Study On Opened-die Forming For High Property Spur Gear

Gear precision forming has the advantages of good product property, high productionrate, low convention cost and energy consumption, and little pollution. As the presentforming method need high force, there is no report about precision forming of spur gearusing in actual production. In order to lowing the forming force and improving the productaccuracy, the paper's study is as follows.The paper put forward the new method of opened-die forming for spur gear, whichmainly consists of 'opened-die upset extrusion' and 'guided flow at axis direction anddivided flow at diameter direction' and study on the new method's means. In the factorsaffecting forming force such as flow stress, contact area between billet and die, frictionforce, the free room in which the metal could freely flow, we find that the most importantfactor affecting forming force is the free room which mentioned above, which put forwardthe research direction from the theory level for the new method of spur gear precisionforming. The opened degree in opened-die upset-extrusion and later sizing quantity is a pairof parameter, which controls with each other and there will be a best value under a certaincondition. The opened-die forming force will be further reduced and the spur gear with highaccuracy will be formed by the method of 'control the deformation gradually' whichreasonably distribute the quantity of deformation of warm forming and cold sizing. 'Pushextrusion sizing' make sure the new method of 'guided flow at axis direction and dividedflow at diameter direction' from the die construction, and the billet is pushed directly fromthe die at the process of push extrusion, which resolved the problem of high ejection forceat the time of spur gear's precision forming.The process of opened-die forming has been studied by the commercial software,numerical simulation results show that the most important factor affecting forming force isthe gear's opened degree at the time of upset-extrusion, which doesn't change even ifchanging the parameters of gear and press. The decreasing of friction and the increasing ofgear's center hole could lower the forming force obviously. The increasing of addendumcoefficient will be in favor of the forming force's reduction. The experiment proved that thenumerical simulation results accord with the actual situation, the error is less than 8%. Atthe same time, we put forward the relationship formulation between the gear's openeddegree and the unit forming pressure. The formulation accords with the numericalsimulation results when the opened degree is less than 80%, especially the error is less than5% when the opened degree is less than 10%.When the gear's opened degree is about 5%, the new method not only can form spurgear with good tooth, but also avoid the forming force's sharp increasing. Therefore, theformulation between the gear's opened degree and unit forming pressure, which is putforward by the author, not only has theory meanings, but also has actual application value.According to the results of numerical simulation and experiment, when modulus is 2-6mm, the good upset-extrusion parameters of technology and die are: if the tooth can takeplace plastic deformation, the more small, the more sizing quantity is good;cone angle ofconcave die is 50-70and bearing height is 5-8mm.In order to make the push-extrusion to be a scientific and practical theory, at the basisof thinking the tooth's change when the die is pushed into the shrinkage ring and the gear'sspring after it was formed, the author deduces the formula of the die's addendum coefficient,the diameter of addendum circle and root circle. The experiment results show that the errorbetween formula and experiment is: the public laws line length of three teeth is from–0.0214 to 0.0024mm, the diameter of addendum circle is from –0.0073to 0.0227mm, thediameter of root circle is from -0.0162 to 0.0127mm.Push-extrusion sizing experiment has been done for the spur gear with the toothnumber of 18, modulus of 2.5, which was produced by the electrical discharge machine.The result shows: a) with the material hardness increasing, the push-extrusion force, thesized gear's public laws line length, diameter of addendum circle and diameter of root circleincrease. The above parameters changes are very small for 20CrMnTi steel between aircooling and annealing treatment after warm forming. b) with the sizing quantity increasing,the above parameters will all increase, but the changes of public laws line length, diameterof addendum circle and diameter of root circle are very small. c) with the quantity ofshrinkage increasing, the forming force will increase, the sized spur gear's public laws linelength, diameter of addendum circle and diameter of root circle will decrease. According tothe above results, push-extrusion sizing can be directly done for carburizing steel afterwarm forming. The diameter of addendum circle and root circle should be equal to the die'scorresponding parameters and the sizing quantity should be as small as possible. The sizedgear's parameters can be adjusted in a certain range by the method of adjusting shrinkagequantity between die and the shrinkage ring, which has been used in the experiment andsmall scale production and has made good results.In order to resolve the problem of tooth's bending when gear with rib is sized bypush-extrusion, the author first put forward the method of push-extrusion through drive loadof working cylinder and driven load of ejection cylinder of hydroforming machine, whichmakes sure the formed gear's accuracy and stability.The microstructure shows that the tooth's grain degree of opened-die formed gear canimproved from No. 7-8, which is produced by traditional process, to 9-11, especially, thegrain of the root is more fine;the new technology can get intact flow line of the tooth,which will improve the strength and toughness of gear.In order to promote the spur gear's new technology of plastic forming using in actualproduction, the position problem between plastic formed gear and the later machine hasbeen resolved by the method of tooth faces' three point position. According to the measureresults, through later machine and heat treatment, the auxiliary variable speed gear andpinion housing formed by opened-die forming absolutely meet the need of product. Furthermore, after heat treatment, the plastic formed gear's consistency is better than that oftraditional process. After heat treatment and machine, the above two opened-die formedgears have been used in actual equipment.In a word, the paper has studied on the spur gear' opened-die forming basic theory,numerical simulation, control accuracy, improving property and die design. At the basis ofthe above results, the author drew up two representative gears' forming process, designedthe die, carried on experiments and small scale production and proved the new method ofthe opened-forming can be used in actual production.