US3358349A

US3358349A - Method of explosion cladding irregular aluminum objects

Info

Publication number: US3358349A
Application number: US387715A
Authority: US
Inventors: Carl G A Rosen
Original assignee: Darlite Corp
Current assignee: Darlite Corp
Priority date: 1964-08-05
Filing date: 1964-08-05
Publication date: 1967-12-19
Anticipated expiration: 1984-12-19
Also published as: GB1078556A; DE1521207A1; SE307884B

Description

Dec. 19, 1967 c. G. A. ROSEN METHOD OF EXPLOSION CLADDING IRREGULAR ALUMI 'NUM OBJECTS Filed Aug. 5. 1964 5 Sheets-Sheet 1 FIG \B FIG INVENTOR Carl 6. A. Rosen Dec. 19, 1967 c. G. A. ROSEN 3,358,349

METHOD OF EXPLOSION CLADDING IRREGULAR ALUMINUM OBJECTS Filed Aug. 5, 1964 S Sheets-Sheet 2 H0: H2 I22 I & |35 134;

INVENTOR Carl 6. A. Rosen Dec. 19, 1967 c. G. A. ROSEN METHOD OF EXPLOSION CLADDING IRREGULAR ALUMINUM OBJECTS 5 Sheets-Shee; 5

Filed Aug. 5. 1964 27 I2 26 2| 4 [U f INVENTOR Carl 6. A. Rosen .FIG IF United States Patent 3 358,349 METHQD {3F EXPLGElliEN CLADDING IRREGULAR ALUMTNUM OBJECTS Carl G. A. Rosen, Woodside, Calif., assignor to Darlite Corporation, Peoria, 111., a corporation of Illinois Filed Aug. 5, 1964, Ser. No. 387,715 13 Claims. (Cl. 29156.5)

This invention relates to an improved method of cladding a cast or forged aluminum body subjected to wide and sudden temperature changes and bodies having nonplanar surfaces with a stainless steel veneer or cladding, and to various products formed thereby.

The term aluminum as used herein encompasses aluminum and aluminum base alloys which contain at least 50% by weight of aluminum, and the term ferrous metal embraces iron and alloys thereof including steel and stainless steel. The metallizing metal described herein as molybdenum includes metals whose boiling point is high enough that a molten spray thereof and its velocity energy directed against the aluminum will vaporize the surface aluminum without such metal reaching its own boiling point. Such would include cobalt, nickel and titanium.

With internal combustion engines and vehicle brakes used more and more in extremely cold climates, particularly under conditions where the warm-up period may be fast from 65 F. the internal stresses and strains can cause shattering where two bonded metals of otherwise desirable characteristics but of different coefiicients of expansion are involved. Although, by way of example, pistons made of a single metal would survive such a short warm-up the use of dual metal pistons is demanded for the long working time of the piston, in order to attain many well-known essential advantages including wear surfaces, particularly with aluminum pistons and brakes. The invention prevents this shattering while further improving piston performance regardless of the conventional head configurations of the piston, whether they be flat or provided with protuberances or cavities for various purposes.

By way of illustration but not by way of limitation the invention is described primarily with a piston presenting the widest abilities of the invention. Having in mind a specfic and particularly dlficult to forge piston body which has a highly rated performance for a multifuel internal combustion engine, the head of the piston is flat with a central open cavity into which the fuel is injected for combustion. Generally most conventional surfaces are not designed to have fuel spread in contact with a piston surface, and some are designed to prevent fuel contacting the surface but in the M (Muerer) system the fuel is injected to flow along the wall of a piston cavity generally referred to as a shrouded toroidal bowl and presents critical heat transfer control problems to provide high output supercharged engine performance. In such a piston the wall of the cavity is maintained at about 600 F. which keeps the liquid fuel contacting it from carbonizing while the cyclonic movement in the cavity progressively vaporizes the exposed surface of the liquid and burns it until the cavity becomes dry on the working or power downstroke of the piston. In some of these pistons an internal closed space in the stock surrounds or partially surrounds the cavity to assist in the heat transfer control to maintain the 600 F.

According to the present invention, the heat conduction through the aluminum piston stock to the piston ring grooves is controlled at the radial faces of the cavity, and a fiat circular heat-conductive shield is applied to the upper face of the head of the piston to reject additional heat into the liquid fuel on the walls of th cavity, as well as from the head into the combustion chamber. This reduces heat accumulation in and around the piston ring grooves. To assure longevity of the piston ring groove contours under all engine operating conditions, a preformed solid band of ferrous metal and of appreciable thickness is initially bonded to the upper side wall por tion of the piston and, thereafter, the ring grooves are radially cut therethrough.

Under ordinary operating conditions, such a band can be satisfactorily applied by a thermal shrinkage operation as described in my application Serial No. 153,483, filed on Nov. 20, 1961, now Patent No. 3,203,321, and entitled, Method and Product and Bonding Ferrous Metal With Aluminum. However, where extremely low start-up temperatures and high ring groove operating temperatures of 500 to 550 F. are experienced, a more effective bond is required. Therefore, according to the present invention, a novel method for accomplishing the compressive bond required is provided involving the sudden liberation of energy from an explosive charge by detonation thereof to prestress the aluminum of the piston under molecular compaction and compression in a direction opposite to its direction of heat expansion and to prestress the ferrous metal of the band in compaction and tension in a direction opposite to its direction of heat expansion, and, simultaneously therewith to diffusion bond weld them in intimate unoxidized metal-to-metal interdiffused relationship with high local deformation at the interface involving a mono layer of particles of a metal such as molybdenum having a melting point above the boiling point of the aluminum.

By such a method a compacting high impact pressure is applied above the dynamic yield stress of the material transverse to the interface as a shock wave moving parallel to the interface at a velocity above 800 feet per second, but less than the speed of sound in the respective materials, to ripple the interfaces and increase the bonding area in order to assist in the preservation and the maintenance of the bond compression stresses throughout the bonded area. Some of these stresses include shear stresses where portions of the interface ripples are disposed at a substantial angle to the main face of the bond. The optimum speed is from 1000 to 1100 feet per second. Application of the flat circular shield to the upper end face of the piston is made by a similar explosive process.

The unoxiclized metal-to-metal relationship avoids the formation of brittle compounds or alloys and the particle layer, which may be a metallized molybednum spray, is made close enough to the aluminum to vaporize away any surface layer of oxidized aluminum and establish and maintain an unoxidized aluminum interface. The layer also acts as a diffusion control against undesirable intermetallic compounds developing at the interface.

Thus, a cladding is provided at the ring grooves, the top of the head and around the throat of any cavity where heat differentials and erosion are quite high. The cladding does not break up nor shatter since the stress factor induced remains above the tension factor throughout the full range of temperature changes and differentials.

The thickness of the ferrous metal on the head is related to the degree of heat transfer rate or combustion heat desired to be rejected back to the combustion chamber or envelope. Such increases the effectiv compression ratio, reduces fuel waste, after-burning and crankcase contamination.

In the accompanying three sheets of drawings pistons having several different configurations embodying the invention are shown with like numerals referring to like parts but the description by way of example is directed to a particularly diificult design for purposes of illustrating various considerations of the invention.

In these drawings:

FIGS. 1A through 1F are'sectional views taken substantially centrally and vertically through bodies constructed in accordance with the method of the present invention; the first five figs. illustrating contours more generally in use for piston heads (FIGS. 1A to FIG. 1B) for disk brakes, FIG. 1A and drum type brakes (FIG. 1F,

see also FIGS. 7 and ll) FIG. 2 is a sectional view taken substantially centrally and vertically through an aluminum piston blank from which the piston of FIG. 1F is constructed,

FIG. 3 is a fragmentary sectional view similar to FIG. 2 illustrating the application of a mono-molecular layer of metallized molybdenum to the upper surface of the piston to provide and preserve nonoxidized surfaces thereof where cladding is desired,

FIG. 4 is a fragmentary sectional view similar to FIG. 2 illustrating the initial application to the upper end face of the piston of an explosive-charged cladding blank preparatory to detonation thereof.

FIG. 5 is a fragmentary sectional view similar to FIG. 4 showing the explosive disk operatively applied to the piston blank after detonation thereof,

FIG. 6 is a fragmentary sectional view similar to FIG. 5 illustrating a cylindrical body treated by machining thereof to prepare the body for cladding with a circular bandincluding the application of metallized molybdenum to the surface,

FIG. 7 is a fragmentary sectional view similar to FIG. 6 illustrating the initial application of an explosive cladding bandpreparatory to detonation thereof,

FIG. 8 is a fragmentary sectional View similar to FIGS. 6 and 7 showing the explosive cladding band operatively applied to the body after detonation thereof,

FIG. 9 is a representation of a photomicrograph of a section taken transversely through the juncture region between the aluminum and one of the cladding elements and in the longitudinal direction of the explosive force employed to effect the bonding of parent elements,

FIG. 10 is a sectional view taken centrally and axially through a piston body embodying the invention, and

FIG. 11 is a fragmentary sectional view through an showing of the final structural character thereof.

The method contemplated by the invention is to provide an aluminum body, preferably forged, and clad it with a wear and heat control metal with a bond that will not fracture under extreme temperature changes. The body shown for purposes of illustration is a forged aluminum piston body having a shrouded toroidal bowl in the head thereof and a sealed annular compartment in the aluminum stock around the bowl, to control the heat conductivity from the bowl to the ring area. A monomolecular layer of metallized molybdenum is applied to the exposed aluminum surface to be clad and this is done with the metallizing gun sufiiciently close (2 to 3 inches) to vaporize away any aluminum oxides on the surface and expose, embed in and preserve an unoxidized aluminum interface therewith. The molybdenum layer extends over the edge and down and around a limited portion of the bowl surface whereby surface temperatures are controlled so as not to carbonize the injected fuel yet be adequate to vaporize same for combustion.

Thereupon a blank from a sheet of stainless steel approximately thick is coated with a wafer of explosive material and one edge is brought to rest on one edge of the piston head with the explosive layer out and the rest of the blank inclined gradually away from the head face at approximately an included angle of 3 The powder is preferably, but notnecessarily, detonated in an atmosphere under a slight vacuum of a few inches of mercury, beginning at the contacting edges. The slight vacuum removes the absorbed layer of air from the mating surfaces to prevent oxide inclusions as a byproduct of the Welding process. The powder burns at a rate of slightly less than 1500 feet per second across the rest of the blank, progressively slamming or impacting it against the head approximately &

or end face with an interface shock wave of high intensity 1 are thereby diffusion welded and the substrate aluminum 7 stock is found to be prestressed by a compression well above the tension or yield stress of the metal over a wide range of temperature changes including -60 F. and 600 F.

When the aluminum body is flat or convex as seen in FIGS. 1A to 1C, the weld is complete all the way across but to illustrate the operation upon the more complex head contour as shown, the sheet metal blooms partially into the bowl and welds down along the edge surfaces of the throat to protect them from erosion of hot combus tion flame and gases erupting from the bowl immediately following the compression stroke and ignition. The unsupported web of the bloom is later cut away and the clad edges polished.

Thereafter the blank portions overhanging the side wall of the piston is machined away and the wall turned down to over the ring groove area. A like coating of metallized molybdenum is applied for the same reasons over the machined area and a band of ferrous metal approximately & to thick and defining a frustum of a cone having an included angle of from 2 to 5 is slipped over the machined surface with its small diameter leading with a close fit until it comes to rest against a shoulder at the end limit of the machined area. A layer of like explosive powder is placed around wardly and contract the ring into a diffusion weld of unoxidized interface metals with the metallized wall and also with the edge of the head layer of ferrous metal. Thereafter the excess of the ring overhanging the head is machined away, the piston is finished to proper size and the piston ring grooves are out. p

The substrate aluminum is prestressed under a compression to a point above the yield point of the aluminum in the bonded region throughout a temperature range extending as low as 65 to as high as +550 F. under loaded engine conditions.

More particularly, a forged piston blank 10 is shown in FIG. 2 as having a fiat head surface 21 representative of all fiat topped pistons and a shrouded bowl 12 generally referred to as a Meurer construction which is representative of any one of a number of different type bowls including open sided or shrouded toroidal, concave or hemispherical bowls having stepped or smooth walls. These numerals with suffix letters identify like parts throughout FIGS. 1A1E.

In the head stock around the bowl 12 is an annular space 17 formed by making a circular groove around the bowl area for oil cooling of the piston. The stock is upset to close the groove at its upper edges in contacting relationship. Heretofore, this has required argon gas welding but this is eliminated by the present invention. The head plate assists in holding the circular groove in closed relationship. The piston is finally tooled to the structure of the blank shown in FIG. 10 which includes wrist pin bosses 118 and skirtportions 120.

The head of the piston body is faced ofi as shown in V dotted lines in FIG. 2 a distance a little less than its ultimate height and the mouth and throat area of the bowl is finished to an edge face 22, also shown in dotted lines, which has appreciable axial width. Then these surfaces are metallized with molten molybdenum particles 23 sprayed from a metallizing gun 24 as shown in FIG. 3, preferably at a spray distance appreciably less than 3 when the piston is at room temperature whereby the heat of the molten particles of molybdenum and their velocity vaporizes away any oxidized surface aluminum and embeds in unoxidized aluminum. The spray coating 25 is only thick enough to seal the aluminum from contact with the air. Generally one pass of the metallizing gun will sufiice. A monomolecular type coating is desirable. The coating need extend own the bowl walls only a slight appreciable distance. This use of the molybdenum greatly reduces the likelihood of an intermediate phase brittle compound being formed at the weld. Slight amounts of interface brittle compound may be acceptable with some uses but is not desirable.

As shown in FIG. 4, a circular disk or blank 26 cut from a metal sheet of desirable thickness from g to 75 thick, preferably stainless steel, is then laid upon top of the head surface 11 with one edge in contact as at 27 and the opposite edge elevated to provide an included angle on the order of 3 Freferably the blank is coextensive in size with the head surface. The disk 26 may be held in its elevated position by a prop 28 fixed to the piston blank by a suitable frangible adhesive. A charge of explosive material 29 in the form of a wafer which is coextensive with the disk 26 and which burns at a lineal rate less than the speed of sound in the environmental atmosphere provided is placed on top of the blank 26 and detonated by means of a suitable detonating cap 30 at the contacting edge. The explosion and shock which follows difiusion welds unoxidized interface metals as previously described and prestresses or work hardens the substrate aluminum by compression to an impressive stress above the dynamic yield strength of the metal at -65 F. with a consistent and predictable value to resist strains to which the bond will be subjected when the piston is in use at its highest working temperature.

In FIG. it will be observed how the blank blooms as shown at 31 into the bowl 12 and bonds marginally to the throat surfaces. The unbonded metal is subsequently cut away and the throat edges are finished off to a sharp edged orifice and polished as shown in FIG. 6.

it should be noted that the blank 26 is preferably fiat. However, where the piston heads have shallow depressions or protuberances, a substantially mating contour can be preimposed on the blank but limited to a space between the two parent parts comparable to the provision of the previously mentioned 3 angle. Where the blank is unsupported over a deep depression the blank will bloom with the explosion and bonds at the edge and a short way into the depression to the extent that the blank is upset by the explosion enough to force a compressive shock contact relationship under the explosive force. This distance depends upon the thickness of the blank, the steepness of the margins of the depression, the relative mildness of the metal in the blank and the force of the explosion. Within the draw limits of the metal or" the blank, these factors can be allowed for and resolved by varying the thickness of the powder charge over the areas of the depression where bonding is to be controlled. Moreover where the depression is not to be cladded, the blank can be cut out thereby permitting the marginal edges over the depression greater freedom to form under the explosion force. Excess material in an unsupported substantial overlap of the blank, however, is evenly sheared off at the edge of terminal support during the welding process. In FIG. 6 the blank 19 is shown as ultimately having the bloom 31 removed and the edge of the cavity machined to a sharp orifice opening which will endure under long and hard use of the piston.

The piston ring groove area is machined to a small diameter as indicated at 33 to receive a stainless steel sleeve 34 such as has been shown FIG. 7. Preferably, the machined area 33 is cylindrical, thus providing an upwardly facing annular shoulder 36 at the bottom of the ring groove area While the sleeve 34 is of frusto-conical design having a small slant or taper angle on the order or 3". The small base of the cone frustum is such that it may seat upon the annular shoulder 36 and the slant height of the cone frustum is such that the upper rim of the sleeve 34 extends a slight distance above the upper surface of the previously applied and explosively deformed d disk 26. Prior to installation of the frusto-conical sleeve 34 on the piston blank 10, the machined ring groove area 33 is treated with the metallizing gun 24 to apply a layer of molybdenum thereto for the reasons set forth in connection with the application of the layer of molybdenum to the walls of the bowl 12.

A coating or jacket 29 (FlG. 7) of explosive material is applied to the outer surface of the frustoconical sleeve 34- coextensively therewith and is detonated by means of a detonator ring 42 positioned near the small base of the cone frustum. Upon detonation, the explosive material burns progressively upwardly and the violent explosive force thereof contracts the sleeve 34 against the machined cylindrical piston ring groove area 33 in a manner similar to that described in connection with the application of the circular disk 26 to the machine and molybdenum treated upper end face 21 of the piston blank 10. During the explosion, the frusto-conical sleeve 34 is deformed to a true cylindrical shape, the deformation taking place progressively in an upward direction with the same phenomena of diffusion welding, scuffing of unoxidized interface metals under extremely high pressure, prestressing of the substrate aluminum stock, etc, described in con nection with the bonding of the blank 26 to the machined end face 21 as well as to the circular end face of the previously machined blank. Additional physical phenomena are attendant upon such interface bonding of the stainless steel material of the disk 26 and sleeve 34 to the end face 21 and piston groove area 33 respectively and these will be described subsequently in connection with FIG. 9 wherein the physical characteristics of the actual bond effected has been illustrated.

After the frusto-conical sleeve 34 has been applied to the piston blank 10 in the manner described in connection with FIGS. 7 and 8, the blank is given a final machining operation wherein the overhanging ring of metal above the horizontal plane of the upper face of the deformed disk 26 is removed and the annular piston ring grooves are cut completely through the sleeve 34 and into the previously machined cylindrical outer face 33 of the piston blank 10. Thereafter the thus machined blank may be polished or otherwise surface treated to produce the completed piston shown in FIG. 1. The completed piston retains many of the shape characteristics of the original blank 19 as do also the applied stainless steel cladding and thus, in order to avoid needless repetition of description, similar reference numerals but of a higher order have been applied to the corresponding parts as between the disclosures of FIGS. 10 and 2. These have been used also on FIGS. 1A1E with sufiix marks where appropriate.

Referring now to FIG. 10, insofar as the shape characteristics of the piston 119 are concerned, it is to be noted that the application of the circular disk 26 to the machined end face 21 of the blank serves to provide a crown 126 on the top of the piston, this crown including a limited peripheral region occasioned by the overlap of the explosion-deformed sleeve 34 (FIG. 8). This crown is relieved as at 127 where the stainless steel metal enters the bowl 112 and is adhered to the wall thereof as previously described.

The explosion-deformed sleeve 34 of FIG. 8 establishes a band of stainless steel around the blank 10 and, when the final machining operations previously described are performed upon the blank, this band is divided into sections numbering two to four depending upon commercial considerations. The sections include a relative wide band 134 embracing the extreme upper regions of the piston head, and narrow bands 134a embracing the land areas between adjacent machined grooves 135. It is well known in connection with conventional piston operation that the greatest groove wear takes place in connection with the various compression ring grooves and that the oil ring groove which invariably is disposed below the compres sion grooves does not wear as rapidly. Thus, according to the present invention, only those land areas which adjoin a compression ring groove 135 are clad with stainless steel, the lowermost groove having no cladding around its lower rim region. Preferably the juncture of the shoulder 36 and sleeve 34 is located where the lowermost groove is located whereby the cutting of the groove cleans up any minor discrepancies and flaws that might possibly have occurred in the explosion welding step.

Explosion welding as a name is not new, and explosives have been used in various Ways as quick sources of power to impel impacts between elements. Although the term explosion Welding can be used in referring to the present invention the method of the present invention is novel in bonding dissimilar metals such as steel and aluminum with non-oxidized interface metals under a washing and sending impact which induces plastic flow of the joining surfaces and which interlocks and diffusion bonds the metal under a compression which is not relieved over wide ranges of temperature changes. The explosive force is applied progressively along the bonding area with a rapid compression and expansion of the two elements and this results in the attainment of a more intimate bond between the metals to be joined together than has heretofore been possible.

Additionally, the preliminary treatment with metallized molybdenum spray of the area of the aluminum metal to which the cladding metal is applied immediately prior to explosive application of the cladding assures non-oxidized metal interfaces with molybdenum particles that can move with the action of the metal at the bonding surface during the explosively applied force to maintain a more perfect union between the base and cladding metals. Furthermore, the progressive burning of the explosive material, coupled with the application of a metallized molybdenum coating, makes it unnecessary to etch or otherwise roughen the surfaces undergoing welding at the interface as has been considered advantageous practice heretofore.

While the precise chemical and physical phenomena involved in connection with the present process may not be entirely understood, the representation of FIG. 9 which is taken from an actual 500 power microphotograph of a section taken transversely through the interface between a portion of a piston and its cladding shows the rippling or wave action attained. Considering this microphotograph representation in conjunction with FIGS. and 8, it is to be noted that since detonation initially takes place on the cladding blank 26 at one extremity thereof which is in contact with the aluminum body it and ignition of the explosive material 29, progresses along the cladding in its direction of divergence between the body and blank, the blank is progressively slammed and scufied into contact with the base metal as indicated in dotted lines in FIGS. 5 and 8 as a shock wave action. Fusing of the two metals at the interface takes place, not only as a result of the heat of the exploding powder, but also as the result of three other factors, namely the outrush or expressing of air from between the base metal and the blank controlled in amount by the partial vacuum; the slamming impact which, although of a progressive scuffing or plastic flow of the metals, is nevertheless appreciable and the heat of molecular compaction of the metals. A certain amount of heat is created by compression and the outrush of air with friction against the metals at the interface. However, the predominant force for making the bond is the heat generated by the pressure wave compacting the molecules of the metals at the interface with a rebound and reestablishment of pressure contact as a vibratory action of microsecond duration. The compaction impact creates heat when it strikes a steel target and a rippling action follows which assures the bond when the explosive charge approaches but does not expend a crushing blow. The combined heat resulting from these phenomena creates sufiicient heat to effect melting of the two metals at the interface and a displacement and diffusion of molecules at the interface.

As to the intimacy of the bond which is created at the interface, a non-oxidized union between the metals at the interface and resulting from the use of the metallized molybdenum spray is, of course, conducive to an intimate union. What is equally important however is the phenomenon which obtains when interfacial turbulence is created by the passage of one fluid media forcibly across the surface of another fiuid media. Waves on the surface of a body of water initiated by a wind strong enough to cause white caps are not truly sinuous waves but rather they have gradual curvature on their trailing sides and sharply curved cavities on their leading sides. Stated othewise, the waves of wind blown Water lean forwardly as their base is retarded by the frictional inertial drag of the main body of water. Such a wave pattern is illustrated in FIG. 9 wherein a wave pattern is established at the interface between the aluminum piston blank 10 and a blank 26. Individual waves 140 are created due to the outrush of air and movement of molten metal between the body and blank and these waves have relatively sharp cavities 142 along their leading edges. These cavities create interlocks between the two metals and enhance the bond therebetween. This is a characteristic representing the establishment of a good weld.

Articles constructed according tothe above-described method and as exemplified by the piston 110 of FIG. 10 are capable of withstanding sudden and extreme temperature changes ranging from as low as 65 F. to engine operating temperatures as high as 550 F., the bond between the base metal of the piston body and the cladding remaining intact and under compression, particularly at the annular surfaces throughout the range of heat expansion. When it is considered that the various phenomena which take place as a result of the explosion lasts on the order of only microseconds, it will be appreciated that the explosive force is not a gradual compressive force such as might be the case if the sleeve were compressed under the influence of pressing dies. Rather the compressive force is an impact force which hammers the extreme outer surface region of the sleeve to a density not transmitted through the entire sleeve thickness and this dense surface skin which is created on the sleeve not only is extremely wear resistant, but 1t also places the sleeve under tension and provides a permanent centripetal force inwardly against the piston body. The piston therefore possesses greater wear characteristics than that of a piston which is similarly clad by conventional shrinkage or other methods.

By way of example with a blank 1 thick of 1010 steel upon a flat surface of a body of 4032 aluminum alloy disposed at an angle of 2% to each other, an explosive sheet of Dupont EL 506-D sheet explosive between 35 and 40 mils thick and detonated by a P-L-H or equivalent detonator will impart a velocity of 25 to 35 IIIH'L/pSCC. to the blank which results in a collision point velocity from 3.35 to 4.0 mm./,usec. and produce a weld that withstands without deterioration rapidly repeated temperature changes between 65 F. and 550 F. occurring within as little as fifteen minutes.

The explosive preferably is preformed in rings of a low cost castable explosive such as composition B (60% RDX and 40% TNT). Other explosives satisfying the suggested burning rate may be used and the amount used increases with the thickness of the applied cladding within the velocities indicated. Even then less than a pound would be required for 12 square inches of stainless steel thick.

In this connection a much larger area is involved with brake drum braking areas and it has been found that a slight modification of the step shown in FIG. 7 provides a capability of bonding against even wider ranges of temperature such as are experienced with vehicle brakes. In performing the process with brakes, an aluminum bake drum 210 tapered slightly on its outer sur- 7 face 240 is wedged into a correspondingly tapered ring anvil member 241 having ejection pins 248 therein. The periphery 243 of the ring anvil supports the skirt of the brake drum against the force of the explosive used. The working face 221 of the drum is machined to 8. cylindrical contour having an annular groove 244 bordering its inner edge and sprayed with a molecular layer of molybdenum 225 in the manner and for the purposes already described.

The liner member 234 is made from ductile mild steel as an integral unit and is formed as a frustrum of a cone having a taper angle of 3. The major diameter is slightly less than the diameter of the working face 225 of the brake drum and preferably for ease of insertion is disposed at the skirt edge of the brake drum with edge 245 at the minor diameter overlapping the groove 244. An explosive band 229 is laid against the inside face of the liner 234 with a detonator ring 242 at the edge having the major diameter.

Thereafter, the detonator is fired, and the explosion bonds the liner to the molybdenum coated face 225 with the inner edge at 245 driven into interlocking relationship with the groove (FIG. 1F). The drum is ejected from the ring anvil 241 and the skirt edge and braking surface are machined to their final form. The product not only has a bonded interface relationship under molecular compression which is not relieved within the ranges of temperature changes experienced under working conditions but high heat conductivity of the bond with a thin bearing liner dissipates the heat at an improved high rate to prevent deterioration of the liner. Moreover, in the embodiment shown the expansion tendency of the liner under brake pressure is in the direction favorable to the re tention of the bonded relationship when heat is being generated at a high rate.

In all instances attenuators are attached to the explosive charges to establish the explosion reaction pressure and direct the working pressure against the blank for welding. The attenuator (not shown) may be a piece of cardboard blotter or thin rubber film between the powder and applied member that varies the rate of pressure rise of the explosion to control the sharpness of the blow on the anvil to provide more closely a sine wave effect.

Various modifications and variations of the present process may be made without departing from the spirit and scope of the present invention as defined in the appended claims.

The invention is not to be limited to the exact arrangement of parts shown in the accompanying drawings or described in this specification as various changes in the details of construction may be resorted to without departing from the spirit of the envention. Neither is the invention to be limited to the exact sequence of method steps set forh herein since they too may be varied within the scope of the invention. For example, whereas in FIG. 7 the confronting surfaces of the piston blank 10 and sleeve 34 are shown as being divergent at an angle on the order of 3 by reason of the frusto-conical shape of the sleeve, it is within the purview of the invention to employ a cylindrical sleeve and to machine the piston ring groove area 33 of the blank 10 on an upwardly tapering bias so that the 3 angular divergence between the confronting surfaces will be preserved. The 3 angle may be changed to a lower angle if a lower velocity powder is developed. Also, the sleeve can be welded before application of the blank if desired. Additionally, while the method set fort-h herein has by way of example been described in connection with the cladding of a generally cylindrical piston blank with various head configurations, the method may, by suitable dimensional modifications as desired, be employed for the cladding of cylindrical and flat objects having rapid and wide temperature changes, such as cylindrical or disk type vehicle brake members where heat dissipation is also important, within the spirit of the invention, the scope of which is commensurate with the appended claims.

What is claimed is:

1. The method of cladding a predetermined surface area of an aluminum object with a substantially rigid ferrous metal veneer of appreciable thickness by a progressive impact welding operation involving the rippling and interface fusion of the metals, comprising: metalizing said surface area with a metal whose melting point is above the boiling point of the aluminum positioning a sheet of the veneer metal having a surface shaped conformably to said metalized surface area and with said shaped surface confronting said surface area and in close proximity thereto and diverging therefrom so as to provide an included angle on the order of 3 with the apex thereof within the confines of said surface area, and detonating an explosive thereafter applying pressure progressively across an exterior surface of said sheet of veneering metal commencing at said apex to thus exert a rolling plastic flow on the sheet in the direction of divergence between said surface area and confronting surface to impart a progressive movement of the sheet into impacting relationship against the aluminum object under motivating pressure sufiicient to express the air from be tween the sheet and object at a rate sufficient to generate appreciable heat of friction and displace the metalizing metal as a diffusion control against undesirable intermetallic compounds developing at the interface, and also sufiicient to generate appreciable heat of impact between the metals, with the combined heat thus generated being sufiicient to melt both the aluminum and ferrous metals at their interface region of union whereby a non-oxidized bond is established at the interface under a compression between said both metals which is not relieved over wide ranges of temperature changes.

2. The method set forth in claim 1, wherein the predetermined surface area of the aluminum object is cylindrical and the sheet of veneering metal is in the form of a frusto-conical sleeve having a slant angle on the order of 3 and having one of its base diameters substantially equal to the diameter of the surface area, the sleeve being held in telescoping relationship with respect to the cylindrical surface area at the time of the application of impact pressure thereto.

3. The combination called for in claim 2 wherein said one of the base diameters is the major diameter and the method includes externally supporting said aluminum object against expansion during detonation of said explosive.

4. The method set forth in claim 2 wherein said one of the base diameters is the small diameter.

5. The method of cladding a predtermined surface area of an aluminum object with a substantially rigid ferrous metal veneer of appreciable thickness by a progressive impact welding operation involving the rippling and interface fusion of the metals, comprising: spraying said surface area with an oxidation-inhibiting substance whose melting point is above the boiling point of the aluminum positioning a sheet of the veneer metal having an inner surface shaped conformably to said sprayed surface area and with said shaped surface confronting said surface area and in close proximity thereto and diverging therefrom so as to provide an included angle on the order of 3 with the apex thereof within the confines of said surface area, and detonating an explosive against the outer surface of said veneer metal and thereby applying pressure progressively across an exterior surface of said sheet of veneering metal commencing at said apex to thus exert a rolling action on the sheet in the direction of divergence between said surface area and confronting surface to impart a progressive movement of the sheet into impacting relationship against the metal object inducing plastic flow of the metals under motivating pressure sufficient to express the air from between the sheet and object at a rate sufficient to generate appreciable heat of friction, and impact to melt and scuif the unoxidized interface metals and displace and diffuse said oxidation-inhibiting substance in a non-oxidized union therewith controlling against undesirable intermetallic compounds developing 1 1 at the interface whereby the metals are bonded under compacting pressure above the dynamic yield stress of the materials which is not relieved over wide ranges of temperature changes.

6. The method set forth in claim 5, wherein the object is a forged aluminum piston, the metal of the veneering is ferrous metal, and wherein the confronting surface to which the oxidation-inhibiting substance is applied is the surface area of the metal object.

7. The method set forth in claim 5, wherein the oxidation-inhibiting substance applied to said one confronting surface is a mono-molecular layer of metallic molybdenum.

8. The method set forth in claim 5, wherein the oxidation-inihibiting substance applied to said surface area is metallic molybdenum and wherein its application is made by the spraying of said surface with a gaseous suspension of metallic molybdenum particles.

9. The method of cladding a predetermined contoured surface area of an aluminum object with a substantially rigid metal veneering of appreciable thickness by a progressive explosion-initiated impact welding operation involving the interface fusion of the metals, comprising: metalizing said surface area with a metal whose melting point is above the boiling point of the aluminum positioning a sheet of the veneering metal having a surface shaped conformably to the contour of said surface area with such surface confronting said surface area in close proximity thereto and diverging therefrom so as to provide an included angle on the order of 3,placing a coating of an explosive substance on an exterior surface of the sheet and in effective coextensive register with the interface area to be fused, detonating said explosive'subarea to thus apply impact pressure to said sheet progressively as burning of the explosive substance progresses in the direction of divergence of the confronting surfaces and exert a rolling action on the sheet in such direction and move the same into impacting relationship against the metal object under motivating pressure suflicient to express the air from between the sheet and object at a is not relieved over wide ranges of temperature changes.

10. The method set forth in claim 9, wherein the predetermined surface area of the aluminum object is cylindrical and the sheet of veneering metal is in the form of a frusto-conical sleeve having a slant angle on the order of 3 and having a small base diameter substantially equal to the diameter of the surface area, the sleeve being placed in telescoping relationship with respect to the cylindrical surface area immediately prior to detonation of the explosive substance.

stance at its region of closest proximity to said surface 11. The method set forth' in claim 9, wherein the predetermined surface area of the aluminum object presents a continuous closed outer band-like contour and the sheet fof veneering metal is in the form of a sleeve, the sleeve being placed in telescoping relationship with respect to the cylindrical surface immediately prior to detonation of the explosive substance so that all circumferential regions of the sleeve an included angle on the order of 3 between the inside surface of the sleeve and the predetermined surface area of the metal object is maintained.

12. The method of cladding a predetermined surface area of an aluminum body element with a mono-molecular film of metalized molybdenum therein with a ferrous metal veneer of appreciable thickness comprising positioning a substantially rigid sheet element of the veneer having a surface shaped conformably to said surface area disposed in close proximity thereto and diverging therefrom to define anvincluded angle therewith on the order of 3 with the apex thereof within the confines of said surface area, driving said sheet element at a velocity within the approximate range of 25 to 35 mm./ .t seconds progressively in a direction away from said apex along the face thereof opposite to said shaped surface to progressively collide said sheet element against said body with extreme shock at a collision point velocity within the range of substantially 3.354.0 mmj seconds and thereby express the air between them and generate a surface melting heat to ripple the interfaces of the elements in bonded molecularly displaced and diffused relationship with the metalized molybdenum over a bonding interface area than the initial area defined by the elements within said included angle whereby the metals are bonded under compacting pressure above the dynamic yield stress of the bonded materials which is not relieved over a range of temperatures from F. to +550 F.

13. The process defined in claim 12 including cutting through a limited area of said veneer and placing an element in said cut in heat exchange contact directly with the aluminum of said body.

References Cited UNITED STATES PATENTS Chudzik 29 -486 JOHN F. CAMPBELL, Primary Examiner.

J. L. CLINE, Assistant Examiner.

Claims

12. THE METHOD OF CLADDING A PREDETERMINED SURFACE AREA OF AN ALUMINUM BODY ELEMENT WITH A MONO-MOLECULAR FILM OF METALIZED MOLYBDENUM THEREIN WITH A FERROUS METAL VENEER OF APPRECIABLE THICKNESS COMPRISING POSITIONING A SUBSTANTIALLY RIGID SHEET ELEMENT OF THE VENEER HAVING A SURFACE SHAPED CONFORMABLY TO SAID SURFACE AREA DISPOSED IN THE CLOSE PROXIMITY THERETO AND DIVERGING THEREFROM TO DEFINE AN INCLUDED ANGLE THEREWITH ON THE ORDER OF 3* WITH THE APEX THEREOF WITHIN THE CONFINES OF SAID SURFACE AREA, DRIVING SAID SHEET ELEMENT AT A VELOCITY WITHIN THE APPROXIMATE RANGE OF 25 TO 35 MM./$ SECONDS PROGRESSIVELY IN A DIRECTION AWAY FROM SAID APEX ALONG THE FACE THEREOF OPPOSITE TO SAID SHAPED SURFACE TO PROGRESSIVELY COLLIDE SAID SHEET ELEMENT AGAINST SAID BODY WITH EXTREME SHOCK AT A COLLISION POINT VELOCITY WITHIN THE RANGE OF SUBSTANTIALLY 3.35-4.0 MM./$ SECONDS AND THEREBY EXPRESS THE AIR BETWEEN THEM AND GENERATE A SURFACE MELTING HEAT TO RIPPLY THE INTERFACES OF THE ELEMENTS IN BONDED MOLECULARLY DISPLACED AND DIFFUSED RELATIONSHIP WITH THE METALIZED MOLYBDENUM OVER A BONDING INTERFACE AREA THAN THE INITIAL AREA DEFINED BY THE ELEMENTS WITHIN SAID INCLUDED ANGLE WHEREBY THE METALS ARE BONDED UNDER COMPACTING PRESSURE ABOVE THE DYNAMIC YIELD STRESS OF THE BONDED MATERIALS WHICH IS NOT RELIEVED OVER A RANGE OF TEMPERATURES FROM -60*F. TO +550*F.