Abstract: A method of producing a spindle that can be easily press fit into a knuckled suspension arm with high productivity. A round bar is forged by a header to form a work in process part which is, in turn, thermally refined. If necessary, shot blast and lubrication are applied to the exterior surface of the work in process part. Subsequently, by rolling the work in process part, screw threads are formed on a male screw portion. The work in process part is set and finished in a press. The peripheral surfaces of the bearing attachment portion as well as the knuckle press fit portion of the work in process part are finished in a press. Since the surface of the knuckle press fit portion of the spindle is formed or extruded in the press, the portion can be easily press fit into a knuckled suspension arm with little resistance. The method of producing the spindle obviates the necessity of machining and grinding thereby providing enhanced productivity.

Abstract: An improved method for fabricating a filter for use in automotive air bag inflators which comprises forming a hollow cylindrical inner core or combustion screen of filter material and outer filter layers wound outward from the surface of the core so as to be maintained in cylindrical relation thereabout. This invention is specifically directed to an improved filter which does not include a perforated support tube and relies on only the interior combustion screen for support in the final wrapping of the remaining filter structure.

Abstract: To provide a hot working method which can reduce working resistance during the early stage of hot plastic working, particularly extrusion and forging using a die.A hot plastic working method characterized by comprising the step of plastically working, using a die, a material having a structure of not more than 50 .mu.m in average grain diameter with dispersed spherical grains ranging in size from 10 to 200 nm, the working material having a recess formed on a surface thereof in its site facing a closed space formed by abutting the working material against the die surface at the time of plastic working.

Abstract: The invention provides a multi-stage forging apparatus for forging a work in transportation through a plurality of forging stations each provided with a die and a punch so that the work is progressively refined, in which the position of the work is changed during the forging procedure. A work, for example, consisting of a shank and a ring-shaped head can be produced. The forging apparatus includes a position change station having a rotation unit instead of a die. The rotation unit contains a pair of rotation bodies with gears. The gears are engaged with racks rotated synchronously with the movement of a crank shaft. When an intermediate work consisting of a shank and a ball-like head is driven into a space between the rotation bodies, the rotation bodies are rotated so as to shift the intermediate work to a vertical position where the shank extends perpendicularly to the driving direction of a punch, and the vertically positioned intermediate work is pushed out of the rotation unit by a knockout pin.

Abstract: A method and apparatus utilizing a single progressive die to cold form a finished lead battery terminal from a lead slug. The apparatus includes a lead pickup station, a progressive die having three stations, a drop off station and a transfer mechanism. The transfer mechanism indexes the lead slug from each station to the next with each cycle of the progressive die.

Abstract: A method of manufacturing an engaging element for a one way clutch requires no special control with respect to such factors as squareness between a cam face and side surfaces, possible flaws, and cut size, and enables production of the engaging element for a one way clutch at low cost. The method includes shearing a material by a press to prepare a sheared member of a predetermined size, and a forging process. The forgoing process includes a first step of striking one sheared surface of the sheared member, a second step of inverting the sheared member and striking the other sheared surface of the sheared member, a third step of inverting the sheared member and striking the one sheared surface of the sheared member, and a fourth step of inverting the sheared member and striking the other sheared surface of the sheared member.

Abstract: A process for producing Phillips-head screwing tools or the like, especially in the form of bits, by cold forming from a workpiece section (W) cut to length from a profiled rod. In order to produce bits of high precision, that the workpiece section (W) which is developed at one end with a hexagon profile and adjoining it with a section with supportable front end (16) is introduced, with axial spring-loaded support, into a press tool (P), whereupon the cheek plates (51) of this press tool (P) produce the Phillips-head shape or the like by a displacement towards the center which is controlled by a conical envelope surface (55) which tapers towards the front end (16).

Abstract: The process consists in increasing the height of the rail to the detriment of the thickness of the web (16) and of the flange (18). Firstly, the thickness of the upper part of the web (16) below the head (14) is reduced by machining and, next, the rest of the web (16) and the flange (18) of the rail (10) are heated up and deformed by forging. This process avoids hardness modifications of the running surface of the rail.

Abstract: A method and apparatus to cold form an L-shaped lead battery terminal. The apparatus includes a forming station for cold forming an L-shaped lead battery terminal having a tower offset from the head. The forming station includes a split die for forming a head having a radial ring. The apparatus also includes a punching station for forming a continuous through hole in the head and a recess in the tower. Another method and apparatus to cold form an L-shaped lead battery terminal includes a forming station, punching station and a rolling station for forming a ring on the terminal. The forming station includes a unitary die to form a head having a uniform diameter and a tower offset from the head. The rolling station includes a fixture, a rolling head having a plurality of rollers, and a drive system for engaging and rotating the rolling head and lead battery terminal relative to each other.

Abstract: An object of the present invention is to provide a die set, which is capable of removing the influence of heat expansion and the change of the number of the collared holes and improving the accuracy of the collar height. In a die set including an upper die and a lower die wherein a metal plate having a collared hole is provided between the dies to form a flange section at an end of the collar, a flare-punch is provided to the upper die and is capable of vertically moving therein. The flare-punch has a flange forming section for forming the flange section. A biasing member biases the flare-punch toward the lower die. A level pin for defining a lower dead point of the flare-pin is provided to the lower die. The level pin is capable of coming into contact with the flare-punch, which has been in the collar, when the upper die and the lower die are closed.

Abstract: A yoke of a universal joint is substantially U-shaped and includes a base portion and first and second arm portions. A method of producing the yoke includes the sequential steps of: (a) shearing a metal plate which is rectangular in shape and has certain uniform width and thickness so as to form a blank which is rectangular in shape and consists of a middle portion and first and second end portions; (b) squeezing the middle portion of the blank by cold forging so that the middle portion is expanded to have first and second peripheral bulge portions which are opposed to each other and that the expanded middle portion becoming substantially oval in shape and thinner than the first and second end portions in thickness; and (c) pressing the blank with a press machine to produce the yoke so that the expanded middle portion and the first and second end portions of the blank are turned into the base portion and the first and second arm portions of the yoke, respectively.

Abstract: This invention is a system for enhancing the performance of a forging press by increasing the size of the workpiece which can be effectively forged within the capacity of the forging press. The system includes the provision of a die set in which one or more of the dies is segmented, that is divided into two or more, and preferably three or more parts. The segmented die is provided with advancement means which allow each of the segments to be selectively advanced ahead of the other segments along the forging axis. The dies are installed in the forging press by mounting each die directly or indirectly to a respective die bed. In advancement means is employed to cause one of the segments to advance and be locked ahead of another segment. The workpiece is forged so that the advanced segment is a primary forging agent, that is, it transfers the vast majority of the force to the workpiece.

Abstract: An expansion sleeve (2) for an expansion dowel (1) has an axially extending expansion region (8) with axially extending slots (5) forming tabs between these slots. To enlarge the surface of the expansion sleeve (2) for assuring the attainment of high anchoring values, the axially extending slots (5) are formed free of any gaps. The gap-free slots (5) can be formed by extrusion including radially pressing together the tabs between the slots (5).

Abstract: A process is provided for the production of a webbing take-up spindle by cold-forming of a cylindrical blank. The cylindrical blank is cold-formed into a preform having a flange-shaped disc portion and a spindle portion extending from and in continuation with said disc portion. Wedge action dies, whose pressing portions are in the form of ratchet teeth, are pressed against an upper and lower sides of an outer peripheral portion of the disc portion, respectively, so that ratchet teeth are partially formed and a thin-walled portion is also formed circumferentially along said partially-formed ratchet teeth. The thin-walled portion is then punched to fully form the ratchet teeth. A forming apparatus suitable for use in the practice of the process is also disclosed.

Abstract: A method for necking an end of a metal container include effecting initial deformation, generally radially inwardly, of an axial portion to establish a necked-in generally convex transition portion and an adjacent portion disposed between the transition portion and the container end which is initially generally cylindrical. Both portions are of reduced diameter with respect to the original can body diameter. Sequentially, through the series of formation steps, the portion to be necked in is further reduced in diameter to produce an outwardly generally convex portion disposed in underlying relationship with respect to an outwardly concave portion. A generally, radially, outwardly directed flange may be established within the end section of the necked-in portion. Apparatus to perform the foregoing forming steps consists of a plurality of die means which are subjected to relative axial movement and contact and reshape the exterior of the container portion that is to be necked in.

Abstract: A flashless metal connecting rod of the type having a one-piece construction and being fracturable into a cap portion and a body portion is produced by providing a precise preform of predetermined dimensions and a precise weight, induction heating the preform to a suitable forging temperature, sequentially compressing the preform between a plurality of unique sets of forging dies. The resulting final forging is both flashless and burrless. Preferably, the sequential compressing of the preform is accomplished through three sets of forging dies which progressively form the precision preform to its ultimate shape.

Abstract: A method for making an internal upset (20A) on metal drill pipe (10) having a transition section (24A) with a curved inner periphery (28A) of a concave curvature extending continuously between the central portion (12) of the pipe (10) and the increased thickness end section (22A) and formed from a radius (R2). An external upset (20) is first formed in forging steps as shown in FIGS. 2 and 4 by radially expanding and squeezing the end of pipe (10). Then the final forging step radially contracts the external upset (20) to form the internal upset (20A) as shown in FIGS. 3 and 5. The finished internal upset 20A as shown in FIG. 7 has a transition section 24A with an inner peripheral curved surface 28A formed from a radius (R2). The forging steps are performed with a single heating of the metal drill time in a minimum of time preferably within around one (1) minute but in any event less than around two (2) minutes.

Abstract: A method is provided for forming threadings in a bushing and includes (a) providing a die; (b) extruding a tubular bushing made of metallic material into the die; (c) providing a punch member to punch into the bushing to form a first threading therein; (d) pressing down the bushing along the die and again providing the puncher member to punch into the bushing to form a second threading therein; and (e) repeating the step (d) until a plurality of predetermined threadings are formed in the bushing.

Abstract: A forged-steel connecting rod blank is formed with intentional-break zones extending over one or both of the broad crankshaft-eye surfaces of the connecting rod or as crevices formed radially in the inner surface of the large-diameter bore of the eye and running from an upper edge to a web of the material which is ultimately punched out.

Abstract: In order to manufacturer a tee nut by plastic working steps, a swollen portion is formed on a metal plate, a through hole is formed in the forward end surface of this swollen portion, and then the outer diameter and therewith the wall thickness of a forward end portion of the swollen portion is relatively reduced as compared to a base portion of the swollen portion. Then, the outer and inner diameters of the base portion are reduced while substantially maintaining its wall thickness. Thus, the forward end portion defines a relatively thin portion to be caulked, and the base portion defines a relatively thick female screw forming portion of the tee nut. Thus, it is possible to form a tee nut having a shaft with a uniform outer diameter and having a relatively thin forward end portion forming the portion to be caulked while the tee nut is held by the metal plate.

Abstract: A method of cold forming a plumbing and heating valve stem by providing a cylindrical blank workpiece, axially stamping the workpiece to circumferentially reduce and axially lengthen a portion of the workpiece, axially stamping the circumferentially larger portion to form a circumferentially enlarged head on the larger portion, while punching a central axial cylindrical cavity in the head to a depth no greater than the axial thickness of said head, and then axially punching the cylindrical axial cavity to a depth greater than the thickness of the head and also stamping a central cylindrical axial cavity into the opposite end, forming self tapping screw cavities. The larger portion is then provided with rolled threads.

Abstract: A method for producing ratchet devices, the method including the steps of forming a circular recess in a blank metal plate by drawing, compressing the metal plate in a pair of dies so as to reduce the depth of the recess and thicken the side wall thereof, and forming ratchet teeth on and along the inner annular surface of the side wall of the recess.

Abstract: A one-piece forged vehicle wheel manufactured from a single piece of metal material thereby forming a strong, lightweight wheel. The wheel is manufactured as a result of extrusion, forging and machining a metal blank to provide the desired contours and configuration. The integral nature of the rim and hub eliminates the need to weld components, improving integrity while reducing manufacturing costs.

Abstract: A method for re-sizing and re-shaping wrapped multiple layered or stack-up cylindrical air bag inflator filter assemblies. This invention is specifically directed to manufacturing cylindrical air bag filter assemblies exhibiting superior dimensioned characteristics such as diameter, wall thickness, roundness, straightness, clylindricity by subjecting the as-wrapped filter assemblies to a rotary swaging operation.

Abstract: A method and apparatus for working one end of a steel pipe by externally upsetting the end in a first die set and sequentially shifting some of the upset internally by pressing in a second die with a reduced diameter mandrel to form a tapered internal shoulder in the pipe upset in only two passes.

Abstract: To manufacture an Al alloy tappet in an internal combustion engine, an intermediate which has a circular upper wall and a cylindrical skirt is formed in the first forging step. In the second forging step, a recess is formed on the lower surface of the upper wall. Relatively large-sized metallic structure in the first forging step is finally collapsed, thereby increasing strength and rigidity of the upper wall around the recess.

Abstract: A method of forming a number of sizes of hollow shaft nutdrivers from a common size metal tube workpiece. The method comprises three steps to form a hex drive socket on one end of a metal tube workpiece, and a fourth step to form a plurality of raised wings on the other end of the metal tube workpiece for retaining the other end of the then finished nutdriver in a handle.

Abstract: Methods and apparatus for reforming drawn and ironed containers are disclosed. The invention permits improvements in bottom profiles by radially expanding arcuate segments against the inner leg that connects the bottom rim of the container to the center panel. The reforming introduced by the present invention permits containers to be constructed of a lighter gauge material without suffering from any loss in strength. The container being reformed is seated on a flat surface and a radially expanding die is used in conjunction with a tapered mandrel to reform the bottom profile. Most preferably, the reforming tool of the present invention is incorporated into a container necking mechanism.

Abstract: An integral, one piece tubular product with a threaded end for mating with threaded connectors is produced by preforming a series of compression and expansion operations on the end of a tubing blank to provide a sufficiently thick wall structure for the formation of rolled threads, and to directly form an external hex head surface for the application of wrenching forces.

Abstract: A method of making an elongated mandrel having an end integral with a drill section, with the method including the steps of subjecting a single columnar piece of material to the heading process so as to make a blank N composed of the mandrel, a short stem having one end integral with the end of the mandrel and having a diameter D greater than a diameter of the mandrel, and a flange formed integral with the other end of the stem. The short stem is then cold forged to produce the drill section having end edges (7a) and (7b) facing the flange, and, subsequently, the drill section is trimmed so as to remove the flange together with a scrap resulting from the cold forging of the stem, in such a manner that the mandrel having the integral drill section can be mass produced from the single piece of raw material, efficiently at a reduced cost.

Abstract: A method of die-necking the open end of a can body to form a reduced diameter neck having a smooth profile comprising first forming a reduced diameter control neck at the open end of the sidewall of the can body, and then totally reforming the control neck and the adjacent portion of the sidewall to form a second reduced diameter neck. The diameter of the second neck is less than the diameter of the control neck, and the axial length of the second neck is substantially greater than the axial length of the control neck.

Abstract: A method of forming a stem and assembling a snap ring in a groove in the stem without expansion of the snap ring. A stem blank is formed having a reduced diameter extension. A snap ring is slid over the extension without expansion of the snap ring and is positioned against a lower support surface. An orbitally rotating punch is inserted at an angle into the top end of the extension thereby deforming the top end and forming a continuous, tear free collar which forms an upper wall of a groove defined between the collar and the support surface. The snap ring lies within the groove and is free to move from the support surface towards the collar.

Abstract: Containers of explosive liquids can be prevented from exploding by filling the containers with meshes made from metal foil which occupies a negligible fraction of the volume of the container although it must completely fill the container. In order to refill the containers, the rib mesh (1) must consist of sufficiently small, spherical bodies (24). The invention also deals with the production of these filling bodies (24) from aluminum strip expanded into a mesh. The aluminum strip is first passed through a calibration opening (4) which compacts it into a bar (2) of circular cross-section which is then compacted perpendicularly to its length and continuously transported in the longitudinal direction as it is being squeezed. The front piece of the bar is then detached and pressed in a mould with a hemispherical bottom (21) by a die with the same inner contour to form a spherical filling body.

Abstract: A one-piece steering knuckle assembly for heavy commercial vehicles such as trucks has a flanged body wherein the tie rod arm and in some instances the steering arm extend from the flanged body in a one-piece manner. The flanged body is constructed and arranged to receive a brake assembly thereon and the wheel spindle extends from the flanged body also in a unitary manner. In a preferred manner, the steering or the tie rod arms are forged to the flanged body through enlarged bosses which provide for connection to an axle by a king pin.

Abstract: This invention pertains to an apparatus for producing ellipsoid forms from an expanded metal net. The apparatus includes a first frame defining a path of travel for a continuous sheet of slitted metal foil, an input feed roller for holding the continuous sheet of slitted metal foil in roll form, multiple work stations located on the frame, and forming pistons which cooperate with forming cylinders to shape cut expanded metal foil into an ellipsoid configuration.

Abstract: A one-piece metallic belt driven pulley has a hub, an annular belt engaging wall having an outer belt engaging surface and a radially extending web that connects the hub and belt engaging wall. The hub has an internal bore defined by a tubular inner surface. At least a portion of the tubular inner surface that defines the bore has a plurality of axially spaced threads to form an axially extending threaded portion. In use, the threaded portion of the bore is threaded onto an axially extending thread on an outer surface of the shaft to secure the pulley to the shaft. One end of the hub takes the form of a nut having a hexagonal outer configuration that is adapted to be engaged by a tool for screwing the pulley onto the shaft. The other end of the hub forms an axially extending integral spacer, the end of which is located outwardly of an end surface of the pulley.

Abstract: An attaching sleeve for a floating nut assembly is formed from rod or wire stock by successive cold heading or cold forming operations. The steps involve cutting off a longitudinal segment from the stock, forming a flange on the front end of the segment, forming a centrally disposed opening through the segment, and forming longitudinally extending ridges projecting outwardly around the periphery of the segment. The attaching sleeves made by the method of the present invention have accurately positioned ridges or knurls which will consistently mate with a similarly configured opening in panels to which the floating nut assembly is to be secured.

Abstract: A method is provided for the production of nodes for tubular truss structures comprised of tubular leg elements connected together by transverse tubular brace elements by means of intermediate joint elements each including a connecting stub element between said leg and brace elements, the improvement wherein said stub element is prepared by the following steps from a steel plate:(a) bending said steel plate to a U-shape to form a steel piece having a curved portion;(b) heating said curved portion of said steel piece;(c) forming a protuberance on said heated portion of said steel piece by cooperative action of said piece with a female die;adjusting the radius of curvature of the thus-formed piece to correspond to the radius of curvature of the leg element;(e) forming an aperture on said thus-formed piece along the centerline of said protuberance; and(f) extruding the thus-formed and pierced piece to the desired final shape of said stub.

Abstract: An end fitting for eye joint is manufactured in the form of half-finished product first through a series of cold forging coming in pressing or drawing, punching and rearward extrusion of a short metallic cylindrical material, and then a finished product is obtained through cutting process applied thereto. For the half-finished product to obtain first, cutting process is not particularly required.

Abstract: A shaft is cold-forged to have a shaped portion at one end of the shaft and a flange portion at a middle of the shaft. A taper portion is provided at a root of the flange portion on the opposite side thereof to the shaped portion. The shaped portion is formed by forward extrusion of a bar material, and the flange portion is formed by upsetting. The taper portion is formed by extruding the root of the flange portion to provide a gently inclined continuous connection between the flange portion and an adjacent portion of the shaft. The apparatus for manufacturing the shaft has at least a first set of dies, at least a second set of dies, and a conveyance system for transferring the shaft between the die sets.

Abstract: A spider or cross for a universal joint is manufactured by first forging the basic configuration of the cross and thereafter extruding the trunnions into their final configuration. The component is initially hot or warm forged into its basic configuration including a central body and a plurality of trunnions. Thereafter, the trunnions are simultaneously extruded into their final configuration eliminating machining and a loss of materials. As a result, the grain flow of the component is not disrupted for a more reliable part.

Abstract: An improved integral rivet button and resulting rivet, and a process and tooling for forming such button, utilizes successive coining steps on material surrounding the base of an initial bubble formed on a can end, causing flow of material along the wall of the button toward its center. The successive coining at progressively lesser radii affords adequate metal in the bubble region to assure ultimate formation of an accurate button, assures a strong boundary region about the base of the button, and assures the rivet head is sufficiently large to prevent tear out of the tab at its juncture with the rivet. The initial coined boundary is located close to the juncture of the initial bubble wall with the remainder of the shell, where curvature of the initial bubble wall is concave in the direction of the bubble top and toward the ultimate public side of the end.

Abstract: A shaped metallic article such as a crankshaft is produced from a hollow pipe which is commercially available. The hollow pipe, which has a predetermined wall thickness, is squeezed into a hollow blank pipe having a predetermined shape and wall thickness. A region of the hollow blank pipe is then heated, and the heated region is upset and bent into a crankshaft, for example. The hollow blank pipe is upset and bent by dies positioned one on each side of the gripped portion of the blank and moving toward each other, and also by punches. After the crankshaft is forged, one of the punches is released from the crankshaft before the dies are separated therefrom.

Abstract: A system for cold-forming shell or cartridge casings in which there are movable tubular dies having open ends and adapted to accommodate a casing, and which includes a feeding station having an upper punch for inserting a casing into a die; a header-forming station including an upper high force punch, a lower punch, and an ejector; an ejection station including a punch for ejecting a casing from the die; and a turntable for sequentially moving a die to the loading station, forming station and ejection station.

Abstract: In a method of making a metallic shell for a glow plug, a columnar blank is extruded to have an enlarged recess on the upper end surface of the blank so as to make an upper tubular portions, while extruded to have an enlarged recess on the lower end surface to make a first tubular end circular in section, an outer diameter of which is smaller than that of the upper tubular portion. The blank is transferred without inverting it, and the blank is reduced at its upper tubular portion to make a second tubular end hexagonal in section, an outer diameter of which is smaller than that of a middle portion of the blank, but greater than that of the first tubular end. Then, the blank is transferred without inverting it, and punched to communicate the first tubular end with the second tubular end by means of an axial bore.

Abstract: A method of manufacturing a hemisphere shoe provided between a piston and a slant plate of a swash plate compressor, said method comprises the steps of: cutting a cylindrical blank corresponding to a weight of the hemisphere shoe; plastic-working the cylindrical blank into a blank to be cold-forged having a large diameter plane portion at one end and a small diameter plane portion at another end and a body portion having a curved surface and a higher height than the finished hemisphere shoe and a smaller maximum diameter than the finished hemisphere shoe in a middle portion of the blank; positioning the blank so that the small diameter plane portion contacts with a recess die sufrace of a first die and the large diameter plane portion contacts with a substantially plane die surface of a second die; cold-forging the blank to be cold-forged by pressing the both dies till the dies are in a close contact with each other by means of a cold-forging press including the first die haivng a hemisphere recess die of a s

Abstract: In accordance with the invention, immediately after the completion of the upsetting process using an upset tool to form a pipe end of increased wall thickness, the upset half shells which have been pressed together are opened and the supporting mandrel is withdrawn. After the lifting of the pipe end out of the tool, the longitudinal upset seams formed during the upset operation are rotated through a predetermined angle in a plane to which the axis of the pipe is perpendicular and out of the parting plane of the upset half shells. The pipe end is again pressed into the working plane while maintaining its previous axial position to the tool. After the reintroduction of the supporting mandrel, the pipe end is additionally pressed radially to substantially eliminate the longitudinal upset seams.

Abstract: The fastener assembly includes a generally solid pin, positioned within a tubular fastener body and a buckle sleeve. The fastener body has a generally cylindrical configuration and includes an enlarged head adjacent one end thereof, an intermediate shank portion, and a nose portion adjacent the other end thereof. The nose portion engage the buckle sleeve, and during installation causes the buckle of the buckle sleeve to form prior to workpiece contact by the interaction between the nose portion of the fastener and the leading edge of the buckle sleeve. The sleeve buckles the intersection between a trailing section and the largest inner diameter at the end of a tapered interior section.

Abstract: A method of manufacturing a hub includes the following steps: rotary swaging a workpiece to form a semi-product, the workpiece is simultaneously struck by three or more dies from the outer peripheral side so that the semi-product is formed smoothly and homogeneously, and two bearing cup seats are simultaneously formed on both ends of the semi-product; and squeezing both ends of the semi-product by a right mold and a left mold so as to form a hub. The hub is produced in a fast speed so that the productivity is greatly increased.

Abstract: An end shell for a container, as well as a method and an apparatus for making the same, is provided, comprising a central wall and an annular groove around and below the general plane of the central wall. The annular groove is defined inwardly by a panel wall integrally connected to the central wall and outwardly by a chuckwall which extends upwardly beyond the general plane of the central wall and outwardly therefrom to form an outwardly projecting peripheral flange. The panel wall is disposed at an angle of less than ninety degrees from the general plane of the central wall.