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The process of manual metal arc welding (MMA) is illustrated - Leaving Cert Engineering - Question a - 2011
Question a
The process of manual metal arc welding (MMA) is illustrated. (i) Describe the principles of operation of MMA welding. (ii) Identify the three main parts A, B and ... show full transcript
Worked Solution & Example Answer:The process of manual metal arc welding (MMA) is illustrated - Leaving Cert Engineering - Question a - 2011
Step 1
Describe the principles of operation of MMA welding.
Answer
MMA welding operates by using an electrode that generates an electric arc between itself and the workpiece. The arc melts both the electrode and the base metal, causing them to fuse together. A slag coating forms as the flux in the electrode melts, protecting the molten weld pool from atmospheric contamination. This process allows for adequate penetration into the base metal while minimizing oxidation. MMA welding can be adjusted for various thicknesses and materials by varying the welding current.
Step 2
Identify the three main parts A, B and C of the MMA welding circuit and state the function of each part.
Answer
A - Transformer: This component steps down the voltage from the power supply to a level suitable for welding, typically between 80-100V.
B - Rectifier: It converts the alternating current (AC) from the transformer into direct current (DC) for a steady arc, utilizing diodes to control the flow during each half-cycle of AC.
C - Capacitor: This part helps to smooth out the DC output, creating a more consistent power supply to maintain a stable welding arc.
Step 3
Describe three important safety features that minimise electrical hazards associated with manual metal arc welding.
Answer
- Insulation: MMA welding machines are equipped with insulated cables and holders to prevent accidental electrical shocks.
- Surge Protection: Welding stations should include circuit protection devices to safeguard against electrical surges that could cause equipment damage or user harm.
- Grounding: Proper grounding of the welding machine and the workpiece minimizes the risk of electrical shock by providing a safe path for stray currents.
Step 4
Outline three methods of preventing atmospheric contamination of the weld area.
Answer
- Using flux: In MMA welding, the flux coating on the electrode provides a protective barrier to shield the molten weld from the air.
- Shielding Gases: In processes like MIG or TIG welding, an inert gas, such as argon or helium, is used to shield the weld area from atmospheric gases.
- Adequate ventilation: Properly ventilating the workspace ensures that contaminants do not interfere with the quality of the weld.
Step 5
Why is tungsten inert gas welding suitable for welding aluminium?
Answer
TIG welding is ideal for aluminium because it uses an inert gas shield, typically argon, to protect the weld area from oxidation, which is critical when welding aluminium. Additionally, the process allows for precise control of heat and eliminates contamination from atmospheric elements, ensuring a clean and strong weld.
Step 6
Explain the function of dissolved acetylene in oxy-acetylene welding.
Answer
Dissolved acetylene is used in oxy-acetylene welding because it can be stored under pressure in liquid form in a cylinder. When released, it rapidly converts to gas, providing a high-temperature flame essential for melting metal. This flame can be adjusted by varying the ratio of oxygen to acetylene, allowing for different welding operations, including braze welding and cutting.
Step 7
Describe, with the aid of a suitable diagram, the main features of seam resistance welding.
Answer
Seam resistance welding uses copper alloy electrodes to apply pressure and electrical current to two overlapping metal pieces. The electrodes are activated at intervals to produce discrete spots that weld the materials together.
The key features include:
- Continuous or intermittent current supply to create welds.
- Overlapping joints to ensure a strong bond.
- An automatic mechanism to control the pressure and electric current during the process.