of the widening cross D is slightly less than the central diameter of the threaded mandrel. Thus, it is prevented during the introduction that fibers or fiber bundles of the individual layers are driven axially or severed by the ends of the cross. As already described in variant A, the building element is hardened in the autoclave. The necessary machining steps are in this case

also identical.

  This variant of the process in accordance with the present one compared to the variant described above has the further advantage that, by

  molded part in the shape of a cross, one can obtain as well a controlled radial widening on the level of the race and the angle as a widening without bending. This allows very precise manufacture and guarantees a high quality of the shape of the thread.

  Variant C of the process according to the invention With this process, the blank made up of several thread parts is widened and assembled already before the individual layers of fabric are screwed in using a suitable tool in the radial direction. The molded part which determines the enlargement stroke has the same external dimensions as the thread of the winding mandrel and has on the ends of the cross also a thread with the difference, however, that the thread pitch is zero at this location. Therefore, it is possible to follow the steps of the "seamless" thread, by alternating segments of a circle with a normal slope and straight sections without slope. In this way, the layers of fabric can be screwed on successively and easily. When screwing the individual layers of fibers, the fibers follow the thread pitches of the winding mandrel A, but are guided by the molded piece without thread slope towards the corresponding thread pitch, therefore exactly towards the pitch at which the fiber would be assigned without the presence of the cross key E. To illustrate, in FIG. 6 is shown the key E in the form of a cross with teeth on the external rib surfaces 20 for mounting the thread parts of the blank (enlargement identical on all sides). Figure 7 shows the section of the threaded mandrel as a key

  cross with teeth in the spread state.

  Unlike the methods described above, the cross key of the thread E can be considered here as a "lost core", since it must necessarily be destroyed during the separation into individual segments taking into account

its dimensions.

  As already mentioned, it is obvious that variant B of the process according to the invention is the most suitable method for manufacturing as efficiently as possible.

a divided raw hoof piece.

Claims (7)

  1. Method for the production of a multi-part propellant shoe for an undersized projectile in a fiber-reinforced construction, with which a) a winding mandrel segmented into n elements is provided with an external thread, which predefines the mechanical closing zone for the projectile to be propelled, b) the segmented elements of the winding mandrel are widened in a certain dimension by the insertion of an enlarging body, c) the winding mandrel is equipped with several layers of fabric along its length, d) the layers of fabric are soaked in a synthetic resin, e) the raw propellant part is hardened in a hollow mold in an autoclave, f) the raw propellant part is hardened is removed from the mold g) the raw propellant part is split along its elements with a separating tool, the shear width of cut corresponding to the enlargement dimension, h) the gross part of propellant undergoes a   final determination of the external shape.   2. Method according to claim 1, characterized in that the number of elements of the winding mandrel is included between 2 and 8.   3. Method according to claim 1 or 2, characterized in that the enlargement body is produced in the form of a   solid cross-shaped body, the external dimension of which is less than the central diameter of the winding mandrel.   4. Method according to claim 1 or 2, characterized in that the enlargement body is an extensible hose and filled with a fluid with a variable internal pressure.   5. Method according to any one of claims 1 to 4, characterized in that the lateral envelope of the hollow mold of the propellant shoe is widened in the same way as with the winding mandrel in a segmented form in quantities which are lost during part separation   rough propellant by a cutting-off tool.   6. Device for applying the method according to claim 1, characterized by a winding mandrel which has segmented elements, which can be disassembled by an amount chosen by the intercalation of a   extensible body, and of a surrounding negative form.   7. Device according to claim 6, characterized in that the surrounding negative form also has a segmented structure composed of individual elements, so that its lateral envelope can be extended by   some locations of parts can be determined.