KR100617948B1 - Single-side hybrid welding method for the reduction of porosity in fillet welds - Google Patents

Abstract

The present invention relates to a single-sided hybrid welding method to reduce the pores of the weld portion during fillet welding of ships and steel structures in which thick plate steel having a thickness of 6 mm or more is widely used.

According to the method of the present invention, the laser output (LP, kw), the welding speed (WS, m / min), and the filler wire feeding speed (FR, m / min) depend on the thickness (t, mm) of the steel to be welded. There are technical features in controlling to satisfy a specific relationship.

In the present invention, the single-sided hybrid welding method for reducing the pores of the fillet welds can significantly improve the overall productivity of the ship or the steel structure since the single-sided hybrid welding can be performed without performing secondary processing on the plasma cut surface and the primer coated surface of the weld joint. It is expected to be possible.

Hybrid welding, pore, fillet welding, laser, arc, arc torch

Description

Single-side hybrid welding method for the reduction of porosity in fillet welds}

1 is a cross-sectional view showing a welding process of the fillet welded joint.

Figure 2 is a cross-sectional view showing the X-ray transmission test method for measuring the pores of the fillet welded joint.

3 is a plan view showing a method for measuring the pore cross-sectional ratio of the X-ray transmission image for the fillet welded joint.

         ((Explanation of symbols for main part of drawing))

           11. GMA welding torch 12. Laser beam

           13. Web 14. Flange

           15. Welding Bead

S. Weld area S _i . Pore area

The present invention relates to a welding method for reducing the pores generated in the fillet seam during single-sided hybrid welding, more specifically, the output of the laser is controlled in accordance with the welding speed and steel thickness and the feed rate of the filler wire, but the welding speed The filler wire supply speed, laser output, steel thickness, etc. satisfy certain relational expressions, and in particular, it is possible to reduce pores generated in fillet welded joints of ships or steel structures in which heavy plate steel having a thickness of 6 mm or more is frequently used. It relates to a single-sided hybrid welding method for reducing the pores of the fillet welds.

Steels that make up ships or steel structures are joined to each other by means of welding, bolts, etc., depending on their location and purpose. Especially, in welding, butt welding, overlap welding, fillet welding, edge welding, edge welding, plug Although various forms of welding, such as welding, are made, the joint part by fillet welding occupies more than 70% of the whole weld joint part.

Therefore, the overall productivity and quality of the vessel or steel structure can be said to be dependent on the fillet welded joints, look at the conventional fillet welding method as follows.

Conventional fillet welded joints are generally made of manual or semi-automatic arc welding, but the penetration depth is limited due to the characteristics of arc welding. Welding is required.

However, as the amount of heat input of the welding increases, thermal deformation of the welded material is required, and thus, additional correction work for the thermal deformation part after welding must be necessarily accompanied, which leads to a decrease in the overall productivity of the welding operation process.

In other words, arc welding, which has been used for a long time for welding thick steels, and which is most widely used even now, does not have a deep penetration depth, and thus increases the welding heat input amount to increase the penetration depth. The degree of thermal deformation increases, as well as the width of the weld portion is wide, which is not preferable in terms of aesthetics, and has a problem in that welding productivity is also reduced.

Therefore, in order to solve the above-mentioned problems of arc welding, there is an increasing demand to apply a high quality welding technique using a laser to welding steel plates or steel plates used in ships.

However, in the case of laser welding, since the diameter of the beam is very small, the gap tolerance of the gap between the joints between welded members is extremely limited. Therefore, in order to perform laser welding, the joints of the welded joints are limited. Precise machining and clamping must be preceded, which results in difficulty in avoiding productivity degradation.

In order to solve the problems caused by the arc welding or laser welding, hybrid welding method incorporating the arc and laser, which can take advantage of the advantages of arc welding having a wide gap tolerance value and laser welding with a deep penetration depth. It has been developed and is actively applied to various fields such as shipbuilding, automobiles, line pipes and pressure vessels.

Even in the case of hybrid welding in which the advantages of arc and laser are mixed as described above, since welding is possible on one side of the butt welding, that is, only one side is welded, excellent welding productivity and weld quality can be obtained. As used together, the number of variables for controlling welding is further increased, and the control is complicated and difficult.

In particular, although excellent welding productivity and weld quality can be obtained, it is urgent to reduce pores generated in the fillet weld during single-sided hybrid welding, but there is no obvious method.

In the case of hybrid welding, the use of the laser and the arc together increases the number of variables for controlling the welding, which makes the control complicated and difficult. In particular, it is not easy to apply the fillet weld seam and there is no established technology. In addition to the situation, in general, the primer coated for rust prevention of shipbuilding steel is a major cause of the generation of the pores of the weld when welding both sides of the arc, so the welding is performed after removing the primer before arc welding.

However, the operation such as the removal of the primer coated on the steel surface as described above will reduce the productivity, there is a need for a method that can be welded without removing the primer as possible.

In addition, when the steel is cut using heat such as plasma, an oxide layer is formed on the cut surface, and the oxide layer causes defects such as pores during laser welding. Therefore, it is preferable to first remove the oxide layer on the cut surface before laser welding. It is common.

However, this operation also reduces productivity, providing a single-sided hybrid welding method that can reduce the pore while performing the welding without removing the primer and the cutting surface oxide layer that can generate weld pores in the single-sided hybrid welding of the fillet joint. Has its purpose.

The above object of the present invention is achieved by a specific relationship between laser power, welding speed, filler wire feeding speed and steel thickness.

The single-sided hybrid welding method for reducing the pores of the fillet welds of the present invention is, in particular, a factor that directly affects the welded portion of a ship or steel structure in which a steel material of 6 mm or more in thickness is used, the thickness of the welding target steel, the laser output, and the welding. The technical characteristics of reducing the pores that can be generated in the fillet welds by controlling the speed and the filler wire feed rate to satisfy a specific relationship, look at the mechanism in which the pores are generated in the fillet welds.

In general, pores formed in the fillet welds can be considered in two aspects, one due to a specific component contained in the steel to be welded, and the other due to an external material coated or formed on the surface of the steel. As a representative example of the former, the carbon contained in the steel is combined with oxygen during welding to form CO, which is not discharged to the outside, and remains in the welded portion, the latter being a primer or oxide layer coated on the surface of the steel The case where the various gas which generate | occur | produced by melt-decomposition at the time of welding is captured by a welding part is mentioned.

Therefore, in arc welding, laser welding, and hybrid welding, an inert gas is supplied to the welding portion so that the welding portion does not come into contact with the atmosphere, thereby preventing or minimizing the generation of pores caused by the electrons.

However, in the latter case, even when the inert gas is supplied to the welded portion, the decomposition of the primer or the oxide layer on the surface of the steel occurs in the inside thereof, and the gas generated therefrom is in contact with the molten metal of the welded portion. It is difficult to reduce the generation of pores only by supplying the gas.

In particular, the ship's construction or steel structure production takes a long time in the exposure to the atmosphere, so the steel for ships or steel structures are not only coated with a primer on the surface for rust prevention, most of the steel is more than 6mm Since it is cut by a melt-type method using heat such as plasma rather than a mechanical method using a saw or the like as a thick material having a thickness, an oxide layer is formed on the cut surface, and an oxide layer on the cut surface that becomes a weld joint together with a primer for rust prevention. This welding is a major cause of generation of weld pores.

That is, the low melting point metal such as Zn contained in the primer coated on the fillet joint is trapped in the welding part after evaporation in the welding part or the oxide layer is mixed in the welding part to reduce the stability of the welding part. The amount of inflow into the keyhole formed by the laser beam and the inflow behavior affect the generation of pores.

Therefore, in order to improve the stability of the welded part, it is necessary to control the formation of the keyhole by the laser beam, the amount of molten metal flowing therein, and the inflow behavior. The thickness of the steel to be welded (t, mm) and the laser as a factor to control the welding Power (LP, kW), welding speed (WS, m / min) and filler wire feed rate (FR, m / min) were selected.

That is, in the single-sided hybrid welding method for reducing the pores of the fillet weld of the present invention, the four factors are controlled to satisfy the following Equations 1 and 2, so that the keyhole is stably formed and the amount and behavior of the molten metal introduced into it. This adjustment reduces the generation of pores in the welded portion, thereby improving the stability of the welded portion.

,

,

,

,

As described above, a healthy fillet weld can be obtained by controlling the laser output, the filler wire feeding speed, and the welding speed so as to satisfy Equations 1 and 2 with respect to a steel having a specific thickness, which will be described in detail through the following examples. As follows.

A thick plate steel of 6 mm thick, single-sided hybrid fillet welded, as shown in Fig. 1, wherein the laser power, the welding speed, and the filler wire feeding speed were 5-12 kW, 0.5-2 m / min, and 4-13 m /, respectively. The range of min was varied and the cross sectional area of pores generated in each fillet weld was investigated.

Pore cross-section ratio of the fillet weld, as shown in Figs. 2 and 3, fillets X-ray two-dimensional weld the total area in the projection image of the weld (S, 10mm × 100mm) occupied by the in pore area (S _i, i Is 1, 2, 3, ...., N, N is a natural number, the pore section ratio (%), which is a ratio of the number of pores formed in the weld part, is calculated by the following Equation 3, and the results are shown in Table 1 below. And 2 are shown.

 No.  L.P (kw)   W.S (m / min)   t (mm)   F.R (m / min)    Porosity cross section (%)   One     5      0.5     6      4    Incomplete penetration   2     5      0.5     6      6    Incomplete penetration   3     7      0.5     6      4       0.03   4     7      0.5     6      6.5       3.03   5     6      One     6      5    Incomplete penetration   6     6      One     6      7    Incomplete penetration   7     8      One     6      6       0.15   8     8      One     6      9       4.27   9     7      1.5     6      7    Incomplete penetration  10     7      1.5     6      9    Incomplete penetration  11     9.5      1.5     6      7.5       0.23  12     9.5      1.5     6      9       0.62  13    10      2     6      9    Incomplete penetration  14    11      2     6      9       0.08  15    12      2     6     11       0.64  16    12      2     6     13       5.65

   No.   Porosity cross section (%)      A    L.P / A     B    One    Incomplete penetration    6.330    0.790 2.0    2   Incomplete penetration    6.030    0.829    4.0    3 0.03    6.330 1.106 2.0    4      3.03    5.955 1.175    4.5    5   Incomplete penetration    7.830    0.766 1.0    6   Incomplete penetration    7.530    0.797 3.0    7 0.15    7.680 1.042 2.0    8      4.27    7.230 1.107    5.0    9   Incomplete penetration    9.180    0.763  1.0   10   Incomplete penetration    8.880    0.788 3.0   11 0.23    9.105 1.043 1.5   12 0.62    8.880 1.070 3.0   13   Incomplete penetration   10.530    0.950 1.0   14  0.08   10.530 1.045 1.0   15 0.64   10.230 1.175 3.0   16      5.65    9.930 1.208    5.0

As a result of performing the one-sided hybrid fillet welding while changing the welding conditions as described above, most of the pores found in the fillet welds were observed in the vicinity of the back bead, and the pore cross-sectional ratio was determined by laser power, filler wire feeding speed, welding. It was found to be closely related to speed and the like.

And, the correlation between pore generation and such hybrid welding conditions shows that there is a close relationship between the stability of the keyhole formed by the laser beam and the flow of the filler wire melted by the arc, as described above. In other words, the molten metal by the arc affects the pore generation by affecting the stability of the keyhole according to the amount and inflow behavior of the molten metal into the keyhole formed by the laser beam.

Therefore, in order to suppress the generation of pores in the single-sided hybrid fillet welds, it is important to reduce the inflow of the molten metal and arc pressure by the arc so that low-melting metal vapors such as Zn evaporated from the welds can be smoothly discharged to the outside. In Equation 1, A is a value related to penetration in single-sided hybrid welding of the fillet welds, and in order to obtain full penetration basically under laser output conditions for pore reduction of the fillet welds, the ratio of the laser power LP to the A value is It should be 1 or more, but the pores will be reduced to 1.2 or less for pore reduction.

This means that when the L.P / A value is greater than 1.2, the force of inflow of the arc molten metal into the keyhole increases, thereby inhibiting the stability of the keyhole.

In addition, the important welding factors, together with the laser power, are the feed speed and the welding speed of the filler wire.

In other words, if the B value is less than 1, the filler wire's feeding speed (FR) is insufficient compared to the welding speed. If the gap is present at the joint due to insufficient molten metal, incomplete penetration may occur. As the amount of molten metal flowing into the keyhole and the arc pressure are increased, not only the keyhole stability is lowered, but also the low-melting point metal vapor discharge such as Zn included in the primer is disturbed, thereby increasing the porosity of the weld.

Therefore, in order to reduce the pores of the fillet welds in single-sided hybrid welding, the laser power, the filler wire feeding speed, and the welding speed must be controlled to satisfy Equations 1 and 2 simultaneously according to the thickness of the steel to be welded, so that EN ISO Welding parts suitable for class B with a porosity of 0.7% or less, which is the highest among the porosity criteria of the laser welded part specified in 13919-1, can be obtained (class D is 6% or less, class C is 2% or less, and class B is 0.7). Grouped under 3%))

As described above, the single-sided hybrid welding method for reducing the pores of the fillet welded part of the present invention, even in the case of welding immediately without removing the primer coated on the steel in the shipbuilding field or performing secondary processing on the plasma cutting surface Since the pores generated in the welding part can be minimized, the production productivity of ships or steel structures can be greatly improved, and accordingly, the investment efficiency for the hybrid welding facility is expected to be improved.

Claims (2)

In the hybrid welding method using the arc and the laser together for the fillet welding seam, the thickness (t, mm) of the steel to be welded, the laser output (LP, kw), the welding speed (WS, m / min), Filler wire feeding speed (FR, m / min) is controlled to satisfy the following equations 1 and 2, the one-sided hybrid welding method for reducing the pores of the fillet weld. Equation 1

,

Equation 2

,

The method of claim 1, wherein the thickness (t, mm) of the steel is 6 mm or more hybrid welding method for reducing the pores of the fillet welds.

Images