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When nuts and screws on galvanized sheets are spot‑welded by medium‑frequency spot welders, applying the same set of welding parameters to both workpieces easily causes defects such as zinc‑splashing, cold‑joint detachment, burnt threads, sheet piercing, and blackened weld spots.

The zinc layer of galvanized sheets vaporizes easily under high temperature and brings unstable resistance, leading to high welding difficulty. Nuts and screws differ in structure, contact surface and heat‑conduction mode.

I General Welding Difficulties for Galvanized Sheets

Both nut‑to‑galvanized‑sheet and screw‑to‑galvanized‑sheet welding share common process challenges. The melting point of zinc layer is far lower than that of steel. Zinc vaporizes rapidly in welding instant, generating spatter, pores and zinc‑slag splashes. Uneven zinc‑layer thickness over sheet surfaces results in unstable welding resistance and fluctuating weld‑spot heat. Excessive heat input burns large‑area zinc layers and causes later‑stage rusting and corrosion of workpieces.

II Essential Structural Differences between Nut Welding and Screw Welding

1.Welding nuts on galvanized sheets

During welding, current and heat concentrate on projection points. Projection points melt and collapse under heat to form full and regular nuggets. Overall heat concentration and stable forming suit assembly conditions requiring high strength and high torque resistance.

2.Welding screws on galvanized sheets

The bottom of welding screws is flat without concentrated projections, belonging to full‑surface contact welding. Large contact area disperses heat without focused local heat accumulation; fusion is realized mainly by resistance heating over the whole contact interface.

III Core Differences in Welding Processes

1.Difference in welding pressure

Nut welding fits medium‑pressure stabilizing operation. Moderate pressure compresses projections, squeezes out zinc vapor and interface gaps to avoid zinc‑splashing and cold joints. Insufficient pressure brings severe spatter and weak welding; excessive pressure flattens projections directly and causes pseudo‑welds and insufficient torque.

Screw welding suits medium‑high‑pressure uniform stabilizing. Flat contact generates numerous gaps; sufficient pressure is required to expel gaps and zinc slag. Insufficient pressure easily produces inclusion‑induced cold joints; uniform pressure guarantees full and dense overall fusion.

2.Difference in current and welding duration

Nut projections feature strong heat‑gathering capacity, fit high‑current short‑time fast nugget formation. Overlong heating causes over‑melted projections, slag‑clogged threads, sheet indentation and large‑area zinc loss and blackening.

Screw flat surfaces disperse heat, fit moderate current with properly extended welding duration. Slow and stable heat ensures full interface‑layer fusion, avoiding sound surface welds with inner cold joints, meanwhile preventing instant high‑temperature sheet piercing and thread burning.

3.Difference in welding sequence

Nut welding adopts long pre‑pressing, fast welding and short pressure‑hold: focus on compressing projections and fast forming to avoid spatter and thread clogging.

Screw welding adopts stabilizing pre‑pressing, staged temperature rise and sufficient pressure‑hold: focus on exhausting zinc vapor, eliminating gaps and preventing porous and cracked weld spots.

IV Welding Defects and Root Causes for Two Kinds of Workpieces

1.Common defects in nut welding

Excessive welding heat and overlong time bring thread annealing‑softening, slag‑clogged threads and thread deformation. Insufficient pressure and poor fit cause zinc‑splashing, local cold joints and sub‑standard torque. Uneven electrodes and positioning offset lead to one‑side sound welding and one‑side cold joints.

2.Common defects in screw welding

Dispersed heat and insufficient heat input easily generate edge cold joints and poor bonding compactness. Excessive pressure and current may pierce or thin galvanized sheets. Overlong welding time burns large‑area surface zinc layers, resulting in blackened weld spots, sheet peeling and cracks.

When nuts and screws on galvanized sheets are spot‑welded by medium‑frequency spot welders, applying the same set of welding parameters to both workpieces easily causes defects such as zinc‑splashing, cold‑joint detachment, burnt threads, sheet piercing, and blackened weld spots.

The zinc layer of galvanized sheets vaporizes easily under high temperature and brings unstable resistance, leading to high welding difficulty. Nuts and screws differ in structure, contact surface and heat‑conduction mode.

I General Welding Difficulties for Galvanized Sheets

Both nut‑to‑galvanized‑sheet and screw‑to‑galvanized‑sheet welding share common process challenges. The melting point of zinc layer is far lower than that of steel. Zinc vaporizes rapidly in welding instant, generating spatter, pores and zinc‑slag splashes. Uneven zinc‑layer thickness over sheet surfaces results in unstable welding resistance and fluctuating weld‑spot heat. Excessive heat input burns large‑area zinc layers and causes later‑stage rusting and corrosion of workpieces.

II Essential Structural Differences between Nut Welding and Screw Welding

1.Welding nuts on galvanized sheets

During welding, current and heat concentrate on projection points. Projection points melt and collapse under heat to form full and regular nuggets. Overall heat concentration and stable forming suit assembly conditions requiring high strength and high torque resistance.

2.Welding screws on galvanized sheets

The bottom of welding screws is flat without concentrated projections, belonging to full‑surface contact welding. Large contact area disperses heat without focused local heat accumulation; fusion is realized mainly by resistance heating over the whole contact interface.

III Core Differences in Welding Processes

1.Difference in welding pressure

Nut welding fits medium‑pressure stabilizing operation. Moderate pressure compresses projections, squeezes out zinc vapor and interface gaps to avoid zinc‑splashing and cold joints. Insufficient pressure brings severe spatter and weak welding; excessive pressure flattens projections directly and causes pseudo‑welds and insufficient torque.

Screw welding suits medium‑high‑pressure uniform stabilizing. Flat contact generates numerous gaps; sufficient pressure is required to expel gaps and zinc slag. Insufficient pressure easily produces inclusion‑induced cold joints; uniform pressure guarantees full and dense overall fusion.

2.Difference in current and welding duration

Nut projections feature strong heat‑gathering capacity, fit high‑current short‑time fast nugget formation. Overlong heating causes over‑melted projections, slag‑clogged threads, sheet indentation and large‑area zinc loss and blackening.

Screw flat surfaces disperse heat, fit moderate current with properly extended welding duration. Slow and stable heat ensures full interface‑layer fusion, avoiding sound surface welds with inner cold joints, meanwhile preventing instant high‑temperature sheet piercing and thread burning.

3.Difference in welding sequence

Nut welding adopts long pre‑pressing, fast welding and short pressure‑hold: focus on compressing projections and fast forming to avoid spatter and thread clogging.

Screw welding adopts stabilizing pre‑pressing, staged temperature rise and sufficient pressure‑hold: focus on exhausting zinc vapor, eliminating gaps and preventing porous and cracked weld spots.

IV Welding Defects and Root Causes for Two Kinds of Workpieces

1.Common defects in nut welding

Excessive welding heat and overlong time bring thread annealing‑softening, slag‑clogged threads and thread deformation. Insufficient pressure and poor fit cause zinc‑splashing, local cold joints and sub‑standard torque. Uneven electrodes and positioning offset lead to one‑side sound welding and one‑side cold joints.

2.Common defects in screw welding

Dispersed heat and insufficient heat input easily generate edge cold joints and poor bonding compactness. Excessive pressure and current may pierce or thin galvanized sheets. Overlong welding time burns large‑area surface zinc layers, resulting in blackened weld spots, sheet peeling and cracks.