JP2006291233A - Method for heat-treating end surface of cylindrical part of machine component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for heat-treating an end surface in a side having larger wall thickness of a cylindrical part of a machine component having the cylindrical part which possesses different wall thicknesses between one end and the other end, without producing a large difference of shrinking quantity between inner diameters of the one end and the other end of the cylindrical part. <P>SOLUTION: This heat treatment method comprises the steps of: heating the end surface B in the side having smaller wall thickness of the cylindrical part 2 formed in the machine component 1, even when the end surface B does not need to be heat-treated; and then heating the end surface A in the side having larger wall thickness of the cylindrical part 2, which needs to be quenched afterwards. By adopting the method, it becomes possible to inhibit the accuracy for dimensions of holes in the one end and the other end of the cylindrical part 2 from degrading and to secure the required accuracy for the dimension of the holes without machining the cylindrical part 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a heat treatment method for heating an end face of a hollow cylindrical portion of an iron-based mechanical component for the purpose of quenching or the like. More specifically, the present invention relates to a heat treatment method that can suppress a decrease in accuracy of components caused by heat treatment.

  Some machine parts used as power system parts for automobiles have a hollow cylindrical portion. For example, a clutch hub, a pulley, a sprocket, and the like for a transmission have a cylindrical portion (boss portion) provided with a shaft hole. FIG. 3 shows an example of such a machine part. The mechanical component 1 is a clutch hub for a transmission, and includes a cylindrical portion 2 having a through hole (shaft hole) 3 at the center.

  Mechanical parts used in automobile power systems and the like use carbon steel, iron-based sintered alloys, and the like as materials, and are reinforced by forging, casting, or quenching necessary portions after sintering. For example, the machine part 1 in FIG. 3 partially quenches one end face (A surface) of the cylindrical part 2 that needs to be quenched because of the mechanism and structure using this part. Therefore, it is performed using an induction hardening device or a flame hardening device.

  By the way, if the machine part 1 of FIG. 3 is a sintered part manufactured by powder metallurgy, the through hole 3 may be naturally tapered due to sintering. The taper may be provided intentionally, and such a component has a thickness difference between one end side and the other end side of the cylindrical portion 2.

  In the mechanical component 1 shown in FIG. 3, the wall surface t2 on the A surface side of the cylindrical portion 2 is larger than the wall surface t1 on the B surface side because the through hole 3 is tapered. From the viewpoint of function, the thickness of one end side of the cylindrical portion 2 may be made larger than the thickness of the other end side.

  When heat treatment such as quenching is applied to the end surface on the side where the wall thickness is large, in the figure, the A surface, the cylindrical portion 2 contracts on the A surface side, and the straight shaft hole is tapered, and is originally tapered. In the case of a shaft hole, the taper of the hole is further increased and the accuracy of the parts is deteriorated, and machining for dimensional correction may be required after heat treatment.

  For example, when an iron-based sintered part having a cylindrical part (boss part) having an inner diameter of about 50 mm, an outer diameter of about 65 mm, and a total length of about 20 mm is taken as an example, the inner diameter and the B side of the cylindrical part 2 A shrinkage difference of about 0.070 mm in radius (average value) may occur in the inner diameter. In addition, since the part formed with molten steel has a martensitic transformation amount larger than a sintered metal, it is thought that the internal diameter difference which generate | occur | produces by heat processing becomes still larger than said numerical value.

  If the inner diameter of the cylindrical portion has a taper exceeding the allowable range, the inner diameter needs to be corrected. Further, correction may not be possible depending on the shape of the part, and at that time, the defect rate of the product increases. In order to eliminate this inconvenience, it is desired to perform the heat treatment of the end face of the machine part having the cylindrical portion as shown in FIG. 3 while suppressing the shrinkage difference between the one end and the other end of the cylindrical portion. However, there is no prior art that can meet the demand.

For example, as a document describing the induction hardening of a part having a cylindrical part, there is the following Patent Document 1, but in the method disclosed in Patent Document 1, it occurs when one end surface of the cylindrical part is quenched. The above-described deterioration of dimensional accuracy cannot be prevented.
Japanese Patent No. 3257416

  An object of the present invention is to enable heat treatment of the end surface of the cylindrical portion without causing a large difference in the amount of shrinkage between the one end side and the other end side of the cylindrical portion in order to suppress a decrease in accuracy of the component.

  In order to solve the above-mentioned problems, in the present invention, the end surface on the small thickness side of the cylindrical part having a difference in thickness between the one end side and the other end side of the machine part is first heated, and then the thickness of the cylindrical part is increased. A method of heating the end face on the thick side is adopted.

  The machine part to which this method is applied may be any of an iron-based sintered part, a forged part made of carbon steel, or a cast part made of carbon steel. In addition, the problem of deterioration of the hole accuracy of the cylindrical portion due to the heat treatment is remarkable when quenching the end face of the cylindrical portion. Therefore, when the heating for quenching is performed by the method of the present invention, a particularly large effect is obtained. I can expect. When the heat treatment is quenching, the quenching may be performed by either flame quenching or induction quenching. In addition, the method of this invention can be utilized also for heat processing other than hardening.

When heat treatment of either one of the two end faces is necessary, conventionally, only the required end face is heated. On the other hand, in the present invention, the end surface on the side where heat treatment is not required is also heat-treated, and the heat treatment is performed on the end surface on the small thickness side first, and then on the end surface on the thick side.
For example, when it is required to heat-treat only the end face on the thick side of the cylindrical portion, the end face on the small thickness side that does not require heat treatment is also heated in the present invention. When the end surface on the small thickness side is heated first, the cylindrical portion shrinks even on the small thickness side. In addition, when the end surface on the small thickness side is heated first, stress is generated and remains inside the part, and the thick side of the cylindrical portion when the thick end surface is heated by the residual stress The amount of shrinkage can be reduced compared to the case where the small thickness side is not heated. By these actions, the taper of the through hole of the cylindrical portion becomes smaller than the conventional one.

  When the end face on the thick side is heated first, and then the end face on the small thickness side is heated, the shrinkage amount on the small thickness side is smaller than when the end face on the thick side is not heated. Therefore, the effect of suppressing the decrease in accuracy of parts is not sufficiently exhibited. Therefore, the heating of the end face precedes the small thickness side.

  Embodiments of the end face quenching method of the present invention will be described below with reference to FIGS. 1 to 3 of the accompanying drawings. A mechanical component 1 shown in FIG. 1 is a cylindrical component, and a tapered through hole 3 is provided at the center of a cylindrical portion 2. 2 has an outer diameter on one end side of the cylindrical portion 2 larger than an outer diameter on the other end side, and a straight through hole 3 is provided in the cylindrical portion 2. Since the mechanical component 1 of FIG. 3 has already been described, the description thereof is omitted.

  When heat-treating the large-diameter side end surfaces of these mechanical parts 1 formed of metal, that is, the A surface of the cylindrical portion 2, in the present invention, the end surfaces on the small-diameter side of the cylindrical portion 2, that is, the B surface is heated first. Then, the A side is heated.

  If the heating of the A surface is performed after the temperature of the B surface is lowered to normal temperature or near normal temperature, it is easy to ensure work safety. Heat treatment is considered to be often quenched for iron-based sintered parts, forged parts and cast parts made of carbon steel, but when heated to a temperature at which the cylindrical part shrinks, it is not quenched. However, the effect of the present invention can be obtained.

-Example-
In the following, more detailed examples will be described. A machine part 1 having the structure shown in FIG. 3 was manufactured, and after sizing the machine part 1, the end face of the cylindrical portion was quenched. The mechanical component 1 employed in this example is obtained by compression molding a raw material powder having a composition of Fe-4.0Ni-2.0Cu-1.5Mo-0.5C (unit: weight ratio) to an average density of 40%. The sintered part is a sintered part, and the through hole 3 at the center of the cylindrical portion 2 is a tapered hole having a small diameter on the A surface side.

The dimensions of the sintered part 1 shown in FIG. 3 are as follows: A-side inner diameter D ₁ of the through hole 2: φ34 mm, B-side inner diameter D ₂ : φ34.50 mm, outer diameter D ₃ of the cylindrical portion 2: φ59 mm, outer ring 4 has an inner diameter D _{4 of} φ88 mm, an outer diameter D ₅ of the outer ring 4 of 97 mm, and a length L ₁ of the cylindrical portion 2 of 19 mm. These numerical values represent an average value of 10 parts.

  Although quenching may be flame quenching, an induction quenching apparatus was used here. As shown in FIG. 4, the induction hardening procedure places the machine part 1 on the work table 5 with the surface to be hardened facing up. The work table 5 has a rotation mechanism and an elevating mechanism (both not shown), and raises the machine part 1 received at the transfer point to a quenching portion where the high-frequency coil 6 is disposed.

  Thereafter, for uniform heating, the high frequency coil 6 is energized while rotating the machine part 1 together with the work table 5 at an appropriate speed to first heat the B surface. The heating temperature at this time may be lower than the quenching temperature when quenching of the B surface is not required.

  For this quenching, the first quenching part and the second quenching part are prepared and the B side is quenched in the first quenching part, and the A side is quenched in the second quenching part. Although mass productivity can be improved, it is also possible to heat the A surface with a high-frequency coil in which the machine part 1 is inverted on the same work table after the B surface is processed and the B surface is heated.

  Next, with the A surface of the machine part 1 facing up, the A surface is heated to a temperature exceeding 1,000 ° C. by the high-frequency coil 6, and after heating, cooling oil is sprayed from the nozzle 7 onto the component and the A surface is baked. I put it in.

The heating conditions by the high frequency coil 6 are as follows: coil output 40 KW, frequency 130 KH _Z , heating time 1.3 seconds, work rotation speed 1300 rpm, cooling time 10 seconds, and cooling oil temperature 20 to 40 on both the B side and A side. C.

  FIG. 5 shows the inner diameter change (average value of 10 parts) of the machined part 1 thus hardened. In the figure, I indicates the inner diameter before heat treatment, II indicates the inner diameter of Comparative Example 1 in which only the A surface is quenched, and III indicates the inner diameter when processed by the method of the present invention. Line L1 indicates the upper limit of the allowable dimension, and line L2 indicates the lower limit of the allowable dimension. In FIG. 5, “upper” is the inner diameter of the end portion on the A surface side of the cylindrical portion, “middle” is the inner diameter of the longitudinal intermediate portion of the cylindrical portion, and “lower” is the inner diameter of the end portion on the B surface side of the cylindrical portion.

  As can be seen from FIG. 5, according to the method of the present invention, the hole dimensional accuracy of the machine part that was not sufficient even if the sizing process was performed can be kept within the required value by the heating process without performing the machining. This is advantageous in terms of productivity and cost.

  For comparison, FIG. 6 investigates the inner diameter V (average value of 10 parts) of machine parts 1 of the same specification in which the A surface is heated first and the B surface is heated thereafter. FIG. 6 shows the heated inner diameter III of FIG. 5 according to the method of the present invention. The inner diameter V of the part that has previously been heated on the A side is out of the required value because of the inner diameter dimension after quenching, and it is necessary to finish the inner diameter dimension by machining. This demonstrates the effectiveness of heating the B side first.

Sectional drawing which shows an example of the machine component heat-processed by the method of this invention Sectional drawing which shows the other example of the mechanical component heat-processed by the method of this invention Sectional drawing which shows the further another example of the mechanical component heat-processed by the method of this invention Sectional view showing the outline of quenching The figure which shows the hole precision of the sintered machine parts which were quenched by the method of the present invention in comparison with the one that was heated only on one side The figure which compares and compares the hole accuracy of the sintered machine parts quenched by the method of the present invention and the parts in which the heating order of the end faces is reversed from that of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Machine part 2 Cylindrical part 3 Through hole 4 Outer ring 5 Worktable 6 High frequency coil 7 Nozzle

Claims (3)

  An iron-based mechanical component has a hollow cylindrical portion having a different thickness on one end side and the other end side, and a heat treatment method for heating the end surface of the cylindrical portion, wherein the end surface on the smaller thickness side of the cylindrical portion is first And then heating the end face on the thick side of the cylindrical portion. A heat treatment method for the end face of the cylindrical portion of the machine part.   The machine part is an iron-based sintered part, a forged part formed of carbon steel or a cast part formed of carbon steel, and the end surface of the cylindrical portion of the part is heated and quenched. The heat processing method of the cylindrical part end surface of machine parts.   The heat treatment method for a cylindrical part end face of a machine part according to claim 2, wherein the quenching is performed by either flame quenching or induction quenching.

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