JPS6184302A - Manufacture of sintered forged parts - Google Patents

Abstract

PURPOSE:To enable accurate forming and to reduce the degree of wear of coining dies by decarburizing the surface layer of a sintered forged blank by a prescribed extent before coining, coining the blank, and carburizing it. CONSTITUTION:Alloy powder consisting of 2wt% Ni, 0.5wt% Mo and the balance Fe is mixed with 0.2-0.5wt% graphite and a lubricant, and the mixture is press-molded. This molded body is sintered in an atmosphere of an endothermic gas,and the sintered body is hot forged and allowed to cool in the air. The surface layer is decarburized up to about 0.1mm depth, and the resulting decarburized sintered blank is cold coined with coining dies after Bonderizing. The decarburized surface layer is then recarburized, and carburization, hardening and tempering are carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing sintered forged parts, particularly a coining method.

[Conventional technology]

In the production of sintered forged parts, cold coining is sometimes performed for the purpose of improving the precision of rough materials. However,
In the conventional manufacturing of sintered forged parts, in order to avoid a decrease in surface hardness, all heating processes are performed using a protective atmosphere such as endothermic gas (RX gas) to decarburize the surface layer of the raw material. is kept to around 0.14. Therefore, the coining process may not be performed well.

(Problem to be solved by the invention) In coining, since the rough material with a hard surface layer has high deformation resistance, the coining load increases during coining.
There is a problem that mold wear increases.

The sintered and forged raw material obtained by the conventional method has a problem in that sufficient accuracy cannot be obtained even after coining in the case of parts that are heavily coined.

An object of the present invention is to provide a method for manufacturing sintered forged parts that can reduce coining load and mold wear during coining and improve part precision.

[Failure to solve the problem]

The method for producing a sintered forged part of the present invention includes decarburizing a predetermined amount of the surface layer of the sintered forged raw material before coining, for example, during heating or normalizing the sintered raw material, and then coining. Special decarburization, which is characterized by carrying out carburizing treatment after that, is aimed at reducing the deformation resistance of the raw material during coining and increasing the deformation of the raw material, and was developed by the inventor of the present invention. For example, the third diagram shows the relationship between the load during coining and the ironing allowance.
As can be seen from the graph in the figure, when coining, conventionally, 1
What used to require a load of 75 tons can now be reduced to just 100 tons by decarburizing, and the spring load has also been significantly reduced from the conventional 0.09 nm to 0'5 m, resulting in reduced dimensions. It is also possible to lower the range of fluctuations.

The depth of decarburization may be determined depending on the required coining amount, but is usually preferably 0.1 to 0.5 fl.

The carburizing treatment performed after coining is to ensure the required strength of the surface portion of the sintered forged part, and can be performed by solid carburizing, gas carburizing, liquid carburizing, or the like. The amount of carburization may be arbitrarily selected depending on the purpose.

The material of the sintered alloy used in the present invention is not particularly limited, but alloys developed for sintering and forging are preferable, and the component composition is, for example, Cr""i"s"0.7 in weight ratio.
% and balance Fe caranal composition weight ratio Ni2%, Mo
Examples include a composition consisting of 0.5% and the balance Fe.

[Effect]

By decarburizing the surface layer of the sintered forged rough material during heating and/or normalizing, the deformation resistance of the rough material surface during coining is lowered, the deformability is increased, the coining load is reduced, and the coining All dimensional accuracy can be easily obtained. Then, by carburizing the surface layer of the rough material after coining, the required strength of the surface portion can be obtained.

〔Example〕

The present invention will be explained by way of an example.

Example 0.2 to 0.5% by weight of Gr (graphite) and 0.8% by weight of zinc stearate as a lubricant were added and mixed into an alloy powder consisting of 2% Ni, MOo, and 5% balance Fe by weight ratio. , and was press-molded into a molded body having a density of 6.5 t/crA.

Next, this compact was sintered by holding it at a temperature of 1150°C for 20 minutes in an endothermic gas atmosphere, then hot forged at a pressure of 10t/-d at a temperature of 1050°C, and then left to cool in the atmosphere. The surface layer was decarburized to a depth of about 0.1 m. Next, normalization was performed in the air to decarburize the surface layer to a depth of about 0.4 cm. This decarburized sintered rough material is bonded to a temporary coining mold to produce 4t/! Cold coining was carried out at a pressure of .

In this way, a sintered forged gear rough material having a highly accurate gear/parking lock 1 as shown in FIG. 1 was obtained.

Next, with the teeth of this gear/parking lock 1 as a reference, a second larger tooth is integrally formed adjacent to the tooth by machining such as gear cutting, as shown in FIG. A high-precision stepped gear in which two large and small teeth are close to each other was obtained. In the figure, 2 is gear counter driven.

Next, this gear was carburized in an endothermic gas at a temperature of 930° C. for 5 hours to recarburize the decarburized surface layer, and then carburized and quenched and tempered.

When manufacturing gear parts that have two or more tooth profiles that are close to each other, conventionally the parts that have two or more tooth profiles were manufactured separately by machining, and then welded together using electron beam welding etc. However, according to the method of the present invention, as described above, at least the teeth with a small outer diameter can be integrally formed with high precision by sinter forging, which simplifies the process, reduces costs, and improves accuracy and strength. It is possible to easily obtain a gear component having two large and small tooth portions that are close to each other and have excellent properties.

Therefore, there is no longer a need for a long mechanical process such as finishing a joint between two tooth-shaped parts with high precision by machining, or a cleaning process for the joint. Furthermore, conventionally, the penetration depth had to be destructively inspected to confirm the quality of electron beam welding, which increased costs, but this inspection is no longer necessary, and costs are reduced.

〔Effect of the invention〕

As described above, in the method for manufacturing sintered forged parts of the present invention, the surface layer of the sintered forged rough material is decarburized by the amount necessary for coining, and then coined, so that the deformation resistance during processing is reduced. As a result, coining can be done with low load, the amount of springback is also reduced, and dimensional fluctuations can be reduced.
Can be formed with high precision. Furthermore, since a low load is required, the degree of die wear during coining can also be reduced.

Furthermore, even parts that are difficult to mold integrally with high precision by machining, such as stepped gears having closely spaced teeth, can be manufactured easily, integrally, and with high precision.

Furthermore, in the method of the present invention, after hot forging, it is allowed to cool in the air,
Since decarburization can be achieved by normalizing in air, there is no need for a new process, and the conventional cooling and normalizing processes can be performed in air or a similar atmosphere. good. As a result, although nitrogen gas or the like has conventionally been used as a protective atmosphere in the heating process, this is no longer necessary and the process can be simplified.

[Brief explanation of the drawing]

FIG. 1(a) is a sectional view of a sintered forged gear rough material according to an embodiment of the present invention, FIG. 1(b) is a plan view of the same, and FIG. 2 is a sintered forged stage of an embodiment of the present invention. The cross-sectional view of the attached gear and Figure 3 are graphs showing the relationship between the load during coining and the ironing allowance. In the diagram, 1...Gear parking lock 2...Gear fist counter drift patent applicant Toyota Motor Corporation @, Shin 2

Claims (1)

[Claims] A method for manufacturing sintered forged parts, which comprises decarburizing a predetermined amount of the surface layer of a sintered forged raw material before coining, performing coining, and then carburizing the material.