JPH07124768A - Laser beam welding method of metal thick plate - Google Patents

Abstract

PURPOSE:To enable the piercing welding not having melt down by setting a heat input quantity to the prescribed condition at executing flat/butt welding of thick plate by laser beam. CONSTITUTION:When a metal thick plate is subjected to flat/butt welding with using laser beam, a heat input quantity Q by laser beam is set so as to satisfy the condition in the inequality and welding is executed. In the inequality, Q: heat input quantity (KJ/cm), h: plate thickness (mm), V: welding speed (cm/min) sigma: surface tension of molten metal (dyn/cm<2>), rho: density of metal (g/cm<3>), t: constant obtained relationship between laser output and piercing thickness, g: acceleration of gravity (cm/sec<2>). When heat input quantity Q can not satisfy the condition of the inequality, piercing welding becomes impossible due to insufficient melt down. When heat input quantity Q exceeds the condition of the inequality, because a molten metal quantity becomes excessive, melt down of molten metal is generated, sound bead is not formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention proposes a welding method which enables penetration welding without burn-through when butt welding a thick metal plate such as a thick steel plate downward with a laser beam.

[0002]

2. Description of the Related Art Since the laser welding method uses a laser beam having a high energy density as a heat source, it has a high speed (low heat input) and a bead shape index (penetration depth / melting depth /
The feature is that a bead with a wide bead width) can be obtained. Therefore, this welding method enables penetration welding with little thermal deformation due to welding heat input, and in recent years, it has been adopted in various places by making use of this characteristic.

[0003]

However, the conventional laser welding method is actually used only for a member having a relatively small plate thickness. For example, JP-A-58-1194
It is also apparent from JP-A No. 81-115592 that the examples of 1 mm and 3.5 mm, and JP-A-56-114592 disclose the examples of 6 mm and 3 mm.
As described above, the main reason why it is difficult to apply the laser welding method to a member having a large plate thickness is as follows. That is, when the plate thickness becomes large, and exceeds 10 mm, for example, the amount of molten metal inevitably increases. This easily causes welding defects such as dripping or bump-like projections on the lower surface side of the bead and undercuts on the upper surface side. However, it is known that these welding defects can be prevented by using a backing metal. However, the use of this backing metal may not be usable depending on the type of structure, and is economically disadvantageous.

Therefore, an object of the present invention is to establish a laser welding technique capable of overcoming the above-mentioned problems of the prior art when welding a thick metal plate by laser light. That is, the present invention, when butt-penetrating welding a metal thick plate downward by laser light, without a backing plate, welding defects such as drooping or hump-shaped projections and undercuts can be further reduced compared to the conventional one. The present invention proposes a laser welding method for thick metal plates that can be used.

[0005]

[Means for Solving the Problems] In order to achieve the above-mentioned objects, welding conditions and bead shapes of various metals and plate thicknesses when a metal plate is welded downward by laser light As a result of detailed research on the relationship between
The inventors have found that when the relationship between them is within a certain range, so-called penetration welding that penetrates from the front surface to the back surface is possible without causing the above-mentioned welding defects.

The present invention has been made based on the above new findings. That is, the gist of the present invention is as follows. 1. When butt-through welding a thick metal plate downward by laser light, the heat input by the laser light is calculated by the following equation: 60 × (h / t) ^10/7 /v≦Q≦1.12σ/ρg+60×(h
/ T) ^10/7 / v where Q: heat input (kJ / cm) h: plate thickness (mm) v: welding speed (cm / min) σ: surface tension of molten metal (dyn / cm ² ) ρ: Metal density (g / cm ³ ) t: Constant obtained from the relationship between laser output and penetration plate thickness g: Welding is performed under welding conditions that satisfy the gravitational acceleration (cm / sec ² ). Laser welding method for thick metal plates.

[0007]

The present invention will be described in more detail below. The inventors first performed downward laser welding by changing the plate thickness, the flow rate of assist gas and the heat input amount, and investigated the influence of welding conditions on the bead shape after welding, and the findings as described below. Got 1) In order to prevent the dropping of the bead, it is necessary to make (plate thickness) x (root bead width) below a certain value determined by the physical properties of the weld metal. 2) The control range is determined by the density of molten metal and the surface tension. 3) The maximum plate thickness that can be penetrated is proportional to the 0.7th power of the laser output. 4) There is the following relationship between the root bead width and the heat input. (Heat input) = (Minimum heat input required for penetration) + Coefficient x (Sheet thickness) x (Bead width at root) 5) If welding conditions are within a certain range, sound is not affected by the flow rate of assist gas A good weld can be obtained.

Based on these findings, the relationship between the welding heat input, the plate thickness, the welding speed, the surface tension of the molten metal, and the density of the metal was examined in more detail, and as a result, these relationships were controlled under certain conditions. It has been concluded that penetration welding with no welding defects is possible.

Next, the reason why the present invention is limited to the above-mentioned gist constitution will be described below. Heat input Q is 60 x
If (h / t) is less than ^10/7 / v, penetration penetration becomes impossible due to insufficient penetration. Therefore, the amount of heat input is 60 x (h / t) ^{10/7 in} order to perform penetration welding in one welding.
/ V or more. However, the heat input is
When 1.12σ / ρg + 60 × (h / t) exceeds ^10/7 / v, the amount of molten metal becomes excessive, so that the molten metal melts down and a healthy bead is not formed. Therefore, the heat input must be 1.12σ / ρg + 60 × (h / t) ^10/7 / v or less. Note that t in each of the above formulas is a proportional constant represented by (maximum plate thickness that can be penetrated) = t × (laser output ^0.7 ), and can be experimentally determined for each metal to be welded. it can. In the case of steel, its proportionality constant is 2.2.

The shape of the groove for applying the method of the present invention may be any shape such as I-type and Y-type, but when a groove other than the I-type groove is adopted, H in the above formula
The size of the root face is used as the value of.

In addition to steel, the method of the present invention can be applied to all kinds of metals based on copper, aluminum and the like.

[0012]

EXAMPLE A thick steel plate having a thickness of 9 mm to 44 mm is used, and the groove is I
As a mold, the flow rate of assist gas is 70-90 l / min,
The amount of heat input and the welding speed were changed to various levels as shown in Table 1, downward laser welding was performed, and the bead width of the root portion and the bead appearance after welding were observed. The experimental conditions and experimental results are shown in Tables 1 and 2. When obtaining the values of Expression 1 and Expression 2 shown in the table, t =
The calculation was made with 2.2, σ = 1400, and ρ = 7.85.

[0013]

[Table 1]

[0014]

[Table 2]

As can be seen from Tables 1 and 2, in each of the examples of the present invention, penetration welding with a stable bead width at the root portion is possible, and the bead appearance is such that drooping, bumpy protrusions, undercuts, etc. It was good with no welding defects. On the other hand, in the comparative example, welding defects such as insufficient penetration or dripping of molten metal occurred.

[0016]

As described above, according to the present invention, in the penetration welding of a thick metal plate, welding defects such as dripping, hump-shaped protrusions, and undercuts are significantly reduced as compared with the prior art.
Since a good bead can be obtained, sound penetration welding without a backing plate can be possible.

Claims (1)

[Claims] 1. When a thick metal plate is butt-welded downward by laser light, the amount of heat input by the laser light is calculated by the following formula: 60 × (h / t) ^10/7 /v≦Q≦1.12σ / Ρg + 60 × (h
/ T) ^10/7 / v where Q: heat input (kJ / cm) h: plate thickness (mm) v: welding speed (cm / min) σ: surface tension of molten metal (dyn / cm ² ) ρ: Metal density (g / cm ³ ) t: Constant obtained from the relationship between laser output and penetration plate thickness g: Welding is performed under welding conditions that satisfy gravity acceleration (cm / sec ² ). Laser welding method for thick metal plates.