Technical Knowledge Of Weld Nuts

A weld nut is a special fastener designed for welding fixation. It is manufactured from weldable and sufficiently thick steel materials, suitable for welding and fixing with plates and profiles. The welding process melts the metal joint surfaces at high temperature to fuse two separate workpieces into an integral structure. After cooling, the connection is maintained by molecular bonding force of the metal. Alloy filling is applied to optimize the weld structure, and the bonding strength after welding is generally higher than that of the base material.

Welding parameters shall be adjusted according to the weld fusion condition by tuning current, voltage, welding time and other factors to ensure full fusion and defect-free welds. Welding quality is closely related to pre-welding treatment. Dust, oxide scales, oil stains and other impurities on the welding surface must be thoroughly cleaned to avoid adverse effects on welding fusion. Welded connections are irreversible and non-detachable, and high welding temperature may easily cause workpiece deformation. Reactive metals such as aluminum and magnesium cannot be welded by conventional methods, and require shielding gas or argon arc welding, which imposes higher requirements on processing accuracy and process specifications.

1. Causes and Solutions for Weld Nut Offset and Displacement

During welding, weld nuts are prone to displacement, angular deviation and positioning errors, resulting in unqualified assembly dimensions. A dedicated positioning tool can be adopted to solve this problem: fabricate a positioning mandrel in advance, fix the mandrel on the welding plate, and sleeve the weld nut onto the mandrel during welding to limit its freedom and fundamentally avoid offset.

If custom tools cannot completely solve the displacement problem, bolts or clamps can be used to compress and fix the weld nut. Meanwhile, the workpiece to be welded shall be firmly locked to keep the relative position between the nut and the workpiece unchanged and ensure welding positioning accuracy.

2. Causes and Solutions for Weld Nut Shedding and Cold Welding

Weld shedding and cold welding are concealed welding defects that are difficult to detect through conventional visual inspection, serving as common quality hazards of weld nuts. They are mainly caused by two factors: inconsistent height of projection welding spots on nuts and fixed current and welding time settings of spot welding machines. Insufficient welding spot height leads to inadequate fusion and easily causes cold welding. In addition, unstable power grid voltage will result in fluctuating output power of spot welding machines, insufficient welding heat and unqualified fusion quality.

Solutions: Strictly control the incoming quality of weld nuts to ensure consistent height and dimension of welding spots; regularly calibrate spot welding equipment to stabilize its output power; install a voltage stabilizer at the power supply end under fluctuating working conditions to ensure stable welding current.

Projection resistance welding is the optimal process for welding nuts on stamping parts. Compared with ordinary electrode welding and CO₂ gas shielded welding, projection welding features concentrated heat, stable forming and high consistency, which effectively prevents cold welding and virtual welding. Ordinary electrode welding can be completely replaced by CO₂ gas shielded welding, which has the advantages of high efficiency, low cost, stable weld quality and low defect rate.

All welding operations shall dynamically adjust parameters based on actual weld fusion conditions to achieve sufficient fusion without pores, cold welding or weld shedding. Strict pre-welding surface cleaning to remove impurities and oil stains in the welding area is the basic prerequisite for guaranteeing welding quality.