A metal forming apparatus comprising: a smelting device, which defines a smelting chamber having a feeding port, and comprises a rotatable crucible disposed within the smelting chamber and configured to contain a raw material, and a heating unit disposed in the smelting chamber and configured to heat the raw material in the crucible to obtain a molten raw material; a molding device defining a molding chamber sealedly communicated with the smelting chamber; an injection device comprising: a charging barrel assembly, which is sealedly disposed at a joint between the molding device and the smelting device, and defines a part extended into the smelting chamber and located below the crucible to receive the molten raw material, and an injection unit, which is sealedly connected with the smelting device, and defines an end extended through the smelting chamber into the charging barrel assembly so as to inject the molten raw material in the charging barrel assembly into the molding chamber; and a vacuumizing device sealedly connected with the smelting device and the molding device respectively so as to vacuumize the smelting chamber and the molding chamber; characterized in that a rear end of the smelting chamber is open and a first flange is disposed at the rear end of the smelting chamber, an adapter flange is disposed at a part of the injection unit located externally of the smelting chamber and sealedly connected with the first flange via a vacuum seal bellow. a smelting device, which defines a smelting chamber having a feeding port, and comprises a rotatable crucible disposed within the smelting chamber and configured to contain a raw material, and a heating unit disposed in the smelting chamber and configured to heat the raw material in the crucible to obtain a molten raw material; a molding device defining a molding chamber sealedly communicated with the smelting chamber; an injection device comprising: a charging barrel assembly, which is sealedly disposed at a joint between the molding device and the smelting device, and defines a part extended into the smelting chamber and located below the crucible to receive the molten raw material, and an injection unit, which is sealedly connected with the smelting device, and defines an end extended through the smelting chamber into the charging barrel assembly so as to inject the molten raw material in the charging barrel assembly into the molding chamber; and a charging barrel assembly, which is sealedly disposed at a joint between the molding device and the smelting device, and defines a part extended into the smelting chamber and located below the crucible to receive the molten raw material, and an injection unit, which is sealedly connected with the smelting device, and defines an end extended through the smelting chamber into the charging barrel assembly so as to inject the molten raw material in the charging barrel assembly into the molding chamber; and a vacuumizing device sealedly connected with the smelting device and the molding device respectively so as to vacuumize the smelting chamber and the molding chamber; characterized in that a rear end of the smelting chamber is open and a first flange is disposed at the rear end of the smelting chamber, an adapter flange is disposed at a part of the injection unit located externally of the smelting chamber and sealedly connected with the first flange via a vacuum seal bellow.