Selection and calculation of semi-automatic welding modes. Selection and calculation of welding modes. Semi-automatic welding in shielding gas

Let's calculate the mode of semi-automatic welding in shielding gases for a butt joint. Type of cutting C12 according to GOST 14771-76.

Figure - Groove C12

Root welding (seam A):

where s is the metal thickness, mm; Set current = 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 is the diameter of the electrode wire, mm.

We accept I sv \u003d 130 ... 140 A.

We accept U d \u003d 26 V.

Based on this, we determine the welding speed by the formula:

that is, it is included in the speed limit of 15 ... 37 m / h for mechanized welding. We accept V sv \u003d 22 m / h, (0.6 cm / s).

4) Calculate the input energy taking the values of the effective efficiency. heating the product with an arc when welding in a mixture of CO 2 ŋ i \u003d 0.80.

where k = 0,79 (coefficient depending on the type and polarity of the current)

8) When welding in a mixture of CO 2, the electrode stick-out l is chosen within 10-20 mm

9) Determine the deposition coefficient α n

α n τ =

10) We determine the electrode wire feed rate from the condition:

(2.39)

Determine the height of the roller. When welding in carbon dioxide in the range of modes that provide satisfactory formation of the seam, the coefficient of completeness of the bead varies within narrow limits and is practically equal to µ B = 0.73.

12) Roller height is (mm):

C=H+ =3 + 1,28 = 4,28mm (2.28)

Ψ in = (2.29)

Ψ in should be within 7 ÷ 10

Filling the groove B (9 passes):

where s is the metal thickness, mm; Set current = 190A

1) the welding current is determined by the formula (2):

We accept U d \u003d 28 V.

3) As is known from practice, the 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 with a diameter of 1.2 mm is in the range of 2000 ... 5000.

Based on this, we determine the welding speed according to the formula (7):

We accept V sv \u003d 19 m / h, (0.52 cm / s).

4) Calculate the heat input, taking the values of the effective efficiency. heating the product with an arc ŋ i \u003d 0.80

5) We determine the penetration shape coefficient according to the formula:

where k = 0,79 (coefficient depending on the type and polarity of the current)

6) Determine the depth of penetration H (cm) when welding in shielding gas:

7) Determine the width of the seam e (mm):

8) When welding in a mixture of CO 2, the electrode stick-out l is chosen within 10-20 mm.

9) We determine the deposition coefficient α n:

α n τ =

α R τ =

10) the electrode wire feed rate is determined from the condition:

(2.39)

where α n is the deposition coefficient;

γ – specific gravity metal for steel γ=7.8 g/cm 3 .

11) F n - the area of the metal deposited for a given pass (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 seam, the coefficient of completeness of the bead varies within narrow limits and is practically equal to µ B = 0.73. Then:

12) Roller height is (mm):

13) Determine the total height of the seam C (mm):

C=H+ = 5.3 + 1.31 = 6.61 mm (2.43)

14) Determine the gain form factor:

Ψ in = (2.44)

For well-formed seams Ψ in should be within 7 ... 10 . Small values of Ψ in take place at narrow high seams, such seams do not have a smooth interface with the base metal and have unsatisfactory performance under variable loads. Large values of Ψ in correspond to wide and low reinforcements, such welds are undesirable for the same reasons as welds with an excessively large value of Ψ in, and also due to a possible decrease in the weld cross section compared to the cross section of the base metal due to fluctuations in the level of the liquid pool .

Let's define the average chemical composition weld metal when welding steel 09G2S with Filarc PZ6114S wire.

Figure 11—Scheme for calculating the areas of welded and deposited metal

where |x| w, |x| om, |x| e is the concentration of the considered element in the weld metal, base and electrode metal;

γ o - the share of the base metal in the formation of the seam, is determined by the formula.

4.1 Calculation of welding conditions for manual arc welding with coated electrodes And.

The determination of welding modes usually begins with the diameter of the electrode, which is assigned depending on the thickness of the sheets when welding 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 edges for welding and the dimensions of the weld are established, which are given in table 6.

Table 4.1 - GOST 5264-80, geometric dimensions of the preparation of edges for welding and the weld

The calculation is made according to the formulas:

Let's determine the area cross section deposited metal according to the formula:

We substitute the data (see table 6) into formula (3) and get:

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 allowable current density:

, (2)

where d e is the electrode diameter;

j - current density, according to for 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 is equal to:

BUT.

The calculated current values differ 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:

Let's 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, is selected based on the recommendations of the certificate for a given brand of electrodes, .

To calculate the magnitude of welding deformations and some other calculations, it may be necessary to take into account the thermal effect on the metal being welded, determined by the heat input, :

(4)

where U d - arc voltage, V;

η and - effective efficiency. arcs; for arc welding methods it is equal to: η and = 0.6 ÷ 0.9;

V sv - welding speed, which is determined by the formula,:

(5)

where α n is the deposition coefficient, g/Ah; α n \u003d 11.5 g / Ah;

γ is the density of the deposited metal γ = 8.1 g/cm3;

F n - area of deposited metal; F n \u003d 0.22 cm 2.

In this way:
.

V sv \u003d 10.3 m / h.

Therefore, the heat input is equal to:

Determine the number of passes required to form a connection.

According to , the number of passes is determined by the formula:

(6)

where F 1 is the cross-sectional area of the metal deposited in one pass;

F n - the cross-sectional area of the metal deposited for the next pass.

The cross-sectional area of the metal deposited in one pass is determined by the formula:

(7)

where d e is the electrode diameter; d e = 4 mm.

In this way:

The cross-sectional area of the metal deposited during the next pass is determined by the formula:

(8)

Therefore, the number of passes is:

We accept n = 1.

The maximum temperature at a distance r is calculated by the formula:

from here we obtain melting isotherms:

, (9)

where qp - linear energy.

where qe is the effective thermal power of the source, W

where cρ= 4.7 J/cm3 deg is the volumetric heat capacity.

Substituting the values we get:

For one pass:

Penetration depth

We take the depth of penetration equal to 4.6 mm.

To do this, we determine the area of penetration by the formula

;

where e=8mm is the width of the seam, H=3.9mm is the penetration depth, (based on table 17).

Weld metal area
.

Calculate the proportion of the base metal in the weld metal according to the formula:

where Fpr is the area of penetration;

Fn is the area of surfacing.

Then: γ 0 =
.

Let us determine 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 = 2.718;

q p \u003d 10150 J / cm;

T pl = 1425°C;

- volumetric heat capacity J/cm3 deg (for austenitic steels
= 4.7 J/cm3 deg);

In this way:

Determine the depth of penetration by the formula:

(11).

In this way:

In the course of these calculations, modes were chosen for manual arc welding with coated electrodes, which ensure the formation of the weld geometry in accordance with GOST 5264-80.

4.2 For submerged arc welding.

Table 4.2 - C2 T-weld for submerged arc welding.

(GOST 8713-79).

Conditional

designation

welded joint

Structural elements

e, no more

prepared edges

parts to be welded

weld

prev. off

For submerged arc welding of plates 5 mm thick, we accept the wire diameter d e = 2 mm.

1) Area of deposited metal:

F n \u003d K 2 / 2, (12)

where K is the leg of the seam, mm;

F n \u003d 7 2 / 2 \u003d 24.5 mm 2 \u003d 0.245 cm 2

2) The strength of the welding current I sv:

I St \u003d π × d e / 4 × j, (13)

where d e is the electrode diameter, mm;

j - allowable current density, A / mm 2.

I St =((3.14 2 2)/4)150=471 A

U d \u003d 20 + 50 × 10 -3 /
e ×I sv, (14)

U d \u003d 20 + ((50 10 -3)/
)471) = 36.8 V.

4) Welding speed:

V sv \u003d (α n I sv) / (3600 γ F Н), (15)

where α n - deposition coefficient, g / A h;

γ=8.1 is the density of the deposited metal, g/cm 3 .

Since the loss of metal in submerged arc welding is 2-3%, then α n α r.

α p =6.3+((70.2 10 -3)/(d e 1.035)) I St, (16)

α p =6.3+((70.2 10 -3)/(2 1,035))471 \u003d 22.44 g / Ah

V sv \u003d (13.46 471)/(36008,10.25)=0.86 cm/s=30.96 m/h

5) Heat input:

g p \u003d I St × AND g × η and /V St, (17)

where I sv - welding current;

And g is the voltage;

V St - welding speed;

η and =0.85 0.95 - effective efficiency for submerged arc methods.

g p =(471 36,80.85)/0.86=17.13 kJ/cm=4111.2 kcal/cm

6) Penetration depth:

H=A , (18)

where A=0.0156 for submerged arc welding.

Ψ pr \u003d K (19-0,01I sv)
, (19)

where K is the penetration coefficient.

K=0.367×i 0.1925 , (20)

K=0.367×45 0.1925=0.763

Ψ pr \u003d 0.763 (19-0,01471)
=10,7

H=0.0156
=0.48 cm

7) Roll width:

e=F n /0.73 q, (21)

e=0.245/0.73 0.2=1.7cm

8) Total seam height:

С=0.48+0.2=0.68 cm

9) Instantaneous metal cooling rate in the near-weld zone:

, (23)

where ω=f() is a dimensionless criterion;

λ – thermal conductivity, W/cm* 0 С;

cρ - volumetric heat capacity, J / cm 3 * 0 С;

T 0 - initial temperature of the product, 0 С;

T is the temperature of the lowest stability of austenite, 0 C.

For most austenitic steels:

λ=0.16; сρ=4.9;

T=550-600 0 С; 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 use welding methods and modes that provide the maximum concentration of thermal energy. The specific resistance of the metal, which is almost 5 times greater than for carbon steels, causes a large heating of the welding wire and electrode metal, which leads to an increased melting coefficient. Given this, when welding, the electrode stickout is reduced and the wire feed speed is increased. 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 melting coefficient can be calculated according to the equation proposed by B. K. Panibrattsev.

(25)

Where - electrode reach, cm; dЭ - electrode diameter, cm.

The electrode stick-out value during submerged arc welding is chosen in the range of 20-80 mm.

Smaller electrode diameters correspond to smaller overhang values and vice versa.

Determine the welding speed:

;

Heat input:

; (26)

where η and =0.85 0.95 - effective efficiency for submerged arc methods;

Let's take η and =0.9;

Instantaneous metal cooling rate in the near-weld zone:

λ= 0.16 W/cm K - thermal conductivity, ;

cρ =4.9 J/cm 3 K - volumetric heat capacity of high-alloy austenitic steels;

T 0 \u003d 20 0 С - initial temperature of the product;

T \u003d 550-600 0 С - temperature of the lowest stability of austenite;

w is a dimensionless criterion of the cooling process, which depends on the properties of the welded metal and welding conditions, expressed through the dimensionless value 1/θ, determined by the formula:

by ω = 0.1 at ;

According to the recommendations, it is desirable to provide an increased cooling rate of the metal after welding in order to refine the structure of the weld metal, and to reduce the degree of segregation of alloying elements. And carry out normalizing tempering at a temperature of 650-700 C to prevent intercrystalline corrosion and reduce internal deformations in the HAZ

Table 18 - Structural elements of the seam GOST 14771 - 76

The main parameters of the mechanized welding mode, which have a significant impact on the size and shape of the welds, are:

Electrode wire diameter, mm;

The value of the current strength, A;

Arc voltage, V;

Welding speed, m/h;

Wire feed speed, m/h;

Heat input of welding, J/mm;

Providing a thermal cycle that provides optimal properties of the heat-affected zone and weld metal.

When determining the welding mode, it is necessary to choose its parameters that will ensure the production of welds of a given size, shape 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 one, seam No. 4 GOST 14771? 76 is taken - C15? UP.

When welding with a wire with a diameter of 1.6 ... 2.0 mm, the area of the first pass is 20 ... 40mm 2, the area of \u200b\u200bthe second pass is 40 ... 60mm 2, the area of subsequent passes is 40 ... 100mm 2 according to.

Determine the strength of the welding current.

where is the diameter of the electrode wire, 1.6 mm;

Current density (160A / mm 2).

Welding current for the first pass

I sv \u003d 270 A.

For the accepted electrode diameter and welding current strength, we determine the optimal arc voltage:

Knowing the welding current, electrode diameter and arc voltage, we determine the penetration shape factor by the formula:

where is a coefficient, the value of which 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 P \u003d - 4.72 + 17.6? 10 -2? - 4.48? 10 -4? ? 2 (15)

W P \u003d - 4.72 + 17.6? 10 -2? 160 - 4.48? 10 -4? 160 2 \u003d 12.4%

Determine the welding speed for the first pass. F = 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 the first passage.

Welding mode for the second pass.

Arc voltage;

Melt factor;

br = 9.4g/Ah

Hardfacing coefficient;

b n \u003d 8.23 g / Ah

Welding speed of the second pass F = 40mm 2 ;

V sv \u003d 0.2344 cm / s \u003d 8.44 m / h

Welding speed, arc voltage, melting ratio will be the same as for the second pass. Cross-sectional area of the seam F = 90mm 2;

V sv \u003d 0.0869 cm / s \u003d 3.13 m / h

V sv \u003d 0.1186 cm / s \u003d 4.27 m / h

Calculation of welding modes in a mixture of Ar + CO2 gases

Table 19 - Optimal modes of IDS in a mixture of gases Ar + 25CO 2 using wire Sv-08G2S with a diameter of 1.6 mm according to

When welding with a wire with a diameter of 1.6 ... 2.0 mm, the area of the first pass is 20 ... 40 mm 2, the area of the second pass is 40 ... 60 mm 2, the area of subsequent passes is 40 ... 100 mm 2 according to.

Let us determine the coefficient of the penetration form by the formula:

where is a coefficient, the value of which 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 factor, depending on the current density in the electrode.

w P = 2.9% [tab.10].

The value of the melting coefficient is calculated by the formula:

where l is the overhang of the electrode, which is 10 ... 20 mm. Taking l \u003d 15mm, we get;

Determine the welding speed for the first pass. F = 30mm 2;

V cv \u003d 0.3015 cm / s \u003d 10.85 m / h

When determining the number of passes required to fill the groove, it must be borne in mind that the maximum cross section of one pass usually does not exceed 100mm 2 .

F n \u003d F 0 n - F n,

where F 0 n is the cross-sectional area of the deposited metal;

F n - the area of the first passage;

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;

Melt factor;

br = 9.37g/Ah

Hardfacing coefficient;

b n \u003d 9.1 g / Ah

welding speed;

V sv \u003d 0.2448 cm / s \u003d 8.8 m / h

Welding mode for the third pass;

Welding speed, arc voltage, melting ratio will be the same as for the second pass. Cross-sectional area of the seam F = 90mm 2;

V sv \u003d 0.1116 cm / s \u003d 4.018 m / h

For the last pass F = 66mm 2 then;

V sv \u003d 0.1522 cm / s \u003d 5.48 m / h

MIG/MAG - Metal Inert / Active Gas- arc welding with a consumable metal electrode (wire) in an inert/active gas environment with automatic feed of filler wire. This is semi-automatic welding in a shielding gas environment - the most versatile and common welding method in the industry.

Process principles, arc characteristics

Technological properties of the arc significantly depend on the physical and chemical properties shielding gases, electrode and welded metals, parameters and other welding conditions. This leads to a variety of methods of welding in shielding gases. Consider the classification of the welding process in shielding gases with a consumable electrode according to the most significant features.

Semi-automatic consumable electrode welding is carried out in inert gases Ag and He (MIG) and their mixtures Ag + He, in active gas CO2 (MAG), as well as in mixtures of inert and active Ag + O2, Ag + CO2, Ag + CO + O2 and active gases CO2 + O2. Solid wires made of unalloyed and alloyed steels and non-ferrous metals (Ni, Cu, Mg, Al, Ti, Mo), as well as non-solid powder and activated wires, are used as electrode wires. Welding with a consumable electrode is carried out mainly with direct current, but pulsed current welding is also used. Other welding methods are also used: at normal and extended reach, with free and forced formation of a seam, without oscillations and with oscillations of the electrode wire, in the atmosphere and under water, in standard and non-standard narrow slotted grooves, etc. The principle of consumable metal arc welding electrode in shielding gas is shown in Fig. one.

Rice. 1. Scheme of semi-automatic welding

The main types, structural elements and dimensions of welded joints made of steels, as well as alloys on iron-nickel and nickel bases, performed by gas-shielded arc welding are specified in GOST 14771.

Depending on the level of mechanization and automation of the process, welding is distinguished:

mechanized, in which the movements of the burner are performed manually, and the wire feed is mechanized;
automated, in which all movements of the burner and 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 welding machine. The 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 adjustment and welding.

The main parameters of automated consumable electrode arc welding 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);
Electrode wire diameter Dpr (~0.8...2.5 mm);
The length of the stick-out electrode wire Lv (~ 8...25 mm);
Electrode wire feed speed 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 electrical 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 consumption;
installation of electrode wire extension (Lв) and corrective movements of the burner;
arc excitation and crater filling;
automatic tracking along the welding line, etc.

When starting the welding machine, the control circuit must provide the following sequence of switching on the parts and mechanisms of the equipment:

Shielding gas supply (Qg), pre-purge of the gas supply system;
Turn on the arc power supply (U);
Electrode wire feed (Vp);
Arc excitation (Ic, Uc);
Movement of the machine with welding speed (Vc):

Q G U V P lcUc Vc

At the end of welding, the sequence of switching off the mechanisms should ensure filling of the crater and protection of the cooling seam:

Vc Vn lc Uc U Q G

Welding in shielding gases with a consumable electrode is carried out as in industrial premises at specially equipped workplaces (welding station, installation, machine tool, RTK), and outside it (construction site, pipeline route, etc.). Welding stations have local ventilation and are protected by shields or screens to protect others from arc radiation and splashes of electrode metal. By purpose, welding equipment is divided into universal, special and specialized. Let us briefly consider the principles of the layout of universal general-purpose welding equipment, which is mass-produced. Installation for mechanized gas-shielded arc welding usually includes:

electrode wire feed mechanism;
welding torch;
cable package;
control unit built into the source or a separate control cabinet;
shielding gas supply system (cylinder, gas heater for CO2), gas reducer, gas mixer, gas hoses, solenoid valve);
control circuit cables;
welding cables with clips;
water cooling system (optional);
device for assembly and tilting welded joint(mechanical equipment).

A set of installation for mechanized arc welding, which is traditionally called a semi-automatic welding machine, is shown in Fig.2.

Fig.2. Installation diagram for mechanized arc welding in CO2

Welding semi-automatic devices are widely used, have various purposes and designs. The main design of semi-automatic devices is according to the method of protecting the arc zone:

for welding in active gases (MAG);
for welding in 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 wire feed systems: push, pull-push, and pull 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 up to 10-20 m and use thin wire with a diameter of less than 1 mm, but the feed mechanism in the burner increases its mass. Adjustment of the wire feed speed is often used smoothly, but smoothly-stepped and stepwise is possible. In the case of flux cored wire, two pairs of feed rollers are used to prevent flattening. According to the radius of the working area, there are semi-automatic monocase (the feed mechanism is installed inside the body of the welding power source, the range 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 a 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. Replacement parts include the collector tip and nozzle, which heat up from arc radiation and spatter.

Installations for automated arc welding with a consumable electrode in shielding gases CO2, Ar, He and mixtures (MIG / MAG) for general purposes usually include:

source of direct or pulsed current;
welding machine (tractor, suspended or self-propelled head) with mechanisms for feeding the electrode wire, moving the welding machine at the welding speed and raising and lowering the torch;
coil or cassette with welding wire;
a burner with a tilt mechanism and corrective movements of it along the height and across the seam;
control panel on the welding machine;
control unit built into the welding machine or located separately in the control cabinet;
shielding gas supply system;
water cooling system.

Welding consumables

MIG/MAG welding uses shielding gases and electrode wires. Table 1 shows the types of gases according to the classification of the International Welding Institute.

Table 1. Types of shielding gases.

Group	Composition of the mixture, %					Chem. activity
	Oxidizers		inert gases		Restorers
	CO2	O2	Ar	He	H2
I1	-	-	100	-	-	Neutral
	-	-	-	100	-
	-	-	27-75	Rest	-
	-	-	85 - 95	-	Rest	Restore.
	-	-	-	-	100	Restore.
M1	-	1 - 3	Rest	-	-	Subacid
M1	2 - 4	-	Rest	-	-	Subacid
M2	15 - 30	-	Rest	-	-	medium acid
	5 - 15	1 - 4	Rest	-	-
	-	4 - 8	Rest	-	-
M3	30 - 40	-	Rest	-	-	strongly acidic
	-	9 - 12	Rest	-	-
	5 - 20	4 - 6	-	-	-
FROM	100	-	-	-	-
FROM	80	20	-	-	-

As can be seen from the table, pure inert and active gases are used, mixtures of gases in various combinations: inert + inert, inert + active and active + active. Hydrogen is not used in consumable electrode welding 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 used to calculate the shielding gas consumption Hg in liters or cubic meters per 1 m of weld is determined mainly for small-scale production according to the following formula:

Hg \u003d (Hug x T + Ndg)

where Hg is the specific flow rate of the protective gas given in Table 3, m3/s (l/min); T is the main welding time of the n-th pass, s (min); Ndg - additional consumption of shielding gas to perform preparatory and final operations during welding of the n-th pass.

Table 2. Specific consumption of protective gas.

Wire diameter, mm	Welding current, A	Gas consumption
Wire diameter, mm	Welding current, A	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

GOST 2246-70 provides for the manufacture of 75 grades of welding wires, including those for welding in shielding gases. Medium and strong oxidizing gases of the M2 and M3 groups (Ar + CO2, Ag + O2, Ag + CO2 + O) and C (CO, CO2 + O2) are used in combination with wires containing deoxidizers Mn, Si, Al, Ti, etc. (for example, SV-08G2S, SV-08GSMT, SV-08KhG2S). It is advisable to give more precise recommendations on the choice of electrode wires when studying the welding of specific groups of structural materials.

Cored wires are used for welding without protection and with additional protection of the welding zone with carbon dioxide (self-shielded and gas-shielded wires). According to the type of core, flux-cored wires can be divided into:

self-protective: rutile-organic, carbonate-fluorite, fluorite;
gas-protective: rutile, rutile-fluorite.

The use of flux-cored wires instead of solid wires makes it possible to alloy the seam over a wide range and increase its resistance to pores and hot cracks, to provide the specified mechanical properties. In addition, the presence of slag reduces spatter and improves the shape of the seam.

Electrode Metal Transfer Types and Their Applications

In consumable electrode welding with 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 arc short circuits and with short circuits;
large-, medium-, small-drop and jet;
without splashing and with splashing.

The most favorable conditions for the transfer of electrode metal are observed when welding in inert monatomic gases argon and helium. There are two types of transfer in argon: large-drop without short circuits with small spatter at subcritical current and jet at a current greater than critical. The type of transfer affects the shape of the penetration. 3:

Rice. 3. Form of metal penetration.

a) less critical;

b) more critical.

Spray transfer welding is recommended on medium thickness metal. In helium, droplet transfer is observed with short circuits (short circuits) of the arc (small current and voltage) and without short circuits. at high current and voltage with little droplet spatter. Welding in helium has less convexity than in argon, since argon increases the surface tension in steels. The use of a mixture of Ar + He allows you to use the advantages of both gases. When welding in CO2, small-droplet transfer with short circuit takes place. and small splashing, large droplets with short circuit. and without short circuit with a lot of splash. At high currents, when the arc plunges into the base metal, the transfer becomes small droplets, spatter is reduced, but the bead has an excessive bulge.

Types of metal transfer in MIG/MAG welding

In MIG/MAG welding, metal transfer occurs mainly in two forms. In the first form, the drop touches the surface of the weld pool even before separation 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 separates from the electrode end without touching the surface of the weld pool and, therefore, this type of transfer is called transfer without short circuits. The latter form of metal transfer is divided into 6 separate types according to the features of the formation and separation of electrode metal droplets from the electrode end. Thus, according to the classification proposed by the International Institute of Welding, there are 7 main types of metal transfer, illustrated in Fig. 4 (conditions for these welds are given in Table 3)

Rice. 4. Types of metal transfer in MIG/MAG welding

Conditions for welding experiments to illustrate the different types of metal transfer presented in Fig. 4 (electronic power supply).

Table 3. Types of metal transfer in 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, short circuit metal transfer occurs at low welding conditions, i.e., low welding current and low arc voltage (a short arc ensures that the drop touches the pool surface before it separates from the electrode end). This type of metal transfer occurs in both MIG and MAG welding. At the beginning of the fault, the arc voltage drops sharply (to the level of the fault voltage) and remains low until the fault ends, while the fault current rises rapidly. The heating of the liquid metal bridge between the end of the electrode and the weld pool (caused by the passing high short circuit current) contributes to its rupture.

Metal transfer in pulsed arc welding

The main feature of the pulsed arc welding process is the possibility of obtaining small-drop transfer of electrode metal at an average value of welding current (Im) below the critical one, which under normal conditions determines the boundary between large-drop and small-drop metal transfer. In this metal transfer control method, the current is forced to change between two levels, called the base current (Ib) and the pulse current (Ii) Fig. 5. The level of the base current is selected from the condition of sufficiency to ensure the maintenance of the arc with a slight effect on the melting of the electrode. A function of the pulse current that exceeds the critical current is the current waveform shown in Figure 5 (one drop per pulse type).

Rice. 5. Pulse arc welding

For practical indicators, steel electrode wire SV08G2S with a diameter of 1.2 mm was taken; shielding gas Ag+5%02; pulse current Ii = 270 A; pulse time ti = 5.5 ms; base current Ib = 70 A; pause time tp = 10 ms; wire feed speed during the pulse Vpi = 3.5 m/min; wire feed speed during pause Vpp = 28 cm/min; electrode protrusion - 18 mm.

Melting of the end of the electrode, the formation of a drop of a certain size and the separation of this drop from the end of the electrode occurs under the action of an electromagnetic force (Pinch effect). During one current pulse, from 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 released arc energy and, consequently, the rate of electrode melting. The sum of the pulse durations tu and pause (tp) determines the current ripple period, and its reciprocal value gives the ripple frequency. The transfer of electrode metal in pulsed arc welding is characterized by the following parameters:

the number of drops formed and passed into the weld pool under the action of one current pulse;
drop size;
the time from the beginning of the current pulse to the breakdown of the first drop;
the moment when the droplet separates from the electrode (in the pulse phase or in the pause phase).

Rice. 6. Transfer of a drop of electrode metal.

Due to the fact that the formation and separation of the drop is controlled by the amplitude and duration of the pulse current (Ii and tu), the base welding current (Ib) can be reduced significantly below the critical current level, which is achieved either by simply increasing the base time (tb), i.e. That is, a decrease in the pulse frequency, or a decrease in the base current (Ib). For example, with low-carbon electrode wire with a diameter of 1 mm, when welding in an argon-based protective atmosphere, controlled small-drop metal transfer can be maintained at a welding current of less than 50 A, although the critical current for these conditions is approximately 180 ... 190 A. Due to the low arc power and electrode melting speed, the weld pool is small and easy to control. Thus, it becomes possible to implement the desired fine droplet transfer of the electrode metal, both when welding thin sheet metal and when welding thick metal in all spatial positions.

Another advantage of the pulsed mode is the possibility of using large diameter wires for deposition rates typical for small diameter wires, which reduces the cost per unit weight of deposited metal. At the same time, the efficiency of surfacing also increases due to the reduction of losses due to spattering 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 much more complex and expensive welding equipment, combined with lower flexibility (versatility) of the process.

Features of welding in carbon dioxide environment

Carbon dioxide is an active gas. At high temperatures, it dissociates (decomposes) with the formation of free oxygen:

2SO 2 2CO + O 2

Molecular oxygen under the action of high temperature of the welding arc dissociates into atomic oxygen according to the formula:

ABOUT 2 2O

Atomic oxygen, being very active, reacts with iron and impurities in steel, according to the following equations:

Si + 2O = SiO2.

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 reactions and reduce oxides by levels:

FeO + Mn = MnO + Fe,

2FeO + Si = SiO2 + 2Fe, etc.

The resulting oxides of silicon and manganese pass into the slag. Based on this, when welding low-carbon and low-carbon steels in carbon dioxide, it is necessary to use silicon-manganese wires, and for welding alloyed steels, special wires.

Table 4. Welding wires for welding mild and alloy steels.

Preparation of metal for welding is as follows. To ensure that there are no pores in the deposited metal, the edges of the welded joints must be cleaned from rust, dirt, oil and moisture to a width of up to 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, as well as degreasing followed by pickling. It should be noted that scale has almost no effect on the quality of the weld, so the parts after flame cutting can be welded immediately after cleaning the slag. Cut the edges for welding in the same way as in semi-automatic welding under a layer of flux.

Choice of welding modes in carbon dioxide environment

The parameters of the welding mode in carbon dioxide include: current type and polarity, electrode wire diameter, welding current strength, arc voltage, wire feed speed, electrode stick out, carbon dioxide consumption, electrode inclination relative to the seam and welding speed.

When welding in carbon dioxide, direct current of reverse polarity is usually used, since welding with direct polarity current 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 to be welded.

Welding current is set depending on the selected diameter of the electrode wire.

The main modes of semi-automatic welding are given in Table 5.

Table 5. Main welding modes.

Metal thickness, mm	Welding wire diameter, mm	welding current, BUT	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

With an increase in the strength of the welding current, the depth of penetration increases and the productivity of the welding process increases.

The arc voltage depends on the arc length. The longer the arc, the greater the voltage on it. With an increase in the 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 rate of the electrode wire is selected in such a way as to ensure stable burning of the arc at the selected voltage on it. Departure of the electrode is the length of the segment of the electrode between its end and its exit from the mouthpiece. The overhang has a great influence on the stability of the welding process and the quality of the weld. With an increase in overhang, the stability of arc burning and weld formation deteriorates, and spatter increases. When welding with a very short overhang, it is difficult to observe the welding process and the contact tip often burns. The overhang 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 workpiece (Table 6), since with an increase in this distance, oxygen and nitrogen from the air can enter the deposited metal and form pores in the weld. The value of the distance from the burner nozzle to the product should 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 weld has a great influence on the depth of penetration and the quality of the weld. Depending on the angle of inclination, welding can be done with an angle to the back and an angle to the front.

When welding at an angle back within 5 - 10 °, the visibility of the welding zone improves, the depth of penetration 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 being welded and guide the electrode accurately into the gaps. In this case, the width of the roller increases, and the penetration depth decreases. This method is recommended for welding thin metal, where there is a risk of 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 high, the end of the electrode may come out from under 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 is performed on direct current of reverse polarity. Basic coated electrodes also require DC reverse polarity, as do welding fluxes for welding high alloy steels based on 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 type of current and polarity. The polarity of the current affects the depth of penetration, the chemical composition of the weld and the quality welded joint.

Welding mode is a set of characteristics of the welding process that ensures the production of welded joints 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 consumption.

The parameters of the welding mode affect the shape of the seam, and hence its dimensions: on the width of the seam - e; seam reinforcement - q; seam depth h.

The shape and dimensions are influenced not only by the main welding parameters, but also by such technological factors as the type and polarity of the current, the inclination of the electrode and the product, the electrode stick-out, the structural shape of the connection and the size of the gap.

2.6.1 Method for calculating the mode of manual arc welding. The surfacing area is determined as the sum of the areas of elementary geometric figures that make up the weld cross section.

Figure 3

The area of surfacing 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 - gap, mm;

e - width, mm;

q - amplification height, mm.

Figure 4

The surface area of a butt weld with a groove of two edges and welding of the root of the weld is determined by the formula, mm

F \u003d S b + (S - c) 2 tg a / 2 + 0.75eq + 0.75e 1 q 1, (15)

where c is the amount of blunting, mm;

e 1 - welding width, mm;

q 1 - welding height, mm;

a - cutting angle, mm.

When welding multi-pass welds, it is necessary to determine the number of passes according to the formula, pcs

where F n - the area of the entire surfacing, mm 2;

F n1 - area of the first passage, mm 2;

F ns - the area of each subsequent pass, mm 2.

At manual welding multi-pass welds, the first pass is performed with electrodes with a diameter of 3-4 mm, since the use of large-diameter electrodes makes it difficult to penetrate the root of the weld. When determining the number of passes, it should be taken into account 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 weld, mm.

The surfacing area of subsequent passes is determined by the formula, mm 2

F ns = (8 - 12) d es, (18)

where F ns is the area of the subsequent passage, mm;

d es - diameter of the electrode for welding the next seams, mm

When welding multi-pass welds, they tend to weld the passes in the same modes, with the exception of the first pass.

The electrode diameter is selected depending on the thickness of the workpiece to be welded. An approximate relationship between the diameter of the electrode and the thickness of the sheets of the workpiece to be welded is given below.

Table 8

The calculation of the strength of the welding current Iw is carried out according to the diameter of the electrode and the allowable current density, A

where i is the allowable current density, A/mm.

The permissible current density depends on the diameter and type of electrode coating.

Table 9 The value of the allowable 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, V

Welding speed is determined from the ratio, m/h

where a n is the deposition coefficient, g/A h;

g is the density of the deposited metal, g/cm;

Fn - cross-sectional area of the deposited metal, mm 2

The length of the arc in manual arc welding should be, mm

Ld \u003d (0.5 - 1.2) d e, (21)

2.6.2 Method for calculating the mode of automatic and semi-automatic submerged arc welding of one-sided butt joints without bevel edges. The main parameters of the automatic and semi-automatic submerged arc welding mode are: welding current, diameter and speed of the welding wire feed, voltage and welding speed.

The calculation of welding modes is always carried out for a specific case, when the type of joint and the thickness of the metal being welded, the brand of wire, flux and the method of protecting the weld pool from air and other data on the seam are known. Therefore, prior to the start of calculations, it is necessary to establish, according to GOST 8713-79 or according to the drawing, the structural elements of a given welded joint and, using a well-known method, determine the area of a multi-pass weld.

In this case, it should be taken into account that the maximum cross section of a single-pass weld, made automatically, should not exceed 100 mm 2. The cross section of the first pass of a multi-pass weld should not exceed 40-50mm 2 .

In double-sided submerged arc welding of a bevelless butt joint (Figure 4), the strength of the welding current is determined by the depth of penetration - h of the base metal; h - in one pass is 8 - 10mm, in forced modes - 12mm, A

Iv \u003d h 1.2 / k, (22)

where h 1.2 is the depth of penetration of the base metal during double-sided welding, without beveling the edges of the parts to be welded, mm;

k - coefficient of proportionality, mm / 100A, depending on the type of current and polarity, electrode diameter, flux grade, ranges from 1-2.

Figure 5 Figure 6

Table 10 K value depending on welding conditions

		K, mm/100 A	Flux grade or shielding gas	Electrode wire diameter, mm	K, mm/100 A
Alternating current	D.C	Alternating current	D.C
Straight polarity	Reverse polarity	Straight 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 formation the seam is resorted to beveled 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 double-sided welding with a thickness of not more than 20 mm (Figure 6), the penetration depth is, mm

h 1,2 = S/2 + (2 - 3), (23)

The diameter of the welding wire de is taken depending on the thickness of the welded metal within 2-6 mm, and then specified by the calculation by the formula, mm

d e = 2 , (24)

where i is the current density, A / mm².

The resulting value d e is taken from the nearest standard.

The current density depending on the wire diameter is shown in table 11

Table 11

The arc voltage is accepted within 32-40V.

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 is the deposition coefficient for submerged arc welding, g/Ah.

The deposition coefficient in submerged arc welding is determined by the formula, g/Ah

α nd = α n + Δα n, (27)

where α n is the deposition coefficient, which does not take into account the increase in the melting rate of the electrode wire due to the preheating of the electrode stick out by the welding current, g/Ah;

Δα n - increase in the deposition coefficient due to preheating of the electrode stick out, g/Ah, is determined from Figure 7.

Figure 7

When welding on direct current of reverse polarity, the deposition coefficient is determined by the formula, g/Ah

α n = 11.6 ± 0.4 (28)

When welding with direct current of direct polarity or alternating current determined by the formula, g/A*h

α n \u003d A + B (Isv / de), (29)

where A and B are coefficients, the values of which for the 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 the electrode wire, mm².

Or the wire feed speed can be determined by the formula, m/h

The welding mode of subsequent passes is selected from the conditions for filling the groove and obtaining a weld surface that has a smooth interface with the base metal.

2.6.3 For double-sided welding of submerged arc butt welds with beveled edges determine the welding mode of the first pass on one and the other side of the seam and subsequent passes separately.

Figure 8

Figure 9

h 1 = h 2 = , (32)

where h 1, 2 - the depth of penetration of the first pass on one and the other side of the seam, mm;

c - the amount of blunting, mm.

The strength of the welding current is determined by the depth of penetration, A

Iw = h 1.2 / k, (33)

where k is the coefficient of proportionality (mm / 100A), depending on the type of current, polarity, electrode diameter, flux grade, fluctuates 1-2A (see table 10).

The calculation of the remaining parameters of the welding mode is carried out in the same order as in submerged arc welding of a double-sided butt bevelless joint according to formulas (16), (24) - (31).

Note: Calculation of the parameters of the submerged arc welding of fillet and tee joints with edge preparation should be carried out according to the procedure for calculating the modes of welding of butt joints with groove (see clause 2.7.3).

2.6.4 Method for calculating the mode of automatic and semi-automatic submerged arc welding of fillet welds without cutting edges:

Knowing the leg of the seam, we determine the area of surfacing, mm²

Fn \u003d k² / 2 + 1.05 kq, (34)

where k is the leg of the seam, mm.

Figure 10

We set the number of passes based on the fact that for the first pass when welding into the “boat”, the maximum leg of the seam can be welded 14mm, and when welding in the lower position with an inclined electrode - 8mm according to the formula (16), where Fns - is taken within 60-80mm².

We choose the diameter of the electrode, bearing in mind that fillet welds with a leg of 3-4 mm can only be obtained using an electrode wire with a diameter of 2 mm, when welding with an electrode wire with a diameter of 4-5 mm, the minimum leg is 5-6 mm. Welding wire with a diameter greater than 5 mm should not be used, as it will not provide root penetration.

For the accepted wire diameter, we select the current density according to the data below and determine the strength of the welding current Iw, 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 surfacing in one pass, welding current and surfacing coefficient, we determine the welding speed, m/h

The electrode wire feed rate is determined by the formula, m/h

where F e is the cross-sectional area of the electrode wire, mm².

The feed rate 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.

We determine the heat input of welding - q p according to the formula, J / cm

q n1,n = 650 F n1, s, (39)

where F n1, s is the cross-sectional area of the first or subsequent passage, mm².

We determine the penetration shape coefficient.

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, that is, hot cracks.

We determine the depth of penetration - h according to 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 arc welding processes are as follows: the diameter of the electrode wire is d e, its reach is l e, the electrode wire feed speed is Vp.p, the current strength is Iw, the arc voltage is Ud and the welding speed is Vw, and also the specific consumption of CO 2 .

Semi-automatic welding in carbon dioxide is performed with a short arc at 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 tilted from the surface axis by 5-20º. Corner joints are welded with the same inclination in the direction of welding and inclination across the seam at an angle of 40-50º to the horizontal, shifting the electrode by 1 - 1.15 mm from the corner to a horizontal shelf.

thin metal weld without oscillatory movements, except for places with an increased gap. Seams with a leg 4-8mm are applied in one pass, moving the electrode along an elongated spiral. The root of the butt weld is welded back and forth, with the next elongated spiral, and the subsequent ones with sickle-shaped movements.

With a wire 0.8-1.2 mm thick, metal is welded in all positions, and at vertical, horizontal and ceiling voltages are reduced to 17-18.5V, and the current strength by 10-20%.

Butt welds of metal up to 2 mm thick, and corner legs - 5 mm and the root of butt welds of a large section are best welded from top to bottom. When welding, it is necessary to provide protection against blowing off gas and air leakage through the gap. To reduce spatter, a throttle can be connected in series in the welding circuit.

The calculation of the mode parameters is carried out in the following order:

Determine the thickness of the welded metal according to the drawings;

Depending on the thickness of the metal to be welded, the diameter of the electrode wire is selected.

Table 13 Dependence of the diameter of the electrode wire on the thickness of the metal being welded

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 welding - in the range of 0.8-2.0 mm.

Departure of the electrode is determined by the formula, mm

l e = 10d e, (41)

Calculate the strength of the welding current according to the formula, A

Iv \u003d I F e, (42)

where i is the current density, A / mm² (the range of welding current densities is from 100 to 200A / mm²), the optimal value is 100-140A / mm²;

F e - cross-sectional area of the electrode wire, mm².

A large value of the current density corresponds to smaller diameters of the electrode wire.

Stable arc burning when welding with consumable electrodes in carbon dioxide is achieved at a current density of more than 100A / mm². Since the determination of the main parameter of the welding mode is based on the interpolation of a wide range of recommended current densities, then Iw must be specified according to table 14.

Table 14 Ranges of welding currents of the main processes of welding in CO 2 with wire Sv-08G2S

Welding process	Electrode wire diameter, mm
0,5	0,8	1,0	1,2
IDS k.z.	30-120	50-120	71-240	85-260
KR without short circuit	100-250	150-300	160-450	190-550
KR with short circuit	30-150	50-180	75-260	65-290
Welding process	Electrode wire diameter, mm
1,4	1,6	2,0
IDS k.z.	90-280	110-290	120-300
Table 14 continued
Welding process	Electrode wire diameter, mm
1,4	1,6	2,0
KR without short circuit	90-320	110-380	150-400	220-500	250-600
KR with short circuit	200-650	210-800	220-1200	250-2000	270-2500

Note: IDS k.z. - impulse with frequent forced short circuits; KR without short circuit – large-drop without short circuits; KR with short circuit - large-drop with short circuits.

When welding in CO 2 with Sv-08G2S wire, a process with frequent forced short circuits and a process with coarse 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 bonded wire, a jet process is used. A process with frequent short forced 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 electrode melting rate and arc pressure.

The process with large-drop transfer is observed when welding with wires with diameters of 0.5-1.5 mm at elevated 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 voltages without them.

When checking the design modes and introducing them into production, it must be remembered that a stable welding process with good technical specifications can only be obtained in a certain range of current strengths, 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 speed of the electrode wire feed. The strength of the current determines the depth of penetration and the productivity of the process. Therefore, the entire calculation of modes is approximate 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 r is the coefficient of melting of the electrode wire, g/Ah;

Iw - welding current, A;

de is the diameter of the electrode wire, mm;

γ is the density of the electrode wire metal g/cm³ (γ=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 Vw – welding speed, m/h;

α n – deposition coefficient, g/Ah;

Iw - welding current, A;

Fn - cross-sectional area, mm²;

γ is the density of the deposited metal, g/cm³;

0.9 is a coefficient that takes into account losses due to waste and splashing.

Surfacing coefficient, g/Ah is determined by the formula, g/Ah

α n \u003d α r (1 - ψ / 100), (47)

where ψ is the loss of the electrode metal due to oxidation, evaporation and splashing, % (ψ = 7-15%, usually ψ = 10% is taken). The losses of the electrode metal increase with increasing arc voltage.

The arc voltage is taken in the range of 16-34V. Larger values correspond to a larger current. The voltage can be determined from the graph (see figure 11).

Figure 11

The arc voltage is pre-selected and can be set when setting, for example, the open-circuit voltage of the current source. The parameters of the welding mode in a carbon dioxide environment include the specific gas consumption - q g, which depends on the position of the seam in space, welding speed, type of joint and thickness of the metal being welded. Welding mode parameters summarize in table 15

Table 15

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