Manual Metal Arc (MMA) welding is the most flexible and one of the most widely used arc welding processes. It involves striking an arc between a covered metal electrode and a workpiece. The heat of the arc melts the parent metal and the electrode which mix together to form, on cooling, a continuous solid mass. The central metal electrode or core wire acts as a consumable, providing the filler metal for the weld. MMA welding can be used to join most steels, stainless steels, cast irons and many non-ferrous materials. For many mild and high-strength carbon steels, it is the preferred joining method.