JPH02194125A - Method for preventing deformation of crank shaft - Google Patents

Abstract

PURPOSE:To prevent the deformation of a crank shaft at the time of hardening and to prevent the generation of defective articles by applying the elongation in the direction reverse from the direction where the elongation is generated by heating to the crank shaft by plastic deformation and rapidly cooling the crank shaft from the state of pressurizing and deforming the part where the yield point is lowered by red heat. CONSTITUTION:The elongation generated at the time of heating of the crank shaft is obtd. by plastically deforming the central part at the end face of the crank shaft by pressurizing this part in the direction toward the opposite end face as shown by a code F. The point where the yield point is lowered by the red heat and where the same state as the state at the time of hardening is obtainable is deformed by the pressurization in the direction toward the opposite end face as shown by a code F1. The crank shaft is rapidly cooled in this state. The crank shaft is deformed in the state in which the yield point is lowered than at the cold time and by the quantity corresponding to the elongation by the martensite expansion which takes place at the time of heating by the previous plastic deformation and, therefore, the correction of the displacement by the plastic deformation is executed and the prescribed shape as the crank shaft is eventually restored.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for preventing deformation of a crankshaft.

(Prior Art) As is well known, the crankshaft 1 of an automobile engine
As shown in the third diagram, pressure is applied to the joint boundary IC between the crank arm IA and the connecting rod IB to create a concave deformation.

The so-called fillet ID is constructed and the elongation occurs in that area.

and to provide resistance to compressive loads.

After the above-described fillet construction, the processed portion is subjected to surface treatment, for example, induction hardening.

(Problem to be Solved by the Invention) By the way, when the fillet construction part is heated during the above-mentioned quenching, this part becomes like the symbol A in FIG.
A phenomenon occurs in which the material warps in the direction shown by , that is, in the direction of expansion.

If the material is bent in the above-mentioned direction due to heating and then rapidly cooled, the bend caused by expansion of martensite due to quenching heating will be slightly corrected by shrinking, but it will not completely return to its original shape. This can result in the production of a defective crankshaft.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method that can prevent deformation during hardening in view of the above-mentioned problems that occur during hardening of a crankshaft.

(Means for Solving the Problems) In order to achieve this object, the present invention provides a method for hardening a crankshaft that has been subjected to fillet processing that causes concave deformation at the joint boundary between the crank arm and the connecting rod. In this case, an elongation in the opposite direction to that caused by the heating performed on the crankshaft is applied in advance by plastic deformation in the axial direction, and then only the portion whose yield point has decreased due to red heat is deformed by applying pressure from the axial direction. The present invention proposes to cancel the previously deformed displacement by expanding the martensite and lowering the yield point by rapidly cooling it from this state.

(Function) According to the present invention, in the plastically deformed part, martensite expansion, which occurs in the opposite direction to the deformation direction, is easily performed by lowering the yield point.

The displacement is offset and the original state is restored.

(Embodiment) Hereinafter, details of an embodiment of the present invention will be explained with reference to FIGS. 1 and 2.

FIG. 1 is a front view showing the overall structure of a crankshaft to which a deformation prevention method according to an embodiment of the present invention is applied.

That is, in this embodiment, hardening is performed by the following procedure.

First, in the above-mentioned crankshaft, the elongation that occurs during heating is measured by applying pressure at the center of the end face of the crankshaft in the direction toward the opposite end face, as shown by the symbol F in FIG. Obtained by plastic deformation.

Next, by heating, so-called red heat that produces the same state as during quenching, the location where the yield point has decreased as shown in FIG. Deformed by applying pressure. The red-hot temperature mentioned above is
It is considered to be above the recrystallization temperature of the tissue. Therefore, the deformation at this point is such that the yield point is as shown in Figure 2.
Since it is considerably lower than that when cold, specifically about 20% of that when cold, deformation due to recrystallization can easily occur, and this can also relieve strain. Facilitated.

On the other hand, rapid cooling is performed in such a deformed state.

In other words, by performing such rapid cooling, the yield point is lower than when it is cold, and because the plastic deformation has already caused an amount of displacement corresponding to the elongation due to martensite expansion that occurs during heating. The displacement caused by the plastic deformation due to martensite expansion is corrected, and as a result, the crankshaft returns to its predetermined shape.

(Effects of the Invention) According to the present invention, the elongation due to the expansion of martensite that occurs during quenching is caused in advance by plastic deformation, so that the elongation due to the expansion of martensite due to the lowering of the yield point during heating is caused. Elongation can be easily corrected, and as a result, the crankshaft can be set to its original shape as desired.

By preventing deformation due to heat treatment, it is possible to prevent the occurrence of defective crankshafts.

[Brief explanation of the drawing]

FIG. 1 is a front view showing the overall structure of a crankshaft to which the hardening method according to an embodiment of the present invention is applied; FIG. 2 is a diagram illustrating the influence of temperature on the yield point of the material of the crankshaft; Figure 3 is a front view showing the main parts of a crankshaft, which is one of the members to be heat treated, and Figure 4 is a partial front view for explaining the problems that occur when hardening the crankshaft shown in Figure 3. . l... Crankshaft, IA... Crank arm, 1 [1... Connecting portion of connecting rod, IC... Connection boundary, 10... Fillet.

Claims (1)

[Claims] A method for hardening a crankshaft that has been subjected to fillet processing to cause concave deformation at the joint boundary between a crank arm and a connecting portion of a connecting rod, the method comprising: heating the crankshaft; Elongation in the opposite direction to the direction in which it occurs is applied in advance by plastic deformation in the axial direction, and then only the portion where the yield point has decreased due to red heat is deformed by applying pressure from the axial direction, and from this state, by rapid cooling, martensite expansion and A method for preventing deformation of a crankshaft, characterized in that the pre-deformed displacement is offset by lowering the yield point.