Final answer:
In arc welding, moving the electrode too fast leads to inadequate metal deposition, resulting in a weaker joint with poor penetration.
Step-by-step explanation:
When arc welding, if the electrode is moved too fast, the issue that occurs is not enough metal will be deposited. This results in what is known as a 'cold' weld, where the weld bead does not have sufficient metal to create a strong, durable joint. Moving too quickly can also result in poor penetration because the heat input is insufficient to properly melt the base material. Optimal welding speed is crucial for ensuring a weld bead with the right characteristics in terms of width, height, and penetration.