By the end of this chapter, you will be able to:
Mastering these skills ensures you work safely and effectively, producing quality work that meets professional standards in the welding trade.
Arc cutting is a fundamental skill for welding professionals in Kenya, essential for separating metal components efficiently and precisely. This process is widely employed in fabrication workshops, maintenance units, and construction sites where controlled cutting of metal plates is required. Mastery of arc cutting enables welders to prepare materials accurately for subsequent joining or repair, thereby enhancing quality and productivity in sectors such as manufacturing, automotive repair, and infrastructure development.
Arc cutting parameters determine the quality, efficiency, and safety of the cutting operation. In Kenya’s metal fabrication workshops and repair garages, understanding and correctly setting these parameters is critical to achieving clean cuts with minimal waste and reduced rework. The parameters influence factors such as cut speed, edge quality, and electrode consumption.
Proper setting of arc cutting parameters involves adjusting equipment and operational variables to suit the metal type, thickness, and desired cut quality. Welders at SACCO workshops or county maintenance yards must tailor these settings precisely to avoid defects such as excessive dross or uneven kerfs.
The current setting must correspond to the electrode size and metal thickness. Higher currents increase cut speed but may cause excessive melting and edge roughness. In Nairobi’s hotel maintenance workshops, setting the current too low results in incomplete cuts, while excessively high currents waste consumables and damage the base metal.
Selecting the correct electrode type and diameter is essential for effective arc cutting. Electrodes with higher current ratings and appropriate coatings improve arc stability and cut quality. For example, a 3.2 mm electrode is commonly used for cutting mild steel up to 6 mm thick in automotive body repairs.
Maintaining an optimal arc length ensures stable melting and clean cutting. A too-long arc causes spatter and poor edge quality, while a too-short arc risks electrode sticking. Voltage should be set to balance arc stability and cutting speed, as practiced in metal workshops servicing county government equipment.
Voltage is a crucial parameter in arc cutting, as it determines the energy available to sustain the arc and influences the stability of the cutting process. In Kenyan technical workshops, such as those at Kenya Railways Corporation, voltage is typically set according to the manufacturer's recommendations for the electrode and material thickness. Too high a voltage can cause the arc to become unstable, resulting in a wider kerf and increased spatter, while too low a voltage may lead to arc outages and poor cut quality. Proper voltage adjustment ensures efficient energy transfer, stable arc operation, and consistent cutting results, which is essential for productivity and safety in busy industrial settings.
Cutting speed controls the heat input and quality of the cut edge. Moving too fast results in incomplete penetration, whereas moving too slowly causes excessive dross and warping. For example, in metal fabrication at a Nairobi-based cooperative, operators adjust speed according to plate thickness and electrode type for consistent results.
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Create a free accountThis chapter covered the essential parameters involved in arc cutting, with particular focus on the correct setting of current to ensure effective cutting. The arc cutting process for materials up to 6 mm thickness was detailed, including a step-by-step procedure to achieve precise and clean cuts. The practical applications of arc cutting in various fabrication and repair tasks were also discussed, highlighting its versatility. Following the cutting process, the chapter explored the types of edge finishing suitable for thin materials, emphasizing the importance of proper finishing to prepare the workpiece for subsequent operations. The finishing procedure was explained to ensure smooth and safe edges, preventing defects and enhancing the quality of the final product. The chapter concluded by outlining the applications of edge finishing in maintaining structural integrity and aesthetic standards in metalwork.
Type: Individual
| Tools & Equipment | Materials |
|---|---|
| Manual Metal Arc cutting equipment and accessories | Mild Steel plates 150 × 100 × 6 mm |
| Angle grinder | E6010 Ø3.2 mm cutting electrodes |
| Steel rule | |
| Scriber | |
| Welding helmet | |
| Leather gloves | |
| Safety boots | |
| Overall (welding coat) |
| S/N | Item | Quantity |
|---|---|---|
| 1 | Mild Steel plates 150 × 100 × 6 mm | 3 Pcs per Candidate |
| 2 | Manual Metal Arc cutting equipment and accessories | 1 set per 3 Candidates |
| 3 | E6010 Ø3.2 mm cutting electrodes | 10 Pcs per Candidate |
| 4 | Angle grinder | 1 per 3 Candidates |
| 5 | Steel rule | 1 per Candidate |
| 6 | Scriber | 1 per Candidate |
| 7 | Welding helmet | 1 per Candidate |
| 8 | Leather gloves | 1 pair per Candidate |
| 9 | Safety boots | 1 pair per Candidate |
| 10 | Overall (welding coat) | 1 per Candidate |
| Items to be Evaluated | Marks Available | Marks Obtained | Comments |
|---|---|---|---|
| TASK 1: Safety and PPE Compliance | |||
| Wore overall welding coat (Award 1 mark if worn correctly, else 0) | 1 | ||
| Wore welding helmet correctly (Award 1 mark if worn correctly, else 0) | 1 | ||
| Wore safety boots (Award 1 mark if worn correctly, else 0) | 1 | ||
| Wore leather gloves (Award 1 mark if worn correctly, else 0) | 1 | ||
| Sub-Total | 4 | ||
| TASK 2: Preparation and Setting of Arc Cutting Parameters | |||
| Inspected and prepared mild steel plate for cutting (Award 1 mark for proper cleaning and marking) | 1 | ||
| Connected arc cutting machine to power source properly (Award 1 mark if connected correctly) | 1 | ||
| Set polarity suitable for arc cutting with E6010 electrode (Award 1 mark if polarity is correct) | 1 | ||
| Adjusted current setting to recommended value for 6 mm thickness (approximately 90-110 A) (Award 2 marks if current is within recommended range and adjusted properly) | 2 | ||
| Tested arc striking and stable arc maintenance (Award 1 mark for successful arc strike and stable arc) | 1 | ||
| Turned off and shut down the machine safely after setting (Award 1 mark for proper shutdown) | 1 | ||
| Sub-Total | 7 | ||
| TASK 3: Use of Tools and Equipment | |||
| Used angle grinder safely for cleaning cut edge (Award 1 mark if used safely and correctly) | 1 | ||
| Used steel rule and scriber correctly to mark the plate (Award 1 mark if marking is accurate and tools used correctly) | 1 | ||
| Sub-Total | 2 | ||
| TASK 4: Housekeeping | |||
| Cleaned working area after setting parameters (Award 1 mark if area is clean and tidy) | 1 | ||
| Properly stored tools and unused materials (Award 1 mark if tools and materials returned correctly) | 1 | ||
| Disposed of waste safely as per workplace procedures (Award 1 mark if waste disposed properly) | 1 | ||
| Sub-Total | 3 | ||
| PRODUCT CHECKLIST | |||
| Arc cutting parameters set correctly for 6 mm mild steel plate including current setting (Award 5 marks if parameters match recommended values and are properly adjusted) | 5 | ||
| Marked dimensions on plate conform to 150 mm by 100 mm with tolerance ±1 mm (Award 3 marks if dimensions within tolerance) | 3 | ||
| Cut edge preparation ready for cutting (clean, correctly marked) (Award 2 marks if plate is clean and correctly marked) | 2 | ||
| Sub-Total | 10 | ||
| GRAND TOTAL | 26 | ||
Type: Individual
| Tools & Equipment | Materials |
|---|---|
| Manual Metal Arc Welding Machine with Arc Cutting Attachment | Mild Steel Plate 150 mm x 100 mm x 6 mm |
| Angle Grinder | E6013 Electrodes Ø3.2 mm |
| Scriber | |
| Steel Rule | |
| Engineer’s Square | |
| Chipping Hammer | |
| Metal Wire Brush | |
| Bench and Vice | |
| Leather Gloves | |
| Welding Helmet | |
| Safety Boots |
| S/N | Item | Quantity |
|---|---|---|
| 1 | Mild Steel Plate 150 mm x 100 mm x 6 mm | 1 Pc per Candidate |
| 2 | Manual Metal Arc Welding Machine with Arc Cutting Attachment | 1 Pc per 3 Candidates |
| 3 | E6013 Electrodes Ø3.2 mm | 10 Pcs per Candidate |
| 4 | Angle Grinder | 1 Pc per 3 Candidates |
| 5 | Grinding Disc for Angle Grinder | 1 Pc per 3 Candidates |
| 6 | Scriber | 1 Pc per Candidate |
| 7 | Steel Rule | 1 Pc per Candidate |
| 8 | Engineer’s Square | 1 Pc per Candidate |
| 9 | Leather Gloves | 1 Pair per Candidate |
| 10 | Welding Helmet | 1 Pc per Candidate |
| 11 | Safety Boots | 1 Pair per Candidate |
| 12 | Bench and Vice | 1 Pc per Candidate |
| 13 | Chipping Hammer | 1 Pc per Candidate |
| 14 | Metal Wire Brush | 1 Pc per Candidate |
| Items to be Evaluated | Marks Available | Marks Obtained | Comments |
|---|---|---|---|
| TASK 1: Safety and Equipment Setup | |||
| Wore and used PPE correctly: welding helmet, leather gloves, safety boots (Award 1 mark for each PPE item worn and used correctly) | 3 | ||
| Demonstrated correct and safe use of angle grinder (Award 1 mark for safe and proper angle grinder use) | 1 | ||
| Set up MMA welding machine for arc cutting on 6 mm plate: connected power, set correct polarity and current (Award 1 mark each for power connection, polarity setting, current setting) | 3 | ||
| Machine shut down correctly after use (Award 1 mark for proper machine shutdown) | 1 | ||
| Sub-Total | 8 | ||
| TASK 2: Arc Cutting Operation | |||
| Marked out cutting line accurately using scriber, steel rule and engineer’s square (Award 2 marks for accurate and clear marking within ±1 mm tolerance) | 2 | ||
| Clamped workpiece securely in vice (Award 1 mark for secure and stable clamping) | 1 | ||
| Performed arc cutting along marked line maintaining correct arc length and speed (Award 1 mark each for correct arc striking, steady movement, correct arc length, and complete cut) | 4 | ||
| Cleaned cut edge with chipping hammer and wire brush removing slag (Award 2 marks for thorough cleaning of cut edge) | 2 | ||
| Sub-Total | 9 | ||
| TASK 3: Housekeeping | |||
| Cleaned working area after arc cutting (Award 1 mark for clean and tidy working area) | 1 | ||
| Disposed of waste materials properly (Award 1 mark for correct segregation and disposal) | 1 | ||
| Returned tools and unused materials to store (Award 1 mark for returning tools and materials) | 1 | ||
| Sub-Total | 3 | ||
| PRODUCT CHECKLIST | |||
| Cut piece dimensions within ±1 mm tolerance: length 150 mm, width 100 mm (Award 2 marks each for length and width within tolerance) | 4 | ||
| Cut edge is straight and smooth with no excessive slag or undercut (Award 3 marks for clean, straight cut edge free of defects) | 3 | ||
| Workpiece is square with 90° ± 1° at cut corners (Award 3 marks for squareness within tolerance) | 3 | ||
| Sub-Total | 10 | ||
| GRAND TOTAL | 30 | ||
At the start of this chapter we promised you would be able to:
Tick each one you can genuinely do.
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