Usually, the bevel gears of larger specifications are formed on special large-tonnage hydraulic block presses, while the bevel gears of smaller sizes are usually formed on ordinary cold forging presses with special block dies. The latter method has the characteristics of high production efficiency and low cost. Only the size of the forging is limited by the occlusion pressure of the mold base, and the forming of large-sized bevel gears cannot be completed.
Considering the economy of gear mold manufacturing, especially for cemented carbide gear molds, electrical discharge machining is still the main mold-making process in the precision forging industry of gears, but the generative machining of tooth-shaped electrodes has been completely replaced by high-speed milling and CNC machining the trend of. For warm forging and hot forging forming dies with a quenching hardness of about 50 degrees Rockwell, high speed milling of high gear processing has far surpassed EDM in terms of processing speed and accuracy, and has obvious advantages in terms of service life of the die. As long as the cost of cutting tools is solved, high-speed milling can completely replace electric discharge machining in terms of warm forging and hot forging gear dies.
Another outstanding advantage of the positive extrusion forming process is that the mold tooth shape is obtained by CNC wire cutting, and the ideal tooth shape can be obtained through programming when machining gears with a small number of teeth without worrying about undercutting. In the case of processing special tooth shape or modifying tooth shape, it is more convenient, faster and more accurate to use CNC wire cutting to process tooth shape than gear generation processing or profiling processing.
Spline cold forging is a special case of gear positive extrusion. The gear machining shape of the involute spline is equivalent to extruding a longer spur gear, and the extrusion of the rectangular spline is similar to that of the involute spline. On the other hand, small modulus spur gears can be obtained by dividing the involute spline shaft.
A method that can improve gear life and reduce damage:
Most gear damage is caused by high contact stress and bending stress. Slotted teeth can reduce these stresses and obtain smooth operation of the machine.
The gear tooth is a typical point contact. Most of its damage is the result of excessive contact (Hertz) stress and bending stress. In this case the gear fatigue life is determined by the high contact stress cycles.
Reducing the Hertz stress or contact stress can prolong the life of the gear and can transmit a higher allowable load, running quietly and improving reliability. Gear life and reliability can be improved if the gear teeth reduce the contact height of the contact area under load.
The other is gear slotting.
These two methods can reduce the contact stress, and also reduce the shear stress in the lubrication failure area, and then reduce the stress concentration at the tooth root of the slotted gear tooth, and finally obtain an equal-strength design that improves the bending stress distribution state of the gear tooth.
In addition, the elasticity of the grooved gear teeth reduces the backlash to a certain minimum value, or even eliminates the backlash, and it is possible to obtain zero clearance between the meshing surfaces of the teeth, so that the dynamic load acting on the teeth is minimized or is equal to zero.