Characteristics and application of precision forging process for spur gears

Compared with ordinary die forgings, the shape of precision forgings is more complex, the machining allowance is less or even zero, and the dimensional accuracy is higher, that is, the dimensional error of precision forgings is only half or even less than that of ordinary forgings; Low surface roughness and good performance of formed products.

Spur gear precision forging is mainly used in two aspects: one is refined blank. Fine forging does not need rough cutting workers, but only needs finishing to get finished parts. Second, the finished products are obtained directly through precision forging, and there are few application examples. For some key parts, the parts with complex shape and difficult to be machined are precision forged, while the rest are still machined. For example, spur gear blank, blade, small and medium-sized universal joint fork and cross shaft all belong to this category. The tooth shape of spur gear is directly precision forged or only the finishing allowance is left. This method of combining precision forging and finishing is more and more widely used.

The precision forging process used in production can be divided into hot precision forging, cold precision forging and warm precision forging.

1. Hot precision forging

A process in which the forming temperature is above the recrystallization temperature. The process makes the material have low deformation resistance and good plasticity, and can process parts with complex shapes. However, due to the high forging temperature of spur gear, oxidation is easy to occur, which reduces the surface quality and dimensional accuracy of parts. At present, the effect of hot forming to prevent oxidation needs to be further studied.

2. Cold precision forging

Precision forging at room temperature. In forming, the shape and size of the workpiece are easy to control, and the strength and precision of the workpiece are high. However, the workpiece has poor plasticity, large deformation resistance and high requirements for molds and equipment. It is often used to form parts with simple shape.

3. Warm precision forging process

Precision forging at a temperature below the recrystallization temperature. Warm forging can improve the disadvantages of cold forging and hot forging, but the warm forging process of spur gear has low forging temperature and narrow temperature range, and requires special high-precision equipment, so the corresponding cost increases, which is economical only in mass production. At present, the related research of warm forging is not very mature, mainly because the die life is not high and the filling performance is not good, which still needs a lot of systematic research.

Compared with the three processing processes, cold forging has the highest precision, but it has strict requirements for forging weight and materials. Hot forging has a wide range of application conditions, but the precision is the lowest. Warm forging requires the highest economic batch and die life, and the rest is between the two.

4. Compound precision forging process

Combining a variety of precision forming processes or multi-step forming processes is called compound forming. This process integrates the advantages of different processes [9] and solves various problems in the forming process. For example, the forming effect is poor by using a single closed die forging. If the floating die or split process is superimposed and combined, the forming effect can be improved and the forming load can be reduced.

At present, warm and cold composite forming process is an ideal plastic forming process with wide development prospects. At present, it has attracted the attention of all countries in the world. For high strength steel, ultra-high strength steel parts and large parts with complex shape and high precision requirements, the compound forming process of warm forging and cold forging is more appropriate, which can improve the mechanical properties, dimensional accuracy and surface roughness of the parts compared with the single process.

Scroll to Top