Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2000-02-11
2001-10-16
Koehler, Robert R. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C072S031130, C072S253100, C083S055000, C188S25000B, C188S25100R, C188S255000, C188S25100R, C192S070110, C192S070300, C419S010000, C419S019000, C428S632000, C428S545000, C428S577000, C428S539500
Reexamination Certificate
active
06303236
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved method for manufacturing an aluminum-based composite plate.
2. Description of the Related Art
Automobile disk brakes have disks which are disposed parallel to tires and sandwiched on both sides by pads to thereby halt the disks by friction. The pads are housed in a caliper along with a piston for operating the pads. The pads are frictional plates each prepared by bonding a friction material (produced by thermoforming and polishing a mixture of fibers, a filler material, a friction adjuster and a binder) to a back plate (back metal). The back plates must be of high strength and lightweight because of heat and the compressive force imposed on them through the pads. Recently, it has become common to use aluminum in automobiles and motorcycles for weight reduction. In particular, use of metal-based composite materials (fiber-reinforced metal-based composite materials (FRMs) or metal matrix composites (MMCs) with aluminum as the base metal (matrix phase) has been increasing.
One known process for manufacturing products by extrusion molding of aluminum-based composite materials is “CYLINDER MANUFACTURING METHOD” disclosed in Japanese Patent Laid-Open Publication No. SHO-59-206154. The steps involved in the disclosed method are as summarized below:
(a) SiC chips are stirred and dispersed in molten aluminum, and the mixture is allowed to solidify.
(b) the solidified product is drawn while heated to about 250° C., to fabricate a pipe.
(c) the pipe is cut into a sleeve shape, fitted into a die casting metal mold and then insertion-cast with an aluminum alloy (JIS-ADC12) to thereby provide a cylinder.
The process described in Japanese Patent Laid-Open Publication No. SHO-59-206154 can be utilized to manufacture back plates used on pads of such disk brakes as described above.
However, since the composite materials manufactured by the disclosed method are obtained by combining SiC chips in molten aluminum, they have high resistance to plastic deformation so that it is not easy to work the composite materials into tubes or plates by extrusion molding. In addition, the interface between the aluminum and SIC is in a simple mechanically bonded state. Therefore, such materials exhibit low elongation and have poor workability, similarly to ordinary composite materials. Consequently, it has been a problem that these composite materials have been difficult to mold when it is attempted to obtain desired shapes by extrusion molding or the like, and that production efficiency has therefore been difficult to increase.
Furthermore, when attempts are made to cut composite materials into predetermined shapes, the composite materials manufactured by the above-described method of manufacture which include a ceramic (SiC) and hence have poor workability by machining such as cutting or polishing, thereby increasing production costs.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method for manufacturing an aluminum-based composite plate, which is easy to mold and inexpensive, as well as a back plate and a method for manufacturing the latter.
According to one aspect of the present invention, there is provided a method for manufacturing an aluminum-based composite plate, which method comprises the steps of: introducing an aluminum alloy and magnesium or a magnesium-generating source into a furnace together with a porous molded body composed of an oxide-based ceramic; reducing the oxide-based ceramic by magnesium nitride to increase wettability of the oxide-based ceramic; causing a molten aluminum alloy to infiltrate into the reduced oxide-based ceramic to provide an aluminum-based composite billet; pressing the aluminum-based composite billet into a sheet form by using an extrusion press; and punching a plate of predetermined shape out from the sheet by using a press.
Reduction of the oxide-based ceramic with magnesium nitride metallizes a porous surface and increases wettability between the oxide-based ceramic and the molten aluminum alloy. The aluminum-based composite material obtained in this manner is an aluminum-based composite material with excellent mold-ability, wherein the aluminum alloy and the reduced oxide-based ceramic as reinforcing materials are bonded with strong chemical bonds. This type of composite material facilitates extrusion molding in the subsequent press-extruding step and allows a higher extrusion ratio. As a result, it is possible to eliminate internal defects in the molded plate and achieve greater densification, thereby increasing the product quality.
Preferably, an extrusion ratio in the pressing step is set to fall in a range of 10-100, where the extrusion ratio is a value resulted from dividing a cross-sectional area of the billet before the pressing step divided by a cross-sectional area of the sheet after the pressing step. An extrusion ratio of
10
or greater will provide an aluminum-based composite material with roughly constant tensile strength and resistance. Because a larger extrusion ratio results in increased plate productivity, a larger extrusion ratio is preferred. However, if the extrusion ratio exceeds 100, the extrusion force becomes too great, thereby requiring new large-sized equipment. By setting the extrusion ratio to be within the range of 10-100, it is possible to increase the tensile strength and resistance of the aluminum-based composite material and reduce production costs by using existing equipment.
In a specific form, the composite plate may be a back plate as a constituent part of a disk brake, in which instance the pressing step may comprise placing an aluminum alloy billet closely to dies of the extrusion press, followed by positioning the aluminum-based composite billet immediately behind the aluminum alloy billet and continuously press-extruding the aluminum-based composite billet such that aluminum alloy is bonded to opposite sides or surfaces of the aluminum-based composite billet, to thereby provide a clad material of flat sheet form. The punching may comprise punching a back plate of predetermined shape out from the extruded clad material.
Upon extrusion molding, the aluminum alloy is positioned proximately to dies of the extrusion press while the aluminum-based composite billet is positioned behind the aluminum alloy. When extrusion is performed in this state, the aluminum alloy covers the aluminum-based composite material as it passes through the die. This results in continuous molding of a sheet-like form wherein the aluminum alloy is attached to both sides of the aluminum-based composite material, thereby facilitating molding of the clad material. Since both sides of the clad material are covered with an aluminum alloy of low hardness, less friction is applied to the dies during extrusion molding, thereby decreasing wear of the dies.
It is preferred that the back plate manufacturing method further comprises surface-processing the back plate to impart a desired degree of surface roughness to opposite surfaces of the back plate. In the surface-processing, the surfaces of the back plate can be ground easily and imparted with a desired level of flatness, because they are surfaced with workable aluminum alloy.
According to a second aspect of the invention, there is provided a back plate for use as a constituent part of a disk brake. The back plate is comprised of a clad material which comprises a flat sheet of aluminum-based composite material and thin plates of aluminum alloy attached to opposite sides of the flat sheet.
Preferably, the flat sheet of aluminum-based composite material comprises a porous molded body composed of oxide-based ceramics reduced by magnesium nitride, with a molten aluminum alloy infiltrated thereinto.
Since it employs an aluminum-based composite material as a core material, the back plate has increased strength and reduced thickness compared to one consisting solely of an aluminum alloy. Further, since the surfaces of the back plate are covered with an aluminum alloy of low hard
Echigo Takaharu
Kato Takashi
Nakao Yasuhiro
Shoji Hiroto
Sugaya Kunitoshi
Honda Giken Kogyo Kabushiki Kaisha
Koehler Robert R.
Merchant & Gould P.C.
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