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What should I check, and in what order, if the weld isn’t holding?
Always start with the basics that can be checked quickly: (1) Gun held vertically + applied pressure, (2) Surface clean/dry, (3) Stroke height (the most common cause of cold welding). Only then should you adjust the current and welding time based on the recommended values. This prevents you from ‘going round in circles’ with the settings, even though the cause is mechanical or due to contamination.
How can I reliably identify a cold weld?
Visually, a cold weld is often not clearly identifiable. It can be reliably identified using the bending test in accordance with DIN EN ISO 14555: the stud is bent to 60°. If the joint breaks in the weld zone (smooth, metallic-looking fracture surface), a cold weld is present. Most common cause: insufficient stroke height.
Why does the stud break during the bending test – and what does the fracture point tell me?
A stud break can have two typical causes: (1) Fracture in the weld zone → indication of cold welding (often stroke height too low or time too short). (2) Fracture in the bolt shank → frequently a material/combination issue (e.g. black-white joints due to martensite formation). Action: In the first case, check stroke height/process time; in the second case, check Duo bolts or material combination.
Physical Phenomena
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.
Materials & Material Combinations
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.
