Common Welding Processes for Thin Plate: Expert Guide

1. Welding method code and basic symbols for welding seams 1.1 Welding method codes and their annotations commonly used in sheet metal fabrication Arabic numeral codes are used to represent various metal welding methods. These numerical codes can be used on the diagram as a symbol for the welding method and should be marked at […]

Table Of Contents

1. Welding method code and basic symbols for welding seams

1.1 Welding method codes and their annotations commonly used in sheet metal fabrication

Arabic numeral codes are used to represent various metal welding methods. These numerical codes can be used on the diagram as a symbol for the welding method and should be marked at the end of the guide line.

For example, the following welding symbol indicates that a fillet weld is made by manual electric arc welding.

(The  indicates a fillet weld, and the Arabic numeral 111 at the end of the reference line indicates that manual electric arc welding is used.)

CodeWelding method
111Manual arc welding (coated electrode consumable electrode arc welding)
131MIG welding (consumable argon arc welding)
135Carbon dioxide gas shielded welding
141TIG welding (tungsten argon arc welding)
311Oxygen acetylene welding
21spot welding
782Stud resistance welding (seed welding)

The numerical codes in the table represent the welding methods commonly used in thin sheet metal welding.

1.2 Basic welding symbols commonly used in thin sheet metal fabrication.

Welding formDockingCorner joint T-jointLapping
Basic symbolsCurled edge weldType I weldFillet weldPlug or slot weldingSpot weld

2. Manual arc welding (manual welding)

Manual arc welding uses coated (flux-coated) welding rods and workpieces as electrodes, using the high heat (6000-7000 ℃) generated by the arc discharge to melt the welding rod and the workpiece, making them into one body.

The welding rod is operated manually. It is flexible, maneuverable, and widely applicable, and can be welded in all positions. The equipment used is simple, durable, and inexpensive. The quality of the weld depends on the operator’s technical level.

2.1 Welding specifications for manual arc welding

Welding specification for manual arc welding refers to the diameter of the welding rod, the current intensity of the welding, the arc voltage, and the type of power supply (AC or DC). In DC manual arc welding, it also includes the selection of polarity.

2.1.1 Diameter of the welding rod

The diameter of the welding rod has a significant impact on the welding quality and is closely related to improving productivity.

Using a welding rod that is too thick will cause incomplete penetration and poor weld formation; using a welding rod that is too thin will reduce productivity. The main basis for selecting the diameter of the welding rod is the thickness of the welded part and the welding position.

Recommended diameter values based on the thickness of the welded part are as follows (mm):

Weldment thickness0.5-1.01.5-2.02.5-3.03.5-4.55.0-7.0
Welding rod diameter1.61.6-

When selecting the diameter of the welding rod, different welding positions should also be considered. A larger diameter welding rod can be used for flat welding.

For vertical welding, horizontal welding, and overhead welding, a smaller diameter welding rod should generally be chosen.

2.1.2 Selection of welding current

The size of the welding current has a significant impact on the quality of the weld. When the welding current is too small, it not only makes arc starting difficult and the arc unstable, but also causes defects such as incomplete penetration and slag inclusion.

When the welding current is too large, it is easy to cause burn-through and undercut defects, and excessive burning of alloying elements will make the weld too hot, affecting the mechanical properties of the weld, and causing slag inclusion due to the peeling and failure of the coating.

The selection of the welding current is related to the type (composition of the coating), diameter of the welding rod, welding position, and formation of the welded joint.

The relationship between welding current intensity and welding rod diameter is:

Welding rod diameter
Current intensity25-4040-7070-9080-130140-200190-280
The relationship between welding current and welding rod diameter is usually expressed as: 

I = K * D 

I – welding current (A)
D – welding rod diameter (mm)
K – empirical coefficient.
Welding rod diameter (mm)1.6-2.02.0-4.04.0-6.0
Experience coefficient K15-3030-4040-60

When using the calculated current value in practical applications, it is necessary to consider different welding positions.

For flat welding, a larger welding current can be used; for vertical welding, the current used should be reduced to 85-90% of the current used for flat welding; for horizontal and overhead welding, the current should be reduced to 80-85% of that used for flat welding.

When welding stainless steel workpieces in flat position, a smaller welding current should be selected because the welding core has high resistance and is prone to turning red.

When selecting the welding current, the following points should be noted:

(1) Is the welding current suitable?

a) It can be determined by observing spatter (large spatter when the current is too large, small spatter when the current is too small, and iron and slag are not easily separated);

b) Observe the weld formation: (if the current is too large, there will be excessive height difference, large fusion depth, and easy undercutting; if the current is too small, there will be large height difference on the weld and poor fusion with the base metal);

c) Observe the welding rod: (if the current is too large, the welding rod turns red and the coating peels off; if the current is too small, the arc is unstable and the rod is easily stuck).

(2) The selection of welding current should also consider the thickness of the workpiece, the form of the joint, the welding position, and the site conditions. For thick workpieces, narrow gaps, low ambient temperatures, but good ventilation conditions, a larger welding current can be used.

(3) In summary, while ensuring the quality of the weld, large-diameter welding rods and high welding currents should be used as much as possible to improve welding productivity.

2.1.3 Arc voltage

Arc voltage refers to the voltage drop between the two ends (two electrodes) of the arc. When the welding rod and the base material are fixed, the arc voltage is high when the arc length is long, and low when the arc length is short.

During welding, the distance between the end of the welding rod and the workpiece is called arc length. The length of the arc has a significant impact on the quality of the weld.

Generally, the following empirical formula can be used to determine the arc length:

L = () D


L – arc length (mm)

D – welding rod diameter (mm)

k – empirical coefficient

When the arc length is greater than the welding rod diameter, it is called a long arc; when the arc length is less than the welding rod diameter, it is called a short arc.

When using acid electrodes, long arc welding should be used so that the arc can burn stably and obtain a good weld joint. When using alkaline electrodes, short arc welding should be used.

During welding, the arc should not be too long, otherwise the arc combustion will be unstable, resulting in poor weld quality and uneven scales on the surface of the weld.

2.1.4 Selection of power supply type and polarity

The main basis for selecting the type of power supply is the type of welding rod. Generally, acid electrodes can use AC or DC power supplies, while alkaline electrodes require DC power supplies to ensure welding quality.

(When both AC and DC can be used, AC power supply should be used as much as possible, because AC power supply has simple structure, low cost, and convenient maintenance.)

If a DC welding machine is used, there is a polarity selection problem. When the positive electrode of the welding machine is connected to the workpiece and the negative electrode is connected to the welding rod, this connection method is called positive connection or positive polarity; when the negative electrode of the welding machine is connected to the workpiece and the positive electrode is connected to the welding rod, it is called reverse connection or reverse polarity.

When using a DC welding machine for welding, the selection of polarity mainly depends on the properties of the welding rod and the heat required by the weldment. The selection principles are as follows:

When welding important structures, alkaline low hydrogen electrodes such as E4315 (J417), E5015 (J507) can be used, and DC reverse polarity welding is specified to reduce the generation of porosity.

When using acid titanium-calcium electrodes such as 4303 (J422), AC or DC welding can be used. When welding thin steel plates, aluminum and aluminum alloys, brass and other welded parts, DC reverse polarity should be used.

2.2 Common defects in manual arc welded joints analysis.

DefectDefect characteristicsCause of occurrencepreventive measure
Dimensional deviationWeld density, reinforcement, weld leg size, etc. are too large or too smallImproper selection of electrode diameter and welding specificationsImproper groove design and poor strip handling gesturesCorrect selection of electrode diameter and welding parameters can improve the level of operation technology.
UndercutDents in the base metal of the weld seam
Improper welding specifications, excessive current, excessively long arc, and excessively fast welding speed. The angle of the welding rod is incorrect, the operation gesture is poor, and the arc blow joint position is incorrectReduce the welding current, do not pull the arc too long, and the speed of the edge conveyor can be slightly slower, while the middle conveyor can be slightly faster. The inclination angle of the welding rod is appropriate
StomaThere are pores sandwiched in the weld seam
The oxide, rust, and oil stains on the surface of the weldment are not cleaned, the welding rod absorbs moisture, the welding current is too small, the arc is too long, the welding speed is too fast, the protective effect of the coating is poor, and the operation gesture is poorClean the welding groove, dry the welding rod according to regulations, increase the welding current appropriately, reduce the welding speed, and prevent gas from escaping
Lack of penetrationIncomplete bonding between welding rod and base metal
Poor groove and gap design, incorrect welding rod angle, poor operation gestures, insufficient heat input, low current, fast welding speed, and incomplete removal of groove welding slag oxidesChoose the appropriate groove size, choose a larger welding current, or slow down the welding speed to improve the operating technology
Burn throughWhen welding thin plates, holes are burned out on the base metal
Incorrect welding specifications (excessive current), incorrect welding methodsSelect a smaller welding current to accelerate the welding speed appropriately

3. Gas metal arc welding with consumable electrode and CO2 shielding gas (CO2 gas welding, MIG welding, MAG welding)

CO2 shielding welding uses CO2 gas as a protective gas and wire as an electrode in consumable electrode gas metal arc welding. Its characteristics are as follows:

a) CO2 gas is widely available and cost-effective, with costs equivalent to 40-50% of manual arc welding;

b) High deposition rate, large penetration depth, no slag, and concentrated heat source, resulting in high productivity;

c) Full-position welding can be performed by using fine wires and short-circuit transition methods;

d) Thin sheets of 1-3mm can be welded using fine wires, with minimal deformation after welding;

e) The hydrogen content in the weld is low, and it has strong corrosion resistance and good crack resistance;

f) CO2 shielding welding is easy for observing the arc and molten pool due to its bright arc welding, allowing for timely detection and adjustment of problems, thereby ensuring the quality of the weld;

g) Due to the strong oxidation effect of CO2 gas in the arc space, splashing occurs easily, and the weld is prone to porosity. CO2 shielding welding is susceptible to interference from airflow, which limits its use for outdoor construction.

3.1 CO2 gas shielding welding specifications:

The main welding parameters for CO2 gas shielding welding are wire diameter, welding current, arc voltage, welding speed, gas flow rate, power polarity, and wire extension length.

3.1.1 Selection of wire diameter:

Welding wire diameter
Droplet transfer formPlate thickness
Weld position
0.5-0.8short circuit1.0-2.5Full position
1.0-1.4short circuit2.0-8.0Full position

The wire diameter used for CO2 gas shielding welding has a wide range. Fine wires can be used for welding thin plates, flat welding, and all-position welding (short-circuit transition). Thick wires are only suitable for welding thick plates and horizontal position welding (globular transition).

3.1.2 Wire material:

For welding low-carbon steel and low-alloy structures, Ho8Mn2SiA solid-core wire is commonly used.

The mechanical properties of the wire include σb ≥ 490MPa and σ ≥ 392MPa.

3.1.3 Selection of welding current and arc voltage:

Welding wire diameter
Short circuit transitionGranular transition

3.1.4 Welding speed:

The suitable welding speed is controlled at 30-60cm/min.

3.1.5 CO2 gas flow rate:

The gas flow rate is usually related to the welding current. When welding thin plates with small currents, the gas flow rate can be lower. When welding thick plates with large currents, the gas flow rate should be appropriately increased.

For fine wire welding, the CO2 gas flow rate is 5-15L/min, and for thick wire welding of thick plates, the CO2 gas flow rate is 15-25L/min.

3.1.6 Power polarity:

When welding low-carbon steel and low-alloy structural steel using CO2 gas shielding welding, direct current reverse connection is usually used (the negative pole of the

DC welding machine is connected to the workpiece, and the positive pole is connected to the electrode, which is called the reverse connection method).

3.1.7 Wire extension length:

The wire extension length refers to the distance from the end of the wire to the nozzle’s conductive mouthpiece. Generally, it is about 10 times the wire diameter.

3.2 CO2 gas shielded welding specifications example

Specifications for thin plate welding using fine wire CO2 gas shielded welding.

Weldment thickness
Joint formAssembly clearance
Welding wire diameter
Arc voltage
Welding current
Gas flow rate

Causes of defects in CO2 gas shielded welding and preventive measures

Defect NameCasuesPrevention measures
CrackThe depth-to-width ratio of the weld is too large.Increase arc voltage or decrease welding current to widen the weld and reduce penetration.
The weld size is too small (especially for fillet welds and root passes).Reduce travel speed to increase the cross-sectional area of the weld.
The arc crater at the end of the weld cools too quickly.Use attenuation measures to reduce cooling rate and properly fill the arc crater.
Slag inclusionThe use of short-circuiting arc multi-pass welding results in the presence of slag-type inclusions.Clean off the shiny slag shell on the weld bead before welding the next pass.
High travel speed results in the presence of oxide film-type inclusions.Reduce travel speed, use welding wire (flux-cored, solid) with higher deoxidizer content, and increase arc voltage.
StomaInsufficient gas protectionIncrease the flow rate of protective gas to remove all air from the welding area. Clean up the splashes inside the gas nozzle to prevent air flow (caused by fans, door opening, etc.) from blowing into the welding area. Use a slower walking speed to reduce the distance between the nozzle and the weldment. The welding gun should be kept at the tail of the weld seam until the arc crater solidifies
Welding wire contaminatedUse clean and dry welding wire to remove any oil stains adhered to the wire in the wire feeding device or wire guide tube
The workpiece is contaminatedBefore welding, remove oil, rust, paint, and dust from the groove, and use welding wire with high deoxidizer
Arc voltage too highReduce arc voltage
The distance between the nozzle and the workpiece is too largeReduce the extension length of the welding wire
UnfusedThere is oxide film or rust on the welding areaRemove oxide skin and impurities from the groove and workpiece surface before welding
Insufficient linear energyIncrease wire feeding speed and arc voltage, reduce walking speed
Inappropriate welding technologyUsing swing operation to achieve an instant stop of sensitivity along the groove, and maintaining the direction of the welding wire at the front of the welding pool
Unreasonable joint designThe included angle of the beveled joint should be maintained large enough to achieve the degree of the groove using appropriate welding wire extension length and arc characteristics. Change the V-shaped groove to a U-shaped groove
Lack of penetrationInappropriate groove sizeThe groove listening design must be reasonable, so that the melting depth can reach the bottom of the groove listening, while maintaining a suitable distance between the nozzle and the workpiece to reduce blunt edges. Set or increase the root gap of the butt joint
Improper welding operationPosition the welding wire at an appropriate walking angle to achieve maximum penetration, while maintaining the arc at the forefront of the welding pool
Inappropriate linear energyIncrease the wire feeding speed to obtain a larger welding current and maintain an appropriate distance between the nozzle and the workpiece.
Large melting penetrationExcessive linear energyReduce wire feeding speed and arc voltage to increase walking speed
Improper groove processingReduce excessive root gaps and increase blunt edges.

4. Non-melting electrode gas shielded welding (TIG)

Non-melting electrode gas shielded welding, also known as tungsten inert gas (TIG) welding, is an arc welding method that uses inert gas (argon) as a shielding gas and tungsten electrode as a non-melting electrode. The heat source for melting is produced by the arc between the tungsten electrode and the base metal (workpiece).

This method can be performed with or without filler metal (welding wire), relying on the melting of the base metal itself (usually used for welding structural components with a thickness of less than or equal to millimeters).

4.1 Tungsten Inert Gas Shielded Welding (hereinafter referred to as TIG Welding) Process

Tungsten inert gas shielded welding (TIG welding) is suitable for thin plate structural welding of materials such as aluminum and aluminum alloys, stainless steel, and ordinary carbon structural steel.

During TIG welding, argon gas only serves as a mechanical protection. It is very sensitive to oil, rust, and other impurities on the surface of the workpiece and filler metal (welding wire). If not properly cleaned, defects such as porosity and slag inclusion are prone to occur in the weld.

Therefore, before welding, the joint surface of the workpiece must be chemically cleaned or mechanically removed of oil stains and rust within a range of 30-50 millimeters (the welding wire should also be cleaned of oil stains and rust), so as to ensure reliable weld quality.

4.1.1 Welding Parameters

The main welding parameters of TIG welding include welding power supply and polarity, welding current, arc voltage, welding speed, tungsten electrode diameter and end shape, nozzle diameter and gas flow rate, distance from the nozzle to the workpiece surface, and welding torch inclination angle.

① Selection of power supply and polarity

Metallic materialsDC power supplyAC power supply
Direct connectionReverse connection
Aluminum alloy
Stainless steel
Carbon steel
Low alloy steel

② Welding Current

Welding current is the most important welding parameter that determines the weld penetration. The welding current is selected based on the required weld depth and the current that the tungsten electrode can withstand.

Various manual TIG welding currents for different joints:

Plate thickness (mm)Joint formWelding current (A)
Flat weldingVertical weldingOverhead welding
Corner joint80-10070-9070-90
Corner joint100-12090-11090-110
Corner joint120-140110-130115-135

Note: When the plate thickness is less than millimeters, millimeters, and millimeters, the welding current can be taken from the lower limit values listed in this table.

③ Arc Voltage

Arc voltage is the main parameter that determines the width of the weld. In TIG welding, a lower arc voltage is usually used to obtain good protection for the weld pool. The commonly used range of arc voltage is 10-20V.

④ Tungsten Electrode Diameter and End Shape

The choice of tungsten electrode diameter depends on the type of welding power source to be used, as well as the polarity and current magnitude.

At the same time, the sharpness of the tungsten electrode end also has a certain impact on the weld depth, width, and stability. The recommended parameters in the table below are available for selection.

Allowable welding current range for various tungsten electrode diameters:

Tungsten electrode diameter (mm)Direct current (A)AC power (A)
Direct connectionReverse connection
Pure tungstenThorium tungsten cerium tungstenPure tungstenThorium tungsten cerium tungstenPure tungstenThorium tungsten cerium tungsten

Before using the tungsten electrode, it is necessary to ensure that its surface is free of burrs and other metal or non-metallic inclusions, and there are no scars, cracks, or other impurities.

Otherwise, arcing may occur in the welding torch clamp and contaminate the weld pool.

The length of the tungsten electrode extension is usually selected 1-2 times the diameter of the tungsten electrode.

Tungsten electrode tip shape and current range:

Tungsten electrode diameter
Tip diameter
Tip angle
DC direct connection
Constant DC
Pulse current

⑤ Welding Speed

The welding speed of TIG welding depends on the thickness of the workpiece and the welding current. Due to the lower current that the tungsten electrode can withstand, the welding speed is usually below 20m/h (controlled within 15-18m/h).

⑥ Gas Flow Rate and Nozzle Diameter

The nozzle diameter depends on the thickness of the workpiece and the joint form, and the gas flow rate needs to be increased correspondingly as the nozzle diameter increases.

When the aperture of the nozzle is 8-12 millimeters, the flow rate of the shielding gas is 5-15 L/min; when the nozzle increases to 14-22 millimeters, the gas flow rate is 10-20 L/min. The gas flow rate is also related to the welding environment.

In the case of strong air flow, the gas flow rate should be increased.

Experienced welders can judge the effect of argon protection by observing the color of the surface of the weld metal during the process.

If the protection effect is not ideal, the argon flow rate should be carefully adjusted, the nozzle diameter should be increased, the area should be increased, and if necessary, the backside argon protection should be increased.

4.2 Typical Process Parameters for Manual Tungsten Inert Gas (TIG) Welding of Aluminum Alloy and Stainless Steel Thin Plates:

Material SciencePlate thickness
Welding positionWelding current
Welding speed
Tungsten electrode diameter
Filler wire diameter
Argon flow rate (L/MIN)Nozzle diameter
Aluminum alloy1.2Horizontal and vertical65-80
2Horizontal and horizontal tilting110-140
3Horizontal and horizontal tilting150-180
4Horizontal and vertical200-230
stainless steel1Flat standing50-80
 Flat standing80-120
 Flat standing105-150     
 Flat standing150-200     

Tungsten inert gas welding process defects.

DefectProduction reasonsPreventive measure
Tungsten inclusion(1) Contact arc ignition (2) Tungsten electrode melting(1) Use a high-frequency oscillator or high-voltage pulse generator to start the arc
(2) reduce the welding current or increase the diameter of the tungsten electrode, tighten the tungsten electrode clamp and reduce the extension length of the tungsten electrode
(3) adjust the cracked or torn tungsten electrode
Poor gas protection effectUnnecessary components such as hydrogen, nitrogen, air, and water vapor are mixed in the gas path(1) Using argon gas with a purity of%
(2) having sufficient advance gas supply and delayed gas stop time
(3) correctly connecting water pipes and gas pipes, avoiding confusion
(4) doing a good job of pre welding cleaning
(5) correctly selecting protective gas flow rate, nozzle size, electrode extension length, etc
Arc instability(1) There is oil stains on the welding part. 
(2) The size of the joint groove is too narrow.
(3) The tungsten electrode is contaminated.
(4) The diameter of the tungsten electrode is too large.
(5) The arc is too long
(1) Do a good job of pre welding cleaning 
(2) Widen the groove, shorten the arc length
(3) Remove the contaminated part
(4) Choose appropriate electrode size and chuck
(5) Lower the nozzle distance
Excessive loss of tungsten electrode(1) Poor gas protection, tungsten electrode oxidation
(2) Reverse polarity connection
(3) Clamp overheating
(4) Tungsten electrode diameter too small
(5) Tungsten electrode oxidation during stopping welding
(1) Clean the nozzle, shorten the nozzle distance, and appropriately increase the large argon flow rate.
(2) Change the polarity of the power supply.
(3) Polish the electrode clamping end and replace it with a new one.
(4) Increase the diameter of the tungsten electrode.
(5) Extend the lag gas supply time by no less than 1S/10A

Note: Except for the unique defects of TIG welding mentioned above, other defects are basically the same as manual arc welding.

5. Spot Welding Process

Resistance spot welding is a resistance welding method that assembles and overlaps the weldment joint, and presses it between two electrodes to melt the mother metal into a weld by resistance heat.

The spot welding process can be divided into three stages: preloading the weldment between the electrodes, heating the welding area to the required temperature, and cooling the welding area under the pressure of the electrodes.

The quality of spot welded joints mainly depends on the size of the fusion zone (diameter and penetration rate).

At the same time, surface defects such as excessive indentation, surface cracks, and adhesion damage will also reduce the fatigue strength of the joint.

Characteristics of spot welding process: low voltage, high current, high production efficiency, small deformation, limited to overlap, no need to add welding materials such as welding rods, wires, and flux, easy to achieve automation, mainly used for thin plate structures.

5.1 Electrode structure and material

Spot welding electrodes consist of four parts: the end, the main body, the tail (taper or pipe thread), and the cooling hole.

There are five common forms of electrodes.

Where 1 represents the end, 2 represents the main body, 3 represents the tail, and 4 represents the cooling water hole.

Standard shapes of spot welding electrodes:

  • a) Tapered electrode,
  • b) Clamp electrode
  • c) Spherical electrode
  • d) Eccentric electrode
  • e) Flat electrode

Spot Welding Electrode Material.

Material nameAlloy composition mass fraction
Tensile strength
Softening temperature
Cold hard pure
Impurities<250-36075-10098150-250Spot welding of rust resistant aluminum 5A02, 2A21 (LF2, LF21)
Cadmium green steel
Cd, the rest are Cu400100-12080-88250-300Hardened aluminum 2A12CZ (LY12CZ) after spot welding and quenching
Engraved bronzeThe rest are Cu480-500110-13565-75510Spot welding of low-carbon steel Q235, 08, 10, 20
Chromium cobalt steel
Cr, the rest are Cu 170-19075≥600Steel and stainless steel

Basic Electrode Dimensions.

Diameter D of the electrode body
 Electrode end diameter d
Tail pipe thread
G (in)
Diameter D of electrode body
Determine based on spot welding process parameters1/2“1”

5.2 Pre-Weld Surface Cleaning

Pre-weld surface cleaning is crucial for spot welding, which involves removing dirt, oxide film, and other contaminants from the surface of the workpiece.

Mechanical cleaning methods such as sandblasting and polishing are commonly used, which include grinding with a grinding wheel, sanding belt, or wire brush.

Chemical cleaning includes alkali washing to remove oil stains and acid washing to remove rust, followed by passivation (note: chemical cleaning should not be used for parts with enclosed shapes or gaps that are difficult for acid or alkali liquids to flow out).

5.3 Spot Welding Working Parameters

The main welding parameters for spot welding include electrode pressure, welding time, welding current, switch and size of the electrode working endface.

The spot welding parameters are usually determined based on the material and type of the workpiece, electrode pressure and welding time, and the required fusion diameter welding current.

Spot welding parameters are mainly selected in the following two ways:

(1) Appropriate matching of welding current and welding time. This combination mainly reflects the heating speed of the welding zone. Large current and short time are the hard specifications; conversely, small current and appropriately extended welding time are the soft specifications.

(2) Appropriate matching of welding current and electrode pressure. This combination is based on the principle of no splashing during the welding process.

5.4 Typical Welding Parameters for Low Carbon Steel Spot Welding.

Plate thickness (mm)Electrode end diameter (mm)Electrode diameter (mm)Minimum point distance (mm)Minimum overlap (mm)Electrode pressure (KN)Welding time (weeks)Welding current (A)Nugget diameter (m)

Note: This form is for 60Hz AC power frequency. When using 50/60Hz AC power, the frequency should be multiplied by 5/6 (see welding time table).

The plate thickness should be based on the thinnest plate thickness in the overlapping parts.

5.5 Causes and Prevention of Spot Welding Defects.

DefectCause of occurrencePreventive methods
Nugget size defectLack of penetration or small nugget sizeWelding current is too low, power on time is too short, and electrode pressure is too highAdjusting welding parameters
Excessive electrode contact areaTrimming electrodes
Poor surface cleaningClean the surface
Excessive penetration rateExcessive welding current, prolonged power on time, insufficient electrode pressureAdjusting welding parameters
Poor electrode cooling conditionsStrengthen cooling and replace with electrode materials with good thermal conductivity
External defectsExcessive indentation of solder joints and surface overheatingThe electrode contact surface is too smallTrimming electrodes
Excessive welding current, prolonged power on time, insufficient electrode pressureAdjusting welding parameters
Poor electrode cooling conditionsStrengthen cooling and replace with electrode materials with good thermal conductivity
Local burn through and overflow on the surface, surface splashingThe electrode is too sharpRepair welding parameters
Foreign objects on the surface of electrodes or welding componentsEnhanced cooling
Insufficient electrode pressure or virtual contact between electrode and weldmentTrimming electrodes
Radial cracks on the surface of solder jointsInsufficient electrode pressure, insufficient forging force or untimely additionClean the surface of electrodes and welding parts
Poor electrode cooling effectIncrease electrode pressure and adjust stroke
Circular cracks on the surface of solder jointsWelding time too longAdjusting welding parameters
Surface adhesion and damage of solder jointsImproper selection of electrode materialsExchange suitable board materials
Tilt of electrode end faceTrimming electrodes
The surface of the solder joint turns black and the coating layer is damagedPoor surface cleaning of electrodes and welding partsClean the surface
Excessive welding current, long welding time, insufficient electrode pressureAdjusting welding parameters

6. Gas Welding and Welding Code

The parameters of gas welding and welding code include the selection of flame energy efficiency, the selection of wire diameter, the selection of oxygen pressure according to the welding distance model, the selection of the inclination angle of the welding nozzle, and the selection of the welding speed.

6.1 Selection of Flame Energy Efficiency

The gas welding flame energy efficiency is expressed in terms of the hourly consumption of acetylene gas (L/H). It is selected based on the thickness of the welded parts, the material properties, and the spatial position of the welded parts.

When welding low carbon steel and alloy steel, the consumption of acetylene can be calculated using the following empirical formula:

  • Leftward welding (for welding thin plates): V = (100 – 120) δ
  • Rightward welding (for welding thick plates): V = (120 – 150) δ

In formula,

δ represents the thickness of the steel plate in millimeters, and V represents the flame energy efficiency (acetylene consumption) in liters per hour.

When welding copper with gas, the acetylene consumption can be calculated by the following empirical formula:


Choose the welding torch model and nozzle number based on the calculated acetylene consumption, or directly choose them based on the welding plate thickness.

Please refer to the table for the injection and suction type welding torch models and their main parameters.

Welding torch modelH01-2H01-6
Welding nozzle number1234512345
Welding nozzle aperture (mm)          
Welding thickness (mm)          
Oxygen pressure (MPe)          
Acetylene pressure (MP)  
Oxygen consumption (m/h)          
Acetylene consumption (L/h)405580120170170240280330430

6.2 Types and Applications of Oxygen-Acetylene Flames

Welded metal materialThe type of flame to be usedWelded metal materialThe type of flame to be used
Low and medium carbon steelNeutral flameAluminum and aluminum alloysNeutral flame or slightly carbonized flame
low alloy steelNeutral flameChromium nickel stainless steelNeutral flame
High carbon steelMild carbonization flameMing stainless steelNeutral flame or slightly carbonized flame
Cast ironNeutral flame or slightly carbonized flameNickelMild carbonization flame
Purple copperNeutral flameMenggangMild carbonization flame
brassMild oxidation flameGalvanized iron sheetMild carbonization flame
Tin bronzeNeutral flameHard alloyMild carbonization flame
Monel alloyMild oxidation flameHigh speed steelMild carbonization flame
Aluminum, tinNeutral flameTungsten carbideMild carbonization flame

6.3 Selection of Welding Wire

6.3.1 The material of welding wire should be similar to the alloy composition of the workpiece.

The following table of welding wires can be used for gas welding of steel, aluminum and aluminum alloys, as well as copper and copper alloys:

A) Welding wires for various types of steel used in gas welding

Welding wire nameWelding wire gradeApplicable steel grade
Low carbon steel, low alloy structural steel, medium carbon steel welding wireH08Q235
H08MnMedium carbon steel
H08MnAQ235, 20, 15g, 20g16Mn, 16MnV, medium carbon steel
H12CrMo20Medium carbon steel
Austenitic stainless steel welding wireHoCrl18Ni90Cr18Ni9 0Cr18Ni9Ti 1Cr18Ni9Ti
HCr18Ni11Mo3Cr18Ni12MoTi Cr18Ni12Mo3Ti

B) Welding wires for aluminum and aluminum alloys used in gas welding.

Welding materialWelding wireCutting or wire of base material
L1S (wire) AL-2L1
L2L1 L2
L3L2 L3
L4L3 L4
L5L4 L5
L6L5  L6
LF2SA1Mg-2 SA1Mg-3LF2 LF3
LF3SA1Mg-3 SA1Mg-5LF3 LF5
LF21SA1Mn SA1Si-2LF12

C) Welding wires for copper and copper alloys used in gas welding.

Welding materialWelding wire nameWelding wire grade
Pure copperCopper wireHsCu
Brass1-4 # brass wireHsCuZn-1~4
White copperZinc white copper wireHsCuZnNi
Copper wireHsCuNi
BronzeSilicon blue copper wireHsCuSi
Tin blue copper wireHsCuSn
Aluminum bronze wireHsCuAl
Nickel aluminum bronze wireHsCuAlNi

6.3.2 Selection of Welding Wire Diameter

The selection of welding wire diameter is mainly based on the thickness of the workpiece material.

If the welding wire is too thin, it will melt too quickly and the melting point will fall on the weld seam, which can easily cause poor fusion and uneven weld seams.

If the welding wire is too thick, the melting time of the welding wire will be prolonged, the heat-affected zone will be enlarged, and overheating tissue may occur, which will reduce the welding quality of the joint.

Relationship between workpiece thickness and welding wire diameter:

Workpiece thickness
Welding wire diameter

6.4 Welding Nozzle Tilt Angle

The tilt angle of the welding nozzle is usually determined based on the thickness of the workpiece, the size of the welding nozzle, and the welding position. A large tilt angle of the welding nozzle results in a concentrated flame, minimal heat loss, high heat input, and rapid heating of the workpiece.

Conversely, a small tilt angle of the welding nozzle results in a dispersed flame, significant heat loss, low heat input, and slow heating of the workpiece. The tilt angle of the welding nozzle is generally within the range of 20°-50°.

Selection of tilt angle for gas welding nozzle:

Weldment thickness
Welding nozzle inclination angle20°30°40°50°60°70°

6.5 Principles for the Selection of Gas Welding Specifications

ParameterSelection principles
Flame typeTypes of oxygen acetylene flames, selected according to the table
Acetylene consumption and oxygen working pressureBased on factors such as the melting point of metals and alloys, the thickness and small size of welding parts, thermal conductivity, and joint form, select welding torque and nozzle with appropriate flame energy rate (acetylene consumption), and adjust the oxygen working pressure appropriately according to acetylene consumption.
Welding wire diameterTable selection based on the relationship between workpiece thickness and welding wire diameter
Welding nozzle numberDetermine based on the thickness, material, and joint form of the weldment
Welding nozzle inclination angleDetermine according to the thickness of the welding piece (see the selection of welding nozzle inclination angle)
Welding speedBased on operational skills and the strength of the flame used, try to increase the welding speed as much as possible while ensuring penetration

6.6 Common Defects and Preventive Measures in Gas Welding

DefectCause of occurrencePreventive measure
CrackleThe sulfur content in the weld metal is too high, the welding stress is too high, the flame energy rate is low, and the weld fusion is poorControl the sulfur content of weld metal, improve flame energy efficiency, and reduce welding stress
StomaPoor cleaning of welding wires and parts, high sulfur content, incorrect flame composition, and fast welding speedStrictly clean the surface of the workpiece and control the metal composition of the welding wire; Reasonable selection of flame and welding speed
The weld size and welding switch do not meet the requirementsImproper angle of welding groove, uneven assembly gap, improper selection of welding parameters, etcReasonable processing of groove angle, strict control of assembly clearance, and correct selection of welding parameters
UndercutExcessive adjustment of flame energy rate, incorrect inclination angle of welding nozzle, improper movement method of welding nozzle and welding wireCorrectly select welding parameters and correct operation methods
Burn throughExcessive heating of welding parts, improper operation process, slow welding speed, and prolonged stay at a certain locationReasonable heating work, adjusting welding speed, and improving operational skills
PitExcessive flame energy rate, incomplete filling of the melt pool at the endPay attention to the welding essentials at the end and choose a reasonable flame energy rate
Slag inclusionWelding edges and layers are not cleaned thoroughly, welding speed is too fast, weld shape coefficient is too small, and welding nozzle inclination angle is not appropriateStrictly clean the edges and welding layers of the welded parts, control the welding speed, and appropriately increase the shape coefficient of the weld seam
Lack of penetrationThere are oxides on the surface of the weldment, the groove angle is too small, the flame energy rate is insufficient, and the welding speed is too fastStrictly clean the surface of the weldment, select appropriate groove angles and gaps, control welding speed and flame energy rate
UnfusedThe flame energy rate is too low or leans towards the groove sideChoose the appropriate flame energy rate to ensure that the flame is not biased
Weld beadingExcessive flame energy rate, slow welding speed, large assembly gap of welding parts, incorrect welding gun movement method, etcSelect appropriate welding speed and flame energy rate; Adjust the assembly gap of the welding parts and use the welding gun correctly
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Founder of MachineMFG

As the founder of MachineMFG, I have dedicated over a decade of my career to the metalworking industry. My extensive experience has allowed me to become an expert in the fields of sheet metal fabrication, machining, mechanical engineering, and machine tools for metals. I am constantly thinking, reading, and writing about these subjects, constantly striving to stay at the forefront of my field. Let my knowledge and expertise be an asset to your business.

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