JP2013181626A - Joint structure and welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a joint structure having secured fatigue strength, and a welding method therefor.SOLUTION: If a length of a butting part 3 in an axial direction (in welded depth direction) is H, and a welded depth in welding parts 5, 6 is A, a differential case 1 (first member) and a ring gear 2 (second member ) are jointed by welding both sides sandwiching a hollow part 4 of the butting part 3 under a condition satisfying A>HX0.2. Accordingly, a joint structure can be constituted so that the breakdown of the welding parts 5, 6 occurs at an outside starting point in a fatigue test, and fatigue strength required as a differential device can be secured.

Description

  The present invention relates to a joint structure and a welding method, and more particularly, to a joint structure for joining members having cavities formed in butt portions by welding, and a welding method thereof.

  For example, when a ring gear having a helical gear formed on the tooth portion is welded to the flange of the differential case, the joint structure described in Patent Document 1 can be employed. In this case, first, the inner periphery of the ring gear is fitted to the outer periphery of the flange of the differential case to form a butt portion between the ring gear and the flange of the differential case. Next, the laser head is operated along a circular orbit along the abutting portion, whereby both sides of the abutting portion (both sides in the ring gear axial direction) are laser welded. As a result, welds are formed on both sides of the butted portion, and the ring gear and the flange of the differential case are joined.

  In a joint structure including a welded portion formed in this way, when the butt portion is in close contact over the entire region, management of the welded portion, particularly management of the penetration depth of each welded portion on both sides of the butt portion. Is difficult. Therefore, the applicant tried to form a cavity in the butt portion by providing a recess in the butt surface of one member (for example, the flange of the differential case). In such a joint structure in which a space portion is formed in the butt portion, a notch (stress) is formed between the toe portion of each welded portion, that is, the inner end (side facing the cavity) and the recessed portion of each welded portion. (Concentrated portion) is formed, and as a result, the fatigue strength may be significantly reduced.

  In addition, by providing a groove in each of the two members (ring gear and flange of the differential case), a cavity is formed in the butt portion so that the above-described notch (stress concentration portion) is not formed in the toe portion of each welded portion. However, in this case, the manufacturing cost is greatly increased, the shape of the toe portion of the welded portion is varied, and the fatigue strength of the welded portion is also varied.

Japanese Patent Laid-Open No. 10-231918

  Then, this invention is made | formed in view of the said situation, and it is made as a subject to provide the joint structure with which fatigue strength is ensured, and its welding method.

  In order to solve the above-described problem, the joint structure of the present invention is a joint structure in which a butt portion between a first member and a second member is welded, and a cavity formed in the butt portion, and the butt portion A weld portion formed on both sides of the cavity, and a stress acting on an end of the weld portion on the cavity side acting as an inner stress, and acting on an end portion on the opposite side of the weld portion from the cavity side. When stress is defined as outer stress, the penetration depth of the weld is determined based on a ratio between the outer stress and the inner stress.

  In order to solve the above-mentioned problem, the welding method of the present invention is a method of welding a butt portion between a first member and a second member to form a weld portion on both sides sandwiching a cavity of the butt portion. When the stress acting on the end of the welded portion on the cavity side is defined as the inner stress, and the stress acting on the end of the welded portion opposite to the cavity side is defined as the outer stress, The welding is performed at a penetration depth determined based on the above.

(Aspect of the Invention)
In the following, aspects of the invention that is recognized as being capable of being claimed in the present application (hereinafter referred to as claimable invention) will be exemplified, and each exemplified aspect will be described. Here, as in the claims, each aspect is divided into paragraphs, numbers are assigned to the respective paragraphs, and the descriptions of other paragraphs are cited as necessary. This is for the purpose of facilitating the understanding of the claimable invention, and is not intended to limit the combination of the constituent elements constituting the claimable invention to those described in the following sections. In other words, the claimable invention should be construed in consideration of the description accompanying each section, the description of the embodiment, etc., and as long as the interpretation is followed, another aspect is added to the aspect of each section. Moreover, the aspect which deleted the component from the aspect of each term can also be one aspect of the claimable invention.
In the following items, each of items (1) to (8) corresponds to each of claims 1 to 8 described in the claims.

(1) A joint structure in which a butt portion between a first member and a second member is welded, and includes a cavity formed in the butt portion and welded portions formed on both sides sandwiching the cavity of the butt portion. If the stress acting on the end of the weld on the cavity side is defined as the inner stress, and the stress acting on the end opposite to the weld on the cavity side is defined as the outer stress, the penetration depth of the weld is A joint structure that is determined based on the ratio of external stress to internal stress.
According to the joint structure described in this section, a welded portion (weld bead) having a penetration depth determined based on the ratio of the outer stress and the inner stress is formed on both sides of the butt cavity and the joint structure is Since the ratio is set, for example, in the fatigue test of the test piece, by setting the fracture so that the fracture does not occur at the inner starting point, that is, the notch starting point of the toe portion on the cavity side of the welded portion, the joint structure The fatigue strength can be secured.
In the aspect of this section, the cavity formed in the butt portion can be formed by providing a recess in the butt surface of the first member or the second member. By forming a cavity in the abutting portion in this way, the manufacturing cost (the number of processing steps) is compared with the case where a recess is provided in the abutting surface of both the first member and the second member to form a cavity in the abutting portion. ) Can be suppressed.

(2) If the penetration depth of the weld is defined as A and the length of the butt portion in the penetration depth direction is defined as H,
The joint structure according to (1), wherein A> H × 0.2.
According to the joint structure described in this section, by setting the penetration depth A of the welded portion to be larger than 0.2 times the length H of the butt portion in the penetration depth direction, The ratio can be set so that the fracture does not occur at the inner starting point in the fatigue test of the specimen. Thereby, the fatigue strength of the joint structure can be ensured. In addition, when using laser welding, a penetration depth direction can be paraphrased with a laser beam irradiation direction.

(3) If the internal stress is defined as σ _A , the external stress as σ _E , and the notch coefficient as β,
The joint structure of (1) and (2) where σ _A / σ _E <1 / β.
According to the joint structure described in this section, by setting the quotient (σ _A / σ _E ) obtained by dividing the inner stress by the outer stress to be smaller than the fatigue reduction rate (1 / β) due to the notch, (1 ) Ratio can be set so that the fracture does not occur at the inside starting point in the fatigue test of the test piece. Thereby, the fatigue strength of the joint structure can be ensured.

(4) If the length of the butt portion in the penetration depth direction is defined as 2B (2B = H) and the length of the cavity in the penetration depth direction is defined as 2b,
The joint structure of (1) to (3) where b / B <0.6.
According to the joint structure described in this section, by setting the quotient obtained by dividing the length in the penetration depth direction of the cavity by the length in the penetration depth direction of the butt portion, by setting it smaller than 0.6, The ratio of (1) can be set so that the fracture does not occur at the inner starting point in the fatigue test of the test piece. Thereby, the fatigue strength of the joint structure can be ensured.
In the aspect of this section, the width (length in the penetration depth direction of the butt portion) of the cross section of the butt portion of the test piece is 2B, and the cross section of the butt portion of the test piece is When the width is t, the notch length (length in the direction of penetration of the cavity) in the test piece is 2b, and the bending moment acting on the test piece by three-point bending is M, the inner stress σ _A and the outer stress σ _E is
σ _A = ³ bM / 2t (B ³ −b ³ ) (Formula 1)
σ _E = 3bM / 2t (B ³ −b ³ ) (Formula 2)
It is. From Equations 1 and 2,
σ _A / σ _E = b / B (Formula 3)
Is guided. That is, by substituting Equation 3 into the inequality of (3),
b / B <1 / β (Formula 4)
Is guided.
Then, as a result of intensive research, the applicant of the present application has found that when the fatigue reduction rate (1 / β) due to the notch of the test piece described above is smaller than 0.6, the fracture of the test piece starts from the outside in the fatigue test. It has been found that the occurrence of the test piece, in other words, the breakage of the test piece does not occur at the inner starting point, that is, at the notch starting point of the toe end portion on the cavity side of the welded portion. Therefore, by substituting 0.6 for 1 / β of Equation 4, the following inequality (Equation 5) is derived.
b / B <0.6 (Formula 5)
Here, since 2B = H, H is substituted for B in Formula 5 and 2b = H-2A. Therefore, H-2A is substituted for b in Formula 5 to transform the formula (2 ) Inequality, ie
A> H × 0.2 (Formula 6)
To be consistent.

(5) A method of forming a welded portion on both sides sandwiching the cavity of the butted portion by welding the butted portion of the first member and the second member, and applying stress acting on the end of the welded portion on the cavity side Welding is performed at a penetration depth determined based on the ratio between the outer stress and the inner stress, when the inner stress and the stress acting on the end opposite to the cavity side of the weld are defined as the outer stress. Method.
According to the welding method described in this section, both sides sandwiching the cavity of the butt portion are welded so that the penetration depth is determined based on the ratio of the outer stress and the inner stress of the welded portion (weld bead). Since the first member and the second member are joined, the ratio is set so that, for example, in the fatigue test of the test piece, the fracture does not occur at the inner starting point, that is, the notch starting point at the toe portion on the cavity side of the welded portion. By setting, the fatigue strength of the joint structure formed by the welding method can be ensured.

(6) If the penetration depth of the weld is defined as A and the length of the butt portion in the penetration depth direction is defined as H,
The welding method according to (1), wherein welding is performed so that A> H × 0.2.
According to the welding method described in this section, by setting the penetration depth A of the welded portion to be larger than 0.2 times the length H of the butt portion in the penetration depth direction, The ratio can be set so that the fracture does not occur at the inner starting point in the fatigue test of the specimen. Thereby, the fatigue strength of the joint structure formed by the welding method can be ensured. In addition, when using laser welding, a penetration depth direction can be paraphrased with a laser beam irradiation direction.

(7) If the inner stress is σ _A , the outer stress is σ _E , and the notch coefficient is β,
The welding method according to (5) or (6), wherein welding is performed so that σ _A / σ _E <1 / β.
According to the welding method described in this section, the quotient (σ _A / σ _E ) obtained by dividing the inner stress by the outer stress is set smaller than the fatigue reduction rate (1 / β) due to the notch (5 ) Ratio can be set so that the fracture does not occur at the inside starting point in the fatigue test of the test piece. Thereby, the fatigue strength of the joint structure formed by the welding method can be ensured.

(8) If the length of the butt portion in the penetration depth direction is defined as 2B (2B = H), and the length of the cavity in the penetration depth direction is defined as 2b,
The welding method of (5) to (7), wherein welding is performed so that b / B <0.6.
According to the welding method described in this section, the quotient obtained by dividing the length of the cavity in the penetration depth direction by the length of the butt portion in the penetration depth direction is set to be smaller than 0.6. By doing so, it is possible to set the ratio of (5) so that the fracture does not occur at the inside starting point in the fatigue test of the test piece. Thereby, the fatigue strength of the joint structure formed by the welding method can be ensured.
In the aspect of this section, the width (length in the penetration depth direction of the butt portion) of the cross section of the butt portion of the test piece is 2B, and the cross section of the butt portion of the test piece is When the width is t, the notch length (length in the direction of penetration of the cavity) in the test piece is 2b, and the bending moment acting on the test piece by three-point bending is M, the inner stress σ _A and the outer stress σ _E is
σ _A = ³ bM / 2t (B ³ −b ³ ) (Formula 1)
σ _E = 3bM / 2t (B ³ −b ³ ) (Formula 2)
It is. From Equations 1 and 2,
σ _A / σ _E = b / B (Formula 3)
Is guided. That is, by substituting Equation 3 into the inequality of (7),
b / B <1 / β (Formula 4)
Is guided.
Then, as a result of intensive research, the applicant of the present application has found that when the fatigue reduction rate (1 / β) due to the notch of the test piece described above is smaller than 0.6, the fracture of the test piece starts from the outside in the fatigue test. It has been found that the occurrence of the test piece, in other words, the breakage of the test piece does not occur at the inner starting point, that is, at the notch starting point of the toe end portion on the cavity side of the welded portion. Therefore, by substituting 0.6 for 1 / β of Equation 4, the following inequality (Equation 5) is derived.
b / B <0.6 (Formula 5)
Here, since 2B = H, H is substituted for B in Formula 5, and 2b = H-2A. Since H-2A is substituted for b in Formula 5, ) Inequality, ie
A> H × 0.2 (Formula 6)
To be consistent.

  ADVANTAGE OF THE INVENTION According to this invention, the joint structure by which fatigue strength is ensured, and its welding method can be provided.

It is a figure which shows the joint structure of this embodiment, and is sectional drawing by the axial plane of the junction part of a differential case and a ring gear. FIG. 2 is an enlarged view of a lower welded portion in FIG. 1. It is explanatory drawing of this embodiment, and is a figure by which the moment which acts on a joint structure, and the external stress and internal stress which generate | occur | produce by it are shown. It is a conceptual diagram of a fatigue test (three-point bending test). It is explanatory drawing of the manufacturing method of the test piece used by a fatigue test. It is a graph which shows the test result of the test piece P11-P15 fatigue test of the classification P1. It is a graph which shows the test result of the test piece P21-P25 fatigue test of the type P2. It is a graph which shows the test result of the test piece P31-P33 fatigue test of the type P3. It is a graph which shows the test result of the test piece P41-P43 fatigue test of the type P4. It is a graph which shows the test result of the test piece P51-P53 fatigue test of the type P5. It is a graph which shows the test result of the test piece P61-P63 fatigue test of the type P6. It is the table | surface which plotted the test result of the fatigue test on the coordinate of the SN diagram which made the vertical axis | shaft nominal stress and the horizontal axis the number of repetitions. It is a figure for comparing the fatigue limit of each kind P1-P6 of the test piece P, and is a graph which made the vertical axis the nominal stress which can endure 1 million times of repetition, and made the horizontal axis b / B. It is a figure which shows the joint structure of other embodiment, and is sectional drawing by the axial plane of the junction part of a differential case and a ring gear.

  An embodiment of the present invention will be described with reference to the accompanying drawings. In the present embodiment, a joint structure between a differential case 1 (first member) and a ring gear 2 (second member) of a differential device and a welding method thereof will be described. In the following description, the vertical direction in FIG. 1 is defined as the axial direction (corresponding to the penetration depth direction in the claims), and the horizontal direction in FIG. 1 is defined as the radial direction. Further, the axis line coincides with the center line of the ring gear 2.

  As shown in FIG. 1, in the joint structure of this embodiment, welded portions 5 and 6 are formed on both sides in the axial direction sandwiching the cavity 4 of the butting portion 3 (hereinafter, butting portion 3) between the differential case 1 and the ring gear 2. The In the ring gear 2, a helical gear is formed on the outer periphery 2a, and the inner periphery 2c (the inner cylindrical surface, see FIG. 2) is fitted to the outer periphery 1a (see FIG. 2) of the differential case 1. The outer periphery 1a of the differential case 1 is formed with a recess 7 that is provided at the center in the axial direction of the outer periphery 1a and extends in the circumferential direction of the outer periphery 1a. The length of the recess 7 in the axial direction determines the length 2b of the cavity 4 in the axial direction (see FIG. 3). In other words, the axial length of the recess 7 is determined according to the penetration depth A of the welds 5 and 6. The depth of the recess 7 with respect to the outer periphery 1a (outer peripheral surface) of the differential case 1 determines the width W of the cavity 4 (see FIG. 1).

  As shown in FIGS. 1 and 2, the recess 7 has an outer cylindrical surface 7a that forms the bottom of the recess 7 and inclined surfaces 7c that are formed on both sides in the axial direction of the outer cylindrical surface 7a. In the cross section of the axial plane when the inner periphery 2c of the ring gear 2 is fitted to the outer periphery 1a of the differential case 1, the inner periphery 2c of the ring gear 2 and each inclined surface 7c of the recess 7 form an acute angle. In other words, both ends in the axial direction of the cavity 4 in this cross section form an acute angle.

  FIG. 2 is an enlarged view of a part of the butt portion 3 including the welded portion 5 (lower portion in FIG. 1). Here, since the welded portion 5 and the welded portion 6 are formed vertically symmetrical in FIG. The welded portion 5 is formed by laser welding one side of the butt portion 3 (the lower side in FIGS. 1 and 2). More specifically, the welded portion 5 irradiates the ridge 8 of the butting portion 3 with laser light in the axial direction (here, upward in FIG. 2) and circularly orbits the laser light along the ridge 8 of the butting portion 3. It is formed by scanning.

As shown in FIG. 2, the welded portion 5 has a length A extending from the surface 1 d of the differential case 1 and the surface 2 d of the ring gear 2 toward the cavity 4 in the cross section by the axial plane. In other words, the weld 5 extends from the ridge 8 toward the cavity 4 and has a penetration depth A. The starting end portion 5e of the welded portion 5 is formed wider and flat with respect to the toe end portion 5a of the welded portion 5. Further, a notch 9 (stress concentration portion) is formed between the toe portion 5 a of the welded portion 5 and the inclined surface 7 c of the concave portion 7. And in this embodiment, the stress which acts on the toe part 5a (end part by the side of the cavity 4) of the welding part 5 is made into inner side stress ((sigma) _{A of} FIG. 3), and the start end part 5e (cavity 4 side side of the welding part 5). Is defined as an outer stress (σ _{E in} FIG. 3), the penetration depth A of the weld 5 is determined based on the ratio of the outer stress and the inner stress. .

Next, how the penetration depth A of the welded portion 5 is specifically determined will be described.
The applicant of the present application uses the test piece P (see FIG. 4) for the fatigue test (three-point bending test) for the purpose of obtaining the condition of the joint structure having the required fatigue strength between the differential case 1 and the ring gear 2. Carried out. The test piece P used in this fatigue test was cut out by wire cutting from the weld butt 10 (see FIG. 5) having an outer diameter of 240 mm, an inner diameter of 70 mm, a weld diameter of 145 mm, and a thickness of 20 mm. Further, the test piece P has a total length L1 (the length in the radial direction of the welding butt 10) of 70 mm, and the weld 5 is formed at the center in the total length L1 direction.

  The welding butt member 10 is made of the same material as that of the differential case 1 with the welded portion 5 as the boundary material of the FCD 450 and the material of the outer peripheral side member 12 with the boundary of the welded portion 5 as the ring gear 2. . In addition, the welding butt member 10 is laser-welded on both sides in the axial direction of the butt portion 3 so that the inner peripheral member 11 and the outer peripheral member 12 are joined. As shown in FIG. 4, the span L2 of the three-point bending in the fatigue test is 50 mm, and the width t of the test piece P is 20 mm.

  6 to 11 are tables in which the test results of the fatigue test are summarized for each of the types P1 to P6 of the test pieces P. FIG. In addition, in order to specify a test piece, a 2-digit number is given after P as necessary. For example, the test piece P12 represents the second test piece of the type P1 test pieces. Moreover, in the test result of the test piece P in which the weld part 5 broke in the static test, it is not described in the charts of FIGS. Here, the test pieces P31 to P33 of the type P3 are solid materials of FCD450. That is, the welded part 5 and the hollow 4 are not formed in the test pieces P31 to P33.

  The cavity 4 is not formed in the butt | matching part 3 in the test pieces P41-P43 of the classification P4. In this case, 2b = 0. Moreover, in each test piece P41-P43, although the welding part 5 has penetrated the butt | matching part 3 to the height (2B) direction (axial direction), the height (2B) direction (axial direction) of the butt | matching part 3 It is the result calculated as equivalent to the case where laser welding is performed at both penetration depths A from both sides. In this case, 2B = 2A.

  FIG. 12 is a plot of the results of the fatigue tests of FIGS. 6 to 11 on the coordinates of the SN diagram with the vertical axis representing the nominal stress and the horizontal axis representing the number of repetitions. As shown in this figure, in this fatigue test, the test piece P in which the welded portion 5 was broken at the inner starting point, that is, the test piece of type P1 in which the welded portion 5 was broken at the notch on the toe 5a side. A straight line Q1 (SN curve) was obtained by plot points of the test pieces P21 to P25 of P11 to P15 and the type P2.

  Further, the test piece P in which the welded portion 5 is broken at the outside starting point, that is, the type P4 test pieces P41 to P43, the type P5 test pieces P51 and P53, and the type P6 in which the welded portion 5 is broken at the starting end 5e side. A straight line Q2 (S—N curve) was obtained by plot points of the test pieces P61 to P63. Thus, the test results of this fatigue test, that is, the plot points of each test piece P where the welded portion 5 breaks at the inner starting point and the plot points of each test piece P where the welded portion 5 breaks at the outer starting point are S- It is coordinated by each straight line Q1, Q2 forming an N curve. A straight line Q3 in FIG. 12 is an SN curve (straight line) obtained by the type P3, that is, the solid specimens P32 and P33.

And since the applicant of the present application cannot easily secure fatigue strength when the welded portion 5 breaks at the inner starting point, the condition for ensuring the fatigue strength is that the welded portion 5 breaks at the outer starting point. Thought to be found by. Therefore, the applicant of the present application applies to the nominal stress σ _E (see FIG. 3) of the test piece P that breaks at the outer origin at a certain number of repetitions (for example, one million repetitions) based on the test results of the fatigue test. The condition (σ) where the ratio (σ _E / σ _A ) of the nominal stress σ _A (see FIG. 3) of the test piece P breaking at the inner starting point is smaller than the fatigue strength reduction rate 1 / β (β: notch coefficient). _{When E} 1 / σ _A <1 / β, hereinafter, condition 1) is satisfied, it is concluded that the weld 5 breaks at the outer origin, that is, fatigue strength is ensured.

  FIG. 13 is for comparing the fatigue limit of each type P1 to P6 of the test piece P, where the vertical axis is the nominal stress that can withstand 1 million cycles, and the horizontal axis is b / B (of the butt 3). It is a chart made into the ratio of the axial direction length of the cavity 4 with respect to the axial direction length. The notch coefficient β of the test piece P having the cavity 4 is set to 1.60 (β = 1.60).

Here, as shown in FIG. 3, the width of the test piece P in the height direction (the length of the butting portion 3 in the penetration depth direction) is 2B, and the width of the test piece P in the thickness direction is t (see FIG. 3). 4), when the notch length (length in the penetration depth direction of the cavity 4) in the test piece P is 2b, and the bending moment acting on the test piece P by three-point bending is M, the inner stress σ _A , The outer stress σ _E is
σ _A = ³ bM / 2t (B ³ −b ³ ) (Formula 1)
σ _E = 3bM / 2t (B ³ −b ³ ) (Formula 2)
It is. From Equations 1 and 2,
σ _A / σ _E = b / B (Formula 3)
Is guided. And by substituting Equation 3 into the inequality of Condition 1,
b / B <1 / β (Formula 4)
Is guided.

From the chart shown in FIG. 13, the b / B value when the fracture mode of the welded portion 5 changes from the inner starting point to the outer starting point is about 0.6. Therefore, when the fatigue strength reduction rate 1 / β is set to 0.6 (1 / β = 0.6), from Equation 4,
b / B <0.6 (Formula 5)
Is guided. In addition, as can be understood from the chart shown in FIG. 13, when the b / B value is 0.59, the test piece P of the type P5 has a fatigue limit drastically decreased, and from the fracture at the outer origin, Convert to break. Even judging from this, it is reasonable to set the fatigue strength reduction rate 1 / β to 0.6.

Here, the width 2B (see FIG. 3) in the height direction of the test piece P coincides with the length H (see FIG. 1) in the axial direction of the abutting portion 3 between the differential case 1 and the ring gear 2, that is, 2B = H Therefore, by substituting H for B in Formula 5, and as can be understood from FIG. 3, by substituting H-2A for b in Formula 5 as 2b = H-2A,
A> H × 0.2 (Formula 6)
Is guided.

Next, the welding method of this embodiment is demonstrated.
First, in the pre-process of laser welding, the inner circumference 2c of the ring gear 2 is fitted to the outer circumference 1a of the differential case 1 (first member), and the axial length between the differential case 1 and the ring gear 2 is H ( 2B) butting portion 3 is formed. The butting portion 3 has a cavity 4 having an axial length of 2b at the axial center. Note that 2b is set so that the penetration depth A of the welds 5 and 6 formed on both sides in the axial direction of the cavity 4 by laser welding satisfies the above formula 6.

  Next, a laser beam is irradiated in the axial direction (upward in FIG. 2) to the ridges 8 (see FIG. 2) on both sides in the axial direction of the abutting portion 3 of the differential case 1 and the ring gear 2, and the laser beam is applied to the ridges 8 Along a circular orbit. Thereby, as shown in FIG. 1, welded portions 5 and 6 having a penetration depth A are formed on both sides of the cavity 4 in the axial direction, and the differential case 1 and the ring gear 2 are joined.

This embodiment has the following effects.
According to this embodiment, the ratio (σ _A / σ _E ) between the outer stress σ _E and the inner stress σ _A of the welds 5, 6, in other words, the cavity with respect to the axial length 2 B (H) of the butt 3. 4. Weld both sides of the butt portion 3 so as to have a penetration depth A determined based on the ratio (b / B) of the axial length 2b of 4, specifically, A> H By welding both sides sandwiching the cavity 4 of the butting portion 3 under the condition satisfying × 0.2 and joining the differential case 1 (first member) and the ring gear 2 (second member), in the fatigue test, the welded portion The joint structure can be configured such that 5,6 breaks occur at the outer origin.
As a result, the welded portion 5 that is the inner starting point regardless of the sharpness (shape factor α) of the notch 9 (stress concentration portion) formed between the cavity 4 and the toe portions 5a and 6a of the welded portions 5 and 6. , 6 can be prevented from breaking at an early stage, and the required fatigue strength can be ensured in the differential having such a joint structure.
Further, since it is possible to omit the groove processing for relaxing the stress concentration caused by the notch 9, the manufacturing cost can be reduced.
Furthermore, since it is not necessary to control the shape of the notch 9 and only the penetration depth A is managed, the number of steps in the inspection process can be reduced.

In addition, embodiment is not limited above, For example, it can comprise as follows.
If the welds 5 and 6 are formed on both sides in the axial direction of the cavity 4, for example, as shown in FIG. 14, the outer diameter D5 of the weld 5 and the outer diameter D6 of the weld 6 are necessarily matched. There is no need. The outer diameters D5 and D6 can be determined according to, for example, the force acting on the differential, the demand for rationalization of the manufacturing process, and the like.

1 Differential case (1st member), 2 Ring gear (2nd member), 3 Butt part, 4 Cavity, 5, 6 Welded part

Claims (8)

A joint structure in which a butt portion between the first member and the second member is welded,
A cavity formed in the butt,
Welds formed on both sides of the butt portion sandwiching the cavity;
With
When the stress acting on the end of the welded portion on the cavity side is defined as inner stress, and the stress acting on the end of the welded portion opposite to the cavity side is defined as outer stress,
The joint structure according to claim 1, wherein the penetration depth of the weld is determined based on a ratio between the outer stress and the inner stress. When the penetration depth of the weld is defined as A and the length of the butt portion in the penetration depth direction is defined as H,
A> H × 0.2
The joint structure according to claim 1, wherein: Defining the inner stress as σ _A , the outer stress as σ _E , and the notch coefficient as β,
σ _A / σ _E <1 / β
The joint structure according to claim 1 or 2, wherein: When the length of the butt portion in the penetration depth direction is defined as 2B (2B = H) and the length of the cavity in the penetration depth direction is defined as 2b,
b / B <0.6
The joint structure according to any one of claims 1 to 3, wherein: A method of forming welds on both sides sandwiching a cavity of the butted portion by welding the butted portion of the first member and the second member,
When the stress acting on the end of the welded portion on the cavity side is defined as inner stress, and the stress acting on the end of the welded portion opposite to the cavity side is defined as outer stress,
The welding method, wherein welding is performed at a penetration depth determined based on a ratio between the outer stress and the inner stress. When the penetration depth of the weld is defined as A and the length of the butt portion in the penetration depth direction is defined as H,
A> H × 0.2
The welding method according to claim 5, wherein welding is performed so that Defining the inner stress as σ _A , the outer stress as σ _E , and the notch coefficient as β,
σ _A / σ _E <1 / β
The welding method according to claim 5 or 6, wherein welding is performed so that When the length of the butt portion in the penetration depth direction is defined as 2B (2B = H) and the length of the cavity in the penetration depth direction is defined as 2b,
b / B <0.6
The welding method according to claim 5, wherein welding is performed so that

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