US3242024A - Method and apparatus for forming honeycomb - Google Patents

Description

Manh 22, 1966 J. D. BovA ETAL 3,242,024-

METHOD AND APPARATUS FOR FORMING HONEYCOMB Filed May 29, 1965 5 Sheets-Sheet 1 March 22, 1966 J. D. BovA ETAL 3,242,024

METHOD AND APPARATUS FOR FORMING HONEYCOMB Filed May 29, 1965 5 Sheets-Sheet 2 March 22, 1966 J. D. BovA ETAL. 3,242,024

METHOD AND APPARATUS FOR FORMING HONEYCOMB -lll IIIIIIIIIIII Illlllllllll March 22, 1966 J. D. BovA ETAL METHOD AND APPARATUS FOR FORMING HONEYCOMB 5 Sheets-Sheet 4.

Filed May 29, 1965 March 22, 1966 J. D. BovA ETAL METHOD AND APPARATUS FOR FORMING HONEYCOMB 5 Sheets-Sheet 5 Filed May 29, 1963 United States Patent O 3,242,024 ME'I'HGD AND APPARATUS FOR FURMING HDNEY (MB Joseph D. Bova, Fallston, and Harry C. Engel, Havre de Grace, Md., assignors to American Cyanamid Company, Stamford, Conn., a corporation of Maine Filed May 29, 1963, Ser. No. 284,097 13 Claims. (Cl. 156-197) This invention relates to an improved method for manufacturing a structural honeycomb material predicated upon the concept of imprinting of transverse glue lines in spaced apart relationship on an indefinite length web.

This invention 4also relates to an apparatus adapted specifically for carrying out the transverse glue line printmg.

Structural honeycombis are commonly formed by rst forming a web of sheet material with parallel equally spaced apart glue or adhesive lines on both faces thereof, the glue lines on opposite faces being staggered relative to each other, cutting equal sections from the web, stacking the sections in face to face contact with every other sheet section being alternated so as to provide a glue line to glue line contact, and thereafter heat setting the glue to laminate the stack. When the laminated stack is expanded, the sheet material deforms into a hexagonally shaped honeycomb structure.

Perhaps the most common technique for forming honeycomb involves imprinting the web of sheet material (e.g. aluminum) with the parallel glue lines extending longitudinally of the web. Longitudinal glue lines permit the successive sections of web to be cut then superposed into a stack of sheets without encountering unduly severe registry problems. For one thing, exactly equal length sections do not have to be cut from the web since ragged ends on such a stack can be trimmed without affecting the ultimate honeycomb. Also, side jogging of the sheets in such a stack affects accurate glue-line to glue-line registry of the individual face to face sheets.

By the same token, however, the number of longitudinal glue lines for -any xed spacing which can be employed is predetermined by the width of the web. In consequence, the ultimate honeycomb has a fixed maximum length inthe ribbon direction. Yet, applications requiring relatively long ribbon lengths exist. Almost obviously desirable is placement of the parallel yglue or adhesive lines transversely of the running web, making possible manufacture of honeycomb with unlimited ribbon lengths. Relatively long, unsupported structural :spans could be fabricated directly from honeycomb having the needed ribbon length.

While a switch from longitudinal glue lines to transverse glue lines would, as indicated, be quite advantageous, .this switch is frought with technical difficulties. Virtually all the alignment or registry techniques employed for sheet sections limprinted with longitudinal glue lines must be substantially altered or replaced. For example, elongated sheets or web sections are diflicult to stack with the proper degree of end to end alignment. When the glue lines extend longitudinally of the sheet, a it end to end overlap of successive sheets in a jogged stack is of little consequence. However, when the glue lines are printed transversely of the web, the more easily achieved side registry of successive web sections in a stack has become less important; end to end registry is now critical. The same 1/4 of overlap between successive web sections will result in a holiday wherein the transversely disposed glue lines of these face to face sheets in the stack do not contact each other. When the laminated stack is expanded, individual cells are deformed; a weakened honeycomb structure results. The problem rice of end to end registry is not hypothetical. Conventional jogging equipment now available does not pretend to achieve an alignment accuracy greater than about AG for stacking inch sheet lengths end to end. Misalignment of this magnitude would cause complete off register of an .060" line for a 1A; cell size honeycomb. With equipment of this accuracy the stack would be completely displaced as jogging error will cause non-contact of the glue lines between 'adjacent sheets.

Still another real problem inherent in use of transverse glue lines resides in the difficulty of severing successive sections of sheet material from an indefinite web. Theoretically, cutting exactly equal web section lengths will provide :sheets which can then be superposed in end to end glue line registry. True equality of length can hardly be attained. Consider again a 100 inch section. Conventional cutting equipment available as `of this date promises a cutting accuracy of about 0.015. However, this .015 error coupled with another .015 error for edge cut and an additional misalignm-ent for jogging 100 sheets end to end would be intolerable when considering that the glue line for a Ik cell honeycomb is only .060 wide.

Formation of satisfactory structural honeycomb material based upon transverse glue lines requires special techniques and equipment.

The present invention has as its principal object provision of a method for imprinting transverse glue lines on both sides of a web at one station in a manner which allows a facile assemblage of successive sheets cut from the transversely printed web into an accurately aligned glue line to glue line honeycomb stack.

A further object of the invention is to provide equipment means for printing transverse glue lines and forming registry slots in accurately spaced apart alignment along the running length of the web.

Other objects and advantages of the present invention will become apparent from the following detailed description thereof made with reference to the accompanying drawings in which a preferred embodiment of the apparatus is illustrated.

In the drawings:

FIGURE 1 is a schematic view diagrammatically illustrating the process and apparatus of the present invention;

FIGURE 2 is a side view diagrammatic-ally illustrating the gear mechanism for the many rollers over which the continuous web travels;

FIGURE 3 is a top view illustrating the transverse glue line printing mechanism, and is taken along the lines 3-3 of FIGURE 2;

FIGURE 4 is a side sectional view along lines 4 4 of FIGURE 3, and illustrates the rollers over which the continuous web sheet material is passed;

FIGURE 5 is an enlarged side sectional View taken along line 5 5 of FIGURE 3, and illustrates a portion of the `glue line printing mechanism;

FIGURE 6 is a side view of the web notching mechanism;

FIGURE 7 is an enlarged fragmentary section taken through line 7-7 of FIGURE 6, and illustrates the details of the web notching mechanism;

FIGURE 8 is an enlarged fragmentary view of the web showing the side notch; and

FIGURE 9 is a diagrammatic view illustrating how sheet sections are stacked in glue line to glue line registry.

Briefly7 the procedure of the present invention in a preferred embodiment as schematically illustrated in FIGURE l, involves feeding a web of sheet material 10 from a roll, lirst through a notching unit 12 wherein side notches 13 are cut into the sheet material at spaced intervals. Thereafter, the web is passed through a printing unit 14 which, by an off-set procedure, prints parallel glue lines transversely on both sides of the web at approximately the same time in the same station. The printing rolls are arranged so that the parallel equally spaced apart transverse glue lines 15 on one face of the web are in staggered relation to the parallel equally spaced apart transverse glue lines 17 printed on the obverse face lof the web.

The web leaving printing unit 14 passes through a drying unit 16 to a cutting mechanism 18. The cutting element, e.g., guillotine 19 (which may be manually operated if such is desired), severs web 10 into approximately equal sized sheets 20. The sheets 20 are passed in alternation (i.e., every other sheet being flipped over) to an aligning rack 22 such as is illustrated in FIGURE 9. As hereinafter explained, notches 13 in the sides of web 10 are exactly related to the position of transverse glue lines 15, 17 on the faces of web 10 so that by alignment of the stacked sheet sections 20 in rack 22 by means of side pins 23 every sheet 20 in the stack 25 is accurately positioned into the desired glue line to glue line contact with its adjacent sheet. As illustrated in FIGURE 9, registry of the sheets 20 in stack 25 by means of side notches 13 and aligning pins 23 will often result in substantial overlap (up to perhaps 1/2) between successive sheets, but such overlap and the need to trim the ends `of stack 25 should not be regarded as disadvantageous because the trim wastage is small compensation for achieving accurate glue line to glue line registry throughout the stack 25.

Characteristic of the practice of the present invention, the equipment provided for printing and notching is meticulously aligned so that the spacing relationship of the side notches 13 to transversely applied parallel glue lines 15, 17 remains constant from the beginning of the web to the end of the web. This accurately constant spacing is what permitsl successive sheet sections 20 of the web 10 to superpose inherently into face to face glue line to glue line contact when the stack 25 is aligned with pins 23 set in side notches 13 of each sheet section 20.

For more details of the notching and printing mechanism than are shown in FIGURE 1, reference is now made to the structure shown on FIGURES 2 and 4. The Iroll of sheet material is mounted on a conventional constant linear speed unrolling mechanism 50 operated by an electric motor (not shown). Transverse or lateral alignment of the unrolling web 10 is maintained through the conventional guidance control mechanism only generally indicated on the drawing. A sensing element schematically indicated at 52 actuates a hydraulic cylinder 54 in accord with the position of the web. Movement of hydraulic cylinder 54 laterally, moves unrolling mechanism 50 on its base 57 appropriately. Such lateral control devices are conventional (in the printing arts) and per se form no part of the present invention. In any event, as the web 10 of sheet material is unrolled from the mechanism 50 at a constant linear speed, it passes first under an idler roll 56 past sensing element 52 under another idler roll 58 and then vertically up through the notching rolls of unit 12.

Notching unit 12 is comprised of male punches on roll 64 and female die sets on roll 62. The punch roll 64 (FIGURE 1) is formed at its ends by cylinders 61, 63 which engage the side marginal edges of web 10, cylinders 61, 63 and their connecting reduced diameter cylinder or shaft 66 forming an integral whole (of roll 64) driven by gear 152 (FIGURE 2). Similarly, female die set roll 62 is formed at its ends by cylinders (of which only one, 69, is show-n in FIGURE 1) joined by a connecting reduced diameter cylinder or shaft and is driven as an integral whole by gear 150 (FIGURE 2). On cylinders 61, 63 are punch elements 70 (FIGURES 4, 6, 7) which elements suitably are hardened steel inserts set in the body of cylinders 61, 63. Correspondingly, the cylinders of female die set roll, e.g., cylinder 69, contain die structures 72 to receive the punchings and eject them through channel 74 to the side of the cylinder. The punchings from cylinder 69 fall clear of driving gear 150. FIGURE 8 shows how punch 70 and die 72 form a semicircular notch 13 at the side edge lof web 10.

Important to the practice of this invention is the provision of punch roll symmetry so that the punches 70 (three being illustrated) are symmetrically disposed on each roll 61, 63 and the punches of roll 61 are exactly aligned on opposite sides of web 10 With the punches of roll 63. Such symmetry permits every other sheet section severed from web 10 to be alternated in stack 25 without upsetting the glue line registry achieved by superposing the notches 13 (FIGURE 9).

While side notches 13 are illustrated, it should be ap- Ipreciated that hemispherical notches (as shown) or equivalent geometric notch shapes, eg., triangular, are but a preferred embodiment of the present invention. Practice of the invention contemplates also such expedients as complete apertures (e.g., circles) punched out of the web 10 near the side marginal edges thereof and the term side apertures as used. hereinafter is intended to include both open geometric shapes, eg.,` notches 13 and closed geometric shapes, eg., circles, squares, etc., adjacent the side marginal edges of the web.

From the notching unit 12, web 10 then passes over idler roll 90, loops around drive rolls 92 and 94 into olfset printing unit 14 whereon the tranverse glue lines 15 are imprinted on one face of web 10 in parallel equally spaced apart relation, while the second set of glue lines 17 are similarly imprinted on the obverse face of web 10. `As can be seen from an exaggerated showing given in the cross-sectional view of FIGURE 4, glue lines 15 on one face of web 10 are exactly staggered relative to the glue lines 17 printed on the obverse face.

As best shown in FIGURES l and 4, printing unit 14 imprints through off-set techniques. A polished steel gravure cylinder with spaced apart transversely disposed line engravings 102 on the surface thereof is mounted for partial submersion in adhesive or glue tank 104. When rotated, steel gravure cylinder 100 will carry the liquid glue or adhesive up past doctor blade 106 (which wipes the glue from all but engraved portions of cylinder 100) and transfer the glue from the engraved areas 102 to a rubber impression or back-up roll 108. In turn, rubber roll 108 transfers the glue to web 10 forming thereon the equally spaced apart parallel tranverse glue lines 15. Similarly, for the obverse face of web 10, gravure cylinder 110 with engraved line portions 112 picks up liquid glue or adhesive from adhesive tank 114, is wiped by doctor blade 116, then transfers glue lines from engraved line portions 112 to rubber impression or backup roll 118 which in turn olf-sets them as parallel transverse glue lines 17 on the obverse face of web 10. As has already been indicated, the transverse glue or adhesive lines 15 and 17 are equally spaced apart but are alternately staggered so that every other sheet section may be alternated and the ultimate laminated stack 25 (FIGURE 9) expanded into a hexagonal honeycomb.

As has already been indicated, the present invention provides an arrangement which insures that the successive side apertures in web 10 stay in a constant spacing relationship to glue lines 15 and 17. The gearing structure in FIGURE 2 illustrates the basic structure by which this constant relationship is maintained throughout the length of web 10. Die and punch rollers 62 and 64 are respectively rotated by a pair of gears and 152 mounted on the same shaft as its roller (62, 64). These gears 150, 152 are driven by a gear 154 which advantageously is journalled on the same shaft as idler roll 90 (although gear 154 and idler roll 90 rotate in opposite directions). Powered gear 156 (mounted on the shaft on which driving roll 92 is mounted) and gear 158 serve to drive the notching roll gear train 150, 152, 154 and also the rollers in printing mechanism 14. Gear 158 (mounted on the same shaft as driving roll 94) also drives a gear 160 through which the gears 162 and 168 for the left side offset roll 118 and gravure cylinder 110 are caused to rotate. Lastly, gear 162 drives gears 164 and 166 to rotate the right hand side olf-set roll 108 and gravure cylinder 100. Advantageously, these gears are all of the same diameter, and the powered rolls (i.e., printing and punching rollers) are all of the same diameter. The direct interconnected drive of these various equal sized gears insures that the printing of glue lines 15, 17 on web 10 remains in a constant spacing relationship to the punching out of side apertures, i.e., notches 13.

Special efforts have been made, also, to avoid any slippage of the web while passing through the notching and printing mechanism. The web is drawn through the rolls of notching unit 10 under tension by the action of driving rolls 92, 94. The rolls of notching unit 12 are intended solely to notch the web and do not assist in movement of web 10 through the notching mechanism. Similarly, the web is drawn through the printing mechanism 14 under a constant tension exerted by the weight of the dancer roll 170 (FIGURE 1), thereby avoiding stress on the rubber offset rolls 108 and 118 and slippage of web 10 in passing through the printing mechanism 14.

The details of the gear and the roll mounting for the printing unit 14 is shown in FIGURE 3 where also is shown part of the arrangement for maintaining the various gears in tight engagement. Selected gears, e.g., gears 162 and 166, are split gears so that the gear halves may be radially displaced to make for a tighter engagement with each other and with their related gears 160, 168 and 164. Similarly, gear 152 and, if desired, other gears in the gear train, may be made of this same split gear or anti-backlash type. In addition to anti-backlash, provision has been made for minor adjustments in the timing relationship of the rolls by provision of (conventional) timing gears for the gears 152, 168 and 166. The timing gear structure (not shown) permits independent movement of the individual roll connected thereto, e.g., printing cylinder 110 or notching roller 64, as much as an eighth of a revolution.

In consequence, minor adjustments can be made in the position of notches 13 relative to the glue lines 15, 17, and/or alternatively of either glue line 15 or 17 to the other and to the notches while web 10 is threaded through the notching and printing mechanism. This adjustment is quite important at start-up since otherwise exactly registering glue lines 15 to the desired position equidistant of the glue lines 17 on the obverse face of web 10 would be virtually impossible. However, with the above described timing gears, the machine can be started, and after it has been determined how far off the desired exactly staggered relationship glue lines 15, 17 fall on web 10 (e.g., by optical examination or caliper measurement), a small adjustment in timing at gear 168 or 166 will shift the glue lines 15, 17 into proper spacing.

Other important adjustability features have been built into the printing mechanism 14, as for example to provide for the occasions when web 10 is being first threaded through the system, or for when there is need to run web 10 through the system without printing glue lines thereon or to print only one side of the web.

By way of introduction to these adjustability features, it should be pointed out that gravure cylinders 100 and 110 should not ever come to rest while adhesive or glue tanks 104 and 114 contain liquid adhesive therein. This is because the exposed adhesive present in engraved lines 102, 112 on the non-submerged or exposed portions of these cylinders tends to dry up thereby fouling the engraved areas of gravure cylinders 100 and 10. Subsequently, imperfect glue lines will become off-set on rubber roll 118 and 108 and in turn on web 10. Accordingly, special provision is made through the gearing relationship to drive cylinders and 110 even when printing on web 10 is not desired. Cylinder 100 and rubber roll 108 can be separated from each other, and/or alternatively the two may be displaced as a paired unit from Contact with web 10. The same can be done with cylinder and rubber roll 118.

As illustrated in FIGURES 3 and 5, movement of cam arm 300 partly rotates an actuating arm 303 which in turn moves gravure cylinder 100 against rubber olf-set roll 108. Similarly, cam arm 301 partially rotates cam 304 to move gravure cylinder 110 against rubber off-set roll 118. Movement of .cam arm 302 partially rotates cam 305 which in turn serves to bring cylinder 100 and rubber roll 108 .as a unit into and out of printing position.

The doctor blades 106 and 116 are made to oscillate by a standard gear arrangement, the same as is normally used in the printing industry, some of this structure being indicated on FIGURE 3 at 105 and 117.

While the present invention lhas been described in considerable detail, it should be understood that much of the detail of illustration and description has been of a preferred embodiment of the invention for purposes of clarity and understanding. Changes and modications therein vare contemplated within the spirit of the invention and the scope of the appended claims. One contemplated instance of such a change is placement of notching elements on the rubber olf-set rollers so that web 10 is notched simultaneously with the printing. Another contemplated variation involves placement of the driving rolls (92, 94) ahead of or after the notching and printing mechanisms inste-ad of between them. Still other changes and minor improvements falling within the scope of the present invention will suggest themselves to those skilled in the art.

What is claimed is:

1. A method of making structural honeycomb from a continuous web of sheet material which comprises the steps of: aperturing the web at spaced apart intervals; printing on both faces of the Web transverse parallel equally spaced apart glue lines, the glue lines on one face being staggered relative to the glue lines on the other face, the transverse glue lines and the apertures being maintained in constant spacing relationship to each other; transversely Acutting the apertured and glue line printed web into web sections of approximate equal length; superposing the sections one upon the other into a stack with the apertures aligned throughout the stack whereby the glue lines of each adjacent two sections are in glue line to glue line contact, the stacked web section thereby defining an expansible honeycomb structure.

2. The method of claim 1 wherein side apertures or notches are rst formed in the web and thereafter the transverse glue lines are imprinted.

3. The method of claim 1 wherein side apertures or notches are formed in the web and the transverse glue lines are imprinted thereon simultaneously'.

4. The method of claim 1 wherein the printing of glue lines on both faces is etfected at approximately the same time.

5. An apparatus for use in the manufacture of structural honeycomb from a continuous web of sheet material which comprises means for aperturing the web at spaced apart intervals; means for printing parallel equally spaced apart yglue lines transversely of the web on both faces thereof; and driving gears interconnecting the aperturing and printing means operative to maintain a constant spacing relationship of the glue lines and apertures on the web whereby a stack of successively cut web sections may be registered accurately in glue line to glue line contact through alignment of the apertures.

6. The apparatus of claim 5 wherein means are provided to pass the web through the printing and aperturing means under tension.

7. The apparatus of claim 5 wherein means are provided to dry the glue then cut the web into sections of approximately equal length, and thereafter stack the sections with the apertures of successive web sections in linear alignment as a stack defining an expansible honey comb structure.

8. An apparatus for use in the manufacture of structural honeycomb from a continuous web of sheet material which comprises:

(a) means for drawing the web under tension through a slide aperturing and printing structure as hereinafter dened;

(b) a pair of rolls having adjacent each side edge thereof at least one coacting punch and die, whereby rotation of the rolls causes side apertures to be punched out of the moving web passing therebetween;

(c) a printing structure including a printing roll for imprinting parallel equally spaced apart transverse glue lines on each face of the moving web as the web passes the printing rolls;

(d) a gear train driving both the aperturing rolls and the printing roll-s operative to maintain a constant spacing relation between the parallel equally spaced apart transverse glue lines imprinted on the moving web and the side apertures punched out of the moving web, whereby a stack of successively cut Web sections may be registered accurately with each adjacent section in glue line to glue line contact through alignment of the side apertures.

9. An apparatus for use in the manufacture of structural honeycomb from a continuous web of sheet material which comprises:

(a) means for drawing the web under tension through a notching and printing structure as hereinafter defined;

(b) a pair of notching rolls having symmetrically disposed at opposite ends thereof at least one coacting punch and die, whereby rotation of the notching rolls and passage of the web therebetween causes spaced apart side notches to be punched out on each side ofthe web;

(c) la. printing structure including a gravure cylinder and an off-set roll associated therewith for imprinting parallel equally spaced apart transverse glue lines on each face of the moving web simultaneously as the web passes between the off-set rolls;

(d) a gear train driving both notching rolls and the associated gravure cylinder and off-set rolls at equal peripheral speeds, the gear tra-in being operative to -maintain a constant spacing relation between the parallel equally spaced apart transverse glue lines imprinted on the moving web and the side notches punched out of the moving web, whereby a stack of successively cut web sections may be registered accurately with each adjacent section in glue line to glue line contact through alignment of the side notches.

10, The apparatus of claim 9 wherein all the gears of the gear train are the same diameter and all the cylinders and rolls are of the same diameter.

11. The apparatus of claim 9 wherein each gravure cylinder can be displaced from its associated off-set roll without disengaging the gravure cylinder from the gear train whereby the web may be passed through the printing Astructure without being imprinted thereon, yet the off-set rolls and gravure cylinder-s continue to rotate.

12. The apparatus of claim 9 wherein one gravure cylinder and its associated off-set roll can be displaced as a unit from the web face whereby the web may be passed through the printing structure without being imprinted on one side.

13. A method for forming structural honey-comb from a continuous web of sheet material which compri-ses the following steps:

(a) aperturing the web at spaced apart intervals;

(b) printing on both faces of the web essentially simultaneously transverse parallel equally spaced apart glue lines with the glue lines on one face being staggered relative to the glue lines on the other face;

(c) maintaining the transverse glue lines and the apertures in constant spacing relationship to each other;

(d) then drying the glue lines;

(e) thereafter transversely cutting the web into sheet sections of approximately equal length;

(f) and superposing successive sheet sections in face to face contact with the apertures aligned to form a stack wherein the glue lines of each adjacent two sheet sections are in glue line t0 glue line contact, the stacked sheet section thereby defining an expansible honeycomb structure.

References Cited by the Examiner UNITED STATES PATENTS 2,507,683 5/1950 Smith 156-519 2,518,164 8/1950 Meyer 156-513 2,734,843 2/1956 Steele 156-197 2,887,425 5/1959 Holland 156-197 2,983,640 5/1961 Knoll et al 156-197 3,049,167 8/1962 Vesak 156-548 3,077,223 2/1963 Hartsell et al. 156-548 3,082,141 3/1963 Steele et al 156-189 EARL M. BERGERT, Primary Examiner.

H. F. EPSTEIN. Assistant Examiner.

Claims (1)

1. A METHOD OF MAKING STRUCTURAL HONEYCOMB FROM A CONTINUOUS WEB OF SHEET MATERIAL WHICH COMPRISES THE STEPS OF: APERTURING THE WEB AT SPACED APART INTERVALS; PRINTING ON BOTH FACES OF THE WEB TRANSVERSE PARALLEL EQUALLY SPACED APART GLUE LINES, THE GLUE LINES ON ONE FACE BEING STAGGERED RELATIVE TO THE GLUE LINES ON THE OTHER FACE, THE TRANSVERSE GLUE LINES AND THE APERTURES BEING MAINTAINED IN CONSTANT SPACING RELATIONSHIP TO EACH OTHER; TRANSVERSELY CUTTING THE APERTURED AND GLUE LINE PRINTED WEB INTO WEB SECTIONS OF APPROXIMATE EQUAL LENGTH; SUPERPOSING THE SECTIONS ONE UPON THE OTHER INTO A STACK WITH THE APERTURES ALIGNED THROUGHOUT THE STACK WHEREBY THE GLUE LINES OF EACH ADJACENT TWO SECTIONS ARE IN GLUE LINES OF EACH ADJACENT TWO SECTIONS ARE IN GLUE LINE TO GLUE LINE CONTACT, THE STACKED WEB SECTION THEREBY DEFINING AN EXPANSIBLE HONEYCOMB STRUTURE.

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