Whether the forging can be out of the die is an important factor that must be considered in forging. The interaction between the die and the forging may occur in the process, which will reduce the accuracy of the forging or even scrap it, and the damage to the die is also fatal. Therefore, the design of the die process is particularly important to avoid excessive die force and improve the precision and die life of spiral bevel gear forgings.
Spiral bevel gear has asymmetry in shape, resulting in nonlinear contact area, contact force and material flow between die and blank during forging. These factors make it necessary to comprehensively consider all aspects of influence during forging, so the forging of spiral bevel gear has not yet realized industrialization.
Combined with the geometry of spiral bevel gear, the die drawing methods of spiral bevel gear can be divided into the following two types:
The first is direct die casting. When there is no interference between the tooth profile surface of the axial die and the spiral bevel gear forging, generally the spiral bevel gear wheel with a large number of teeth, that is, a large pitch cone angle, only needs to overcome the friction between the die and the forging when the die is pulled out. Under the action of the springback of the forging, a large interaction force is generated between the forging and the die, and the friction may be greater than the gravity of the forging itself, External force is required to separate the die from the forging. Using the ejector rod to directly eject the forging, the die process is fast, and the contact time between the workpiece and the die is very short.
The other is spiral die. There is overlap between the tooth profile surface of the axial die and the forging, that is, there is interference. Generally, it is a spiral bevel gear small wheel with small number of teeth or small surface cone angle. This forging form not only needs to overcome the friction between the die and the forging, but also has large axial force and large synthetic force. It is very difficult to consider spiral die drawing. If the small wheel can screw out the die: first, the geometry of the tooth profile cannot interfere in the process of screw out the die, otherwise the tooth profile will be damaged; Secondly, if there is no interference in the spiral die out, the die needs a set of precise spiral die out mechanism, and the design of the mechanism will be very complex. At the same time, the die out consumes a long time, and the contact time between the workpiece and the die will be very long, which is easy to cause the temperature rise of the die, accelerate the thermal fatigue of the die, and shorten the service life of the die. Therefore, for the small wheel of spiral bevel gear, if the pitch cone angle is less than 45 degrees, there will be die interference, which is very difficult to realize precision forging.
For the large spiral bevel gear wheel that can be directly ejected from the die, the forging can be directly ejected from the die cavity by setting the ejection device; For the small wheel with axial interference between the die and the forging, the spiral die out mode is used to set the die rotation angle and the axial speed of the spiral bevel gear, so as to reduce the influence of the axial force on the spiral bevel gear and prevent the serious change of the tooth shape.