Tungsten - Arc Gas Shielded Welding - Overhead — Skills and Education Group Awards Vocationally-Related Qualification Manufacturing & Engineering Revision
This element focuses on the advanced Tungsten-Arc Gas Shielded (TAGS) welding process executed in the overhead position on low carbon steel up to 3mm thick
Topic Synopsis
This element focuses on the advanced Tungsten-Arc Gas Shielded (TAGS) welding process executed in the overhead position on low carbon steel up to 3mm thick. Learners develop the manual dexterity and procedural knowledge to produce code-quality welds while managing the increased difficulty of overhead welding, including gravity effects on the weld pool. Mastery involves not only safe practice and consumable selection but also precise control of parameters and techniques to minimise defects and distortion in components typically used in aerospace, pipework, and structural fabrication.
Key Concepts & Core Principles
- Welding Processes: Understanding the principles and applications of MIG (Metal Inert Gas), TIG (Tungsten Inert Gas), and MMA (Manual Metal Arc) welding, including parameter selection and defect prevention.
- Material Properties: Knowledge of ferrous and non-ferrous metals, their mechanical properties, and how heat treatment affects weldability and strength.
- Weld Defects and Inspection: Identifying common defects such as porosity, cracking, and lack of fusion, and using visual inspection and NDT methods to ensure quality.
- Health and Safety: Compliance with COSHH regulations, use of PPE, safe handling of gases and electrical equipment, and risk assessment procedures.
- Engineering Drawings: Interpreting symbols, dimensions, and welding symbols (BS EN ISO standards) to fabricate components accurately.
Exam Tips & Revision Strategies
- During practical assessments, maintain a torch angle of 70-80 degrees to the workpiece and push the pool slightly ahead to prevent the molten metal from sagging – examiners look for precise torch manipulation.
- For written tasks on distortion control, always reference specific methods (back-step sequencing, offset clamping, patterned tack welding) and relate them to the stresses induced by overhead TAGS welding heat input.
- When explaining consumable selection, emphasise the matching of filler metal specification (e.g., ER70S-6) to the base material and the use of 2% thoriated tungsten for DCEN to ensure stable arc initiation in overhead positions.
Common Misconceptions & Mistakes to Avoid
- Failing to shorten the tungsten extension and reduce amperage adequately for overhead welding, leading to excessive melt-through or carbide contamination.
- Neglecting to clean the base metal and filler rods of mill scale, oil, or moisture, causing hydrogen-induced porosity that is often misinterpreted as shielding gas failure.
- Assuming that the techniques for flat-position TAGS welding can be directly transferred to the overhead position without adjusting travel speed, torch angle, or filler rod manipulation.
- Overlooking the requirement to purge the back of the weld joint for corrosion-resistant applications, wrongly believing it is only necessary for thicker materials.
Examiner Marking Points
- Award credit for demonstrating consistent electrode extension of 3-6mm during overhead runs, maintaining shielding gas coverage and arc stability.
- Award credit for adjusting amperage settings within ±5 amps of the Welding Procedure Specification (WPS) and documenting the actual values used.
- Award credit for performing a root penetration test on a 3mm thick overhead T-joint, achieving full fusion with less than 1mm excess penetration.
- Award credit for correctly identifying and rectifying four common defects (porosity, lack of fusion, undercut, crater cracks) using post-weld inspection and appropriate remedial techniques.
- Award credit for preparing the workstation in compliance with risk assessments, including fume extraction gauges and correct PPE for overhead welding.