JPH042706A - Manufacture of piston - Google Patents

Abstract

PURPOSE:To manufacture a piston having low thermal expansion, light wt. and excellent heat resistance by varying ratio of complex particles of Al and Ti-Al alloy in between Ti-Al alloy material and Al alloy material, laminating and sintering while compress-compacting. CONSTITUTION:Pre-compacting products 7, 9a, 9b, 9c, 8 are set as laminating in a sintering chamber 11 in an electric conduction sintering device 10 composed of punching electrodes 13 and mold frames 14. The pre-compacting product 7 at top part side of a piston of the Ti-Al alloy material and the pre-compacting product 8 at skirt side of the piston of the Al alloy material, are formed, respectively. The pre- compacting product 9a set between these, is composed of a first complex granule with the surface of the Al particles covered with the Ti-Al alloy powder. The pre- compacting product 9c on the upper layer of Al alloy material 8 is composed of a second complex body with the surface of the Ti-Al alloy particles covered with the Al powder and the pre-compacting product 9b at the intermediate position is made of the mixed body of these. These are conducted with electric current and sintered while compress-compacting into the piston-shape through the punching electrodes 13. By this method, the Ti-Al alloy-made piston having small coefft. of thermal expansion and excellent heat resistance, is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a piston used in an internal combustion engine.

2. Prior Art] The pistons of internal combustion engines such as diesel engines and gasoline engines are mainly formed from aluminum alloy in order to reduce their inertia.

However, this aluminum alloy piston
Since its coefficient of thermal expansion is large and its heat resistance is poor, in recent years T1-Al, which has a small coefficient of thermal expansion and excellent heat resistance, has been used.
1 alloy pistons are being researched and developed.

The coefficient of thermal expansion of the T 1-Al alloy is Bxlo-'/'C, which is about 1/3 of the coefficient of thermal expansion of aluminum, 21 x 10-'/'C. In addition, regarding heat resistance, T
The heat resistance temperature of the 1-Al alloy is about 900°C, which is about three times as high as the heat resistance of aluminum, which is 350°C.

In this way, if a piston is molded from a T1-Al alloy that has a low coefficient of thermal expansion and high heat resistance, the molded T1-Al alloy piston will be as good as a piston made of cast aluminum or a piston made of forged aluminum. The following advantages can be obtained compared to

■Since the coefficient of thermal expansion is small, the clearance between the piston and cylinder, which is formed by adjusting the thermal expansion of the piston under full load, can be reduced. Therefore, the dead volume between the top land of the piston and the cylinder is reduced and the combustion efficiency is improved. It is possible to reduce the slap sound caused by

■Due to its high heat resistance, it eliminates the need for a ring tray made of Niresist cast iron, which is required with aluminum pistons that have high high-temperature hardness. Therefore, the temperature gradient in the ring group portion becomes a natural shape, and there is no temperature concentrated portion.

■Since it has high heat resistance, it has high heat resistance strength and allows for thinner pistons. Therefore, the weight of the piston can be reduced.

[Problems to be Solved by the Invention] When manufacturing a piston made of T1-Al alloy that has such various advantages, the piston is manufactured integrally by casting or forging the T1-Al alloy. The thing is, T
The 1-Al alloy itself is expensive, and the Ti-Al alloy has poor machinability, so it is not a good idea.

Therefore, the inventor of the present invention formed the top side of the piston, which has a large heat load, from a Ti-Al alloy that has excellent heat resistance and a low coefficient of thermal expansion, and molded the skirt side of the piston, which has a small heat load, from a Ti-Al alloy that has good workability and is inexpensive. I came up with the idea of molding it with Al alloy.

However, in the piston of this composite structure, the thermal expansion coefficient (8X10-
'/'C) and the thermal expansion coefficient of Al alloy (21x 10-'/
A thermal stress gradient is generated due to the difference in thermal expansion with 'C).

Therefore, thermal stress based on this thermal stress gradient causes thermal distortion in the piston, leading to seizure of the piston.

As a related technology, Japanese Patent Application Laid-Open No. 62-156938 “
There is a method for producing functionally graded materials.

The object of the present invention, which was created in consideration of the above circumstances, is to manufacture a piston with a composite structure in which the top side of the piston is a Ti-Al alloy and the skirt side of the piston is an Al alloy. - A method for manufacturing a piston is provided in which thermal stress generated at a joint between an Al alloy and an Al alloy on the piston skirt side due to a difference in thermal expansion is alleviated.

[Means for Solving the Problems] In order to achieve the above object, the method for manufacturing a piston of the present invention includes a method of manufacturing a piston by combining a Ti-Al alloy material disposed on the piston top side and an Al alloy material disposed on the piston skirt side. Between,
A first composite granule in which the surface of the Al particle is coated with Ti-Al alloy powder and a second composite granule in which the surface of the Ti-Al alloy particle is coated with Al powder are placed on the T1-Al alloy material side. After laminating the first composite grains and the second composite grains while changing the mixing ratio so that the first composite grains are dense and the second composite grains are dense on the Al alloy material side. , these are compressed into a piston shape and sintered.

Two Actions] According to the above method, the T1-Al alloy material and the Al A mixed layer of TiAl and AlI is formed between the alloy material and the thermal stress caused by the difference in thermal expansion between the Ti-Al alloy material and the Al alloy material is alleviated by this mixed layer. Therefore, thermal distortion of the piston due to this thermal stress is reduced.

In addition, the first composite particles densely arranged on the Ti-Al alloy material side on the top side of the piston are coated with Ti-
Al! The alloy powder is quickly and soundly bonded to the Ti-Al alloy material, which is the same type of metal.

Similarly, the second composite particles densely arranged on the Al alloy material side of the piston skirt are quickly and soundly bonded to the Al alloy material, the Al powder coated on the surface of which is the same type of metal.

Therefore, the Ti-Al alloy material, the first and second composite particles, and the
Since the interfaces (joint surfaces) between the two materials are made of the same type of metal, they are quickly and firmly bonded together soundly.

[Example code] An embodiment of the present invention will be described with reference to the accompanying drawings.

As shown in FIG. 1, first composite particles 3 are manufactured by coating the surfaces of Al particles 1 of about 100 μm with Ti-A7 alloy powder 2 of about 10 μm or less. Specifically, the first composite particles 3 are produced by kneading the Al powder particles and the Ti-A7 alloy powder 2 in an electrostatic container (not shown) to form Al as core particles.
After electrostatically depositing the Ti-A7 alloy powder 2 as a child particle on the surface of the particle 1, it was heated at 2000 rpm to 8000 rpm.
The electrostatically deposited Tl was placed in a container (not shown) equipped with a rotating blade at 100 rpm and subjected to impact force by high-speed airflow for several minutes.
-Al alloy powder 2! It is obtained by firmly embedding it into 1 m of particles.

Similarly, as shown in Fig. 2, about 100 μm
T 1 - A of about 10 μm or less on the surface of the Al alloy particles 4
A second composite granule 6 coated with powder 5 is produced.

Next, as shown in FIG. 3, a piston top side pre-formed product 7 that will eventually become the top side of the piston is cast from a Ti-Al alloy material. Similarly, a piston skirt side pre-formed product 8, which will eventually become the skirt side of the piston, is cast or forged from an Al alloy material.

Between the piston top side pre-formed product 7 and the piston skirt side pre-formed product 8, a piston intermediate pre-formed product 9 in which the above-mentioned first and second composite particles 3 and 6 are appropriately laminated and sintered is arranged. do.

As shown in the figure, this piston intermediate pre-molded product 9 is made by aggregating and sintering only the first composite granules 3, and an equal amount of the first composite granules 3 and second composite granules 6. When aggregated and sintered, the glue b and the second composite particles 6 are aggregated and sintered, and these are separated from the piston top side pre-formed product 7 side to the piston skirt side pre-formed product 8. They are stacked sideways in the above order.

That is, the first composite particles 3 are densely packed on the piston top side pre-molded product 7 side, and the piston skirt side molded product 1]! I
The second composite particles 6 are densely arranged.

These preformed products 7.9a, 9b, 9c, and 8 are set in the sintering chamber 11 of the current sintering device 10 shown in FIG.
The piston 12 shown in the figure is manufactured.

To explain the electric sintering device 10 in detail, the electric sintering device 10 includes punch electrodes 13 facing each other vertically,
A formwork 14 consisting of an insulator (alumina, etc.) provided between these punch electrodes [i:1
The sintering chamber 11 is defined by the mold 3 and the mold 14 into a piston shape as shown in FIG.

In addition, a predetermined compression pressure P1 is applied to the punch electric #113 in the axial direction of the piston by a hydraulic mechanism (not shown), and a special power source in which high frequency is superimposed on direct current is connected via a switch. wired.

On the other hand, as shown in FIG. 6, the mold frame 14 is vertically divided into two parts so that a predetermined compression pressure P2 is applied in a direction perpendicular to the axial direction of the piston.

According to this energization sintering apparatus 10, the current, voltage, and pressure P1 of the punch electrode 13. By controlling the operation by changing the pressure P2 of the mold frame 14 over time, the pre-formed products 7.9a, 9b, which are superimposed and set in the sintering chamber 11.
9c and 8 are compression-molded into a piston shape, and electric discharge occurs appropriately between the first and second composite particles 3 and 6 in the pre-molded products 9a + 9b and 9c, and the fifth column is formed in a short period of several tens of columns.
The piston 12 shown in the figure is manufactured by sintering. (Electrical sintering method using so-called plasma discharge) At this time, the pre-formed product 9a adjacent to the piston top side pre-formed product 7 made of T1-Al alloy is made of Al particles 1, as shown in FIG. Since the T1-Al alloy is composed of a first composite particle 3 whose surface is coated with T1-A7 alloy powder 2, the T1-Al alloy powder 2 on the surface of the particle 3 is the same kind of metal. It is quickly and soundly connected to the piston top side pre-molded product 7 made by the manufacturer.

On the other hand, the pre-formed product 9C adjacent to the piston skirt-side pre-formed product 8 made of Al alloy is made of Ti.
- Since it is composed of the second composite particles 6 in which the surface of the Al alloy particles 4 is coated with Al powder 5, the Al alloy piston skirt side where the Al powder 5 on the surface of the particles 6 is the same kind of metal. It is quickly and soundly bonded to the pre-molded product 8.

Therefore, the preformed products 7.9a, 9b, 9c, and 8 set in a stacked manner in the sintering chamber 11 have good electrical sinterability because their interfaces (joint surfaces) are made of the same type of metal. As a result, they will be quickly and firmly connected to each other in a sound manner.

As a result, as shown in FIG. 5, the piston 12 obtained has a T
The piston skirt side is formed from an Al alloy that is inexpensive and has excellent workability, and the piston top side is made of Ti-Al! Alloy and piston skirt 01
1Al alloy by the first and second composite particles 3.6 between Ti-Al and Al! The result is a molded mixture of layers.

Therefore, the piston top side T 1-Al alloy (thermal expansion coefficient 8
X10-'/''C) and piston skirt side Al! alloy (
Thermal stress caused by the difference in thermal expansion with the thermal expansion coefficient of 21×10-'/''C) is alleviated by the mixed layer, and the thermal strain of the piston 12 is reduced.

Furthermore, according to this piston 12 shown in FIG. 5, the ring groove 17 of the top ring is made of a T I-Al alloy with excellent heat resistance and high high-temperature strength (temperature resistance: 900°C). There is no need for a ring tray made of Ni-resist cast iron, which is required for a piston made of an alloy (heat-resistant temperature: 350°C). Therefore, the temperature gradient in the ring group portion becomes natural, and there is no temperature concentrated portion.

In addition, the top land portion of the piston 12 has a low coefficient of thermal expansion.
Since it is made of i-Al alloy (coefficient of thermal expansion 8X10-'/'C), it is made of ordinary Al alloy (coefficient of thermal expansion 21X
10-'/'C), the clearance between the piston 12 and the cylinder (not shown) can be made smaller. Therefore, dead volume between the top land 18 of the piston 12 and the cylinder is reduced, and combustion efficiency is improved. Furthermore, the piston 12 oscillates within the range of the clearance, and the slap noise caused by the piston 12 slamming against the cylinder side wall can be reduced.

In addition, since the Ti-Al alloy has excellent heat resistance and high heat resistance strength, the piston 12 can be made thinner.
can promote weight reduction.

A modified embodiment of this embodiment will be explained with reference to FIGS. 7 and 8. As shown in FIG. 3,6,
- It is characterized by not being coated in multiple layers, but in multiple layers such as double, triple, or quadruple layers.

This multiple coating method involves producing a single composite granule in which the surface of a core particle is coated with a single layer of child particles, and then coating the surface of this multiple composite granule with a double layer by electrostatic force. Particles are attached and firmly embedded into the core particle side by an impact method in a high-speed air stream to obtain a double composite granule. By repeating this operation, triple or quadruple composite particles can be obtained.

By coating the surface of the core particle with multiple child particles in this way, the weight ratio between the weight of the metal in the core particle and the weight of the metal in the child particles can be determined as desired.

Therefore, as shown in FIG. 7, the Ti-Al of the Ti-Al alloy powder 2 on the child particle side is
The preformed product 9a shown in FIG. 3 is sintered using the triple or quadruple first composite grains 3a in which the amount of alloy is larger, and T 1- on the core particle side is similarly shown in FIG. Using triple or quadruple second composite particles 6a, the third composite particle 6a has more Al in the AI powder on the child particle side than the Ti-Al alloy of the A7 alloy particles 4.
If the pre-formed product 9C shown in the figure is sintered and a piston is manufactured using these pre-formed products 9a and 9c in the same manner as in the previous example, the resulting piston will have Ti-A on the top side of the piston.
There is a Ti alloy between the L alloy and the Al alloy on the piston skirt side.
The material is graded in three stages from dense to Al dense, and T
Thermal stress based on the difference in thermal expansion between i-Al and Al is further alleviated.

``Effects of the Invention'' As explained above, according to the present invention, the following excellent effects can be achieved.

(1) Thermal distortion of the piston caused by the difference in thermal expansion of the Ti-Al gold alloy on the piston top side and the Al gold alloy on the piston skirt side can be suppressed and reduced.

(2) The Ti-Al gold alloy on the piston top side and the Al alloy on the piston skirt side can be soundly and firmly bonded.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view showing a first composite granule used in a piston manufacturing method according to an embodiment of the present invention, FIG. 2 is a side sectional view similarly showing a second composite granule, and FIG. 3 is the above-mentioned A schematic diagram for explaining the process of laminating the first and second composite particles, Figure 4 is a side cross-sectional view showing the electrical sintering device, also for explaining the sintering process, and Figure 5 is a diagram showing the manufactured granules. FIG. 6 is a perspective view showing a piston; FIG. 6 is a perspective view showing the formwork in FIG. 4; FIG. 8 are side sectional views showing a second composite granule of a modified example. In the figure, 1 is Al powder particle 2 is T1-Al alloy powder, 3 is first composite particle, 4 is Ti-Al alloy particle, 5 is Al powder, 6 is second composite particle, 7 is piston top A pre-formed product made of a Ti-Al alloy material is placed on the side, and 8 is a pre-formed product made of an Al alloy material placed on the piston skirt side. Patent Applicant Isuri Motor Co., Ltd. Agent Patent Attorney Nobuo Kinutani Figure 1 Figure 2 Figure 4 Figure 3 Figure 6 Figure 5F! ! J 6a Figure 26-1

Claims (1)

[Claims] 1. Between the Ti-Al alloy material placed on the piston top side and the Al alloy material placed on the piston skirt side,
A first composite particle whose surface is coated with Ti-Al alloy powder and a second composite particle whose surface is coated with Al powder are placed on the Ti-Al alloy material side. After laminating the first composite grains and the second composite grains while changing the mixing ratio so that the first composite grains are dense and the second composite grains are dense on the Al alloy material side, A method for manufacturing a piston, which comprises compression molding these into a piston shape and sintering them.