JPH1177192A - Energizing caulking method for aluminum alloy casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To join an aluminum alloy casting to an opponent material with a sound caulked part not having a crack, a fusion, etc. SOLUTION: An aluminum alloy casting is laid on an opponent material in a state that a caulking protrusion 2 arranged to the aluminum alloy casting 1 is fitted into a hole part 4 of the opponent material 3. The aluminum alloy casting 1 including the caulking protrusion 2 is sandwiched between a pair of electrodes 5, 6, while pressing the aluminum alloy casting 1, energizing heating is repeated several times while interposing a non-energizing period and a low current energizing period. In energizing heating, a supply current and an energizing time are adjusted so that the protrusion 2 has a temp. of < the fusion temp. Between a non-energizing period and a low current energizing period, a time is adjusted so that the protrusion 2 is kept at >=250 deg.C. The welding force applied to the protrusion 2 is adjusted to a value that a pressing stress obtained by dividing the welding force with a cross sectional area of the protrusion 2 is smaller than a proof stress of a material to be caulked at a normal temp. in order to prevent the protrusion 2 from deforming in a low temp. range where the deformation ability is poor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an energization crimping method for firmly connecting an aluminum alloy casting having poor plastic workability without cracking.

[0002]

2. Description of the Related Art A caulking method has been conventionally known as one of means for mechanically joining metal materials. In the connection by caulking, a projection is formed on a part of the material to be joined to be joined, the projection is fitted into the hole formed in the mating material, and the projection protruding from the hole is plastically deformed by pressing etc. Engage with the material. In order to obtain sufficient joining strength by caulking, it is important to enhance the plastic workability of the material to be caulked and to sufficiently mesh with the counterpart material after plastic deformation.
Therefore, in Japanese Patent Application Laid-Open No. 55-122637, plastic deformation at the time of pressurization is promoted by energizing and heating the material to be swaged to soften it. In Japanese Unexamined Patent Publication No. Sho 59-215224, caulking is performed by applying an alternating current having a frequency at which the surface portion of the material to be caulked is preferentially heated. JP-A-3-
In the patent publication 86381, when connecting an aluminum die-cast product and a dissimilar metal, the dissimilar metal is fitted to a caulking boss provided on the aluminum die-cast product, and the caulking boss is heated to a semi-molten state by energization to perform caulking.

[0003]

In any of the conventional energization crimping methods, the projections are heated by one energization in any of the methods, so that the temperature distribution of the raised projections tends to be non-uniform. Therefore, a portion that is difficult to be plastically deformed remains, and a necessary deformability may not be obtained at the time of caulking. In particular, when an aluminum alloy casting with poor plastic workability manufactured by sand casting, die casting, etc. is used as the material to be caulked, if the projections are not heated to the temperature that shows the required deformability, the low deformability will be obtained. The resulting cracks are more likely to occur. Conversely, when the crimped material is heated for a long time to obtain high deformability, the protruding portions are heated to a high temperature of 600 ° C. or more, and melting is likely to occur. As a result, a defect caused by melting occurs in the swaged portion. The present invention has been devised in order to solve such a problem, and by repeatedly applying current to the crimping protrusions a plurality of times, stably maintaining the protrusions in a temperature range showing good deformability, An object of the present invention is to join an aluminum alloy casting with high joining strength while suppressing the occurrence of defects such as cracking and melting.

[0004]

According to the present invention, in order to attain the object, a current caulking method according to the present invention is a method in which a hole of a mating material is fitted to a caulking projection provided on a material to be caulked made of an aluminum alloy casting. Overlap the mating material on the material to be caulked, sandwich the material to be caulked including the protrusion for caulking between a pair of electrodes,
It is characterized in that energization and heating are repeated a plurality of times during a non-energization period or a low current energization period while pressing the material to be caulked.

[0005] At the time of electric heating, the supply current and / or the electric current time are adjusted so that the temperature of the projections becomes lower than the melting temperature. During the non-energizing period or the low current energizing period, the protrusion is 250
The time of the non-energization period or the low-current energization period is adjusted so as to be maintained at a temperature of not less than ° C. The pressing force applied to the projection is 0.2% proof stress of the caulked material at room temperature, in which the pressing stress obtained by dividing the pressing force by the cross-sectional area of the projection is used to prevent the deformation of the projection in the low temperature range where the deformability is small It is preferable to adjust to a smaller value. When one or more stepped enlarged portions are provided at the upper opening edge of the hole provided in the counterpart material, or when a hole is formed with a corner, the metal of the projection deformed in the caulking process is a stepped enlarged portion or a recess. The crimped portion flows into the portion, and the swaged material and the counterpart material are prevented from rotating.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION As a material to be crimped by a caulking method according to the present invention, there is an aluminum alloy casting manufactured by sand casting, die casting, die casting or the like. In addition to similar aluminum alloy castings, steel, stainless steel,
There are different metal materials such as copper and non-metal materials such as ceramics and resins. In the following description, an aluminum die-cast product will be described as an example of a material to be caulked, and a steel material will be described as an example of a counterpart material. The crimped material 1 has an integral projection 2
Are formed. Note that, instead of the integral projection 2, the projection 2 may be formed by screwing a projection into a hole with a female thread formed in the material to be caulked 1. A hole 4 through which the projection 2 is inserted is formed in the mating member 3. The projection 2 needs to have a length protruding from the hole 4 when the mating material 3 is superimposed on the material to be caulked 1 as shown in the left of FIG.

The swaged material 1 with the mating material 3 superimposed thereon is
It is arranged between the lower electrode 5 and the upper electrode 6. Lower electrode 5
For example, a fixed electrode made of a 5% Cr—Cu alloy is used. As the upper electrode 6, for example, a movable electrode made of W or a W alloy that can move in the vertical direction is used. The upper electrode 6 is lowered and pressed against the top surface of the projection 2 as shown in FIG. Next, a current is caused to flow between the lower electrode 5 and the upper electrode 6 at least twice, and the protrusion 2 is heated by conduction. Examples of the current to be supplied include an alternating current, a direct current, a pulse current, or a current having a waveform controlled by a combination thereof. The current is supplied so that the protrusion 2 is heated to a temperature range from 250 ° C. to a melting point or lower. The input power is adjusted. The period between the first energization and the energization after the next is set to a non-energization period in which no current is supplied or a period in which a small amount of current is supplied.

The projection 2 is stably maintained in a temperature range showing good deformability by repeating the electric heating a plurality of times. For example, between the lower electrode 5 and the upper electrode 6, 50
After supplying a current of 00 A for 0.34 seconds and leaving a non-conducting period of 0.016 seconds, a second current of 5000 A was supplied for 0.425 seconds, and the temperature of the protrusion 2 is shown by a solid line in FIG. Changed. In other words, the temperature of the protrusion 2 which has been raised to 400 ° C. by the first energization falls during the non-energization period, but the heat input by the energization heating is diffused throughout the protrusion 2. Then, when the second energization heating is performed before the temperature of the protrusion 2 falls to 250 ° C. or lower, the temperature of the protrusion 2 rises to 400 ° C. again.
At this time, since the temperature difference between the temperature of the projection 2 during the non-energization period and the maximum attained temperature during the re-energization period is small and the projection 2 is in a high temperature state of 250 ° C. or more, heating by the re-energization causes the entire projection 2 to be heated. Go around. As a result, protrusion 2
Is a temperature range showing good deformability, specifically 250 to 5
The projection 2 is stably maintained at 00 ° C.

On the other hand, when the projection 2 is heated by a short-time one-time energization, the temperature of the entire projection 2 does not rise to a required temperature range, and the temperature of the projection 2 decreases in a short time after the energization is stopped.
Sufficient crimping deformation cannot be obtained. Conversely, when the projections 2 are heated by a single energization for a long time, the projections 2 are partially melted, and a sound caulked portion cannot be obtained. Further, when the protrusion 2 is heated by a single current for a long time at a low current, the time required for the protrusion 2 to rise to a required temperature range becomes longer,
Since the caulking process is started in a low temperature range, a large crack is easily generated in the caulked portion.

[0010] The projection 2 heated as described above is uniformly held in a temperature range showing a good deformability, and thus the upper electrode 6 is maintained.
And plastically deforms uniformly without generating defects such as cracks, and becomes the locking portion 7 as shown in FIG. Therefore,
A swaged portion having a large bonding strength is obtained. The pressing force applied to the protrusion 2 by the upper electrode 6 during the caulking process is set so that the pressing stress obtained by dividing the pressing force by the area of the protrusion is not more than 0.2% proof stress of the material 1 to be crimped at normal temperature. It is valid. When the protrusion 2 is pressed with a pressing stress of 0.2% proof stress or less, plastic deformation is started only when the protrusion 2 reaches a predetermined temperature range, and a sound crimped portion is obtained. On the other hand, when a pressing force that generates a stress exceeding 0.2% proof stress is applied to the projections 2, the deformation starts in a low temperature region where the deformability is small,
It causes defects such as cracks.

As a caulked portion obtained by plastically working the projection 2, it is also effective to provide a protruding portion 8 projecting in the radial direction as shown in FIGS. 3 (a) and 3 (b). The overhang portion 8 is formed by caulking using the counterpart material 3 having the hole portion 4 in which the stepped enlarged diameter portions 9 and 9 shown in FIG. Or Figure 3
As shown in (d). The hole 4 provided with the corner 10 may be formed. In this case, since the overhang portion 8 meshes with the stepped enlarged diameter portion 9 or the corner portion 10, the crimped material 1 and the mating material 3 are joined in a state where they are prevented from rotating.

[0012]

【Example】

Example 1: (Effect by Two-Time Energization) As the material 1 to be crimped, a die-cast product having a thickness of 11 mm made of an aluminum alloy ADC3 (0.2% proof stress 170 to 220 N / mm ^{2 at} normal temperature) was used. This die-cast product is 4.5 mm in diameter and 10 mm in height to be joined by crimping to a 2.6 mm thick HT80 steel counterpart material 3.
mm projection 2. A hole 4 having an inner diameter of 4.7 mm into which the projection 2 is fitted is formed in the mating member 3. The protrusion 2 was fitted into the hole 4, the material to be caulked 1 and the mating material 3 were overlapped, and arranged between the lower electrode 5 and the upper electrode 6. The projection 2 was heated by applying a current of 5000 A two to three times under the conditions shown in Table 1. The protrusions 2 which were heated by the electric heating were plastically deformed by the pressing force at a working ratio of more than 70%, and all formed good crimped portions having good joining strength and no cracks. In addition, as shown in FIG. 6, the degree of processing was represented by a reduction ratio of the height H ₁ after crimping to the height H ₀ of the protrusion 2 before crimping.

For Test No. 1, the temperature and displacement of the protrusion 2 during caulking were measured, and the deformation starting temperature of the protrusion 2 was investigated. As can be seen from the investigation results in FIG. 4, the protrusion 2 does not deform at the start of energization, and deformation starts when the temperature of the protrusion 2 exceeds 300 ° C. by the first energization heating, and the first energization heating starts After the protrusion 2 reached the maximum temperature of 470 ° C., the deformation of the protrusion 2 temporarily stopped. The deformation stop period of the protrusion 2 continued until the time when the non-energization period ended and the time when the protrusion 2 reached 300 ° C. by the second energization heating. When the temperature of the projection 2 exceeded 300 ° C. by the second energization heating, the deformation of the projection 2 started again, and finally a crimped portion as shown in the right side of FIG. 1 was formed. The reason why the deformation does not progress between the point and the time is presumed to be due to the decrease in the deformation stress accompanying the increase in the cross-sectional area due to the deformation of the projection 2.

[0014]

Comparative Example: (Single energization) A crimping operation was performed under the same conditions as in the example except that the conditions for heating the projections 2 by one energization in Table 2 were employed. Test No. 4 is a case where the protrusion 2 was heated by a short-time single energization, but the temperature of the protrusion 2 did not reach a sufficient temperature as shown in FIG. To lower the temperature,
The deformability was low, and the degree of processing of the projection 2 was only 54%. Therefore, sufficient caulking deformation was not obtained, and the bonding strength also showed a low value.

Test No. 5 is a case where the pressing force is small and the projection 2 is heated by a short-time one-time energization. However, the working degree of the projection 2 is further reduced to 53%, and sufficient crimping deformation cannot be obtained. Was. Test No. 6 is a case where the energization time was set to be long, and the protrusion 2 was heated to a temperature exceeding 500 ° C. as shown in FIG. Therefore, although a high working ratio of 91% was obtained, a crimped portion required for joining the crimped material 1 and the mating material 3 was not formed. Test Nos. 7 and 8 are the cases where the current was applied once for a long time at a low current, but as shown in FIG. 2, the temperature rise of the projection 2 was slow, and the caulking process by pressurization was started at a low temperature inferior in deformability. . As a result, a large vertical crack was generated in the swaged portion.

[0017]

Embodiment 2: (Effect of Pressing Force) The pressing force applied to the material to be caulked 1 and the counterpart material 3 sandwiched between the lower electrode 5 and the upper electrode 6 is changed, and the pressing force applied to the formation of the caulked portion is changed. The effect of was investigated. In each case, the energization conditions were as follows: a current of 5000 A was supplied for 0.33 seconds, the energization was interrupted for 0.016 seconds, and then again
The current A was supplied twice for 0.42 seconds. Also,
The measured 0.2% proof stress of the material 1 to be caulked is 220 N / m.
m ² . As can be seen from the survey results in Table 3, 78
In Test No. 9 in which a large pressing force of 40 N was applied, cracks occurred before energization, and it was not possible to shift to caulking work. In Test No. 10 in which a pressure of 6860 N which was slightly lower than Test No. 9 but not less than 0.2% proof stress at normal temperature was applied, a crimped portion having a large vertical crack was formed. At this time, the deformation starting temperature of the projection is 1 as shown in FIG.
00 ° C. From this, it is inferred that the deformation starts at a stage where the softening of the projection 2 is not sufficient, and that the obtained crimped portion has cracked.

Even if the pressing force was further reduced, the test number 1
As shown in Nos. 1 and 12, as long as a stress exceeding the proof stress of the material to be caulked 1 was applied, a crimped portion was formed, although the magnitude of the vertical cracks was different but cracked. On the other hand, Test No. 1 in which a pressing force less than the normal temperature proof stress of the material to be caulked 1 was applied
In No. 3, the deformation starting temperature was 240 ° C., and a pressing force slightly exceeding the 0.2% proof stress was applied, but a sound crimped portion having no crack in appearance was formed. However, when the crimped portion was observed in detail with a microscope, fine cracks were observed. In Test No. 14, the deformation start temperature was 250 ° C. or higher, and the projections 2 were formed in a temperature range showing good deformability.
As a result, the obtained crimped portion had no cracks by visual observation and had high bonding strength. Also, no fine cracks were detected by microscopic observation.

[0020]

Embodiment 3 (Example in which a hole having a stepped enlarged diameter portion is provided in a mating member) A hole 4 having an inner diameter of 4.7 mm is formed in a mating member 3 having a thickness of 3 mm. 1.5mm in depth, 2mm in width,
A steel plate was prepared in which two and four stepped enlarged diameter portions 9 having a depth of 4 mm (FIG. 3c) were formed at equal intervals in the circumferential direction. As the material to be caulked 1, an aluminum alloy die-cast material having a thickness of 4.5 mm and a height of 10 mm formed with a projection 2 having a diameter of 4.5 mm to be fitted into the hole 4 (0.2% proof stress at room temperature, 220 N / mm)
² ) Prepared. The projection 2 is inserted into the hole 4 so that the mating material 1 is overlaid on the material to be caulked 1, and the lower electrode 5 and the upper electrode 6
And placed between. Pressing force 3430 via electrodes 5 and 6
N (stress: 215.7 N / mm ² ) was applied, and current was supplied twice under the same conditions as in Example 2.

When the formed crimped portion was cut and the cross section was observed, a part of the plastically deformed projection 2 flowed into the stepped enlarged portion 9. Therefore, the to-be-caulked material 1 and the mating material 3 are joined in a state where they are prevented from rotating by mechanical engagement. The hole 4 having the corner 10 (see FIG. 3)
When electric current caulking was carried out under the same conditions using the mating member 3 formed in d), a part of the plastically deformed projections 2 flowed into the corners 10 of the holes 4, and also in this case, the rotation was stopped. In this state, the material to be swaged 1 and the mating material 3 were joined.

[0023]

As described above, according to the caulking method of the present invention, the current applied to the caulked material pressurized between the current-carrying electrodes during the non-current period or the low current period is applied. Is repeated several times. The heat input by the first energization heating spreads over the caulking projections of the material to be caulked during the non-energization period or the low-current energization period, and is used for caulking in the temperature range where the plastically deformed portion shows good deformability in the second and subsequent energization heating The protrusions are uniformly heated. In addition, by setting the pressing force to be equal to or less than the normal temperature proof stress of the crimped material, plastic deformation starts only when the crimping projection is heated to a predetermined temperature range. A joint having high bonding strength can be obtained by forming a healthy caulked portion free of defects such as defects.

[Brief description of the drawings]

FIG. 1 is a process diagram for explaining a caulking method according to the present invention.

FIG. 2 is a graph showing the effect of various energizing conditions on the temperature change of a caulking protrusion.

FIG. 3 is a plan view (a), a cross-sectional view (b), a perspective view of a hole with a stepped enlarged portion (c), and a hole with a corner showing a mating member provided with a non-circular hole. Perspective view of part (d)

FIG. 4 is a graph showing a relationship between a temperature change and a displacement amount of a caulking projection when a current is applied twice by applying a pressing force equal to or lower than a normal temperature proof stress.

FIG. 5 is a graph showing a relationship between a temperature change and a displacement amount of a caulking protrusion when a pressing force exceeding a normal temperature proof stress is applied and current is applied twice.

FIG. 6 is a diagram for explaining a degree of processing of a projection;

[Explanation of symbols]

1: Material to be caulked (aluminum alloy die-cast product) 2:
Caulking projection 3: Counterpart material (steel material) 4: Hole
5: Lower electrode 6: Upper electrode 7: Locking portion 8: Overhang portion 9: Stepped enlarged portion 10: Corner portion

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[Procedure amendment]

[Submission date] September 17, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0019

[Correction method] Change

[Correction contents]

Even if the pressing force was further reduced, the test number 1
As shown in Nos. 1 and 12, as long as a stress exceeding the proof stress of the material to be caulked 1 was applied, a crimped portion was formed, although the magnitude of the vertical cracks was different but cracked. On the other hand, in Test No. 13, the deformation start temperature was 240 ° C. and 0.2%
Although a pressure slightly higher than the proof stress was applied, a sound crimped portion was formed without cracks in appearance. However, when the crimped portion was observed in detail with a microscope, fine cracks were observed.
In Test No. 14, the deformation start temperature was 250 ° C. or higher, and the projections 2 were formed in a temperature range showing good deformability. As a result, the obtained crimped portion had no cracks by visual observation and had high bonding strength. Also, no fine cracks were detected by microscopic observation.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hisashi Hori 1-34-1, Kambara, Kambara-cho, Anbara-gun, Shizuoka Prefecture Nippon Light Metal Co., Ltd. Group Technology Center

Claims (5)

[Claims] 1. A crimping material including a crimping projection, wherein the mating material is overlapped with the crimping material in a state where the hole of the mating material is fitted to the crimping projection provided on the crimping material made of an aluminum alloy casting. Energizing heating of a cast aluminum alloy, wherein the energizing heating is repeated a plurality of times during a non-energizing period or a low-current energizing period while pressing the material to be swaged with a pair of electrodes. 2. The energization caulking method according to claim 1, wherein the supply current and / or energization time during energization heating is adjusted so that the temperature of the caulking projection is lower than the melting temperature of the material to be caulked. 3. The energizing caulking method according to claim 1, wherein the time of the non-energizing period or the low current energizing period is adjusted so that the caulking protrusion is maintained at a temperature of 250 ° C. or higher. 4. The pressure applied to the caulking projection divided by the sectional area of the caulking projection is adjusted to a value smaller than the 0.2% proof stress of the material to be caulked at room temperature.
The method of caulking according to any one of the above. 5. A material according to claim 1, wherein a hole having one or a plurality of stepped enlarged diameter portions or a cornered hole is formed on the upper opening edge. Electric crimping method.