JP2006009118A - Method for producing iron-based sintered mechanical component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate the degradation of production yield rate the deterioration of productivity due to a resizing process by providing a method for producing an iron-based sintered hanical component by which the deterioration of the dimensional precision is suppressedd by offsetting the influence to the dimensional precision with local heating. <P>SOLUTION: The inner diameter hole 3 in the iron-based sintered mechanical component 10 obtained by sintering is corrected into a reverse-tapered hole having the larger inner diameter at the sticking-out part in the diameter direction, that is, at the tooth part 2 side and thereafter, a high frequency-hardening and a tempering to the tooth part 2 are applied so as to approach to the straight-shape to the inner diameter hole 3 after heat-treatment by utilizing the difference of shrinkage amount at each part in the axial direction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  This invention is an iron-based sintered machine component having a toothed portion and a radial protruding portion such as a flaw strengthened by induction hardening on the outer periphery of one end side of a cylindrical shaft portion with high accuracy without increasing the correction process. The present invention relates to a method for manufacturing iron-based sintered machine parts that can be manufactured.

  Typical examples of the iron-based sintered machine parts mentioned above include sintered sprockets and sintered gears having a boss portion. These sintered sprockets and sintered gears are subjected to dimensional correction by sizing after sintering, and then induction hardening and tempering of teeth on the outer periphery of one end are performed.

  The dimension correction is performed by a method of squeezing the inner diameter hole with a straight core. An example of a cross section of the iron-based sintered machine part 10 after the dimension correction is shown in FIG.

  An iron-based sintered machine component 10 shown in the figure is a sintered sprocket or sintered gear, and has a tooth portion 2 on one outer periphery of a boss portion (cylindrical shaft portion) 1, and the calibrated inner diameter hole 3 is straight. It is a hole.

  The iron-based sintered machine component 10 performs heat treatment for strengthening the tooth portion 2 after dimensional correction, that is, induction hardening and tempering. The heating by the quenching and tempering is performed only for the tooth portion 2. Due to this local heating, a local dimensional change occurs in the iron-based sintered machine part 10 after the heat treatment (the heated portion shrinks), and as shown in FIG. I will.

  Due to this dimensional change, the required dimensional accuracy may not be satisfied, and the manufacturing yield (non-defective product rate) deteriorates. In addition, if the dimensions after heat treatment deviate from the required accuracy, re-sizing is performed after heat treatment to reduce defective products, but if this method is used, productivity will deteriorate and cost will be affected. .

In Patent Document 1 below, in order to enable stable correction of iron-based sintered machine parts, a plurality of protrusions are provided on the inner surface of a die used for sizing and the outer surface of a core rod, and the object to be corrected is ironed by the protrusions. However, this method cannot be a solution to the above problem.
JP-A-8-215756

  The present invention provides a method for manufacturing an iron-based sintered machine part in which the influence on the dimensional accuracy due to local heating is offset and the deterioration of the dimensional accuracy of the inner diameter hole is suppressed, and the manufacturing yield is deteriorated and resizing is performed. The problem is to eliminate the deterioration of productivity caused by

  In order to solve the above-mentioned problems, in the present invention, one end of the cylindrical shaft portion is subjected to a step of mixing raw material powder, a step of compacting the mixed raw material powder to obtain a molded body, and a step of sintering the molded body. After producing an iron-based sintered machine component having a radially protruding portion on the outer periphery, correcting the inner diameter hole of the iron-based sintered machine component into a tapered hole having a larger inner diameter on the side having the protruding portion; and Provided is a method for manufacturing an iron-based sintered machine part that undergoes induction hardening and tempering of a radially protruding portion.

  The correction of the inner diameter hole can be performed by machining, but correction by sizing is efficient and preferable.

  Typical iron-based sintered machine parts include sintered sprockets and sintered gears having teeth on the outer periphery of one end of the boss. These parts are often mass-produced, and a particularly great effect can be expected when the present invention is applied to the mass-produced products. In the sintered sprocket and the sintered gear, the inner diameter hole of the boss portion is corrected to a tapered hole, and then the induction hardening and tempering of the tooth portion are performed.

  In this invention, the inner diameter hole of the iron-based sintered machine part is corrected to a tapered hole having a larger diameter on the side where the dimensional change is caused by the heat treatment, and the dimensional shrinkage due to the heat treatment is absorbed by the difference in the hole diameter of the tapered hole. . Therefore, the inner diameter hole after the heat treatment becomes almost straight, and the dimensional accuracy of the hole is improved and the manufacturing yield is improved. Further, the improvement in the dimensional accuracy of the inner diameter hole eliminates the need for resizing after the heat treatment, thereby improving the productivity.

  Embodiments of the present invention will be described below with reference to FIGS. 1 to 7 of the accompanying drawings. Reference numeral 10 in FIG. 1 denotes an iron-based sintered machine component such as a sintered sprocket or a sintered gear having a tooth portion 2 on one end side outer periphery of the boss portion 1. The iron-based sintered machine part 10 is manufactured through a process of mixing raw material powder, a process of compacting the mixed raw material powder to obtain a molded body, and a process of sintering the molded body.

  The inner diameter hole 3 of the iron-based sintered machine part 10 is a straight hole when the sintering is completed. Therefore, the inner diameter hole 3 is corrected to a tapered hole as shown in FIG. 1 (a) in which the side where the tooth portion 2 is located has a larger diameter (the taper gradient is exaggerated).

  Hole correction is performed by sizing because productivity is poor in machining. The sintered iron-based sintered machine part 10 is set on a die (not shown), and in this state, a core rod having a tapered outer periphery is press-fitted into the inner diameter hole 3, and the hole surface is squeezed with the core rod to obtain a straight hole. Is changed to a tapered hole.

  The iron-based sintered machine part 10 thus corrected is subjected to heat treatment to induction-harden and temper the tooth portion 2. Induction hardening is performed using a high-frequency induction heating apparatus 20 as shown in FIG. The illustrated high-frequency induction heating device 20 is a combination of a high-frequency induction heating coil 21 and an annular cooling jacket 22 having a coolant injection hole 22a. As shown in FIG. The iron-based sintering machine component 10 supported by the work table 23 is lifted to enter the inside of the high-frequency induction heating device 20, and the high-frequency induction heating coil 21 is energized while rotating the iron-based sintering machine component 10. The tooth part 2 is heated until it reaches a predetermined temperature. Next, cooling liquid is injected from the injection hole 22a of the cooling jacket 22 to cool the tooth portion 2 at an appropriate speed until the temperature reaches a predetermined temperature, and the quenching is completed.

  Thereafter, the iron-based sintered machine part 10 is conveyed to a subsequent process and tempered. The tempering can be performed by an in-furnace tempering method in which a part is put in a furnace and heated, but it is preferable to perform the tempering by an induction tempering method that can achieve a line of equipment. In the induction tempering, a part supported by a work table is entered inside a low frequency induction heating coil, and the target part is induction heated while rotating the part. The cooling after heating in this induction tempering may be air cooling.

  When the above heat treatment is performed, the inner diameter hole 3 corrected so as to have a taper gradient by sizing becomes almost straight as shown in FIG. 1B, and the dimensional accuracy of the hole is improved and the production yield is improved. Become. For this reason, re-sizing after heat treatment becomes unnecessary.

-Example-
In order to evaluate the effect of the present invention, the sintered sprocket of FIG. 4 formed of an iron-based sintered alloy having a composition of 2 wt% Cu-0.8 wt% C-residual Fe was manufactured by the method of the present invention.

The design dimensions of this sintered sprocket having a tooth portion 2 on one end outer periphery of the boss portion 1 and having five ribs 4 provided at a constant pitch on the inner surface of the inner diameter hole 3 are a tooth tip diameter: 127 mm, a tooth bottom Diameter: 116 mm, boss part diameter: 87 mm, large diameter part diameter d ₂ of the inner diameter hole 13: 80 mm, small diameter part diameter d ₁ : 54 mm, full length (L in FIG. 5): 20 mm, tooth thickness (t in FIG. 5) : 9 mm, number of teeth: 42. The molding density of the boss part 1 is 6.95 g / cm ³ , and the molding density of the tooth part 2 and the rib 4 is 7.0 g / cm ³ .

  The sintered sprocket was sized with a tapered core after sintering to correct the inner diameter hole 3 into a tapered hole. As the taper core, the outer diameter change amount per 10 mm in length was set to 0.070 mm for the small diameter portion molding portion of the inner diameter hole and 0.074 mm for the large diameter portion molding portion. The size of the taper per 10 mm length was determined by determining the amount of dimensional change due to high-frequency heat treatment from the average value of 30 pieces.

  The teeth 2 of the sintered sprocket after correction were quenched using a high frequency induction heating device, and then induction tempering was further performed.

  The dimensional change of each axial portion of the small diameter portion and large diameter portion of the inner diameter hole of the sintered sprocket thus obtained was examined. FIG. 5 is an explanatory diagram of the measurement position. The ridge surface (end surface of the ridge with teeth formed on the outer periphery) 5 is the starting point of height 0, and the position 2 mm away from this in the axial direction is 2 mm from the ridge surface, and the position 4 mm away from the ridge surface The dimensional change of each part in the axial direction with a height of 4 mm was measured at intervals of 2 mm from the flange surface 5 to a position of height 18 mm.

  The results are shown in FIGS. 6 and 7 are data on the average number of 30 samples, where A is the dimensional change of the inner diameter hole of the sintered body before correction, B is the dimensional change of the taper core used for correction, and C is the value after correction. The dimensional change of the inner diameter hole, D, shows the dimensional change of the inner diameter hole after the hole correction and the tooth part heat treatment. The dimensional difference at the same measurement point of B and C is due to the spring back after sizing.

  The dimensional standard of the inner diameter hole in this case is a small diameter portion: φ54 + 0.06 / −0 and a large diameter portion: φ80 ± 0.04, and the range is shown by vertical thick lines in FIGS. As can be seen from these figures, the inner diameter hole after the heat treatment is almost straight and is within the standard size.

  In the conventional method of correcting the inner diameter hole before the heat treatment with the straight core, for example, the post-heat treatment dimension at the position of 2 mm in height from the flange surface 5 is kept within the standard for the large diameter portion of the inner diameter hole. Then, the dimension after heat treatment at the position of 18 mm in height from the collar surface is out of the standard, and if the dimension after heat treatment at the position of 18 mm in height from the collar surface is within the standard, The dimension after heat treatment at the position of 2 mm in height is out of the standard.

(A) Cross-sectional view of iron-based sintered machine part whose inner diameter hole is corrected by the method of the present invention, (b) Cross-sectional view after heat treatment of iron-based sintered machine part of FIG. 1 (a) A perspective view showing an outline of a high-frequency induction heating device Sectional drawing which shows the heating state of the tooth | gear part in a high frequency induction heating apparatus Front view of sintered sprocket used for evaluation test Illustration of dimension measurement position The figure which shows the evaluation test result of the dimensional change of the small diameter part of an internal diameter hole The figure which shows the evaluation test result of the dimensional change of the large diameter part of an internal diameter hole (A) Cross-sectional view of an iron-based sintered machine part whose inner diameter hole has been corrected by a conventional method, (b) Cross-sectional view after heat treatment of the iron-based sintered machine part of FIG. 8 (a)

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Boss part 2 Tooth part 3 Inner diameter hole 4 Rib 5 Face 10 Iron-type sintering machine component 20 High frequency induction heating apparatus 21 High frequency induction heating coil 22 Cooling jacket 22a Injection hole

Claims (3)

  Iron-based sintering having a radially protruding portion on the outer periphery of one end of the cylindrical shaft through a step of mixing raw material powder, a step of compacting the mixed raw material powder to obtain a molded body, and a step of sintering the molded body After the machine part is manufactured, a process of correcting the inner diameter hole of the iron-based sintered machine part into a tapered hole having a larger inner diameter on the side where the protruding part is provided, and induction hardening and tempering of the radial protruding part are performed. A method of manufacturing an iron-based sintered machine part that undergoes a heat treatment process.   The method for manufacturing an iron-based sintered machine part according to claim 1, wherein the correction of the inner diameter hole is performed by sizing.   The iron-based sintered machine part is a sintered sprocket or sintered gear having a tooth portion on one end side outer periphery of the boss portion, and the inner diameter hole of the boss portion of the sintered sprocket or sintered gear is corrected to a taper hole, Then, the manufacturing method of the iron-type sintered machine part of Claim 1 or 2 which performs induction hardening and tempering of the said tooth | gear part.

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