Welding Fabrication Manufacturers

I. Core Principles of Welding

• Fusion Welding: The base metal melts locally, and filler material can be used as needed. The weld seam is formed by the solidification of molten metal.
• Pressure Welding: Pressure is applied to ensure tight contact between the workpiece surfaces. Atomic bonding is achieved through plastic deformation, and some processes require auxiliary heating.
• Brazing: Only the brazing filler metal melts without melting the base metal. The molten filler metal wets the base metal surface and fills the gaps via capillary action to form a connection.

II. Classification and Characteristics of Common Welding Methods

1. Fusion Welding (Most Widely Used)

2. Pressure Welding

• Resistance Welding: Utilizes resistance heat generated by electric current passing through the contact surfaces of workpieces, with simultaneous pressure application to complete welding. It is divided into spot welding, seam welding and butt welding. Spot welding is widely used in automotive body welding; seam welding is applied to sealed components such as fuel tanks.
• Friction Welding: Generates heat through high-speed friction between workpieces. When the contact surfaces reach a plastic state, pressure is applied for welding. It features stable joint quality and is suitable for welding dissimilar metals, e.g., butt welding of shaft parts.

3. Brazing

• Torch Brazing: Uses oxyacetylene flame for heating, featuring simple operation; Vacuum Brazing: Performed in a vacuum environment to avoid oxidation, suitable for precision and complex components such as aero-engine blades.
• The advantage of brazing is minimal welding deformation, while the disadvantage is that the joint strength is generally lower than that of the base metal.

III. Welding Materials

1. Welding Electrodes: Exclusive for SMAW, consisting of a core wire (filler metal) and a coating. The coating functions to stabilize the arc, form slag, deoxidize and alloy the weld metal.
2. Welding Wires: Used in gas-shielded welding and submerged arc welding, divided into solid wires and flux-cored wires. Flux-cored wires have built-in protective components and offer stronger adaptability.
3. Welding Flux: Applied in submerged arc welding, categorized into fused flux and non-fused flux. It plays roles in protecting the weld pool, deoxidizing and improving weld formation.
4. Brazing Filler Metals: Specialized for brazing, with a melting point lower than that of the base metal. Common types include copper-based and silver-based brazing filler metals.

IV. Key Elements of Welding Technology

1. Welding Parameters: Including welding current, voltage, welding speed, shielding gas flow rate, etc. Parameters directly affect the weld penetration, formation and quality. For example, excessive current may cause burn-through, while insufficient current leads to insufficient penetration.
2. Groove Design: For welding thick plates, grooves (such as V-groove, X-groove) need to be pre-processed to ensure full weld penetration and reduce incomplete penetration defects.
3. Preheating and Post-heating: For crack-sensitive materials such as high-strength steel and cast iron, preheating before welding can reduce the cooling rate and avoid cold cracking; post-heating after welding can eliminate residual stress and improve microstructure and properties.

V. Welding Quality Inspection

Visual Inspection: Checks weld formation, dimensions and surface defects (e.g., porosity, cracks, undercut) with the naked eye or with the help of a magnifying glass.

1. Non-Destructive Testing (NDT): Does not damage the workpiece, including Ultrasonic Testing (UT, for detecting internal defects), Radiographic Testing (RT, for detecting internal porosity and slag inclusion), Magnetic Particle Testing (MT, for detecting surface defects of ferromagnetic materials).
2. Destructive Testing: Takes weld samples for tensile, bending and impact tests to evaluate the mechanical properties of the welded joint.

VI. Welding Safety and Protection

• Arc Light Radiation Protection: Ultraviolet and infrared rays in welding arc light can burn the skin and eyes, requiring the use of welding helmets and protective clothing.
• Harmful Gas Protection: Ozone, nitrogen oxides and other harmful gases are generated during welding, so good ventilation in the working environment must be ensured.

Electric Shock Protection: Welding equipment must be grounded, and operators need to wear insulating gloves and shoes.

VII. Frequently Asked Questions 

Q1: Why are some metals (e.g., Aluminum) harder to weld than steel?

• A: Aluminum has high thermal conductivity and rapid oxidation. It dissipates heat so quickly that forming a stable molten pool is difficult. Additionally, the aluminum oxide layer ($Al_2O_3$) has a melting point of over 2050°C, much higher than the metal itself (660°C). This usually requires AC TIG or specialized pulse MIG welding.

Q2: What is the Heat Affected Zone (HAZ) and why is it critical?

• A: The HAZ is the area of base metal not melted, but whose microstructure has been altered by heat. This area can become brittle or lose strength due to the thermal cycle. Most structural failures, such as cracks, occur within the HAZ.

Q3: How is welding distortion caused and how can it be prevented?

• A: Distortion is caused by uneven thermal expansion and contraction. Prevention methods include:

  • Pre-setting: Angling the parts in the opposite direction before welding.

  • Symmetric Welding: Welding from the center outward or in a balanced sequence.

  • Reducing Heat Input: Using high-energy-density processes like Laser welding.

Q4: Why is post-heating or "Hydrogen Release" necessary?

• A: Hydrogen atoms can cause delayed cracking in the weld. Post-heating allows hydrogen to diffuse out of the metal, which is crucial for high-strength steels and thick plates.

Q5: Can robotic welding fully replace manual welding?

• • A: While robots excel in high-volume, standardized production (e.g., automotive), human welders remain irreplaceable for fieldwork, complex spatial joints, one-off custom jobs, and tasks requiring real-time sensory adjustment.