Primary Study On Precision Forming Of Spur Gear With One Step By The Added Die Cavity

Technologies of realizing the precision forming of spur gear can be summarized in three methods including one step, two steps and multiple steps. There are some deficiencies in these technologies such as tooth corner is not full, large forming force, complex mold structure and requirements of equipment action. To overcome the above problems, we take a spur gear with modulus being 4, number of teeth being 12 and tooth width being 30 mm as our object of study and do numerical simulation using Deform-3D and physical experiments using lead to develop a new technology. The new technology set an added cavity at the bottom of die corner and the spur gear is formed by no-flash forging in one step.New technology includes two phases, upsetting and ejection. When the upsetting is finished, the top corner is filled well and a proper volume of material flows into the expansive cavity although the bottom corner is not full. In the phase of ejection, the slant side of the added cavity leads to the backflow of the bulge near the bottom corner to fill the bottom corner.35 steel is used as the material and the numerical simulation is carried out under 1000 degrees Celsius. Optimize the shape of the expansive cavity first and then analyze control variables of parameters. Main geometric parameters include the angle ?, expansive scope b at gear width and expansive scope h at gear height h of the expansive cavity. The results show that the forming force is smaller and the output force is larger with larger ? and b. When ? ranges from 10° to 16°and b ranges from 10 mm to 14 mm, a good forming effect can be realized. A larger b is available with a smaller ? in a reasonable range and vice versa. h cannot be too large. When h is 3mm, the qualified gear without waste materials can be formed under the condition of maintaining die strength.By using the function of point tracking and flow net of Deform-3D, we can observe uniform deformation, continuous metal flow and fibrous tissue and their reasonable distribution which enhance teeth's mechanical property and fatigue resistance. Comparing with the two-step method was studied by our research group, metal flow is not cut off and fibrous tissue distributes along the gear profile. Physical experiment produces the qualified lead gear which is identical to the result of numerical simulation, so it can be applied to production.The results indicate that the new technology have advantages of no flash forming, divided flow forming and push-through forming. Comparing with traditional no-flash die forging, upsetting force is smaller than a half and output force is far smaller than forming force. The new technology use not-so-complex structure of mold and requires simple equipment movements and produces no waste materials, so it is suitable to form spur gear and even gear with a large number of modulus and large diameter.