JPS63162852A - Production of forged camshaft - Google Patents

Abstract

PURPOSE:To produce a forged camshaft having high wear resistance and high straightness, by heating and forging a steel material to form stock having cam parts and by subjecting the stock to normalizing, lathing, strain relief annealing and soft-nitriding at a lower temp. than the annealing temp. CONSTITUTION:A soft-nitriding steel material is cut to required dimensions, heated to about 1,200 deg.C and hot forged to form stock having many cam parts and journal parts in the axial direction. The stock is normalized at about 880-960 deg.C optionally after leveling to provide hardness necessary for a product. The journal parts of the stock are lathed and strain relief annealing is carried out at about 600-650 deg.C to relieve stress produced by the lathing. The stock is then finished to prescribed dimensional accuracy by polishing and soft-nitrided at a lower temp. than the annealing temp., e.g., at about 580 deg.C. Thus, a camshaft free from blow holes, requiring no leveling after surface hardening and having high wear resistance is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing a forged camshaft for internal combustion engines such as automobiles.

Conventional Technology Methods for manufacturing this type of camshaft that require high wear resistance include a method in which a cast-molded chill camshaft material is subjected to nitrocarburizing treatment after polishing the cam part, and a method in which a forged camshaft material is subjected to soft nitriding treatment. A known method is to apply carburizing quenching or induction quenching to the steel.

Problems to be Solved by the Invention The cast chill camshaft has a camshaft after the cam part has been polished7)
There is a drawback that the casting cavities are exposed as cavities on the cam profile surface during completion R, and there is a high probability that a material defect will be discovered at that stage and the processed camshaft will be rejected as a defective product.

In this regard, although forged camshafts do not suffer from production losses due to exposure of casting cavities, during the manufacturing process shown in Figure 3, when carburizing and quenching is performed, the bending of the material becomes noticeable. It has the disadvantage of requiring Moreover, this straightening of the bending involves the risk of cracking in the carburized layer.

Also, in the case of induction hardening, quench cracking may occur.

Therefore, from the viewpoint of production efficiency, there has been a need for a rational method for manufacturing a camshaft that is free from hole defects, does not require correction of bends after surface hardening, and has high wear resistance.

Another way to solve the problem is to heat a soft-nitriding steel material that has been cut into the required holes to a temperature suitable for hot forging, and then forge it to create a material that has many cam parts in the axial direction. This material is then normalized to give it the necessary hardness as a product, and after lace processing is applied to this material, strain relief annealing is performed to remove the stress caused by the lace processing. After polishing this material, the strain relief annealing process is performed and then soft nitriding treatment is performed at a low temperature of 1 ρ.

Despite the forged camshaft, even if the heating temperature of strain relief annealing after racing and soft nitriding treatment after polishing is gradually lowered compared to the previous material heating, carburizing and quenching or induction heating after racing Higher wear resistance than hardened camshafts is achieved with high straightness.

Example Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 shows a forged camshaft material 8 for an internal combustion engine, in which there are many cam parts 9 and journal parts 10 in the axial direction.
and has.

In forming the above-mentioned material 8, first, a rod-shaped material of steel for nitrocarburizing is cut into required holes.

The cut material is heated to a temperature suitable for hot forging, for example 120
Heating to 00C, then as shown in the process sequence of Figure 1,
This is hot forged to form a material having a large number of cam portions 9 and journal portions IO in the axial direction.

Note that when the material heating temperature is 1000° C. or less, the forming resistance of the material is high, the mold life is short, and underfilling occurs.

Next, after bending correction 2 is applied to this material as necessary, this material is subjected to normalization processing 3 as shown by heat curve A in Fig. 2 to give the necessary hardness and increase the overall strength of the material. enhance

The heating temperature in this normalizing process is 880°C to 96°C.
The temperature is brought to 0°C, maintained at that temperature for 1 to 2 hours, and then cooled.

Note that if the heating temperature is lower than 88,000°C, the crystal grains will be small and the machinability will be reduced, and if it is higher than 960°C, the crystal grains will be coarse and the strength will be reduced.

Furthermore, the cooling rate during normalizing is generally forced air cooling when the carbon content is low, and slow cooling when the carbon content is high.

Furthermore, lace processing 4 is applied to the journal part 10 etc. of this material.
After this, the material is subjected to strain relief annealing 5, as shown by heat curve B in FIG. 2, in order to remove the stress caused by the lace processing.

This strain relief annealing 5 is applied to the normalizing process 3 performed previously.

Next, the cam part 9 and journal part 10 of this material are polished to finish this forged camshaft material 8 to a predetermined dimensional accuracy.
As shown in Figure 2, the steel is held at a lower temperature than the strain relief annealing 5 for about 3 hours, for example around 580°C, and then subjected to a soft nitriding process 7 in which it is cooled in oil.

Through this soft nitriding treatment 7, a compound layer with high seizure resistance is formed on the outermost surface of this material, which improves the initial fit with the mating sliding contact member when the camshaft is first used, and the compound layer A hard nitride layer is formed underneath, so
The compound layer and the nitrided layer sufficiently increase the wear resistance of the cam portion.

As is clear from Fig. 2, since the heating temperature is lowered in the order of normalizing, strain relief annealing, and tufting, there is very little bending of the material due to heating, and no bending is possible. A straightening process is also no longer necessary.

Effects As described above, according to the present invention, despite the forged camshaft, the heating temperatures for strain relief annealing after racing and soft nitriding treatment after polishing can be gradually lowered compared to the previous material heating. Even if the camshaft is carburized or induction hardened after racing, it has higher wear resistance and higher straightness than a camshaft that has been carburized or induction hardened after racing. Camshafts with high wear resistance can be efficiently produced without the risk of cracks occurring in the carburized layer or the like.

[Brief explanation of the drawing]

1 to 3 show an embodiment of the present invention, and FIG. 1 is a process sequence diagram of a forged camshaft manufacturing method. Figure 2 is a temperature-hour diagram of heat treatment. Figure 3 is a plan view of the forged camshaft material. Figure 4 is a process sequence diagram of the conventional forged camshaft manufacturing method.0 (Explanation of symbols) ■...Hot forging. 3... Normalizing process. 4......S. 5...--Strain relief annealing. 6...Polishing. 7.--Soft-nitriding treatment. Figure 2 Figure 3

Claims (1)

[Claims] A material made of soft-nitriding steel cut to the required size is heated to a temperature suitable for hot forging, then forged to form a material having a large number of cam parts in the axial direction, and then this material is The material was normalized to give it the necessary hardness as a product, and after lace processing was applied to this material, strain relief annealing was performed to remove the stress caused by the lace processing, and then this material was polished. A method for producing a forged camshaft, the method comprising carrying out nitrocarburizing treatment at a temperature lower than the strain relief annealing.