Method for manufacturing ceramic reinforced piston

A method for manufacturing a ceramic reinforced piston and a molding machine therefor. A composite product composed of a cast product made of aluminum alloy or the like and shaped inorganic short fiber, particles or the like is obtained so that mechanical strength, wear resistance, heat resistance and the like of such composite product can be increased. Furthermore, mass production of such composite products becomes possible. A suitable amount of ceramic particles or a shaped inorganic short fiber is introduced in a casting mold, a molten metal such as an aluminum alloy and the like is then poured in the casting mold, and an upper punch is suitably pushed down on the molten metal to pressurize such molten metal in the casting mold. Push rams are additionally introduced laterally into the mold before or during the pouring of the molten metal to compensate for any shortage of molten metal and assure the metal penetrates the particles of fiber. The metal solidifies under pressure. The concave portions produced by the push rams correspond to the location of the piston pin cavity, and thus do not adversely affect the piston.

TECHNICAL FIELD 
The present invention relates to a method for manufacturing a ceramic 
reinforced piston and a casting machine therefor by which a composite 
product composed of a cast product made of an aluminum alloy or the like 
and shaped inorganic short fiber, particles or the like is obtained so 
that mechanical strength, wear resistance, heat resistance and the like of 
such composite product can be increased, and mass production thereof 
becomes possible. 
BACKGROUND OF THE INVENTION 
Heretofore, there are disclosed the techniques with respect to a method for 
manufacturing a ceramic reinforced piston as enumerated hereinbelow. 
In Japanese Patent Laid-open No. 128832/1977, there is described a method 
for manufacturing a cast product exhibiting thermal insulation properties 
in which a composite product is prepared from at least a part of a shaped 
inorganic fiber and an aluminum or magnesium alloy cast product in 
accordance with either a high pressure solidification casting method or a 
combined use of a high pressure casting method and a gravity casting 
method. Furthermore, in Japanese Patent Laid-open No. 93560/1983, there is 
disclosed a method for manufacturing a fiber composite alloy metallic 
material in which a fiber product is shaped so as to conform to a site 
upon which reinforcement is desired as well as a site which is to be cut 
out after its working, the resulting shaped fiber product is set at a 
prescribed position in a metallic mold, and then casting is effected. 
Moreover, there is described in Japanese Patent Application No. 
22457/1987, proposed by the present inventor, a method for manufacturing a 
fiber reinforced composite product in which a number of cohered balls of 
an inorganic short fiber material which have been previously prepared are 
combined and formed into a predetermined shape by the use of a binder, the 
resulting formed material is set at a predetermined position in a casting 
mold, and a molten metal is poured thereinto to cast the product. In 
Japanese Patent Application No. 270032/1987, also proposed by the present 
inventor, there is disclosed a method for manufacturing a fiber reinforced 
composite casting product in which a shaped product having a predetermined 
shape is obtained from an inorganic short fiber material which has been 
previously deposited in the horizontal direction by the use of a binder, 
the resulting shaped product is set at a prescribed position in a casting 
mold, and then a molten metal such as an aluminum alloy or the like is 
poured in said casting mold thereby effecting casting. 
However, the above described conventional manufacturing methods and the 
machines therefor relate to, as shown in FIGS. 1 and 3, such a 
manufacturing method wherein ceramic particles or a shaped inorganic short 
fiber product (13) has been previously placed at a prescribed position in 
a casting mold defined by a heated mold main body (2) and a heated 
knock-out die (4), a molten metal (14) is poured in the interior of the 
casting mold, whereby the molten metal (14) such as aluminum alloy or the 
like is caused to penetrate into the shaped product (13) while applying a 
pressure by means of an upper punch (3), and the molten metal is 
solidified to partially reinforce only the crown surface of a piston. 
According to this method, however, variation in a thickness A--A of the 
crown surface arises dependent upon slight scattering of the molten metal 
(14) poured. When the amount of the molten metal poured is short, pressure 
of the molten metal (14) is reduced so that internal defects, such as 
incomplete penetration of the molten metal (14) into the shaped product 
(13) placed in the crown surface portion, appearance of blowholes inside 
the resulting product and the like, easily occur. In these circumstances, 
such conventional methods as described above have been practiced in such a 
manner that, for the sake of avoiding the internal defects as described 
above, a somewhat larger amount of the molten metal is used to form a 
thicker crown thickness A--A than the prescribed thickness, and thereafter 
the resulting crown thickness is reduced by means of machine work to 
finally obtain a predetermined thickness of the crown surface. Such 
cutting of a crown surface in these conventional methods tends to cut out 
a part of the shaped product (13) which has been already reinforced, so 
that mechanical strength, wear resistance, heat resistance and the like of 
such crown surface becomes worse than expected. In addition, since the 
crown surface has been reinforced with short fiber ceramics or the like, 
machinability of the resulting product is very poor and hence, wear and 
tear of cutting tools are increased. 
Accordingly, the present invention has been made to solve the problems in 
these conventional methods. In this connection, in the present invention 
it is noticed that a piston generally has a piston pin cavity into which 
the piston pin is to be inserted and such piston pin cavity is defined in 
the machining process after the casting process, and hence there is no 
problem if a portion of a piston corresponding to the piston pin cavity 
thereof presents a concave form, so that such concave form is utilized for 
absorbing scattering of molten metal poured. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide a method for 
manufacturing a ceramic reinforced piston and a molding machine therefor 
in which an amount pushed out by push rams forms a cavity for a piston, 
scattering of molten metal poured is absorbed by utilizing a condition of 
such cavity so that a crown surface of the piston is formed with a 
constant prescribed thickness A--A, whereby no machining is required for 
the crown surface and mass production of ceramic reinforced pistons become 
possible. 
In accordance with the method for manufacturing a ceramic reinforced piston 
and a molding machine therefor which realizes the above described object, 
either ceramic particles or a shaped inorganic short fiber, which has been 
previously heated is suitably introduced into or placed in a prescribed 
position in a heated casting mold, a molten metal such as aluminum alloy 
and the like is poured in the casting mold to keep an upper punch at a 
prescribed position, and furthermore push rams which are freely inserted 
in and out of a mold main body at the position corresponding to a piston 
pin cavity are suitably pushed out to solidify the molten metal in the 
casting mold while pressurizing the molten metal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In order to more fully explain the present invention, the invention will be 
described with reference to the accompanying drawings. 
First the molding machine according to the present invention will be 
described. In the drawing, reference numeral (1) designates a die holder 
for forging molten metal, and (2) designates a block-like mold main body. 
Reference numeral (3) designates an upper punch disposed above the mold 
main body (2) and the upper punch (3) is movable up and down by means of a 
press machine (not shown). Reference numeral (4) designates a disc-shaped 
knock-out die disposed internally at the lower part of the mold main body 
(2). Reference numeral (5) designates a knock-out device having a suitable 
mechanism (not shown) provided with a knock-out pin (5a) movable up and 
down and disposed below the knock-out die. (6) designates a pair of push 
rams each corresponding to the position of a piston pin cavity and each 
being freely movable in and out of the interior of the mold main body (2) 
in the lateral direction thereof. (7) designates a pair of pedestals 
installed vertically on and fixed to the die holder (1) to fix the same. 
The pedestals are suitably spaced from the mold main body (2), and these 
pedestals (7) are used for installing the push rams (6) on the mold main 
body (2). (8) designates an insulating material applied on the surface of 
the pedestal (7) on the side facing the mold main body (2). (9) designates 
a receiving plate secured to the upper part of the mold main body (2), and 
the receiving plate (9) functions as a stopper for the upper punch (3). 
(10) designates a press machine for the push rams (6). (11a) designates an 
actuation adjusting means and this means (11a) comprises an actuation 
adjusting means main body (11a) secured to the upper part of the pedestal 
(7), a connecting rod (11b) connecting said actuation adjusting means main 
body (11a) with a push ram (6), and a connecting line (11c) connecting 
said actuation adjusting means main body (11a) with the press machine 
(10). Reference numeral (12) designates a fastening member composed of a 
bolt or the like, and (13) designates a shaped fiber for reinforcing a 
piston. 
Next, the manufacturing method according to the present invention will be 
described. First, either alumina particles consisting of 100% 
.alpha.-alumina and having an average particle diameter of 63 .mu.m which 
has been heated to 800.degree. C. in a crucible made of an inorganic 
material, or the shaped fiber (13), having a thickness of 10 mm and heated 
to 700.degree. C., which has been shaped from an alumina short fiber 
material having an average diameter of 3 .mu.m and an average length of 
0.7 mm, is thrown into or set in a casting mold defined between the mold 
main body (2) and the knock-out die (4), which has been previously heated 
to 300.degree. C. Thereafter, a molten JIS-AC8A alloy (14) is poured into 
the casting mold at 750.degree. C. in an amount somewhat smaller than a 
conventional amount. In this case, it is desirable that a temperature to 
which said particles or shaped inorganic short fiber (13) is to be heated 
is higher than the melting point of the aluminum alloy, but 800.degree. C. 
or less. 
Immediately after pouring the molten metal, the upper punch (3) is lowered 
until it abuts against the receiving plate (9). At the same time of 
stopping the upper punch (3), the pair of push rams are pushed out from 
the lateral direction of the mold main body (2) corresponding to the 
position of the piston pin cavity inside towards the molten metal (14). In 
this case, a second applied pressure of the push rams (6) is set somewhat 
smaller than that of a first applied pressure of the upper punch (3). 
Thus, the pressure of the molten metal (14) in the casting mold is 
elevated by means of the push rams (6) so that the push rams (6) are 
pushed out until the pressure reaches a prescribed pressure. As a result, 
the molten metal (14) permeates sufficiently into the reinforced portion 
of the particles or shaped fiber (13). An inserted length of the push rams 
(6) forms a concave portion of the piston pin cavity and hence, the piston 
is cast in the best condition, where scattering of the molten metal (14) 
poured is absorbed dependent upon a depth of the concave portion. The 
applied pressure in this case differs depending upon whether the particles 
are used or the shaped fiber (13) is employed. In this connection, the 
applied pressures of the upper punch (3) and of the push rams (6) are 950 
kg/cm.sup.2 and 800 kg/cm.sup.2, respectively, in the case of particles, 
whilst such applied pressures of the upper punch (3) and that of the push 
rams (6) are 1100 kg/cm.sup.2 and 840 kg/cm.sup.2, respectively, when 
using the shaped fiber (13). The timing for pushing out the push rams (6) 
may be before or at the same time of pouring such molten metal. In such a 
case, since the applied pressure of the push rams (6) is small with 
respect to the upper punch (3), the push rams (6) which have been 
projected into the molten metal are returned automatically towards the 
direction of the mold main body (2) by means of the pressure of the molten 
metal pressurized by the upper punch (3) until the pressure of the molten 
metal reaches a prescribed value. 
In these circumstances, the upper punch (3) and the push rams (6) continue 
the pressurization until solidification of the molten metal (14) is 
completed. After solidification, the upper punch (3) is returned to the 
original position above the mold main body (2) and further, the push rams 
(6) are also restored to the former state. In this case, the connecting 
rod (11b) secured to the push rams (6) is also returned so that one end of 
the connecting rod (11b) pushes the actuation adjusting means main body 
(11a), whereby the driving of the press machine (10) is stopped. The 
extreme end of a push ram (6) is in a state somewhat retracted from the 
inner surface of the mold main body (2). Thereafter, the knock-out pin 
(5a) of the knock-out means (5) is pushed up, and the knock-out die (4) is 
also pushed up in response thereto whereby a cast piston is taken out. 
Next, a ceramic reinforced piston manufactured in accordance with the 
manufacturing method and machine therefor according to the present 
invention will be compared to that manufactured in accordance with a 
conventional manufacturing method by means of cutting work with respect of 
heat-resisting heat-fatigue. 
EXAMPLE OF HEAT-FATIGUE RESISTANCE TEST 
The ceramic reinforced piston according to the manufacturing method of the 
present invention was compared with that according to a conventional 
manufacturing method as per the following manner. Heat-fatigue resistance 
test was repeated in accordance with the testing method shown in FIG. 4 as 
one cycle (=60 sec.) in the heat-fatigue resistance test process in which 
the test was continued until cracks appeared initially on the crown 
surface of a ceramic reinforced piston tested, and the results of the test 
are shown by the number of cycles in the following Table. 
It is to be noted that a reinforced piston according to a conventional 
manufacturing method used in the test has been machined such that a 
thickness A--A of the crown surface of the piston was reduced by 2 mm with 
cutting in order to obtain a prescribed dimension of the piston. 
______________________________________ 
Experimental Results 
Piston of 
Items the Invention 
Piston of Prior Art 
______________________________________ 
Distance between A-A 
15 mm 15 mm 
Thickness of Composite 
10 mm 8 mm 
Material Layer 
Number of Cycles Until 
6583 4542 
Cracks Appear on Crown 
Surface of Piston 
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Since the reinforced piston according to the manufacturing method of the 
present invention can be formed with a predetermined thickness A--A of the 
crown surface, in other words, it requires no cutting work, the 
heat-resisting fatigue strength thereof can be remarkably improved as much 
as 1.5 times in comparison with that of a conventional one, and in 
addition a cast product with good precision could be manufactured. 
As described above, according to the method for manufacturing a ceramic 
reinforced piston and the molding machine therefor of the present 
invention, scattering of the molten metal (14) poured is absorbed, and 
furthermore internal defects in a casting mold used can be substantially 
eliminated by solidifying the molten metal (14) while pressurizing the 
same, so that a thickness A--A of the crown surface of the ceramic 
reinforced piston can be formed with high precision because no machining 
process is necessary in this case. Accordingly, mechanical strength, wear 
resistance, heat-resistance and the like of such piston are improved, and 
in addition, mass production of the ceramic reinforced piston becomes 
possible. The present invention is also suitable for manufacturing an 
ordinary metallic piston which has not been reinforced with ceramics and 
the like. 
Although the particular embodiments of the invention have been shown and 
described, it will occur to those with ordinary skill in the art that 
other modifications and embodiments exist as will fall within the true 
spirit and scope of the invention as set forth in the appending claims.