Jan 092014

The gas metal arc welding torch is made of the following components:
-welding power supply with mains supply and welding lead
-wire feeding with wire spool and wire feed unit
-shielding gas supply and inert gas flow meter and magnet valve
-control module for central control and handling of the machine
-hose package with torch


Welding Power Supplies
Welding power supplies transfer the electric energy which supplies the necessary amount of heat in the arc during different welding processes. Welding process and welding power supply form a system which has a great influence on the quality of the weld seam.
In addition to conventional power supplies electronic machines have more and more been developed and used.
Those can be basically split up in two parts:
a)    the power component
b)    the handling component
Indicated are the mostly used welding torches for gas metal arc welding.

Jan 062014

Clamped in the welding torch is a tungsten electrode in which the welding current is introduced.

Between the tungsten electrode and the workpiece an arc is formed which fuses the base material and melts the added filler metal.
Inert shielding gas streams out of the welding torch and screens off the glowing tungsten electrode as well as the welding pool from air.
the welding torchThe welding torch contains the tightly clamped tungsten electrode and the gas nozzle as well as, dependent on the current load, the channels for the water-cooling.
Usual shielding gas flow rate amount for argon, depending on the diameter of the gas nozzle and the welding condition is, 5 to 10 l/min. In the case of partly mechanized welding the filler will be added mechanically, not through the hose package, but separately.
The filler metal feed is regularly switched on separately whereas the turning on and off of the welding process is controlled by the torch.

The power supply consists of a steeply falling (constant current-) characteristics which has the effect that the amperage remains almost constant when the arc length changes.

schematic view of TIG-welding

Jan 062014

Usually it is welded with direct current with the positive pole at the wire electrode. Other polarities are also possible.
The power supplies are usually rectifiers. It has to be considered that, due to the high stage of mechanism, there are high intensities of current placed at disposal at a duty cycle of 100 %.
A downward power supply characteristic (external regulation) is used at wire electrodes exceeding 3 mm, if the wire electrode diameter is small, a constant current characteristic is used.

Welding Seam Preparation: Due to the deep penetration a special seam preparation and the use of backing is necessary.
Backing is standardised according to DIN EN ISO 9692-2.

The Voltage Influences Seam Width

seam widthSeam width as function of voltage. The usual voltage is at approx. 30 V.




The Amperage Mainly Influences the Penetration

voltageAs reference value 100 A can be chosen in order to create a penetration of approx. 1 mm in the square butt joint.
Usual amperage at a wire electrode’s diameter of 4 mm is at I = 600 A.
From these values a current load results which is usually at about 150 A/mm wire diameter. Then the current density is at about 48 A/mm2.
It has to be considered that the current density, not the amperage, strongly influences the extend of the penetration.

The Welding Speed Influences the Weld Width as well as the Weld Depth

welding speedThe usual welding speed is at about 55 cm/min. If too low welding speeds have been chosen the arc burns on the forward travelling welding pool which has a flat penetration and also lacks of fusion.
From the single parameter results a welding parameter replacement of
I    =    600    A
U    =    30    V
v    =    55    cm/min
Wire diameter    =    4    mm
which is to be seen as basic parameter. From these values results a for the submerged arc welding typical energy per unit length of approx. 20 kJ/cm.

schematic design of a submerged arc welding system


Jan 062014
submerged machine

The arc burns invisibly between a melting electrode and the work piece, or between two melting electrodes. Arc and welding zone are covered by a layer of flux. The weld pool is protected from the admission of the atmosphere by slag developed by the flux.

Model of Submerged Arc Welding

The shown cross-section shows that the weld pool is covered by the powder which results in a very good thermal operating ratio which is to be found in a high deposition efficiency wel-ding process.
During the submerged arc welding process there are metallurgic processes in the stage of drops, in the pool reaction and in the area of dilution with the base material.
The reaction in the drop stage and in the pool reaction are determined by a welding flux and the used welding filler.
There are influences of the welding filler and the base material in the area of the dilution. That shows that chemical combi-nations of the weld metal and its mechanic-technological characteristics extremely depend on the used wire-power-combination which always have to be related to the base material.

In the diagram deposition efficiency of conventional welding processes are compared.


When submerged arc welding the usual deposition efficiency with a wire electrode diameter of 4 mm is at 7 to 8 kg/h if the duty cycle is at 100 %.
From this point of view it can be concluded that this welding process has to be fully mechanised since when manual welding such deposition efficiencies do not lead to such high deposition efficiency.
It has also to be taken into consideration realise that sub-merged arc welding is a high-capacity process that normally can be used with a material thickness starting from 6 mm.

areea of usage

Furthermore, a very important area of usage is the cladding of materials in order to protect them from corrosion and/or tear. For cladding tasks usually the two wire submerged arc welding or the submerged-arc strip welding process are used since with both processes a drastic dilution decrease of the base material can be achieved.
According to the wide field of use, f. ex. container construction, shipbuilding and pipe construction, there is also a wide range of materials used.

The material groups which today are fabricated with submerged arc welding
the material groups

Jan 062014

This technique (autogenous (lat.) = self working) means working with materials or heating of workpieces by means of a flame. The term “Autogenous Technique” includes different processes, where the process heat is generated by a flame.

Important Flame Processes
The heat source is a chemical reaction resulting from the combustion of the fuel gas with oxygen. This is an exothermic reaction.

Flame StraighteningFlame straightening is an efficient method of correcting distorted parts.
It is based on the physical principle that metals expand when heated and contract when cooled. If expansion is limited, compressive stresses built up and result in plastic deformations. Upon cooling, the plastic deformations remain, and they shorten the heated area.


The term “flame heating” refers to processes in which heat is transferred to the workpiece by means of a flame without the workpiece melting or material being removed. There are a lot of different processes.


Flame HeatingFlame Hardening. When flame heating the workpiece surface is hardened by local limited heating and immediate quenching.
The core area of the component is not influenced by the heating process.



Flame Spraying

Flame Spraying. The flame heating process is used for machining of the workpiece surface. The surfaces of steel and concrete, for example, can be cleaned or prepared for the following coating.
Concrete and rocks can, for optical or adhesion improvement effects, also be surface roughened.


cutting with the packed lance.Thermal Cutting of e.g. concrete. The oxygen-lance cutting with the oxygen lance is a thermal hole piercing.
The oxygen lance burns off with the oxygen inflow, the reaction heat enables to deposit steel or concrete as well as rocks.



Oxy-Acetylene Welding


When Oxy-Acetylene Welding a weld pool is created by immediate, locally restricted influence of an oxygen-fuel or an air-fuel flame.
The advantages of Oxy-Acetylene Welding are as follows:
-low investment costs
-variable use of the equipment
-good to use in out-of-position welding.


soldering and brasingSoldering and Brazing. When soldering a solder filling metal with a lower melting point than the one of the base material is deposited with a flame. By wetting of the metal surfaces a joint between the workpiece is achieved.




When autogenous Oxy-Fuel-Cutting the working material is oxidised by the oxygen jet. Oxy-Fuel-Cutting
The resulting heat enables continuous cutting. The oxide products are pushed out of the kerf by the oxygen jet. For this reason also extremely thick workpieces can be cut.



flame gougingThe flame gouging works according to the same principle as the oxy-fuel cutting. The surface of the workpieces can be gouged by this method.

Jan 062014

Manual arc welding is a manual welding process. The arc (about 5000 ° C) is the heat source, which burns between the coated welding electrode and the workpiece. The arc decomposes the electrode coating into slag and shielding gas to protect the passing drop and the weld from atmosphere.

The main difference for this welding process, compared to other welding processes, is that the shielding gas is produced by the coating of the electrode.
The kind of the coating has influence on the chemical composition of the welding material, the drop size and flow behavior of the slag and the melted mass.
Manual arc welding is used in many areas and in all welding positions and it can achieve a melting deposition rate of approximately 1.5 kg/h.

The advantages of manual stick electrode welding in comparison to gas metal arc welding are:
-lower demand for investments
-easy to handle.
-lower deposition efficiency
-higher slag formation
-often changing electrodes.



Example of a Welding Transformer

Example of a Welding Transformer

Jan 052014

The main difference between the tungsten arc welding process and the MIG process is indifference of the electrodes. Whereas the tungsten electrodes at the tungsten arc welding process are only arc producing electrodes (non depositing electrodes), the almost endless spooled wire electrodes are at gas metal arc welding arc producing electrodes and depositing filler material. The arc space, the dissolving filler and the melting pool are screened from the air atmosphere by the active and inert shielding gases. The operative range of steels and non iron metals determines the choice of wire and shielding gas combinations. In the case of steel welding only active shielding gases are used and in the case of treatment of non iron metals inert gases are usually used. Gas Metal Arc Welding: Active Gas Metal MAG and Metal – Inert gas MIG electrod mag

how to weld a 2g mig bend test plate

Jan 052014

The technical usage of steel is for one reason based on the fact that a various number of possible heat treatments lead to different properties of one certain material. These different properties are adjustable due to allotropic modification of the steel lattice.
Steels without a α/γ-transformation like austenitic of ferritic steels are neither hardenable nor able to normalize. The various heat treatments can be divided into annealing, hardening and quenching/tempering.
heat tratament
The reason for annealing a material is to create a certain pro-cessability (for example: cold forming, cutting properties). The changing of material properties is done by the following:
-Transformation of structures
-Transformation of grain size, arrangement,
-Stress relieving
The different ways of annealing are seperated in heating up to a certain temperature (set-point), holding at this temperature and cooling down to the room temperature. During the heating of a material the appearance of an increasing tension between outer and inner areas of the material might cause problems. Therefore the thickness of the material as well as the thermal conductivity should be noticed to avoid for example stress cracking. The same could appear during the cooling process of the material.

Removal of Non-Uniform Structures: Diffusion Annealing, Normalizing
Increasing of Workability: Coarse-Grain Annealin, Soft Annealing, Recrystallization Annealing, Crystal Recovery Annealing
Reducing of Stresse: Stress-Relief Annealin, Stress-Relieving Treatment
Transformation of Structure: Tempering
Special Cases: Controlled Cooling:Quenchin, Bainitic Transformation

heat tratament 2

The purpose of hardening is to obtain a hard structure. There are various processes of hardening as normal or surface hardening which all rely on the material.

Normal Hardening: Hardening from Hot-Forming HeatBroken Hardening, Martempering
Surface Hardening: Flame Hardening, Induction Hardening, Dip Hardening, Case Hardening, Nitriding, Gas-Nitro Carbonising.

heat tratament3

The characteristic of a hardened material is the hardness which on the other hand leads to a reduced toughness. To get a hard but tough material another heat treatment has to be done which is called quenching and tempering.

Jan 042014

Scheme of the cracks in welded joints according to size, propagation and cause

scheme of the welded joints

Types of Failures in Fusion Welded Joints


a-longitudinal crack
b – transverse crack
c – pore
d – wormhole
e – localised porosity
f – linear porosity
g – shrinkage cavity
h – slag inclusion
i – incomplete penetration
j – lack of inter-run fusion
k – lack of sidewall fusion
l – root notch
m – reinforcement
n – penetration bead
o – incompletely filled groove
p – overlap
q – edge misalignment

Jan 042014

tensile test logoWithin destructive material testing the tensile test has a great importance as this test delivers the material characteristic values for the calculation of the strength of the shape. Further, it gives information on the deformability of a material.

Due to the fact that the results of tensile tests are of great importance for e.g. working and process tests it must be guaranteed that the test can be reproduced. Therefore, all possible parameters influencing the test, e.g. the type of the test equipment, the shape of the test piece, the execution of the tensile test must be avoided. This is possible by the compliance with the corresponding standards only.

Standards Refering to Tensile Test
DIN EN ISO 6892-1
Metallic Materials – Tensile Testing – Part 1:
Method of Test at room temperature
This standard applies to the tensile test for all metal-     lic material with and without fine strain measurement
DIN 50125
Tensile test specimens, directions for their preparation
EN 895 
Destructive test on welds in metallic materials
Transverse tensile test
EN 876
Destructive test on welds in metallic materials
Longitudinal tensile test

Execution of the Tensile Test
During the tensile test one or several of the characteristic values of strength and deformation described in the following will be determined. In doing so, a tensile test piece is elon-gated to fracture. The shapes of test pieces most frequently used are:

Tensile test piece form A – Round specimen with smooth cylinders heads for clamping
Tensile test piece form A
d0    diameter of specimen
d1    diameter of grip (» 1.2 d0)
L0    gauge length (L0 = 5 d0)
Lc    parallel length (Lc ³ L0 + d0)
Lt    total length
h    height of grip

Tensile test piece form B – Round specimen with screw thread
Tensile test piece form Bd0    diameter of specimen
d1    diameter of grip
L0    gauge length (L0 = 5 d0)Lc    parallel length (Lc ³ L0 + d0)
Lt    total length
h    height of grip


Tensile test piece form E – Flat specimen
Tensile test piece form Ea    thickness of specimen
b    width of specimen
B    width of grip (» 1.2 b + 3 mm)
h    height of grip (» 2 b + 10 mm)
L0    gauge length
Lc    parallel length (Lc ³ L0 + 1.5 ÖS0)
Lt    total length

Proportional test pieces according to DIN 50125 are tensile test pieces for which a fixed ratio between the initial measuring length L0 and the initial cross section S0 exists. For test pieces with a circular cross section L0 = 5 x d0 is valid in general. For test pieces with a prismatic cross section the initial measuring length
L0 = 5.65 • √S0
will result.
The tensile test on weld joints serves to determine the strength and deformation behaviour of weld joints transverse to the weld seam by means of determining the tensile strength, position and type of the crack.
The flat tensile test pieces are of such nature that the weld metal, the heat effected zone as well as the non-affected parent material are exposed to almost the same stresses. The shapes of the test piece according to EN 895 bzw. EN 876, respectively are listed below.

further test pieces