Method For Making A Sintered Body Having Integral Portions Of Different Density

Abstract

A method for forming a sintered body having integral porous, low density and non-porous, high density portions, comprising the steps of sintering and compacting a powder of a material selected from various metals, alloys, or cermets, in a form approximating a desired configuration, and compressing that portion only of the sintered compaction which is required to be of high density.

Parent Case Text

This is a continuation of application Ser. No. 4,352, filed Jan. 20, 1970 and now abandoned.

Description

BACKGROUND OF THE INVENTION

This invention relates to a method of forming a sintered compact body, such as a sintered alloy, having portions of different density by compressing separate portions of the body under different compression ratios.

Bodies formed of sintered materials are used for filters, oil-less bearings, and the like, because of their porosity, but they have disadvantages, such as low strength and low toughness, arising out of their high porosity.

Conventionally, when it has been desired to make and utilize products of high porosity and which also have great strength and toughness, it has been usual to provide reinforcement to the porous sintered material by backing the same with a material of high strength. However, such reinforcement complicates the manufacturing process, requiring numerous steps involving the added reinforcement materials and reinforcing treatment.

SUMMARY OF THE INVENTION

The present invention relates to a method of forming a sintered compact body having portions with different properties and functions and which comprises the steps of sintering a metal, alloy, or cermet powder to form a body having approximately the shape and size of a desired product, and further compressing a portion of the body to higher density than that of the original porous sintered material, and thereby easily producing the product having integral low density, porous and high density, non-porous portions, wherein the high strength and toughness of the high density portion reinforces the weak, porous portion. Thus, the present method avoids the conventional complicated treatment such as backing with high strength material, or insertion into high strength parts. Such portion of the product as is required to be of high strength and toughness is subjected to compression at, or below the sintering temperature, or at room temperature. The boundary between the porous portion and the high density portion of the product is naturally and continuously extended yielding strong, integral connection of the low and high density portions for reinforcement of the porous portion by the high density portion. The present invention yields a product having the advantages of simple processing, reduction of material costs by integral forming, and increase of production yield and efficiency.

It will be apparent from the above that the primary object of the present invention is to provide a method for forming a sintered product having portions of different density and which obviates the defects and disadvantages of conventional methods for forming such products.

Another object of the invention is to provide a method for simultaneously forming a sintered product having portions evidencing different physical characteristics and enabling versatile uses.

A further object of the invention is to provide a method for forming a sintered product which is easy to practice, and inexpensive and economical to follow.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features that are considered characteristic of the invention are set forth with particularity in the appended claims. The invention, itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment when read in connection with the accompanying drawings, wherein like reference characters indicate like parts throughout the several figures, and in which:

FIG. 1 is a cross-sectional view of a mold apparatus used in the process according to the invention for forming the final product as a body of sintered material having portions of different density;

FIG. 2 is a cross-sectional view of a body formed of porous sintered material as initially formed prior to placement in the mold of FIG. 1;

FIG. 3 is a cross-sectional view of the final compacted product showing the body of FIG. 2 after it has been subjected to compression in the mold apparatus of FIG. 1;

FIG. 4 is a photomicrograph showing a cross-section of a portion of the product shown in FIG. 3; and

FIG. 5 is an enlarged photomicrographic view showing the integral boundary of the high and low density portions of FIG. 4.

DESCRIPTION OF A PREFERRED EMBODIMENT

The method of the present invention will be described as related to the forming of a synchronizer ring for use as a gear transmission part for automobiles.

Iron and carbon powders as a powder to be sintered are mixed in the proportion Fe-0.5%C and compacted in a die and sintered at 1,100.degree.C. for 30 minutes to form the porous sintered ring 40 having a main ring body 41 with an inner peripheral surface 43, an outer peripheral surface 44, and an annular flange, or rim 42, having an upper surface 45 at an upper portion of the periphery of said ring body.

Another sample of the ring 40 was formed from Fe-2% Cu powder compacted in the die and sintered at 1,100.degree.C. for 15 minutes.

The rim 42 of the porous sintered ring 40 was formed with a thickness larger than that of the corresponding rim of the product to be manufactured. The ring 40 was placed between die 10 and punch 20, FIG. 1, and further compressed at elevated temperature, thereby forming the product of desired configuration and dimensions and eliminating the pores in the rim 42 to obtain a rim of high density and reduced thickness. The elevated temperature used may be sintering temperature, or less, and may be reduced to room temperature.

The compression apparatus shown in FIG. 1 includes a metal die 10 and a punch 20, or ram, said die having an inner bottom surface 11, an inner cylindrical surface 12 directed vertically upwardly from the bottom surface, a stepped surface 13, or shoulder, directed outwardly from the surface 12 and having an appreciable inward, downward inclination, a side peripheral surface 14 directed upwardly vertically from the shoulder 13, an upper end surface 15 directed outwardly at right angle to the surface 14, and a recess 19 in surface 15.

The punch 20 has a lower end surface 23, an outer peripheral surface 22 directed upwardly with an outward inclination from the surface 23, and a stepped surface 21, or shoulder, directed horizontally outwardly from the surface 22. Accordingly, when the punch 20 is inserted into the metal die 10 to a position in which the die shoulder 15 contacts the punch shoulder 21, there remains a space 30 between the punch and die, as shown in FIG. 1. In space 30, the distance between boundary walls defined by die surface 12 and the punch surface 22 is approximately the same as the thickness of the main ring body 41, FIG. 2.

In use of the compression apparatus, the punch 20 is lifted out of the die 10 and the ring 40, heated at about 900.degree.C, is inserted in the die so that the outer peripheral surface 44 of the ring 40 engages the inner die surface 12. The punch 20 is then inserted into the metal die 10 under compressive force. Thus, the ring 40 is formed into a product 50, as shown in FIG. 3, which has a main ring body 51 with an inner peripheral surface 53, an outer peripheral surface 54, and an upper surface 55.

During compression by punch 20, the main ring body 41 is only slightly compressed, if at all, because die space 30 has the same dimensions as ring body 41. However, the flange 42 is compressed considerably since its thickness is greater than the corresponding space between the shoulders 13 and 15. Therefore, the main body 51 of product 50 retains about the same porosity as that of portion 41 of the ring 40, but the compressed flange 52 has a much higher density. In other words, the resultant product has a porous portion 51 and a non-porous portion, or high density portion 52.

The temperature during compression by punch 20 may preferably be about the temperature for sintering, or somewhat lower, for materials which have high compressibility, while those materials having a smaller compression ratio may be compressed at room temperature.

The difference in density between portions 51,52 of the synchronizer ring 50 will be apparent from the photomicrograph, FIG. 4, showing a cross-section of the ring obtained by sintering Fe-0.5% C powder compact and thereafter compressing only the rim portion thereof, according to the present invention. In the photomicrograph, the black dots denote pores so that a greater number of black dots in a given-sized area shows a portion of higher porosity, and the fewer black dots in a given-sized area shows a portion of higher density. Examination of FIG. 4 reveals that the main ring body has high porosity, while the horizontal rim, or flange, has high density.

FIG. 5 is an enlarged photomicrographic view of that portion of body 50 including the outer curved edge 57 between the main ring body 51 and the flange 52. This is the boundary between the porous ring 51 and the compressed, non-porous flange 52. As is apparent from the Figure, this boundary is not clearly, or sharply defined, both portions being connected by a fiber-like structure, which indicates that the porous and non-porous portions are integrally connected in a continuous and natural manner.

Sample rings formed of iron carbon alloys, as previously noted, were made in the manner described above. The excess portion 56 of the flange on each ring was then cut off, in a conventional way, and teeth, not shown, were machined on said flange portion 52 for gearing into the hub sleeve of an automobile transmission part, thus obtaining finished, or completed synchronizer rings. The completed, sample synchronizer rings were then each subjected to an abrasion test, a strength test, and a practical stroke abrasion test, the results of which are detailed below:

In order to carry out the abrasion test in as practical a manner as possible, the inner peripheral surface 53 of the synchronizer ring was periodically rubbed against a tapered shaft under the following conditions; friction speed 4.4m/sec.; friction load 15 kg; oil temperature 40.degree.-50.degree.C, load cycle 16 times/min. and load time 1.45 sec. a cycle, for 5,000 times. The wear was measured by the variation in the degree of insertion of the tapered shaft due to wear of the ring. The tapered shaft was made of chrome steel having a hardness of Hv 600. (Hv: Hardness Vickers).

In the strength test, the load when the ring was ruptured by the insertion of the tapered shaft and the load when all the teeth in the chamfer, or flange, portion were simultaneously bent and ruptured were measured: The stroke abrasion test was carried out by assembling a sample synchronizer ring into an automobile transmission operating at 2,600 rpm of the propeller shaft; the automobile gear was shifted between 4,280 rpm and 2,600 rpm 32 times/min., for 50,000 times, and wear was measured by insertion of a tapered shaft into the disassembled ring, hereinbefore described.

The following table shows the test results of the sample synchronizerrings as compared with a conventional synchronizer ring made by forging Fe-0.5%C steel: ##SPC1##

As is apparent from the table, the porous ring portion of Sample 1 has no appreciable difference in coefficient of friction as compared with Sample 3 obtained by conventionally forging the same material as Sample 1, while Sample 1 has remarkably less wear both in the abrasion test and stroke abrasion test. In the flange having high density, both samples have about the same strength and hardness. In comparing Sample 2 with conventional Sample 3 the results are only slightly less favorable on the part of Sample 2 than Sample 1.

The synchronizer ring is required to have good wear resistance and a high coefficient of friction on the inner side of the ring portion, and the flange is required to have high strength for meshing with the inside gear of the transmission hub sleeve. It has been proved by the above tests and also by actual tests in cars that the sintered product of the present invention can be applied to parts which require high strength as has been indicated in the above table samples.

While the described synchronizer ring shows an example of the present invention in which the porous and high density portions are provided on opposite ends, it is possible to make a sintered product having said different portions disposed alternately. It is also possible to make a product having more than two portions which vary in density by suitably modifying the punch to exert different compressive forces in different areas.

In the described example of a synchronizing ring, compression was applied to the flange only, and weak, or no compression, such as not to change the porous characteristics, was applied to the main ring portion. For other products, the entire configuration and size, i.e., of all portions, may be modified simultaneously by the compression and molding step.

Although a certain specific embodiment of the invention has been shown and described, it is obvious that many modifications thereof are possible. The invention, therefore, is not intended to be restricted to the exact showing of the drawings and description thereof, but is considered to include reasonable and obvious equivalents.

Claims

1. A method for producing a synchronizer ring, having a main ring body and outwardly directed teeth on the periphery of said ring body, comprising: the steps of compacting a powder to be sintered to form a green compact having a main ring body and an outwardly directed annular flange forming a rim at the upper portion of said body, both said rim and said body having substantially the same and uniform density;

sintering said compact;

compressing said sintered compact in a die at about the sintering temperature of said compact or slightly lower by a single punch so constructed and arranged in relation to said die as to compress the rim more than the main ring body so as to form a fiber-like structure connecting the rim and body and to provide a compressed sintered compact whose density is higher in said outwardly directed rim than in the main ring body;

and machining said rim to form outwardly directed teeth whereby said body and teeth are integrally formed of the same sintered material and connected to said ring body in a continuous and natural manner by said fiber-like structure, and said teeth have higher density than said main

2. A method for producing a synchronizer ring, according to claim 1, wherein said powder to be sintered is a ferrous metal powder selected from

3. A synchronizer ring, comprising a main ring body and outwardly directed teeth at the upper portion of the periphery of said ring body, said body and teeth both being integrally formed of the same sintered material and connected in a continuous and natural manner by a fiber-like structure,

4. A synchronizer ring according to claim 3, wherein said sintered material is selected from the group consisting of iron-carbon alloy and iron-copper alloy.