Refrigerators, stoves and air conditioners, in particular, are excellent sources of copper because they require a larger power supply and therefore tend to contain thick, insulated copper wire. Copper is one of the three most consumed metals on the planet, second only to iron and aluminum. It's everywhere, naturally in the Earth's crust. Copper is also one of the first metals used by humans.
At present, the underground extraction depth of copper mines is generally 300 to 800 m, and individual mines reach more than 1000 m. This requires relatively high safety requirements for copper mining equipment. CNC milling is more common in copper alloys because they have better machinability and produce precise and intricate parts.