Blank dimensions of spur gears

During precision forging blanking, the blank must be accurate. Due to the large hole of spur gear, there are two shapes of blank, solid and hollow cylindrical blank. Because the hollow blank needs additional blank making process, the blank height is large and the stability is poor, which leads to the difficulty of blank making, so the solid blank is often selected in actual production. In order to put the straight tooth cylindrical gear blank into the die cavity easily and facilitate the blank positioning and filling the tooth cavity, the blank diameter is slightly less than or equal to the tooth root circle diameter of the die, which is convenient for blank positioning. During warm forging, the diameter of die cavity tooth root circle is 138.8mm, and the diameter of blank is 138mm. The height of blank can be calculated according to the principle of constant total volume.

Because the precision forging of spur gear requires accurate blanking volume, it is understood that the volume of blank should be composed of several parts. First, because the warm forging adopts medium frequency induction heating, there will be partial loss of volume, and the fire consumption coefficient needs to be increased δ (generally 1%). Second, the volume of connecting skin left after punching can be calculated according to the designed connecting skin size. Third, the volume of finishing allowance. When calculating the blank volume, it should be taken into account and the calculation formula.

Through the calculation function of the Three-dimensional Modeling Software Solidworks, the volume of the cold forging plus the reserved finishing allowance can be 426528mm3. According to the size of the connecting skin in the drawing of spur gear pre forging, the connecting skin volume is 16578mm3. According to the principle of equal total volume, the blank volume shall be slightly larger than the calculated volume during blanking, and the blank height is taken as 31mm.

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