US3795129A

US3795129A - Method of forging sintered articles of high density

Info

Publication number: US3795129A
Application number: US00219652A
Authority: US
Inventors: S Goto
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-10-07
Filing date: 1972-01-21
Publication date: 1974-03-05
Anticipated expiration: 1991-03-05
Also published as: JPS518616B2; DE2205493A1; JPS4842905A

Abstract

A method of forging sintered articles of high density characterized in that pre-shaped powdery articles are heated to a temperature of 1120*-1200*C and then are forged by a tool, which is pre-warmed to 80*-120*C and maintained at such pre-warming temperature, at a tool speed of 7-10m/second. The articles thus forged are rapidly separated from the tool through the medium of an ejector provided on the forging machine.

Description

United States Patent Gate Mar. 5, 1974 [54] METHOD OF FORGING SINTERED 2,821,016 H1958 Dickson 72/342 ARTICLES OF H DENSITY 3,645,728 2/1972 Hrinevich, Jr. 29/4205 3,605,245 9 1971 Zapf 29 4205 [76] Inventor: Saburo Goto, 49-Banchl, Shrchrku Kamiumenoki-cho, Kita-ku, Kyoto, Japan Primary ExamznerL0well A. Larson Attorney, Agent, or FirmWenderoth, Lind & Ponack [22] Filed: Jan. 21, 1972 l [2 1 App] No 219,652 ABSTRACT [30] Foreign Application Pri i Data A method of forging sintered articles of high density Oct 7 I971 Ja an M8909 characterized in that pre-shaped powdery articles are p heated to a temperature of ll20l200C and then are forged by a tool, which is pre-warmed to 8|. 72/342,B and maintained at Such pre warming term I peramre, at a too] speed of 7 10m/second The arti [58] Field of ch 29/4205 72/342 cles thus forged are rapidly separated from the tool [56] References Cited through the medium of an ejector provided on the forging machine.

UNITED STATES PATENTS 8/1956 Boegehold et al. 29/4205 3 Claims, 1 Drawing Figure METHOD OF FORGING SINTERED ARTICLES OF HIGH DENSITY BACKGROUND OF THE INVENTION This invention relates to a method of forging whereby the necessity of the precise forged articles of high density can be produced without re-sintering process of moulding.

This invention is characterized in that powdery articles, pre-shaped by a conventional method or by a specific method, are heated to a temperature of ll20 1200C, while a tool is pre-warmed to a temperature of from 80 to 120C and is maintained at this prewarming temperature. The heated articles then are forged in the tool at a speed of 7 lm/second. forging, the finished forged article and the tool are separated rapidly by a separating apparatus provided on the forging machine.

High density is essential for sintered articles such as forged machine parts. In this respect, US. Pat. No. 3,410,683 discloses the method whereby a molded article is heated to a temperature of about 750C 1 100C before it is re-pressed, and the press tool is pre-warmed to a temperature of 150C 350C and is maintained at this pre-warming temperature throughout the repressing operation, in order to keep the recrystallisation conditions of the article during re-processing constant. It appears that the purpose of this method is to obtain precise finished articles by maintaining the temperature of the press tool high and by maintaining the temperature of article low or from 750C to 1 100C so as to reduce the temperature difference between the tool and the material, thereby avoiding temperature drop of the article as far as possible and thus increasing the fluidity of the material. However, the lower temperature of the actually material results in lowering the fluidity and consequently lowering the degree of preciseness of the finished article. Moreover, since the press tool is bulky, it is extremely difficult to maintain its temperature high.

The most important problem raised in hot forging is that during the processing of a highly heated article on the press tool, the surface temperature of the tool rises and the surface of tool is transformed due to thermal fatigue and wear. A finished article, after separation from the tool, is cooled by compulsory cooling but it is difficult to prevent the rising of its temperature due to conduction of heat at the contact surface with the tool during processing. Thus, the best way for forging a powdery substance is to process the heated substance as quickly as possible. Furthermore, a faster tool speed and a shorter processing time improve the flow of the material of a preshaped sintered article, decrease the coefficient of kinetic friction and effect the uniform distribution of pressing force into every part of the finished article, with the result of uniform density. The forging machine primarily used is an oil-pressure forging press of low processing speed (0.6m/second or lower). Presses such as the drop hammer, friction press, etc., work at the medium speed or 2 4m/second, and a forging machine of the upward pressurizing type works at the high speed of 7 lOm/second.

As is obvious from the foregoing, the time during which the tool makes contact with a heated article decreases in inverse proportion to the tool speed. Therefore, when using a forging machine of low speed, the

temperature of the tool must be kept at least as high as 350C, or otherwise the article undergoes a large temperature drop at the area in contact with the tool, with the result of uneven density due to the partial difference in cooling speed. On the other hand, when a forging machine with a high processing speed, such as DYNAPACK, is used, the wear of the tool is large due to the longer time required for separation, even though the operating speed is high (12 l9m/second).

SUMMARY OF THE INVENTION In the present invention, a forging machine having a high processing speed and a shorter tool separation time is used, for example, a forging machine of the KJ H series. This type of forging machine belongs to the group of hammering machines of the upward pressurizing type. It works at a speed of 7 lOm/second and is equipped with a tool separating apparatus such as an ejector. It provides optimum conditions for obtaining the uniformly high density of the powdery article during forging because of the synchronization of the dropping of an upper tool and the rising of a lower tool. In the present invention, a lubricant may be applied to the tool, instead of adding a lubricant to the powdery substance.

BRIEF DESCRIPTION OF THE DRAWINGS The single FIGURE is a microscopic photograph of a finished article forged in accordance with the present invention.

EXAMPLE OF INVENTION The result of test forging carried out by using the above discussed forging machine in accordance with the temperature and other limitations of the process of this invention was as follows:

Forging conditions:

Pre-shaped powder: Electrolytic iron powder Pressed powder density: 6.8g/cm Forging temperature: 1 180C Heating duration: 30 minutes (hydrogen atmosphere) Processing energy: 0.7 ton m Tensile Charpy Density strength Elongation impact value g/cc kg/mm Kgm/cm 7.85 26.24 55.7 30 or more As is obvious from the above test results, forged articles produced according to the present invention exhibit superior physical properties to conventionally forged articles.

What is claimed is:

l. A method for forging a sintered article having a high density, said method comprising:

pre-heating to a temperature of 80-120C the forging tool of a forging machine of the type having an upper element and a lower element movable together in syncronization;

heating a pre-shaped powdery article to a temperature of ll20l200C;

forging said heated pre-shaped powdery article by said pre-heated tool at a forging operating speed of ing is accomplished by a synchronized lowering of said upper element and raising of said lower element.

3. A method as claimed in claim 1, wherein said preshaped powdery article is heated to a temperature of 1 -l200C.

Claims

2. A method as claimed in claim 1, wherein said forging is accomplished by a synchronized lowering of said upper element and raising of said lower element.
3. A method as claimed in claim 1, wherein said preshaped powdery article is heated to a temperature of 1180*-1200*C.