请将下列句子翻译成中文。 It is often necessary when referring to processes to mention the way they are used, particularly whether the operation is manual or automatic. The practical operation of welding can be divided into three main parts: (a) The control of welding conditions, particularly arc length ( 电弧长度 ) and electrode (焊条) or filler wire (填充焊丝) feed rate and time. (b) The movement and guiding of the electrode, torch (焊炬) or welding head (焊接机头) along the weld line. (c) The transfer of parts for welding.