GB2143161A

GB2143161A - Sintered metal body with at least one toothing

Info

Publication number: GB2143161A
Application number: GB08417019A
Authority: GB
Inventors: Winfried Huppmann
Original assignee: Sintermetallwerk Krebsoege GmbH
Current assignee: Sintermetallwerk Krebsoege GmbH
Priority date: 1983-07-11
Filing date: 1984-07-04
Publication date: 1985-02-06
Also published as: IN162188B; ES8504365A1; GB2143161B; FR2548933A1; AU2989784A; AU549505B2; FR2548933B1; ES529656A0; BR8401326A; SE8400679L; CH662760A5; GB8417019D0; IT1173398B; ZA842000B; SE8400679D0; IT8419836A0; DE3325037C1; CA1219471A; JPS6040638A; SE449705B

Abstract

A sintered metal body has at least one toothing formed in a blank 1 by metal forming, wherein the final toothing is hot or cold rolled into the blank 1 by means of two rolling tools 2 and 3. The blank may have pre-toothing formed therein. <IMAGE>

Description

SPECIFICATION Sintered metal body with at least one toothing This invention relates to a sintered metal body with at least one toothing which is formed in a blank by metal forming, and to a process for producing such a sintered metal body.

German Patent No 26 59 733 discloses a sintered metal body with at least one toothing in which the toothing is formed in a blank with or without pre-toothing by metal forming.

According to this process, the toothed gears are manufactured with a profile shift which changes continuously and monotonously from one front face,of the toothing to the other front face with a bevelled enveloped surface of the toothing. For this purpose a master gear is made by a cutting process, then from the master gear, using an image-forming manufacturing process, a die is manufactured, and the toothing of the gear is produced in the die under heat by means of a shaping process. A prescribed final temperature at the end of the shaping process is strictly adhered to, and the contraction of and the modular change in the toothing upon cooling-down of the workpiece from the prescribed final temperature are compensated by the corresponding admeasure in the master gear.The toothed gear produced in the die is calibrated with the nominal dimensions using a calibrated die which is manufactured by an image-forming manufacturing process from a second master gear made by a cutting process. In the course of the manufacture of the toothed gear by a sintering process, the contraction of and the modular change in the toothing during sintering and cooling down of the workpiece are corrected in the case of the master gear by the corresponding admeasure.Based on the suggested measures, by which the toothed gear is forged in a process using an initial master gear and the manufacture of a die from this master gear, whereby the contraction of and the modular change in the toothing is taken into consideration, and by which the toothed gear is calibrated in a calibrating die manufactured according to a second master gear, which deviates from the initial master gear, it is possible, in the case of a good tool-life of the dies to manufacture gears with a cylindrical rolled surface for gearings with the very highest degree of precision.

The process involves very high costs of production and is only likely to be applicable in special cases.

As is known from United States Patent No.

3772935, it is elso possible to form the toothing in a blank made of sintered metal material by metal forming (see Figures 5 and 6 and the corresponding description). In accordance with this, a type of stamping tool is used to press the material into a form, in order to produce the workpiece. The teeth are subsequently ground or cut, that is, they require a finish machining process.

According to a procedure described in "Machine design", 1972, pp. 72-72, the final toothing is achieved from a pre-toothed sintered metal blank by one or more metal forming processes.

Considering the known properties of toothed gears manufactured by powdermetallurgical processes, it has previously been thought that highly-stressed gears, such as those used in gear boxes of automobiles, could only be manufactured by conventional processes, for instance by a cutting and/or grinding process, particularly since the cold forming of toothings in solid blanks had proved to be unsatisfactory. Surprisingly, however, it has been discovered that, starting from a blank made of sintered material, the desired toothing, for instance the tooth forms usually used for highly-stressed toothed gears, such as involutes, cycloids, epicycloids, as used for example on bevel gears, particularly curved-tooth bevel gears, can be manufactured by rolling the toothing into the-sintered metal blank.

Accordingly, viewed from one aspect the invention provides a sintered metal body with at least one toothing which is formed in a blank by metal forming, wherein the final toothing is rolled into the blank.

Viewed from another aspect the invention provides a process for forming a sintered metal body with at least one toothing which is formed in a blank by metal forming, comprising rolling the final toothing into the blank.

The blank may be with or without pretoothing, and said final toothing may be cold rolled or hot rolled into the blank.

An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 shows a body made of a suitable sintered material, cylindrically formed on its outer surface, and to be used to form a sintered metal body with at least one toothing in accordance with the invention; Figure 2 is a plan view of apparatus for rolling a body to form a sintered metal body with at least one toothing in accordance with the invention; Figure 3 is an end elevation of the rolling apparatus; and Figure 4 is a cross-sectional view of a sintered metal body with a toothing, shown on a large scale.

The drawings illustrate the manufacture of cylindrical toothed gears which have, for example, an involute toothing. A blank is made of a suitable sintered material and in this embodiment is of a cylindrical form. The toothing is formed into this cylindrical blank by a cold forming process using the apparatus illustrated in Figures 2 and 3. The blank 1 is accommodated between points which are not shown in the drawings. The longitudinal axis of the blank 1 is, for example, parallel to and in the same plane as the longitudinal axes of the two tools 2 and 3, of which one at least is driven by a motor.

Both tools 2 and 3 are provided with a suitable profile corresponding to the desired toothing. In the constructional form illustrated, tool 2 is stationary, while tool 3 can be moved in direction X or Y respectively. A hydraulic cylinder, not shown in the drawing, moves tool 3, which is supported in a carriage, towards the blank 1 until both tools 2 and 3 penetrate into the blank 1 and the toothing is produced by cold forming. The blank 1 is set into rotation by frictional resistance. This way it is possible to cold form the toothing in one operation.

It has been found that even under a small load (roll pressure), the sintered material flows at the highest possible rate. The effect of the speed of rotation is significantly greater in the case of sintered materials as compared to carbon steels. The reason for this is to be found in the different structure.

During the forming, compression of the material takes place, resulting in a high rolling strength of the tooth flanks and high strength of the tooth bases in the region near the teeth, i.e. particularly at the top of the tooth 4, at the two flanks 5 and 6 and at the base or bottom 7 of the tooth. Because of the space which can be filled up inside such sintered material blanks, it is possible to displace-the material itself for the purpose of forming the toothing into the blank, and it is of course advantageous that hardening occurs in the region of the teeth, particularly for highly-stressed toothed gears.It has been shown, for instance, that the strength of the rolled flanks of the teeth and that of the base or dedendum of toothed pinions made for gear boxes of automobiles in accordance with the invention are fully comparable or conform with those of toothed gears manufactured by conventional toothing processes. Thus the strength limitations applying to gears manufactured by powder-metallurgical processes do not exist in this case.

Further, however, the tooth geometry is practically insignificant in the process described so that the relevant limitation applying to gears manufactured by powdermetallurgical processes is equally no longer existant. Thus not only can toothed gears, for example such as pinions, cylinder gears and bevel gears be manufactured, but also other bodies with toothings, for instance splined shafts, or worm gears of the kind as used for example for plastics extruders.

Thus in conclusion it will be seen that by the described process a sintered metal body with at least one toothing may be produced, which is capable of withstanding high degrees of stress, to which the strength limitations existing in toothed gears manufactured by powder-metallurgical processes for example do not apply, and in which the tooth geometry is practically insignificant.

Claims

1. A sintered metal body with at least one toothing which is formed in a blank by metal forming, wherein the final toothing is rolled into the blank.

2. A sintered metal body as claimed in claim 1, wherein said blank is pre-toothed.

3. A sintered metal body as claimed in claim 1, wherein said blank is not pretoothed.

4. A sintered metal body as claimed in any of claims 1 to 3, wherein said final toothing is cold rolled into said blank.

5. A sintered metal body as claimed in any of claims 1 to 3, wherein said final toothing is hot rolled into said blank.

6. A sintered metal body with at least one toothing substantially as hereinbefore described with reference to the accompanying drawings.

7. A process for forming a sintered metal body with at least one toothing which is formed in a blank by metal forming, comprising rolling the final toothing into the blank.

8. A process as claimed in claim 7, wherein said blank is initially pre-toothed.

9. A process as claimed in claim 7, wherein said blank is initially not pre-toothed.

10. A process for forming a sintered metal body with at least one toothing substantially as hereinbefore described with reference to the accompanying drawings.