Precision forging (net forming or near net forming) refers to the forming technology that only needs a small amount of processing to meet the design requirements after parts are forged. It is an important branch of precision forming. It is a modern manufacturing technology based on the original forging technology, which integrates materials, hydraulic pressure, automatic control, digitization, detection, surface treatment and other technologies. At present, precision forged parts products are mainly concentrated in various mechanical transmission parts, such as tractor straight bevel gear, tractor straight gear, tractor spline shaft, tractor spline sleeve, tractor joint gear, tractor universal joint, tractor cross shaft, tractor synchronizer gear ring, tractor planetary gear ring, etc.
Precision forging has the following advantages:
1) High material utilization and small machining allowance. Taking tire nut as an example, using bar cutting, the material utilization rate is only 37%; Using traditional die forging process, the utilization rate is 72%; By using cold extrusion (cold forging) process, the material utilization rate is 92%.
2) Good product performance. Because the metal fiber of precision forging is distributed along the contour of the part, continuous and dense, the product performance is greatly improved. Taking the widely used straight bevel gear of cold forging tractor as an example, compared with cutting (forging blank), the grain size is increased from Grade 7 to grade 9, the strength is increased by 25%, the fatigue life is increased by 40%, and the heat treatment deformation is reduced by 30%. If combined with the structural improvement shown in the figure, the improvement rate of various properties is higher.
3) High production efficiency. Taking the straight bevel gear for tractor as an example, the average cutting (forging blank) of the gear part is 0.7 pieces / min, while the automatic cold precision forging can achieve 15 pieces / min and the production efficiency can be increased by more than 20 times.
4) The product consistency is good, and the quality can be effectively controlled. At the same time, it can also reduce the labor intensity of workers, improve working conditions and reduce environmental pollution.
Precision forging has many advantages, but its development and application are also limited. At present, there are mainly three points as follows:
1) Equipment tonnage. Product parts are subject to the tonnage pressure of the equipment. At present, mass production can be realized for straight teeth with a diameter of about 200 mm, and the diameter of tractor bevel gear can reach 350 mm.
2) Die life. Die cost accounts for a considerable proportion in the cost of precision forging products. In addition to the impact of die material, structure and process on its cost, product batch, production beat, specific forging process and process auxiliary materials also have a considerable impact on it.
3) Part shape. Although with the progress of technology, the types of precision forgings are constantly expanding, and the original die forgings are constantly transforming to precision forgings, due to the process characteristics of material plastic forging, some parts, such as tractor spiral bevel gears and straight teeth requiring modification, are still in the laboratory stage.