JP5226594B2 - Defect improvement method for cast steel crank throw - Google Patents

Description

  The present invention relates to a defect improvement method for a cast steel crank throw that efficiently eliminates defects in a cast steel crank throw surface layer portion that is a component part of an assembled crankshaft.

As for diesel engine crankshafts used for ships and generators, there are assembled crankshafts and integral crankshafts. The assembly-type crankshaft is assembled and manufactured by shrink-fitting a crank throw and a journal, which are constituent parts, and the journals are all made of forged steel. For crank throws, there are forged steel and cast steel.
For the crank throw made of forged steel, first, the round bar material forged steel ingot material is subjected to the necessary processing such as a recess to be pushed in with a punch at the time of mold insertion molding. After producing the columnar material with the recess, the die is formed by pressing the recess with a punch using a molding die formed by a die fitted with an anvil at the bottom and the punch. In other words, it is described that a forged steel crank throw with a small yield and a high yield can be obtained by die-pressing and forming (see Patent Document 1). Although this forged steel crank throw can provide a highly reliable crankshaft with excellent fatigue strength due to the forging effect, it has a problem of low productivity because the manufacturing process is complicated.
On the other hand, cast steel crank throws have the advantage of higher productivity than forged steel crank throws, but they are not considered to have the same fatigue strength as forged steel crank throws. There was a lack of reliability, such as inability to apply to institutions. For this reason, the cylindrical part is pressed and clamped between a work roll and a backup roll with respect to a cast steel material having a cylindrical outer peripheral surface such as a cast steel crank throw, and the cast steel material is rotated around the axis of the cylindrical part. In order to improve the fatigue strength and improve the surface finish of the product by pressing and reducing the minute casting defects near the surface by hot roll processing that plastically deforms the cylindrical part by the work roll. A method for improving the properties of cast steel with high productivity is disclosed (see Patent Document 2) .

JP 52-111183 A JP 2000-213528 A

  However, although the method for improving the properties of cast steel by hot roll processing described in Patent Document 2 has the effect of crimping defects, it has a problem of poor yield because it performs machining after hot roll processing. It was.

  Therefore, the object of the present invention is to solve these parts for defects such as micro-shrinkage that are unavoidably present in the surface layer part by casting of the pin part and pin fillet part which are important parts of the crank throw made of cast steel. The present invention is to provide a defect improvement method for a cast steel crank throw that efficiently and continuously eliminates defects present in the surface layer portion by applying shear strain over the entire surface layer portion.

  In order to solve the above problems, the present invention employs the following configuration.

The invention of claim 1, both sides of the U E blanking pin portion, a defective method for improving the crank throw of assembly-type crankshaft is provided with a shaft hole fitting the journal portion, it casts the crank throw When the workpiece is heated to the required temperature range and hot working is performed to apply shear strain to the pin part and the pin fillet part, the crank throw part has the web on both sides around the axis of the pin part. It is cast in a state where it is relatively rotated by a required angle, and the hot working is performed at a relative rotation angle that is a required angle obtained by rotating the webs on both sides relatively around the axis of the pin portion. This is a crank-throw defect improvement method characterized by twisting by twisting a pin portion by rotating in a direction in which the angle becomes smaller.

According to a second aspect of the present invention, in the crank throw defect improving method according to the first aspect, a required rotation angle range in the hot working is 20 ° to 100 °.

The invention according to claim 3 is the crank throw defect improving method according to claim 1 or 2 , wherein the hot working is performed after heating the whole crank throw shaped material to 900 ° C or more. To do.

According to a fourth aspect of the present invention, in the crank throw defect improving method according to the first or second aspect, only the pin portion and the pin fillet portion of the crank throw are partially heated to 600 ° C. or more, and then the hot working is performed. It is characterized by performing.

  In the present invention, after the cast crank throw shaped material is heated to a required temperature range, the pin portion and the pin fillet portion are subjected to shear strain by twisting to twist the pin portion. Void defects existing in the vicinity of the surface layer of these parts can be eliminated continuously and efficiently with torsion. As a result, a crankshaft having high fatigue strength and improved reliability can be manufactured in a shorter period of time than before.

The (a) is explanatory drawing which shows the structure of an assembly-type crankshaft. The (b) is explanatory drawing (vertical side view) which showed typically the surroundings of the pin part of (a). The (a) is explanatory drawing (side view) which shows typically the shape of the raw material of a crank throw, and embodiment of a twist process. The (b) is explanatory drawing (side view) which shows typically the shape after giving the twist process to the pin part of the original shape material of (a). The (a) is explanatory drawing which shows typically other embodiment of a twist process (before process) . Part (b) is a same illustration (after processing). It is explanatory drawing which shows typically distribution of the shearing strain introduce | transduced into the edge part and pin fillet part of the pin part after giving a twist process to a pin part. It is explanatory drawing which grasped | ascertained by the analysis the extent to which the void defect in a pin part cross section disappears by twisting. Part (a) is an explanatory view showing a cylindrical test piece (front view). Part (b) is a coaxial diagram (side view).

  Embodiments of the present invention will be described below with reference to the accompanying FIGS.

  FIG. 1A shows the crank throw and journal components for one cylinder of the assembled crankshaft. The crank throw 1 includes a journal shaft hole 2 into which journal steel shafts 2a and 2b made of forged steel at the center of rotation of the crankshaft are fitted, a pin shaft 3 at an eccentric position with respect to the journal shaft hole 2, and In order to reduce stress concentration, the main part is shown in FIG. 1 (b) at the boundary portion between the lower ends of both ends of the pin portion (pin shaft) 3 and the webs 4 and 4a. As described above, pin fillet portions (hereinafter referred to as fillet portions) 5 and 5a are formed. The assembly type crankshaft is assembled and manufactured by shrink-fitting the journals 2a and 2b into the journal shaft hole 2. FIG. 2A shows the crank throw shaped material 1a of the embodiment, in which the webs 4 and 4a are relatively rotated about the axis C of the pin portion 3 by a rotation angle (torsion angle) θ by θa. It is cast and molded into a displaced shape. After this raw material 1a is charged into a heating furnace and heated to a required temperature within a temperature range of 900 ° C. to 1300 ° C., it is placed on the lower die plate of the press and placed on the die plate with a jig. After fixing, the web 4 is rolled down by a die (not shown) attached to the upper die plate until the angle 4 around the pin portion axis C becomes zero as shown in FIG. 2B. In other words, the pin portion 3 can be twisted at a twist angle θa by rotating the angle of the relatively displaced angle by the angle θa. Further, as shown in FIG. 3, a cylindrical portion 6b in which a base material 1a is inserted into a lower die 6 and a concave portion that fits the pin portion 3 is formed at the tip of the upper die 6a of the press. Can be formed into the crank throw 1 by twisting the pin portion 3 at a twist angle θa. The reason why the base material 1a is heated to a temperature of 900 ° C. or higher is to promote the disappearance by partially adhering the void defects whose size is reduced by the twisting process. The upper limit of the heating temperature is 1300 ° C. in order to prevent partial melting of the surface layer portion of the shaped member 1a.

  The twist angle θ is preferably selected in the range of 20 ° to 100 °. As will be described later, if the torsion angle θ is less than 20 °, the cross-sectional area of defects in the pin portion surface layer cannot be reduced by 10% or more, and if the torsion angle θ reaches 100 °, the pin portion surface layer It is possible to almost completely eliminate defects in. When the twist angle θ is set to 90 ° or more, the web is pressed by the horizontal press, for example, at the initial stage of twisting until the pin can be twisted by pressing the web with the vertical press. It is necessary to rotationally displace around the axis of the pin part.

  FIG. 4 is a cross-sectional view taken along line AA when the pin portion is twisted as shown in FIGS. 2A and 2B under the processing conditions shown in Table 1 (see FIG. 2B). Of the distribution of shear strain (indicated by diagonal lines) introduced into the axial end of the pin portion 3 and the pin fillet portion 5 in FIG. 5 using a general-purpose deformation analysis means (rigid plastic finite element method) It is shown. In Table 1, in the analysis models 1 and 2, as shown in FIG. 4, the shape between the fillet portions 5 and 5a in the raw material shown by the solid line is different, and in the analysis model 1, the analysis is performed in a semicircular shape. In model 2, small semicircular depressions are formed on the fillet portions 5 and 5a. The shape indicated by the broken line schematically shows the shape of the crank throw after machining.

  From FIG. 4, in both the analysis models 1 and 2, shear strain is introduced not only into the pin portion 3 but also into the fillet portions 5 and 5 a by twisting the pin portion 3. The larger θa is, the higher the material temperature (pin portion temperature) is. When the twist angle θa is 45 °, it can be seen that in both the analysis models 1 and 2, the shear strain is introduced up to the fillet portions 5 and 5a after machining indicated by broken lines.

  FIG. 5 shows the deformation analysis means (rigid plastic finite element method), in which one end of a cylindrical test piece (FIG. 6) having a diameter of 45 mm and a length of 70 mm is fixed to the pin portion and the other end is rotated. When twisted, the respective positions in the radial direction in the cross-section at the central portion in the axial direction of the cylindrical specimen (shown in FIG. 5 as the radial distance from the center with respect to the radius r = 22.5 mm) The degree of disappearance of the void defect (Φ2 mm) is shown. The sectional area ratio S / S0 on the vertical axis represents the ratio of the sectional area S0 of the defect at each twist angle to the sectional area S0 of the initial defect. From the figure, the position where the distance from the center of the cylindrical test piece corresponding to the axis C of the pin portion is larger, the smaller the cross-sectional area ratio S / S0 with respect to the same twist angle, that is, the extent of defect disappearance. It can be seen that is increasing. Further, in the surface layer portion (Δ: 20 / r22.5) having a depth of 2.5 mm in the radial direction from the surface of the cylindrical specimen, when the twist angle is 45 °, the defect disappears by about 30% (S / When S0 = 0.7) and 90 °, it is almost disappeared with about 85% (S / S0 = 0.15). From this analysis result, by introducing shear strain accompanying torsional processing toward the surface from the axial center (center) of the cylindrical specimen, that is, the axial center (center) of the pin portion of the crank throw, It can be seen that the rate of reduction in size increases, and that twisting is an effective means for efficiently reducing defects in the surface portion of the pin portion.

  When the pin portion diameter of the cast throw (equivalent to S45C) crank throw is 200 mm, a defect (shrinkage) of 0.56 mm in diameter is formed on the surface layer portion (a position 12 mm deep in the radial direction from the surface) of a 200 mm diameter cylindrical test piece Hole), using a deformation analysis means (rigid plastic finite element method), torsion is applied to the cylindrical specimen under the heating conditions and torsion angles shown in Table 2, and shear strain is applied to the cross section (surface layer) of the specimen. The degree of reduction of the defect cross-sectional area after introducing was investigated. Then, the diameter of a circle having a cross-sectional area equal to the defect cross-sectional area after introduction of the shear strain, that is, the equivalent diameter was calculated, and when the defect cross-sectional area was reduced to 0.3 mm or less, it was determined that there was no defect. The defect criterion with the equivalent diameter of 0.3 mm as a boundary value is based on actual machine data, and it has been found that a defect with an equivalent diameter of 0.3 mm or less does not affect the fatigue strength characteristics. ing.

  As shown in Table 2, when the material heating conditions and hot working conditions (twisting angle) of the present invention are satisfied (No.1, No.4, No.5), the initial defect has a cross-sectional area. The equivalent diameter was reduced to 0.3 mm or less, and it was determined that there was no defect. On the other hand, when the material heating condition and hot working condition (twisting angle) of the present invention are not satisfied (No.2, No.3, No.6), the initial defect has a cross-sectional area equivalent diameter. It did not decrease to 0.3 mm or less, and was judged to be defective. The analysis results shown in Table 2 confirmed the effectiveness of the present invention for efficiently and continuously eliminating defects existing in the surface layer of the crank throw pin and fillet.

1: Crank throw 2: Journal shaft hole 2a, 2b: Journal shaft 3; Pin part (pin shaft) 4, 4a: Web 5, 5a: Pin fillet part 6: Lower mold 6a: Upper mold 6b: Mold cylinder Part

Claims (4)

And both sides of the U E blanking pin portion, a defective method for improving the crank throw of assembly-type crankshaft is provided with a shaft hole fitting the journal portion, cast required temperature the formed and fabricated material of the crank throw After heating to the area, when performing hot working to give shear strain to the pin part and pin fillet part, the crank throw shape material is relatively moved around the axis of the pin part by the required angle. cast into a state of being rotated, the hot working, about the axis of the pin portion, the required angle of the sides of the U E blanking was the relative rotation in the direction of this relative rotation angle becomes smaller A crank throw defect improving method, characterized by twisting a pin portion by rotating it. The crank throw defect improving method according to claim 1 , wherein a required rotation angle range in the hot working is 20 ° to 100 °. 3. The crank throw defect improvement method according to claim 1, wherein the hot working is performed after heating the entire crank throw shaped material to 900 ° C. or more. 4. 3. The crank throw defect improvement method according to claim 1, wherein only the pin portion and the pin fillet portion of the crank throw are partially heated to 600 ° C. or higher, and then the hot working is performed.

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