RU2252116C2 - Method for electric-arc welding of multi-pass joints - Google Patents

Abstract

FIELD: welding processes and equipment, manufacture of metallic structures.

SUBSTANCE: method comprises steps of welding filling layers of multi-pass joints at electric current intensity, voltage, welding rate and heating temperature determined with allowance ±5% according to preset length of welded joint, depth fusion of previous pass and critical cooling rate with use of given equation system.

EFFECT: enhanced quality of welded joints due to elimination of quenching structure formation in metal of welded multi-pass joint, lowered time period of welding, reduced cost of production process.

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Description

The invention relates to welding production and can be used in the manufacture of metal structures to increase labor productivity and welding quality.

A known method of arc welding of products [1], including welding on the calculated number of passes, calculated the strength of the welding current, voltage and welding speed, at which the calculation is made according to the penetration depth of the i-th pass. The mode defined in this way ensures the minimum execution time of the process. However, the disadvantage of this method is that it does not take into account the cooling rate of the weld metal in a critical temperature range, which is determined by the strength of the welding current, voltage and welding speed. This circumstance during surfacing of medium alloyed hardened steels can lead to the formation of quenching structures in the weld metal, and therefore to cold cracks.

The closest in technical essence to the claimed is the method of arc welding [2], which includes calculating the cross-sectional area of the weld metal of the connection, the number of passes, welding of the root pass and welding of the filling layers on the calculated welding current strength, voltage and welding speed. The disadvantage of this method is that it does not take into account the cooling rate of the weld metal in a critical temperature range, which is determined by the strength of the welding current, voltage and welding speed. When welding medium alloyed hardened steels, this circumstance can lead to the formation of quenching structures in the weld metal and, therefore, to cold cracks.

The technical task of the invention is to improve the quality of welded joints by eliminating the formation of quenching structures in the welded metal and reducing production costs by reducing welding time.

The technical result is achieved by the fact that in arc welding in carbon dioxide of multi-pass joints, the length of the welded joint, the penetration depth of the previous pass and the critical cooling rate are set, and the filling layers are welded with a heating temperature, welding current strength, voltage and welding speed, determined with a tolerance of ± 5% ratio

Where

- коэффициент расплавления электродной проволоки (l_э - вылет электрода, мм);

λ _i - неопределенные множители Лагранжа (i=1,... 6), h - заданная глубина проплавления предыдущего слоя, мм; ω - критическая скорость охлаждения свариваемого металла, ° С/с; х₁=1,098, x₂=-0,451, x₃=1,37, x₇=0,32, x₈=-0,64, x₉=0,38, x₁₀=0,616, ξ =1,11, К_u=3,65, ξ ₁=0,554, при этом в случае схемы нагрева свариваемого соединения в виде “пластина” х₄=1, x₅=2, x₆=3, а в случае в схемы нагрева свариваемого соединения в виде “полубесконечное тело” - х₄=0, x₅=1, x₆=2, К₂=2· π · λ _t· cγ ^x4, - где η _u λ _t, a, cγ - соответственно эффективный кпд нагрева изделия, коэффициенты теплопроводности Вт/(м· ° С), температуропроводности м²/с и объемной теплоемкости Дж/(м³· ° С); I_min, I_max - технологические ограничения на силу сварочного тока, A; V_min, V_max - технологические ограничения на скорость сварки, м/час, i, ν - фиктивные переменные.L _W - weld length, m; S is the cross-sectional area of the seam, m ² , I _St , V _St , T, T _n , d _e - respectively, the welding current strength, A; welding speed, m / h; metal melting temperature, heating temperature, ° C; diameter of electrode wire, mm;

- the coefficient of fusion of the electrode wire (l _e - the departure of the electrode, mm);

λ _i — indefinite Lagrange multipliers (i = 1, ... 6), h — given depth of penetration of the previous layer, mm; ω is the critical cooling rate of the welded metal, ° C / s; x ₁ = 1.098, x ₂ = -0.451, x ₃ = 1.37, x ₇ = 0.32, x ₈ = -0.64, x ₉ = 0.38, x ₁₀ = 0.616, ξ = 1.11 , K _u = 3.65, ξ ₁ = 0.554, while in the case of the heating circuit of the welded joint in the form of a “plate” x ₄ = 1, x ₅ = 2, x ₆ = 3, and in the case of the heating circuit of the welded joint in in the form of a “semi-infinite body” - x ₄ = 0, x ₅ = 1, x ₆ = 2, K ₂ = 2 · π · λ _t · cγ ^x4 , - where η _u λ _t , a, cγ are, respectively, the effective efficiency of heating the product , coefficients of thermal conductivity W / (m · ° C), thermal diffusivity m ² / s and volumetric heat capacity J / (m ³ · ° C); I _min , I _max - technological restrictions on the strength of the welding current, A; V _min , V _max - technological restrictions on the welding speed, m / h, i, ν - dummy variables.

One of the methods to increase the competitiveness of welding production is to reduce costs, in particular the main time of the welding process. Based on experimental studies, the task of welding multi-pass joints with the cross-sectional area of the deposited metal of the welded joint S, the length of the joint L, the diameter d _e and the reach of the electrode was reduced to welding at the calculated optimal welding current strength I _cv , arc voltage U∂, speed welding V _St. , and the heating temperature by searching for a minimum of the main welding time as a function of the above parameters. The main time for welding multi-pass joints on the one hand is defined as N · t (N is the number of passes, t is the execution time of one pass), and with the other,

where γ is the density of the metal, Ψ is the loss coefficient of electrode metal due to fumes and spatter, α _P is the coefficient of fusion of the welding wire.

The fusion coefficient of the welding wire in the case of welding in carbon dioxide is determined as a function of the welding current strength, the outreach l _e and the electrode diameter d _e

where x ₇ = 0.32, x ₈ = -0.64, x ₉ = 0.38, x ₁₀ = 0.616 are experimentally determined coefficients.

When performing the welding operation of multi-pass joints, it is required to achieve the specified penetration of the previous layer. When experimentally welding in carbon dioxide, the dependences were obtained between the penetration depth h on the one hand and the welding current strength, arc voltage, welding speed and heating temperature T _n , thermophysical properties of the metal being welded (η _u λ _t , and, respectively, the effective efficiency of heating the product , thermal conductivity, thermal diffusivity) with another

ξ =1,11, x₁=1,098, х₂=-0,451, х₃=1,37, К_U=3,65 - экспериментально определяемые коэффициенты.Where

ξ = 1.11, x ₁ = 1.098, x ₂ = -0.451, x ₃ = 1.37, K _U = 3.65 - experimentally determined coefficients.

The critical cooling rate of the weld metal is determined from the ratio

where the coefficients x ₄ = 1, x ₅ = 2, x ₆ = 3, if the welded joint refers to the "plate" heating scheme, if the welded joint refers to the semi-infinite body heating scheme, then x ₄ = 0, x ₅ = 1 , x ₆ = 2.

In practice, when performing welding operations, technological limitations are imposed on the strength of the welding current, arc voltage and welding speed. The welding speed is limited, on the one hand, by the minimum possible value of V _min provided by the equipment or the welder during semi-automatic welding, or by the probability of formation of weld defects such as sagging, on the other hand, by the maximum possible value of V _max provided by the equipment or by the welder, or the probability of formation of weld defects type of undercut, or steady burning arc

V _{St. min} <V _St. <V _{St. max}

Similarly, restrictions on the strength of the welding current are associated with the stability of the arc, the formation of the seam and the technical capabilities of the welding equipment:

I _{St min} <I _St <I _{St max} .

The limitation on the arc voltage is imposed in the form of an experimentally established relationship between voltage and welding current strength for high-quality weld formation

Then the task of determining the strength of the welding current, arc voltage, welding speed and heating temperature after applying the Lagrange rule takes the form

where λ ₁ - indefinite Lagrange multipliers (i = 1, ... 6), I _min , I _max - technological limitations on the strength of the welding current, A; V _min , V _max - technological restrictions on the welding speed, m / h, i, ν - dummy variables, serve to convert inequalities into equalities, being a means of solving the problem.

To find a solution to the problem, solve the system of differential equations formed from the previous equation:

- точки экстремума, j=1,2, k=1,2,1=1,2,3,4,6.Where

- points of extremum, j = 1,2, k = 1,2,1 = 1,2,3,4,6.

An example implementation of the proposed method.

A compound of medium alloyed steel 10 mm thick with a bevel of 30 ° is welded in carbon dioxide, the cross-sectional area of the deposited metal is 59 mm ² , the length of the joint is 1000 mm. We take the thermophysical properties of the process and material according to the reference literature: density γ = 7850 kg / m ³ , effective heating efficiency of the product η _u = 0.8, thermal conductivity λ _t = 0.42 W / (cm · K), thermal diffusivity a = 0.08 cm ² / s and volumetric heat capacity with γ = 4.8 J / (cm ³ K), melting temperature T = 1530 ° C. A critical cooling rate of ω = 20 ° C / s was set. Welding is carried out by direct current of reverse polarity with a wire with a diameter of 1.6 mm, the reach of the electrode is 16 mm. Adopted the heating circuit "plate". The penetration depth of the previous layer was set h = 3 mm.

The experimentally determined coefficients in this case take the values: x ₁ = 1.098, x ₂ = -0.451, x ₃ = 1.37, x ₇ = 0.32, x ₈ = -0.64, x ₉ = 0.38, x ₁₀ = 0.616, ξ = 1.11, K _u = 3.65, ξ ₁ = 0.554. Technological restrictions on the welding current strength I _min , I _max are 100 A and 600 A, respectively, technological restrictions on the welding speed V _min , V _max are 7 m / h and 80 m / h, respectively.

The solution of the problem was carried out by means of the mathematical package Mathcad. The calculated mode parameters: welding current strength 234 ± 12 A, arc voltage 27 ± 1.5 V, welding speed 32 ± 1.6 m / h, heating temperature 198 ° C, number of passes 5.

Welded in carbon dioxide GOST 8050 specified compound of steel 17GS in the calculated modes with wire Sv-08G2S GOST 2246 with a diameter of 1.6 mm (electrode reach 15 ... 17 mm). We used a tractor-type welding machine ADG-502 with a welding power source VDU-504. To record the thermal cycle, the KSP-4 automatic electronic potentiometer with chromel-alumel thermocouples with a diameter of 0.5 mm was used. At first, welding of the horse passage was carried out. The temperature of 200 ± 20 ° C at the site of surfacing was achieved by imposing additional seams. Then, welding of filling passages was performed in the following mode: welding current strength 230 ± 10 A, arc voltage 26 ± 2 V, welding speed 32 ± 0.5 m / h. To complete the cutting of the edges, 5 passes were performed. The overlay of each subsequent pass began at a temperature of 200 ± 5 ° C in the place of surfacing. By processing the experimental data obtained using the KSP-4 potentiometer, it was found that the cooling rate in the OZZ of filling passages was 15 ± 5 ° С.

The technical and economic advantage of the invention is to improve the quality of welded joints by eliminating the formation of quenching structures in the welded metal and reducing production costs by reducing welding time. The method does not require capital expenditures, has ample opportunities and can be used when using any type of joints with cutting edges.

Sources of information

1. Vasiliev N.G. Optimization of deposition technology for worn-out products. // Welding production, 1994, No. 7, p. 4-7.

2. Krivosheya V.E., Babkin A.S. Dialogue design on a computer of the technological process of welding in CO ₂ // Automatic welding, No. 1, 1990, p. 62-65.

Claims (1)

A method of arc welding of multi-pass joints, including determining the area of the deposited metal of the joint, the number of passes, welding in the carbon dioxide of the root pass and filling layers at specific welding current strength, voltage and welding speed, characterized in that the length of the welded joint, the penetration depth of the previous pass and critical cooling rate, and the filling layers are welded with a heating temperature, welding current strength, voltage and welding speed, determined with a tolerance of ± 5% per second relations:

Where

L _W - weld length, m; S is the cross-sectional area of the weld metal of the compound, m ² ; I _St , V _St , T, T _n , d _e - respectively, the welding current strength, A; welding speed, m / h; metal melting temperature, heating temperature, ° C; diameter of electrode wire, mm;

- the coefficient of fusion of the electrode wire (l _e - the departure of the electrode, mm);

λ _i — indefinite Lagrange multipliers (i = 1, ... 6), h — given depth of penetration of the previous layer, mm; ω is the critical cooling rate of the welded metal, ° C / s; X ₁ = 1.098, X ₂ = -0.451, X ₃ = 1.37, X ₇ = 0.32, X ₈ = -0.64, X ₉ = 0.38, X ₁₀ = 0.616, ξ = 1.11 , K _u = 3.65, ξ ₁ = 0.554, while in the case of the heating circuit of the welded joint in the form of a “plate” X ₄ = 1, X ₅ = 2, X ₆ = 3, and in the case of the heating circuit of the welded joint in the form "semi-infinite body" - X ₄ = 0, X ₅ = 1, X ₆ = 2, K ₂ = 2 · π · λ _t · cγ ^x4 , where η _and , λ _t , а, сγ are the effective heating efficiency of the product, respectively coefficients of thermal conductivity W / (m ° C), thermal diffusivity cm ² / s and volumetric heat capacity J / (m ³ C); I _min , I _max - technological restrictions on the strength of the welding current, A; V _min , V _max - technological restrictions on the welding speed, m / h, i, v - dummy variables.