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FAQs
What is arc blow in stud welding and how does it occur?
Arc blow is caused by electromagnetic fields that inevitably form around current-carrying conductors. These magnetic fields interact with each other and influence the arc. This can create turbulence that forces air and shielding gas into the weld pool, potentially reducing weld quality. Arc blow occurs exclusively in arc welding and is strongly influenced by the geometry of the components, the position of the welding gun (cable bend), and the routing of the ground cables.
Which stud welding processes are best suited for aluminum?
In the thin sheet range (0.5–3 mm), the tip ignition process is used because the heat input is very low (approx. 2 ms process time) and the fusion zone is no more than 0.5 mm deep. For the gap process, stud diameters from M3 to M6 are suitable. In drawn arc stud welding, the short-cycle process is recommended, which must be performed with sufficient shielding gas (argon, helium). Polarity plays an important role: for sheet thicknesses up to 2 mm, negatively poled studs are advantageous; for greater thicknesses, positively poled studs are preferable.
Can you weld on hot-dip galvanized components?
Welding on hot-dip galvanized base materials should generally be avoided! If it is absolutely necessary, the zinc layer at the welding spot must be completely removed. Simply “rubbing” the zinc layer briefly with a flap disc is not enough – the material must be ground completely clean to bare metal.
On the first attempt, the zinc coating was only roughly removed with a flap disc. The welding result is not acceptable.
Inside the ceramic ring, the evaporating zinc created such enormous pressure that the ring exploded.
Only after the zinc coating was completely removed and the material was ground perfectly clean was welding possible without any issues.
What problems occur when welding unalloyed to alloyed steels?
Welds between ferritic and austenitic materials (black-and-white joints) lead to a brittle martensitic structure in the weld metal. In drawn arc stud welding with a ceramic ferrule and welding times over 100 ms, it is generally not possible to achieve sufficient strength for stud diameters greater than 12 mm. This is stated in the General Construction Approval/General Type Approval Z-30.3-6 issued by the DIBt.
How can problems with black-and-white joints be solved?
In such cases, so-called duo studs can be used. Duo studs are composite studs in which an alloyed and an unalloyed material are joined by friction welding. The tip is made of a material matching the base metal, suitable for welding in grade 4.8, while the threaded section is made of 1.4301 or 1.4571 stainless steel. This design prevents problematic martensite formation during the welding process.
Glossary
Here you’ll find all the key terms related to welding problems and their solutions. Each term is clearly explained, showing you how to successfully overcome common challenges in stud welding.
Arc blow
Direct current is usually used for drawn arc stud welding. This supports the establishment of an even arc and usually leads to the desired result. However, direct current welding can have an unpleasant side effect:
the electromagnetic fields and their interaction at the tip of the electrode can cause turbulence that leads to air and welding gas entering the weld pool. The consequences can include oxidations, penetrations or pores that reduce the quality of the weld as well as joins with a stronger weld on one side. This phenomenon is referred to as “arc blow”, which only occurs when welding with arcs and presents a particular challenge for stud welds from a diameter of around 14 mm. This is because studs with larger diameters require longer welding times, which also makes arc blow more likely. A high level of expertise is necessary to prevent this phenomenon during arc welding. This fault has many causes. As a result, the measure to be taken to prevent arc blow needs to be decided on site.
Typical countermeasures are:
- Move the connecting terminal on the workpiece
- Create weld templates made of NF materials
- Lift the welding cable
- Implement compensating measures in edge welds
Hardness test
The hardness test is used to check the resistance of a stud weld in terms of strength and toughness, and assesses the hardness profile of the weld zones. The calculation of characteristic values (hardness values) enables the assessment of a stud weld for a technically relevant component, which requires official acceptance as part of general quality assurance. During the hardness test, an indenter with a defined dimension and defined load is pushed into the weld zone to be tested. The hardness is determined by measuring the size of the imprint left by the indenter and the associated test force.
Visual inspection
The quality of a stud weld connection can be negatively affected by external influences. An unnoticed draft, moisture, and impurities at the weld point as well as an insufficient power supply all impact the welding process. In addition, careless calibration or parameter configuration errors can have a significant adverse impact on the quality of the stud weld A trained eye and, where necessary, a magnifying glass are all that are needed to detect external defects.
Typical error patterns in stud welds are:
- slanted studs
- blowholes
- penetrations
- pores
Tensile test
The tensile test in line with DIN EN ISO 6892-1 determines the tensile strength and yield strength of a component. Two key pieces of information for assessing quality. The specimen is stressed such that it initially buckles and then breaks. While the result of a tensile test merely provides an indication of the quality of the specimen, it allows indirect conclusions to be drawn as to the behavior of the finished component in its installed state. Consistent sampling allows potential deviations from the defined tolerances to be identified early on.
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