JPH01154861A - Production of gear - Google Patents

Abstract

PURPOSE:To obtain a gear having light wt., high strength and high wear resistance by continuously changing concn. of reinforcing material in matrix metal from center part of the gear toward teeth part in a mold by rotation of the mold for centrifugal casting having gear shaped cavity. CONSTITUTION:The reinforcing material 21 of alumina grains (density about 4) having two kinds of grain sizes, such as 20mum and 3mum average grain size, respectively is added in molten aluminum alloy (sp. gr. about 2.8) 22 as the matrix. Then, this mixing material is sufficiently stirred to obtain the molten metal 23 as composite material. Successively, the molten metal 23 is held at 700-800 deg.C and poured into the metallic mold 24 having teeth type grooves at the inner circumferential face, preheating at 440-550 deg.C and rotating at about 2000rpm. After holding for the specific time, at the time, when the grains 21 sufficiently coagulate near the teeth part of the gear, the metallic mold 24 is rapidly cooled and the molten metal 23 is solidified and separated from the mold. In this result, the gear forming of the metal based composite material part 25 having high alumina containing ratio at outer circumferential part of the gear, the metal based composite material part 26 having relatively low alumina containing ratio at inner side and the metal material part 27 containing scarcely the alumina at center part, respectively, is obtd.

Description

[Detailed description of the invention] [Objective of the invention] (Industrial application field) The present invention manufactures a gear that is lightweight and has excellent wear resistance by partially using a metal matrix composite material reinforced with fibers, particles, etc. In particular, the present invention relates to a method for manufacturing gears that makes it possible to manufacture gears with excellent heat resistance and strength.

(Conventional technology) Industrial robots and machine tools require high speed and precision of movement, so it is important to make gears smaller, reduce power loss (improve transmission efficiency), and reduce vibration and noise. It is being In recent years, metal matrix composite materials, which are lightweight, have high strength, high rigidity, and excellent wear resistance, have attracted attention as materials for such gears.

For example, aluminum (A), magnesium (Mg)
Metal matrix composite materials made by reinforcing alloys such as ceramic fibers and particles with ceramic fibers and particles are lighter and stronger than iron-based materials, and gears made of such metal matrix composite materials have a small rotational moment of inertia and are highly wear resistant. It is also excellent in sex. therefore,
There are advantages such as reduced gear wear, reduced power loss, and improved transmission efficiency.

However, many metal matrix composite materials have a larger coefficient of friction and poorer thermal conductivity than metal materials, so they have the disadvantage that rotational precision decreases due to thermal expansion of gears due to increased tooth temperature during operation. Furthermore, since the vibration damping properties are poor, vibrations during operation tend to remain, and it is predicted that the noise will increase accordingly.

In order to improve these drawbacks, the inventors fabricated a metal base with high strength, high rigidity, and excellent wear resistance only in the vicinity of the teeth of gear a and the root of the teeth of the base, as shown in Fig. 3. We proposed a gear that is made of a composite material and the other base part is made of a metal material C that has excellent thermal conductivity and vibration damping properties.

A conventional manufacturing method in which such a metal matrix composite material is partially arranged will be explained using FIGS. 4(a) to 4(h).

First, after weighing a predetermined amount of ceramic reinforcing material 1 such as 1181 particles, a solvent such as water or a binder is added to it as needed, and the mixture is thoroughly stirred with a stirrer 2 to obtain a mixed powder 3 (see Fig. 4). a)). Next, the mixed powder 3 is put into a mold 5 having a cylindrical core 4, and is compression-molded from above and below using a cylindrical upper bunch 6 and a lower bunch 7 (FIG. 2(b)), and then released from the mold. A hollow preformed body 8 is obtained (Figure (C)). The preformed body 8 is thoroughly dried and inserted into an infiltration mold 9 (Figure (D)). ((e) in the same figure). Molten matrix metal 11 into mold 1
The piston 13 pours the molten metal into the molten metal 11 (see figure (f)).
By applying pressure, the preformed body 8 is impregnated with molten matrix gold j111 to form a composite part 14 ((Q) in the same figure). Thereafter, the piston 13 is further pushed down to completely impregnate the matrix metal 11 into the preform 8, and after solidification, it is taken out from the mold 12 and cut. Gear material 17
((h) in the same figure), and then gear cutting is performed by machining.

(Problem to be Solved by the Invention) However, the coefficient of thermal expansion of the metal matrix composite material containing ceramic fibers, particles, etc. is significantly smaller than that of the metal material of the matrix, so the gear manufactured by the method shown in Fig. 4 As shown in Fig. 3, due to thermal stress generated during cooling, heat treatment, or operation, the metal matrix composite material part and the metal material part C
There is a problem that a crack d occurs at the interface of the film and peeling occurs at this part.

Therefore, as a method for reducing the thermal stress generated at the interface between the metal matrix composite material part and the metal material part C, it is considered effective to continuously change the concentration of the reinforcing material along the radial direction.

However, with the method described above using the preform 8, it is almost impossible to obtain such a reinforcement distribution. In addition, preforms made of reinforcing materials are brittle and have low strength, so it is not only difficult to form preforms in the shape of gear teeth, but also can be crushed or damaged by the infiltration pressure during compounding. This is often the case, and the yield is low.

The present invention was made in view of these circumstances, and provides a gear that is lightweight, has high strength, has high wear resistance, has good heat dissipation, and has excellent heat resistance, thermal shock resistance, etc., with a high yield and low cost. The purpose is to provide a method of manufacturing at low cost.

[Structure of the invention]

(Means and effects for solving the problems) The present invention adds fibers, whiskers, or particulate reinforcing material to a molten light metal as a matrix metal, and injects this into a mold to improve the quality of the teeth of a gear and its vicinity. In a method for manufacturing a gear, the gear part is formed of a composite material of the matrix metal and the reinforcing material, and the base part of the gear is formed only of the matrix metal,
A centrifugal casting mold having a gear-shaped cavity is used as the mold, and by rotating the mold and creating a centrifugal force field, the concentration of the reinforcing material is continuously changed from the center of the gear toward the teeth. It is characterized by

That is, the centrifugal force F acting on an object is generally F=m−r・
ω2 (1) m: mass of substance r: distance from center ω: given by angular velocity. Therefore, for example, alumina (8ρ20
3), A, l!, such as titanium carbide (T i C), zirconium oxide (ZrO2), etc. , Aρ, MQ alloy containing a ceramic component with a higher density than that of the MO alloy, etc. When centrifugal force is applied to the melt, the ceramic component tends to aggregate on the outer peripheral side of the teeth and its surroundings, reducing the durability of the gear. Abrasion resistance is dramatically improved. Also, from equation (1), even if the same substance has a large particle size and a large mass, it will be subject to a large centrifugal force, so naturally, large particle size particles will be distributed on the outside, and small particles will be distributed on the inside. do. As a result, according to the present invention, the ceramic content on the outside is high and the content on the inside is low. Therefore, when thermal stress conditions are severe and it is desired to change the coefficient of thermal expansion more continuously, it is effective to add ceramic fibers or particles with different particle size distributions or ceramic components with different densities in advance in a composite manner.

(Example 1) Hereinafter, an example of the present invention will be described with reference to FIGS. 1 and 2.

FIGS. 1(a), (b), and (C) show the gear manufacturing process. In this example, reinforcing materials with two types of particle sizes, alumina particles with an average particle size of 20 μm (density 4) and alumina particles with an average particle size of 3 μm, were used as a matrix.
Composite addition to alloys.

First, as shown in FIG. 1(a), alumina particles 21 having the above-mentioned particle size distribution are added to a molten Jl5A6061/1 alloy (specific gravity: 2.8) 22, and the alumina particles are thoroughly stirred mechanically. A composite material solution 123 containing particles is made. This molten metal 23 is maintained at 700 to 800°C and poured into a mold 24 having tooth-shaped grooves on its inner peripheral surface, preheated to 400 to 550°C, and rotating at about 200 rpm. Same figure (
As shown in b), the fully poured state is held for several minutes, and when the alumina particles 21 have sufficiently aggregated near the gear teeth, the mold 24 is rapidly cooled, and after solidification, the mold 24 is rotated. Stop and release from the mold. As shown in FIG. 2C, a metal matrix composite material part 25 with a high alumina content is formed on the outer periphery of the gear, and a metal matrix composite material part 26 with a relatively low alumina content is formed inside thereof. A gear 29 is formed having a center hole 28 in which a metal material portion 27 containing almost no alumina is formed in the center. and,
Alumina particles with a large particle size accumulate on the outer periphery of the gear 29.

When the Gockers hardness distribution from the tip of the gear toward the center of the gear 29 manufactured by the method of this example was investigated, the results shown by curve A in FIG. 2 were obtained. That is, the Vickers hardness is high at the tip of the tooth, and decreases continuously with a gentle slope toward the center. This is considered to be based on the distribution state of alumina particles. It is known that the thermal expansion coefficient and hardness of metal matrix composite materials increase with the reinforcing material content, and the smaller the reinforcing material content, the lower the thermal expansion coefficient and hardness of the matrix. approach. Therefore, since the coefficient of thermal expansion of the gear 29 changes continuously from the tooth tip side toward the center side, it can be expected that the thermal stress is extremely small.

Table 1 below shows gears 100%
The occurrence of cracks at the interface of the matrix/composite material part when quenched from a temperature of ~550°C is shown below. The results are shown below. In the gear manufactured according to this example, A6
It was confirmed that almost no cracking occurred even when water-cooled from 550° C., which is the solution treatment temperature for 061 alloy. This shows that the gear obtained by the method of the present invention has extremely excellent thermal shock resistance.

(Example 2) A particle size of approximately 20 μm was obtained using substantially the same method as in Example 1 described above.
Alumina particles of a single particle size (density 4) were added to the 6061 alloy as a matrix metal to produce gears.

In the case of this method as well, a metal matrix composite material with a high alumina particle content is formed on the tooth tip side, a metal matrix composite material with a relatively low alumina content is formed on the tooth root, and alumina particles are formed in the center. A metal material portion containing almost no metal was formed.

As shown by curve B in Figure 2, the Gockers hardness distribution of the gear manufactured by the method of this example has a larger inclination angle than that of Example 1, but is continuous from the tooth tip side to the center side. It was observed that the hardness changed over time.

Regarding thermal shock resistance, as shown in Table 2 below, although some cracks occurred at the interface due to quenching from 550°C, no interface cracks occurred when quenching from a temperature lower than that. confirmed.

Therefore, in this example as well, substantially the same strength improvement effect as in Example 1 can be obtained.

(Conventional Example) A gear was manufactured by adding alumina particles having an average particle size of 20 μm to A6061 alloy as a matrix metal by the conventional method shown in FIG.

As mentioned above, in the gear manufactured by this method, the interface between the matrix metal part and the metal matrix composite material part was clear.

When we investigated the Vickers hardness distribution of gears manufactured using this method, we found that, as shown by curve C in Figure 2, a certain distance position (10 to 120
It was observed that the hardness decreased extremely at the position (m).

That is, it can be seen that due to the difference in coefficient of thermal expansion between the metal matrix composite material part and the matrix part, the thermal stress at the boundary part when subjected to a thermal load is extremely large.

Regarding heat resistance WJ impact resistance, as shown in Table 2 below,
It was observed that interfacial cracking occurred in all cases during quenching from a temperature above 300'C.

[Margin below]

Table 1 △: Partial cracking at the interface ×: Cracking at the interface As described above, according to the above example, the tooth portion and the vicinity of the tooth root are lightweight, have high strength, and have a metal matrix composite with excellent wear resistance. It is possible to manufacture a high-performance gear in which the other base portion is made of a metal material with excellent thermal conductivity and vibration damping properties. Moreover, the thermal shock resistance is significantly improved, and cracking and peeling at the interface between the metal matrix composite material and the metal material during heat treatment, which is essential for Al1 alloys, can be completely prevented.

Furthermore, unlike conventional methods, there is no need for the time-consuming process of forming a preform, and the Ne
Since casting can be performed in the state of ar-Net-3 hape, manufacturing costs can be significantly reduced compared to the conventional method in which gear cutting is performed from a flat disk.

(Effects of the Invention) As described above, according to the present invention, gears that are lightweight, have high strength, have high wear resistance, have good heat dissipation, and have excellent heat resistance and thermal shock resistance can be produced with high yield. This has the advantage that it can be manufactured at low cost.

[Brief explanation of the drawing]

FIGS. 1(a) to (C) are diagrams showing an example of the gear manufacturing method according to the present invention in the order of steps, and FIG. 2 is a graph showing the hardness characteristics of the gear manufactured by the method of the example. Figure 3 shows a gear manufactured by the conventional method, Figure 4 (a
) to (h) are diagrams showing the conventional method in the order of steps. 21...Alumina particles (reinforcement material), 22...AfJ
Molten alloy (matrix gold Wb>, 23... Molten metal of composite material, 24... Mold (mold), 29... Gear. (α) (b) Distance between self-forces in Figure 1 ( myn) Figure 2 Figure 3

Claims (1)

[Claims] 1. Fibers, whiskers, or particulate reinforcing material is added to a molten light metal as a matrix metal, and this is injected into a mold to form the toothed part of a gear and its vicinity by adding the matrix metal and the reinforcing material. In this manufacturing method, a centrifugal casting mold with a gear-shaped cavity is used as a mold, and the mold is rotated to generate a centrifugal force. A method for manufacturing a gear, characterized in that the concentration of the reinforcing material is continuously changed from the center of the gear toward the teeth. 2. The method for manufacturing a gear according to claim 1, wherein reinforcing materials having different densities or particle size distributions are used, and the reinforcing material with a large density or particle size is arranged on the outer circumferential side of the gear. 3. The method for manufacturing a gear according to claim 1, wherein Al, Mg, Ti or an alloy thereof is used as the matrix metal. 4. The method for manufacturing a gear according to claim 1, in which short fibers, whiskers, or particles of oxides, nitrides, or carbides of Ti, Zr, Al, and Si are used as reinforcing materials.