Die-casting method and die-casting apparatus

A method of die-casting a die-cast article having at least one of an inner circumferential surface and an outer circumferential surface, whose cross sectional shape is a circle, the die-casting article being formed with a die-casting apparatus having a mold cavity therein and a molding portion for forming one of the inner and outer circumferential surfaces of the die-cast article, the method comprising the steps of introducing a molten metal into the mold cavity; and separating the die-cast article and the molding portion from each other while the die-cast article and the molding portion are rotated relative to each other, after the molten metal has solidified into the die-cast article. A die-casting apparatus for practicing the method is also disclosed.

It is therefore an object of the present invention to provide a method of die- casting a die- cast article having at least one of an inner and outer circumferential surfaces, whose cross sectional shape is a circle, the method permitting reduction in the angle of inclination provided on the inner or outer circumferential surface. It is another object of the invention to provide a die- casting apparatus suitably used for the method.

This object may be achieved according to any one of the following modes of the present invention, each of which is numbered like the appended claims and depends from the other mode or modes, where appropriate, to indicate and clarify possible combinations of elements or technical features of the present invention, for easier understanding of the invention. It is to be understood that the present invention is not limited to the technical features or any combinations thereof which will be described for illustrative purpose only. It is to be further understood that a plurality of elements or features included in any one of the following modes of the invention are not necessarily provided all together, and that the invention may be embodied without some of the elements or features described with respect to the same mode.

(1) A method of die- casting a die- cast having at least one of an inner circumferential surface and an outer circumferential surface, whose cross sectional shape is a circle, the die- casting article being formed with a die- casting apparatus having a mold cavity therein and a molding portion for forming one of the inner and outer circumferential surfaces of the die- cast article, the method comprising the steps of: introducing a molten metal into the mold cavity; and separating the die- cast article and the molding portion from each other while the die- cast article and the molding portion are rotated relative to each other, after the molten metal has solidified into the die- cast article.

If a die- cast article to be produced needs to have an inner or an outer circumferential surface, a die- casting apparatus is arranged to have a molding portion which partially defines a mold cavity and which has an outer or an inner circumferential surface for forming the corresponding inner or outer circumferential surface of the die- cast article. The die- cast article may have one of, or both of, the inner and outer circumferential surfaces whose transverse cross sectional shape is a circle. Even if the die- cast article has both of the inner and outer circumferential surfaces, it is not essential that both of the inner and outer circumferential surfaces are formed according to the principle of the present invention. Similarly, where the die- cast article has a plurality of inner or outer circumferential surfaces, all of the plurality of the inner or outer circumferential surfaces need not be formed according to the principle of the present invention, but at least one of the plurality of the inner or outer circumferential surfaces may be formed according to the present invention.

The molding portion of the die- casting apparatus which forms one of the inner and outer circumferential surfaces of the die- cast article is removed or separated from the corresponding one of the outer and inner circumferential surfaces of the die- cast article, after the molten metal has solidified into the die- cast article. In this case, the die- cast article and the molding portion can be more easily removed or separated from each other by a combination of a relative axial movement between the molding portion and the die- cast article, and a relative rotation therebetween, than an arrangement wherein the die- cast article and the molding portion are removed or separated from each other simply by only the relative axial movement. Accordingly, even where the angle of inclination of the inner or outer circumferential surface of the die- cast article is made smaller than that in a conventional arrangement, the die- cast article can be easily removed from the molding portion. Depending upon various conditions such as a ratio of the diameter of the inner or outer circumferential surface to its axial length or a relationship between the thermal expansion coefficients of the portion of the die- cast article having the inner or outer circumferential surface, and the molding portion of the die- cast apparatus, the draft to be provided on the molding portion of the die- cast apparatus can be eliminated. In this respect, the principle of the present invention does not necessarily exclude the technique disclosed in the publication described above, but permits the disclosed technique to be used in combination, for thereby increasing a degree of freedom in selecting the material for the molding portion of the die- casting apparatus which forms the inner and outer circumferential surface of the die- cast article.

In the present method wherein the angle of inclination of the inner or outer circumferential surface of the die- cast article can be minimized, it is possible to reduce the required amount of stock removal by a cutting operation conducted on the inner or outer circumferential surface of the die- cast article after the die-casting process, for thereby improving the yield and reducing the cost of the cutting operation. Alternatively, the inner or outer circumferential surface of the die- cast article can be finished only by a grinding operation without a cutting operation. Even the grinding operation can be eliminated. Further, it is possible to totally eliminate any machining operation. Where the machining operation is totally eliminated, the cost of manufacture of the die- cast article can be effectively minimized, and the die- cast article exhibits improved durability and wear resistance owing to the hard surface layer so-called ¡°chilled layer¡± which remains uncut on the superficial portion (i.e. the inner and outer circumferential surface) of the die- cast article. As is apparent from the description given above, the present method is applicable to an arrangement wherein the inner or outer circumferential surface of the die- cast article to be produced needs to be a straight cylindrical surface having a constant diameter over a suitable axial length. The present method is also applicable to an arrangement wherein the inner or outer circumferential surface has an angle of inclination. In the latter arrangement, too, the reduction or elimination of the angle of inclination on the inner or outer circumferential surface of the die- cast article is effective to reduce a weight of a final product obtained from the die- cast article and improve the yield in the die- casting process.

(2) A method according to the above mode (1), wherein the die- cast article has a cylindrical hole, the molding portion consisting of a cylindrical portion which forms the cylindrical hole, the cylindrical portion being rotated relative to the die- cast article when the die- cast article and the cylindrical portion are separated from each other.

While the present method can reduce or eliminate the angle of inclination on both of the inner and outer circumferential surfaces of the die- cast article, the present method advantageously reduces or eliminates the angle of inclination on the inner circumferential surface since it is rather easy to arrange a slide core to be not only axially movable but also rotatable, which slide core is generally used for forming the inner circumferential surface and which is described in the following mode (3).

(3) A method according to the above mode (2), wherein the die- casting apparatus includes: a mold assembly as a main body; and a slide core which has a circular shape in transverse cross section and which is rotatable and axially movable relative to the mold assembly, the slide core being rotated relative to the mold assembly when the slide core is separated from the cylindrical hole of the die- cast article, after the die- cast article has been formed in the mold cavity.

(4) A method according to any one of the above modes (1)-(3), wherein the one of the inner and outer circumferential surfaces of the die- cast article includes a plurality of axial portions which have respective different diameters and which are coaxial with one another.

For instance, the above-described valve hole formed in the housing of the compressor for accommodating the control valve therein, in general, consists of a plurality of axial portions which have respective different diameters. In this case, the die- cast article having such a cylindrical hole which have different diameters can be more easily removed from the die- casting apparatus than the die- cast article having a simple cylindrical hole which has a constant diameter over its axial length, where those cylindrical holes have the same axial length. The present mode is one of particularly advantageous arrangements according to the present invention.

(5) A method according to any one of the above modes (1)-(4), wherein the die- cast article is a housing which is used for a compressor and which has a cylindrical hole, the inner circumferential surface of the die- cast article being an inner circumferential surface of the cylindrical hole of the housing.

The cylindrical hole includes the above-described valve hole, and a recess of the housing which partially defines the crank chamber of the compressor and whose inner circumferential surface is provided for sliding contact with a rotation preventive part provided on the piston for preventing a rotary motion of the piston about its centerline.

(6) A method according to any one of the above modes (1)-(4), wherein the die- cast article is a cylinder block which is used for a compressor and which has a plurality of cylinder bores, the inner circumferential surface of the die- cast article being an inner circumferential surface of each of the cylinder bores.

(7) A die casting apparatus for die- casting a die- cast article having at least one of an inner circumferential surface and an outer circumferential surface, whose cross sectional shape is a circle, the apparatus comprising: a first molding member for forming one of the inner and outer circumferential surfaces of the die- cast article; a second molding member for forming at least one surface of the die- cast article other than the one of the inner and outer circumferential surfaces, the first molding member being rotatable and axially movable relative to the second molding member; and a drive device for moving the first and second molding members relative to each other in an axial direction thereof while rotating the first and second molding members relative to each other.

The present die- casting apparatus is suitably used for practicing the die- casting method according to the above mode (1). As described in the following DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS, a substantial part of the die- cast article is generally formed by a pair of molds such that at least one of the inner and outer circumferential surfaces having a circular transverse cross sectional shape is formed in a portion of the die- cast article. In this case, the above-indicated first molding member for forming one of the inner and outer circumferential surfaces of the die- cast article is usually made rotatable and axially movable relative to the pair of molds. Depending upon the configuration of the die- cast article, the first molding member for forming one of the inner and outer circumferential surfaces of the die- cast article is provided on a first mold which is one of the pair of molds, as an integral part of the first mold. The first molding member as the integral part of the first mold may be rotated relative to a second mold which is the other of the pair of molds, by opening and closing the first and second molds while being rotated relative to each other. In this case, the die- cast article is arranged to be held by the second mold when the two molds are separated from each other.

(8) An apparatus according to the above mode (7), wherein the drive device includes: a drive source operable to effect one of a relative rotation and a relative axial movement between the first and second molding members; and a motion-generating device operable to effect the other of the relative rotation and the relative axial movement, based on the above-indicated one of the relative rotation and the relative axial movement.

If one of the relative rotation and relative axial movement between the first and second molding members is caused by the drive source while the other of the relative rotation and axial movement is caused by the motion-generating device based on the above-indicated one of the relative rotation and relative axial movement, both of the relative rotation and axial movement can be caused by utilizing the single drive source. Accordingly, the present arrangement permits a simplified structure of the die- casting apparatus.

(9) An apparatus according to the above mode (7) or (8), wherein the first molding member consists of a cylindrical portion for forming the inner circumferential surface of the die- cast article.

(10) An apparatus according to any one of the above modes (7)-(9), wherein the first molding member includes a slide core for forming the inner circumferential surface of the die- cast article while the second molding member includes a pair of molds which are opened and closed for forming at least one surface of the die- cast article other than the inner circumferential surface.

(11) An apparatus according to the above mode (10), wherein the drive device includes:

an axial moving member which is axially movable relative to the pair of molds;

an actuator operable to axially move the axial moving member relative to the pair of molds;

a connecting device disposed between the axial moving member and the slide core and operable to connect the axial moving member and the slide core such that the axial moving member and the slide core are rotatable relative to each other and axially immovable relative to each other; and

a first engaging portion and a second engaging portion which are provided on the pair of molds and the slide core, respectively, the first and second engaging portions being held in engagement with each other and operable to cause the pair of molds and the slide core to be rotated relative to each other on the basis of an axial movement of the pair of molds and the slide core relative to each other.

The drive device according to the mode (11) is one embodiment of the drive device described in the above mode (8). The axial moving member in the above mode (11) may be axially movable relative to at least one of the pair of molds. The actuator in the above mode (11) may be operable to axially move the axial moving member relative to at least one of the pair of molds. The first and second engaging portions in the above mode (11) may be operable to cause at least one of the pair of molds and the slide core to be rotated relative to each other on the basis of an axial movement of at least one of the pair of molds and the slide core relative to each other. The axial moving member is preferably arranged not to be rotatable relative to the pair of molds. In the drive device according to the above mode (11), if a movable sleeve which forms an outer circumferential surface of a cylindrical protrusion of a die- cast article is used in place of the slide core which forms the inner circumferential surface of the cylindrical hole of the die- cast article, the movable sleeve and the cylindrical protrusion of the die- cast article can be easily separated from each other.

An apparatus according to the above mode (11), wherein the pair of molds and the slide core have respective two fitting surfaces which engage each other, and wherein the first and second engaging portions have one and the other of an engaging groove and an engaging protrusion fitted in the engaging groove, the engaging groove being formed in one of the two fitting surfaces and having an inclined portion which extends in a direction inclined with respect to an axial direction of the slide core, the engaging protrusion being formed on the other of the two fitting surfaces.

According to the mode (12), the first and second engaging portions in the above mode (11) can be easily provided. In particular, an arrangement wherein the engaging groove is formed in the fitting surface (outer circumferential surface) of the slide core and the engaging protrusion is formed on the fitting surface (inner circumferential surface) of the pair of molds permits more easier formation of the engaging groove by a machining operation than an arrangement wherein the engaging groove is formed in the fitting surface of the pair of molds and the engaging protrusion is formed on the fitting surface of the slide core.