JPH0547304B2 - - Google Patents

Description

[Detailed description of the invention]

〓Field of Industrial Application〓 The present invention relates to a piston for internal combustion engines and a method for manufacturing the same, and particularly to a piston for internal combustion engines in which at least a portion thereof is reinforced by composite with a porous molded body of an inorganic fiber aggregate or fine powder particles. This invention relates to a piston and its manufacturing method. <Prior Art> In recent years, the thermal and mechanical loads applied to pistons for internal combustion engines, particularly pistons made of aluminum alloy, have been gradually increasing. Therefore, some kind of material countermeasure against such high loads is required. Pressure forging technology called molten metal forging or fiber composite reinforcement (so-called FRM) technology that applies this technology corresponds to this. Attempts are being made to For example, as shown in Fig. 1, the top ring groove 2 of the piston 1 is composited with an inorganic fiber aggregate or a porous molded body 4, thereby improving the wear resistance of the top ring groove 2 in particular. I try to let them do it. Alternatively, as shown in FIG. 2, an inorganic fiber aggregate or a porous metal molded body 4 may be composited onto the top surface 3 of the piston 1, thereby improving the heat cracking resistance of the top surface 3. ing. In this way, when the inorganic fiber aggregate or the porous molded body 4 is locally combined with the piston 1,
By applying pressure casting, an inorganic fiber aggregate 4 made of, for example, ceramic fiber is placed in the relevant part of the mold, and the molten casting alloy injected into the mold is pressurized to form the inorganic fiber aggregate. Infiltrate the void,
A composite material is formed using this alloy as a base material. Pistons manufactured using such conventional composite reinforcement methods are limited to partial composite reinforcement. When this piston is partially composited, it is necessary to create a porous molded body that matches the shape of the required composite part, fix this molded body to a designated part of the mold, and place it inside the mold. Pressurize the molten metal while injecting it, and form the piston by pressure casting. At this time, the molten metal of the casting alloy is simultaneously infiltrated into the voids of the molded body, and the molded body is combined with the molded body at a required portion of the piston to form a composite material. In such conventional fiber-reinforced pistons, it is very difficult to make the entire piston composite. This is because it is difficult to produce a porous molded body that conforms to the overall shape of the piston, and even if it could be produced, it would be very costly. Furthermore, since such conventional pistons are pressure cast products, the cooling rate during solidification is faster than that of normal pressure cast products, and a corresponding increase in material strength can be expected to some extent. However, this increase in strength is only within the range of cast products, and the strength and toughness that can be achieved with forged materials cannot be expected. Therefore, the conventional piston of this type has the drawback that even if it can be partially reinforced with fibers, sufficient strength and toughness cannot be obtained. 〓Object of the invention〓 The present invention has been made in view of the above-mentioned problems, and it is possible to obtain high strength and toughness, and also to provide not only local composite reinforcement but also composite reinforcement of the whole as necessary. An object of the present invention is to provide a piston for an internal combustion engine and a method for manufacturing the same. 〓Structure and operation of the invention〓 According to the present invention, high strength and toughness are obtained by forming the entire piston by solid forging, and at least a portion or the entire piston is made of inorganic material such as ceramic fiber. The present invention relates to a piston for an internal combustion engine that is compositely reinforced with a porous molded body of fiber aggregates or fine powder particles, and a method for manufacturing the same, which preferably incorporates a method for manufacturing conventional composite materials. We are trying to adopt a method of gas pressurization that is not seen in Japan. In particular, the first feature of the present invention is that the entire piston or only the necessary parts are compositely reinforced with an inorganic fiber aggregate or a porous molded body of fine powder particles, and are formed by plastic working by forging. This is something that is becoming more and more common. The part of the piston that requires the most strength or toughness is the pin boss for forming the pin hole, and the strength and toughness of a cast material may not be sufficient and that of a forged material may be required. According to the invention, therefore:
It is also possible to provide a piston in which the pin boss portion has high strength and toughness. The following table shows the tensile strength and elongation of aluminum alloys made of AC8A material as a base material, as-cast and forged, in single and composite materials. As is clear from this table, forging can provide greater strength and toughness than casting even for the same material, and it is clear that composite reinforcement with fibers can further improve strength. . In this table, in the case of reinforcement with inorganic fibers, 15% SiC is composited.

[Table] A second feature of the present invention is that the composite material, which is wholly or partially composited, is formed in a billet before forging. There are screwing, shrink fitting, and other methods for making only the lower part of the piston, including the pin boss, a forged material, but these use a two-part joining method, and cutting, grinding, etc. It has the disadvantage that it requires machining. Forging composite materials is more difficult than ordinary wrought materials, and especially in the case of partially composite materials, the hardness and softness of the plastic working object is uneven, so there is a problem of not knowing where the composite reinforced part will be located in the final product. This will be accompanied by However, this problem can be solved by selecting the plastic working method for the dummy billet (preliminary plastic working body) so that it can be correctly placed at a predetermined position. The third feature of the present invention is that, in addition to the plunger pressurization method for producing billet composite materials before forging,
Preferably, a pressurization method using gas is proposed. In the case of plunger pressurization, the pressurizing force is
Although it depends on the large value of 500Kgf/cm2 or ^more , the plunger is made of metal and has high thermal conductivity even if a heat insulating film is formed, so the molten metal that comes into contact with the plunger is partially In order to overcome the solidification and apply further pressure to the molten metal, even higher pressure is required. On the other hand, in the case of gas pressurization, since gas is a good heat insulating material, the molten metal can be hydrostatically pressurized even at a pressure of about 10 kgf/cm ² without cooling the molten metal in the mold. It becomes possible. Figures 3 to 5 show cases in which the same volume of molten metal is pressurized by a large plunger 6 (Figure 3), a small plunger 7 (Figure 4), and a gas supplied through a pipe 8. This figure illustrates the early solidification inside the mold 9 when it is pressed (FIG. 5). When applying pressure using the plungers 6 and 7, the inner surface of the mold 9 and the plungers 6 and 7
Solidification starts from the bottom surface of the cap-shaped early solidification area 1
0 will be formed. Therefore, it is necessary to apply a pressure greater than that which crushes the early solidified portion 10. On the other hand, in the case of gas pressurization, since gas is a poor conductor of heat, the mold 9
Only early coagulation was observed on the inner surface of the
A small pressing force will be sufficient. In FIGS. 3 to 5, disposed below the mold 9 is the inorganic fiber aggregate 2 into which the molten metal 11 enters the void and is composited. 〓Example〓 The present invention will be explained below with reference to the illustrated example. Embodiment 1 FIG. 6 shows an apparatus for manufacturing a billet for a piston for an internal combustion engine according to this embodiment, and this billet manufacturing apparatus is equipped with a base 15. A tubular mold 16 is disposed upright on the base 15. The upper and lower parts of this mold 16 are an upper closed mold 17 and a lower closed mold 1, respectively.
8, and the lower sealing mold 18 is pressed by a lower pressing mold 19. Further, a pipe 21 to which a valve 20 is connected is attached to the side surface of the tubular mold 16 so as to communicate with the pipe 21 . The other end of this pipe 21 is connected to a pressurized gas tank 22. The inlet on the opposite side of the tank 22 is connected via a pipe 23 and a valve 24 to a pressurized gas supply source (not shown). Next, the operation of making a billet using the above-mentioned device will be explained. First, the lower end of this tubular mold 16 is closed by the lower sealing mold 18, and
This lower sealing mold 18 is pressed down by a lower pressing mold 19. Then, a ceramic porous body 25 is placed inside the tubular mold 16 and below it. In this state, a predetermined amount of a molten metal 26 of a casting alloy, for example, an aluminum alloy, is poured into the tubular mold 16 from the upper opening. After this, the upper opening of the tubular mold 16 is closed by the upper sealing mold 17. Gas pressure is applied to the inside of the tubular mold 16 whose upper portion is closed while the ceramic porous body 25 and the molten metal 26 are contained therein. This pressurization can be applied to the tank 22 by opening the valve 20.
The pressurized gas inside is passed through the pipe 21 to the tubular mold 16.
It is done by leading within. As a result, a predetermined pressure is applied to the molten metal in the mold 16, and the molten metal 26 penetrates into the voids of the ceramic porous body 25, whereby the porous body 25 is composited. When the pressurization is finished, the valve 20 is closed, and after the molten metal 26 has solidified, the upper closed mold 17 is first released. Next, the lower presser die 19 is lowered to remove the lower sealing die 18, and then the lower presser die 19 is raised. The composite billet 27 (see FIG. 7) is then pushed upward. Although dry air is sufficient as the gas used for the above pressurization, it is preferable to use a pressure of about 10 Kgf/cm ² . FIG. 7 shows a composite billet 27 produced in this way, which billet 27 is partially reinforced by a ceramic porous body 25. That is, the portion indicated by dotted diagonal lines constitutes a composite portion. And billet 2 like this
By forming by forging using 7,
A piston 28 as shown in FIG. 8 is obtained. The top ring groove 29 of the piston 28 is compositely reinforced by the ceramic porous body 25. As shown in FIG. 9, the material constituting the piston 28 is provided with a piston boss portion 31 for forming a pin hole 30 therein. Therefore, in the direction perpendicular to the height direction of the piston 28,
As shown in FIG. 10, in the X direction and Y direction,
Their wall thickness and shape are different. Therefore, such a piston 28 is formed into a billet 27 as shown in FIG.
Even if the composite material 25 is directly forged, the molding itself is difficult, and the position of the composite material 25 also changes. Therefore, in this embodiment, in order to avoid such defects, by plastic working into the shape of an intermediate dummy billet and forging through this intermediate dummy billet, there is no slight deformation as shown in Fig. 8. In this case, a piston 28 is obtained in which the composite material 25 is applied almost at a predetermined position. Embodiment 2 Next, a second embodiment of the present invention will be described with reference to FIGS. 11 to 1.
This will be explained with reference to 3 figures. In this example,
Parts corresponding to those in the first embodiment are given the same reference numerals, and descriptions of parts having the same configuration will be omitted. The features of this second embodiment are:
As shown in FIG. 11, a ceramic porous body 25 having a substantially disc shape is placed at the bottom of the tubular mold 16.
A billet 27 as shown in FIG. 12 is formed by pressure casting. This billet 27 is forged through an intermediate dummy billet in the same manner as in the first embodiment, thereby obtaining a piston 28 as shown in FIG. 13. This piston 28
is the top surface 3 instead of the top spring groove part.
The ceramic porous body 25 is compositely reinforced in the portion 2, thereby improving the heat cracking resistance. Embodiment 3 Next, a third embodiment of the present invention will be described with reference to FIGS. 14 to 1.
To explain with reference to Figure 6, in this embodiment the piston 2
As shown in FIG. 14, a ceramic porous body 25 having dimensions slightly higher than the height of the billet is placed in the tubular mold 16. The molten metal 26 is poured into the mold 16, and the valve 20 is opened to supply air in the tank 22 into the mold 26 to pressurize it. In this way, a billet 27 as shown in FIG. 15 is obtained. Since this billet 27 has ceramic fibers distributed over its entire length, by forging such a billet 27, a piston 28 as shown in FIG. 16 can be obtained, and its top ring groove 29,
The top surface 32 and the piston boss portion 31 in which the pin hole 30 is formed are compositely reinforced with ceramic fibers. The present invention has been described above using three embodiments,
The present invention is not limited to these embodiments, and various modifications can be made based on the technical idea of the present invention. For example, in all of the above three embodiments, air is used to pressurize when casting a billet, but it is not necessarily necessary to use air to pressurize, but instead pressurize is performed using a plunger. You can do it like this. The present invention is also applicable to a piston having a combustion chamber formed of a concave portion on its top surface, and is also applicable to a piston whose opening edge is compositely reinforced with ceramic porous material. 〓Effects of the Invention〓 As described above, the present invention uses a billet, which is formed by compositely casting at least a portion of an inorganic fiber aggregate or a porous molded body of fine powder particles, and is formed by solid forging. The present invention relates to a piston for an internal combustion engine and a method for manufacturing the same. Therefore, according to the present invention, it is possible to provide a piston for internal combustion engines that not only can withstand high thermal or mechanical loads, but also has high strength and toughness due to solid forging, which cannot be expected from conventional casting. It becomes possible to provide Moreover, because the inorganic fiber aggregate or the porous molded body of microfluid powder is composited and bonded into the base material, the bonding strength of the composite part is high, and the composite part separates from other parts and peels off. will not occur.

[Brief explanation of the drawing]

Figure 1 is a vertical cross-sectional view showing a conventional piston, Figure 2 is a longitudinal sectional view showing a conventional piston.
Figure 3 is a vertical cross-sectional view of another conventional piston, Figure 3 is a vertical cross-sectional view of a billet manufacturing apparatus using a large plunger, Figure 4 is a vertical cross-sectional view of a billet manufacturing apparatus using a small plunger, and Figure 5 is a vertical cross-sectional view of a billet manufacturing apparatus using a small plunger. The figure is a longitudinal cross-sectional view of a billet manufacturing apparatus that performs pressurization with gas, FIG. 6 is a vertical cross-sectional view showing the state of billet manufacturing according to the first embodiment of the present invention, and FIG. FIG. 8 is a vertical cross-sectional view of a piston forged from this billet, FIG. 9 is a vertical cross-sectional view showing a general piston, and FIG. 10 is a cross-sectional view taken from X to X in FIG. 11 is a longitudinal sectional view showing the state of manufacture of the billet according to the second embodiment of the present invention, FIG. 12 is a longitudinal sectional view of the billet thus obtained, and FIG. FIG. 14 is a longitudinal cross-sectional view of a piston obtained by forging a billet, FIG. 14 is a longitudinal cross-sectional view showing the state of manufacturing a billet according to the third embodiment of the present invention, and FIG. 15 is a longitudinal cross-sectional view of a piston obtained by forging a billet. FIG. 16 is a longitudinal sectional view of a piston obtained by forging this billet. The names of the main parts in the drawings are as follows. 16...Tubular mold, 17...Top closed mold, 18
... Bottom sealed type, 20 ... Valve, 22 ... Pressurized gas tank, 25 ... Ceramic porous body, 26 ...
... Molten aluminum alloy, 27... Billet,
28... Piston, 29... Top spring groove, 3
1...Pin boss part, 32...Top surface.

Claims (1)

[Scope of Claims] 1. A billet is cast in a state in which a porous molded body made of an inorganic fiber aggregate or an inorganic fine powder is composited with at least a portion of a base material, and the billet is formed by solid forging. A piston for an internal combustion engine characterized by: 2. Claim 1, characterized in that the porous molded body made of the inorganic fiber aggregate or inorganic fine powder particles is locally composited in the ring groove portion, the top surface, or the pin boss portion. Pistons for internal combustion engines as described in . 3. The piston for an internal combustion engine according to claim 1, wherein the porous molded body made of the inorganic fiber aggregate or the inorganic fine powder is composited over the entire base material. 4 A porous molded body made of an inorganic fiber aggregate or inorganic fine powder having a predetermined shape is placed at a predetermined position in a mold, a billet is cast, and the inorganic fiber aggregate or inorganic fine powder is placed in the billet. A method for manufacturing a piston for an internal combustion engine, comprising the steps of: combining a porous molded body made of granules; and forming a piston by solid forging the billet. 5. The method of manufacturing a piston for an internal combustion engine according to claim 4, wherein pressure is applied to the molten metal during casting of the billet. 6. The method of manufacturing a piston for an internal combustion engine according to claim 4, characterized in that gas is used as a medium for applying pressure to the molten metal.