Welding Technology: Processes and Electronics

General Introduction to Welding Technology

• Manual arc welding uses fusible electrodes.
• Friction welding is not a fusion welding process.
• The code 114 corresponds to welding with flux-cored consumable electrode wire, without gas.

Gas Welding and Related processes

• The flame should be adjusted to reducing when welding mild steel by the oxy-fuel process.
• In oxyacetylene welding, the filler metal is marketed in the form of rods.
• An insufficient gas outlet speed can cause a flashback in a torch.

Electronics Reminders

• Diodes and thyristors are often used in rectifier bridges of welding machines.
• The main role of the thyristor is to rectify the current and regulate the welding intensity.
• The presence of residual magnetism in a material causes a deflection of the arc and the molten zone.
• If the current goes from 100 to 200 amps, the voltage drop in the welding cable will double.
• When a current source provides a direct current whose intensity varies abruptly from zero to a high value, to an electric circuit that includes a coil mounted in series, the current takes some time to rise from zero then remains constant to a given value.

The Arc

• In an electric arc, an emission of electrons occurs at the cathode level.
• In an electric arc, an electron bombardment occurs at the anode level.
• Ohm's law is U = R x I

Arc Welding Current Sources

• Magnetic blowing is more important in direct current.
• "Direct polarity" in welding means connecting the electrode to the negative pole of the welding current source.
• Rectifier, a generator coupled to a diesel engine, and a source with an inverter can produce direct current.
• When the electrical circuit is open, the voltage (U) is maximum and the current (I) = 0.

Introduction to Gas Shielded Arc Welding

• In MAG welding of unalloyed or low-alloy steels, inductance placed in the welding circuit mainly reduces molten metal projections.

TIG Welding

• Argon gas is best suited for MIG-MAG welding of non-alloyed steels.
• The use of the high frequency device in TIG welding with alternating sinusoidal current improves arc stability.
• In TIG welding, contact of the electrode with the part or the molten bath should be avoided because it causes tungsten inclusions.
• Direct current, straight polarity is used for TIG welding of stainless steels.
• In TIG welding, some tungsten electrodes contain lanthanum oxide to increase thermo-emissivity and electrode life.

MIG/MAG and Flux Cored Wire Welding

MIG/MAG Welding

• In MIG/MAG welding, the contact tube condition of the welding torch should be frequently checked to ensure that it is properly tightened and that it ensures a correct transfer of current to the filler wire.
• In MAG welding, a gas flow rate of 8 to 12 l/min is best suited with a 12 mm diameter nozzle.
• The copper that covers the filler wires in MAG welding facilitates the transmission of current from the contact tube.
• Carbon dioxide is the shielding gas allows short-circuit transfer in MIG-MAG welding.
• A short arc in MAG welding, obtained by increasing the wire feed speed, results in a higher deposition rate and higher penetration.

Flux Cored Wire Welding

• A flux-cored wire consists of a metal tube containing flux or metal powder.
• Some flux-cored wires can be used in a wide range of welding positions because they form a slag that maintains the weld pool in place.
• The significant risk of flux-cored wire welding is that it produces a greater quantity of smoke.

Manual Metal Arc Welding

• Basaltic coated electrode does not exist.
• The assembly requires the most dexterity from a welder in coated electrode welding is a full penetration butt weld of fixed pipes, horizontal axis, 12 mm thick.
• A baking must be carried out before welding for basic coated manual electrodess.
• The feature of rutile, basic or acid type of a manual arc welding electrode depends on the composition of the coating.
• Electrode E 42 3 B 32 H 5, the deposited metal on construction steels will have the best resilience and the best tenacity.

Submerged arc welding

• Agglomerated fluxes have the highest capacity to add alloying elements to the molten metal.
• The role of the flux in submerged arc welding is to protect the weld pool from the atmosphere, clean the molten metal bath and modify the chemical composition of the metal.
• In submerged arc welding, an alternating current source with a drooping characteristic requires the wire feed to be servo-controlled to the arc voltage in order to maintain a constant arc length.
• Using an alternating current on the second wire makes it possible to avoid disturbing the arc when submerged arc welding with two wire electrodes.

Resistance Welding

• A button test is best suited for controlling the quality of spot welds in production.
• Resistance welding of copper: is only possible for thicknesses less than 1 mm with electrodes with tungsten or molybdenum inserts.

Other welding processes

Laser, electron beam, Plasma.

• Copper in high thickness cannot be assembled by Laser welding.
• Regarding electron beam and laser welding, the welding is carried out on straight and joining edges and filler metal may be used if necessary, to improve the metallurgical weldability and compensate for the presence of small gaps (in the case of laser welding).

Other welding processes

• An argon / helium mixture can be used as a plasma gas in plasma welding.
• Explosion welding allows for steel / aluminum bonding.

Cutting and Edge Preparation Processes

• Continuous current electrode to the negative pole with transferred plasma is the energy source and mode of arc transfer in plasma cutting.
• Too short a nozzle/part distance in flame cutting results in the fusion of the upper edge of the cut.
• Oxycutting is not suitable for cutting stainless steels.

Recharge And Projection

• A temperature of fusion of the resulting oxides > temperature of the combination reaction can make an alloy unsuitable for oxycutting.
• Recharging uses submerged arc welding in direct current with the electrode to the positive pole and submerged arc welding with strip in direct current electrode to the negative pole.
• Hot wire TIG welding and oxyacetylene welding can be used for reconditioning.
• MIG welding is not used in thermal spraying.

Fully Mechanized and Automated Processes; Robotics

• The use of a MIG welding robot increases the operating factor.

Brazing and Soldering

• Pre-probing does not allow for the correction of trajectory during welding with robotic arc welding.
• Resistance welding is best suited for being robotized.
• Brazing can be used without flux.
• In brazing, the edge preparations are similar to those use in gas welding and the joint strength is higher.
• Capillary rise of a brazing filler metal in a brazed joint is facilitated when there is a small gap between the parts (0.05 to 0.15 mm.)

Plastics Assembly Procedures

• Cold pressure welding is not used to weld plastic materials.