Selection and calculation of welding modes by semiautomatic device. Selection and calculation of welding modes. Semi-automatic shielded gas welding
We calculate the mode of semi-automatic welding in a protective gas environment for a butt joint. Cutting type C12 according to GOST 14771-76.
Figure - Edging C12
Seam root welding (seam A):
where s is the thickness of the metal, mm; We set the current \u003d 120 A
1) The welding current is determined by the formula (2.15):
where a is the current density in the electrode wire, A / mm 2 (When welding in CO 2 a \u003d 110 ... 130 A / mm 2;)
d e - the diameter of the electrode wire, mm
We take I St \u003d 130 ... 140 A.
Take U d \u003d 26 V.
Based on this, we determine the welding speed by the formula:
that is, included in the speed limit of 15 ... 37 m / h for mechanized welding. We take V St. \u003d 22 m / h (0.6 cm / s).
4) We calculate the linear energy taking the values \u200b\u200bof the effective efficiency heating the product by an arc when welding in a mixture of CO 2 ŋ and \u003d 0.80.
where k = 0,79 (coefficient depending on the type and polarity of the current)
8) When welding in a CO 2 mixture, the overhang of the electrode l is chosen within 10-20 mm
9) Determine the deposition coefficient α n
α n τ \u003d 
10) The feed rate of the electrode wire is determined from the condition:
(2.39)
Determine the height of the roller. When welding in carbon dioxide in the range of modes that ensure satisfactory formation of the weld, the coefficient of completeness of the roller varies within narrow limits and is almost equal to μ B \u003d 0.73.
12) The height of the roller is (mm):
C \u003d H + =3 + 1,28 = 4,28 mm (2.28)
Ψ
in
= 
(2.29)
Ψ in must be within 7 ÷ 10
Filling the seam B (9 passes):
where s is the thickness of the metal, mm; We set the current \u003d 190A
1) the welding current is determined by the formula (2):
Take U d \u003d 28 V.
3) As is known from practice, a seam is formed satisfactorily when the product of the current strength (A) and the welding speed (m / h) during automatic welding with an electrode wire of 1.2 mm in diameter is in the range of 2000 ... 5000.
Based on this, we determine the welding speed by the formula (7):
We take V St. \u003d 19 m / h, (0.52 cm / s).
4) We calculate the linear energy, taking the values \u200b\u200bof the effective efficiency heating the product with an arc ŋ and \u003d 0.80
5) Determine the coefficient of the form of penetration by the formula:
where k = 0,79 (coefficient depending on the type and polarity of the current)
6) Determine the penetration depth N (cm) when welding in shielding gas:
7) Determine the width of the seam e (mm):
8) When welding in a CO 2 mixture, the overhang of the electrode l is selected within 10–20 mm.
9) Determine the deposition coefficient α n:
α n τ =
α r τ =
10) the feed rate of the electrode wire is determined from the condition:
(2.39)
where α n is the surfacing coefficient;
γ is the specific gravity of the metal for steel γ \u003d 7.8 g / cm 3.
11) F n - the area of \u200b\u200bmetal deposited over a given passage (cm 2);
Determine the height of the roller. When welding in a mixture of gases in the range of modes that ensure satisfactory formation of the weld, the coefficient of completeness of the bead varies within narrow limits and is almost equal to µ B \u003d 0.73. Then:
12) the height of the roller is (mm):
13) Determine the total height of the seam C (mm):
C \u003d H + = 5.3 + 1.31 \u003d 6.61 mm (2.43)
14) Determine the gain form factor:
Ψ
in
= 
(2.44)
For well-formed joints Ψ in must be within 7 ... 10 . Small values \u200b\u200bof Ψ in occur at narrow high seams, such seams do not smoothly interface with the base metal and have unsatisfactory performance under variable loads. Large values \u200b\u200bof Ψ in correspond to wide and low reinforcements, such seams are undesirable for the same reasons as seams with an excessively large value of Ψ in, as well as in connection with a possible decrease in the cross section of the weld compared to the cross section of the base metal due to fluctuations in the level of the liquid bath .
We determine the average chemical composition of the weld metal when welding steel 09G2S with Filarс PZ6114S wire.
Figure 11– The scheme for calculating the areas of molten and deposited metal
where | x | w, | x | ohm | x | e is the concentration of the element in question in the weld metal, base and electrode metal;
γ about - the participation of the base metal in the formation of the weld, is determined by the formula.
4.1 Calculation of welding modes for manual arc welding of coated electrodesand.
The determination of welding conditions usually begins with the diameter of the electrode, which is assigned depending on the thickness of the sheets when welding the joints of the butt joints.
So with a sheet thickness of 4-8 mm, the diameter of the electrode is: d e \u003d 4 mm.
In manual arc welding, in accordance with GOST 5264-80, the following geometric dimensions of the preparation of the edges for welding and the dimensions of the weld are shown in Table 6.
Table 4.1 - GOST 5264-80, the geometric dimensions of the preparation of the edges for welding and the weld
We calculate according to the formulas:
Determine the cross-sectional area of \u200b\u200bthe weld metal by the formula:
The data (see table 6) substitute in the formula (3) and get:
We determine the strength of the welding current.
In manual arc welding, the current strength is selected depending on the diameter of the electrode and the permissible current density:
,
(2)
where d e is the diameter of the electrode;
j is the current density, according to the electrodes with calcium fluoride coating and a diameter of 4 mm, the current density is: j \u003d 10 - 14.5 A / mm 2.
Then, the current strength is equal to:
A.
The calculated current values \u200b\u200bdiffer from the actual ones, then for electrodes of the TsL-11 brand with a diameter of 4 mm for welding in the lower position according to GOST 9466-60, we accept:
We determine the arc voltage by the formula:
,
(3)
The arc voltage during manual arc welding varies within relatively narrow limits, and when designing welding processes, it is selected based on the recommendations of the certificate for this brand of electrodes,.
To calculate the magnitude of welding strains and some other calculations, it may be necessary to take into account the thermal effect on the metal being welded, determined by the linear energy:
(4)
where U d - arc voltage, V;
η and - effective K.P.D. arcs; for arc welding methods it is equal to: η and \u003d 0.6 ÷ 0.9;
V St - welding speed, which is determined by the formula:
(5)
where α n - deposition coefficient, g / A · h; α n \u003d 11.5 g / A · h;
γ is the density of the deposited metal γ \u003d 8.1 g / cm 3;
F n - the area of \u200b\u200bthe weld metal; F n \u003d 0.22 cm 2.
Thus: 
.
V St. \u003d 10.3 m / h.
Therefore, the linear energy is equal to:
.
We determine the number of passes that are necessary for the formation of the connection.
According to, the number of passes is determined by the formula:
(6)
where F 1 - the cross-sectional area of \u200b\u200bthe metal deposited in one pass;
F n - the cross-sectional area of \u200b\u200bthe metal deposited for the subsequent passage.
The cross-sectional area of \u200b\u200bthe metal deposited in one pass is determined by the formula:
(7)
where d e is the diameter of the electrode; d e \u003d 4 mm.
Thus:
The cross-sectional area of \u200b\u200bthe weld metal for the subsequent pass is determined by the formula:
(8)
Therefore, the number of passes is:
.
We accept n \u003d 1.
The maximum temperature at a distance r is calculated by the formula:
from here we get the isotherms of melting:
,
(9)
where qп - linear energy.
where qe is the effective thermal power of the source, W
where сρ \u003d 4.7 J / cm3 · deg - volumetric heat capacity.
Substituting the values \u200b\u200bwe get:
For one run:
Penetration depth
We take the penetration depth equal to 4.6 mm.
To do this, we determine the area of \u200b\u200bpenetration by the formula
;
where e \u003d 8mm - the width of the seam, N \u003d 3.9mm - the depth of penetration, (based on table 17).
Area of \u200b\u200bweld metal 
.
We calculate the share of the base metal in the weld metal by the formula:
where Fpr is the area of \u200b\u200bpenetration;
Fн is the area of \u200b\u200bsurfacing.
Then: γ 0 \u003d 
.
We define the distance from the center of the weld pool to the melting isotherm, which for low-carbon steels is calculated by the formula:
,
(10)
where e \u003d 2.718;
q p \u003d 10150 J / cm;
Mp \u003d 1425 ° C;
- volumetric heat capacity J / cm3 · deg (for austenitic steels 
\u003d 4.7 J / cm3 deg);
Thus:
.
Determine the penetration depth by the formula:
(11).
Thus:
In the course of these calculations, we chose the modes for manual arc welding with coated electrodes, which ensure the formation of the weld geometry according to GOST 5264-80.
4.2 For welding under a flux layer.
Table 4.2 -T-welded joint C2 for submerged arc welding.
(GOST 8713-79).
|
Conditional designation welded joint |
Structural elements |
e, no more | ||||||
|
prepared edges welded parts |
weld |
before off |
before off |
|||||
For submerged arc welding of plates with a thickness of 5 mm, we take the wire diameter d e \u003d 2 mm.
1) Area of \u200b\u200bweld metal:
F n \u003d K 2/2, (12)
where K is the leg of the seam, mm;
F n \u003d 7 2/2 \u003d 24.5mm 2 \u003d 0.245cm 2
2) Welding current strength I St:
I St \u003d π × d e / 4 × j, (13)
where d e is the diameter of the electrode, mm;
j is the permissible current density, A / mm 2.
I St \u003d ((3.14 
2 2)/4)
150 \u003d 471 A
U d \u003d 20 + 50 × 10 -3 / 
e × I St., (14)
U d \u003d 20 + ((50 
10 -3)/
)
471) \u003d 36.8 V.
4) Welding speed:
V St \u003d (α n 
I St.) / (3600 
γ 
F H), (15)
where α n - deposition coefficient, g / A h;
γ \u003d 8.1 is the density of the deposited metal, g / cm 3.
Since when welding under flux, metal losses are 2-3%, then α n α p.
α p \u003d 6.3 + ((70.2 
10 -3) / (d e 1.035)) 
I St., (16)
α p \u003d 6.3 + ((70.2 
10 -3)/(2 1,035))
471 \u003d 22.44 g / Ah
V St. \u003d (13.46 
471)/(3600
8,1
0.25) \u003d 0.86 cm / s \u003d 30.96 m / h
5) Linear energy:
g p \u003d I St × And g × η and / V St, (17)
where I St - welding current;
And g is the voltage;
V St - welding speed;
η and \u003d 0.85 
0.95 - effective efficiency for submerged arc methods.
g p \u003d (471 
36,8
0.85) / 0.86 \u003d 17.13 kJ / cm \u003d 4111.2 kCall / cm
6) Depth of penetration:
H \u003d A 
,
(18)
where A \u003d 0.0156 for submerged arc welding.
Ψ ol \u003d K 
(19-0,01
I sv) 
,
(19)
where K is the penetration coefficient.
K \u003d 0.367 × i 0.1925, (20)
K \u003d 0.367 × 45 0.1925 \u003d 0.763
Ψ ol \u003d 0.763 
(19-0,01
471)
=10,7
H \u003d 0.0156 
\u003d 0.48 cm
7) Cushion Width:
e \u003d F n / 0.73 
q, (21)
e \u003d 0.245 / 0.73 
0.2 \u003d 1.7cm
8) Total seam height:
C \u003d 0.48 + 0.2 \u003d 0.68 cm
9) Instantaneous cooling rate of the metal in the heat-affected zone:
,
(23)
where ω \u003d f () is a dimensionless criterion;
λ - thermal conductivity, W / cm * 0 C;
сρ - volumetric heat capacity, J / cm 3 * 0 С;
T 0 - the initial temperature of the product, 0 C;
T is the temperature of least stability of austenite, 0 C.
For most austenitic steels:
λ \u003d 0.16; cρ \u003d 4.9;
T \u003d 550-600 0 C; T 0 \u003d 20 0 C
(24)
0 s / s
According to the recommendations for welding a given steel grade in order to avoid warping, it is necessary to apply welding methods and modes that ensure the maximum concentration of thermal energy. Almost 5 times greater than for carbon steels, the specific resistance of the metal is the reason for the large heating of the welding wire and electrode metal, which leads to an increased melting coefficient. Considering this, during welding, the electrode overhang is reduced and the wire feed speed is increased. Will accept 
.
Because when welding with direct current of reverse polarity, the specific amount of heat released in the near-electrode region varies within small limits, and the component 
The value of the second component of the melt coefficient can be calculated according to the equation proposed by B. K. Panibrattsev.
(25)
Where 
- electrode extension, cm; dE - electrode diameter, cm.
The magnitude of the electrode stick-out during submerged arc welding is selected within the range of 20-80 mm.
Smaller electrode diameters correspond to lower values \u200b\u200bof offset and vice versa.
Determine the welding speed:
;
Linear energy:
;
(26)
where η and \u003d 0.85 
0.95 - effective efficiency for submerged arc methods;
We take η and \u003d 0.9;
Instant metal cooling rate in the heat affected zone:
λ \u003d 0.16 W / cm K - thermal conductivity,;
cρ \u003d 4.9 J / cm 3 K — volumetric heat capacity of high alloy austenitic steels;
T 0 \u003d 20 0 C is the initial temperature of the product;
T \u003d 550-600 0 C - temperature of least stability of austenite;
w is the dimensionless criterion of the cooling process, which depends on the properties of the metal being welded and the welding conditions expressed in terms of the dimensionless value 1 / θ determined by the formula:
by ω \u003d 0.1 for 
;
According to the recommendations, it is desirable to provide an increased cooling rate of the metal after welding to grind the weld metal structure and reduce the degree of segregation of alloying elements. And make a normalizing vacation at a temperature of 650-700 C to prevent inter-crystalline corrosion and reduce internal deformations in the HAZ
Table 18 - Structural elements of the weld GOST14771 - 76
The main parameters of the mechanized welding mode, which have a significant impact on the size and shape of the welds are:
Diameter of electrode wire, mm;
The value of current, A;
Arc voltage, V;
Welding speed, m / h;
Wire feed speed, m / h;
Linear energy of welding, J / mm;
Ensuring a thermal cycle providing optimal properties of the heat-affected zone and the weld metal.
When determining the welding mode, it is necessary to select such parameters that will ensure the receipt of seams of the given sizes, shapes and quality.
To calculate the welding mode, one main seam will be taken. The mode of the remaining seams is selected according to the tables. As the main, the seam No. 4 of GOST 14771? 76 - C15? UP
When welding with wire with a diameter of 1.6 ... 2.0mm, the area of \u200b\u200bthe first pass is 20 ... 40mm 2, the area of \u200b\u200bthe second pass is 40 ... 60mm 2, the area of \u200b\u200bsubsequent passes is 40 ... 100mm 2 according to.
We determine the strength of the welding current.
where the diameter of the electrode wire is 1.6 mm;
Current density (160A / mm 2).
Welding current for the first pass
I St. \u003d 270 A.
For the adopted electrode diameter and welding current strength, we determine the optimal arc voltage:
Knowing the welding current, the diameter of the electrode and the voltage on the arc, we determine the shape factor of the weld by the formula:
where is a coefficient whose value depends on the type and polarity of the current. \u003d 0.92 at a current density of 160A / mm 2 when welding with direct current of reverse polarity.
W П \u003d - 4.72 + 17.6? 10 -2? Ј - 4.48? 10 -4? Ј 2 (15)
W P \u003d - 4.72 + 17.6? 10 -2? 160 - 4.48? 10 -4? 160 2 \u003d 12.4%
Define the welding speed for the first pass. F \u003d 30mm 2
V cv \u003d 0.1956 cm / s \u003d 7.04 m / h
F n \u003d F 0 n - F n, (18)
F n - the area of \u200b\u200bthe first pass.
Welding mode for the second pass.
Arc voltage
Fusion coefficient;
br \u003d 9.4g / Ah
Surfacing coefficient;
b n \u003d 8.23 \u200b\u200bg / Ah
The welding speed of the second pass F \u003d 40mm 2;
V sv \u003d 0.2344cm / s \u003d 8.44m / h
Welding speed, arc voltage, melting coefficient will be the same as for the second pass. The cross-sectional area of \u200b\u200bthe seam F \u003d 90mm 2;
V sv \u003d 0.0869cm / s \u003d 3.13m / h
V sv \u003d 0.1186cm / s \u003d 4.27m / h
Calculation of welding modes in a mixture of gases Ar + CO2
Table 19 - Optimum IDS modes in a gas mixture of Ar + 25CO 2 using Sv-08G2S wire with a diameter of 1.6 mm according to
When welding with wire with a diameter of 1.6 ... 2.0mm, the area of \u200b\u200bthe first pass is 20 ... 40mm 2, the area of \u200b\u200bthe second pass is 40 ... 60mm 2, the area of \u200b\u200bsubsequent passes is 40 ... 100mm 2 according to.
Define the coefficient of the form of penetration by the formula:
where is a coefficient whose value depends on the type and polarity of the current. \u003d 0.92 at a current density of 160 A / mm 2 when welding with direct current of reverse polarity.
To determine the welding speed, it is necessary to find the value of the deposition coefficient b N according to the formula:
where w P - loss coefficient, depending on the current density in the electrode.
w P \u003d 2.9% [Tab. 10].
The value of the melting coefficient is calculated by the formula:
where l is the electrode overhang of 10 ... 20 mm. Accepting l \u003d 15mm, we get;
Determine the welding speed for the first pass. F \u003d 30mm 2;
V cv \u003d 0.3015 cm / s \u003d 10.85 m / h
When determining the number of passes required to fill a groove, it must be borne in mind that the maximum cross-section of one passage usually does not exceed 100 mm 2.
F n \u003d F 0 n - F n,
where F 0 n is the cross-sectional area of \u200b\u200bthe weld metal;
F n - the area of \u200b\u200bthe first pass;
The welding mode of subsequent passes and their number are selected from the conditions for filling the groove and smooth conjugation of the weld with the base metal.
Welding mode for the second pass;
Arc voltage
Fusion coefficient;
br \u003d 9.37g / Ah
Surfacing coefficient;
b n \u003d 9.1g / Ah
Welding speed;
V sv \u003d 0.2448cm / s \u003d 8.8m / h
Welding mode for the third pass;
Welding speed, arc voltage, melting coefficient will be the same as for the second pass. The cross-sectional area of \u200b\u200bthe seam F \u003d 90mm 2;
V sv \u003d 0.1116cm / s \u003d 4.018m / h
For the last pass F \u003d 66mm 2, then;
V St. \u003d 0.1522cm / s \u003d 5.48m / h
MIG / MAG - Metal Inert / Active Gas - arc welding with a consumable metal electrode (wire) in an inert / active gas environment with automatic filler wire feed. This is a semi-automatic welding in a shielding gas environment - the most universal and common welding method in the industry.
Principles of the process, characteristics of the arc
The technological properties of the arc substantially depend on the physical and chemical properties of the shielding gases, electrode and welded metals, parameters and other welding conditions. This leads to a variety of methods of welding in shielding gases. Let us consider the classification of the process of welding in shielding gases by a consumable electrode according to the most essential features.
Semi-automatic welding with a consumable electrode is performed in inert gases Ar and He (MIG) and their mixtures Ar + He, in the active gas CO2 (MAG), as well as in mixtures of inert and active Ar + O2, Ar + CO2, Ar + CO + O2 and active gases CO2 + O2. As electrode wires, solid ones made of unalloyed and alloyed steels and non-ferrous metals (Ni, Cu, Mg, Al, Ti, Mo), as well as non-continuous powder and activated ones, are used. Welding with a consumable electrode is carried out mainly with direct current, and pulsed current welding is also used. Other welding methods are also being used: at normal and extended reach, with free and forced formation of a seam, without oscillations and with vibrations of the electrode wire, in the atmosphere and under water, into standard and non-standard narrow slotted edges, etc. The principle of arc welding with melting metal the electrode in the shielding gas is shown in Fig. 1.
Fig. 1. The scheme of semi-automatic welding
The main types, structural elements and sizes of welded joints of steels, as well as alloys on iron-nickel and nickel bases, performed by arc welding in protective gas are specified in GOST 14771.
Depending on the level of mechanization and automation of the process, welding is distinguished:
- mechanized, in which the torch moves are carried out manually, and the wire feed is mechanized;
- automated, in which all the movements of the torch and the wire feed are mechanized, and the welding process is controlled by the operator-welder;
- automatic (robotic), in which the welding process is controlled without the direct participation of the operator-welder.
welding equipment
The welding equipment includes a welding current source and a welding machine. Components of welding equipment and their functions are determined by the level of mechanization and automation of the process, the parameters of the welding mode, the need for their installation and adjustment in the mode of commissioning and welding.
The main parameters of automated arc welding with a consumable electrode in CO2, Ar, He and gas mixtures (MAG, MIG) are:
- Welding current Ic (~ 40.,. 600 A);
- Welding voltage Uc (~ 16 ... 40 V);
- Welding speed Vc (~ 4 ... 20 mm / s), (-14.4 ... 72 m / h);
- Diameter of electrode wire Dpr (~ 0.8 ... 2.5 mm);
- Departure length of the electrode wire Lв (~ 8 ... 25 mm);
- The feed speed of the electrode wire Vp (~ 35 ... 250 mm / s);
- Shielding gas consumption Qg (~ 3 ... 60 l / min).
The principle of arc welding in shielding gases determines the main functions of the equipment:
- approach to the arc of electric energy and its regulation (Ic, Uc);
- movement of the torch with welding speed (Vc) and its regulation;
- supply of electrode wire (Vp) to the welding zone and regulation of its speed;
- shielding gas supply (Qg) to the welding zone and regulation of its flow rate;
- installation of the departure of the electrode wire (Lв) and corrective movements of the burner;
- arc excitation and crater welding;
- automatic tracking along the welding line, etc.
When starting the welding machine, the control circuit must provide the following sequence of switching parts and mechanisms of equipment:
- Shielding gas supply (Qg), preliminary purging of the gas supply system;
- Turning on the arc power source (U);
- Submission of electrode wire (Vp);
- Arc excitation (Ic, Uc);
- Movement of the device with welding speed (Vc):
Q g U V p lcUc Vc
At the end of welding, the shutdown sequence of the mechanisms should ensure the crater is welded and the cooling joint is protected:
Vc Vn lc Uc U Q g
Welding in shielding gases by a consumable electrode is carried out both in the production room at specially equipped workplaces (welding station, installation, machine, RTK), and outside it (construction site, pipeline route, etc.). Welding stations have local ventilation and are shielded with shields or shields to protect others from arc radiation and electrode metal spatter. By appointment, the welding equipment is divided into universal, special and specialized. Let us briefly consider the principles of layout of general-purpose universal welding equipment, which is produced in series. Installation for mechanized arc welding with a consumable electrode in shielding gases usually includes:
- electrode wire feed mechanism;
- welding torch;
- cable package;
- a control unit integrated in the source or a separate control cabinet;
- shielding gas supply system (cylinder, gas heater for CO2), gas reducer, gas mixer, gas hoses, electrovalve);
- control circuit cables;
- welding cables with clamps;
- water cooling system (optional);
- fixture for assembly and tilting of the welded unit (mechanical equipment).
The installation kit for mechanized arc welding, which is traditionally called a semiautomatic welding machine, is shown in Fig. 2.
Fig. 2. Installation diagram for mechanized arc welding in CO2
Semiautomatic welding machines find the widest application, have different purposes and design. The main version of semiautomatic devices is the method of protecting the arc zone:
- for welding in active gases (MAG);
- for welding inert gases (MIG);
- for welding in inert and active gases (MIG / MAG);
- for welding with flux-cored or self-shielded electrode wire (FCAW).
There are three main systems for feeding the electrode wire: pushing, pulling, pushing and pulling types. The most common is the push type feed system, which limits the length of the burner to 5 m, but is simple and light in weight. Other systems allow you to increase the length of the hoses to 10-20 m and use a thin wire with a diameter of less than 1 mm, but the feed mechanism in the burner increases its mass. The adjustment of the wire feed speed is often used smoothly, but smooth-step and step are possible. In the case of cored wire, two pairs of feed rollers are used to prevent flattening. According to the radius of the working zone, there are single-body semi-automatic machines (the feed mechanism is installed inside the body of the welding current source, the radius of the welder is determined by the length of the welding torch), mobile (the feed mechanism can be moved relative to the source up to 15 m) and portable (special or “case” type with cable length -package up to 40-50 m).
The collector tip is a replaceable wear part. The stability of the welding process depends on the reliability of the contact in it. Interchangeable parts include a collector tip and nozzle, which are heated by arc radiation and splashing.
Plants for automated arc welding with a consumable electrode in protective gases CO2, Ar, He and mixtures (MIG / MAG) for general purposes usually include:
- source of direct or pulsed current;
- a welding machine (tractor, outboard or self-propelled head) with mechanisms for feeding electrode wire, moving the welding machine with welding speed and raising and lowering the torch;
- a coil or cassette with a welding wire;
- a torch with a tilt mechanism and corrective movements of it along the height and across the seam;
- control panel on the welding machine;
- a control unit integrated in the welding machine or a separately located control cabinet;
- shielding gas supply system;
- water cooling system.
Welding consumables
When welding MIG / MAG, shielding gases and electrode wires are used. Table 1 shows the types of gases classified by the International Institute of Welding.
Table 1. Types of shielding gases.
| Group | The composition of the mixture,% | Chem. activity | ||||
| Oxidizing agents | Inert gases | Reducing agents | ||||
| CO2 | O2 | Ar | He | H2 | ||
| I1 | - | - | 100 | - | - | Neutral |
| - | - | - | 100 | - | ||
| - | - | 27-75 | Ost. | - | ||
| - | - | 85 - 95 | - | Ost. | Will restore. | |
| - | - | - | - | 100 | ||
| M1 | - | 1 - 3 | Ost. | - | - | Weak acid. |
| 2 - 4 | - | Ost. | - | - | ||
| M2 | 15 - 30 | - | Ost. | - | - | Medium acid |
| 5 - 15 | 1 - 4 | Ost. | - | - | ||
| - | 4 - 8 | Ost. | - | - | ||
| M3 | 30 - 40 | - | Ost. | - | - | Strong acid |
| - | 9 - 12 | Ost. | - | - | ||
| 5 - 20 | 4 - 6 | - | - | - | ||
| FROM | 100 | - | - | - | - | |
| 80 | 20 | - | - | - | ||
As can be seen from the table, pure inert and active gases are used, gas mixtures in various combinations: inert + inert, inert + active and active + active. Hydrogen is not used when welding with a consumable electrode due to high spatter. Active gas carbon dioxide (CO2) is regulated according to GOST 8050-85, gaseous oxygen according to GOST 5583-78.
The method of calculating the shielding gas consumption Ng in liters or cubic meters per 1 m of a seam is used. It is determined mainly for small production using the following formula:
Ng \u003d (Noug x T + Ndg)
where Noug is the specific consumption of shielding gas shown in Table 3, m3 / s (l / min); T is the main welding time of the nth passage, s (min); Ndg - additional shielding gas consumption for preparatory and final operations during the welding of the nth passage.
Table 2. Specific shielding gas consumption.
| Wire diameter, mm | Welding current, A | Gas consumption | |
| m 3 / s 10 4 | l / min | ||
| 0,8 | 60 - 120 | 1,33 - 1,50 | 8 - 9 |
| 1,0 | 60 - 160 | 1,33 - 1,50 | 8 - 9 |
| 1,2 | 100 - 250 | 1,50 - 2,00 | 9 - 12 |
| 1,6 | 240 - 260 | 2,30 - 2,50 | 14 - 15 |
| 1,6 | 260 - 380 | 2,50 - 3,00 | 15 - 18 |
| 2,0 | 240 - 280 | 2,50 - 3,00 | 15 - 18 |
| 2,0 | 280 - 450 | 3,00 - 3,33 | 18 - 20 |
According to GOST 2246-70, it is planned to manufacture 75 grades of welding wires, including for welding in shielding gases. Medium and highly oxidizing gases of the M2 and MZ groups (Ar + CO2, Ar + O2, Ar + CO2 + O) and C (CO, CO2 + O2) are used in combination with wires containing deoxidants Mn, Si, Al, Ti, etc. . (e.g. SV-08G2S, SV-08GSMT, SV-08HG2S). It is advisable to give more accurate recommendations on the selection of electrode wires when studying the welding of specific groups of structural materials.
Flux cored wires are used for welding without protection and with additional protection of the carbon dioxide welding zone (self-protective and gas-protective wires). According to the type of core, flux-cored wires can be divided into:
- self-protective: rutile-organic, carbonate-fluorite, fluorite;
- gas shields: rutile, rutile fluorite.
The use of flux-cored wires instead of solid wires allows alloying the seam over a wide range and increasing its resistance to pores and hot cracks, and to provide the specified mechanical properties. In addition, the presence of slag reduces spatter and improves the shape of the seam.
Types of electrode metal transfer and their application
When welding with a consumable electrode by an open arc, the transfer of electrode metal is a complex process. Many factors affect the transfer: the composition and properties of the shielding gas, the composition and properties of the electrode metal, the type of current and polarity, the parameters of the welding mode, the current-voltage characteristic of the current source and its dynamic properties, etc.
The following types of electrode metal transfer can be distinguished:
- without short circuits of the arc and with short circuits;
- large, medium, small droplet and jet;
- without spraying and with spraying.
The most favorable conditions for the transfer of electrode metal are observed when welding in inert monatomic gases argon and helium. In argon, there are two types of transfer: large droplet without short circuits with a small spatter at subcritical current and jet at a current greater than critical. The type of transfer affects the form of penetration. 3:
Fig. 3. The form of metal penetration.
a) less than critical;
b) more than critical.
Jet transfer welding is recommended on medium-thick metal. In helium, droplet transfer with short circuits (short circuits) of the arc (low current and voltage) and without short circuits is observed. at increased current and voltage with a slight droplet spray. Welding in helium has a lower bulge than in argon, since argon increases the surface tension in steels. The use of the Ar + mixture does not allow one to take advantage of both gases. When welding in CO2, small-droplet transfer with short-circuiting takes place. and sprinkled with a little bit of gibbering, large-drop with short-circuit and without short-circuit with a lot of spray. At high currents, when the arc is immersed in the base metal, the transfer becomes small-droplet, the spraying decreases, however, the roller has an excessive bulge.
MIG / MAG welding transfer types
In MIG / MAG welding, metal transfer is carried out mainly in two forms. In the first form, a drop touches the surface of the weld pool even before it is separated from the end of the electrode, forming a short circuit, which is why this type of transfer is called transfer with short circuits. In the second form, the drop is separated from the end of the electrode without touching the surface of the weld pool and, therefore, this type of transfer is called transfer without short circuits. The last form of metal transfer is divided into 6 separate types according to the features of the formation and separation of drops of electrode metal from the end of the electrode. Thus, according to the classification proposed by the International Institute of Welding, there are 7 main types of metal transfer, illustrated in Fig. 4 (the conditions of these welds are given in Table 3)
Fig. 4. Types of metal transfer during MIG / MAG welding
Experimental welding conditions to illustrate the different types of metal transfer shown in Fig. 4 (electronic power supply).
Table 3. Types of metal transfer during MIG / MAG welding.
When transferring metal with short circuits, the end of the electrode with a drop of molten electrode metal on it periodically touches the surface of the weld pool, causing short circuits and extinction of the arc. Typically, the transfer of metal with short circuits occurs at low welding conditions, i.e., low welding current and low arc voltage (a short arc ensures that the drop touches the surface of the bath before it separates from the end of the electrode). This type of metal transfer occurs both in MIG welding and in MAG welding. At the beginning of a short circuit, the arc voltage drops sharply (to the level of the short circuit voltage) and remains low until it ends, while the short circuit current rises rapidly. Heating the liquid metal jumper between the end of the electrode and the weld pool (caused by a passing high short circuit current) contributes to its rupture.
Metal transfer during pulsed arc welding
The main feature of the pulse-arc welding process is the ability to obtain a droplet transfer of electrode metal with an average value of the welding current (Im) below the critical value, which under normal conditions determines the boundary between coarse and droplet transfer of metal. In this metal transfer control method, the current is forcedly changed between two levels, called the base current (Ib) and the pulse current (Ii). 5. The level of the base current is selected from the condition of sufficiency to ensure the maintenance of arc burning with a slight effect on the melting of the electrode. The function of the pulse current, which exceeds the critical current, is the shape of the current shown in Figure 5 (“one drop per pulse” type).
Fig. 5. Pulse arc welding
For practical indicators, a steel electrode wire SV08G2S with a diameter of 1.2 mm was taken; protective gas Ar + 5% 02; pulse current Ii \u003d 270 A; pulse time ti \u003d 5.5 ms; basic current Ib \u003d 70 A; pause time tp \u003d 10 ms; wire feed speed during a pulse Vpi \u003d 3.5 m / min; wire feed speed during a pause Vpp \u003d 28 cm / min; electrode overhang - 18 mm.
Melting of the end of the electrode, the formation of a droplet of a certain size and the breakdown of this drop from the end of the electrode occurs under the influence of electromagnetic force (Pinch effect). During one current pulse, one to several drops can be formed and transferred to the weld pool. The repetition rate of current pulses, their amplitude and duration (ti) determine the arc energy released, and therefore the electrode melting rate. The sum of the pulse durations tu and pauses (tп) determines the period of the ripple current, and its inverse gives the ripple frequency. The transfer of electrode metal during arc welding with a pulse is characterized by the following parameters:
- the number of droplets formed and transferred to the weld pool under the action of a single current pulse;
- droplet size;
- time from the beginning of the current pulse to the stall of the first drop;
- the moment when the droplet separates from the electrode (at the pulse phase or at the pause phase).
Fig. 6. Transfer of a drop of electrode metal.
Due to the fact that the formation and separation of the droplet is controlled by the amplitude and duration of the pulse current (I and tu), the base welding current (Ib) can be reduced significantly below the critical current level, which is achieved either by a simple increase in the base time (tb), t. E., by reducing the frequency of the pulses, or by reducing the base current (Ib). For example, as applied to a low-carbon electrode wire with a diameter of 1 mm, when welding in a protective medium based on argon, controlled droplet transfer of metal at a welding current of less than 50 A can be supported, although the critical current for these conditions is approximately 180 ... 190 A. Due to the low arc power and the melting speed of the electrode, the weld pool is small and easily controllable. Thus, it becomes possible to realize the desired small-droplet transfer of electrode metal, both in the welding of sheet metal and in welding of thick metal in all spatial positions.
Another advantage of the pulsed mode is the possibility of using large-diameter wires for surfacing speeds typical for small-diameter wires, which reduces the cost per unit weight of the deposited metal. At the same time, the deposition efficiency increases due to the reduction of losses due to spatter of the electrode metal.
The disadvantages of this process include the possible lack of penetration due to low heat input into the weld pool. In addition, increased requirements for the qualifications of welders, as well as the use of significantly more complex and expensive welding equipment, combined with lower flexibility (universality) of the process.
Features of carbon dioxide welding
Carbon dioxide is an active gas. At high temperatures, its dissociation (decomposition) occurs with the formation of free oxygen:
2CO 2 2CO + O 2
Molecular oxygen under the action of a high temperature of the welding arc dissociates into atomic by the formula:
ABOUT 2 2O
Atomic oxygen, being very active, reacts with iron and impurities located in steel, according to the following equations:
Si + 2O \u003d SiО2.
To suppress the oxidation reaction of carbon and iron during welding in carbon dioxide, deoxidizers (manganese and silicon) are introduced into the weld pool, which inhibit the oxidation reaction and reduce oxides by levels:
FeO + Mn \u003d MnO + Fe,
2FeO + Si \u003d SiО2 + 2Fe, etc.
The resulting oxides of silicon and manganese pass into slag. On this basis, when welding low carbon and low carbon steels in carbon dioxide, it is necessary to use silicon-manganese wires, and for welding alloy steels - special wires.
Table 4. Welding wires for welding low-carbon and alloy steels.
Preparation of metal for welding is as follows. To avoid pores in the weld metal, the edges of the welded joints must be cleaned from rust, dirt, oil and moisture up to a width of 30 mm on both sides of the gap. Depending on the degree of contamination, the edges can be cleaned by wiping with a rag, cleaning with a steel brush, sandblasting, and also degreasing with subsequent etching. It should be noted that the scale almost does not affect the quality of the weld, therefore, parts after gas cutting can be welded immediately after the slag is cleaned. Cut the edges for welding in the same way as with semi-automatic welding under a flux layer.
Selection of welding modes in a carbon dioxide environment
The parameters of the carbon dioxide welding mode include: current type and polarity, diameter of the electrode wire, welding current strength, arc voltage, wire feed speed, electrode overhang, carbon dioxide consumption, electrode inclination relative to the weld and welding speed.
When welding in carbon dioxide, a direct current of reverse polarity is usually used, since welding with a current of direct polarity leads to unstable arc burning. Alternating current can only be used with an oscillator, but in most cases it is recommended to use direct current.
The diameter of the electrode wire should be selected depending on the thickness of the metal being welded.
The welding current is set depending on the selected diameter of the electrode wire.
The main modes of semi-automatic welding are shown in Table 5.
Table 5. The main modes of welding.
| Metal thickness mm | Diameter of a welding wire, mm |
Welding current A |
Welding voltage, V | Wire feed speed, m / h |
Shielding gas consumption l / min |
Departure of an electrode, mm |
| 1,5 | 0,8 – 1,0 | 95 – 125 | 19 – 20 | 150 – 220 | 6 – 7 | 6 – 10 |
| 1,5 | 1,2 | 130 – 150 | 20 – 21 | 150 – 200 | 6 – 7 | 10 – 13 |
| 2,0 | 1,2 | 130 – 170 | 21 – 22 | 150 – 250 | 6 – 7 | 10 – 13 |
| 3,0 | 1,2 | 200 – 300 | 22 – 25 | 380 – 490 | 8 – 11 | 10 – 13 |
| 4,0 – 5,0 | 1,2 – 1,6 | 200 – 300 | 25 – 30 | 490 – 680 | 11 – 16 | 10 – 20 |
| 6.0 - 8.0 and more | 1,2 – 1,6 | 200 – 300 | 25 – 30 | 490 – 680 | 11 – 16 | 10 – 20 |
As the welding current increases, the penetration depth increases and the productivity of the welding process increases.
The voltage on the arc depends on the length of the arc. The longer the arc, the greater the voltage on it. With increasing voltage on the arc, the width of the seam increases and the depth of its penetration decreases. The arc voltage is set depending on the selected welding current strength.
The feed speed of the electrode wire is selected in such a way as to ensure stable burning of the arc at a selected voltage on it. The electrode extension is the length of the electrode segment between its end and its exit from the mouthpiece. The magnitude of the departure has a great influence on the stability of the welding process and the quality of the weld. With an increase in the overhang, the stability of the burning of the arc and the formation of the seam deteriorate, and also the spraying increases. When welding with a very short overhang, it is difficult to observe the welding process and often burns the contact tip. Departure value is recommended to be selected depending on the diameter of the electrode wire.
In addition to the electrode stick-out, it is necessary to maintain a certain distance from the burner nozzle to the product (Table 6), since with increasing this distance oxygen and nitrogen can enter the weld metal and form pores in the weld. The distance from the burner nozzle to the product must be maintained in the given values.
The consumption of carbon dioxide is determined depending on the current strength, welding speed, type of connection and electrode extension. On average, gas is consumed from 5 to 20 l / min. The inclination of the electrode relative to the seam has a great influence on the penetration depth and quality of the seam. Depending on the angle of inclination, welding can be done with a backward angle and a forward angle.
When welding at an angle backward within 5 - 10 °, the visibility of the welding zone improves, the penetration depth increases, and the deposited metal is more dense. When welding at an angle forward, it is more difficult to observe the formation of the seam, but it is better to observe the edges to be welded and to direct the electrode precisely along the gaps. The width of the roller increases while the penetration depth decreases. This method is recommended for welding thin metal, where there is a danger of through burn through. The welding speed is set by the welder himself, depending on the thickness of the metal and the required cross-sectional area of \u200b\u200bthe weld. If the welding speed is too fast, the end of the electrode may escape from the gas protection zone and oxidize in air.
When welding, both alternating and direct current are used. Direct current has the advantage that the arc burns more steadily. But alternating current is cheaper, so its use in welding is preferable. But there are welding methods in which only direct current is used. Welding in shielding gases and submerged arc welding is carried out with direct current of reverse polarity. Electrodes with a basic coating also require direct current of reverse polarity, as well as welding fluxes for welding high alloy steels, the basis of which is fluorspar. In these cases, the arc is saturated with oxygen or fluorine, which has a high electron affinity. Therefore, it is necessary to reveal the essence of the processes occurring in the arc when it is saturated with oxygen or fluorine and justify the use of the kind of current and polarity. The polarity of the current affects the penetration depth, the chemical composition of the weld and the quality of the welded joint.
Welding mode is a set of characteristics of the welding process, providing welds of a given size, shape and quality. For all arc welding methods, such characteristics are the following parameters: electrode diameter, welding current strength, arc voltage, electrode movement speed along the seam, current type and polarity. With mechanized welding methods, one more parameter is added - the feed rate of the welding wire, and when welding in shielding gases - the specific gas flow rate.
The parameters of the welding mode affect the shape of the seam, and therefore its dimensions: the width of the seam - e;joint reinforcement - q; seam depth - h.
The shape and dimensions are influenced not only by the main welding parameters, but also by technological factors such as the type and polarity of the current, the slope of the electrode and the product, the extension of the electrode, the structural form of the joint and the gap.
2.6.1 Method for calculating the manual arc welding mode. The area of \u200b\u200bsurfacing is determined as the sum of the areas of elementary geometric shapes that make up the cross-section of the seam.
Figure 3
The area of \u200b\u200bsurfacing of a one-sided weld, made with a gap, is determined by the formula, mm
F n \u003d 2F 1 + F 2, (13)
F n \u003d S b + 0.75 eq, (14)
where S is the thickness of the parts, mm;
b is the clearance, mm;
e is the width, mm;
q - gain height, mm.
Figure 4
 |
The weld area surfacing with the cutting of two edges and the weld root weld is determined by the formula, mm
F \u003d S b + (S - s) 2 tg a / 2 + 0.75eq + 0.75e 1 q 1, (15)
where c is the bluntness, mm;
e 1 is the width of the weld, mm;
q 1 is the height of the weld, mm;
a - cutting angle, mm.
When welding multipass seams, it is necessary to determine the number of passes according to the formula, pcs
where F n - the area of \u200b\u200bthe entire surfacing, mm 2;
F n1 - the area of \u200b\u200bthe first passage, mm 2;
F ns - the area of \u200b\u200beach subsequent passage, mm 2.
In manual welding of multipass seams, the first pass is performed by electrodes with a diameter of 3-4 mm, since the use of large diameter electrodes makes it difficult to penetrate the root of the seam. When determining the number of passes, it should be borne in mind that the cross section of the first pass should not exceed 30-35 mm 2 and can be determined by the formula, mm 2
F n1 \u003d (6 - 8) d e, (17)
where de is the diameter of the electrode for welding the root seam, mm
The surfacing area of \u200b\u200bsubsequent passes is determined by the formula, mm 2
F ns \u003d (8 - 12) d es, (18)
where F ns - the area of \u200b\u200bthe subsequent passage, mm;
d es - electrode diameter for welding the following seams, mm
When welding multi-pass seams, they tend to weld passages in the same modes except for the first pass.
The diameter of the electrode is selected depending on the thickness of the welded product. An approximate relationship between the diameter of the electrode and the thickness of the sheets of the welded product is given below.
Table 8
Calculation of the welding current strength Isb is made according to the diameter of the electrode and the permissible current density, A
where i is the permissible current density, A / mm.
Permissible current density depends on the diameter and type of electrode coating.
Table 9 The value of the permissible current density in the electrode during manual arc welding
The voltage on the arc is not regulated and is accepted within 20 ... 36V, that is, Ud \u003d 20 - 36, B
The welding speed is determined from the ratio, m / h
where a n - deposition coefficient, g / A h;
g is the density of the deposited metal, g / cm;
Fн - cross-sectional area of \u200b\u200bthe weld metal, mm 2
Arc length for manual arc welding should be, mm
Ld \u003d (0.5 - 1.2) d e, (21)
2.6.2 Calculation procedure for automatic and semi-automatic submerged-arc welding of butt joints of unilateral without bevel edges. The main parameters of the automatic and semi-automatic submerged arc welding are: welding current, diameter and feed speed of the welding wire, voltage and speed of welding.
Calculation of welding modes is always made for a specific case when the type of joint and thickness of the metal being welded, the grade of wire, flux and method of protecting the weld pool from air and other data on the seam are known. Therefore, before starting the calculations, it is necessary to establish the structural elements of the specified welded joint according to GOST8713-79 or according to the drawing and determine the area of \u200b\u200bthe multipass seam using the well-known method.
It should be borne in mind that the maximum cross-section of a single-pass seam, made automatically, should not exceed 100 mm 2. The cross section of the first pass of the multi-pass seam should not exceed 40-50 mm 2.
In two-sided submerged arc welding of a butt-less bevel joint (Figure 4), the welding current strength is determined by the penetration depth - h of the base metal; h - in one pass is 8 - 10 mm, in forced modes - 12 mm, A
Isv \u003d h 1,2 / k, (22)
where h 1,2 is the penetration depth of the base metal in two-sided welding, without beveling the edges of the welded parts, mm;
k - proportionality coefficient, mm / 100A, depending on the type of current and polarity, electrode diameter, grade of flux, varies from 1-2.
Figure 5 Figure 6
Table 10 K value depending on the welding conditions
| K, mm / 100 A | Flux grade or shielding gas | Diameter of electrode wire, mm | K, mm / 100 A | ||||||
| Alternating current | D.C | Alternating current | D.C | ||||||
| Direct polarity | Reverse polarity | Direct polarity | Reverse polarity | ||||||
| OTsS-45 | 1,30 | 1,15 | 1,45 | AN-348 | 0,95 | 0,85 | 1,05 | ||
| 1,15 | 0,95 | 1,30 | 0,90 | ||||||
| 1,05 | 0,85 | 1,15 | |||||||
| 0,95 | 0,75 | 1,10 | |||||||
| 0,90 | |||||||||
| AN-348A | 1,25 | 1,15 | 1,40 | Carbon dioxide | 1,2 | 2,10 | |||
| 1,10 | 0,95 | 1,25 | 1,6 | 1,75 | |||||
| 1,00 | 0,90 | 1,10 | 2,0 | 1,55 | |||||
| 3,0 | 1,45 | ||||||||
| 4,0 | 1,35 | ||||||||
| 5,0 | 1,20 |
Metal with a thickness of over 20 mm is welded in several passes. To avoid lack of penetration during submerged arc welding and to achieve normal weld formation, they resort to bevel edges. For a single-pass butt weld with a thickness of not more than 10-12 mm, the penetration depth is equal to the thickness of the parts to be welded (Figure 5), for two-sided welding with a thickness of not more than 20 mm (Figure 6), the penetration depth is, mm
h 1,2 \u003d S / 2 + (2 - 3), (23)
The diameter of the welding wire de is taken, depending on the thickness of the metal being welded, within 2-6 mm, and then it is specified by calculation using the formula, mm
d e \u003d 2, (24)
where i is the current density, A / mm².
The obtained value of d e is taken from the nearest standard.
The current density depending on the diameter of the wire is shown in table 11
Table 11
The voltage on the arc is taken within 32-40V.
The welding speed is determined by the formula, m / h
Vsv \u003d A / Isv, (25)
where A should be taken within the limits given below
Table 12
| de mm | A m / h |
| 1,2 | (2 – 5) 10 3 |
| 1,6 | (5 – 8) 10 3 |
| 2,0 | (8 – 12) 10 3 |
| 3,0 | (12 – 16) 10 3 |
| 4,0 | (16 – 20) 10 3 |
| 5,0 | (20 – 25) 10 3 |
| 6,0 | (25 –30) 10 3 |
where α nd - deposition coefficient during submerged arc welding, g / Ah.
The surfacing coefficient during submerged arc welding is determined by the formula, g / Ah
α nd \u003d α n + Δα n, (27)
where α n is the surfacing coefficient, not taking into account the increase in the melting rate of the electrode wire due to the preheating of the electrode stick-out by welding current, g / Ah;
Δα n - increase in the deposition coefficient due to the preliminary heating of the electrode stick-out, g / Ah, is determined according to Figure 7.
Figure 7
When welding with direct current of reverse polarity, the deposition coefficient is determined by the formula, g / Ah
α n \u003d 11.6 ± 0.4 (28)
When welding with direct current of direct polarity or alternating current is determined by the formula, g / A * h
α n \u003d A + B (Isv / de), (29)
where A and B are coefficients whose values \u200b\u200bfor flux are given below.
Table 12
Wire feed speed V p.p determined by the formula, m / h
where Fe is the cross-sectional area of \u200b\u200bthe electrode wire, mm².
Or the wire feed speed can be determined by the formula, m / h
The welding mode of the subsequent passes is selected from the conditions for filling the grooves and obtaining a weld surface that has a smooth interface with the base metal.
2.6.3 For two-sided welding of butt welds submerged arc with bevel edgesdetermine the welding mode of the first pass from one and the other side of the seam and subsequent passes separately.
Figure 8
Figure 9
h 1 \u003d h 2 \u003d, (32)
where h 1, 2 is the penetration depth of the first pass from one and the other side of the seam, mm;
c is the bluntness value, mm.
The welding current strength is determined by the penetration depth, A
Isv \u003d h 1,2 / k, (33)
where k is the proportionality coefficient (mm / 100A), depending on the type of current, polarity, electrode diameter, grade of flux, fluctuates 1-2A (see table 10).
The calculation of the remaining parameters of the welding mode is carried out in the same order as for submerged-arc welding of a two-sided butt -less joint according to formulas (16), (24) - (31).
Note: Calculation of the parameters of the submerged-arc welding of angular and tee joints with edge cutting is carried out according to the method for calculating the welding modes of butt joints with edge cutting (see clause 2.7.3).
2.6.4 Calculation method for automatic and semi-automatic submerged arc welding of fillet welds without cutting edges:
Knowing the leg of the seam, we determine the area of \u200b\u200bsurfacing, mm²
Fн \u003d k² / 2 + 1.05 kq, (34)
where k is the weld leg, mm.
Figure 10
We set the number of passes on the basis of the fact that during the first pass when welding in a “boat” the maximum leg of the seam can be welded 14 mm, and when welding in the lower position with an inclined electrode - 8 mm according to formula (16), where Fns - we accept within 60-80mm².
We choose the diameter of the electrode, bearing in mind that the fillet welds with a 3-4 mm leg can only be obtained using an electrode wire of 2 mm diameter, while welding with an electrode wire of 4-5 mm in diameter, the minimum leg is 5-6 mm. Welding wire with a diameter greater than 5 mm should not be used, since it will not provide penetration of the root of the seam.
For the adopted wire diameter, we select the current density according to the data below and determine the strength of the welding current Isb, A
We determine the deposition coefficient from the previously given formulas (27), (28), (29), depending on the type of current and polarity.
Knowing the area of \u200b\u200bsurfacing in one pass, welding current and deposition coefficient, we determine the welding speed, m / h
The feed speed of the electrode wire is determined by the formula, m / h
where F e - the cross-sectional area of \u200b\u200bthe electrode wire, mm².
The feed speed of the electrode wire can be determined by the formula, m / h
We determine the voltage on the arc - Ud, it varies from 28 to 36V.
Determine the linear energy of welding - q p according to the formula, J / cm
q p1, n \u003d 650 F n1, s, (39)
where F n1, s is the cross-sectional area of \u200b\u200bthe first or subsequent passage, mm².
Determine the coefficient of the form of penetration.
The penetration shape factor should be no more than 2 mm, otherwise undercuts appear, but at the same time it should not be excessively small, since the seams are too deep and narrow, prone to the formation of crystallization cracks, i.e. hot cracks.
Determine the penetration depth - h by the formula, mm
. (40)
2.6.5 Calculation of welding modes in carbon dioxide, in argon. It is known that the main parameters of the modes of mechanized processes of arc welding are as follows: the diameter of the electrode wire is d e, its reach is l e, the feed speed of the electrode wire is Vp.p, the current strength is Isv, the arc voltage is Ud and the welding speed is Vsv, and also specific consumption of CO 2.
Semi-automatic welding in carbon dioxide is performed by a short arc at a direct current of reverse polarity.
The distance from the burner nozzle to the product must not exceed 22mm. Butt welds in the lower position are welded with the electrode inclined from the surface axis by 5-20º. Corner joints are welded with the same inclination in the welding direction and inclined across the seam at an angle of 40-50º to the horizontal, shifting the electrode 1 - 1.15 mm from the angle on the horizontal shelf.
Thin metal is welded without vibrational movements, with the exception of places with increased clearance. 4-8 mm leg sutures are applied in one pass, moving the electrode along an elongated spiral. The root of the butt weld is brewed back - forward, with the next elongated spiral, and the subsequent ones with crescent movements.
A wire with a thickness of 0.8-1.2 mm welds the metal in all positions, and with vertical, horizontal and ceiling voltage is reduced to 17-18.5V, and the current strength by 10-20%.
Butt welds of metal up to 2 mm thick, and corner butt joints - 5 mm and the root of butt welds of a large cross section is best welded from top to bottom. When welding, it is necessary to provide protection against gas blowing off and air suction through the gap. To reduce spatter, a choke can be connected in series to the welding circuit.
The calculation of the parameters of the modes is performed in the following order:
Determine the thickness of the welded metal according to the drawings;
Depending on the thickness of the metal being welded, the diameter of the electrode wire is selected.
Table 13 The dependence of the diameter of the electrode wire from the thickness of the welded metal
The diameter of the electrode wire for automatic welding can be in the range of 0.7-3.0 mm and above, and for semi-automatic wire in the range of 0.8-2.0 mm.
Departure of the electrode is determined by the formula, mm
l e \u003d 10d e, (41)
The strength of the welding current is calculated by the formula, A
Isv \u003d I F e, (42)
where i is the current density, A / mm² (range of welding current densities from 100 to 200A / mm²), the optimal value is 100-140A / mm²;
F e - the cross-sectional area of \u200b\u200bthe electrode wire, mm².
A large current density corresponds to smaller diameters of the electrode wire.
Sustainable arc burning when welding consumable electrodes in carbon dioxide is achieved at current densities above 100A / mm². Since the definition of the main parameter of the welding mode is based on the interpolation of a wide range of recommended current densities, Ibc must be specified in table 14.
Table 14 Ranges of welding currents of the main processes of welding in CO 2 with wire Sv-08G2S
| Welding process | Diameter of electrode wire, mm | ||||||||||
| 0,5 | 0,8 | 1,0 | 1,2 | ||||||||
| IDS short | 30-120 | 50-120 | 71-240 | 85-260 | |||||||
| KR without short circuit | 100-250 | 150-300 | 160-450 | 190-550 | |||||||
| KR with KZ | 30-150 | 50-180 | 75-260 | 65-290 | |||||||
| Welding process | Diameter of electrode wire, mm | ||||||||||
| 1,4 | 1,6 | 2,0 | |||||||||
| IDS short | 90-280 | 110-290 | 120-300 | ||||||||
| Continuation of table 14 | |||||||||||
| Welding process | Diameter of electrode wire, mm | ||||||||||
| 1,4 | 1,6 | 2,0 | |||||||||
| KR without short circuit | 90-320 | 110-380 | 150-400 | 220-500 | 250-600 | ||||||
| KR with KZ | 200-650 | 210-800 | 220-1200 | 250-2000 | 270-2500 | ||||||
Note: IDS short - pulse with frequent forced short circuits; KR without short circuit - large droplet without short circuits; KR with KZ - large-droplet with short circuits.
When welding in CO 2 with Sv-08G2S wire, the process with frequent forced short circuits and the process with large droplet transfer are mainly used (table 12). When welding with flux-cored wires, a process with continuous arc burning is used, and when welding with activated wire, a jet process is used. A process with frequent short forced short circuits is obtained when welding in CO 2 with wires with a diameter of 0.5-1.4 mm by programming the welding current, which provides a change in the melting speed of the electrode and arc pressure.
The process with large droplet transfer is observed when welding with wires with diameters of 0.5-1.5 mm at high voltages, and with diameters of more than 1.6 - in the entire range of welding modes with silicon-manganese wires (see table 13). At low voltages, the process proceeds with short circuits, and at high without them.
When checking the design conditions and introducing them into production, it is necessary to remember that a stable welding process with good technical characteristics can be obtained only in a certain range of currents, which depends on the diameter and composition of the electrode and the type of protective gas (see table 13).
Regulates the current strength by changing the feed rate of the electrode wire. The strength of the current determines the penetration depth and process performance. Therefore, the entire calculation of the modes is indicative and in practice requires clarification.
The feed rate of the electrode wire is determined by the formula, m / h
where Vp.p - wire feed speed, m / h;
α p - coefficient of fusion of the electrode wire, g / Ah;
Isv - welding current, A;
de is the diameter of the electrode wire, mm;
γ is the density of the metal of the electrode wire g / cm³ (γ \u003d 0.0078g / mm³).
The melting coefficient is determined by the formula, g / Ah
α p \u003d 3.6 · 10 -1, (44)
The welding speed is determined by the formula, m / h
, (46)
where Vсв - welding speed, m / h;
α n - deposition coefficient, g / Ah;
Isv - welding current, A;
Fн - cross-sectional area, mm²;
γ is the density of the deposited metal, g / cm³;
0.9 - coefficient taking into account losses due to fumes and spatter.
The deposition coefficient, g / Ah is determined by the formula, g / Ah
α n \u003d α p (1 - ψ / 100), (47)
where ψ is the loss of electrode metal due to oxidation, evaporation and spraying,% (ψ \u003d 7-15%, usually take ψ \u003d 10%). The loss of electrode metal increases with increasing voltage on the arc.
The voltage on the arc is taken in the range of 16-34V. Larger values \u200b\u200bcorrespond to a larger current value. The voltage can be determined by the schedule (see Figure 11).
Figure 11
The voltage on the arc is pre-selected and can be set during adjustment, for example, by the open circuit voltage of the current source. The specific mode of gas consumption - q g, which depends on the position of the seam in space, the welding speed, the type of joint and the thickness of the metal being welded, refers to the parameters of the welding mode in a carbon dioxide medium. The parameters of the welding mode are summarized in table 15
Table 15
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