Welding Guide: How to Select Materials, Machines, Filler Metals and Welding Parameters

Welding is a precise and essential manufacturing process widely applied in structural fabrication, equipment maintenance, and industrial production. Standardized pre-weld assessment, parameter setting, operational techniques, and quality control are critical to ensuring stable welding performance, reliable joint strength, and consistent finished quality.

I. Pre‑Weld Assessment Three fundamental parameters shall be determined prior to welding:

1. Base Material

Carbon steel: good weldability, suitable for most common processes

Stainless steel: requires controlled heat input, TIG or stainless steel electrodes recommended to prevent intergranular corrosion

Aluminum and alloys: high thermal conductivity and refractory oxide film require AC TIG or dedicated aluminum wire

Cast iron: poor weldability, requires preheating (200~400°C), slow cooling, and nickel‑based electrodes

2. Material Thickness

≤1 mm: risk of burn‑through, TIG or low‑current MIG recommended

1~6 mm: SMAW or MIG both applicable

≥6 mm: preheating required, multi‑pass technique

3. Welding Position

Flat: lowest difficulty

Horizontal, vertical, overhead: increasing difficulty, current reduced by 10%~20% from flat position

II. Welding Machine Selection

Selection notes:

Inverter‑type machines are preferred over conventional transformer types for energy efficiency and portability

Rated current need not be maximized; practical operating range is typically mid‑scale

Machines with hot‑start and arc‑force functions reduce striking difficulty and electrode sticking

III. Filler Material Selection

Critical process requirements:

Electrodes must be dried before use: J422 at 150°C for 1 hour; stainless steel electrodes at 250°C for 2 hours to remove moisture and prevent hydrogen porosity

CO₂ purity for MIG shall be ≥99.5%; mixed gas (80% Ar + 20% CO₂) improves bead appearance

IV. Welding Current Reference

SMAW empirical formula:

I (A) = Electrode diameter (mm) × 30~40

Φ2.5 mm → 75~100 A

Φ3.2 mm → 96~128 A

Φ4.0 mm → 120~160 A

MIG reference values:

I (A) = Plate thickness (mm) × 30~50

1 mm → 30~50 A

3 mm → 90~150 A

6 mm → 180~300 A

Diagnostic criteria:

Excessive current: burn‑through and undercut

Insufficient current: lack of penetration, slag inclusion, electrode sticking

Test piece back‑side penetration trace and front bead profile shall be used as final adjustment reference

V. Weld Quality Standards

A qualified weld shall satisfy three basic requirements:

Sufficient penetration depth: minimum 1/3 of base material thickness in cross‑section

No porosity or slag inclusion: no honeycomb cavities or dark inclusions on surface or internally

No cracks: no longitudinal or transverse cracks upon cooling; tapping test may be used as preliminary check

VI. Operational Techniques by Process

SMAW

Striking: scratch‑start or tap‑start; avoid prolonged contact causing electrode sticking

Electrode angle: 70°~80° to workpiece surface, tilted in direction of travel

Weaving pattern: straight line for thin sheets; zigzag for medium thickness; crescent for thick plates with grooves; oscillation width ≤3× electrode diameter

Arc length: approximately equal to electrode diameter; excessive length increases spatter, insufficient length causes sticking

MIG/MAG

Stick‑out: approximately 10× wire diameter (Φ0.8 mm → 8~10 mm)

Torch angle: perpendicular or slight drag angle (5°~15°), push technique

Gas flow: 15~20 L/min; welding area shall be shielded from cross‑drafts

TIG

Tungsten electrode tip: ground to 30°~45° cone, centered on joint line

Arc length: 2~4 mm

Filler rod feeding: dip into leading edge of weld pool, avoid direct entry into arc column

Aluminum welding: AC mode required, current increased 20%~30%

VII. Safety Requirements

Welding is an open‑flame operation. The following controls shall be enforced:

Eye protection: auto‑darkening helmet with shade No. 11 minimum to prevent arc burns to cornea

Respiratory protection: stainless steel and galvanized materials produce toxic fumes; wear appropriate respirator or use fume extraction, maintain upwind position

Fire prevention: arc temperature exceeds 3000°C; combustible materials shall be cleared within 2 m radius; fire extinguisher shall be accessible

VIII. Common Welding Defects and Corrective Actions

IX. Post‑Weld Procedure

Deslagging: remove flux with chipping hammer, clean residue with wire brush

Visual inspection: verify entire bead is free of visible defects

Rust prevention: carbon steel components shall be coated with anti‑corrosion paint or oil immediately after cooling