Stud welding requires using a special tool, metal fasteners and, sometimes ferrules. When performed properly, welds produced are both strong in tensile testing as well as providing desirable appearance and expulsion properties.
As soon as a calculated weld time is reached, the stud weld tool lifts the fastener to an exact height, creating an arc between it and plate material which melts both parent metals – including both fasteners.
Welding Parameters
Maintaining accurate control over stud welding parameters is the cornerstone of producing consistent and high-quality welds. Two of the most critical settings are lift height and plunge depth – these must both be tailored specifically for an application; any incorrect adjustments could lead to welds that either fail to fuse together completely or produce incomplete fillets; performing daily verification can detect even small misadjustments before they have an adverse impact on production welds.
Drawn arc welding may take more time and patience than traditional arc welding processes, but its welds are extremely strong and provide leak-proof fastening in many applications. Furthermore, drawn arc welding can often be used for welding thicker or heavier materials like steel that cannot be done using short cycle arc welding technology.
Stud welding requires a specialized power source with few mechanical parts, so its maintenance requirements are lower than conventional arc welding equipment. Still, to prevent dust and dirt accumulation in its components that could ultimately cause them to fail prematurely, its power source should be cleaned regularly, with dust blowout sessions conducted annually in order to remove heat build-up inside its components as well as collect heat that builds up in its internal components that could cause premature failures of its components. Furthermore, insulation must be ensured against electric shock in wet or damp locations.
Welding Equipment
Stud welding requires pressing a fastener (known as a “stud”) against a base material before drawing an electric arc across them to melt both ends of the weld stud and small areas of base metal, creating an effective full-fusion weld in milliseconds. A spring held inside the gun then pushes down on it until its contents resolidify, creating the weld bond.
There are two primary types of stud welding equipment: capacitor discharge and resistance arc welders. Capacitor discharge welders tend to be best used with thinner metal studs as their process is much simpler – using a capacitor charged up with voltage, discharged immediately through the stud without needing skilled operators, or automated by robot.
Resistance arc welders provide another form of stud welding, employing electrodes continuously fed from a wire feeder. It is the most widely-used form of this form of welding; suitable for thick materials (whether ferrous or non-ferrous), producing high quality welds with minimal spatter or distortion and joining dissimilar metals together seamlessly.
Welding Process
Stud welding is an efficient and straightforward process. A capacitor with pre-set voltage releases its stored energy as an arc between a stud pip and the base material, melting both locally before fusing them together permanently. After remaining in a molten pool for a predetermined period, the weld is then pushed together with force from either side to form one strong weld; similar in strength to manual spot welding but with greater flexibility to work with dissimilar metals.
The drawn arc stud welding process produces strong, penetrative welds that penetrate uneven or dirty surfaces. This automated technique works best on hot rolled/coated materials with CD studs at lower costs than ever. Ceramic ferrules must be used to shape and contain the molten metal while supporting parent material thicknesses up to one third of stud diameter.
Short cycle stud welding is an easy and efficient way to automate welding on many materials, with the exception of pure aluminium. No ferrules are necessary; rather it relies on inert shielding gas as protection. Although its penetration levels may be lower than Drawn Arc welding methods, short cycle welding offers fast welding times ideal for high volume applications requiring speed. When considering this option it should only be utilized where speed and simplicity of operation is more important.
Welding Applications
Many welding applications utilizing stud welding require the use of studs to join components together quickly and effortlessly. As opposed to manual riveting applications, which take more time and effort than stud welding allows operators to easily join components quickly.
Automotive production requires numerous automated stud welding operations to affix various components to the car body, while auto body shops often employ this method for minor dent repairs as it avoids more invasive procedures.
Insulating furnaces or power plants is another popular application. Technicians apply insulation with thermal sealant caps on pins that then fuse together, creating an airtight seal against any leakage of heat through insulation. Sometimes the pins are turned into anchors to secure insulation into place.
Capacitor Discharge (CD) Stud Welding is ideal for smaller-diameter studs and thinner base materials, and more forgiving of uneven and dirty surfaces than drawn arc and short cycle welding processes. When operating under optimal parameters, CD stud welding provides high tensile strength welds stronger than the stud shank with minimal expulsion or undercut issues; when shielding gas is tri-mix or argon + carbon dioxide tri-mix shielding gas current + shorter arc time reduce undercut and expulsion while greater arc polarity + less lift provide uniform flash rings and reliable process signals.