JPH042702A - Manufacture of piston - Google Patents

Abstract

PURPOSE:To easily manufacture a Ti-Al alloy piston having uniform quality and low thermal expansion by aggregating coated particles formed by covering Ti particle surface with Al particles and sintering while compress-compacting into piston shape. CONSTITUTION:The marcketed Ti particles having about 100 mum particle size and the Al particles having about 10 mum particle size, are kneaded in an electrostatic vessel. By this method, the Al particles are stuck on the surfaces of Ti particles with electrostatic force. Successively, impact force is given to this particles with high speed air flow, and the Al particles are firmly bitten into the Ti particles. By this method, the Ti particles are made to core and the Al particles are applied on the surface thereof to form the coated particles. The complex particles 3 are packed into a sintering chamber 5 formed to the piston shape in an electric conduction sintering device 4 composed of punching electrodes 6 and insulating mold frames 7. Successively, the coated particles 3 are conducted with electric current superimposing high frequency current on DC from a special electric power source 8 while pressurizing with the punching electrodes 6 and the mold frames 7. By this method, the Al particles in the complex particles 3 are thermally diffused into the Ti particles side to develop the Ti-Al alloy phase and the piston having complicate shape and low thermal expansion is obtd. without any cutting-machining.

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.

"Prior Art" Pistons for automobile diesel engines, gasoline engines, etc. are mainly cast from aluminum alloy in order to reduce their inertia. Pistons made of aluminum alloy casting (JIS AC8A AC8C, etc.) are Its coefficient of thermal expansion (21X 10-6.・'°C
) is the coefficient of thermal expansion of the cast iron cylinder (10x 10-'
/ It is nearly twice as large as “C).

Therefore, in order to prevent seizure of the piston, it is necessary to provide a clearance between the piston and the cylinder that takes into account the thermal expansion of the piston when the engine is at full power, although this is harmful when the engine is cold.

This clearance is designed so that when the engine is at full power, the piston thermally expands and fits neatly into the cylinder, so when the engine is cold, the piston inside the cylinder becomes loose.

Therefore, the dead volume between the top land of the piston and the cylinder increases, and combustion efficiency deteriorates.

In addition, the piston reciprocating within the cylinder swings within the range of the above-mentioned clearance, causing the piston to slam against the cylinder side wall, producing a slapping sound (especially during idling).

In order to suppress and reduce the deterioration of combustion efficiency and the generation of slap noise, it is sufficient to reduce the clearance between the piston and the cylinder. good.

Therefore, various technologies are being researched and developed to reduce the thermal expansion of pistons9.For example, there is a so-called automatic piston, which has a steel plate cast inside the piston to reduce thermal expansion. High cost.

In addition, there is a ceramic fiber composite piston in which the area around the combustion chamber of the piston is composited with ceramic fiber to reduce thermal expansion, but the coefficient of thermal expansion of the part where this ceramic fiber is composited is 18 x 10-'/'
C, and compared to aluminum's thermal expansion coefficient of 21x10-'/'C, its thermal expansion reduction effect is as small as about 15%, and cannot be said to have a sufficient effect.

On the other hand, when a piston is formed from a Ti-Al intermetallic compound, the coefficient of thermal expansion of the Ti-Al intermetallic compound is 8.
xlo-'/'C, and the thermal expansion coefficient of aluminum is 21X
Compared to 10-'/'C, it is about 173, which makes it possible to significantly reduce thermal expansion.

Problem to be solved by the J invention U1 However, since the Ti-Al alloy has poor castability and poor machinability, it is difficult to reduce the number of cutting parts of the cast product by using special precision manufacturing methods such as the suction method. It is necessary to manufacture pistons. Therefore, the product yield deteriorates.

The inventors believe that powder metallurgy sintering (e.g.
Ti-A
It has been discovered that by manufacturing pistons made of j' alloy, pistons with complex shapes can be manufactured without cutting.

However, atomized powder for sintering Ti-Al gold alloys is difficult to obtain because of its poor marketability. Therefore, Ti atomized powder for sintering, which is easily available, and Al
However, simply kneading Ti powder and Al powder does not make them uniform enough, and the sintered Ti-A
, 11 alloy pistons will have Ti-only parts and Al-only parts. Thermal expansion coefficient of Ti (8,5:
<10-'/'C) and the thermal expansion coefficient of Al (21x 10-
'/'C) is more than twice as different from Ti, so when this piston is heated and the engine is running, thermal distortion occurs in the piston due to the difference in coefficient of thermal expansion between A, & and Ti, resulting in seizure. .

The purpose of the present invention, which was created in consideration of the above circumstances, is to manufacture a piston made of Ti-Al alloy that can significantly reduce thermal expansion by using easily available Ti powder and AlI powder. ” and Ti should not be biased (Ti-Al!
The present invention provides a method for manufacturing a piston in which an alloy is uniformly produced inside the piston.

[Method P1 for Solving the Problems] In order to achieve the above object, the piston manufacturing method of the present invention uses Ti particles as core bodies and coats Al particles on the surface to form composite particles, and Ti-Aj! is assembled and compression-molded into a piston shape and sintered, and the Al particles of the composite particles are thermally diffused to the Ti particles side to produce Ti-Aj! It is designed to generate an alloy phase.

[Operation] Composite particles in which the surfaces of Ti particles as core bodies are coated with Al particles are aggregated, and this aggregate is compressed into a piston shape and sintered, so that Ti and Al! Ti-Al! is uniformly kneaded and obtained by sintering! The alloy phase is uniformly distributed inside the piston.

Furthermore, by performing highly accurate compression molding and sintering, pistons with complex shapes can be manufactured without cutting.

[Example] A method of manufacturing a piston as an example of the present invention will be described with reference to the accompanying drawings.

First, commercially available Ti particles of approximately 100 μm and Al particles of approximately 10 μm or less are prepared.

Then, these Ti particles and Al particles are kneaded in an electrostatic container, and as shown in FIG.
Al particles 2 of approximately 10 μm or less are on the surface of the nucleus.
are attached by electrostatic force.

As shown in 2, Ti particles 1 with A and R particles 2 attached to their surfaces are placed in a container (not shown) equipped with a rotary blade of 2000 rpm to 8000 rpm, and subjected to impact force (centrifugal transfer) due to high-speed airflow for several minutes. give. This impact action causes the second
As shown in the figure, the electrostatically attached A and 9 particles 2 are firmly embedded in the Ti particle 1, which is the nucleus, and the surface of the Ti particle 1 becomes A.
Composite particles 3 coated with l particles 2 are formed.

The weight ratio of Ti and Aj in the composite particles 3 is preferably about 7=3.

The composite particles 3 are charged and filled into a sintering chamber 5 of an electric sintering device 4 shown in FIG. The composite particles 3 at this time are in a state where a large number of composite particles 3 are simply aggregated, as shown in FIG. As shown in FIG. 5, the sintering chamber 5 of the energizing sintering device 5 is constructed by vertically opposed punch electrodes 6 and a formwork 7 made of an insulator (alumina or the like) provided therebetween. It is sectioned into a piston shape as shown in Figure 7. A predetermined compression pressure P1 is applied to the punch t&6 in the axial direction of the piston by a hydraulic mechanism, and it is connected via a switch 9 to a special power source 8 that superimposes a high frequency wave on direct current.

Further, as shown in FIG. 6, the mold 7 is divided into two parts so that a predetermined compression pressure P2 is applied in a direction perpendicular to the axial direction of the piston.

Current, voltage, pressure P1 of the punch electrode 6, and the formwork 7
By controlling the operation by changing the pressure P2 over time,
The composite particles 3 filled in the sintering chamber 5 are compression-molded into a piston shape, and appropriate electrical discharge occurs between the particles 3, so that the piston 10 shown in FIG. 7 is sintered and manufactured in a short period of several tens of seconds. (So-called current sintering method using plasma discharge).

During this current sintering, by preheating the sintering chamber 5 to approximately 600 to 800°C, which is higher than the melting point of Al and lower than the melting point of Ti, the composite charged into the sintering chamber 5 can be heated. particle 3
The Al particles 2 on the surface layer of T are thermally diffused toward the Ti particles 1 as core bodies, and as shown in FIG.
An i-AlJ gold phase 11 is produced.

At the same time, the A of the surface layer of the adjacent composite particles 3
The l particles 2 are sintered with each other, and the composite particles 3 are bonded with each other.

That is, according to this piston manufacturing method, the sintering chamber 5
The composite particles 3 filled in the interior change from a state in which the composite particles 3 are simply aggregated as shown in FIG. At the same time, the Ti-Al base alloy phase 11 is generated so as to diffuse and encapsulate the Ti particles 1, and at the same time, the Al on the surface layer of the adjacent composite particles 3 is generated.
The particles 2 are in a mutually sintered state, and a Ti--Al gold alloy piston 10 as shown in FIG. 7 is manufactured.

Since this piston 10 is made of composite particles 3 consisting of A and R particles 2 and Ti particles 1 as a sintered material, the Ti phase and the A and N phases are not biased (Ti- AlJ
The gold phase 11 is uniformly distributed inside the piston 10.

Therefore, the piston 10 based on the difference in thermal expansion between Al and Ti
thermal distortion is suppressed.

Further, the piston 10 made of Ti-AlJ gold has a thermal expansion coefficient of 8 x 10-6/° as shown in Fig. 4.
C, and the thermal and expansion coefficients of Ti as the core are 8.5.
xlo-6/°C, the thermal expansion can be significantly reduced compared to an AlIIJ piston (the coefficient of thermal expansion of Al is 21 x 10-6."C). Therefore, the distance between the piston 10 and the cylinder The clearance of
Combustion efficiency can be improved by reducing the dead volume between the top land 10a of the piston 10 and the cylinder shown in FIG. Slap sound can be reduced.

Further, by performing highly accurate compression molding and energization sintering, the piston 10 with a complicated shape can be manufactured without cutting.

[Effects of the Invention] As explained above, according to the present invention, the following excellent effects can be exhibited.

(1) When manufacturing a Ti-Al alloy piston that can significantly reduce thermal expansion, easily available sintering Ti particles and AA powder particles are used to sinter Ti and Al evenly. The Ti-Al alloy phase obtained by this process can be uniformly dispersed and generated inside the piston.

(2) By performing highly accurate compression molding and sintering, pistons with complex shapes can be manufactured without cutting.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing Al2 particles electrostatically attached to the surface of Ti particles, and Figure 2 is a cross-sectional view of the Al particles shown in Figure 1.
A cross-sectional view showing a composite particle firmly embedded in an i-particle, FIG. 3 is a cross-sectional view showing an aggregate of composite particles shown in FIG. 2, and FIG. 4 is a cross-sectional view showing an aggregate of composite particles shown in FIG. A sectional view showing the sintered product, FIG. 5 is a side sectional view of the current sintering device, and FIG. 6 is a perspective view showing the formwork of the current sintering device shown in FIG.
FIG. 7 shows a Ti-Al alloy piston manufactured by the current sintering apparatus shown in FIG. 5. In the figure, 1 is a Ti particle, 2 is an Al particle, 3 is a composite particle, 1
1 is a Ti-Al alloy phase. 3rd 2...N particle 3--Shabu Ruiko 77...r7-At gold all-metal phase Figure 4

Claims (1)

[Claims] 1. Form a composite particle by using Ti particles as a core and coating the surface with Al particles.The composite particles are aggregated and sintered while compression molding into a piston shape.
A method for manufacturing a piston, characterized in that a Ti--Al alloy phase is generated by thermal diffusion to the particle side.