Method of forming fragmentation wrap for explosive weapons
United States Patent 1 Shea [ Apr. 22, 1975 1 1 METHOD OF FORMING FRAGMENTATION WRAP FOR EXPLOSIVE WEAPONS [75] Inventor: Frank M. Shea, Cincinnati. Ohio [73] Assignee: The United States of America as represented by the Secretary of the Air Force, Washington, DC.  
 [22] Filed: June 25, 1973 [2i] Appl. No.: 373,059  
 Related [1.8. Application Data [63] Continuation-impart of Scr. No. I4S 695. Ma 21 1971, abandoned.  
 [52] US. Cl. 72/326; 72/332; 83/51; 113/1 [6 A [51] Int. Cl B2ld 31/02 [58] Field of Search 72/326. 332; 29/61 6.2. 29/l.1l. 1.1; 113/116 A; 83/51 [56] References Cited UNITED STATES PATENTS 1.l6l.l9l 11/1915 Cook 29/432 IOO PRESELECTED HEIGHT 1.272.890 7/1918 Bates t. 113/15 R 2.508.758 5/1950 Hollerith l. 83/51 2,789,524 4/1957 Crawford ct a1 H 113/1 l6 3.138.981 6/1964 Werthman 83/51 3.590759 7/1971 Hendric 113/116 A 3.628343 12/197] Phol 29/625 Primary E.\&#39;aminerRichard .I. Herbst Assislum Etaminen-James R. Duzan Attorney. Agent. or FirmArsen Tashjian [57] ABSTRACT A method of manufacturing fragmentation wrap provides for the progressive flattening. controlled or preselected depth shearing and/or indenting of hot or cold rolled steel. The method fabricates a fragmentation sheet of relatively heavy gauge metal for explosive weapons having predefined fragmentation shapes formed therein.  
 6 Claims. 22 Drawing Figures pgygpnmmzzi rs 3.878.704  
 sum 1 o ORIGINAL STOCK E t THICKNESS PHENTEU Z 3.878.704  
 sum 2 HF 53 STROKE G 3878.704 saw 3 erg;  
 SHEARING EDGE FEED PER STROKE q STROKE- SHEARING EDGE METHOD OF FORMING FRAGMENTATION WRAP FOR EXPLOSIVE WEAPONS The invention herein described was made in the course of or under a contract with the Department of Defense.  
  This application is a continuation-in-part of my copending United States Patent application Ser. No. l45.695. filed May 2l. l97l. now abandoned.  
 BACKGROUND OF THE INVENTION The present invention relates generally to explosive weapons of the fragmentation type and more particularly to a new and improved method for producing controlled fragmentation wraps for projectiles and missiles in which the fragmentation wrap may be mass produced having predefined fragmentation shapes.  
  Various methods have been used heretofore to produce fragments of varying size and shape when a fragmentation-type weapon is exploded. None of the previous methods are entirely satisfactory for producing fragmentation wraps of a sufficient size to encompass large bombs. missiles and the like. One well-known method of fabricating controlled fragmentation warheads is by the process of casting the warheads in a casting form having a groove pattern. Due to the time intervals involved in the casting operation and the required size of wraps needed for the large bombs. this method is impractical for mass production purposes since it requires numerous casting forms in order to compensate for the time losses in each casting form and a prohibitively large manufacturing plant to install the numerous casting forms required. Moreover. experi ence has shown that cast-produced warheads are unsatisfactory due to erratic fragmentation and due to pulverization into useless chaff a substantial portion of the warhead.  
  Another less than satisfactory procedure which has been suggested is the use of presized fragments held in place by thin sheets of metal and adapted to be disbursed upon the detonation of the explosive charge associated therewith.  
  A still further less-than-satisfactory method consists of sawing notches or grooves in stock bars. forming the bars into rings and welding the ends thereof together. Surface grinding the faces of the rings to make them flat and parallel. supercoincidentally stacking the rings in a suitable jig. and copper brazing. in a hydrogen furnace. the side faces of adjacent rings to form a hollow tube for encasing an explosive charge. These methods are inherently complex. time-consuming. and impractical for mass production of fragmentation wraps of large dimensions.  
  Accordingly. it is an object of this invention to provide a new and improved method of mass producing controlled fragmentation wraps. which method is fast, inexpensive and capable of being carried out in most manufacturing plants.  
  A further object of this invention is to provide a method for producing fragmentation wraps having predetermined shapes. the fragmentation wrap being of such a dimension that it may be utilized in conjunction with large explosive weapons.  
 SUMMARY OF THE INVENTION This invention provides a new and improved method for producing fragmentation wraps for explosive weapons. The method of this invention calls for the controlled feeding of a hot or cold rolled steel sheet pro gressively through shearing dies. The die makes repeated controlled or preselected depth shearing cuts and/or indentations in the sheet at a predetermined angle from the normal of the sheet direction. This action simultaneously flattens the sheet. Each controlled or preselected depth shearing cut is displaced by a predetermined linear feed. The repeated shearing cuts and/or indentations combine to define and provide the desired fragmentation shape. The fragmentation sheet so fabricated may be used in a single layer wrap for the explosive weapon or a plurality of sheets in sandwich form may be utilized.  
  Other details. uses. and advantages of this invention will become apparent as the following description of the exemplary embodiment hereof presented in the accompanying drawings proceeds.  
 BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings show present exemplary embodiments of this invention in which:  
  FIG. I is a diagrammatic perspective view illustrating the manner of fabricating a progressive shear pattern of a controlled or preselected depth in a sheet in accordance with the preferred concept of this invention:  
  FIG. la is an elevational view illustrating the concept of FIG. 1;  
  FIG. 2 is a plan view of a portion of a fragmentation wrap sheet made in accordance with the present invention;  
  FIG. 3 is an elevational view taken along lines 33 of FIG. 2;  
  FIG. 4 is a cross sectional view taken on the line 4-4 of FIG. 2;  
  FIG. 5 is a diagrammatic representation of a desired fragment shape generally shown in FIG. 2;  
  FIG. 6 is a diagrammatic plan view of the die illustrated in FIG. I;  
  FIG. 7 is a diagrammatic partial view of the fragmentation pattern of FIG. 2;  
  FIG. 8 is a diagrammatic representation illustrating another exemplary fragment shape without indentation;  
  FIG. 9 is a diagrammatic plan view illustrating another exemplary die to form the fragment shape of FIG.  
  FIG. I0 is a diagrammatic partial view of the fragment pattern formed by the die of FIG. 9;  
  FIG. II is a diagrammatic representation illustrating a further exemplary fragment shape without indentation.  
  FIG. 12 is a diagrammatic plan view of a die used to form the fragment shape of FIG. II;  
  FIG. I3 is a diagrammatic partial view of the fragment pattern formed by the die of FIG. 12&#39;.  
  FIG. 14 is a diagrammatic representation illustrating a still further exemplary fragment shape;  
  FIG. I5 is a diagrammatic plan view of a die used to produce the fragment shape of FIG. I4;  
  FIG. I6 is a diagrammatic partial view ofa fragment pattern formed by the die of FIG. 15;  
  FIG. 17 is a diagrammatic representation illustrating another exemplary fragment shape;  
  FIG. 18 is a diagrammatic plan view of a die used to produce the fragment shape of FIG. 17;  
  FIG. 19 is a diagrammatic partial view of a fragment pattern formed by the die of FIG. I8;  
  FIG. 20 is an elevational view of a typical bomb incorporating the fragmentation wrap of this invention; and  
  FIG. 2] is a partial elevational view of a multi-layer fragmentation wrap.  
 DESCRIPTION OF ILLUSTRATED EMBODIMENTS Referring now to FIGS. I and la in describing the method of the invention. a planar sheet of hot or cold rolled steel I00. or of any metallic material or alloy suitable for such purposes. is passed axially in the direction of arrow I10 between opposing dies I02 and 104. The dies are constructed to have a cooperating shear edge I06 ofa predetermined height which is a function of stock thickness In the first embodiment of this invention. the dies also have indented die elements 108 displaced from the shearing edge I06. The dies 102 and I04 may both be movable in a vertical direction. In the illustrated embodiment shown. die I04 is stationary. The die I02 is then vertically driven towards the stationary die I04 by a suitable press (not shown). The dies I02 and I04 will cooperatively engage the sheet I to perform the desired flattening, controlled or preselected depth shearing and/or indenting functions described hereinbelow. Means are provided to move the sheet 100 through the die at a predetermined linear feed or rate.  
  The means for feeding the sheet and press. which are not shown. may be driven by any suitable motive power means and may be interconnectingly geared and synchronized so that the sheet is fed a predetermined incremental distance during each press stroke. At the end of each stroke. the dies perform the flattening. controlled or preselected depth shearing and/or indenting whereupon the sheet is again moved the prescribed dis&#39; tance for the subsequent action of the dies. Each action of the dies provides a partial fragment pattern on the sheet. Each pattern is placed at an angle to the axial feed of the sheet. As the sheet is incrementally fed through the dies at the predetermined feed per stroke. additional partial patterns are formed sequentially on the sheet. The sequential partial patterns combine to provide the desired fragment effect.  
  One desired fragment shape is generally shown in FIG. 5. The pattern shape is fully defined by its symmetry and the dimensions P, G and r. From these dimensions. the following relationships exist:  
  FIG. 7 illustrates how the individual fragments of FIG. may be arranged within the sheet 100 to gain 100 percent material utilization. The arrow IIO indi cates the direction of feed of the sheet I00 relative to the dies. It may be observed that the lines AB. BC and CB are repeated as A B I3,C and C 8 by the linear displacement a. A subsequent displacement by the distance a will generate lines A 8 B C and CzBg. Referring now to FIG. 6, an exemplary die utilized to provide the fragmentation pattern of FIG. 7 is shown in diagrammatic plan view. The die is provided with a continuous shearing edge 106. As the sheet 100 is passed between the dies at a feed stroke a. the dies will progressively shear the sheet I00 along the lines AB. BC. then A,B,. B C then A 8 B C etc.. for each linear displacement of the sheet I00. It is thus seen that the shearing edge 106 will progressively shear the frag menting pattern into the sheet except that the short sides C8,. C8 etc.. will not be provided.  
  The lines CB (18 etc.. may be provided by utilizing a progressive die setup wherein a plurality of indenting dies or punchesl08 are linearly displaced from the shearing edge 106 by a distance of at least the stroke a or a multiple thereof. Since the sheet I00 will expand along the shearing edge due to the heat generated therein due to the shearing operation. it is necessary that the indenting step take place separate from the shearing step in order to compensate for the die expansion due to heat rise. It should be noted that the indenting punches I08 may be displaced either behind or ahead of the shearing edge I06. In order to have the fragmentation sheet 100 held together along the rows of fragments without the necessity ofjoining each fragment to another. the sides C8,. C 8 etc. are indented rather than partially sheared. In this way, the individual fragments are held together by the indented area. An unsheared zone is left at each edge of the sheet I00 in order to insure coherency of the sheets. Furthermore. the shearing edge I06 may be interrupted as at IIZ to provide a solid unsheared bar the linear length of the sheet 100 to provide an additional zone for maintaining the individual fragment in place. FIG. 2 shows a plan view of a fragmentation sheet I00 formed with the die described in FIG. 6. The individual fragment shapes or elements 114 are held together by the indented area 116 (FIGS. 3 and 4) while adjacent rows are held together by the partially sheared areas. A zone where shearing is omitted is indicated generally at 118 in FIG. 2. The zone 118 results when the shearing edge I06 (FIG. 6) has an interrupted shearing edge 112.  
  Another exemplary embodiment of this invention is shown in FIGS. 8 and I0. The fragment element I20 is seen to be a diamond shape. In this embodiment. the indenting step is not needed. The individual fragment elements I20 are held together by a tie connection I22. The fragment sheet of FIG. 10 may be fabricated by using a controlled or preselected depth shearing die 124 (FIG. 9) which has the desired shearing edge 126. The die I24 is seen to comprise a similar shearing edge I28. The use of controlled or preselected depth shearing edges 126 and 128 permits the full width of the fragment sheet to be sheared simultaneously. It is seen that the shearing edges I26 and 128 are separated by a non-shearing area 130. Thus, a zone of non-sheared sheet will effectively join both sides of the finished fragmentation sheet. Additional strength and support for the fragmentation sheet may be provided through the use of additional interruptions I32 and 134 in the shearing edges so as to provide additional linear zones of nonshearing. It should be noted. however. that the die I24 may comprise only a single controlled or preselected depth shearing edge similar to FIG. 6 and still provide the desired fragmentation sheet structure. In FIG. 10, the edge 136 represents a sheared pattern formed by the shearing edge I26 of die I24. The next sheared edge 138 is linearly separated from edge 136 by a distance equal to stroke av Referring now to FIGS. II and 13, the fragment element I40 is seen to be square shaped. The fragment elements I40 are joined by the non-sheared connecting tie 142. The die 144 comprises controlled or preselected depth shearing edges I46 and 148 interrupted by a nonshear area 150. In FIG. 15. the sheared edges 152 and 154. formed by shearing edge 146. are separated by a linear distance of stroke a&#34;. Due to the method of progressively advancing the fragment sheet through the dies. it may be noted that the resulting controlled or preselected depth sheared edges are commonly in a straight line along the outlines of the fragments. This provides for a greater uniformity of dispersal of the fragments.  
  By utilizing a die 156 in the shape shown in FIG. IS. the fragment shape 158 (FIGS. I4 and I6) is shown. The die 156 has dual controlled or preselected depth shearing edges for the left half and right half of the fragmentation sheet. Each shearing edge has a plurality of narrow interrupted nonshearing portions I60 to provide tie areas 162 between each fragment element I58. In this instance. it is seen that each individual fragment 158 has a tie 162 along each of its geometric edges. The fragment elements 158 are formed by the progressive cross-shearing of prior sheared edges.  
  The die I64 of FIG. I8 is similar to that described for the diamond shaped die in FIG. IS. The die I64 provides a fragmentation sheet having individual fragment elements 166 (FIGS. 17 and 19) tied together by tie areas 168.  
  Although the dies hereinabove described have been illustrated as planar. it may be noted that roll-type dies may also be utilized to provide the necessary controlled or preselected depth shearing and/or indenting to make the necessary fragment elements. In the fragmentation wrap design formed by the method of this invention (FIGS. 16 and 19) each fragment is attached to its neighbor by an unsheared bridge or tie. These bridges can be alternated from top to bottom for each specific shearing edge by the placement of the interrupting nonshearing portions of the shear edge. This produces the sheet uniformly tied together which may eliminate the continuous linear tie bar from end to end of the sheet except at the center where the notching dies or rolls face each other.  
  In general. the function of the dies are the same and variations in the fragmentation design is incorporated into the die proper. In all cases. the material passes through the dies in repetitive steps or increments of a given feed stroke (in the case of planar dies) or at a proper spacing between shearing edges (for roll dies).  
  In the case of roll dies. the shearing pattern is interrupted as required to provide necessary tie bars between individual fragment elements.  
  FIG. generally shows a bomb 170 about which a fragment wrap 172 has been placed. The fragmentation wrap I72 is contoured to match the exterior shape of the bomb. An outer aluminum skin or the like 174 (partially cut away) serves in a dual capacity as a structural member and fairing to provide a smooth aerodynamic surface. Suitable means such as steel bands or the like I76 secure the skin and fragmentation wrap to the bomb together with a retention device (not shown).  
  The fragmentation wrap I72 may be a single layer (FIG. 3) ma multi-layer. as the designs dictate. FIG.  
 2! shows an elevational view of a typical multi-layer fragmentation wrap. To avoid welding of the individual fragments to one another due to the energy generated by the explosion. a layer of kraft paper or the like 178 is cemented inside each of the fragmentation layers I and I82. This paper may also be used to identify the side of the sheet for correct forming.  
  It can be seen from the foregoing description. that this invention provides a novel method for producing fragmentation wraps through the use of progressive controlled or preselected depth shearing of partial fragment patterns repetitively on a sheet of material. The partial patterns are formed so as to combine to provide the desired fragment shapes. lndenting dies may be used together with the controlled or preselected depth shearing dies for some designs. Accordingly. the objec tives of this invention hereinabove set forth have been accomplished.  
  While present exemplary embodiments of this invention have been illustrated and described. it will be recognized that the method of this invention and fragmentation wrap thereby formed may be otherwise variously embodied and practiced by those skilled in the art.  
 What is claimed is:  
  I. A method of fabricating a fragmentation wrap for explosive weapons comprising the steps of feeding a planar sheet of metal in one direction through opposed cooperating dies; shearing said sheet a preselected depth to form a partial fragmentation pattern in the sheet; progressively advancing said sheet in linear increments and repeating the preselected depth shearing: flattening said sheet to its original thickness after each increment to define the boundaries ofa predetermined overall pattern wherein the partial patterns combine to define individual fragment elements joined together by partially sheared areas; and wrapping the fabricated sheet around the outer surface of an explosive weapon. said fabricated sheet fragmenting into the individual fragment elements upon detonation of the explosive weapon.  
  2. The method according to claim 1 in which the sheared patterns are formed transversely under preselected angles to the motion of said sheet.  
  3. The method according to claim 2 further compris ing the step of regulating the linear increment of move ment of the sheet to determine the size of each individ ual fragment element and its nonsheared interconnecting link.  
  4. The method according to claim 3 in which the shearing cuts transversely of the sheet are partially discontinuous wherein nonsheared areas are formed.  
  5. The method according to claim 4 further comprising the step of indenting said sheared sheet along separate intermediate lines with an indenting die to form a fragment element defined by the sheared areas and the indented areas. each area having a preselected depth.  
  6. The method according to claim I in which the advancement of said sheet is continuous wherein the preselected depth of shearing and subsequent flattening of the sheet are applied through roll dies cooperatively engaging the continuous advancing sheet.  
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