JPS63203226A - Manufacture of high strength crank shaft - Google Patents

Abstract

PURPOSE:To remove the strain due to a surface hardening and to obtain the crank shaft excellent in the strength and profitability by high temp. tempering a pin part and journal part excluding at least before and behind after surface hardening the pin part and journal part including a fillet part by working the structural steel in a limited carbon amt. in an intermediate product. CONSTITUTION:The roughing product with the structural carbon steel of 0.4-0.6wt.% carbon as the blank and cooled after its hot forging is made an intermediate product by machining. All of the pin part 1, journal part 2 and fillet parts 3, 4 of the intermediate product are subjected to surface hardening by a high frequency heating device to obtain surface hardening layers 5, 5.... All of the pin part 1, journal part 2 and each fillet part 3, 4 excluding the pins 1P, 4P at the front and rear ends and journals 1J-5J are subjected to tempering at high temp. by said device. Then, the journals 2J, 4J are supported by a supporter 7, a load P is given to the intermediate journal 3J to perform the correction in bending. After grinding a crank shaft is finished by subjecting all of the pin part 1, journal part 2 and fillet parts 3, 4 to a shot peening.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a crankshaft 7F having excellent strength characteristics.

(Prior Art) Crankshafts are subject to bending stress, screw stress, etc. due to explosive force and inertia force, and therefore are required to be strong enough to withstand these stresses. The parts of the crankshaft that are subjected to bending stress and torsional stress are the pin part and the journal part, and in particular, the stress concentrates on the fillet part, which is the connection part between the pin part and journal part and the crank arm part. An important issue is how to increase the strength of the pin portion and journal portion including the fillet portion.

Conventionally, various measures have been taken to strengthen the pin section and journal section including the fillet section.
-Measures to increase the strength of the base material by increasing the hardness (use of Mo steel, etc.); ■Measures to apply compressive residual stress and work harden by applying roll processing to the fillet portion; ■Measures to apply compressive residual stress and work harden only to the fillet portion. , or surface hardening of the pin part and journal part including the fillet part (Japanese Unexamined Patent Publication No. 4
8-101311, Japanese Patent Publication No. 59-69516), ■ Countermeasures for applying 7-yot peening to the pin portion or its fillet portion (Japanese Patent Application Laid-open No. 58-223562, Japanese Patent Publication No. 61-16573), ■ Measures to apply soft nitriding treatment to the pin part or journal part including the fillet part (Japanese Unexamined Patent Publication No. 193478/1983, Japanese Patent Application No. 61-3
No. 4865) etc. have been implemented.

(Problems to be Solved by the Invention) However, the above conventional countermeasures have the following problems.

In other words, if the material is upgraded (■,
As the hardness increases, machinability deteriorates, which, combined with an increase in material cost, may lead to a significant increase in manufacturing costs. In addition, unless the entire body is heat treated (quenching, tempering), no improvement in strength can be expected, which leads to an increase in heat treatment deformation, which requires a large number of man-hours to correct, further increasing the economic burden. be.

In addition, if the fillet part is rolled (■,
Since the brocade is formed in the fillet portion, this groove acts as a notch, leading to a decrease in strength, especially fatigue strength, and there is a problem in that a substantial improvement in strength cannot be expected.

In addition, if surface hardening is applied to the fillet part, or the pin part and journal part including the fillet part,
As a result of a portion of the surface hardening layer being removed by the subsequent grinding process, the compressive residual stress that has been generated is released, and there is a problem in that the strength cannot be improved as desired.

In addition, distortion (deformation) occurs due to surface hardening, and in order to remove this distortion, the crankshaft is usually supported on both sides in the subsequent process, and a mechanical load is applied to it to remove the distortion (correction). However, during this straightening, tensile stress acts on the hardened surface layer, and as a result, the compressive residual stress is canceled out, causing the same problem that the strength cannot be improved as expected. Furthermore, cracks may occur in the hardened surface layer during the straightening process, and in general, it has been difficult to achieve the desired effect with this surface hardening measure.

In addition, in the above-mentioned Japanese Patent Application Laid-open No. 48-101311, the area other than the fillet part is processed to be larger than the finished dimension, and after the fillet part is quenched, this excess thickness is removed to leave a surface hardened layer. On the other hand, Japanese Unexamined Patent Publication No. 59-69516 discloses a method of changing the depth of the hardened surface layer in the circumferential direction to prevent distortion from occurring. In the case of the latter, the pin part and the journal part become unheated parts, resulting in insufficient strength in these parts, while in the case of the latter, it is difficult to obtain the desired deviation hardened layer pattern, and both have the problem of poor reliability. .

In addition, when applying shot peening ■ and when applying soft nitriding treatment ■, the effectiveness of both depends on the strength of the base material, so it is recommended to increase the hardness in advance by surface hardening or to upgrade the material. Therefore, the same problem as mentioned above will occur.

The present invention was made in order to solve the various problems in the above-mentioned prior art, and an object of the present invention is to provide a method for manufacturing a crankshaft that is excellent in strength, economy, and reliability.

(Means for Solving the Problems) Therefore, the present invention uses structural carbon steel with a carbon content of 0.4 to α6wt as a material, first obtains an intermediate product by hot forging and machining, and then fillets it. Surface hardening of all the pin parts and journal parts, including the front and rear ends, followed by high-temperature tempering of the pin parts and journal parts, excluding at least the front and rear ends, followed by grinding and shot peening. The main point is that the parts and journal parts were finished.

In the present invention, the carbon content of the structural carbon steel material is set to (14 to
Q, □wt was selected because if it is less than Q, Jwt, the desired strength cannot be obtained, and if it exceeds Q, 5wt%, there is a risk of unnecessarily reducing machinability and causing quench cracking during surface hardening. For some reason.

In addition, in the present invention, after hot forging, the forged product is subjected to machining without heat refining, but if the carbon content is within the above range, the hardness of the forged product in the air-cooled state after hot forging is H ma 180~180. 270
This is only a small amount and does not impair later machinability.

In addition, in the present invention, the surface hardness after high temperature tempering is
It is desirable that HY be about 300 to 500. this is,
This is because if the hardness is too low, no improvement in strength can be expected by subsequent shot peening, while if the hardness is high, subsequent correction becomes difficult.

Furthermore, when carrying out the above-mentioned shot peening, it is desirable to select 7-yoat grains that are harder than the surface hardness of the hardened surface layer, so that the peening effect can be produced effectively in a short period of time.

(Function) In the method for manufacturing a crankshaft having the above configuration, all of the pin portions and journal portions including the fillet portions are surface hardened, and then the pin portions and journal portions excluding at least the front and rear ends are tempered at a high temperature. As a result, the plastic deformability of the axially intermediate portion is increased, and correction can be easily performed. In addition, final shot peening was applied to compensate for the strength loss caused by the high-temperature tempering and subsequent grinding, ensuring a high level of strength even though the material is made of low-grade structural carbon steel. become able to. Moreover, the use of said low-grade materials and the manufacturing process without special processing and heat treatments makes it possible to achieve manufacturing simplification.

(Example) Hereinafter, an example of the present invention will be described based on the accompanying drawings.

Example JIS structural carbon steel 545C is used as a material, first about 125
The product was hot forged at a temperature of 0°C, air cooled to room temperature after forging to obtain a rough product with a hardness of approximately Hv 180, and then machined to produce a 4-cylinder crankshaft intermediate product as shown in Figure 1. Obtained. In Fig. 1, l is a pin part, 2 is a journal part,
3 represents a pin side fillet portion, and 4 represents a journal side fillet portion. The pin part 1 and journal part 2 are collectively represented, and the pin part 1 has four pins IP, 2P, 3 arranged from the front end to the rear end.
F, 4P, while the journal part 2 has five journals IJ l arranged from the front end to the rear end.
2J, I, 3J, 4J, and 5J, respectively.

Next, for the above intermediate product, all of its pin portion 11 journal portion 2 and each fillet portion 3, 4 are heated at a frequency of 10
The surface is hardened using a KHz high frequency heating device to obtain a surface hardened layer 5.5 with a surface hardness of approximately H mallo 50, followed by pins IF, 4P and journals IJ, 5 at the front and rear ends.
All pin portions 1, journal portions 2, and fillet portions 3 and 4 except for J were heated to about 630 mm by the high-frequency heating device.
C. to obtain hardened surface layers 6, 6... having a surface hardness of approximately HV440.

Next, the surface-hardened and high-temperature tempered intermediate product was subjected to a straightening device to straighten the curvature. Correction is the second
As shown in C, the journal 2 is one inch inside from the front and rear ends.
A three-point bending method was adopted in which J, 4J, were supported by supports 7, 7, and a load P was applied to the intermediate journal 3J.

After that, grinding is performed to obtain a pin diameter of 45 mm, a journal diameter of 50 mm, and a fillet R2O.Finally, all the pin parts 1 and journal parts 2 are made of shot grains with a grain size of 0.6 cm and a hardness of about HV700. and each fillet part 3
．． 4 was subjected to shot peening by blasting it through an air nozzle for 20 seconds, and the completed crankshaft was subjected to a fatigue test and a residual stress measurement test, which will be described later.
“Comparative Example 1 A crankshaft intermediate product was obtained by the same method as in the above example, and surface hardening was applied to only one cylinder portion (one pin portion and journal fillet portions at both ends) under the same conditions as in the above example. After that, high-temperature tempering and straightening were omitted, and a comparative product 1 was obtained that was finished only by grinding (short blasting was also omitted), and this was subjected to the fatigue test described below.

Comparative Example 2 Comparative Example 2 was obtained by adding straightening before grinding to the method of Comparative Example 1 (shot blasting was omitted) and subjected to the fatigue test and residual stress measurement test described below.

Comparative Example 3 A flank shaft intermediate product was obtained by the same method as in the above example, and surface hardening was performed only on the pin portion 1 and journal portion 2 excluding the fillet portions 3 and 4, and then high temperature quenching was performed in the same manner as in the example. Comparative product 3 was obtained by restoring, straightening, grinding, and shot blasting, and was subjected to the fatigue test described below.

Comparative Example 4 A 2-rank shaft intermediate product was obtained by the same method as in the above example, and then finished only by grinding to obtain a comparative product 4, which was subjected to the fatigue test described below.

Hereinafter, the products of the present invention obtained in the above Examples and Comparative 1
The test results for comparative products 1 to 4 obtained in steps 1 to 4 will be described below.

The fatigue test was carried out by extracting one cylinder, applying a double vibration bending moment to the pin part l using a resonance fatigue testing machine, and determining the double vibration bending fatigue limit of the pin side fillet part 3. FIG. 3 shows the test results, and it was revealed that the product of the present invention had a fatigue strength that was 15fi superior to the comparative product. In other words, Comparative product 1 was not tempered at high temperatures and straightened from the bent edges, and considering that the straightening process cannot be avoided in the manufacture of crankshafts, it is equivalent to or better than this. The method of the present invention capable of obtaining a crankshaft having fatigue resistance includes:
This method can be said to be extremely useful in practice.

This is also clear from the fact that compared to Comparative Product 1, the fatigue strength of Comparative Product 2, which was simply straightened, was significantly lower. The fatigue strength of Comparative Product 3, in which surface hardening of the fillet portion was omitted, and Comparative Product 4, in which no special surface treatment was performed, was extremely low, and the superiority of the strength of the product of the present invention can also be seen in comparison with these.

On the other hand, the residual stress measurement test was conducted by measuring the residual stress distribution in the fillet portion using X-ray diffraction. Figure 4 shows
The results are shown below. Comparative product 2, which has undergone straightening and grinding, has lower compressive residual stress on the surface side, whereas the product of the present invention, which has undergone final shot blasting, has high compression even on the surface side. It is assumed that this difference is the difference in fatigue strength.

In the above embodiment, an example of application to a four-cylinder crankshaft was shown, but the present invention is not limited to the number of cylinders, and can of course be applied to a crankshaft with a larger number of cylinders. Further, the present invention is not limited to the shape of the fillet, and can also be applied to a fillet portion that has been subjected to groove processing, for example.

Further, in the above embodiment, all of the pin portion, journal portion, and fillet portion except the rear end of the front cover were subjected to high-temperature annealing, but instead of this.

In particular, high-temperature tempering may be applied only to a portion that requires straightening.

(Effects of the Invention) As described above in detail, the method for manufacturing a high-strength crankshaft according to the present invention includes surface hardening all of the pin portions and journal portions including the fillet portions, and then at least the (e) Since the pin portion and the journal portion except for the rear end were tempered at a high temperature, it was possible to easily remove distortion caused by surface hardening. In addition, since the final shot peening was applied to finish the product, it was possible to reduce costs and improve manufacturability even though low-grade materials were used, resulting in an economical effect.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a crankshaft obtained by the manufacturing method of the present invention, Figure 2 is an explanatory diagram showing the straightening process of the crankshaft, and Figure 3 is a diagram showing the fatigue characteristics of the crankshaft of the present invention and a comparative product. FIG. 4 is a graph showing the residual stress distribution of the present crankshaft in comparison with a comparative material. l...Pin part 2...Journal part 3.4-...Fillet part Patent applicant Toyota Motor Corporation 23 Illustration Esu KL number, (times) Fang 4 illustration

Claims (1)

[Claims] (1) Using structural carbon steel with a carbon content of 0.4 to 0.6 wt% as a material, first obtain an intermediate product by hot forging and machining, then surface all the pin parts and journal parts including the fillet part. The pin portion and the journal portion are hardened, and then the pin portion and the journal portion except at least the front and rear ends are tempered at a high temperature, and then ground and shot peened are further applied to finish the pin portion and the journal portion. A method for manufacturing high-strength crankshafts.