The image below shows a part of the MIG welding apparatus - NSC Agricultural Technology - Question 4 - 2024 - Paper 1

The MIG welding process involves the following steps:

1. Current Flow: The MIG welding machine sends a continuous feed of the positive wire to the welding area when the operator presses the trigger.
2. Short Circuit: An electric arc is created, generating a short circuit between the wire and the workpiece.
3. Heat Generation: The heat produced by the short circuit melts the filler metal, allowing it to mix with the base material.
4. Gas Protection: An inert shielding gas protects the area from contamination.
5. Cooling: Once the arc is removed, the molten metal begins to cool and solidify, forming a fused weld joint.

The typical composition of the MIG welding shielding gas includes:

1. Argon
2. Helium
3. Carbon dioxide (CO₂)

Four problems that can prevent the welding wire from feeding are:

1. Blocked or defective contact tip.
2. Loose or broken wire drive rollers.
3. Wire entangled in the delivery pipe.
4. Wrong size of wire roller or jammed spool.

The welding defect indicated by A is undercutting. Two possible causes are:

1. Speed being too fast.
2. Current set too high.

When preparing galvanised metal for welding, the following steps should be followed:

1. Remove Galvanised Coating: Clean the surface to remove any galvanised coating to ensure good weld quality.
2. Wear Protective Gear: Always wear a gas mask to protect against hazardous fumes released during the welding process.

Sketch the horizontal square butt weld with labels indicating the following:

• Work piece: The metal pieces being joined.
• Direction of Travel: Arrow indicating the direction of welding.
• Welding Electrode: Line or representation showing where the welding electrode interacts with the work piece at an angle, typically around 90 degrees.

Three common pipe welding positions include:

1. Horizontal fixed position.
2. Horizontal movable position.
3. Vertical position.

Metals that should not be cut with the oxyacetylene cutting apparatus include:

1. Aluminium: High thermal conductivity results in rapid melting and a porous cut.
2. Stainless Steel: Nickel and molybdenum content leads to complications due to the formation of an oxide layer during cutting.

When the torch is moved too quickly across a thick metal plate:

1. The molten puddle may not properly fuse and stick to one another, resulting in weak joints.
2. The flame may not penetrate the metal sufficiently, leaving uncut areas or producing slag on the surface.

The material commonly used for the plasma cutter combustion cap is porcelain.

Three properties of porcelain include:

1. Heat Resistance: It can withstand high temperatures without melting or deforming.
2. Durability: Resistant to wearing and mechanical stress.
3. Non-conductive: It does not conduct electricity, making it safe for use in welding applications.