Answer any three of the following: (i) Outline two methods used to prevent porosity occurring in welds - Leaving Cert Engineering - Question 5 - 2015

In MIG welding, the electrode is a bare wire fed from a reel through the welding gun. This consumable electrode provides filler material directly into the weld pool. In contrast, TIG welding employs a non-consumable tungsten electrode, which maintains the arc but does not melt. Instead, filler material is added separately to the weld pool in TIG welding.

The carburising flame in oxy-acetylene welding is characterized by its bright luminous inner cone and an enveloping outer flame. It has a temperature of approximately 3150°C and contains excess acetylene. This particular flame is used to weld aluminum and alloy steels, as it prevents oxidation during the welding process due to the protective atmosphere it creates.

To protect against electric shock during welding, it is essential to ensure all electrical connections are secure and insulated properly. Operators should be equipped with proper personal protective equipment and ensure that all welding equipment is periodically checked for wear and tear to prevent accidental contact with live electrical parts.

To shield others from intense light during welding, it's advisable to use a welding mask with a suitable filter lens. This helps protect the welder’s eyes and skin from harmful UV radiation generated during the welding process. Furthermore, installing barriers or using curtains around the welding area can help protect nearby workers.

To protect against harmful welding fumes, it is important to use a fume extraction system that captures fumes at the point of generation. Additionally, utilizing appropriate ventilation systems in the welding area helps reduce airborne contaminants, ensuring a safer working environment.

For joining the mild steel frame of the kart, Metal Inert Gas (MIG) welding is a suitable process. It is easy to set up and operate, making it ideal for quickly assembling the frame components.

MIG welding is a semi-automatic process where a consumable wire electrode is fed continuously into the weld pool through the welding gun. An inert gas shield, typically argon or a mixture containing argon, protects the weld area from contamination. The operator can control the arc length and thus the heat input, allowing for adjustments in the welding technique, essential for effectively joining the mild steel frame.

In resistance spot welding, the electrode is typically shaped like a rounded barrel, allowing it to make contact with the workpieces at a single point. In contrast, resistance seam welding uses disc-shaped electrodes that rotate to provide a continuous weld along the length of the workpieces being joined.

Resistance spot welding operates by pressing two workpieces between electrodes and passing a current through them, generating heat at the junction. Resistance seam welding also operates on the same principle but uses continuous wheel-like electrodes that move along the seams, providing a consistent weld without the need to separate and reposition the materials.

In resistance spot welding, the weld joint is made at specific points, creating individual nuggets that result in discrete mechanical connections. Conversely, resistance seam welding creates a continuous weld joint with overlapping nuggets that provide enhanced strength along the length of the seam.

Resistance spot welding is commonly used in the automotive industry for body panel assembly, where multiple overlapping components are joined at discrete locations. In contrast, resistance seam welding is suited for applications requiring an uninterrupted weld, such as in manufacturing fuel tanks, drums, and domestic radiators.