Composite structures and methods of manufacturing the same

Abstract: A composite structure is manufactured by joining a first material (2) preferably made of a magnetically permeable material having a first joining surface (11a) in which a recess (7) having an overhang surface (6) is formed, to a second material (3) preferably made of an electrically conductive material having a second joining surface (11b), to be joined to the first joining surface (11a) of the first material. On the second joining surface (11b), a protrusion (9) having an outer configuration substantially corresponding to the inner shape of the recess (7) is integrally formed. The first and second materials (2, 3) are firmly mechanically joined to each other by, for example, a casting method, a rolling method, a pressing method, or a method by utilizing a plastic flow of the second material (3).

Description: This invention relates to a method of manufacturing the composite structure according to the precharacterizing portion of claim 1 to be utilized, for example, as a secondary plate of a linear motor car railway track, for inducing electric driving force for such motor car. A method according to the precharacterizing portion of claim 1 is known from US-A-4,023,613. As is well known, traffic facilities have occupied a significant and important position in the social life, and among various traffic facilities, transportation means such as railways play an important role in the rapid mass transportation apart from the transportation by means of automobiles. However, as speeding up of the railway transportation has been desired, vibrations and noises caused by the transportation means has become factors which cannot be neglected in the social life. In another aspect, excavating and drilling operations as for a underground railway tunnel have become large scale ones with more and more increasing cost, and for this reason, development of a linear motor car capable of travelling along an iron railway track without generating violent vibrations or noises is highly desired and has been partially realized. In connection with the linear motor car of the character described above, a structure of a secondary plate, which functions to produce eddy current, in a primary side of the motor car for producing a driving force, must be used on the railway track. Such secondary plate is required to have high electric conductivity and magnetic permiability as well as a great resistance against shearing forces and separating forces which are generated as counter forces against the great driving force. However, in the current technique, a single metal or metallic material having these characteristics has not been developed, and accordingly, a composite structure fabricated by tightly and firmly joining materials of different kinds having a high electric conductivity and a high magnetic permiability, respectively, is utilized as the secondary plates. For example, there are known composite structures fabricated by fixedly joining face to face an aluminum plate having a high electric conductivity on a soft steel plate having a high magnetic permiability. In an example of such composite structures, the aluminum plate is press-fitted at the opposite ends thereof on the two end surfaces of the soft steel plate, and fastening screws are passed through the aluminum plate into the soft steel plate to mechanically join both the plates as a combined metallic structure. In another example, a composite structure is obtained by joining the aluminum plate to the soft steel plate by an explosion bonding method into an explosion bonded clad plate. However, as described hereinbefore, it is required for the secondary plate to possess a mechanical strength against the strong reacting forces to the driving force, acting frequently and repeatedly, and accordingly, the secondary plate must have a large resistance against shearing forces along the interface between the two elementary plates as well as against vertical separating forces imparted to the two elementary plates of the secondary plate. Particularly, when a composite structure is applied to the railway track of a subway, it is required for the composite structure to have mechanical strength or resistance against additional thermal behavior and separating forces due to temperature variations and dynamic vibrations. However, the composite structures fabricated by press-forming the two plates and then clamping by fastening screws or fabricated by the explosion bonding method cannot maintain sufficient resistance for a long period of time. Particularly, the composite structure, in which an aluminum plate and a soft steel plate are mechanically joined by pressing them and clamping them by means of bolts, tends to be loosened as time elapses, while the explosion bonding method is extremely expensive, thus being not advantageous. Moreover, when the composite structures of the characters described above are applied to the railway track of the subways, for example, sited near seasides, the railway tracks are exposed to severe environmental conditions such as corrosion or submergence and the interface between the soft steel plate and the aluminum plate are corroded. When corrosion occurs, the composite structure cannot attain the function as the secondary plate for the railway track. Accordingly, an object of this invention is to substantially eliminate defects or drawbacks encountered in the conventional technique described hereinbefore and to provide a method of manufacturing composite structures fabricated by materials of different kinds capable of maintaining for a long time firm mechanically joined condition of the different materials without causing relative shifting and separation of the joined surfaces of the materials even when the composite structure is exposed to an environment in which repeatedly acting strong shearing stresses and violent thermal behavior are imparted to the composite structure. Another object of this invention is to provide a method of manufacturing composite structures of the characters described above with low cost. These and other objects can be achieved by the method according to claim 1. In preferred embodiments of this invention, the first material is made of a magnetically permiable material and the second material is made of an electrically conductive material. The composite structure thus manufactured can provide a firm mechanically joined condition between the first and second materials by virtue of the firm engagement of the overhang surface of the recess of the first material with the underhang surface of the protrusion of the second material. In the accompanying drawings: Fig. 1A is a cross sectional view of one embodiment of a composite structure comprising materials of different kinds manufactured according to this invention; Fig. 1B is a cross sectional view of the materials, shown as being separated, of the composite structure shown in Fig. 1A; Figs. 2 to 5 are cross sectional views of further embodiments of the composite structures, respectively, manufactured according to this invention; Fig. 6 is a fragmentary perspective view of a still further embodiment of the composite structure manufactured according to this invention; Figs. 7 and 8 are fragmentary perspective views illustrative of recesses formed in first materials of further embodiments manufactured according to this invention; Fig. 9 is a cross sectional view of a first material in which a recess is to be formed; Fig. 10 is a cross sectional view showing a step to form a recess in the material shown in Fig. 9; Fig. 11 is a cross sectional view showing a next step subsequent to the step shown in Fig. 10 to form the recess; Fig. 12 is a cross sectional view representing a step to form a recess in a surface of a first material of a composite structure according to a further embodiment of this invention; Fig. 13 is a plan view showing a portion of the first material in which a recess is formed by the step shown in Fig. 12; Figs. 14 to 16 are cross sectional views illustrative of steps in sequence of forming recesses in a first material constituting a composite structure, according to this invention; Figs. 17 to 21 are views explanatory of steps in sequence of forming a composite structure by a casting method for joining two different materials; Preferred embodiments of this invention will be described hereunder with reference to a secondary plate of an iron track for a linear motor car railway in conjunction with the accompanying drawings. Fig. 1A shows an embodiment manufactured according to this invention in the form of a secondary plate 111 of an iron track, formed as a composite structure made of materials of dissimilar or different kinds. The composite structure comprises a soft steel plate 2 as a first material having a high magnetic permiability, and an aluminum plate 3 as a second material having a good electric conductivity and disposed on the soft steel plate 2, both plates 2 and 3 being joined mechanically along an interface 11. Fig. 1B shows the composite structure in a state wherein the two plates 2 and 3 are separated. As is apparent from Fig. 1B the steel plate 2 is provided with an upper joining surface 11a in which are formed a plurality of grooves or recesses 7 each converging downwardly in cross section to form a V-shape and each being obliquely oriented so as to have one side surface 6 constituted as an overhang surface, which protrudes horizontally as it extends upwards as viewed in Fig. 1B. The angle of the oblique direction and the arrangement of the grooves 7 may be changed or modified in accordance with conditions of design. The aluminum plate 3 is provided with a lower joining surface 11b on which are formed a plurality of projections or protrusions 9 each converging downwardly in cross section to form a V-shape and each obliquely projecting obliquely so as to have one side surface 8 constituted as an underhang surface which protrudes horizontally as it extends downwards as viewed in Fig. 1B. The locations and shapes of the grooves 7 of the steel plate 2 are made to accord with those of the corresponding projections 9 of the aluminum plate 3 in the joined state. Although, in the illustration of Fig. 1B, the plates 2 and 3 are separated, actually these plates 2 and 3 are firmly mechanically joined together in the manufacturing process of the composite structure 111 according to this invention by casting the projections into the grooves 7 to establish firm engagement of the projections 9 with the corresponding grooves 7 as described in detail hereafter. The composite structure 111 can thus be formed integrally as one body with extremely high joining force and resistance aginst shearing forces in both the longitudinal and transverse directions, as well as against vertical separating forces based on the thermal behavior due to temperature changes. With the composite structure of the character described above, in a case where a linear motor car, not shown, travels above the secondary plate 111 with a predetermined height of floatation, eddy currents are generated through the aluminum plate 3, which produces a driving force for the linear motor car. During the travel of the car, the aluminum plate 3 receives a large reaction force as a result of the driving force in the longitudinal direction thereof. However, because of great resisting forces aginst the reaction forces and the shearing forces in a direction normal to the longitudinal direction and because of a great resistance in a vertical direction as viewed in Fig. 1A against separation of the two plates due to the strong mechanical engagement between the overhang surfaces 6 of the grooves 7 of the steel plate 2 and the underhang surfaces 8 of the projections 9 of the aluminum plate 3, the secondary plate is prevented from shifting in height more than a designed allowable change in height. In addition, the tight joining along the interface between the steel plate 2 and the aluminum plate 3 can positively prevent the possibility of corrosion which may be caused by salty sea winds or submergence by flooding and so on, whereby the two plates are prevented from separating, constantly maintaining the bonded condition originally designed, thereby enabling a linear motor car to travel as designed. Fig. 2 shows another embodiment of a composite structure 112 manufactured according to this invention, in which all grooves or recesses 7 formed in the upper joining surface of the steel plate 2 have therein intermediate ridges or projections 10 directed upwardly to enlarge the joining surface area of the grooves 7 to thereby increase the resistance against the shearing forces. Fig. 3 shows an other composite structure 114 manufactured according to this invention, in which the grooves or recesses 7 of the steel plate 2 and the projections or protrusions 9 of the aluminum plate 3 are both formed in a dovetail shape in cross-section with suitable distances between adjoining pairs of the recess 7 and the projection 9. The composite structure 114 according to this embodiment is advantageous in that it can be produced at low cost with a possibility of various design and arrangement of the recesses 7 and the projections 9. Fig. 4 shows a further composite structure 116 manufactured according to this invention, in which a layer 12 of thin plate made of an electrically insulating material is interposed between the joining surfaces of the soft steel plate 2 and the aluminum plate 3, instead of the direct contact of the metallic materials of different kinds constituting the metal plates 2 and 3 in the aforementioned embodiments. According to the construction of the composite structure 116 shown in Fig. 4, corrosion, which may be caused by an electric potential difference generated between both the plates 2 and 3, can be effectively prevented. In addition, since the steel plate 2 and the aluminum plate 3 are tightly joined through the layer 16, a sufficient resisting force against the shearing forces and separating forces can be obtained. Fig. 5 shows a further composite structure 117 manufactured according to this invention, in which a corrosion proof priming coat 12' is applied to the lower surface of the insulating layer 12 of the embodiment of Fig. 6 for increasing corrosion proof effect for the steel plate 2. In a preferred modification a bonding agent having a corrosion proof characteristic may be applied instead of the corrosion proof coat. The arrangements or orientations of the grooves or recesses 7 having the overhang surfaces 6 and the projections or protrusions 9 having the underhang surfaces 8 may be optionally made as shown in Figs. 6, 7 and 8, but not limited to these arrangements. In Fig. 6, the recesses 7 and projections 9 extend linearly in the same longitudinal or transverse direction. In Fig. 7, the recesses 7 and the projections not shown have a bent form. In Fig. 8, the recesses 7 and the projections not shown extend obliquely. The composite structures shown in Figs. 7 and 8 are advantageous in that the resistance against shearing forces in all directions along the interface can be increased. It should be noted that the composite structures of this invention have been described hereinbefore with reference to the preferred embodiments, but it is not limited to these embodiments and other various changes or modifications within the scope defined by the claims may be made. For example, ridges or grooves may be formed in zigzag shape on the underhang surfaces and overhang surfaces in plural stages in the direction of height of the protrusions and of the depth of the recesses, respectively. Further, the soft steel plate 2 and the aluminum plate 3 may be replaced with other metallic plate members of different kinds, respectively. Moreover, the composite structures manufactured according to this invention can be used not only as a secondary plate of a linear motor car track but also as composite structures requiring firm engagement between two plates or members, for example, for use in motor cars, machine tools, or as composite structures which are used under severe, violent conditions accompanied by sliding movements, vibrations or temperature variations. According to the composite structures of the characters described above, a firm engaging state between two materials can be maintained stably even under great, frequently repeated shearing and separating forces imparted to the composite structures, with the result that the function or operation of a linear motor car, for instance, can be stably maintained as designed. In addition, the joining surfaces of the two metal plates are kept in tightly bonded state in a manner of a labyrinth seal, so that separation of the two materials does not occur and any corrosive substance does not intrude to the interface even if the composite structure is exposed to corrosive atmosphere. A method of formation of a groove 7 having such a shape as shown in Fig. 2 will be described with reference to Fig. 10. In this method, a pulley-type formation roll 20a is pressed against the joining surface 11a of the blank soft steel plate 2 shown in Fig. 9. When the formation roll 20a is rolled on the joining surface 11a while pressing the same, a groove having an intermediate ridge 28, substantially vertical side walls and raised portions 29 is formed, and by repeating the rolling steps, a V-shaped valley portion for the groove and the raised portions 29 each having a predetermined height are formed. In the next step, when a cylindrical formation roll 27a is rolled by a predetermined number of revolution on the valley portion of the joining surface 11a, the raised portions 29 are pressed into a flat state, and a groove having overhang surfaces 6 sloping outwards with respect to the ridge portion 28 can be formed. Fig. 12 is explanatory of a further method of forming grooves 7 in the joining surface of the steel plate 2. In this method a pulley-type formation roll 20a similar to that shown in Fig. 10 is utilized. A plurality of depressions 30 are formed in the outer surface of the roll 20a so as to extend in the axial direction in circumferentially equally spaced relation. When the formation roll 20a is rolled on the joining surface of the steel plate 2, protrusions 31 are formed at equal intervals on the bottom of the groove 7 as shown in Fig. 13. Instead of the depressions 30, protrusions may be provided. In this case, depressions are formed in the bottom of the groove 7. According to this embodiment, the projections of the aluminum plate 3 can be firmly engaged with the protrusions 31 when the aluminum plate 3 is joined with the steel plate 2, and accordingly, resistance of the grooves 7 against external forces in the longitudinal direction thereof is increased. Figs. 14 to 16 are explanatory of a method of forming grooves, each having a shape similar to that shown in Fig. 3, in the joining surface of the steel plate. According to this method, as shown in Fig. 14, a formation roll provided with annular roll portions 45 having a substantially rectangular cross-sectional shape is pressed against and then rolled on the joining surface 11a of the steel plate 2 to effect plastic working and to form grooves therein with raised portions 46 on both sides thereof. In the next step, as shown in Fig. 15, a roll 48 provided with circumferential grooves 47 of a substantially triangular cross section at portions corresponding to the locations of the grooves 7 of the steel plate 2 formed by the formation roll 45 is pressed and rolled so as to plastically deform the raised portions 46 towards the insides of the grooves 7 as denoted by the reference numeral 46'. In the final stage, as shown in Fig. 16, when a formation roll 49 having a cylindrical configuration is pressed against and rolled on the joining surface 11a, the raised portion 46' are further deformed inwardly to thereby form the grooves 7 each having the overhang surfaces 6 on both sides. A steel plate 2 having grooves provided with the overhang surfaces formed by the methods described hereinbefore or a machining method can be firmly engaged or joined with an aluminum plate 3 having projections provided with the underhang surfaces in the manners and by the methods described hereunder. In order to fabricate the composite structure of the character shown in Fig. 2, for example, the grooves 7 having the overhang surfaces 6 are first formed in the upper surface and, in a certain case, in both side surfaces, of the soft steel plate 2 as shown in Fig. 17, and thereafter, a pair of the thus prepared metal plates 2 are integrally bonded at the opposing back surfaces thereof through a release agent 63 such as plaster, as shown in Fig. 18, for the purpose of mass production of the composite structure. The thus bonded steel plates 2 are then placed in a casting mold 65 as shown in Fig. 19 and a molten aluminum bath 3' is poured through a gate 67 of the mold 65 into a cavity defined between the inner wall of the mold 65 and the outer joining surfaces and the side surfaces of the bonded steel plates 2. During this process, a care must be taken for entirely and completely charging the molten aluminum bath 3' over the entire overhang surfaces 6 of the grooves 7 of the steel plates 2. The mold 65 is opened, after a predetermined time has elapsed to cool and coagulate the aluminum molten bath 3', to obtain a block in which the aluminum material 3 covers the entire outer surfaces of the steel plates 2 and is completely charged into all of the grooves 7 of the steel plates 2 along the overhang surfaces 6 thereof, as shown in Fig. 20. The block is then cut along the release agent 63 to obtain secondary plates such as shown in Fig. 21. In the embodiment described above, an anti-corrosion coating process can be interposed between the processes or steps carried out with reference to Figs. 18 and 19 to form a corrosion proof film made of an insulating material for preventing electrolytic corrosion between the steel and aluminum materials, on the joining surface between the steel plate 2 and the aluminum plate 3. The coated steel plates 2 are thereafter placed in the mold 65 and the molten aluminum bath 3' is poured into the mold cavity in the same manner as described before. It should be course be understood that one of the two different materials which is more easily fusible than the other can be fused and poured into the mold in the molding process described hereinbefore. A final product can be obtained by carrying out a trimming operation on the thus obtained composite block of the plates 2 and 3. The methods of forming the recesses in the first material, as described hereinbefore, can be used in any type of the composite structures described hereinbefore.

Claims: A method of manufacturing a composite structure made from a pair of members formed of material of different types mechanically joined to each other, wherein a first member (2) of a first material is formed with a joining surface having raised engagement portions, and a second material in molten state is poured onto the joining surface of the first member (2) and solidified to form a second member (3) fixedly joined to the first member, characterised by comprising the steps of: before joining the second member (3) to the first member (2), rolling a pulley-shaped formation roll (45) against the joining surface (11a) of the first member (2) to plastically form in the first member (2) at least one groove having along two longitudinal sides thereof raised portions (46) which delimit the said formed groove from said joining surface (11a) and which are raised above said joining surface: rolling a cylindrical roll (48) having a circumferential groove (47) of triangular cross-sectional shape against said first joining surface (11a) in such a manner that said triangular circumferential groove (47) confronts said formed groove (7) and said raised portions (46), thereby to form overhung side surfaces of said formed groove as a result of inward deformation of said raised portions (46) centrally into said formed groove (7) due to the action of surfaces of said cylindrical roll defining said circumferential groove (47) of triangular cross-sectional shape; rolling a further cylindrical roll (49) against said first joining surface (11a) and thereby leveling the inwardly deformed raised portions (46') with said first joining surface; placing said first member (2) in a casting mold (65) in a manner to leave a space having a predetermined width between said joining surface of said first member (2) and an inner surface of the casting mold (65); pouring the second material in molten state into said space and filling said second material into said formed groove (7); solidifying said second material to form the second member (3) bonded entirely to said joining surface of said first member (2); and removing the thus bonded first and second members (2, 3) from said casting molding (65). The method according to claim 1, further comprising the steps of: providing a peripheral groove along the periphery of said pulley-shaped formation roll; and thereby forming an intermediate ridge (28) along and in a bottom of said groove as a result of said rolling of said formation roll against said first joining surface (11a), thereby to provide said groove with a fork-shaped cross section. The method according to claim 1, further comprising providing said formation roll with a circumferential surface having formed at intervals therealong a plurality of recesses (30) or protrusions, and thereby forming protrusions (31) or recesses disposed at intervals along the bottom of said groove (7) as a result of said rolling of said formation roll against said first joining surface. The method according to claim 1, wherein an additional first member (2) of the first material is subjected to said rolling steps using the pulley-shaped formation roll (45), the cylindrical roll (48) and the cylindrical roll (49), and a pair of the first members (2) are placed in the casting mold (65) with the joining surface of one said first member disposed remote from the joining surface of the other said first member and with said first members (2) secured back to back with respect to each other, in a manner to leave spaces of predetermined width between each of said joining surfaces and the inner surfaces of the casting mold (65), and wherein the second material is poured into said spaces so as to also fill said grooves (7), the bonded first and second members (2, 3) are removed from within the casting mold (65), and the first members (2) are separated from each other such that each said first member has bonded thereto a respective portion of said second member. The method according to claim 4, further comprising the steps of: forming at least a groove having overhang side surfaces in each of side surfaces of said first members (2); forming side spaces between said side surfaces of each of said first members (2) and inner surfaces of said casting mold (65); and pouring said second material (3') into said side spaces and filling said second material into said side spaces and said grooves adjoining said side spaces, thereby to enable bonding of said second member to said side surfaces of said first members.

Inventors: ASARI HIROATSU, KOE SHIGEKI, KUMON YASUHIRO, MATSUI SHIGEMOTO, MATSUMURA HIROYUKI, OKAZAKI SHOZO, UEKADO MASAKI, YAMADA TAKESHI, YAMAMOTO AKITOSHI, ASARI, HIROATSU, KOE, SHIGEKI, KUMON, YASUHIRO, MATSUI, SHIGEMOTO, MATSUMURA, HIROYUKI, OKAZAKI, SHOZO, UEKADO, MASAKI, YAMADA, TAKESHI, YAMAMOTO, AKITOSHI
Applicants: KAWASAKI HEAVY IND LTD, KAWASAKI JUKOGYO KABUSHIKI KAISHA
Application year: 1988
Main classification: B21H7
IPC codes: B21D39, B22D19, H02K41, B23P11, B21H7, B21K25, H02K15