JPH06122079A - Method for continuously spot-welding sandwiched high damping steel sheet with short interval - Google Patents

Abstract

PURPOSE:To enable continuous spot welding with a short interval by applying a specified welding current normally after small current is applied at the initial stage of welding an thermosetting resin is softened and wasted from the lower part of a welded chip. CONSTITUTION:Before prescribed welding current is applied for a prescribed time in accordance with the sheet thickness of a high damping steel sheet, the thermosetting resin dispersed with metallic grains is softened by applying a method for applying electric current preliminarily at two stages between two thin steel sheets and discharged from the lower part of the welded chip, thereafter, a sandwich type high damping steel sheet is continuously spot-welded with a short interval. The ratio of a preliminarily applied current value of the small current at the initial stage of welding to the normally applied current value is preferred to be 0.375-0.875. Further, the preliminary energizing time is preferred to be the preliminary energizing time (sec) >=-0.16X(preliminarily applied current value/normally applied current value)+0.18. In this way, the occurrence of welding defects is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has a low welding defect occurrence rate when performing continuous spot welding at short distance intervals on a sandwich type vibration damping steel plate sandwiching a thermosetting resin having excellent vibration damping ability. The present invention relates to a spot welding method for sandwich type vibration-damping steel sheets having excellent welding stability.

[0002]

2. Description of the Related Art In recent years, demands for quietness and quietness have been increasing in various fields, and vibration damping steel sheets have been actively applied to household electric appliances, automobiles and building materials. With the widespread use of damping steel sheets, it has become important to be able to handle them like ordinary cold-rolled steel sheets.

However, since the vibration-damping steel plate is sandwiched by viscoelastic resin which is an electric insulator, spot welding cannot be performed as it is. Therefore, a damping steel plate capable of direct spot welding has been developed by dispersing metal particles inside a resin. In order to improve the weldability of the vibration-damping steel plate, there is a method of examining the welding conditions in addition to the method of examining the structure of the vibration-damping steel plate such as the average particle size of the metal particles and the compounding amount. Many patents are known about spot welding methods for damping steel sheets, but as an example of applying the two-step energization method to damping steel sheets, a large current is passed for a short time at the initial stage of welding to obtain high weld joint strength. This method is disclosed in JP-A-3-86380. However, when a large current is applied in the initial stage of welding, welding defects are likely to occur, and the spot weldability of the vibration damping steel plate is not always improved. This tendency is particularly remarkable in short-distance-interval continuous spot welding, in which vibration-damping steel plates are welded at a plurality of places at short-distance intervals.

[0004]

In the actual product processing and assembling processes, continuous spot welding may be performed at short distance intervals, and in this case, no welding defect occurred at the first spot. A welding defect may occur at the second and subsequent hit points. As welding defects that occur at this time, the so-called "circumferential break" in which the skin steel plate forming the damping steel plate burns down along the circumference of the welding tip, and the skin steel sheet near the welding tip melts and scatters. There is "table dust". In any of the welding defects, the skin steel sheet near the welding tip is melted. The cause of the welding defect is that the welding current is shunted to the existing welding points existing in the vicinity during spot welding, the current density around the welding tip becomes high, and the skin steel sheet melts. Therefore, in order to improve the continuous spot weldability of the damping steel plate at a short distance, the skin steel plate immediately below the welding tip is directly conducted at an early stage of the spot welding process to reduce the amount of shunt current. is important.

With a vibration-damping steel sheet using a thermoplastic resin having a low melt viscosity, the resin immediately below the welding tip can be eliminated at an early stage of the spot welding process, so that continuous spot weldability at a short distance is improved, but on the other hand , Inferior in workability, heat resistance and corrosion resistance. Therefore, the present invention provides a spot welding method that can obtain continuous spot weldability at good short distance intervals in a damping steel sheet using a thermosetting resin having excellent workability, heat resistance, corrosion resistance, and the like. The purpose is.

That is, it is difficult to eliminate the resin layer at the welding point especially in the vibration-damping steel plate using the thermosetting resin.
As a result, a shunt current flows for a long time to the already-welded point during continuous spot welding at short distances, so that circumferential breakage is particularly likely to occur. Therefore, it is necessary to study a welding method that can obtain good continuous spot weldability at a short distance in a damping steel sheet using a thermosetting resin.

[0007]

SUMMARY OF THE INVENTION According to the present invention, continuous spot welding at a short distance is performed on a sandwich type vibration damping steel plate in which a thermosetting resin having metal particles dispersed is sandwiched between two thin steel plates. At the time of application, first, a small current is applied for a predetermined time at the initial stage of welding, the thermosetting resin is softened to be removed from under the welding tip, and then a predetermined welding current is applied, which is characterized by sandwich type vibration damping. This is a short spot distance continuous spot welding method for steel sheets.More specifically, the preliminary energization time of a small current at the initial stage of welding satisfies the following equation for the ratio of the preliminary energization current value and the main energization current value, and This is a continuous spot welding method for short distance intervals of sandwich type damping steel sheets, in which the ratio of the energizing current value to the main energizing current value is 0.375 or more and 0.875 or less.

Preliminary energizing time (sec) ≧ −0.16 × (preliminary energizing current value / main energizing current value) +0.18

[0009]

According to the present invention, before a predetermined welding current corresponding to the thickness of the damping steel plate is passed for a predetermined time (hereinafter, this is referred to as main conduction), a small current less than the above-mentioned welding current is applied for an appropriate time. By applying a so-called two-step energization method of energizing (hereinafter referred to as preliminary energizing), the thermosetting resin that is the core material of the damping steel plate is softened and removed from under the welding tip, and then 2
Since spot-damped steel sheets are spot-welded, the occurrence of welding defects in continuous spot welding with a short distance is reduced.

FIG. 1 shows a schematic diagram of an energization pattern of two-step energization. The current value for pre-energization is determined by the ratio of the current value for pre-energization and the current value for main energization, and the ratio is 0.375 or more.
0.875 or less is suitable. At a current of less than 0.375, the removal of the resin directly under the chip does not proceed, and at a current of more than 0.875,
Since an excessive voltage is applied to the damping steel plate in the initial stage of pre-energization, welding defects occur. Further, the energization time of the pre-energization may be longer than the time required to remove the resin immediately under the chip when the predetermined current is energized, and the smaller the pre-energization current is, the longer the energization time required. Specifically, the preliminary energizing time (sec) ≧ −0.16 × (preliminary energizing current value / main energizing current value) +0.18. Even if the energization time of the pre-energization is longer than necessary, there is no particular problem in continuous spot weldability of the vibration-damping steel plate at a short distance, but it is not preferable in terms of workability and cost.

Further, the present invention is preferably applied to continuous spot welding (where the same steel plate is spot-welded at a plurality of places) when the welding point interval is 100 mm or less. The thermosetting resin used in the sandwich type vibration-damping steel sheet of the present invention is not particularly limited, but examples thereof include thermosetting polyester resin, epoxy resin, polyurethane resin, acrylic resin, and the like, and the present invention is a saturated polyester resin. It is more suitably applied to a sandwich type vibration damping steel plate using a thermosetting polyester resin composed of an isocyanate curing agent.

Next, the present invention will be described in more detail based on examples.

[0013]

[Examples] Two cold-rolled steel sheets of equal thickness 0.3 mm, 0.4 mm, 0.5 mm, and 0.6 mm were coated with a resin containing metal particles,
A vibration-damping steel plate was produced by laminating with an induction heating roll. The resin is based on 100 parts by weight of the main component, saturated polyester resin, and 4 parts of trifunctional polyisocyanate, which is a curing agent.
Parts, compounded. The resin thickness is 35 μm. As the metal particles, Ni powder having an average particle diameter of 65 μm was used, and was mixed with the resin in an amount of 1 vol%.

As the welding tip shape, a conflat type having a tip diameter of 5 mm was used. The pressure applied during welding depends on the total thickness of the damping steel plate.
In the case of 0.6 mm, 160 kgf, in 0.8 mm, 180 kgf, in 1.0 mm, 220 kgf, and in 1.2 mm, 270 kgf. When the current and the duration of the main energization are 0.6 mm, 0.14se at 7 kA
c, 0.8mm, 8kA, 0.16sec, 1.0mm, 9kA
In the case of 0.20sec and 1.2mm, it was fixed at 0.24sec at 10kA, and the pre-current and current were changed. The welded joint is the same damping steel plate.

Based on the above conditions, two damping steel plates were
"Circle break" when continuous spot welding is performed at 15 mm intervals
The occurrence rates of welding defects such as “Table dust” and the like are shown in Tables 1 to 4.
Moreover, these are collectively shown in FIG. In addition, the welding defect occurrence rate, when performing the 15 mm pitch continuous spot welding of the vibration-damping steel plate, the presence or absence of the circumferential breakage and the occurrence of surface dust was investigated, and the total number of points where any defect occurred was determined. The percentage of the score is shown as a percentage. Total thickness of damping steel plate is 0.8mm
In case of (Table 2), the conventional welding method (without pre-energization)
Although 60% of welding defects were generated, the application rate of pre-energization and the two-stage energization where the energization time was 4 kA and 0.14 sec resulted in a welding defect occurrence rate of 0% during continuous spot welding.
Became. Even if the pre-energization current is 4 kA, if the energization time is as short as 0.08 sec, the welding defect occurrence rate is 35%, and it is possible to remove the resin directly under the chip during the pre-energization at short distance intervals. It is important to improve continuous spot weldability. That is, it is understood from FIG. 2 that it is desirable that the preliminary energization time satisfies the following formula: preliminary energization time (sec) ≧ −0.16 × (preliminary energization current value / main energization current value) +0.18.

The ratio between the preliminary energizing current value and the main energizing current value is
The range of 0.375 or more and 0.875 or less is desirable. Under the same conditions as the example in the known Japanese Patent Application Laid-Open No. 3-86380 in which the two-step energization is applied to the damping steel plate, that is, the pre-energization current and energization time are 9 kA and 2 cycles (0.04 sec), respectively. Main energization is 8
When continuous spot welding with 15 mm intervals was performed under conditions of kA and 8 cycles (Table 2), the incidence of welding defects was as high as 55%,
Good weldability was not obtained. Even when the pre-energization current is the same and the energization time is extended to 4 cycles (0.08 sec), the occurrence rate of welding defects is high, and the effect obtained by the present invention is the same as in the case of the known Japanese Patent Laid-Open No. 3-86380. Different from

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

[Table 3]

[0020]

[Table 4]

[0021]

INDUSTRIAL APPLICABILITY The present invention has excellent workability, heat resistance, corrosion resistance and the like, but on the other hand, after applying a small current for a predetermined time at the initial stage of welding to a damping steel sheet using a thermosetting resin having poor weldability,
By adopting the two-step energization method in which a predetermined welding current is applied, it is possible to perform continuous spot welding with a short distance.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an energization pattern in two-step energization according to the present invention.

FIG. 2 is a graph showing the effects of preliminary energization current value / main energization current value and preliminary energization time on occurrence of welding defects. A: Energization time in pre-energization B: Current in pre-energization C: Energization time in main energization D: Current in main energization

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Fuminori Mukaihara, 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Technical Research Division, Kawasaki Steel Co., Ltd. (72) Masazumi Izawa, 1 Kawasaki-cho, Chuo-ku, Chiba Kawasaki Steel Corporation Technical Research Division

Claims (2)

[Claims] 1. When performing continuous spot welding at short distance intervals on a sandwich-type vibration-damping steel plate in which a thermosetting resin in which metal particles are dispersed is sandwiched between two thin steel plates, first a small initial Pre-energizing the current for a predetermined time, after softening the thermosetting resin to eliminate it from under the welding tip, then continuously apply a predetermined welding current to the sandwich type vibration damping steel plate for a short distance. Spot welding method. 2. The preliminary energization time of a small current at the initial stage of welding satisfies the following expression with respect to the ratio of the preliminary energization current value and the main energization current value, and the ratio of the preliminary energization current value and the main energization current value is 0.375 or more. The method of continuous spot welding of short distance intervals of sandwich type vibration damping steel plate according to claim 1, wherein the method is 0.875 or less. Pre-energization time (sec) ≥ -0.16 x (preliminary energizing current value / main energizing current value) + 0.18