In addition to large and medium-sized free forgings that use steel ingots as blanks, general forgings use various metal bars as blanks. Before the metal forging process, generally, the bars are cut into sections according to the required size on a special blanking equipment. The commonly used blanking methods are as follows.
Saw cutting are often carried out on circular saws, bow saws and high-speed band saws.
The circular saw is driven by the motor-driven toothed saw disc to rotate and move to cut the bar. The maximum diameter of the saw disc can reach 2m, and the diameter of the sawing bar is less than 750mm.
The bow saw is driven by the motor-driven toothed saw blade to move back and forth to cut the bar. The diameter of the sawing bar is below 100mm. Bars of extremely small diameters can also be sawed in bundles.
The characteristics of sawing are that the cut section is flat and the size is accurate; but at the same time the productivity is low, and there is saw cutting loss, and the loss of saw blade and saw disk is also relatively large. However, the high-speed band saw is a kind of relatively advanced cutting equipment with high production efficiency and regular blank shapes.
Shearing is generally carried out on a shearing machine, which can cut off billets with a diameter of less than 200mm. When the billet is in cold shearing, a large stress will be generated at the sheared part and so cracks will appear. Therefore, high-carbon steel, alloy steel and billets with larger cross-sectional dimensions need to be preheated to 350~700℃ before shearing; Steel billets with smaller cross-sectional dimensions such as low carbon steel and medium carbon steel can be cold sheared.
The feature of the shearing machine is that it can be equipped with an automatic feeding and discharging mechanism, because the working conditions of the workers are better, the production efficiency is high, the metal is saved, and the utilization rate of the material is improved. However, the shearing end face is uneven and slightly skewed, especially when shearing billets with large diameters under hot conditions. Shearing machines are commonly used in mass production die forging workshops.
Shear blanking can also be carried out on edge-trimming punches, friction presses and other equipment.
3. Broken blanking
The breaking and blanking are carried out on a hydraulic press or a crank press. The pressure is transmitted to the material through the punch, so that the material is broken along the pre-cut. Before breaking, the pre-cut is usually made by sawing or gas cutting of which purpose is to cause a large stress concentration at the cut, so as to ensure that when the material in metal forge is broken at a certain position, it does not produce large plastic deformation and thus will not affect the quality of the section.
Fracture is suitable for high-carbon steel and high alloy steel with higher hardness.
4. Grinding wheel cutting
The grinding wheel cutting is carried out on the grinding wheel cutting machine. The grinding wheel cutting machine is driven by the motor-driven thin sheet grinding wheel (generally less than 3mm in thickness)to rotate at high speed, and manually or motorized to make it move up and down to cut the billet. The grinding wheel cutting machine can cut metal blanks with any hardness with diameters below 40mm.
The characteristics of grinding wheel cutting are high productivity and smooth cutting section; however, the loss of thin grinding wheels is large, the working conditions of workers are poor, and good ventilation facilities is required.
5. Flame cutting
Flame cutting is also called gas cutting. The principle is to use a gas cutter or an ordinary welding torch to locally heat the steel to the melting temperature with an oxygen gas flow to fuse it gradually. It is mainly used for large section cutting of large billets and forgings (the thickness of the cutting section can reach more than 1500mm), and it can also be used for trimming of large die forgings produced in small batches.
6. Anode cutting
The principle is to use electric corrosion and electrochemical corrosion to cut metal forging material.
The size of the material to be cut is 30-300mm. Anode cutting is characterized by high productivity, less waste, can cut any hardness of metal materials, and has a smooth section.